JP7048944B2 - Titanium and / or germanium-substituted lithium-manganese-based composite oxide and its production method - Google Patents

Description

The present invention relates to a titanium and / or germanium-substituted lithium-manganese-based composite oxide and a method for producing the same.

Currently, in Japan, most of the secondary batteries installed in portable devices such as mobile phones, smartphones, notebook computers, and tablet personal computers are lithium ion secondary batteries. Lithium-ion secondary batteries are being put to practical use as large-sized batteries for electric vehicles, power load leveling systems, etc., and their importance is increasing.

Currently, in a lithium ion secondary battery, a lithium-containing transition metal oxide is used as a positive electrode material, and a carbon material such as graphite is used as a negative electrode material. In particular, in the positive electrode material, the amount of lithium ions reversibly desorbed (corresponding to charging) and inserted (corresponding to discharge) determines the capacity of the battery, and the voltage at the time of desorption and insertion determines the operating voltage of the battery. Battery capacity and operating voltage are determined by the positive electrode. Further, the battery component cost is highest for the positive electrode active material, and the selection of the positive electrode material is the most important in the development of the lithium ion secondary battery.

Therefore, it is expected that the demand for positive electrode materials will further increase with the expansion of applications and the increase in size of lithium ion secondary batteries. However, lithium cobalt oxide, which is usually used as a positive electrode material, contains a large amount of cobalt, which is a rare metal, and is one of the factors that increase the material cost of lithium ion secondary batteries. Furthermore, considering that about 20% of cobalt resources are currently used in the battery industry, it is considered difficult to meet future demand expansion with only the positive electrode material consisting of LiCoO ₂ . Therefore, in particular, in order to use it in a large-sized lithium ion secondary battery for automobiles and the like, there is a demand for an oxide positive electrode material using a resource-rich element.

Currently, as a cheaper and less resource-constrained positive electrode material, we have found a layered rock salt-type solid solution (Li _{1 + x} (Fe)) consisting of lithium manganese oxide (Li ₂ MnO ₃ ) and lithium ferrite. _y Mn _1-y ) _1-x O ₂ (0 <x <1/3, 0 <y <1), sometimes referred to as "iron-containing Li ₂ MnO ₃ ") is a charge / discharge test at room temperature. Has been found to have an average discharge voltage close to 4 V, which is comparable to that of lithium cobalt oxide (see, for example, Patent Document 1).

In addition, the present inventors have found that lithium manganese oxide containing nickel, which is abundant in resources as well as iron (iron and nickel-containing Li ₂ MnO ₃ , etc.), can significantly improve cycle deterioration in the 4V region (iron and nickel-containing Li 2 MnO 3, etc.). For example, see Patent Document 2).

Furthermore, the present inventors have shown that lithium manganese oxides containing titanium, which is abundant in resources and inexpensive as well as iron (titanium-containing Li ₂ MnO ₃ , iron and titanium-containing Li ₂ MnO ₃ , etc.), show high capacity. In particular, they have found that they are excellent in discharge characteristics under high current density at room temperature and discharge characteristics at low temperature in a specific chemical composition and transition metal ion distribution (see, for example, Patent Document 3).

As described above, various reports have been made on lithium manganese-based positive electrode materials that can replace lithium-cobalt-based positive electrode materials, but further improvement in charge / discharge characteristics is desired.

Japanese Unexamined Patent Publication No. 2002-066748 Japanese Patent Application Laid-Open No. 2003-048718 Japanese Unexamined Patent Publication No. 2008-063211

However, when the lithium manganese-based composite oxides of Patent Documents 1 and 2 are used, the crystal phase of the layered rock salt type structure is gradually changed to the crystal phase of the spinnel type structure or the lithium excess crystal phase by repeating charging and discharging. Due to the changes, a sharp drop in potential is seen at around 3.5V at discharge, and additional capacitance appears at around 2.2V at discharge. Industrially, it is preferable that the charge / discharge curve shape can be maintained even after 100 cycles or 1000 cycles have elapsed, but in this method, the charge / discharge characteristics are deteriorated before that. Therefore, in the lithium manganese-based composite oxides of Patent Documents 1 and 2, the charge / discharge curve shape changes remarkably due to these two types of crystal structure transitions, and the similarity of the charge / discharge curves during the charge / discharge cycle cannot be maintained. Practically unfavorable.

Further, the lithium manganese-based composite oxide of Patent Document 3 has a low discharge voltage and a large charge / discharge curve hysteresis.

The present invention has been made in view of the current state of the prior art described above, and has a high capacity when used as a positive electrode material for a lithium ion secondary battery while using an inexpensive element with few resource restrictions. The main purpose of the present invention is to provide a novel material which has a high discharge voltage and is excellent in long-term cycle characteristics because it can maintain the similarity of the charge / discharge curve shape at the time of charge / discharge cycle.

The present inventors have carried out diligent research to achieve the above-mentioned object. As a result, the composite oxide obtained by dissolving a specific amount of titanium and / or germanium in a Li ₂ MnO type ₃ composite oxide containing a specific amount of iron and / or nickel is inexpensive due to less resource restrictions. When used as a positive electrode material for lithium-ion secondary batteries, it has a high capacity, a high discharge voltage, and the similarity of the charge / discharge curve shape during the charge / discharge cycle. It was found that it is excellent in long-term cycle characteristics because it can be maintained. Based on such findings, the present inventors have further studied and completed the present invention. That is, the present invention includes the following configurations.
Item 1. General formula (1):
Li _{1 + x} (M ¹ _y M ² _z Mn _1-yz ) _1-x O ₂ (1)
[In the formula, M ¹ indicates Fe and / or Ni. M ² indicates Ti and / or Ge. x, y and z indicate 0 <x <1/3, 0 ≤ y ≤ 0.4, 0 <z ≤ 0.3. ]
Represented by and
A lithium manganese-based composite oxide containing a crystalline phase having a monoclinic layered rock salt structure or a hexagonal layered rock salt structure.
Item 2. Item 2. The lithium manganese-based composite oxide according to Item 1, wherein M ¹ contains Ni in the general formula (1).
Item 3. Item 2. The lithium manganese-based composite oxide according to Item 1 or 2, which comprises only a crystal phase having a monoclinic layered rock salt type structure.
Item 4. Item 3. The method for producing a lithium manganese-based composite oxide according to any one of Items 1 to 3.
(1) A step of forming a precipitate by treating a mixture containing a manganese compound and at least one compound selected from the group consisting of an iron compound and a nickel compound as alkaline.
(2) A step of subjecting the precipitate obtained in step 1 to a wet oxidation treatment and aging it.
(3) A production method comprising a step of heating the aged product obtained in step 2 in the coexistence of a raw material compound containing a lithium compound in this order.
Item 5. Item 4. The production method according to Item 4, wherein the mixture in step 1 further contains a titanium compound.
Item 6. Item 6. The production method according to Item 4 or 5, wherein the raw material compound in the step 3 further contains a germanium compound.
Item 7. Item 6. The production method according to any one of Items 4 to 6, wherein the step 3 is a step of mixing the aged product obtained in the step 2 with the raw material compound and then heating the mixture.
Item 8. Item 2. The production method according to any one of Items 4 to 7, wherein the heating in step 3 is a step of heating in the atmosphere and then heating again in the atmosphere or in an inert atmosphere.
Item 9. A positive electrode material for a lithium ion secondary battery made of the lithium manganese-based composite oxide according to any one of Items 1 to 3.
Item 10. Item 9. A lithium ion secondary battery having the positive electrode material for the lithium ion secondary battery as a component.

According to the present invention, when used as a positive electrode material for a lithium ion secondary battery while using an inexpensive element with few resource restrictions, it has a high capacity, a high discharge voltage, and is charged. Since the similarity of the charge / discharge curve shape during the discharge cycle can be maintained, it is possible to provide a novel material having excellent long-term cycle characteristics.

In particular, since the lithium manganese-based composite oxide of the present invention is chemically stable even when charged to a high potential, it can exhibit excellent charge / discharge characteristics even during a long-term cycle.

The measured (+) and calculated (solid) X-ray diffraction patterns of the sample obtained in Example 1 are shown. The charge / discharge curve of a lithium secondary battery using the sample obtained in Example 1 as a positive electrode material and metallic lithium as a negative electrode material is shown. The measured (+) and calculated (solid) X-ray diffraction patterns of the sample obtained in Comparative Example 1 are shown. The charge / discharge curve of a lithium secondary battery using the sample obtained in Comparative Example 1 as a positive electrode material and metallic lithium as a negative electrode material is shown. The measured (+) and calculated (solid) X-ray diffraction patterns of the sample obtained in Example 2 are shown. The charge / discharge curve of a lithium secondary battery using the sample obtained in Example 2 as a positive electrode material and metallic lithium as a negative electrode material is shown. The measured (+) and calculated (solid) X-ray diffraction patterns of the sample obtained in Comparative Example 2 are shown. The charge / discharge curve of a lithium secondary battery using the sample obtained in Comparative Example 2 as a positive electrode material and metallic lithium as a negative electrode material is shown. The measured (+) and calculated (solid) X-ray diffraction patterns of the sample obtained in Example 3 are shown. The charge / discharge curve of a lithium secondary battery using the sample obtained in Example 3 as a positive electrode material and metallic lithium as a negative electrode material is shown. The measured (+) and calculated (solid) X-ray diffraction patterns of the sample obtained in Comparative Example 3 are shown. The charge / discharge curve of a lithium secondary battery using the sample obtained in Comparative Example 3 as a positive electrode material and metallic lithium as a negative electrode material is shown. The measured (+) and calculated (solid) X-ray diffraction patterns of the sample obtained in Example 4 are shown. The charge / discharge curve of a lithium secondary battery using the sample obtained in Example 4 as a positive electrode material and metallic lithium as a negative electrode material is shown. The measured (+) and calculated (solid) X-ray diffraction patterns of the sample obtained in Comparative Example 4 are shown. The charge / discharge curve of a lithium secondary battery using the sample obtained in Comparative Example 4 as a positive electrode material and metallic lithium as a negative electrode material is shown. The measured (+) and calculated (solid) X-ray diffraction patterns of the sample obtained in Example 5 are shown. The charge / discharge curve of a lithium secondary battery using the sample obtained in Example 5 as a positive electrode material and metallic lithium as a negative electrode material is shown.

1. 1. Lithium-manganese-based composite oxide The lithium-manganese-based composite oxide of the present invention has the general formula (1) :.
Li _{1 + x} (M ¹ _y M ² _z Mn _1-yz ) _1-x O ₂ (1)
[In the formula, M ¹ indicates Fe and / or Ni. M ² indicates Ti and / or Ge. x, y and z indicate 0 <x <1/3, 0 ≤ y ≤ 0.4, 0 <z ≤ 0.3. ]
It is a compound represented by, and contains a crystal phase of a monoclinic layered rock salt type structure or a hexagonal layered rock salt type structure based on a rock salt type structure.

The monoclinic layered rock salt type structure is a space group:

Li ₂ MnO type ₃ monoclinic layered rock salt consisting only of crystal phases having unit cells similar to Li ₂ MnO ₃ from the viewpoint of volume and cycle characteristics. It is preferably a crystal phase having a mold structure.

On the other hand, the hexagonal layered rock salt type structure is a space group:

It is a crystal phase that can be assigned in, and specifically, from the viewpoint of capacity and cycle characteristics, a crystal phase having a LiNiO type ₂ hexagonal layered rock salt structure consisting only of a crystal phase having unit cells similar to LiNiO ₂ . Is preferable.

The lithium manganese-based composite oxide of the present invention may have only one of the above-mentioned crystal phases of the monoclinic layered rock salt type structure and the hexagonal layered rock salt type structure, or may have both. May be good. In any case, the lithium manganese-based composite oxide of the present invention has a high capacity, a high discharge voltage, and during a charge / discharge cycle when used as a positive electrode material for a lithium ion secondary battery. It is a material with excellent long-term cycle characteristics because it can maintain the similarity of the charge / discharge curve shape.

When the lithium manganese-based composite oxide of the present invention has both the above-mentioned crystal phases of the monoclinic layered rock salt type structure and the hexagonal layered rock salt type structure, the ratio of each crystal phase is not particularly limited and is usually layered. Assuming that the total amount of crystalline phase of the rock salt type structure is 100% by weight, the crystalline phase of the monoclinic layered rock salt type structure is 1 to 99% by weight (especially 5 to 95% by weight, and further 10 to 90% by weight), and the hexagonal layered rock salt. The crystal phase of the mold structure is preferably 1 to 99% by weight (particularly 5 to 95% by weight, more preferably 10 to 90% by weight).

On the other hand, the lithium manganese-based composite oxide of the present invention may contain the crystal phase of the above-mentioned monoclinic layered rock salt type structure or hexagonal layered rock salt type structure, and other rock salt type structures having different cation distributions ( For example, it may be a mixed phase containing a crystalline phase (such as a cubic rock salt type structure). Further, the lithium manganese-based composite oxide of the present invention may be a material consisting only of the crystal phases of the above-mentioned monoclinic layered rock salt type structure and / or hexagonal layered rock salt type structure.

According to the production method of the present invention described later, the obtained lithium manganese-based composite oxide is likely to form a material consisting only of the crystal phases of the above-mentioned monoclinic layered rock salt type structure and / or hexagonal layered rock salt type structure. However, for example, when synthesized at a low temperature of 600 ° C. or lower, a crystalline phase having a cubic rock salt type structure may be contained. Since the crystal phase of this cubic rock salt type structure also has a crystal structure that exhibits excellent charge / discharge characteristics, it does not matter if it has this crystal structure.

However, in the present invention, since it has a crystal phase of a monoclinic layered rock salt type structure and a hexagonal layered rock salt type structure, it has a high capacity and high capacity when used as a positive electrode material for a lithium ion secondary battery. Since it is a material that has a discharge voltage and is excellent in long-term cycle characteristics because it can maintain the similarity of the charge / discharge curve shape during the charge / discharge cycle, it has a monoclinic layered rock salt structure and a hexagonal layered rock salt. It is preferable that the abundance ratio of the crystal phase of the mold structure is high. From this point of view, when the lithium manganese-based composite oxide of the present invention has another rock salt type structure (cubic rock salt type structure, etc.) having a different cation distribution, the ratio with the crystal phase of the layered rock salt type structure is Usually, the total amount of the lithium manganese-based composite oxide of the present invention is 100% by weight, and the crystal phase of the layered rock salt type structure is 1 to 99% by weight (particularly 10 to 95% by weight, further 50 to 90% by weight), etc. The crystalline phase of the rock salt type structure (cubic rock salt type structure, etc.) is preferably 1 to 99% by weight (particularly 5 to 90% by weight, further 10 to 50% by weight).

As represented by the above general formula (1), the lithium manganese-based composite oxide of the present invention contains Li, Mn and M ² as essential elements, and further dissolves M ¹ as necessary. I'm letting you.

When the lithium manganese-based composite oxide of the present invention contains M ¹ (when M ¹ is solid-dissolved), the amount of M ¹ ions to be solid-dissolved (y value; M ¹ / (M ¹ + M ² +) Mn)) is 40% or less (0 <y ≤ 0.4), preferably 5 to 35% (0.05 ≤ y ≤ 0.35), and more preferably 10 to 30% (0.1 ≤ y) of the total amount of metal ions other than Li ions. ≤0.3). When the solid solution amount (y value) of the M ¹ ion is excessive, the Mn amount is relatively small, so that the lithium content per composition formula is lowered and the charge / discharge capacity is remarkably lowered. On the other hand, by setting the lower limit of the solid solution amount (y value) of the M ¹ ion in the above range, the discharge potential can be further increased and the hysteresis can be further reduced.

When the lithium manganese-based composite oxide of the present invention contains M ¹ (when M ¹ is dissolved), it is present in the layered rock salt type structure in the form of substituting Li, Mn, etc. As it seems, it may contain only one of Fe and Ni, or it may contain both Fe and Ni. More specifically, Fe is cheaper than Ni, but since Ni has a higher redox potential, it is easier to increase the discharge voltage, so applications that require high potential (large lithium-ion secondary for automobile applications, etc.) Suitable for batteries, etc.). Therefore, it is preferable to appropriately set the amounts of Fe and Ni used according to the intended use. For example, when both Fe and Ni are contained, the total amount of M ¹ element is 100% by weight, and Fe is preferably 10 to 90% by weight (particularly 30 to 70% by weight, further 40 to 60% by weight). The amount of Ni used is set so that the total amount with the amount of Fe used is 100% by weight.

The amount of M ² ions (z value; M ² / (M ¹ + M ² + Mn)) dissolved in the lithium manganese-based composite oxide of the present invention is 30% or less of the total amount of metal ions other than Li ions (z value; M 2 / (M 1 + M 2 + Mn)). 0 <z ≤ 0.3), preferably 1 to 25% (0.01 ≤ z ≤ 0.25). When Ti is used as M ² , the amount of M ² ions is preferably 10 to 25% (0.10 ≤ z ≤ 0.25), and when Ge is used, the amount of M ² ions is 1 to 10% (0.01 ≤). z ≦ 0.10) is preferable. When both Ti and Ge are used as M ² , it is preferable to set them appropriately according to the ratio. When the solid solution amount (z value) of M ² ions is excessive, the charge / discharge capacity is significantly reduced due to the low electrochemical activity of M ² ions. On the other hand, if the solid solution amount (z value) of M ² ions is too small, it is difficult to maintain the similarity of the charge / discharge curve shapes during the charge / discharge cycle, and the cycle characteristics are inferior when the charge / discharge cycle is performed for a long period of time.

Similar to M ¹ , M ² in the lithium manganese-based composite oxide of the present invention seems to exist in the layered rock salt type structure in the form of substituting Li, Mn, etc., but only one of Ti and Ge is considered to be present. It may contain both Ti and Ge. More specifically, Ti is cheaper than Ge, but since Ge can exert an excellent effect with a small amount of elements, it is possible to reduce the amount of raw materials used when Ge is used. Therefore, it is preferable to appropriately set the amounts of Ti and Ge used according to the intended use. For example, when both Ti and Ge are contained, the total amount of M ² elements is 100% by weight, and Ti is preferably 10 to 90% by weight (particularly 30 to 70% by weight, further 40 to 60% by weight). The amount of Ge used is set so that the total with the amount of Ti used is 100% by weight.

The total amount (y + z) of M ¹ and M ² to be dissolved in the lithium manganese-based composite oxide of the present invention is preferably 70% or less (0 <y + z ≦ 0.7) in the general formula (1). 10 to 60% (0.1 ≤ y + z ≤ 0.6) is more preferable, 20 to 50% (0.2 ≤ y + z ≤ 0.5) is further preferable, and 25 to 45% (0.25 ≤ y + z ≤ 0.45) is particularly preferable. .. As a result, when used as a positive electrode material for a lithium-ion secondary battery, the capacity can be made higher, the discharge voltage can be made higher, and the similarity of the charge / discharge curve shape during the charge / discharge cycle can be easily maintained. The cycle characteristics of the period can be made better.

Further, in the lithium manganese-based composite oxide of the present invention, the Li ion amount (x) is the average value of the transition metal as long as the crystal phase of the monoclinic layered rock salt structure or the hexagonal layered rock salt structure can be maintained. Depending on the number, it can take a value between 0 and 1/3. Usually, 0.100 to 0.300 is preferable, 0.200 to 0.280 is more preferable, and 0.230 to 0.270 is further preferable.

Further, the lithium manganese-based composite oxide of the present invention includes lithium hydroxide, lithium carbonate, iron compounds, nickel compounds, titanium compounds, germanium compounds, manganese compounds, and compounds thereof within a range that does not significantly affect the charge / discharge characteristics. Hydrate; may contain an impurity phase such as a composite metal compound containing two or more of lithium, iron, nickel, titanium and germanium. Regarding the amount of impurity phases other than the crystalline phase of monoclinic layered rock salt type structure, hexagonal layered rock salt type structure and other rock salt type structures with different cation distribution (cubic rock salt type structure, etc.), the effect of the present invention is applied. It can be in a range that does not impair, and for example, 0 to 10% by weight is preferable, and 0 to 5% by weight is more preferable in the lithium manganese-based composite oxide of the present invention.

The lithium manganese-based composite oxide of the present invention satisfying the above conditions can maintain the similarity of the charge / discharge curve shape even during a long-term charge / discharge cycle, and spinnel from the crystal phase of the layered rock salt type structure. A sharp drop in potential around 3.5 V at the time of discharge based on the phase transition to the crystalline phase of the mold structure and an addition near 2.2 V at the time of discharge based on the phase transition from the crystalline phase of the layered rock salt type structure to the lithium excess crystal phase. The lithium manganese-based composite oxide of the present invention not only has a high capacity and a high discharge voltage, but also has excellent cycle characteristics even during a long-term charge / discharge cycle because it can suppress the appearance of various capacities. Have. Therefore, the lithium manganese-based composite oxide of the present invention is extremely useful as a positive electrode material for not only small consumer lithium ion secondary batteries but also large lithium ion secondary batteries for automobiles and the like.

2. 2. Method for Producing Lithium Manganese-based Composite Oxide The lithium manganese-based composite oxide of the present invention can be synthesized by using an ordinary composite oxide synthesis method. Specifically, it can be synthesized by a coprecipitation-firing method, a coprecipitation-hydrothermal-firing method, a solid phase reaction method, or the like. It is preferable to adopt the coprecipitation-calcination method from the viewpoint that a composite oxide having particularly excellent charge / discharge characteristics can be easily produced.

For example, when adopting the coprecipitation-firing method, for example,
(1) A step of forming a precipitate by treating a mixture containing a manganese compound, at least one compound selected from the group consisting of an iron compound and a nickel compound, and a titanium compound, if necessary, as alkaline (hereinafter referred to as step 1). I may say),
(2) A step of subjecting the precipitate obtained in step 1 to a wet oxidation treatment and aging it (hereinafter, also referred to as step 2).
(3) Production comprising a step of heating the aged product obtained in step 2 in the coexistence of a lithium compound and, if necessary, a raw material compound containing a germanium compound (hereinafter, also referred to as step 3). By the method, the lithium manganese-based composite oxide of the present invention can be obtained.

(2-1) Process 1
In step 1, a mixture containing a manganese compound and at least one compound selected from the group consisting of an iron compound and a nickel compound is regarded as alkaline to form a precipitate. Specifically, it is convenient to form an alkaline precipitate from a solution of a mixture containing a manganese compound and at least one compound selected from the group consisting of iron compounds and nickel compounds.

In the lithium manganese-based composite oxide of the present invention to be finally obtained, when the Ti element is contained, a manganese compound and at least one compound selected from the group consisting of an iron compound and a nickel compound are used. , It is preferable to use the mixture containing the titanium compound as an alkaline step to form a precipitate. Specifically, it is convenient to add a solution of a mixture containing a manganese compound, at least one compound selected from the group consisting of an iron compound and a nickel compound, and a titanium compound to an alkali to form a precipitate. ..

As the manganese compound, iron compound, nickel compound and titanium compound, a component capable of forming a mixed aqueous solution containing these compounds is preferable. It is preferable to use a water-soluble compound. Specific examples of such water-soluble compounds include water-soluble salts such as chlorides of manganese, iron, nickel or titanium, nitrates, sulfates, oxalates and acetates; hydroxides and the like. can. Further, a compound containing a plurality of metal species such as manganese titanate, nickel titanate, nickel nitrite, iron manganate and the like can also be used. As the manganese compound, permanganate such as potassium permanganate can also make the distribution of metals other than lithium ions uniform, and can further improve the charge / discharge characteristics. Both anhydrous and hydrated compounds can be adopted as these water-soluble compounds. Further, even a water-insoluble compound such as an oxide of manganese, iron, nickel or titanium, or a metal can be dissolved with an acid such as sulfuric acid or hydrochloric acid and used as an aqueous solution. Each of these raw material compounds may be used alone for each metal source, or may be used in combination of two or more.

The mixing ratio of the manganese compound, the iron compound, the nickel compound and the titanium compound can be the same as the element ratio of each element in the target lithium manganese-based composite oxide of the present invention.

The concentration of each compound in the case of a mixed aqueous solution is not particularly limited, and can be appropriately determined so that a uniform mixed aqueous solution can be formed and a coprecipitate can be smoothly formed. Usually, the total concentration of the manganese compound, the iron compound, the nickel compound and the titanium compound is preferably 0.01 to 5 mol / L, particularly preferably 0.1 to 2 mol / L.

As the solvent for preparing the mixed aqueous solution, water may be used alone, or a water-alcohol mixed solvent containing a water-soluble alcohol such as methanol or ethanol may be used. By using a water-alcohol mixed solvent, the alcohol acts as an antifreeze liquid, and precipitation can be formed at a temperature below 0 ° C. By forming the precipitate at a low temperature, the formation of impurities such as lithium ferrite and manganese ferrite, which are likely to occur during precipitation formation when Fe is contained as the M ¹ element, is further suppressed, that is, the transition metal distribution is more uniform. You can get a deposit. Further, since a manganese source such as potassium permanganate, which is difficult to form a precipitate with water alone, can be adopted, the range of selection of raw materials is further expanded. The amount of alcohol used can be appropriately determined according to the target precipitation temperature, etc., and is usually 50 parts by weight or less (for example, 10 to 50 parts by weight) with respect to 100 parts by weight of water. Is appropriate.

By making the mixture (particularly the mixed aqueous solution) alkaline, a precipitate (coprecipitate) can be produced. The conditions for forming a good precipitate cannot be unconditionally defined because they differ depending on the type, concentration, etc. of each compound contained in the mixture (particularly the mixed aqueous solution), but usually pH 8 or higher (for example, pH 8 to 14) is preferable. , PH 11 or higher (eg pH 11-14) is more preferred.

The method for making the mixture (particularly the mixed aqueous solution) alkaline is not particularly limited, and usually, the mixture (particularly the mixed aqueous solution) is added to the alkaline-containing aqueous solution in order to form a uniform precipitate. A precipitate (co-precipitate) can also be formed by the method. A precipitate can also be obtained by adding an alkali or an aqueous solution containing an alkali to the mixed aqueous solution.

As the alkali used to make the mixture (particularly the mixed aqueous solution) alkaline, for example, alkali metal hydroxides such as potassium hydroxide, sodium hydroxide and lithium hydroxide, ammonia and the like can be used. When these alkalis are used as an aqueous solution, they can be used, for example, as an aqueous solution having a concentration of 0.1 to 20 mol / L, particularly 0.3 to 10 mol / L. Further, the alkali can be dissolved in a water-alcohol mixed solvent containing a water-soluble alcohol, similarly to the above-mentioned mixed aqueous solution of a metal compound.

At the time of precipitation formation, the temperature of the mixture (particularly the mixed aqueous solution) is usually set to -50 to 50 ° C, particularly -20 to 30 ° C, so that when Fe is contained as M ¹ , during the reaction. The formation of spinel ferrite due to the generation of sum of heat is further suppressed, and a fine and homogeneous precipitate (co-precipitate) is easily formed, so that the reactivity with the lithium compound described later is further enhanced, and the lithium of the present invention is used. It becomes easier to synthesize manganese-based composite oxides. Further, in order to form a precipitate (coprecipitate) satisfactorily in this step, in order to further suppress the generation of heat of neutralization, the mixture (particularly the mixed aqueous solution) is applied to the alkali for at least several hours. The method of gradually dropping the solution is preferable. The longer the reaction time is, the better, but in practice, 1 hour to 1 day, particularly 2 to 12 hours is preferable.

(2-2) Process 2
After the precipitate (coprecipitate) is formed in the above step 1, the precipitate (coprecipitate) is aged by wet oxidation. Specifically, in step 2, the precipitate (coprecipitate) obtained in step 1 is subjected to a wet oxidation treatment and aged. More specifically, the alkaline aqueous solution containing the precipitate (coprecipitate) obtained in the above step 1 can be aged by blowing a gas containing oxygen with a compressor, an oxygen gas generator, etc. and bubbling. can.

The gas to be blown preferably contains a certain amount of oxygen. Specifically, it preferably contains 10 to 100% by volume of oxygen of the gas to be blown. Examples of such a gas to be blown include air, oxygen and the like, and oxygen is preferable.

The aging temperature is not particularly limited, and a temperature at which the wet oxidation treatment of the precipitate (coprecipitate) can be performed is preferable. Usually, 0 to 150 ° C. is preferable, and 10 to 100 ° C. is more preferable. Further, the aging time is not particularly limited, and a time during which a wet oxidation treatment of a precipitate (coprecipitate) can be performed is preferable. The longer this aging time is, the better, but in practice, 0.5 to 7 days is preferable, and 2 to 4 days is more preferable.

It is also possible to purify the precipitate by washing the obtained precipitate with distilled water or the like as necessary to remove excess alkaline components, residual raw materials and the like, and filtering the obtained precipitate.

(2-3) Process 3
Next, in step 3, the aged product obtained in step 2 is heated in the coexistence of a raw material compound containing a lithium compound. Specifically, an aqueous solution containing the aged product obtained in step 2 and a raw material compound containing a lithium compound can be heated (particularly fired) after forming a slurry, drying and pulverizing, if necessary. preferable.

The content of the aged product obtained in the above step 2 in the aqueous solution to be used is usually preferably 100 to 3000 g, more preferably 500 to 2000 g per 1 L of water.

As the lithium compound, for example, a water-soluble lithium salt such as lithium chloride, lithium iodide, lithium nitrate, lithium acetate and lithium hydroxide; lithium carbonate and the like can be used. These lithium compounds can be used alone or in combination of two or more. Further, as the lithium compound, either an anhydride or a hydrate can be adopted. In particular, when the lithium manganese-based composite oxide of the present invention contains Ge, it is preferable to use lithium hydroxide as the lithium compound because the water-insoluble germanium compound can be easily dissolved.

The amount of the lithium compound used is preferably Li / (M ¹ + M ² ) = 1 to 5, preferably 1.5 to 3, based on the total amount of the aged product obtained in the above step 2 and the germanium compound described later. More preferred.

The concentration of the lithium compound in the aqueous solution is usually preferably 0.1 to 10 mol / L, more preferably 1 to 8 mol / L.

When the lithium manganese-based composite oxide of the present invention contains Ge, it is preferable to use a germanium compound as a raw material compound.

Examples of the germanium compound include water-soluble germanium compounds such as germanium chloride and germanium iodide; and water-insoluble germanium compounds such as germanium oxide and metallic germanium. When a water-insoluble germanium compound is used, the reactivity with the aged product obtained in step 2 is improved by dissolving the germanium compound with an acid or the above-mentioned alkali, taking advantage of the fact that germanium is an amphoteric element. Is preferable. When lithium hydroxide is used as the lithium compound, the water-insoluble germanium compound can be dissolved without using a separate acid or alkali.

When the cleaning treatment is performed after heating, the amount of germanium to be washed away is large, so that the amount of the germanium compound added (charged amount) is preferably larger than the content in the composite oxide to be obtained. From this point of view, the amount of the germanium compound used is preferably Ge / (M ¹ + M ² ) = 0.01 to 0.5, based on the total amount of the aged product obtained in the above step 2 and the germanium compound. 0.1 to 0.4 is more preferable.

The concentration of the germanium compound in the aqueous solution is usually preferably 0.05 to 1.0 mol / L, more preferably 0.1 to 0.7 mol / L.

The mixing method of the aged product obtained in step 2 with the lithium compound and, if necessary, the zirconium compound is not particularly limited. For example, the aged product obtained in step 2 is added to an aqueous solution of a water-soluble lithium compound, stirred and dispersed, and then a separately prepared aqueous solution of the water-soluble germanium compound or an alkaline solution of the water-insoluble germanium compound is added. After stirring well, it is preferable to dry and grind as necessary.

As the stirring, a usual method can be adopted, and for example, it is preferable to stir with a known mixer such as a mixer, a V-type mixer, a W-type mixer, or a ribbon mixer.

When drying, the drying conditions are not particularly limited. The drying temperature is, for example, preferably 20 to 100 ° C, more preferably 30 to 80 ° C. The drying time is preferably, for example, 1 hour to 5 days, more preferably 12 hours to 3 days.

It is preferable to grind in order to improve the reactivity in the subsequent heat treatment. Regarding the degree of pulverization, it is preferable that the mixture does not contain coarse particles and has a uniform color tone. In the case of pulverization, a usual method can be adopted, and for example, pulverization can be performed by a vibration mill, a ball mill, a jet mill or the like. Further, the crushing can be repeated twice or more. Further, the heat treatment can be carried out by raising the heating temperature step by step.

The heat treatment is usually preferably performed in a closed container (electric furnace or the like).

The heating conditions are not particularly limited, but it is preferable that the final heating temperature is 750 ° C. or higher in order to further stabilize the charge / discharge cycle characteristics. The heating temperature is preferably 1000 ° C. or lower so that lithium does not easily volatilize. The final heating temperature is particularly preferably 800 to 950 ° C. By heating (especially firing) in this range, lithium manganese not only has a higher capacity and a higher discharge voltage in a shorter firing time, but also has better cycle characteristics even during a long-term charge / discharge cycle. It is easy to obtain a system composite oxide.

The heating atmosphere (particularly the firing atmosphere) is not particularly limited. When the final heating atmosphere is an inert atmosphere such as nitrogen or argon or a reducing atmosphere, the sample is heated in advance at a low temperature of 500 to 750 ° C (particularly 550 to 700 ° C) in the air to suppress decomposition of the sample (especially 550 to 700 ° C). It is preferable to perform final heating (particularly final firing) in an inert atmosphere or a reducing atmosphere after (particularly firing). Further, even when the final heating atmosphere is in the atmosphere, two-step heating (particularly firing) can be performed in order to more precisely control the Li content, powder characteristics, and the like. When the final heating atmosphere is a reducing atmosphere, for example, by firing in the presence of organic substances, carbon powder, etc. in an inert atmosphere, heat treatment (particularly firing) in the reducing atmosphere is possible. be.

The organic substance is not particularly limited, and a carbon-containing compound that can be decomposed at the above heating temperature (particularly the firing temperature) to form a reducing atmosphere is preferable. In particular, when a water-soluble organic substance is used, it is advantageous because it can be dispersed and mixed with the lithium manganese-based composite oxide powder in an aqueous solution state. Specific examples of such organic substances include sucrose, glucose, starch, acetic acid, citric acid, oxalic acid, benzoic acid, aminoacetic acid and the like.

As the carbon powder, for example, carbon powder obtained by thermal decomposition of an organic substance, for example, graphite, acetylene black or the like can be used.

The above-mentioned organic substances and carbon powders can be used alone or in combination of two or more.

The amount of at least one component selected from the group consisting of organic substances and carbon powder is preferably 0.001 to 5 times mol, and 0.01 to 1 times mol, in terms of carbon molar amount, with respect to the lithium manganese-based composite oxide. More preferred. When used as an aqueous solution, the concentration of the organic substance or the like can be appropriately determined so as to be within the above-mentioned range of the amount used.

The heating time is also not particularly limited. More specifically, the holding time at the final heating temperature is preferably 10 minutes to 24 hours, more preferably 30 minutes to 12 hours. When performing two-step heat treatment, the holding time at the heating temperature of the first step is preferably 10 minutes to 24 hours (particularly 30 minutes to 12 hours), and the holding time at the final heating temperature of the second step is 10 minutes. It is preferably about 24 hours (particularly 30 minutes to 12 hours).

After obtaining the lithium manganese-based composite oxide of the present invention by the above-mentioned method, the obtained calcined product may be subjected to water washing treatment, solvent washing treatment, etc. in order to remove excess lithium compound, if necessary. can. After that, it can be filtered and dried by heating at, for example, 80 ° C. or higher, preferably 100 ° C. or higher.

Further, if necessary, the lithium manganese-based composite oxide is obtained by repeating a series of operations of crushing the heat-dried product, adding a lithium compound and an organic substance, heating (particularly firing), washing, and drying. It is also possible to further improve the excellent characteristics of.

3. 3. Lithium Ion Secondary Battery The lithium ion secondary battery using the lithium manganese-based composite oxide of the present invention can be manufactured by a known method. For example, the lithium manganese-based composite oxide of the present invention is used as the positive electrode material, and known metallic lithium, carbon-based materials (activated carbon, graphite, etc.), silicon, silicon oxide, Si-SiO-based material, and lithium are used as the negative electrode material. A solution (organic electrolysis) in which a lithium salt such as lithium perchlorate or LiPF ₆ is dissolved in a solvent consisting of one or more of known ethylene carbonate, dimethyl carbonate, diethyl carbonate, etc. as an electrolytic solution using titanium oxide or the like. Liquid), inorganic solid electrolytes (Li ₂ S-P ₂ S ₅ series, Li ₂ S-GeS ₂ -P ₂ S ₅ series, etc.), and other known battery components are used in the conventional method. According to this, the lithium ion secondary battery can be assembled. In the present invention, the "lithium ion secondary battery" is a concept including a "lithium secondary battery" using metallic lithium as a negative electrode material. Further, in the present invention, the "lithium ion secondary battery" is either a "non-aqueous lithium ion secondary battery" using a non-aqueous electrolyte solution or an "all-solid-state lithium ion secondary battery" using a solid electrolyte. It is a concept to be included.

Hereinafter, examples and comparative examples will be shown to further clarify the features of the present invention, but the present invention is not limited to the following examples.

[Example 1]
Sample synthesis, structure and composition evaluation
Iron (III) Nitrate 9 hydrate 10.10 g, Nickel Nitrate (II) Hexahydrate 7.27 g, 30% Titanium Sulfate (IV) aqueous solution 40.00 g, Manganese (II) chloride tetrahydrate 29.69 g (total amount 0.25 mol) , Fe: Ni: Ti: Mn molar ratio 1: 1: 2: 6) was added to 500 mL of distilled water to completely dissolve it. 50 g of sodium hydroxide was weighed in another beaker, 500 mL of distilled water was added, and the mixture was dissolved with stirring to prepare an aqueous sodium hydroxide solution. This aqueous sodium hydroxide solution was placed in a titanium beaker and allowed to stand in a constant temperature bath kept at 20 ° C. Next, the aqueous metal salt solution was gradually added dropwise to this sodium hydroxide solution over about 3 hours to form a Fe—Ni—Ti—Mn precipitate (coprecipitate). After confirming that the reaction solution was completely alkaline, oxygen was blown into the reaction solution containing the coprecipitate under stirring for 2 days at room temperature for wet oxidation treatment, and the precipitate was aged.

The obtained precipitate was washed with distilled water, filtered off, and mixed with 18.47 g of 0.25 mol lithium carbonate dispersed in distilled water with a mixer to form a uniform slurry. The slurry was transferred to a tetrafluoroethylene petri dish, dried at 50 ° C. for 2 days, and then pulverized to prepare a raw material for firing.

Next, the obtained powder was heated to 650 ° C. over 1 hour, kept at that temperature for 5 hours, and then cooled to near room temperature in a furnace. After crushing, the temperature was raised to 850 ° C. over 1 hour under a nitrogen stream using an electric furnace again, and the temperature was maintained at that temperature for 5 hours, and then cooled to near room temperature in the furnace. That is, the sample was prepared by firing in the atmosphere in the first stage and in the nitrogen atmosphere in the second stage. To remove the calcined product from the electric furnace and remove excess lithium salts, the calcined product is washed with distilled water, filtered, dried and powdered with the target iron, nickel and titanium substituted Li ₂ MnO ₃ . Obtained as a state product.

Evaluation by X-ray Diffraction The measured (+) and calculated (solid) X-ray diffraction patterns of this final product are shown in FIG. From the analysis results by the Rietveld analysis program RIETAN-FP, all peaks can be indexed by the lattice constants shown in Table 1 below, and only the crystal phase having a monoclinic Li ₂ MnO ₃ unit cell (C2 / m). It turned out to consist of. Further, when the transition metal ion distribution in the structure of Table 2 was confirmed, the sample of Example 1 had a smaller amount of transition metal in the Li—Mn layer than the sample of Comparative Example 1 containing no Ti, which will be described later, and the Li single layer. It can be seen that the amount of transition metal is large, and that the introduction of Ti tends to cause irregular arrangement of transition metal ions. Further, it can be seen that the sample of Example 1 has a higher degree of hexagonal network regular arrangement than the sample of Comparative Example 1 which does not contain Ti, which will be described later.

Evaluation by chemical analysis, etc. From chemical analysis, the Fe, Ni, and Ti contents with respect to the total amount of metals other than lithium are 10 mol%, 10 mol% (equivalent to y value 0.20), and 20 mol% (equivalent to z value 0.20), respectively. Since it is maintained and the Li / (M ¹ + M ² + Mn) ratio is 1.68 (x value conversion 0.254), the desired composition formula Li _{1 + x} (M ¹ _y M ² _z Mn _1-yz ) ₁ It is clear that a lithium manganese-based composite oxide with _-x O ₂ was obtained.

Charging / discharging characteristic evaluation For details, follow the procedure described in the charging / discharging characteristic evaluation described later to prepare a lithium secondary battery using the obtained sample as the positive electrode material and metallic lithium as the negative electrode material, and perform activation treatment and cycle test. rice field.

From the results of FIGS. 2 and 4, the sample of Example 1 not only showed a charge / discharge capacity close to 240 mAh / g after activation, but also did not contain the M ² element described later, and was a comparative example obtained under the same production conditions. Compared with the sample of 1, not only the charge / discharge characteristics at 1 cycle after activation treatment are almost the same, but also the charge / discharge curve similar to that at 20 cycles after activation treatment up to 50 cycles after activation treatment. Shows. That is, a sharp drop in potential from around 3.7V due to structural transition from layered rock salt structure to spinel phase during 50-cycle discharge after activation treatment, and Li ₂ (Ni, Mn) O ₂ phase from layered rock salt structure. It is clear that it is a positive electrode material with high capacity and excellent long-term cycle characteristics, as no additional capacity appears below 2.2V due to structural transition to.

[Comparative Example 1]
As starting materials, iron (III) nitrate 9 hydrate 10.10 g, nickel (II) nitrate hexahydrate 7.27 g, manganese chloride (II) tetrahydrate 39.58 g (total amount 0.25 mol, Fe: Ni: Mn mol) Ratio 1: 1: 8) was added to 500 mL of distilled water to completely dissolve it. After that, the positive electrode material was prepared in the same manner as in Example 1.

The measured (+) and calculated (solid) X-ray diffraction patterns of this final product are shown in FIG. From the analysis results by the Rietveld analysis program RIETAN-FP, all peaks can be indexed by the lattice constants shown in Table 1 below, and only from the crystal phase having the unit cell (C2 / m) of the monoclinic Li ₂ MnO ₃ . It turned out to be.

In addition, from chemical analysis, the Fe and Ni contents with respect to the total amount of metals other than lithium are maintained at 10 mol% and 10 mol% (equivalent to y value 0.20), which are the charged amounts, respectively, and the Li / (M ¹ + Mn) ratio. Since it is also 1.71 (x value conversion 0.262), a lithium manganese-based composite oxide having the composition formula Li _{1 + x} (M ¹ _y Mn _1-y ) _1-x O ₂ containing no M ² was obtained. Is clear.

Further, in detail, according to the procedure described in the charge / discharge characteristic evaluation described later, a lithium secondary battery using the obtained sample as a positive electrode material and metallic lithium as a negative electrode material was produced, and an activation treatment and a cycle test were performed. The evaluation results of the charge / discharge characteristics are shown in FIGS. 4 and 3. From FIGS. 4 and 3, the sample of Comparative Example 1 shows a charge / discharge capacity close to 250 mAh / g after activation, but during 50-cycle discharge after activation treatment, 3.7 due to structural transition from layered rock salt type structure to spinel phase. Implementation due to a sharp drop in potential from near V and the appearance of additional capacitance below 2.2V due to structural transition from layered rock salt structure to Li ₂ (Ni, Mn) O ₂ phase. It is clear that the positive electrode material is inferior in long-term cycle characteristics to the lithium manganese-based composite oxide of Example 1.

[Example 2]
Samples were prepared in the same manner as in Example 1 except that the final firing atmosphere was set to the atmosphere. That is, the sample was prepared by firing twice in the atmosphere. The measured (+) and calculated (solid) X-ray diffraction patterns of this final product are shown in FIG. From the analysis results by the Rietveld analysis program RIETAN-FP, all peaks can be indexed by the lattice constants shown in Table 1 below, and only from the crystal phase having the unit cell (C2 / m) of the monoclinic Li ₂ MnO ₃ . It turned out to be.

Further, when the distribution of transition metal ions in the structure in Table 2 described later was confirmed, the sample in Example 2 had a smaller amount of transition metal in the Li—Mn layer than the sample in Comparative Example 2 not containing Ti, which will be described later, and Li. It can be seen that the amount of transition metal in the single layer is large, and that the introduction of Ti tends to cause irregular arrangement of transition metal ions. Further, it can be seen that the sample of Example 2 has a higher degree of hexagonal network regular arrangement than the sample of Comparative Example 2 which does not contain Ti, which will be described later.

In addition, from chemical analysis, the Fe, Ni, and Ti contents with respect to the total amount of metals other than lithium were maintained at 10 mol%, 10 mol% (equivalent to y value 0.20), and 20 mol% (equivalent to z value 0.20), respectively. Since the Li / (M ¹ + M ² + Mn) ratio is also 1.72 (x value conversion 0.265), the desired composition formula Li _{1 + x} (M ¹ _y M ² _z Mn _1-yz ) _1-x O It is clear that a lithium manganese-based composite oxide having ₂ was obtained.

Further, in detail, according to the procedure described in the charge / discharge characteristic evaluation described later, a lithium secondary battery using the obtained sample as a positive electrode material and metallic lithium as a negative electrode material was produced, and an activation treatment and a cycle test were performed. The evaluation results of the charge / discharge characteristics are shown in FIGS. 6 and 3. From FIG. 6 and Table 3, the sample of Example 2 not only showed a charge / discharge capacity close to 240 mAh / g after activation, but also did not contain the M ² element described later, and was obtained in Comparative Example 2 under the same production conditions. Compared with the sample, not only the charge / discharge characteristics at 1 cycle after activation treatment are almost the same, but also the charge / discharge curves similar to those at 20 cycles after activation treatment up to 50 cycles after activation treatment are shown. There is. That is, a sharp drop in potential from around 3.7 V due to structural transition from layered rock salt structure to spinel phase during 50-cycle discharge after activation treatment, and Li ₂ (Ni, Mn) O ₂ phase from layered rock salt structure. It is clear that it is a positive electrode material with high capacity and excellent long-term cycle characteristics, as no additional capacity appears below 2.2 V due to structural transition to.

[Comparative Example 2]
As starting materials, iron (III) nitrate 9 hydrate 10.10 g, nickel (II) nitrate hexahydrate 7.27 g, manganese chloride (II) tetrahydrate 39.58 g (total amount 0.25 mol, Fe: Ni: Mn mol) Ratio 1: 1: 8) was added to 500 mL of distilled water to completely dissolve it. After that, the positive electrode material was prepared in the same manner as in Example 2.

The measured (+) and calculated (solid) X-ray diffraction patterns of this final product are shown in FIG. From the analysis results by the Rietveld analysis program RIETAN-FP, all peaks can be indexed by the lattice constants shown in Table 1 below, and only from the crystal phase having the unit cell (C2 / m) of the monoclinic Li ₂ MnO ₃ . It turned out to be.

In addition, from chemical analysis, the Fe and Ni contents with respect to the total amount of metals other than lithium are maintained at 10 mol% and 10 mol% (equivalent to y value 0.20), which are the charged amounts, respectively, and the Li / (M ¹ + Mn) ratio. Since it is also 1.73 (x value conversion 0.267), a lithium manganese-based composite oxide having the composition formula Li _{1 + x} (M ¹ _y Mn _1-y ) _1-x O ₂ containing no M ² was obtained. Is clear.

Further, in detail, according to the procedure described in the charge / discharge characteristic evaluation described later, a lithium secondary battery using the obtained sample as a positive electrode material and metallic lithium as a negative electrode material was produced, and an activation treatment and a cycle test were performed. The evaluation results of the charge / discharge characteristics are shown in FIGS. 8 and 3. From FIGS. 8 and 3, the sample of Comparative Example 2 shows a charge / discharge capacity close to 250 mAh / g after activation, but during 50-cycle discharge after activation treatment, 3.7 due to structural transition from layered rock salt type structure to spinel phase. Implementation due to a sharp drop in potential from near V and the appearance of additional capacitance below 2.2V due to structural transition from layered rock salt structure to Li ₂ (Ni, Mn) O ₂ phase. It is clear that the positive electrode material is inferior in long-term cycle characteristics to the lithium manganese-based composite oxide of Example 2.

[Example 3]
Samples were prepared in the same manner as in Example 1 except that the final firing conditions were 900 ° C., 5 hours, and the atmosphere. That is, the sample was prepared by firing twice in the atmosphere. The measured (+) and calculated (solid) X-ray diffraction patterns of this final product are shown in FIG. From the analysis results by the Rietveld analysis program RIETAN-FP, all peaks can be indexed by the lattice constants shown in Table 1 below, and only from the crystal phase having the unit cell (C2 / m) of the monoclinic Li ₂ MnO ₃ . It turned out to be.

Further, when the distribution of transition metal ions in the structure in Table 2 described later was confirmed, the sample in Example 3 had a smaller amount of transition metal in the Li—Mn layer than the sample in Comparative Example 3 not containing Ti, which will be described later, and Li. It can be seen that the amount of transition metal in the single layer is large, and that the introduction of Ti tends to cause irregular arrangement of transition metal ions. Further, it can be seen that the sample of Example 3 has a higher degree of hexagonal mesh regular arrangement than the sample of Comparative Example 3 which does not contain Ti, which will be described later.

In addition, from chemical analysis, the Fe, Ni, and Ti contents with respect to the total amount of metals other than lithium were maintained at 10 mol%, 10 mol% (equivalent to y value 0.20), and 20 mol% (equivalent to z value 0.20), respectively. Since the Li / (M ¹ + M ² + Mn) ratio is also 1.74 (x value conversion 0.270), the desired composition formula Li _{1 + x} (M ¹ _y M ² _z Mn _1-yz ) _1-x O It is clear that a lithium manganese-based composite oxide having ₂ was obtained.

Further, in detail, according to the procedure described in the charge / discharge characteristic evaluation described later, a lithium secondary battery using the obtained sample as a positive electrode material and metallic lithium as a negative electrode material was produced, and an activation treatment and a cycle test were performed. The evaluation results of the charge / discharge characteristics are shown in FIGS. 10 and 3. From FIG. 10 and Table 3, the sample of Example 3 not only showed a charge / discharge capacity close to 200 mAh / g after activation, but also did not contain the M ² element described later, and was obtained under the same preparation conditions as the sample of Comparative Example 3. Not only is the charge / discharge characteristics at 1 cycle after activation treatment almost the same, but the charge / discharge curve is similar to that at 20 cycles after activation treatment up to 50 cycles after activation treatment. .. That is, a sharp drop in potential from around 3.7V due to structural transition from layered rock salt structure to spinel phase during 50-cycle discharge after activation treatment, and Li ₂ (Ni, Mn) O ₂ phase from layered rock salt structure. It is clear that it is a positive electrode material with high capacity and excellent long-term cycle characteristics, as no additional capacity appears below 2.2V due to structural transition to.

[Comparative Example 3]
As starting materials, iron (III) nitrate 9 hydrate 10.10 g, nickel (II) nitrate hexahydrate 7.27 g, manganese chloride (II) tetrahydrate 39.58 g (total amount 0.25 mol, Fe: Ni: Mn mol) Ratio 1: 1: 8) was added to 500 mL of distilled water to completely dissolve it. After that, the positive electrode material was prepared in the same manner as in Example 3.

The measured (+) and calculated (solid) X-ray diffraction patterns of this final product are shown in FIG. From the analysis results by the Rietveld analysis program RIETAN-FP, all peaks can be indexed by the lattice constants shown in Table 1 below, and only from the crystal phase having the unit cell (C2 / m) of the monoclinic Li ₂ MnO ₃ . It turned out to be.

In addition, from chemical analysis, the Fe and Ni contents with respect to the total amount of metals other than lithium are maintained at 10 mol% and 10 mol% (equivalent to y value 0.20), which are the charged amounts, respectively, and the Li / (M ¹ + Mn) ratio. Since it is also 1.71 (x value conversion 0.262), a lithium manganese-based composite oxide having the composition formula Li _{1 + x} (M ¹ _y Mn _1-y ) _1-x O ₂ containing no M ² was obtained. Is clear.

Further, in detail, according to the procedure described in the charge / discharge characteristic evaluation described later, a lithium secondary battery using the obtained sample as a positive electrode material and metallic lithium as a negative electrode material was produced, and an activation treatment and a cycle test were performed. The evaluation results of the charge / discharge characteristics are shown in FIGS. 12 and 3. From FIGS. 12 and Table 3, the sample of Comparative Example 3 shows a charge / discharge capacity close to 230 mAh / g after activation, but at 50 cycle discharge after activation treatment, 3.7 due to structural transition from layered rock salt type structure to spinel phase. Implementation due to a sharp drop in potential from near V and the appearance of additional capacitance below 2.2V due to structural transition from layered rock salt structure to Li ₂ (Ni, Mn) O ₂ phase. It is clear that the positive electrode material is inferior in long-term cycle characteristics to the lithium manganese-based composite oxide of Example 3.

[Example 4]
Samples were prepared in the same manner as in Example 1 except that the final firing conditions were 900 ° C., 5 hours, and in a nitrogen stream. The measured (+) and calculated (solid) X-ray diffraction patterns of this final product are shown in FIG. From the analysis results by the Rietveld analysis program RIETAN-FP, all peaks can be indexed by the lattice constants shown in Table 1 below, and only from the crystal phase having the unit cell (C2 / m) of the monoclinic Li ₂ MnO ₃ . It turned out to be.

Further, when the distribution of transition metal ions in the structure in Table 2 described later was confirmed, the sample of Example 4 had a smaller amount of transition metal in the Li—Mn layer than the sample of Comparative Example 4 not containing Ti, which will be described later, and Li. It can be seen that the amount of transition metal in the single layer is large, and that the introduction of Ti tends to cause irregular arrangement of transition metal ions. Further, it can be seen that the sample of Example 4 has a higher degree of hexagonal mesh regular arrangement than the sample of Comparative Example 4 which does not contain Ti, which will be described later.

In addition, from chemical analysis, the Fe, Ni, and Ti contents with respect to the total amount of metals other than lithium were maintained at 10 mol%, 10 mol% (equivalent to y value 0.20), and 20 mol% (equivalent to z value 0.20), respectively. Since the Li / (M ¹ + M ² + Mn) ratio is also 1.64 (x value conversion 0.242), the desired composition formula Li _{1 + x} (M ¹ _y M ² _z Mn _1-yz ) _1-x O It is clear that a lithium manganese-based composite oxide having ₂ was obtained.

Further, in detail, according to the procedure described in the charge / discharge characteristic evaluation described later, a lithium secondary battery using the obtained sample as a positive electrode material and metallic lithium as a negative electrode material was produced, and an activation treatment and a cycle test were performed. The evaluation results of the charge / discharge characteristics are shown in FIGS. 14 and 3. From FIG. 14 and Table 3, the sample of Example 4 not only showed a charge / discharge capacity close to 200 mAh / g after activation, but also did not contain the M ² element described later, and was obtained under the same preparation conditions as the sample of Comparative Example 4. Not only is the charge / discharge characteristics at 1 cycle after activation treatment almost the same, but the charge / discharge curve is similar to that at 20 cycles after activation treatment up to 50 cycles after activation treatment. .. That is, a sharp drop in potential from around 3.7V due to structural transition from layered rock salt structure to spinel phase during 50-cycle discharge after activation treatment, and Li ₂ (Ni, Mn) O ₂ phase from layered rock salt structure. It is clear that it is a positive electrode material with high capacity and excellent long-term cycle characteristics, as no additional capacity appears below 2.2V due to structural transition to.

[Comparative Example 4]
As starting materials, iron (III) nitrate 9 hydrate 10.10 g, nickel (II) nitrate hexahydrate 7.27 g, manganese chloride (II) tetrahydrate 39.58 g (total amount 0.25 mol, Fe: Ni: Mn mol) Ratio 1: 1: 8) was added to 500 mL of distilled water to completely dissolve it. After that, the positive electrode material was prepared in the same manner as in Example 4.

The measured (+) and calculated (solid) X-ray diffraction patterns of this final product are shown in FIG. From the analysis results by the Rietveld analysis program RIETAN-FP, all peaks can be indexed by the lattice constants shown in Table 1 below, and only from the crystal phase having the unit cell (C2 / m) of the monoclinic Li ₂ MnO ₃ . It turned out to be.

In addition, from chemical analysis, the Fe and Ni contents with respect to the total amount of metals other than lithium are maintained at 10 mol% and 10 mol% (equivalent to y value 0.20), which are the charged amounts, respectively, and the Li / (M ¹ + Mn) ratio. Since it is also 1.72 (x value conversion 0.265), a lithium manganese-based composite oxide having the composition formula Li _{1 + x} (M ¹ _y Mn _1-y ) _1-x O ₂ containing no M ² was obtained. Is clear.

Further, in detail, according to the procedure described in the charge / discharge characteristic evaluation described later, a lithium secondary battery using the obtained sample as a positive electrode material and metallic lithium as a negative electrode material was produced, and an activation treatment and a cycle test were performed. The evaluation results of the charge / discharge characteristics are shown in FIGS. 16 and 3. From FIGS. 16 and 3, the sample of Comparative Example 4 shows a charge / discharge capacity close to 200 mAh / g after activation, but during 50-cycle discharge after activation treatment, 3.7 due to structural transition from layered rock salt type structure to spinel phase. Implementation due to a sharp drop in potential from near V and the appearance of additional capacitance below 2.2V due to structural transition from layered rock salt structure to Li ₂ (Ni, Mn) O ₂ phase. It is clear that the positive electrode material is inferior in long-term cycle characteristics to the lithium manganese-based composite oxide of Example 4.

[Example 5]
Sample synthesis, structure and composition evaluation
Iron (III) Nitrate 9 Hydrate 10.10g, Nickel Nitrate (II) Hexahydrate 7.27g, Manganese (II) Chloride Tetrahydrate 29.69g (Total 0.25mol, Fe: Ni: Mn Mol ratio 1: 1 : 6) was added to 500 mL of distilled water to completely dissolve it. 50 g of sodium hydroxide was weighed in another beaker, 500 mL of distilled water was added, and the mixture was dissolved with stirring to prepare an aqueous sodium hydroxide solution. This aqueous sodium hydroxide solution was placed in a titanium beaker and allowed to stand in a constant temperature bath kept at 20 ° C. Next, the aqueous metal salt solution was gradually added dropwise to this sodium hydroxide solution over about 3 hours to form a Fe—Ni—Mn precipitate (coprecipitate). After confirming that the reaction solution was completely alkaline, oxygen was blown into the reaction solution containing the coprecipitate under stirring for 2 days at room temperature for wet oxidation treatment, and the precipitate was aged.

The obtained precipitate was washed with distilled water, filtered off, dispersed with distilled water and completely dissolved, and mixed with 20.98 g (0.5 mol) of lithium hydroxide monohydrate and 5.23 g (0.05 mol) of GeO ₂ . It was mixed to form a uniform slurry. The slurry was transferred to a tetrafluoroethylene petri dish, dried at 50 ° C. for 2 days, and then pulverized to prepare a raw material for firing.

Next, the obtained powder was heated to 650 ° C. over 1 hour, kept at that temperature for 5 hours, and then cooled to near room temperature in a furnace. After crushing, the temperature was raised to 900 ° C. over 1 hour under a nitrogen stream using an electric furnace again, and the temperature was maintained at that temperature for 5 hours, and then cooled to near room temperature in the furnace. To remove the calcined product from the electric furnace and remove excess lithium salts, the calcined product is washed with distilled water, filtered, dried and powdered with the iron, nickel and germanium-substituted Li ₂ MnO ₃ of interest. Obtained as a state product.

Evaluation by X-ray Diffraction The measured (+) and calculated (solid) X-ray diffraction patterns of this final product are shown in FIG. From the analysis results by the Rietveld analysis program RIETAN-FP, all peaks can be indexed by the lattice constants shown in Table 1 below, and only the crystal phase having a monoclinic Li ₂ MnO ₃ unit cell (C2 / m). It turned out to consist of. Further, when the transition metal ion distribution in the structure of Table 2 was confirmed, the sample of Example 5 had a smaller amount of transition metal in the Li—Mn layer than the sample of Comparative Example 4 which did not contain Ge, and the Li single layer. It can be seen that the amount of transition metal is large, and that transition metal ions tend to be irregularly arranged due to the introduction of Ge. Further, it can be seen that the sample of Example 5 has a higher degree of hexagonal network regular arrangement than the sample of Comparative Example 4 which does not contain Ge described above.

Evaluation by chemical analysis, etc. From chemical analysis, although the Fe, Ni, and Ge contents with respect to the total amount of metals other than lithium are different from the charged amount, they are 12 mol%, 12 mol% (equivalent to y value 0.24), and 4 mol% (z value, respectively). Since it is equivalent to 0.04) and the Li / (M ¹ + M ² + Mn) ratio is 1.65 (x value conversion 0.245), the target composition formula Li _{1 + x} (M ¹ _y M ² _z Mn _1-yz ) It is clear that a lithium manganese-based composite oxide with _1-x O ₂ was obtained. It is considered that the content deviated from the charged amount because Ge was partially eluted during washing with water after firing because of the amphoteric metal. However, since it is not completely eliminated, it is possible to increase the amount of charge in order to increase the Ge content.

Charging / discharging characteristic evaluation For details, follow the procedure described in the charging / discharging characteristic evaluation described later to prepare a lithium secondary battery using the obtained sample as the positive electrode material and metallic lithium as the negative electrode material, and perform activation treatment and cycle test. rice field. From the results of FIGS. 18 and 4, the sample of Example 5 not only showed a charge / discharge capacity close to 250 mAh / g after activation, but also did not contain the above-mentioned M ² element, and was a comparative example obtained under the same production conditions. Compared with the sample of 4, not only the charge / discharge characteristics at 1 cycle after activation treatment are improved, but also the charge / discharge curve similar to that at 20 cycles after activation treatment is obtained up to 50 cycles after activation treatment. Shows. That is, a sharp drop in potential from around 3.7 V due to structural transition from layered rock salt structure to spinel phase during 50-cycle discharge after activation treatment, and Li ₂ (Ni, Mn) O ₂ phase from layered rock salt structure. It is clear that it is a positive electrode material with high capacity and excellent long-term cycle characteristics, as no additional capacity appears below 2.2 V due to structural transition to.

[Test results]
Evaluation by X-ray diffraction
From the X-ray diffraction patterns of the samples obtained in Examples 1 to 5 and Comparative Examples 1 to 4, the Rietveld analysis program RIETAN-FP (F. Izumi, K. Momma, "Three-Dimensional Visualization in Powder Diffraction", Solid State From the analysis results by Phenomena, Vol. 130, pp. 15-20, 2007), the lattice constant and lattice volume of each sample were evaluated. The results are shown in Table 1. In Table 1, a, b, and c indicate the length of each axis, and β indicates the angle between the ridges c and a. In addition, V indicates the lattice volume.

Next, from the X-ray diffraction patterns of the samples obtained in Examples 1 to 5 and Comparative Examples 1 to 4, the calculation pattern obtained from the structural model in which the transition metal amount at each lattice position is variable is combined with the measured pattern. The transition metal ion distribution in the structure was evaluated by. The results are shown in Table 2.

In Li ₂ MnO ₃ , which is a known substance, when Mn ions are in a regular arrangement state, Mn occupies 100% at the hexagonal network lattice configuration position (4g) position, and the hexagonal network center position (2b) which is the Li position. ) And other positions do not have Mn ions, but in reality, 100% of Mn ions do not exist at the 4g position, and some Mn ions are placed at the three Li positions. In Table 2, g _4g indicates the Mn occupancy at the hexagonal mesh grid configuration position (4g), g _2b indicates the Mn occupancy at the 2b position, g _2c indicates the Mn occupancy at the 2c position, and g _4h indicates the Mn occupancy at the 2c position. The Mn occupancy rate at the 4h position is shown. The difference in Mn occupancy between the 4g and 2b positions (g _4g －g _2b ) is defined as the hexagonal network regular arrangement, and the larger it is, the more ideal Li ₂ MnO type ₃ monoclinic layered rock salt structure. do. The average value 1 indicates the average occupancy rate (element ratio (%)) of the transition metal elements at the lattice positions (4g and 2b positions) in the Li—Mn layer, and the average value 2 indicates the lattice in the Li single layer. The average occupancy rate (element ratio (%)) of transition metal elements at positions (4h and 2c positions) is shown. The total amount of transition metals is the occupancy rate (element ratio (%)) of transition metal elements at the lattice positions (4g and 2b) in the Li-Mn layer when using the monoclinic layered rock salt type structural model. The sum of the occupancy rates (element ratios (%)) of transition metal elements at the lattice positions (4h and 2c) in a single layer is shown. The smaller the average value 1 and the larger the average value 2, the more irregularly arranged the transition metal ions.

Evaluation by chemical analysis, etc. The samples obtained in Examples 1 to 5 and Comparative Examples 1 to 4 were chemically analyzed by ICP emission analysis. The results are shown in Table 3. The results are shown in Table 3.

Charging / Discharging Characteristic Evaluation The charging / discharging tests were performed using the samples obtained in Examples 1 to 5 and Comparative Examples 1 to 4 as the positive electrode material. Specifically, 5 mg of the samples obtained in Examples 1 to 5 and Comparative Examples 1 to 4 are well mixed with 5 mg of acetylene black, 0.5 mg of polytetrafluoroethylene powder is added and bound, and the sample is pressure-bonded onto an Al mesh. To prepare a positive electrode. The obtained positive electrode was vacuum dried at 120 ° C. overnight, and then a lithium secondary battery was prepared in a glove box. A solution prepared by dissolving LiPF ₆ in a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) (volume ratio 3: 7) was used as the electrolytic solution, and metallic lithium was used as the negative electrode.

The charge / discharge test was transferred to a cycle deterioration test after a stepwise charge treatment for obtaining an activated sample. The test is performed at the start of charging, and the charging capacity is increased in the order of 80, 120, 160, 200mAh / g at a potential range of 2.0-4.8V, a test temperature of 30 ° C, and a current density of 40mA / g. Activation treatment was performed by constant current-constant voltage charging up to 4.8V (current termination at 4.8V is 10mA / g). The stepwise charge activation treatment is indispensable for evaluating the charge / discharge characteristics of the lithium manganese-based composite oxide of the present invention. In particular, it is an essential process when Fe is included as the M ¹ element. After the activation treatment, by evaluating up to 50 cycles with constant current charge / discharge at 2.0-4.8 V, the charge / discharge curve changes with the passage of cycles (especially the deviation from the similar shape seen after 20 cycles). ) Was evaluated. In particular, as mentioned above, in the discharge curve at 50-cycle discharge (54-cycle discharge: 54d) after activation treatment, (1) rapid at around 3.7V due to structural transition from layered rock salt structure to spinel phase. We evaluated the presence or absence of a significant potential drop and (2) the appearance of additional capacitance below 2.2 V associated with structural transitions to the Li ₂ (Mn, Ni) O ₂ phase. The results are shown in FIGS. 2, 4, 6, 8, 10, 12, 14, 16 and 18, and Table 4. In FIGS. 2, 4, 6, 8, 10, 12, 14, 16 and 18, the charging curve (5c) during 1-cycle charging after activation treatment and the charging curve during 20-cycle charging after activation treatment (5c). 24c), charge curve during 50-cycle charge after activation treatment (54c), discharge curve during 1-cycle discharge after activation treatment (5d), discharge curve during 20-cycle discharge after activation treatment (24d), and activity. The discharge curve (54d) at the time of 50-cycle discharge after the conversion process is shown. The upward-sloping curve corresponds to charging, and the downward-sloping curve corresponds to discharging. Further, in Table 4, Q _5c is the capacity at the time of 1-cycle charging after the activation treatment, Q _5d is the capacity at the time of 1-cycle discharge after the activation treatment, and Q _54d is the capacity at the time of 50-cycle discharge after the activation treatment, (Q). _1d to Q _5d sum) / (Q _1c to Q _5c sum) is the sum of the discharge capacities of each cycle during the stepwise charge activation process divided by the sum of the charge capacities of each cycle. V _{5d · ave} shows the initial average discharge voltage at the time of one cycle discharge after activation treatment.

As is clear from the above Examples and Comparative Examples, the lithium manganese-based composite oxide of the present invention not only exhibits a large charge / discharge capacity of 200 mAh / g or more at the first time, but also has two side reactions that occur after the cycle. It was confirmed that the substance has excellent long-term cycle characteristics and suppresses the change in crystal structure due to the above.

Claims (10)

General formula (1): Li _{1 + x} (M ¹ _y M ² _z Mn _1-y-z ) _1-x O ₂ (1)
[In the formula, M ¹ represents Fe and Ni . M ² represents Ti and / or Ge. x, y and z indicate 0 <x <1/3, 0 <y ≦ 0.4 , 0 <z ≦ 0.3. ]
Represented by and
A lithium manganese-based composite oxide containing a crystalline phase having a monoclinic layered rock salt structure or a hexagonal layered rock salt structure. The ratio of Fe and Ni represented by M ¹ in the general formula (1) is according to claim 1, wherein Fe is 10 to 90% by weight and the rest is Ni, where the total amount of M ¹ elements is 100% by weight. Lithium-manganese-based composite oxide. The lithium manganese-based composite oxide according to claim 1 or 2, which comprises only a crystalline phase having a monoclinic layered rock salt type structure. The method for producing a lithium manganese-based composite oxide according to any one of claims 1 to 3.
(1) A step of forming a precipitate by treating a mixture containing a manganese compound , an iron compound and a nickel compound as alkaline.
(2) A step of subjecting the precipitate obtained in step 1 to a wet oxidation treatment and aging it.
(3) A production method comprising a step of heating the aged product obtained in step 2 in the coexistence of a raw material compound containing a lithium compound in this order. The production method according to claim 4, wherein the mixture in the step 1 further contains a titanium compound. The production method according to claim 4 or 5, wherein the raw material compound in the step 3 further contains a germanium compound. The production method according to any one of claims 4 to 6, wherein the step 3 is a step of mixing the aged product obtained in the step 2 with the raw material compound and then heating the mixture. The production method according to any one of claims 4 to 7, wherein the heating in the step 3 is a step of heating in the atmosphere and then heating again in the atmosphere or in an inert atmosphere. A positive electrode material for a lithium ion secondary battery made of the lithium manganese-based composite oxide according to any one of claims 1 to 3. A lithium ion secondary battery comprising the positive electrode material for the lithium ion secondary battery according to claim 9 as a component.

Images