CN1856890A - Lithium composite oxide particles for lithium secondary battery positive electrode material, lithium secondary battery positive electrode, and lithium secondary battery using the same - Google Patents

Abstract

An improved positive electrode material for a lithium secondary battery, which can enhance the low-temperature load characteristics of the battery and also can enhance the coatability when manufacturing the positive electrode. In the measurement by the mercury intrusion method, the following condition is satisfied and at least one of the following conditions (B) and (C) is satisfied at the same time. Condition : the mercury penetration amount is less than or equal to 0.02cm when the pressure is increased from 50MPa to 150MPa on mercury penetration curve³(ii) in terms of/g. Condition (B): the mercury penetration amount is greater than or equal to 0.01cm when the pressure is increased from 50MPa to 150MPa on mercury penetration curve³(ii) in terms of/g. Condition (C): the average pore radius is 10nm to 100nm, and the pore size distribution curve has a main peak whose peak top is at a pore radius of 0.5 μm to 50 μm, and a sub-peak whose peak top is at a pore radius of 80nm to 300 nm.

Description

Lithium composite oxide particles for lithium secondary battery positive electrode material, lithium secondary battery positive electrode, and lithium secondary battery using the same

technical field

The present invention relates to lithium composite oxide particles used as positive electrode materials for lithium secondary batteries, and also relates to positive electrodes for lithium secondary batteries and lithium secondary batteries using the positive electrodes. The positive electrode material according to the present invention exhibits excellent coatability, and can provide a positive electrode for a secondary battery having excellent load characteristics even when used in a low-temperature environment.

Background technique

Recently, lithium secondary batteries have attracted attention due to their use as power sources for miniaturized and lightweight mobile electronic devices and mobile communication devices and as power sources for vehicles. Lithium secondary batteries generally provide high output and high energy density, and for their positive electrodes, lithium transition metal composite oxides whose standard compositions are represented by LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , etc. are used as positive electrode active materials.

Among various lithium-transition metal composite oxides, in consideration of safety and material cost, noteworthy positive electrode active materials are those that have a layered structure similar to _LiCoO2 and _LiNiO2 and whose transition metal sites are replaced by other materials such as manganese. The material with which the element is partially substituted. As disclosed in Non-Patent Documents 1 to 3 and Patent Document 1, an example of such a lithium transition metal composite oxide is LiNi _(1-a) Mn _a prepared by partially substituting Mn for Ni sites in LiNiO ₂ O ₂ , and LiNi _(1-α-β) Mn _α Co _β O ₂ prepared by partially replacing Ni sites in LiNiO ₂ with Mn and Co.

In addition, when such lithium transition metal composite oxides disclosed in Non-Patent Documents 1 to 3 and Patent Document 1 are used as positive electrode active materials, the lithium transition metal composite oxides are formed into fine particles, thereby increasing the positive electrode activity The contact area between the material surface and the electrolyte and improve the load characteristics. However, microparticles of lithium-transition metal composite oxides also reduce the filling efficiency of cathode active materials into the cathode and limit the battery capacity.

On the other hand, Patent Document 2 discloses that as a positive electrode active material for a nonaqueous secondary battery, porous particles of a lithium composite oxide containing at least one element selected from Co, Ni, and Mn and as Lithium as the main component, having an average pore radius of 0.1 μm to 1 μm obtained by measurement of pore radius distribution by mercury intrusion porosimetry, and a total volume of pores with a diameter of 0.01 μm to 1 μm greater than or equal to 0.01 cm ³ /g. This document also discloses that the use of the particles can enhance the load characteristics of the resulting battery without compromising the filling efficiency of the positive electrode active material into the positive electrode.

Patent Document 3 discloses that Li-Mn-Ni-Co composite oxide particles whose primary particles have an average diameter of 3.0 μm or less and whose specific surface area is greater than or equal to 0.2 m ² /g can be used as positive electrodes for lithium secondary batteries active material, and the resulting lithium secondary battery exhibits high discharge capacity and excellent cycle performance.

Patent Document 4 discloses that Li-Mn-Ni-Co composite oxide particles prepared by spray-drying Li-Mn-Ni-Co slurry followed by calcining the spray-dried particles can be used as positive electrode active for lithium secondary batteries material, and the resulting lithium secondary battery exhibits high discharge capacity and excellent cycle performance.

[Non-Patent Document 1] Journal of Materials Chemistry, Vol. 6, 1996, p. 1149

[Non-Patent Document 2] Journal of the Electrochemical Society, Vol. 145, 1998, p. 1113

[Non-Patent Document 3] Preliminary Drafts of the 41st Battery Symposium in Japan, 2000, p. 460

[Patent Document 1] Japanese Patent Laid-Open No. 2003-17052

[Patent Document 2] Japanese Patent Laid-Open No. 2000-323123

[Patent Document 3] Japanese Patent Laid-Open No. 2003-68299

[Patent Document 4] Japanese Unexamined Patent Publication No. 2003-51308

Contents of the invention

Problems solved by the present invention

However, according to the techniques disclosed in Non-Patent Documents 1 to 3 and Patent Document 1, when the lithium transition metal oxide is formed into fine particles as described above, there is a limitation in the filling efficiency of the positive electrode active material into the positive electrode and thus it is impossible to ensure problem of adequate load characteristics.

The formation of fine particles is also accompanied by the problem that when the particles are used for coating, the coating layer becomes hard and brittle in terms of mechanical properties, and is easily separated from the positive electrode in the winding step of assembling the battery, so Sufficient spreadability cannot be guaranteed. When the ratio of Ni:Mn:Co in the composition of lithium transition metal oxide LiNi _(1-α-β) Mn _α Co _β O ₂ is close to 1-α-β:α:β (wherein 0.05≤α≤0.5 and 0.05 ≤β≤0.5) This problem is especially obvious.

The lithium composite oxide particles disclosed in Patent Document 2 exhibit improved coatability, but still have a problem of insufficient load characteristics at low temperature (low temperature load characteristics).

Also, the lithium composite oxide particles disclosed in Patent Document 3 for anode materials for lithium secondary batteries still have the problem of insufficient load characteristics at low temperatures.

The lithium composite oxide particles for lithium secondary battery cathode materials disclosed in Patent Document 4 tend to exhibit very low bulk density and have problems with coatability.

In view of the above-mentioned problems, an object of the present invention is to provide lithium composite oxide particles for lithium secondary battery positive electrode materials, which can improve the low-temperature load characteristics of the resulting lithium secondary battery and exhibit excellent performance in the manufacture of positive electrodes. coating properties.

means of solving problems

As a result of diligent research to solve the above-mentioned problems, the present inventors have found that lithium composite oxide particles satisfying the following conditions can be used as preferable lithium disulfide having improved low-temperature load characteristics and excellent coatability in the production of positive electrodes. Secondary battery cathode material. That is, based on the measurement by mercury intrusion porosimetry, (A) the indented volume of mercury under a specific high-pressure load is equal to or less than a predetermined upper limit, and (B) the indented volume of mercury is equal to or greater than a predetermined or (C) when the pore size distribution curve has sub-peaks other than the traditional main peak with peaks within the predetermined range of pore radii, the average pore radius is within the predetermined range. Based on the above findings, the inventors have achieved the present invention.

According to one aspect of the present invention, there is provided a lithium composite oxide particle for a lithium secondary battery positive electrode material, when the mercury intrusion porosimetry is measured, the particle satisfies the following condition (A), And at least one of the following conditions (B) or (C) is satisfied.

Condition (A)

According to the mercury intrusion curve, when the pressure increases from 50MPa to 150MPa, the mercury intrusion volume is less than or equal to 0.02cm ³ /g.

Condition (B)

According to the mercury intrusion curve, when the pressure increases from 50MPa to 150MPa, the mercury intrusion volume is greater than or equal to 0.01cm ³ /g.

condition (C)

The average pore radius is 10nm-100nm, and the pore size distribution curve has a main peak with a peak at a pore radius of 0.5μm-50μm, and a sub-peak with a peak at a pore radius of 80nm-300nm.

As a preferable feature, the lithium composite oxide particles contain at least Ni and Co.

As another preferred feature, the lithium composite oxide particles have a composition represented by the following composition formula (1):

Li _x Ni _(1-yz) Co _y M _z O ₂ (1)

Where M represents at least one element selected from Mn, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn and Nb, x represents the value of 0<x≤1.2, and y represents the value of 0.05≤y≤0.5 , and z represents a value of 0.01≤z≤0.5.

According to another aspect of the present invention, there is provided a positive electrode for a lithium secondary battery, the positive electrode comprising: a current collector; and a positive electrode active material layer disposed on the current collector; wherein the positive electrode active material layer Contains at least the above-mentioned lithium composite oxide particles for lithium secondary battery positive electrode materials.

According to still another aspect of the present invention, there is provided a lithium secondary battery comprising: a positive electrode capable of releasing and absorbing lithium; a negative electrode capable of absorbing and releasing lithium; and an organic electrolyte solution containing a lithium salt as an electrolyte; wherein The positive electrode is the above-mentioned positive electrode for a lithium secondary battery.

Advantageous effect of the present invention

The lithium composite oxide particles of the present invention can improve the low-temperature load characteristics of the resulting lithium secondary battery, and have excellent coatability when used in manufacturing a positive electrode. In view of this, the lithium composite oxide particles of the present invention are preferably used as positive electrode materials for lithium secondary batteries. In addition, using the lithium composite oxide particles of the present invention as a cathode material can provide a lithium secondary battery cathode material and a lithium secondary battery having excellent low-temperature load characteristics.

Description of drawings

1 is a graph showing pore size distribution curves of lithium composite oxide particles (positive electrode materials) of Example 1 and Comparative Examples 1 and 2. FIG.

FIG. 2 is a partially enlarged view of the graph of FIG. 1 .

Detailed ways

Hereinafter, embodiments of the present invention will be described in detail, but the present invention is by no means limited to the following description, and various changes are allowed within the scope of the gist of the present invention.

I. Lithium composite oxide particles

Mercury intrusion porosimetry

Lithium composite oxide particles (hereinafter also referred to as "lithium composite oxide particles of the present invention", or simply "particles of the present invention") used as positive electrode materials for lithium secondary batteries are characterized in that when mercury is pressed into the porosity These particles satisfy certain conditions when the assay is performed. For a better understanding of the present invention, a brief description of mercury intrusion porosimetry will be given before describing the particles of the present invention.

Mercury intrusion porosimetry is a method in which mercury is forcibly pressed into the pores of a sample such as porous particles to obtain information about the specific surface area based on the relationship between the pressure of mercury and the amount of mercury pressed into the pores. , pore radius distribution and other information.

Specifically, the container containing the sample is evacuated and then filled with mercury. Because mercury has a high surface tension, it does not spontaneously enter the pores on the sample surface. As the pressure applied to the mercury in the container gradually increases, the mercury gradually enters the pores starting from the larger diameter holes and then into the smaller diameter holes. As the pressure continues to increase, by monitoring the mercury level (i.e., the volume of mercury pressed into the hole), a mercury intrusion curve can be obtained, which represents the difference between the pressure applied to the mercury and the volume of mercury indented. relationship between.

Assuming that the hole is cylindrical, the force in the direction of extruding mercury from the hole is represented by -2πrδ(cosθ), where r represents the average radius of the hole, δ represents the surface tension of mercury, and θ represents the contact angle (when When θ>90°, θ takes a positive value). On the other hand, the force in the direction of pressing mercury into the hole is represented by πr ² P, where P represents the pressure. The following equations (1) and (2) are derived from the balance of these two forces.

-2πrδ(cosθ)＝πr ² P (1)

Pr＝-2δ(cosθ) (2)

It is generally assumed that the surface tension δ of mercury is about 480 dynes/centimeter (dyn/cm), and the contact angle θ of mercury is about 140°. From these approximations, the radius of the hole into which mercury is pressed at the pressure P is expressed by the following equation (A).

$\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; nm</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 7.5</span>}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; 10</span>}}^{\mathrm{<span\; class="notranslate">\; 8</span>}}}{\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; Pa</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; )</span>$

Thus, there is a correlation between the pressure P applied to the mercury and the radius r of the hole into which the mercury is pressed. Therefore, the mercury intrusion curve can be converted into a pore size distribution curve, which represents the relationship between the pore radius and the volume of the sample. For example, when the pressure P varies from 0.1 MPa to 100 MPa, pores in the range of about 7500 nm to 7.5 nm can be measured.

The approximate range of pore radii measured by mercury intrusion porosimetry has a lower limit of about 3 nm or greater and an upper limit of about 200 nm or less. Therefore, compared with the nitrogen adsorption method described below, the mercury intrusion porosimetry method is more suitable for analyzing the pore distribution in the larger pore radius region.

Measurement by mercury intrusion porosimetry can be performed by using equipment such as a mercury porosimeter, examples of which include Autopore(R) manufactured by Micromeritics Corporation, and PoreMaster(R) manufactured by Quantachrome Corporation.

The particles of the present invention are characterized in that, when measured by mercury intrusion porosimetry, the particles satisfy condition (A) and satisfy at least one of condition (B) or condition (C), these Conditions are defined as follows.

Condition (A)

According to the mercury intrusion curve, when the pressure increases from 50MPa to 150MPa, the mercury intrusion volume is less than or equal to 0.02cm ³ /g.

Condition (B)

According to the mercury intrusion curve, when the pressure increases from 50MPa to 150MPa, the mercury intrusion volume is greater than or equal to 0.01cm ³ /g.

condition (C)

The average pore radius is 10nm to 100nm, and

The pore size distribution curve has a main peak with a peak at a pore radius of 0.5 μm to 50 μm, and a sub-peak with a peak at a pore radius of 80 nm to 300 nm.

Conditions related to mercury intrusion curve (Conditions (A) and (B))

When the mercury intrusion curve and the pore size distribution curve are obtained by measuring the particles of the present invention by mercury intrusion porosimetry, the range on the mercury intrusion curve is that the pressure zone of 50MPa～150MPa corresponds to a range of 15nm～ A pore radius region of 5 nm, that is, an extremely small pore radius region. Since the pore radius region is close to the above-mentioned lower limit of measurement, the fact that the mercury indentation volume is within the above specified range at the aforementioned pressure does not mean that the particles of the present invention have a pore radius within the corresponding range. In contrast, it is judged that the particles of the present invention hardly have such fine pores because the nitrogen adsorption method described below shows that the total volume of pores with a radius of 50 nm or less is usually 0.01 cm ³ /g or less. Therefore, it is considered that the characteristic related to the volume of mercury indentation under the pressure of 50 MPa to 150 MPa is not caused by the presence of minute pores in the particles of the present invention.

Although studies by the present inventors have not been elucidated, it is presumed that the pressure region ranging from 50 MPa to 150 MPa in the above mercury intrusion curve corresponds to the pressure region where the grain structure changes due to high pressure load. Thereby it is considered that because the mercury indentation volume in the pressure zone satisfies the above-mentioned conditions, the compressive structural strength of the particles of the present invention is within a specific range, and will not be too high or too low, and the optimal structural strength produces Various preferred properties of the particles of the present invention for use as positive electrode materials have been identified.

Specifically, according to the mercury intrusion curve, when the pressure is increased from 50 MPa to 150 MPa, the upper limit of the mercury intrusion volume of the particles of the present invention is as specified in the above condition (A), usually less than or equal to 0.02 cm ³ /g, preferably less than Or equal to 0.0195 cm ³ /g, more preferably less than or equal to 0.019 cm ³ /g. Particles whose mercury indentation volume exceeds the upper limit are excessively split into finer particles due to their low structural strength, resulting in deterioration of coatability. If these particles are used to coat the positive electrode, the resulting coating layer becomes hard and brittle in terms of mechanical properties, and is easily separated from the positive electrode during the winding step of assembling the battery. Therefore, the particles are not suitable for a positive electrode.

On the other hand, the preferred lower limit of the mercury indentation volume of the particles of the present invention is as specified in the above-mentioned condition (B), which is generally greater than or equal to 0.01 cm ³ /g, more preferably greater than or equal to 0.011 cm ³ /g, and even more preferably Greater than or equal to 0.012 cm ³ /g. Positive electrode particles having a mercury intrusion volume below the lower limit cannot secure a sufficient degree of their effective contact area with the electrolyte, and thus the load characteristics of the resulting battery are degraded.

Properties related to pore radius (Condition (C))

average pore radius

The average pore radius of the particles of the present invention is as specified in the above condition (C), usually greater than or equal to 10 nm, preferably greater than or equal to 12 nm, and less than or equal to 100 nm, preferably less than or equal to 50 nm. The average pore radius within the above range means that in the particles of the present invention, pores having an appropriate size are formed between primary particles to be described below, compared with conventional lithium composite oxide particles. Particles with an average pore radius exceeding the upper limit are not preferred because they have such a small pore area per unit volume that when they are used as a positive active material, they reduce the contact of the surface of the positive active material with the electrolyte area, the resulting battery exhibits insufficient load characteristics. On the contrary, particles having an average pore radius lower than the lower limit are not preferable because they cause lithium ions to be insufficiently diffused into the pores of the positive active material when used as a positive active material, and the resulting battery shows deteriorated load characteristics. Incidentally, in the present invention, in order to eliminate the influence of voids between secondary particles, the average pore radius measured by mercury intrusion porosimetry is calculated on the basis of pores with a radius of 0.005 μm to 0.5 μm .

Pore size distribution curve

From the pore distribution curve measured by mercury intrusion porosimetry, the particles of the present invention generally show main peaks and sub-peaks as explained below.

In this specification, the term "pore size distribution curve" refers to a dot diagram, the abscissa of which represents the pore radius of each point, and its ordinate represents the pore size obtained by making the radius per unit weight (usually 1 g) greater than or equal to the pore radius of each point. The value obtained by differentiating the total volume of pores to the logarithm of the pore radius. The pore size distribution curve is usually displayed in the form of a graph connecting the points drawn. In particular, the pore size distribution curve obtained by measuring the particles of the present invention by mercury intrusion porosimetry is referred to as "the pore size distribution curve according to the present invention".

Also, in this specification, the term "main peak" represents the largest peak among peaks on the pore size distribution curve, which is generally related to voids formed between secondary particles, which will be explained below. The term "subpeak" refers to each peak on the pore size distribution curve other than the main peak.

In addition, in this specification, the term "peak top" refers to a point having the largest ordinate value among the respective peaks of the pore size distribution curve.

main peak

The main peak of the pore size distribution curve according to the present invention has a peak top, and its pore radius is generally greater than or equal to 0.5 μm, preferably greater than or equal to 0.7 μm, and generally less than or equal to 50 μm, preferably less than or equal to 20 μm, more preferably less than or equal to 15 μm . If a porous particle whose main peak top exceeds the upper limit is used as a positive electrode material of a battery, the resulting battery suffers from deterioration in load characteristics due to insufficient diffusion of lithium in the positive electrode or lack of conductive channels. On the other hand, if porous particles whose main peak top is lower than the lower limit are used as a material for making the positive electrode, since the amount of the required conductive material and binder increases, the active material is loaded into the positive electrode (i.e., the positive electrode current collector) will be limited in filling efficiency, thereby resulting in a decrease in battery capacity. Besides, as the particles are made finer, the coating layer containing the particles becomes hard or brittle in terms of mechanical properties, and is easily separated from the positive electrode in the winding step of assembling the battery.

In addition, according to the pore size distribution curve of the present invention, the pore volume of the main peak is generally greater than or equal to 0.1 cm ³ /g, preferably greater than or equal to 0.15 cm ³ /g, and generally less than or equal to 0.5 cm ³ /g, preferably less than or equal to 0.4 cm ³ /g. Particles whose pore volume of the main peak exceeds the upper limit tends to have such a large volume in the interstices between secondary particles that when used as a cathode material, the filling efficiency of the active material into the cathode is limited, thereby resulting in Decrease in battery capacity. Conversely, particles whose main peak has a pore volume below the lower limit tends to have such a small volume in the voids between secondary particles that when used as a positive electrode material, lithium diffusion between secondary particles is suppressed, and the resulting battery The load characteristics are degraded.

Yafeng

In addition to the above-mentioned main peak, the pore size distribution curve according to the present invention preferably has a specific sub-peak (hereinafter referred to as "specific sub-peak"), and its peak top is generally greater than or equal to 80 nm, preferably greater than or equal to 100 nm, more preferably greater than or equal to It is within the range of pore radius equal to 120nm, and generally less than or equal to 300nm, preferably less than or equal to 250nm. The presence of specific subpeaks indicates the presence of voids with pore radii within the above-mentioned ranges between the primary particles of the present invention (to be described below). It is judged that the presence of said voids enables the particles of the invention to combine low temperature load characteristics with favorable coating properties. Particles whose peak tops of specific subpeaks exceed the upper limit of the above-mentioned range are not preferable on the grounds that when they are used as positive electrode active materials, the contact area of the surface of the positive electrode active material with the electrolyte is reduced, and the load characteristics of the resulting battery are lowered. . On the other hand, particles whose peak tops of specific subpeaks are lower than the lower limit of the above-mentioned range are not preferable because the diffusion of lithium ions in pores is suppressed when they are used in the manufacture of lithium secondary batteries, And the load characteristic is degraded.

The pore volume of a specific subpeak (that is, the ordinate value at the peak top of a specific subpeak) is generally greater than or equal to 0.005 cm ³ /g, preferably greater than or equal to 0.01 cm ³ /g, and generally less than or equal to 0.05 cm ^{3 /} g g, preferably less than or equal to 0.03 cm ³ /g. Particles whose pore volume of the specific subpeak exceeds the upper limit are not preferred, on the grounds that when they are used for coating, the resulting coating layer becomes hard or brittle in terms of mechanical properties, and is prone to be damaged during the production of batteries. Separation from the positive electrode in the winding step leads to deterioration of coatability. On the other hand, particles whose specific subpeaks have a pore volume below the stated lower limit are not preferable on the grounds that when they are used as cathode materials in battery manufacture, the diffusion of lithium in the cathode tends to be suppressed, and the load characteristics decline.

The ratio of the pore volume of the main peak to the pore volume of the specific sub-peak (that is, the ratio of the ordinate value of the main peak peak to the ordinate value of the specific sub-peak peak), expressed in the form of [sub-peak]: [main peak], Usually it is greater than or equal to 1:100, preferably greater than or equal to 1:50, and generally less than or equal to 1:2, preferably less than or equal to 1:5. It is not preferable that the ratio of the pore volume of the sub-peak to the pore volume of the main peak is too large because it tends to deteriorate the coatability. On the other hand, it is not preferable that the ratio of the pore volume of the sub-peak to the pore volume of the main peak is too small because it tends to cause a decrease in low-temperature load characteristics.

other

The particles of the present invention may have some pores outside the range of the main peak and sub-peak as long as the above-mentioned constraints are satisfied. However, also in this case, the specific subpeak characteristic of the present invention preferably has the largest pore volume in a pore radius region smaller than that at the top of the main peak.

Reasons for the advantageous effects of the present invention

Although the present inventors have made studies, the reason why the advantageous effects of enhancing the low-temperature load characteristics and improving coatability of the resulting battery can be produced when the particles of the present invention are used for a positive electrode has not been fully elucidated, but it can be presumed roughly as follows.

The lithium composite oxide particle of the present invention has a particle structure of appropriate strength, and unlike conventional lithium composite oxide particles commonly used as positive electrode materials in lithium secondary batteries, as the particle volume changes due to charge and discharge , this structure enables the particles to gradually and moderately split into finer particles. This increases the effective contact area between the particles of the invention and the electrolyte, thereby improving the load characteristics required by the battery, especially the load characteristics at low temperatures. Presumably from the above reasons, the particles of the present invention can achieve both improved low-temperature load characteristics and excellent coatability.

In addition, since there are pores of an appropriate size between the primary particles, the lithium composite oxide particles of the present invention can increase their contact area with the electrolyte solution when used in the manufacture of batteries, unlike conventional particles. Without excessively increasing its pore volume, it improves the load characteristics required for positive electrode active materials, especially at low temperatures. This may be another reason why the particles of the invention are able to simultaneously combine improved low-temperature load characteristics with excellent coatability.

In order to achieve the above-mentioned advantageous effects (ie, improvement of low-temperature load characteristics of batteries and improvement of coatability in positive electrode production), the particles of the present invention must always satisfy condition (A). Regarding the remaining conditions (B) and (C), it is sufficient that at least one of the condition (B) or the condition (C) is satisfied. However, in order to achieve the above-mentioned advantageous effects to a greater extent, it is preferable to satisfy at least the condition (B) in addition to the condition (A).

Other preferred embodiments

Further properties of the particles of the invention are described below, but they should only be considered as preferred features. As long as the particles of the present invention have the above properties, the particles should by no means be particularly limited to these properties.

Properties related to nitrogen adsorption

In addition to the above-mentioned features with regard to mercury intrusion porosimetry, the particles of the invention are preferably characterized in that they have a total number of pores with a pore radius of 50 nm or less as determined by the BJH (Barret-Joyer-Halenda) method by the nitrogen absorption method. The volume is that the unit weight of the particles is less than or equal to 0.01 cm ³ /g.

Nitrogen adsorption method (BJH method) is a method in which a sample such as porous particles is made to absorb nitrogen gas, thereby obtaining various information on specific surface area, etc., such as pore radius distribution based on the relationship between the pressure of nitrogen gas and the adsorption amount of nitrogen gas .

The measurement by the nitrogen adsorption method can be selectively performed using various devices depending on the specific method of analyzing the pore radius distribution. A typical example of such equipment is a measuring device for nitrogen adsorption pore distribution, such as the Autosorb(R) manufactured by Quantachrome Corporation.

The particle according to the present invention, whose total volume of pores with a radius of 50 nm or less obtained by the nitrogen adsorption method is preferably less than or equal to 0.05 cm ³ /g, more preferably less than or equal to 0.01 cm ³ /g, as described above, More preferably, it is less than or equal to 0.008 cm ³ /g. The aforementioned particles having a total volume of pores larger than the upper limit are not preferable on the grounds that they contain a large number of pores having an excessively small diameter and thus show a low filling efficiency of the active material into the positive electrode, resulting in a decrease in battery capacity .

particle shape

The shape of the particles of the present invention is not particularly limited, but they are generally similar to the shape of conventional lithium composite oxide particles generally used as positive electrode active materials for lithium secondary batteries. Specifically, primary particles are aggregated or sintered to form secondary particles, each of which is larger in size than a single primary particle. Hereinafter, the term "particles of the present invention" refers to secondary particles.

specific surface area

The specific surface area of the particles of the present invention should by no means be specifically limited, but a preferred specific surface area is generally greater than or equal to 0.1 m ² /g, more preferably greater than or equal to 0.2 m ² /g, and generally less than or equal to 2 m ² /g, More preferably, it is less than or equal to 1.8 m ² /g. The specific surface area of the particles is mainly affected by the diameter of the primary particles and the degree of sintering of the primary particles. If the specific surface area of the particles exceeds the upper limit, the amount of dispersion medium required for coating increases, and the required amount of conductive material and binder also increases, resulting in a limitation in the filling efficiency of the active material into the positive electrode, Consequently, the battery capacity tends to decrease. On the contrary, if the specific area is smaller than the lower limit, the contact area between the surface of the particles in the positive electrode and the electrolyte decreases, resulting in a decrease in the load characteristics of the resulting battery.

In this specification, the term "specific surface area" refers to a specific surface area obtained by the BET (Brunauer, Emmett, and Teller) method using a nitrogen adsorption method (BET specific surface area). The BET method is a method in which the monomolecular layer adsorption amount of nitrogen gas is obtained from an adsorption isotherm and the surface area is determined from the cross-section of the adsorbed nitrogen gas molecule, whereby the specific surface area of a sample (BET specific surface area) is calculated. Measurement by the BET method can be performed by using various types of BET measuring devices.

primary particle diameter

The diameter of the primary particles forming the particles (secondary particles) of the present invention should not be particularly limited, but is preferably usually greater than or equal to 0.5 μm, more preferably greater than or equal to 0.6 μm, and less than or equal to 2 μm, more preferably less than or equal to 1.8 μm. The diameter of the primary particles can be affected by factors such as the diameter of the pulverized particles of the raw material and the temperature and atmosphere during the calcination. If the diameter of the primary particles exceeds the upper limit of the above range, the diffusion of lithium ions and the conduction of electrons in the primary particles tend to decrease, resulting in a decrease in load characteristics. On the contrary, if the diameter of the primary particle is lower than the lower limit of the above-mentioned range, the amount of dispersion medium required for coating increases, and the required amount of conductive material and binder also increases, resulting in a decrease in the filling efficiency of the active material into the positive electrode. , and the battery capacity tends to decrease accordingly.

The diameter of the primary particles is measured by observation with a scanning electron microscope (SEM). Specifically, the diameter of the primary particle can be calculated with a photo enlarged by 10,000 times, for example, the maximum length of the intercept of the horizontal line from the left end to the right end of the particle can be obtained for each primary particle in 50 randomly selected primary particles, The lengths of 50 of the primary particles were averaged and obtained.

Tap density

The tap density of the particles of the present invention should by no means be specifically limited, but is generally greater than or equal to 1.4 g/cm ³ , preferably greater than or equal to 1.5 g/cm ³ , and generally less than or equal to 2.5 g/cm ³ , preferably less than or equal to Equal to 2g/cm ³ . In this specification, the term "tap density" refers to a value representing the powder weight per unit powder volume tapped and filled in a container. The higher the tap density exhibited by the particle, the better the packing capacity is believed to be provided by the particle. If the tap density of the particles exceeds the upper limit of the above range, the diffusion of lithium ions in the positive electrode through the electrolyte solution as a medium is restricted, resulting in a decrease in load characteristics. On the other hand, if the tap density of the particles is lower than the lower limit of the above-mentioned range, the amount of the dispersion medium required for coating increases, and the required amount of the conductive material and the binder also increases, causing the active material to be filled into the positive electrode. Filling efficiency decreases, and battery capacity tends to decrease accordingly.

The tap density can be obtained by the method specified in JIS (Japanese Industrial Standard) K5101, or by putting a predetermined weight of pellets into a graduated cylinder, tapping the put pellets, and measuring the volume of the pellets.

Median particle size

The average value of the diameters of the particles (secondary particles) of the present invention (hereinafter also referred to as "median particle size") is usually greater than or equal to 1 μm, preferably greater than or equal to 2 μm, and usually less than or equal to 20 μm, preferably less than or equal to 15 μm . Particles whose median diameter exceeds the upper limit of the above-mentioned range are not preferable, on the grounds that when they are used as a positive electrode material in the manufacture of batteries, lithium diffusion in the positive electrode is inhibited, and insufficient conduction channels occur, resulting in poor battery life. The load characteristics are degraded. On the other hand, particles having a median particle diameter lower than the lower limit of the above-mentioned range are not preferable because they increase the amount of conductive material and binder required for the manufacture of the positive electrode, and the active material enters the positive electrode (positive electrode current collector). ) filling efficiency decreases, leading to a decrease in battery capacity. Besides, when finer particles are used for coating, the coating layer becomes hard or brittle in terms of its mechanical properties, and is easy to separate from the cathode during the winding step of assembling the battery. The median diameter of the particles can be determined by laser diffraction/scattering methods.

composition

The composition of the particles of the present invention should by no means be limited, but it is preferable to contain at least Ni and Co in view of energy density and stability in the crystal structure.

First, the particles of the present invention preferably have a composition represented by the following composition formula (1).

Li _x Ni _(1-yz) Co _y M _z O ₂ composition formula (1)

In the above composition formula (1), M represents at least one element selected from the group consisting of Mn, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn and Nb. Preferably M is Mn and/or Al, more preferably M is Mn.

In addition, in the composition formula (1), x is a value generally greater than 0, preferably greater than or equal to 0.1, and generally less than or equal to 1.2, preferably less than or equal to 1.1. If x exceeds the upper limit of the above range, there is a possibility that the particles do not form a single crystal phase and lithium is replaced by transition metal sites, resulting in a tendency for the charge and discharge capacity of the resulting lithium secondary battery to decrease. On the other hand, a composition at which x is approximately the lower limit corresponds to a state of charge in which lithium is released, and it is not preferable to charge the battery to an extent where x is lower than the lower limit because the crystal structure of the particles may deteriorate.

In the above compositional formula (1), y takes a value of usually 0.05 or more, preferably 0.1 or more, and usually 0.5 or less, preferably 0.4 or less. Particles having a composition in which y is greater than the upper limit are not preferred on the grounds that when they are used as cathode materials, the capacity of the resulting battery tends to decrease, and are also not preferred in view of cost since Co is a rare and expensive resource . On the other hand, particles having a composition in which y is lower than the lower limit tend to have lower crystal structure stability, and thus are not preferable.

Furthermore, in the above composition formula (1), z is a value of usually 0.01 or more, preferably 0.02 or more, and usually 0.5 or less, preferably 0.4 or less. Particles having a composition where z is greater than the upper limit are not preferable because it is difficult for them to form a single crystalline phase, and also because when they are used as a positive electrode active material, the discharge capacity of the resulting lithium secondary battery tends to decrease. Particles having a composition in which z is smaller than the lower limit are also not preferable because the stability of the crystal structure of the particles tends to decrease.

II. Method for producing lithium composite oxide particles

Next, a production method of particles whose composition is represented by the above formula (1) (hereinafter referred to as "production method of the present invention") will be described as an example of a production method of the particles of the present invention. Of course the granules of the present invention should by no means be limited to products obtained by the manufacturing methods described below. In addition, the production method of particles whose composition is represented by formula (1) should by no means be limited to the method described below.

The production method of the present invention uses a lithium raw material, a nickel raw material, a cobalt raw material, and a raw material of the element M as raw materials to manufacture the particles of the present invention.

raw material

Lithium raw material

The lithium raw material is not particularly limited as long as it contains lithium.

Examples of lithium raw materials include: inorganic lithium salts such as Li ₂ CO ₃ and LiNO ₃ ; lithium hydroxides such as LiOH and LiOH·H ₂ O; lithium halides such as LiCl and LiI; inorganic lithium compounds such as Li ₂ O; and organolithium compounds such as alkyllithium and fatty acid lithium. Among the above examples, Li ₂ CO ₃ , LiNO ₃ , LiOH and lithium acetate are preferred. Among them, Li ₂ CO ₃ and LiOH contain neither nitrogen nor sulfur, so they have the advantage of not generating toxic substances during the calcination process.

The above-mentioned examples of lithium raw materials may be used alone, or any two or more of them may be used in combination in any proportion.

Nickel raw material

The nickel raw material is not particularly limited as long as it contains nickel.

Examples of nickel raw materials include Ni(OH) ₂ , NiO, NiOOH, NiCO ₃ 2Ni(OH) ₂ 4H ₂ O, NiC ₂ O ₄ 2H ₂ O, Ni(NO ₃ ) ₂ 6H ₂ O, NiSO ₄ , NiSO ₄ ·6H ₂ O, nickel-containing fatty acids and nickel halides. Among them, compounds containing neither nitrogen nor sulfur such as Ni(OH) ₂ , NiO, NiOOH, NiCO ₃ .2Ni(OH) ₂ .4H ₂ O, and NiC ₂ O ₄ .2H ₂ O are preferable, which are Because they do not produce toxic substances during the calcination process. Ni(OH) ₂ , NiO and NiOOH are particularly preferred because they are available as industrial raw materials at low cost and also because of their high reactivity during calcination.

The above-mentioned examples of nickel raw materials may be used alone, or any two or more of them may be used in combination in any proportion.

Cobalt raw material

The cobalt raw material is not particularly limited as long as it contains cobalt.

Examples of cobalt raw materials include CoO, Co ₂ O ₃ , Co ₃ O ₄ , Co(OH) ₂ , CoOOH, Co(NO ₃ ) ₂ 6H ₂ O, CoSO ₄ 7H ₂ O, organic cobalt compounds, and halogenated cobalt. thing. Among them, CoO, Co ₂ O ₃ , Co ₃ O ₄ , Co(OH) ₂ and CoOOH are preferable.

The above-mentioned examples of cobalt raw materials may be used alone, or any two or more of them may be used in combination in any proportion.

Raw material for element M

The raw material of the element M is not particularly limited as long as it contains the element M defined in the description of the composition formula (1).

The raw material of the element M can be exemplified by oxides, hydroxides, oxyhydroxides, fatty acid salts and halides of the element M, similarly to the above-mentioned nickel raw material and cobalt raw material. Among them, oxides, hydroxides, and oxyhydroxides are preferable.

Examples of the raw materials of the above-mentioned element M may be used alone, or any two or more of them may be used in combination in any ratio.

Part or all of the nickel raw material, cobalt raw material and element M raw material can also be selected from: co-precipitated hydroxides and co-precipitated carbonates of two or more elements selected from nickel, cobalt and element M; and A composite oxide obtained by calcining any one of the coprecipitated hydroxide and the coprecipitated carbonate.

Pulverization and mixing of nickel raw materials, cobalt raw materials, and elemental M raw materials

The nickel raw material, the cobalt raw material and the raw material of the element M are dispersed in a dispersion medium and pulverized and mixed by a wet method to make a slurry. In this stage, part of the required lithium raw material can be added in advance so that lithium exists in the slurry in the form of aqueous solution or particles.

The dispersion medium used in this stage may be any liquid, but water is particularly preferable in view of environmental load. However, if a water-soluble compound is used as the nickel raw material, cobalt raw material and/or element M raw material, it is preferable to select a liquid that does not dissolve any of the nickel raw material, cobalt raw material and element M raw material. Otherwise hollow particles may be obtained by spray drying as described below, and the filling efficiency of the active material into the positive electrode is thus limited.

The equipment for pulverizing and mixing the raw materials should by no means be limited, but can be arbitrarily selected, and the equipment can be exemplified by bead mills, ball mills, and vibration mills.

The nickel raw material, the cobalt raw material, and the raw material of the element M are pulverized to such an extent that the median diameter of the raw material particles in the slurry obtained by pulverization is usually 2 μm or less, preferably 1 μm or less, more preferably 1 μm or less 0.5 μm. If the median diameter of the raw material particles is larger than the above range, the reactivity during calcination decreases. In addition, the sphericity of the granules obtained by spray drying as described below is compromised, resulting in a decrease in the final packing density of the granules. The above tendency is particularly evident when trying to produce particles with a median diameter of 20 μm or less.

On the other hand, since crushing the raw material into too fine powder will increase the cost of crushing, it is preferable to crush the raw material so that the median particle size is generally greater than or equal to 0.01 μm, preferably greater than or equal to 0.02 μm, and more preferably greater than or equal to 0.1 μm.

Granulation/drying

After wet pulverization and mixing of nickel raw material, cobalt raw material, and element M raw material, the particles dispersed in the slurry are aggregated to form larger granular matter (aggregated particles, secondary particles), that is, granulated, and simultaneously dried the granular matter. As the method of granulation and drying, spray drying using a spray dryer is preferably adopted because the obtained granules (aggregated particles) have excellent uniformity, powder fluidity and powder handling properties, and, due to granulation and drying Simultaneously, it is possible to efficiently form secondary particles.

The diameter of the granules obtained by spray drying can almost exactly define the diameter of the secondary particles which are the particles of the present invention. In view of this, the particle diameter of the granules obtained by drying is generally greater than or equal to 1 μm, preferably greater than or equal to 2 μm, and generally less than or equal to 20 μm, preferably less than or equal to 15 μm. Particle diameter can also be controlled by choice of spray pattern, supply rate of pressurized gas, supply rate of slurry, drying temperature and/or other factors.

Alternatively, granulation and drying can also be carried out by other methods than spray drying. Another example of the granulation method is a co-precipitation method in which an aqueous solution containing nickel, cobalt and the element M is reacted with an alkaline aqueous solution to obtain a hydroxide, wherein the stirring rate, pH and temperature are appropriately determined.

In this case, the hydroxide granulated by the coprecipitation method is filtered and subjected to treatment such as washing, followed by drying with a drying oven or the like.

Mixed with lithium raw material

The granulated matter obtained through the above-mentioned granulation and drying process is then dry-blended with a lithium raw material to make a mixture powder.

In order to improve the mixing efficiency with the granular matter obtained by spray drying and improve the capacity of the resulting battery, the average particle diameter of the lithium raw material is usually less than or equal to 500 μm, preferably less than or equal to 100 μm, more preferably less than or equal to 50 μm, most preferably less than or equal to Equal to 20μm. However, since too small an average particle diameter will lead to low stability of the particles in the atmosphere, the lower limit of the average particle diameter is generally greater than or equal to 0.01 μm, preferably greater than or equal to 0.1 μm, more preferably greater than or equal to 0.2 μm, It is preferably at most 0.5 μm or more.

The method for performing dry blending should not be limited, but it is preferable to use a powder mixer used in general industrial use. Particulates and lithium feedstock can be mixed in any ratio, depending on the composition or other properties of the target porous particles.

Grading / Calcination

Subsequently, the resulting mixed powder is subjected to a calcination process by which the primary particles are sintered to form secondary particles.

The calcination process can be performed in any manner, for example, using a box furnace, a tubular furnace, a tunnel furnace, a rotary kiln, and the like. The calcination process generally consists of three steps: raising the temperature; maintaining the maximum temperature; and lowering the temperature. The second step (maintaining the highest temperature) is by no means limited to a single stage, but can have two or more stages as desired.

Moreover, during the calcination process, the above-mentioned steps of raising the temperature, maintaining the highest temperature and lowering the temperature can be repeated twice or more. It is also possible optionally to interpose a series of two calcinations with a comminution process which breaks down the aggregates to such an extent that the secondary particles are not destroyed.

heating step

In the temperature raising step, the temperature in the furnace is raised at a temperature raising rate of usually 0.2° C./min to 20° C./min. An excessively low temperature increase rate requires a long time, and thus is disadvantageous from an industrial point of view. On the contrary, an excessively high heating rate will cause the actual temperature in the furnace to be inconsistent with the set temperature of the furnace.

Maximum temperature holding step

The calcination temperature in the highest temperature holding step varies depending on the type, composition ratio, and mixing timing of the lithium raw material, nickel raw material, cobalt raw material, and element M raw material used, but is usually 500°C or higher, preferably 600°C or higher , more preferably greater than or equal to 800°C, and usually less than or equal to 1200°C, preferably less than or equal to 1100°C. If the calcination temperature is lower than the above lower limit, there is a tendency that a longer calcination time is required in order to obtain particles having good crystallinity and suitable strength. On the other hand, if the calcination temperature is higher than the above upper limit, the resulting porous particles have excessive strength or have many defects such as lack of oxygen. Thus, if the porous particles are used as a positive electrode active material, the resulting lithium secondary battery suffers from a decrease in low-temperature load characteristics, or deterioration due to charge and discharge damage due to the crystal structure of the particles.

The temperature holding time in the highest temperature holding step is usually selected from a wide range of 1 hour to 100 hours. If the calcination time is too short, it is difficult to obtain particles with good crystallinity and suitable strength.

cooling step

In the temperature lowering step, the temperature in the furnace is usually lowered at a cooling rate of 0.1° C./min to 20° C./min. Too low a rate requires longer time and is therefore disadvantageous from an industrial point of view, while too high a rate can lead to a lack of uniformity in the product and accelerate deterioration of the container.

other

The strength of the particles of the present invention also varies depending on the atmosphere of calcination. Assuming the same calcination temperature, the less oxygen contained in the calcination atmosphere, the harder the structure of the resulting particles. The atmosphere during calcination should therefore be properly selected in consideration of the calcination temperature. Generally, the calcination process is preferably carried out in an atmosphere having an oxygen content of greater than or equal to 10% by volume, such as air. Too low an oxygen content may cause the particles to have many defects such as lack of oxygen.

The lithium composite oxide obtained by calcination is disintegrated and classified as the particles of the present invention, if necessary. Disintegration and classification can be performed by known methods, for example using a vibrating sieve with compacting balls.

Notes during production

In order to obtain the particles of the present invention, it is important to consider some aspects related to production, which are described below.

It is important to control the mixed state of the nickel, cobalt, and element M wet pulverized raw materials and the lithium raw material. In particular, it is important to ascertain that most of the lithium raw material remains outside the granulated particles produced by granulation of wet pulverized raw materials of nickel, cobalt and element M in the mixture powder before performing the calcination process. A calcination process is performed on the mixture powder to produce particles with suitable strength.

However, when the nickel, cobalt and element M raw materials are granulated by co-precipitation, the granules obtained through the calcination process tend to be too hard in structure even if most of the lithium raw material in the mixture powder is outside the granulated particles. Thus, if the raw materials of nickel, cobalt and element M are prepared by co-precipitation, it is important to first wet pulverize these raw materials and then granulate them into granulated particles, followed by dry blending with lithium raw materials. Thus, the particles of the present invention can be obtained.

If the main part of the lithium raw material is in the granulated particles obtained by granulating wet pulverized raw materials of nickel, cobalt and element M, the particles obtained by the calcination process tend to be too weak in structure. Even in this case, the strength of the pellets can be improved by mixing a sintering agent, although the use of the sintering agent is difficult to control and the resulting pellets tend to be structurally too hard.

For the above reasons, in order to obtain the particles of the present invention, it is important to dry blend wet pulverized raw materials of nickel, cobalt and element M, or granulated particles obtained by granulating wet pulverized co-precipitated raw materials, with lithium raw materials.

The specific procedure for obtaining the particles of the present invention is by no means limited, but may be selected from various methods in consideration of the kind of each raw material used. For example, if NiO, Co(OH) ₂ , and manganese raw materials such as Mn ₃ O ₄ are used as raw materials for nickel raw material, cobalt raw material, and element M, respectively, an example of the procedure is to use NiO Wet blending with cobalt and manganese raw materials, followed by spray drying and finally dry blending with lithium raw materials.

II. Positive electrodes for lithium secondary batteries

The positive electrode for a lithium secondary battery of the present invention is characterized in that the positive electrode active material layer formed on the current collector contains the above-mentioned particles and the binder of the present invention.

The positive electrode for a lithium secondary battery of the present invention is manufactured by forming a positive electrode active material layer containing the particles of the present invention and a binder on a current collector.

Fabrication of positive electrodes containing the particles of the invention can be accomplished according to conventional methods. Specifically, the particles and binder of the present invention, optionally with other ingredients such as conductive material and thickener, are dry-blended to form a sheet when necessary, and attached to a positive electrode current collector with pressure. Alternatively, these ingredients are dissolved or dispersed in a dispersion medium to form a slurry, which is applied on a positive electrode current collector and dried. Alternatively, any method that can produce a positive electrode active material layer on a current collector is used.

The particles of the present invention are preferably used in such a manner that the content of the particles in the positive electrode active material layer is generally greater than or equal to 10% by weight, preferably greater than or equal to 30% by weight, more preferably greater than or equal to 50% by weight, and Usually less than or equal to 99.9% by weight. If the content is lower than the above range, sufficient conductive capacity cannot be ensured. On the contrary, if the content is higher than the above range, the strength of the positive electrode is insufficient.

As the binder, any substance can be used as long as it is stable in the dispersion medium. Adhesive material can be enumerated: such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, aromatic polyamide, cellulose and nitrocellulose and other resin polymers; such as SBR ( Rubber-like polymers such as styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), fluororubber, isoprene rubber, butadiene rubber, and ethylene-propylene rubber; such as styrene-butadiene rubber Ethylene-styrene block copolymer and its hydrogenated products, EPDM (ethylene-propylene-diene terpolymer), styrene-ethylene-butadiene-ethylene copolymer, styrene-isoprene-styrene Thermoplastic elastomeric polymers such as block copolymers and their hydrogenated compounds; such as syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymer and propylene-α-olefin copolymer, etc. Soft resinous polymers; fluoride polymers such as polyvinylidene fluoride, polytetrafluoroethylene, perfluoropolyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymers; and polymers with alkali metal ions (especially lithium ions) ) of ion-conducting polymer complexes. Examples of the above-mentioned binders may be used alone, or in any combination of two or more in any ratio.

It is preferable to use the binder in such a manner that its content in the positive electrode active material layer is generally greater than or equal to 0.1% by weight, preferably greater than or equal to 1% by weight, further preferably greater than or equal to 5% by weight, and usually less than or equal to It is equal to 80% by weight, preferably 60% by weight or less, more preferably 40% by weight or less. If the content of the binder is lower than the above range, the cathode active material may not be sufficiently fixed, resulting in insufficient mechanical strength of the cathode and degradation of battery performance such as cycle performance. On the other hand, if the content of the binder is higher than the above range, the battery capacity or conductivity decreases.

As the conductive material, any known conductive material can be used. As the conductive material, various materials can be cited, including: metal materials such as copper and nickel; graphite such as natural graphite and artificial graphite; carbon black such as acetylene black; and carbon materials such as amorphous carbon such as needle coke. The conductive materials can be used alone, or in combination of any two or more in any proportion.

It is preferable to use the conductive material in such a manner that its content in the positive electrode active material is generally greater than or equal to 0.01% by weight, preferably greater than or equal to 0.1% by weight, more preferably greater than or equal to 1% by weight, and generally less than or equal to 50% by weight. % by weight, preferably less than or equal to 30% by weight, more preferably less than or equal to 15% by weight. If the content of the conductive material is below the range, sufficient conductivity cannot be ensured. On the contrary, if the content of the conductive material is higher than the range, the battery capacity decreases.

The dispersion medium used to prepare the slurry should by no means be limited as long as it can dissolve or disperse the positive electrode material, binder, conductive material, and thickener, and it may be an aqueous medium or an organic medium.

Examples of aqueous media include water and alcohols.

Examples of organic media are: aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, and methylnaphthalene; heterocyclic compounds such as quinoline and pyridine; acetone, methyl ethyl ketone, etc. Ketones such as cyclohexanone and cyclohexanone; esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and N-N-dimethylaminopropylamine; such as dimethyl ether, ethylene oxide and tetrahydrofuran (THF) ethers; amides such as N-methylpyrrolidone (NMP), dimethylformamide, and dimethylacetamide; and aprotic polar solvents such as hexamethylphosphoric acid amide and dimethyl sulfoxide. Especially when an aqueous medium is used as the dispersion medium, it is preferable to mix the dispersion medium with a thickener and make a slurry with latex such as SBR. Examples of the dispersion medium may be used alone, or in combination of any two or more of them in any ratio.

The positive electrode active material layer preferably has a thickness of 10 μm to 200 μm.

The material of the positive electrode current collector is not particularly limited, and may be arbitrarily selected from known materials. Examples of the material are: metal materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum; and carbon materials such as carbon cross and carbon paper. Among them, metal materials, especially aluminum, are preferably used.

Current collectors can be made into any shape, examples of which include: in the case of metallic materials, metal foils, metal posts, metal coils, metal plates, metal films, expanded metal, punched metal, metal foam and other shapes; In the case of carbon materials, there are shapes selected from carbon plates, carbon films, carbon pillars, and others; metal films are preferred in said examples. If the current collector is made into a film, it can be formed into a mesh if desired. The thickness of the film is not limited, but is generally greater than or equal to 1 μm, preferably greater than or equal to 3 μm, more preferably greater than or equal to 5 μm, and generally less than or equal to 1 mm, preferably less than or equal to 100 μm, more preferably less than or equal to 50 μm. A film having a thickness below the above range has insufficient strength required as a current collector. A film having a thickness higher than the above range is difficult to process.

In order to increase the packing density of the positive electrode active material, it is preferable to press the positive electrode active material layer formed by coating and drying with a roll pressing machine.

III. Lithium secondary battery

The lithium secondary battery of the present invention will be described below.

The lithium secondary battery of the present invention includes a positive electrode and a negative electrode capable of absorbing and releasing lithium ions and an organic electrolyte solution containing lithium salt as an electrolyte, and is characterized in that the positive electrode is made of the particles of the present invention.

The negative electrode used in the lithium secondary battery of the present invention is not specifically limited, as long as the negative electrode can absorb and release lithium. The negative electrode may be manufactured using any method, for example, by forming a negative electrode active material layer on a negative electrode current collector.

The material of the negative electrode current collector can be selected from any known materials. Examples of the material are: metal materials such as copper, nickel, stainless steel, and nickel-plated steel; and carbon materials such as carbon cross and carbon paper. The metal material can be made into a shape selected from metal foil, metal pillar, metal coil, metal plate, metal film, etc., and the carbon material can be made into a shape selected from carbon plate, carbon film, and carbon pillar. Among them, a metal film is preferable. If the current collector is made into a film, it can be formed into a mesh if desired. The thickness of the film is not limited but is generally greater than or equal to 1 μm, preferably greater than or equal to 3 μm, more preferably greater than or equal to 5 μm, and usually less than or equal to 1 mm, preferably less than or equal to 100 μm, more preferably less than or equal to 50 μm. A film having a thickness below the above range has insufficient strength required as a current collector. On the other hand, a film having a thickness higher than the above range is difficult to process.

The negative electrode active material contained in the negative electrode active material layer can be made of any material, as long as the material can absorb and release lithium ions electrochemically, but due to the high safety of carbon materials, the negative electrode active material is usually made of materials that can absorb and release lithium ions. and carbon materials that release lithium ions.

Examples of the carbon material include: graphite such as artificial graphite and natural graphite; and thermal decomposition products of organic compounds obtained under various thermal decomposition conditions. Thermal decomposition products of organic compounds include: coal coke, petroleum coke, carbides of coal tar pitch; carbides of petroleum pitch; oxidized coal or carbides of petroleum pitch; needle coke, pitch coke, phenol resin, crystalline fiber carbon materials obtained by partially graphitizing the above materials; and furnace black, acetylene black, pitch carbon fibers, and others. Among the above-mentioned examples, it is preferable to use graphite, especially artificial graphite produced by high-temperature heat treatment of tin-graphite pitch made of various materials, purified natural graphite, and their pitch-containing ones with various surface treatments. graphite material. Examples of the above-mentioned carbon materials may be used alone, or any two or more of them may be used in combination.

When a graphite material is used, it is preferable that the d value (interlayer spacing) of the lattice plane (002 plane) obtained by X-ray diffraction by the Gakushin method (method prescribed by the Japan Society for the Promotion of Science) is usually 0.335 nm or more and usually Materials less than or equal to 0.34 nm, especially less than or equal to 0.337 nm. The ash content in the graphite material is generally less than or equal to 1 wt%, preferably less than or equal to 0.5 wt%, more preferably less than or equal to 0.1 wt%, relative to the weight of the graphite material. The crystal size (Lc) of the graphite material obtained by X-ray diffraction by the Gakushin method is generally greater than or equal to 30 nm, preferably greater than or equal to 50 nm, more preferably greater than or equal to 100 nm. The median particle size of the graphite material obtained by the laser diffraction/scattering method is usually greater than or equal to 1 μm, preferably greater than or equal to 3 μm, more preferably greater than or equal to 5 μm, further preferably greater than or equal to 7 μm, and usually less than or equal to 100 μm, preferably less than Or equal to 50 μm, more preferably less than or equal to 40 μm, further preferably less than or equal to 30 μm.

The specific surface area of the graphite material measured according to the BET method is usually greater than or equal to 0.5m ² /g, preferably greater than or equal to 0.7m ² /g, more preferably greater than or equal to 1.0m ² /g, further preferably greater than or equal to 1.5m ² /g, and usually less than or equal to 25.0m ² /g, preferably less than or equal to 20.0m ² /g, more preferably less than or equal to 15.0m ² /g, further preferably less than or equal to 10.0m ² /g. When a graphite material is measured by Raman spectroscopic analysis using an argon laser beam, the peak P _A detected in the range of 1580 cm ^-1 to 1620 cm ^-1 and the peak P _B detected in the range of 1350 cm ^-1 to 1370 cm ^-1 The intensity ratio I _A / _IB is preferably greater than or equal to 0 and less than or equal to 0.5, and the half-width value of the peak _PA is preferably less than or equal to 26 cm ^-1 , more preferably less than or equal to 25 cm ^-1 .

Examples of negative electrode active materials other than carbon materials include: metal oxides such as tin oxide and silicon dioxide; pure lithium and lithium alloys such as lithium aluminum alloy; and the like. These examples may be used alone or in any combination of two or more, and may also be used in combination with a carbon material.

The negative active material layer can be formed in the same manner as the positive active material layer. Specifically, a negative electrode active material, a binder, and an optional thickener and a conductive material are made into a slurry together with a dispersion medium, and then the slurry is coated on a negative electrode current collector and dried to form a negative electrode active material layer. As the dispersion medium, binder, conductive material, and thickener used in the negative electrode active material, the same materials as those used in the positive electrode active material can be used.

Examples of the electrolyte include organic electrolytes, polymer solid electrolytes, gel electrolytes, and inorganic solid electrolytes, among which organic electrolytes are preferred.

As the organic electrolytic solution, any known organic solution can be used. Examples of organic solutions are: carbonates such as dimethyl carbonate, diethyl carbonate, propylene carbonate, ethylene carbonate, and vinylene carbonate; carbonates such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-diox alkanes, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,3-dioxolane, 4-methyl-1,3-dioxolane and diethyl Ethers such as ether; ketones such as 4-methyl-2-pentanone; sulfolane compounds such as sulfolane and methyl sulfolane; sulfoxide compounds such as dimethyl sulfoxide; lactones such as gamma-butyrolactone nitriles such as acetonitrile, propionitrile, benzonitrile, butyronitrile, and valeronitrile; hydrocarbon chlorides such as 1,2-dichloroethane; amines; esters; amides such as dimethylformamide; and Phosphate compounds such as trimethyl phosphate and triethyl phosphate. These examples can be used alone, or in any combination of two or more.

For dissociating the electrolyte, it is preferable that the organic electrolyte solution contains a high dielectric medium with a relative permittivity of 20 or more at 25°C. Among them, the organic electrolytic solution preferably contains an organic medium selected from ethylene carbonate, propylene carbonate, and their derivatives in which any hydrogen atom is replaced by a halogen atom, an alkyl group, or the like. Relative to the whole organic electrolyte, the content of the high dielectric medium in the organic electrolyte is generally greater than or equal to 20 wt%, preferably greater than or equal to 30 wt%, more preferably greater than or equal to 40 wt%. Optionally, it is also preferred to add additives such as gases (such as CO ₂ , N ₂ O, CO and SO ₂ ) and polysulfides S _x ^2- to the organic electrolyte in any proportion, so that the formed on the surface of the negative electrode required coating layer, thereby enabling efficient charging/discharging of lithium ions.

As the solute, any known lithium salt can be used. Examples of lithium salts are LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiB(C ₆ H ₅ ) ₄ , LiCl, LiBr, CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, LiN(SO ₂ CF ₃ ) ₂ , LiN(SO ₂ C ₂ F ₅ ) ₂ , LiC(SO ₂ CF ₃ ) ₃ and LiN(SO ₃ CF ₃ ) ₂ . These salts may be used alone or in any combination of two or more in any ratio.

The lithium salt concentration in the electrolyte is usually greater than or equal to 0.5 mol/L and less than or equal to 1.5 mol/L. If the concentration is too high or too low, conductivity decreases and battery performance deteriorates. It is thus preferable that the lower limit of the concentration is greater than or equal to 0.75 mol/L and the upper limit is less than or equal to 1.25 mol/L.

When the inorganic solid electrolyte is used for the organic electrolyte, it can be selected from any material known to be useful as the inorganic solid electrolyte, either crystalline or amorphous. Examples of crystalline inorganic solid electrolytes are LiI, Li ₃ N, Li _(1+x) M ¹ _x Ti _(2-x) (PO ₄ ) ₃ and Li _(0.5-3x) RE _(0.5+x) TiO ₃ ( wherein M ¹ is Al, Sc, Y or La, RE is La, Pr, Nd or Sm, and x is a number satisfying 0≤x≤2). Examples of amorphous _{inorganic solid electrolytes are oxide glasses such as 4.9LiI-34.1Li2O-61B2O5 and 33.3Li2O - 66.7SiO2} . These examples may be used alone or in any combination of two or more in any ratio.

In order to prevent a short circuit between electrodes, the secondary battery preferably has a separator interposed between the positive electrode and the negative electrode and holding the non-aqueous electrolyte.

The separator may be formed of any material and in any shape as long as it is stable to the electrolyte solution, has excellent liquid retention, and can securely prevent short circuits between electrodes. For example, the separator can be a microporous film, a sheet, or a non-woven fabric made of any polymer material. Examples of polymer materials are nylon, cellulose acetate, nitrocellulose, polysulfone, polyacrylonitrile, polyvinylidene fluoride, and polyolefin polymers such as polypropylene, polyethylene, and polybutene. Among them, polyolefin polymers are preferable in view of chemical stability and electrochemical stability, and polyethylene is preferable in view of the self-blocking temperature of the resulting battery. As polyethylene, ultra-high molecular weight polyethylene is preferable because it has excellent shape retention properties at high temperatures. The molecular weight of polyethylene is preferably greater than or equal to 5.0×10 ⁵ and less than or equal to 5.0×10 ⁶ . Polyethylene with a smaller molecular weight cannot maintain the same molecular shape at high temperatures. Accordingly, the molecular weight is preferably greater than or equal to 1.0×10 ⁶ , more preferably greater than or equal to 1.5×10 ⁶ . In contrast, polyethylene with an excessively high molecular weight has such low fluidity that the pores of the separator are not blocked when heated. In consideration of the above aspects, the molecular weight of polyethylene is preferably 4.0×10 ⁶ or less, more preferably 3.0×10 ⁶ or less.

The shape of the lithium secondary battery can be selected from various commonly used shapes according to the application. Examples of the shape are: a cylindrical shape in which a sheet electrode and a separator are made into a spiral shape; an inner zinc outer carbon type cylindrical shape in which a sheet electrode is combined with a separator; a button shape in which a sheet electrode is laminated electrodes and separators. The lithium secondary battery of the present invention can be manufactured by any known method according to a desired shape of the battery.

Example

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is by no means limited to the following Examples.

Production of Lithium Composite Oxide Particles

Example 1

NiO, Co(OH) ₂ , and Mn ₃ O ₄ , which are nickel, cobalt, and manganese raw materials, respectively, were weighed so that the molar ratio of Ni:Co:Mn was 0.33:0.33:0.33. Pure water was added to the weighed raw materials to prepare a slurry. Then, under stirring, the slurry was wet pulverized by a circulating medium agitation type wet bead mill until the average particle diameter of the solid matter in the slurry was 0.3 μm.

The slurry was then spray-dried in a spray dryer to form roughly spherical granulated particles with a diameter of about 5 μm and composed of nickel, cobalt and manganese raw materials. LiOH powder having a median particle diameter of 3 μm was added to the granulated particles thus obtained so that the molar ratio of Li was 1.05 relative to the total moles of Ni, Co and Mn, followed by mixing with a high-speed stirrer. Thereby, a mixture powder of granulated particles of nickel, cobalt and manganese raw materials and lithium raw material can be obtained.

The mixture powder was calcined at 950° C. (heating rate and cooling rate 5° C./min) under air flow for 12 hours, and then the resulting product was disintegrated and sieved with a 45 μm mesh sieve to finally obtain lithium composite oxide particles (hereinafter referred to as "lithium composite oxide particles of Example 1").

Example 2

Weigh NiO, Co(OH) ₂ , Mn ₃ O ₄ and LiOH·H ₂ O as nickel, cobalt, manganese and lithium raw materials respectively, so that the molar ratio of Ni:Co:Mn:Li is 0.33:0.33:0.33: 0.05. Pure water was added to the weighed raw materials to prepare a slurry. Then, the slurry was wet pulverized with a circulating medium agitation type wet bead mill under stirring until the average particle diameter of the solid matter was 0.20 μm.

The slurry was then spray dried with a spray dryer to form roughly spherical granulated particles with a diameter of about 6 μm and composed of nickel, cobalt, manganese and lithium raw materials. LiOH powder having a median diameter of 3 μm was added to the granulated particles thus obtained so that the molar ratio of Li was 1.00 relative to the total moles of Ni, Co and Mn, followed by mixing with a high-speed stirrer. Thereby, a mixture powder of granulated particles made of Ni, Co, Mn and lithium raw material and lithium raw material can be obtained. The mixture powder was calcined in a tunnel furnace at 955° C. for 15 hours under air flow, and then the resulting product was disintegrated and sieved with a 45 μm mesh sieve to finally obtain lithium composite oxide particles (hereinafter referred to as “lithium composite oxide of Example 2”). oxide particles").

Example 3

Except for using CoOOH as the cobalt raw material, operations were carried out in the same manner as in Example 2, thereby obtaining lithium composite oxide particles (hereinafter referred to as "lithium composite oxide particles of Example 3").

Comparative example 1

LiOH·H ₂ O, NiO, Co(OH) ₂ and Mn ₃ O ₄ were weighed so that the molar ratio of Li:Ni:Co:Mn was 1.05:0.33:0.33:0.33. The weighed raw materials were made into a slurry, and wet pulverized in the same manner as in Example 1.

The slurry was then spray-dried with a spray dryer to form roughly spherical granulated particles with a diameter of about 10 μm and containing NiO, Co(OH) ₂ , Mn ₃ O ₄ and LiOH·H ₂ O.

The granulated particles were calcined and disintegrated in an air stream in the same manner as in Example 1, thereby obtaining lithium composite oxide particles (hereinafter referred to as "lithium composite oxide particles of Comparative Example 1").

Comparative example 2

In the same manner as Comparative Example 1, each raw material was weighed, wet pulverized, and spray-dried to obtain a particle diameter of about 10 μm and containing NiO, Co(OH) ₂ , Mn ₃ O ₄ and LiOH·H ₂ O Roughly spherical granulated particles.

Bi ₂ O ₃ powder was added to the granulated particles thus obtained so that the molar ratio of Bi was 0.01 with respect to the total moles of Ni, Co, and Mn, followed by mixing with a high-speed stirrer. Thus, granulated particles containing NiO, Co(OH) ₂ , Mn ₃ O ₄ and LiOH·H ₂ O and a mixture powder of Bi ₂ O ₃ can be produced.

Then the mixed powder was calcined at 900°C (heating rate and cooling rate of 5°C/min) for 12 hours, and then the resulting product was disintegrated and sieved with a 45 μm mesh sieve to finally obtain lithium composite oxide particles (hereinafter referred to as "Lithium Composite Oxide Particles of Comparative Example 2")

Comparative example 3

Particles prepared by the co-precipitation method containing nickel, cobalt, and manganese in a molar ratio of 0.33:0.33:0.33 and having an average diameter of 15 µm were used. LiOH powder having a median diameter of 3 μm was added to the particles so that the molar ratio of LiOH was 1.05 relative to the total moles of nickel, cobalt and manganese, followed by mixing. Thereby, a mixture powder of the granulated particles and the lithium raw material can be obtained.

Then, the mixture powder was calcined in a tunnel furnace at 900° C. for 12 hours under air flow, and then the product was sieved with a 45 μm mesh sieve to obtain lithium composite oxide particles (hereinafter referred to as “lithium composite oxide of Comparative Example 3”). Particles")

Evaluation of Lithium Composite Oxide Particles

Determination of various properties by mercury intrusion porosimetry and other methods

The pore size distribution curves of the lithium composite oxide particles obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were measured by mercury intrusion porosimetry. As a measuring device for mercury intrusion porosimetry, Autopore(R) III 9420 manufactured by Micromeritics was used. Mercury intrusion porosimetry is carried out at room temperature, and the pressure of mercury increases from 3.8KPa to 410MPa. Assuming that the surface tension of mercury is 480 dyn/cm, the contact angle of mercury is 141.3°.

The pore size distribution curves of the lithium composite oxide particles of Example 1 and Comparative Examples 1 and 2 are represented by solid lines in FIGS. 1 and 2 . Both Fig. 1 and Fig. 2 show the pore size distribution curve by taking the pore radius of the lithium composite oxide particle as the abscissa pair and passing the total volume of the pores whose radii are greater than or equal to the pore radius at the corresponding abscissa point versus the The value obtained by differentiating the logarithm of the pore radius was plotted as an ordinate. FIG. 2 is a partially enlarged view of FIG. 1 .

In addition, the lithium composite oxide particles of Examples 1-3 and Comparative Examples 1-3 were measured by nitrogen adsorption BJH (Barrett, Joyner, Halenda) method to obtain the pore radius distribution of the particles. As a measuring instrument for the nitrogen adsorption BJH method, Autosorb(R) 1 manufactured by Quantachrome Corporation was used, and the measurement was performed at liquid nitrogen temperature.

In addition, the particle size distribution was measured using a particle size distribution meter (LA-920 manufactured by HORIBA), and the median diameter of the particles was calculated from the particle size distribution.

For each of the lithium composite oxide particles of Examples 1 to 3 and Comparative Examples 1 to 3, Table 1 shows: the mercury indentation volume obtained from the above pore size distribution curve using the formula (A) when the pressure is increased from 50 MPa to 150 MPa; The pore volume and average pore radius of the main peak and sub-peak obtained from the pore size distribution curve; the total volume of pores with a radius less than or equal to 50nm per 1 gram of lithium composite oxide particles measured by nitrogen adsorption BJH method; BET specific surface area; and the median particle size obtained with a particle size distribution meter. In order to eliminate the influence of voids between secondary particles, the average pore radius shown here is obtained for pores with a radius of 0.005 μm to 0.5 μm.

Determination of other properties

The median diameter, BET specific surface area, primary particle diameter, and tap density of each lithium composite oxide particle of Examples 1 to 3 and Comparative Examples 1 to 3 were measured. The measurement of the median diameter was performed using a particle size distribution meter (LA-920 manufactured by HORIBA). The measurement of the BET specific surface area was performed using Autosorb(R) 1 manufactured by Quantachrome Corporation. Tap density was determined by placing granules (5 g) in a 10 mL glass measuring cup and tapping the granules 200 times. The measurement of primary particle diameter is carried out by SEM observation. The results are listed in Table 1.

Determination of low temperature load characteristics

Using each of the lithium composite oxide particles of Examples 1 to 3 and Comparative Examples 1 to 3 (hereinafter collectively referred to as "positive electrode materials" unless distinction is required), a secondary battery was manufactured according to the following method and the battery's performance was measured. Low temperature load characteristics.

The positive electrode material (75% by weight), acetylene black (20% by weight), and polytetrafluoroethylene powder (5% by weight) were weighed and thoroughly mixed in a mortar. The mixture was formed into flakes and pressed into discs with a diameter of 12 mm and the weight of the discs was adjusted to about 17 mg. A positive electrode was obtained by attaching the disc to an Al expanded metal mesh under pressure.

Graphite powder (d ₀₀₂ =3.35 Å) with an average particle diameter of 8-10 μm is used as the negative electrode active material, and polyvinylidene fluoride is used as the binder. Weigh negative electrode active material and binder, make weight ratio (negative electrode active material: binder) be 92.5: 7.5, and mix in N-methylpyrrolidone solvent, to obtain negative electrode composition slurry, this slurry Coated on one surface of copper foil with a thickness of 20 μm and then dried. The copper foil was pressed into a disk having a diameter of 12 mm and pressed at 0.5 ton/cm ² , whereby a negative electrode was prepared.

The battery is designed so that the capacity balance ratio R of the positive electrode to the negative electrode is 1.2 to 1.5. The capacity balance ratio R is determined according to the formula R=(Q _a ×W _a )/(Q _c ×W _c ), where Q _a represents the capacity (mAh/g) of Li ions that the negative electrode can absorb without precipitating Li metal, Q _c represents the capacity (mAh/g) of Li ions released by the positive electrode, and W _a and W _c represent the weight (g) of the negative electrode active material and the positive electrode active material, respectively. The determination of _Qa and _Qc is carried out as follows: a 2032 type button cell is assembled using a positive or negative electrode, together with Li metal as a counter electrode, a separator, and an electrolyte; and at a current density as low as possible, e.g., less than or equal to 20 mA /g (active material), the charge (Li absorption) capacity between the natural potential and the lower limit of 5 mV for the negative electrode or the charge capacity between the natural potential and 4.2 V for the positive electrode was determined.

A button cell was assembled using the above positive and negative electrodes together with a non-aqueous electrolyte obtained by dissolving _LiPF in ethylene carbonate (EC) + dimethyl carbonate (DMC) + ethyl methyl carbonate ( EMC) (volume ratio 3:3:4) in a mixed solvent so that the concentration of LiPF ₆ is 1 mol/L. Using the assembled cells, initial conditioning of two charge/discharge cycles was performed at the lowest possible current density with upper and lower limit voltages of 4.1 V and 3.0 V, respectively. The discharge capacity [Q _d (mAh/g)] per unit weight of the cathode active material was measured in the second cycle.

After sufficient relaxation, the battery was charged at a constant current of 1/3C for 72 minutes, assuming a 1-hour rate current [1C (mA)] = [Q _d (mAh/g) × weight (g) of positive electrode active material]. After standing still for 1 hour, the battery was kept in a low-temperature atmosphere of -30° C. for more than 1 hour. The battery was then discharged at 1/4C for 10 seconds while measuring the difference (ΔV) between the current value (I) at the time of discharge and the OCV (open circuit voltage) immediately before discharge and 10 seconds after discharge. The resistance (R) is calculated by the following formula.

R=ΔV/I

Table 1 shows the resistance values of batteries in which the positive electrode materials of Examples 1 to 3 and Comparative Examples 1 to 3 were used as positive electrode active materials. It is estimated that the smaller the resistance value, the better the low-temperature load characteristics. Determination of coatability

The coatability of the positive electrode materials of Examples 1 to 3 and Comparative Examples 1 and 2 was measured by the following method.

Add positive electrode material (85% by weight), acetylene black (10% by weight), polyvinylidene fluoride (5% by weight) to N-methylpyrrolidone together with 0.3% by weight of oxalic acid dihydrate relative to the weight of the positive electrode material Neutralize and disperse to form a slurry. Polyvinylidene fluoride and oxalic acid hydrate were previously dissolved in N-methylpyrrolidone. The ratio of the total volume of the positive electrode material, acetylene black, and polyvinylidene fluoride to the entire slurry was adjusted to the value shown in Table 1 (42% by weight or 43% by weight). The viscosity of the slurry at a shear rate of 20 s ⁻¹ was measured with an E-type viscometer at 25° C. Each slurry was tested on the day the slurry was prepared (Day 1), and a portion of the slurry was tested on the day following preparation (Day 2). The prepared slurry was sealed and stored at room temperature and pressure.

The viscosities measured by the above method are listed in Table 1. It is estimated that the lower the viscosity, the better the spreadability.

Table 1 Example 1 Example 2 Example 3 Comparative example 1 Comparative example 2 Comparative example 3 Mercury indentation volume at a pressure of 50MPa～150MPa (cm ³ /g) 0.0183 0.0120 0.0116 0.0213 0.0094 0.0090 Pore radius of the main peak (nm) 950 1200 1400 1200 2000 2900 Subpeak Pore Radius (nm) 170 210 72 - ^* 400 73 Pore volume of the main peak (cm ³ /g) 0.326 0.310 0.294 0.617 0.341 0.009 Subpeak Pore Volume (cm ³ /g) 0.020 0.037 0.012 - ^* 0.049 0.216 Average pore radius (nm) 20.8 31.5 14.8 13.3 41.5 13.8 Pore volume measured by BJH method (cm ³ /g) 0.003 - ^** - ^** 0.002 0.002 - ^** Particle median diameter (μm) 4.4 5.8 5.7 9.6 9.1 13.3 BET specific surface area (m ² /g) 1.20 1.12 0.77 1.00 0.90 0.40 Tap density (g/cm ³ ) 1.6 1.6 1.9 1.2 1.9 2.6 Primary particle diameter (μm) 0.8 1.2 0.7 1.0 - ^** 0.8 Resistance value at -30°C (Ω) 388 290 286 390 535 516 Solid content (weight%) 42 42 42 42 43 - ^** Slurry viscosity (first day) (cp) 2830 5230 3814 6625 5682 - ^** Slurry viscosity (the next day) (cp) 3342 - ^** - ^** 8280 5290 - ^**

^* Any subpeaks identified.

^** No data available.

evaluation of data

Regarding the lithium composite oxide particles of Comparative Example 1, it can be seen from FIG. 1 that although no clearly identifiable sub-peak was observed, a main peak with a peak at a radius of 1200 nm was observed on the pore size distribution curve. In addition, it can be clearly seen from Table 1 that as the pressure increases from 50MPa to 150MPa, the mercury indentation volume is 0.0213cm ³ /g, which is greater than the range specified by the present invention. The lithium composite oxide particles of Comparative Example 1 thus did not simultaneously satisfy the conditions (A) and (C) of the present invention.

In addition, Table 1 clearly shows that the lithium composite oxide particles of Comparative Example 1 have a good resistance value at -30°C, but the viscosity of the slurry is very high, especially increasing sharply from the first day to the second day. The results indicated that the lithium composite oxide particles of Comparative Example 1 could not obtain sufficient coatability.

Regarding the lithium composite oxide particles of Comparative Example 2, it can be seen from FIG. 1 that, in addition to the main peak with the peak at a radius of 2000 nm, a sub-peak is also observed on the pore size distribution curve, but the peak of the sub-peak is located at a radius of 400 nm. At the radius, the value is greater than the range specified by the present invention. In addition, it can be clearly seen from Table 1 that the mercury indentation volume is 0.0094 cm ³ /g, which fails to reach the range specified by the present invention. The results indicate that none of the lithium composite oxide particles of Comparative Example 2 satisfies the conditions (B) and (C) of the present invention.

As shown in Table 1, the lithium composite oxide particles of Comparative Example 2 had a resistance value as high as 535Ω at -30°C, and thus were considered not to have sufficient low-temperature load characteristics.

Regarding the lithium composite oxide particles of Comparative Example 3, the pore size distribution curve shows that the peak top is located at the main peak and the sub-peak at a radius of 2900 nm, however, the peak top of the sub-peak is located at a radius of 73 nm, which is lower than the range specified in the present invention . In addition, it can be seen from Table 1 that the mercury indentation volume is 0.0090 cm ³ /g, which does not reach the range of the present invention. Therefore, the lithium composite oxide particles of Comparative Example 3 also did not satisfy the conditions (B) and (C) of the present invention.

Also, since the resistance value at -30°C was as high as 516Ω, it is considered that the lithium composite oxide particles of Comparative Example 3 did not have sufficient low-temperature load characteristics.

On the other hand, as shown in Table 1, the lithium composite oxide particles of Example 1 showed a main peak at a pore radius of 950 nm and a sub-peak at a pore radius of 170 nm on the pore size distribution curve. In addition, the mercury indentation volume is 0.0183 cm ³ /g, which is within the scope of the present invention. In addition, as shown in Table 1, each lithium composite oxide particle of Example 2 and Example 3 has a sub-peak within the range of the present invention and a mercury intrusion within the range specified by the present invention on the pore size distribution curve. volume. Therefore, each of the lithium composite oxide particles in Examples 1 to 3 satisfies all of the conditions (A) to (C) of the present invention.

In addition, Table 1 shows that the lithium composite oxide particles of Examples 1 to 3 have both a low resistance value at -30°C and a low slurry viscosity, so it is considered that they have both excellent low-temperature load characteristics and coating properties. Cloth.

The present invention has been described in detail with reference to specific embodiments, but it will be apparent to those skilled in the art that various modifications can be made without departing from the scope of the present invention.

This application is based on Japanese Patent Application Nos. 2003-336335, 2003-336336, and 2003-336337 filed on September 26, 2003, and Japanese Patent Application No. 2004-278953 filed on September 27, 2004. The entire contents are hereby incorporated by reference.

Industrial Applicability

The lithium composite oxide particles for lithium secondary battery positive electrode materials according to the present invention can be used together with a binder to form an active material layer on a current collector, and the resulting positive electrode is suitable for a wide range of uses of lithium secondary batteries , such as mobile electronic devices, communication devices, and vehicle drive power supplies. Therefore, the present invention has great industrial value.

Claims (6)

1. lithium composite xoide particle that is used for positive electrode material of lithium secondary cell, wherein when being pressed into porosimetry with mercury and measuring, described lithium composite xoide particle satisfies condition (A), and satisfy condition (B) or condition (C) at least one condition, wherein:

Condition (A) representative is pressed into curve according to mercury, and when 50MPa increased to 150MPa, mercury was pressed into volume for being less than or equal to 0.02cm at pressure ³/ g;

Condition (B) representative is pressed into curve according to mercury, and when 50MPa increased to 150MPa, mercury was pressed into volume for more than or equal to 0.01cm at pressure ³/ g; With

It is 10nm～100nm that condition (C) is represented the average pore radius, and the pore size distribution curve has the main peak that summit is positioned at the pore radius place of 0.5 μ m～50 μ m, and summit is positioned at the inferior peak at the pore radius place of 80nm～300nm.

2. the lithium composite xoide particle that is used for positive electrode material of lithium secondary cell as claimed in claim 1, wherein when measuring with nitrogen adsorption method, the cumulative volume that radius is less than or equal to the hole of 50nm in the described lithium composite xoide particle of every gram is less than or equal to 0.01cm ³

3. the lithium composite xoide particle that is used for positive electrode material of lithium secondary cell as claimed in claim 1 or 2, wherein said lithium composite xoide particle contains Ni and Co at least.

4. as each described lithium composite xoide particle that is used for positive electrode material of lithium secondary cell of claim 1～3, wherein form by following formula (1) expression,

Li _xNi _(1-y-z)Co _yM _zO ₂ (1)

Wherein

The M representative is selected from least a element among Mn, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn and the Nb,

X represents the numerical value of 0＜x≤1.2,

Y represent 0.05≤y≤0.5 numerical value and

Z represents the numerical value of 0.01≤z≤0.5.

5. positive pole that is used for lithium secondary battery, described positive pole comprises:

Current-collector; With

Be arranged on the anode active material layer on the described current-collector;

Wherein said anode active material layer contains each described lithium composite xoide particle that is used for positive electrode material of lithium secondary cell of adhesive and claim 1～4 at least.

6. lithium secondary battery, described battery comprises:

Can absorb and discharge the positive pole of lithium;

Can absorb and discharge the negative pole of lithium; With

Contain lithium salts as electrolytical organic electrolyte;

Wherein said positive pole is the described positive pole that is used for lithium secondary battery of claim 5.

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