JP2000264638A - Method for producing lithium manganese composite oxide for lithium secondary battery positive electrode active material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a lithium manganese composite oxide having a spinel structure, which can be used as a positive electrode active material for a lithium secondary battery, in a simple and easy manner. Provided is a method capable of producing at low cost. A nitrate aqueous solution serving as a manganese source or another element source capable of replacing manganese and manganese sites, and a lithium source or an alkali metal element source capable of replacing lithium and lithium sites are provided. Hydroxide H ₂ O ₂
An aqueous solution is mixed, and a solution reaction is performed to deposit a composite oxide precursor having a layered rock salt structure, and the deposited precursor is kept at a relatively low temperature and aged to change the crystal structure from the layered rock salt structure. And a ripening step of transferring to a spinel structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a lithium manganese composite oxide as a positive electrode active material of a lithium secondary battery utilizing a phenomenon of insertion and extraction of lithium ions.

[0002]

2. Description of the Related Art As mobile phones and personal computers become smaller,
Secondary batteries with high energy density are required, and lithium secondary batteries have come into widespread use in the fields of communication devices and information-related devices. In addition, demands for electric vehicles are increasing in the field of automobiles due to resource problems and environmental problems, and the development of lithium secondary batteries that are inexpensive, have large capacities, and have good cycle characteristics is urgently required.

At present, as a positive electrode active material of a lithium secondary battery, LiCoO ₂ having an ordered layered rock salt structure has been adopted as a material capable of forming a 4V-class secondary battery. LiCoO ₂ is easy to synthesize and relatively easy to handle, and is excellent in charge / discharge cycle characteristics. Therefore, a secondary battery using LiCoO ₂ as a positive electrode active material is mainly used.

[0004] However, cobalt is a scarce resource, and a secondary battery using LiCoO ₂ as a positive electrode active material is difficult to cope with future mass production and size enlargement of automobile batteries, and also in terms of price. It must be very expensive. Therefore, instead of cobalt, an attempt has been made to employ a lithium manganese composite oxide containing manganese, which is relatively abundant and inexpensive as a constituent element, as a positive electrode active material.

[0005] A lithium manganese composite oxide which can constitute a 4V-class lithium secondary battery by being used as a positive electrode active material is composed of an ordered layered rock salt structure LiMnO ₂ ,
Zigzag layered structure LiMnO ₂ , spinel structure LiMn ₂
Those of O ₄ is known. Spinel structure LiMn ₂ O ₄
Among them, the crystal structure is relatively stable, and although the theoretical capacity is small, the amount of lithium that can be inserted and released reversibly is large, and when a lithium secondary battery is constructed, the above LiCoO ₂ is used. Since the same discharge capacity as that described above can be obtained, it can be a promising positive electrode active material for the next lithium secondary battery.

Hitherto, as a method for producing a spinel-structured LiMn ₂ O ₄ , there has been a solid-state reaction described below. (1) Mn ₂ O ₃ or MnO ₂ and Li ₂ CO ₃
n: Li is mixed at a molar ratio of 2: 1 and the mixture is heated at 650 ° C. in air for 6 hours to 850 ° C.
Baking at 14 ° C. for 14 hours (JP-A-63-187569).
(2) A method of adding a lithium salt to γ-MnOOH and heating to 800 ° C. (JP-A-3-4445) (3) Manganese oxide (MnO ₂ , Mn ₂ O ₃ , Mn)
The mixture of ₃ O ₄ ) and LiNO ₃ is
(4) MnO ₂ and LiNO _{3 in a} molar ratio of Mn: Li of 2.2: 1.0 to 1.8: 1.0. And mix
A method in which this mixture is fired in air at a temperature in the range of 800 ° C. to 1000 ° C. (JP-A-3-127453).
(5) LiNO ₃ or LiOH and MnO ₂ are mixed and the mixture is kept at 260 ° C.
A method of firing at a temperature of 0 ° C. and firing at a temperature of 600 to 700 ° C. again (JP-A-7-245106).

[0007]

In the above-mentioned conventional production method, the firing atmosphere is adjusted in order to obtain a highly crystalline spinel-structured lithium manganese composite oxide, and the temperature of 500 ° C. or more is adjusted in this adjusted atmosphere. Baking at high temperature is performed. Therefore, there is a problem that a large amount of energy is required and the manufacturing cost itself is increased. In the case of the solid-phase reaction, it is necessary to match the mixing ratio of the starting materials, that is, the composition ratio of each constituent element in the so-called preparation stage, with the composition ratio of the final product, and the mixing itself is sufficient. There was also a problem that the process had to be performed uniformly and a complicated process had to be performed.

When the spinel-structured lithium manganese composite oxide is used as a positive electrode active material, the composition formula is LiMn ₂ O ₄
Not only those represented by. In order to improve the cycle characteristics of the lithium secondary battery, a portion of the Li site or Mn sites in the crystal was substituted by another element, for example, the composition formula _{Li 1-z A z Mn 2} -y Me y O 2 May be used as the positive electrode active material. When attempting to produce such a spinel-structured lithium manganese composite oxide substituted with another element, uniform mixing of the raw materials is even more difficult, and the above-described conventional solid-phase reaction method has a problem in that the substitution ratio of the entire crystal is reduced. Even with the problem of uniformity, the lithium manganese composite oxide according to the conventional method cannot form a lithium secondary battery having good charge / discharge characteristics.

The present invention has been made in order to solve the above-mentioned problems of the conventional production method, and is a method for producing a lithium manganese composite oxide having a spinel structure which can be used as a positive electrode active material for a lithium secondary battery, An object of the present invention is to provide a production method capable of producing a lithium manganese composite oxide having excellent crystal composition uniformity easily and at low cost.

[0010]

The lithium secondary battery of the present invention
Of Lithium-Manganese Composite Oxide for Pond Positive Electrode Active Material
Is Me (NO_Three)_m(Me is Mn, Ni, Co, Cr,
At least one selected from the group consisting of Fe, Al, and Ti
Containing at least Mn, m is the value corresponding to the valence of Me)
A dissolved nitrate solution and AOH (A is an alkali metal
At least one selected from the group consisting of at least Li)
To H_TwoO_TwoHydroxide H dissolved in aqueous solution _TwoO_TwoWith the aqueous solution
The mixture was mixed to form a mixed solution, and the composition formula A was added to the mixed solution._xM
eO_Two・ NH_TwoO (0 <x ≦ 1, 0.1 ≦ n ≦ 1)
To deposit complex oxide precursor with layered rock salt structure
And the mixed oxide precursor in the mixed solution after deposition.
Aging body, formula AMe_TwoO_FourSpinel structure represented by
Aging step to obtain a lithium manganese composite oxide
It is characterized by becoming.

That is, the method for producing a lithium manganese composite oxide according to the present invention is a method for producing a lithium manganese composite oxide having a spinel structure, wherein a nitrate aqueous solution serving as a manganese source or another element source capable of replacing manganese and manganese sites is provided. And an aqueous H ₂ O ₂ solution of a hydroxide serving as a lithium source or a source of an alkali metal element capable of replacing lithium and a lithium site, and by a solution reaction, a composite oxide precursor having a layered rock salt structure is precipitated, Thereafter, the deposited precursor is kept at a relatively low temperature and aged, and the crystal structure is changed from a layered rock salt structure to a spinel structure.

The method for producing a lithium-manganese composite oxide according to the present invention is different from the conventional method using a solid-phase reaction, in which a precursor is synthesized by a solution reaction, whereby sufficient mixing of the raw materials is ensured, and The spinel-structured lithium manganese composite oxide, which is a product, has excellent composition uniformity throughout the product. Further, the aging step is a relatively low-temperature treatment different from the conventional calcination, so that it does not require as much energy as heating at a high temperature, and has a low fuel consumption and a low production cost. Furthermore,
Since the aging process utilizes the transition phenomenon in the mixed solution of the raw material solutions, the change of the mixing ratio of the raw material solutions, that is, the change of the composition ratio of manganese and lithium in the charging stage, is caused by the spinel structure lithium manganese composite as the final product. The effect on the composition ratio of the oxide is small. Therefore, the method for producing a lithium manganese composite oxide according to the present invention is a simple production method because it is not necessary to pay great attention to mixing of the raw material solutions.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a method for producing a lithium manganese composite oxide for a positive electrode active material of a lithium secondary battery according to the present invention will be described. The aging process will be described in the following order, and thereafter, a lithium secondary battery which is a use form of the manufactured lithium manganese composite oxide will be described.

<Lithium manganese composite acid to be produced
> Lithium for the positive electrode active material of the lithium secondary battery of the present invention
Manufactured by the manganese composite oxide manufacturing method
Manganese composite oxide is a spinel-structured lithium
Ngan composite oxide. Target lithium manganese
The composite oxide has a composition formula of LiMn_TwoO_FourStoichiometry expressed by
It is not limited to the composition. Attributed to stabilization of crystal structure
Cycle characteristics, storage characteristics, etc.
A group in which a part of the Mn site is replaced by an atom Me ′ of another element
Formula LiMn_2-yMe '_yO_FourRepresented by, or
Part of the Li site is replaced with another alkali metal atom A '
Substituted composition formula Li_1-zA '_zMn_TwoO_FourRepresented by
Is also included. Further, both the Mn site and the Li site
The composition formula Li in which part of the formula is replaced with atoms of another element_1-z
A ' _zMn_2-yMe '_yO_FourIncluded in manufacturing targets
It is.

When a part of the Mn site is substituted with another element, the substitution ratio, that is, the value of y in the composition formula is 0 <
It is desirable to manufacture those satisfying y ≦ 0.5. The reason for this is that, when the substitution ratio of Me ′, which is partially stable in divalent, exceeds 0.5, Mn becomes tetravalent and there is no Mn ³⁺ that can be charged and discharged, and the capacity is drastically reduced. . When a part of the Li site is substituted with another alkali metal atom, the substitution ratio, that is, the value of z in the composition formula, is 0 <z ≦ 0.3.
It is desirable that The reason for this is that the capacity will be reduced to 置換 or less if replaced further.

When used as a positive electrode active material, other atoms Me ′ capable of substituting Mn sites include N
i, Co, Cr, Fe, Al, and Ti. These are all trivalent and stable atoms and play a role in stabilizing the layered structure. Among these, M
It is more desirable to use Ni for e ′. This is because Ni has almost no distortion in the crystal because the trivalent ionic radius is substantially equal to Mn ³⁺ . The alkali metal A ′ capable of substituting the Li site includes Na, K, P
b and Cs. These alkali metals exist between the layers irrespective of charge and discharge, and play a role of always maintaining the space between the layers. Among these, it is more desirable to use K for A ′. This is because K has an ionic radius about twice as large as that of Li and is inexpensive.

<Precipitation Step> The first precipitation step performed in the present manufacturing method is Me (NO ₃ ) _m (Me is Mn, N
a nitrate aqueous solution in which at least one selected from i, Co, Cr, Fe, Al and Ti and containing at least Mn, m is a value corresponding to the valency of Me) in water;
(A is at least one selected from alkali metals and contains at least Li) is mixed with an aqueous solution of hydroxide H ₂ O ₂ in which an aqueous solution of H ₂ O ₂ is dissolved to form a mixed solution. The composition formula A _x MeO ₂ .nH ₂ O (0 <x ≦ 1,
This is to precipitate a composite oxide precursor having a layered rock salt structure represented by 0.1 ≦ n ≦ 1).

Me (NO ₃ ) _m changes the Mn site to another element M
When not substituted with an atom of e ′ (one or more selected from Ni, Co, Cr, Fe, Al, and Ti), Mn (N
O ₃ ) ₂ may be used. Part of the Mn site is replaced with another element M
When substituting with the atom of e ′, Mn (NO ₃ ) ₂ and Me ′
(NO ₃ ) _{m ′} (m ′ is a value corresponding to the valence of Me ′) and M
What is necessary is just to mix so that the molar ratio of n and Me 'is 2-y: y (y is the above-mentioned substitution ratio), and to dissolve in water. The concentration of the aqueous solution of Me (NO ₃ ) _m is desirably 0.1 to 1M. This is because when the concentration is less than 0.1 M, the amount of precipitation is small, and when it exceeds 1 M, generation of oxygen increases, which may be dangerous.

AOH may be used when the Li site is not replaced by an atom of another alkali metal element A '(at least one selected from alkali metals except Li). When a part of the Li site is replaced with an atom of another alkali metal element A ′, LiOH and A′OH are replaced by L
The molar ratio between i and A 'is 1-z: z (z is the above substitution ratio)
What is necessary is just to mix and melt | dissolve so that it may become.

The reason for using an aqueous solution of H ₂ O ₂ as a solvent for dissolving AOH is to oxidize water-soluble Mn ²⁺ to insoluble Mn ³⁺ . The concentration of the H ₂ O ₂ aqueous solution is desirably 1 to 10 wt% in consideration of the safety of the reaction. The concentration of AOH dissolved in the aqueous solution of H ₂ O ₂ is desirably 0.2 to 5 M in order to perform a uniform reaction.

The mixing ratio of the aqueous solution of Me (NO ₃ ) _m nitrate and the aqueous solution of AOH hydroxide H ₂ O ₂ in the precipitation step is determined by the composition formula A _x MeO ₂ .nH ₂ of the composite oxide precursor to be deposited.
What is necessary is just to change according to the value of x in O (existence ratio of A). When it is desired to precipitate those in the range of 0 <x ≦ 1, Me: A is mixed at a molar ratio of 1: 3 to 1:10.

In the production method of the present invention, regardless of the value of x in the composition formula A _x MeO ₂ .nH ₂ O of the composite oxide precursor deposited in the precipitation step, lithium manganese having a spinel structure, which is a final product, The composite oxide is represented by the composition formula AMe ₂ O ₄ . Therefore, since the mixing ratio of the aqueous solution of Me (NO ₃ ) _m nitrate and the aqueous solution of AOH hydroxide H ₂ O ₂ does not affect the composition of the final product, great care must be paid to the mixing ratio of both solutions. Therefore, it can be said that this is a simple manufacturing method. However, if consideration is given to the subsequent aging step, washing method, drying step, etc., the precursor A _x MeO ₂ .nH ₂ O
It is practical to set the value of x in the range of 0.2 ≦ x ≦ 0.7. For this purpose, a mixture of an aqueous solution of Me (NO ₃ ) _m nitrate and an aqueous solution of AOH hydroxide H ₂ O ₂ is used. The ratio is Me: A
Are desirably mixed such that the molar ratio is 1: 3 to 1: 5.

By the way, if an aqueous solution in which Mn (NO ₃ ) ₂ is dissolved and an aqueous solution of H ₂ O ₂ in which LiOH is mixed to cause a precipitation reaction, the composite oxide precursor to be deposited has a composition formula of Li _x MnO ₂ · nH ₂ O. Similarly, if an aqueous solution in which Mn (NO ₃ ) ₂ and Me ′ (NO ₃ ) _{m ′} are dissolved and an aqueous solution of H ₂ O ₂ in which LiOH is dissolved, the composite oxide precursor has a composition formula Li _x Mn
_{1-y / 2} Me'y _{/ 2} O ₂ · nH ₂ O, and an aqueous solution in which Mn (NO ₃ ) ₂ is dissolved and an H ₂ O in which LiOH and A'OH are dissolved ₂ aqueous solution, the composite oxide precursor has the composition formula (Li _1-z A ′ _z ) _x MnO
₂ · nH ₂ O, and Mn
By mixing an aqueous solution in which (NO ₃ ) ₂ and Me ′ (NO ₃ ) _{m ′} are dissolved and an aqueous solution of H ₂ O _{2 in} which LiOH and A′OH are dissolved, the composite oxide precursor has a composition The formula (Li
_1-z A ′ _z ) _x Mn _{1−y / 2} Me ′ _{y / 2} O ₂ .nH ₂ O

In the precipitation step, an aqueous nitrate solution and hydroxide H _{2 are used.}
This is performed by uniformly mixing with an O ₂ aqueous solution. In order to ensure this uniformity, it is desirable to mix the two while stirring. The method of stirring is not particularly limited, and a known method of stirring a normal solution may be used. The reaction temperature in the precipitation step is desirably 10 to 30 ° C. because it involves an exothermic reaction. Also,
The reaction time in the precipitation step may be 1 to 30 minutes, which is a relatively quick step.

The composite oxide deposited by this precipitation step
The precursor has the composition formula A_xMeO_Two・ NH _TwoO (0.1 ≦ n ≦
1) containing water of hydration as is clear from the composition formula
And the crystallinity is low. The ratio of this hydration water, that is, the composition formula
The value of n in the table depends on the reaction conditions in the precipitation
It is not clear in the range of 0.1 ≦ n ≦ 1. the value of n
Is any value in this range,
Removed, and the final product, lithium, with spinel structure
Water of hydration no longer exists in the manganese composite oxide. Chi
By the way, 0.3M Me (NO_Three)_mAqueous solution and 0.6M
3 wt% H of AOH_TwoO_TwoMixed with an aqueous solution at 20 ° C
When reacted at a temperature for 5 minutes, the value of n is about 0.6
Become.

<Aging Step> The aging step in the production method of the present invention comprises a composition formula A _x MeO ₂ .nH ₂ O (0 <x ≦ 1,
The complex oxide precursor having a layered rock salt structure represented by 0.1 ≦ n ≦ 1) is aged (so-called aging) in a mixed solution after the precipitation of the precursor while maintaining the temperature within a predetermined range. This is a step of transferring to a lithium manganese composite oxide having a spinel structure represented by a composition formula AMe ₂ O ₄ .

Suitable at holding temperature, that is, aging temperature
Temperature range, part of the Mn site is replaced with another element
It depends on whether or not to do so. Place Mn site
In the case of manufacturing a product not to be exchanged, that is, the composition formula LiMn
_TwoO_FourOr Li_1-zA '_zMn_TwoO_FourLithium represented by
When manufacturing a manganese composite oxide, use
It is desirable to keep the temperature below 00 ° C. for aging.
In addition, when manufacturing a product in which a part of the Mn site is substituted,
In other words, LiMn_2-yMe '_yO_FourOr Li _1-zA '_z
Mn_2-yMe '_yO_FourLithium manganese composite oxidation represented by
In the case of manufacturing products, the temperature is more than 50 ℃ and less than 300 ℃
It is desirable to keep and aged.

When the aging temperature is 50 ° C. or lower, an unreacted substance whose crystal structure does not change, in other words, a phase as a precursor remains. On the other hand, when the temperature is 200 ° C. or 300 ° C. or higher, in addition to the spinel structure, a regular layered rock salt structure not containing hydration water is by-produced by the transformation, and the two phases also coexist. The existence of such a phase other than the spinel structure serving as the impurity phase is caused when a lithium secondary battery is formed using this lithium manganese composite oxide.
It causes deterioration of the charge / discharge cycle characteristics of the battery. Therefore, in order to produce a single-phase lithium manganese composite oxide having a spinel structure, it is desirable that the ripening be performed in the above-mentioned preferable temperature range. Note that Mn
The maximum temperature changes depending on whether the site is replaced or not.
It is considered that Mn ⁴⁺ appears due to the presence of a divalent stable substituent atom, and spinel becomes a stable phase.

When a single phase having a more pure spinel structure is to be produced, it is preferable to avoid the vicinity of the upper limit or the lower limit of the above-mentioned preferable ripening temperature range. If you manufacture
It is more preferable that the temperature is 70 ° C. or more and 150 ° C. or less.
In the case of manufacturing a product in which a part of a site is replaced with an atom of another element, it is more preferable that the temperature be 70 ° C or more and 200 ° C or less.

The aging time varies depending on conditions such as the aging temperature and the like, but may be any time as long as the aging reaction can be completely completed, and is usually performed for 6 hours or more. Since aging after the completion of the reaction leads to elongation of the whole production process, it is desirable to shorten the time as much as possible. In the aging step, for example, the solution obtained in the precipitation step is placed in an autoclave lined with Teflon, and
The temperature can be kept at 50 ° C. for 12 hours, then cooled to 60 ° C. or less, and then taken out. However,
If the ripening temperature is around 100 ° C. or more than 100 ° C., evaporation of the mixed solution itself becomes a problem.
When the temperature is higher than 00 ° C., it is necessary to carry out in an autoclave container or the like. From the viewpoint of performing the ripening step with a simpler apparatus, the ripening temperature is desirably in the range of 60 ° C to 90 ° C.

By the aging step performed as described above, the composite oxide precursor is transformed from the layered rock salt structure, the water of hydration contained at the same time is removed, and the single phase of spinel structure containing no water of hydration is removed. Produced as lithium manganese composite oxide. Incidentally, the composite oxide precursor has a composition formula of Li _x MnO ₂
What is represented by nH ₂ O is represented by the composition formula LiMn ₂ O ₄ , and similarly, Li _x Mn _{1-y / 2} Me ′ _{y / 2} O ₂
The one represented by nH ₂ O is LiMn _2-y Me ′ _y O ₄ ;
Further, those represented by (Li _{1 -z} A ' _z ) _x MnO ₂ · nH ₂ O are referred to as Li _{1 -z} A' _z Mn ₂ O ₄ and further (Li
_{1-z A 'z) x} Mn 1-y / 2 Me' y / 2 O 2 · nH those represented by ₂ O becomes _{Li 1-z A 'z Mn} 2-y Me' y O 4. The produced spinel-structured lithium manganese composite oxide is separated from the solution by filtration, washed with water, and then dried to form a powder. The drying method is not particularly limited, and may be performed in a drying furnace or the like at a temperature of 50 to 120 ° C. for about 60 to 180 minutes, as is generally performed.

<Lithium Secondary Battery> An embodiment of a lithium secondary battery, which is an application of the spinel-structured lithium manganese composite oxide obtained by the production method of the present invention, will be described. Generally, a lithium secondary battery includes a positive electrode and a negative electrode that occlude and release lithium ions, a separator that is interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte that moves lithium ions between the positive electrode and the negative electrode. Consists of Since the secondary battery of the present embodiment also follows this configuration, the following description will be made for each of these components.

The positive electrode can absorb and release lithium ions.
Mix the conductive material and binder with the positive electrode active material
An appropriate solvent was added to make a paste-like positive electrode mixture.
Is applied to the surface of a current collector made of metal foil such as aluminum,
Drying and then pressing to increase the active material density
Formed by In the present embodiment, the positive electrode active material
Is the composition formula AMe obtained by the above-mentioned production method. _TwoO_FourRepresented by
Using spinel-structured lithium manganese composite oxide
You. Substitution ratio of Mn site with other element atom, Li site
Can vary depending on the percentage of substitution with other alkali metal atoms.
A lithium manganese composite compound can be a positive electrode active material.
In the secondary battery of the present embodiment, one of these
Can be used as a positive electrode active material, or two or more
Can also be used as a mixture. In addition, the above lithium
Manganese compounds and other known positive electrode active materials
Quality, for example LiCoO _Two, LiNiO_TwoMixed with
May be used.

The conductive material used for the positive electrode is for ensuring the electric conductivity of the positive electrode active material layer, and is made of a carbon material powder such as carbon black, acetylene black, graphite or the like.
A species or a mixture of two or more species can be used.
The binder plays a role of binding the active material particles, and may be a fluororesin such as polytetrafluoroethylene, polyvinylidene fluoride, or fluororubber, or a thermoplastic resin such as polypropylene or polyethylene. As a solvent in which the active material, the conductive material, and the binder are dispersed, an organic solvent such as N-methyl-2-pyrrolidone can be used.

The negative electrode in the present embodiment is formed by sheeting metal lithium, which is the negative electrode active material, into a current collector network such as nickel or stainless steel in the same manner as that of a general battery. It is formed by pressing. As the negative electrode active material, a lithium alloy or a lithium compound can be used instead of metal lithium. As another embodiment of the negative electrode, the negative electrode can be formed using a carbon material capable of inserting and extracting lithium ions as the negative electrode active material.
Examples of the carbon substance that can be used include natural or artificial graphite, fired organic compounds such as phenolic resins, and powders such as coke. In this case, the binder is mixed with the negative electrode active material, and a suitable solvent is added thereto to form a paste-like negative electrode mixture on a surface of a metal foil current collector of copper or the like, followed by drying.

When the carbon material is used as the negative electrode active material, a fluorine-containing resin such as polyvinylidene fluoride or the like is used as the negative electrode binder and an organic solvent such as N-methyl-2-pyrrolidone is used as the solvent, similarly to the positive electrode. Can be. The separator sandwiched between the positive electrode and the negative electrode is for separating the positive electrode and the negative electrode and holding the electrolytic solution to allow the passage of ions, and a thin microporous film of polyethylene, polypropylene, or the like can be used.

The non-aqueous electrolyte is obtained by dissolving an electrolyte in an organic solvent. Examples of the organic solvent include aprotic organic solvents such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and the like.
One kind of γ-butyrolactone, acetonitrile, dimethoxyethane, tetrahydrofuran, dioxolane, methylene chloride and the like, or a mixture of two or more kinds thereof can be used. As the electrolyte to be dissolved, LiI, LiCl which generates lithium ions when dissolved are used.
O ₄ , LiAsF ₆ , LiBF ₄ , LiPF _{6 and the} like can be used. Note that a solid electrolyte or the like can be used instead of the non-aqueous electrolyte.

The lithium secondary battery of the present embodiment composed of the above-mentioned ones can have various shapes such as a coin type, a stacked type and a cylindrical type. In any case, a separator is sandwiched between the positive electrode and the negative electrode to form an electrode body, and the electrode body is made to conduct from the positive electrode and the negative electrode to the positive electrode terminal and the negative electrode terminal communicating with the outside, respectively. Together with the non-aqueous electrolyte in a battery case to complete the battery.

[0039]

EXAMPLES In order to confirm that a good lithium manganese composite oxide for a positive electrode active material can be produced by the above production method of the present invention, lithium manganese composite oxides were produced by various methods and evaluated. Hereinafter, an embodiment will be described. <Lithium-manganese composite oxide by precipitation aging method A> An aqueous solution in which Mn (NO ₃ ) ₂ is dissolved and LiOH
Is mixed with an aqueous solution of H ₂ O ₂ in which is dissolved to precipitate a composite oxide precursor, and the precursor is aged at various temperatures. It is a lithium manganese composite oxide. In addition,
The production method comprising the precipitation step and the aging step, which is the production method of the present invention, is hereinafter referred to as “precipitation aging method”.

First, a 0.3 M Mn (NO ₃ ) ₂ aqueous solution 1
00ml in by mixing LiOH / 3wt% H ₂ O ₂ aqueous solution 200ml of 0.6M and the mixed solution, and reacted for 5 minutes while vigorously stirred with a Sutarapisu (stirrer), the compositional formula Li _0.6 MnO ₂ · 0 A composite oxide precursor having a layered rock salt structure represented by 0.5H ₂ O was precipitated. Next, this precursor was placed in a container lined with Teflon together with the mixed solution after deposition, aged at room temperature and various temperatures in the range of 50 ° C. to 200 ° C. for 2 days, and then separated by filtration.
After washing with water and drying, various lithium manganese composite oxides were obtained. And these were made into the lithium manganese composite oxide by the precipitation ripening manufacturing method A.

<Lithium-manganese composite oxide by precipitation aging method B> An aqueous solution in which Mn (NO ₃ ) ₂ and Ni (NO ₃ ) ₂ are dissolved and an aqueous H ₂ O ₂ solution in which LiOH is dissolved are mixed to form a composite. An oxide precursor was precipitated, and this precursor was aged at various temperatures.
Is a lithium manganese composite oxide substituted with

First, a 0.3 M Mn (NO ₃ ) ₂ aqueous solution and a 0.3 M Ni (NO ₃ ) ₂ aqueous solution were mixed so that the molar ratio of Mn: Ni was 19: 1 and 18: 2. 100 ml of each of the two aqueous solutions was prepared. Each aqueous solution contains 0.6M LiOH / 3wt% H ₂ O ₂ aqueous solution 20
0 ml was mixed to form a mixed solution, and the mixture was reacted for 5 minutes with vigorous stirring using a stirrer piece to obtain a composition formula of Li _0.6 Mn _0.95 Ni _0.05 O ₂ .0.4H ₂ O, Li
Two types of composite oxide precursors having a layered rock salt structure represented by _0.5 Mn _0.9 Ni _0.1 O ₂ · _0.5 H ₂ O were deposited. Next, these precursors were placed in a container lined with Teflon together with the mixed solution after deposition, and, as in the case of the above-mentioned precipitation aging method A, at room temperature and at various temperatures in the range of 50 ° C to 200 ° C,
It was aged for 2 days, and then filtered, washed with water and dried to obtain various lithium manganese composite oxides. And these were made into the lithium manganese composite oxide by the precipitation aging method B.

<Lithium-manganese composite oxide by precipitation aging method C> An aqueous solution in which Mn (NO ₃ ) ₂ and Ni (NO ₃ ) ₂ are dissolved and an aqueous solution of H ₂ O _{2 in} which LiOH and KOH are dissolved are mixed. To form a composite oxide precursor, and aged at a variety of temperatures to produce a lithium manganese composite in which a part of the Mn site was replaced by Ni and a part of the Li site was replaced by K. It is an oxide.

First, an aqueous nitrate solution was prepared by mixing a 0.3 M aqueous solution of Mn (NO ₃ ) ₂ and a 0.3 M aqueous solution of Ni (NO ₃ ) _{2 so} that the molar ratio of Mn: Ni was 19: 1.
0 ml was prepared. Then, 0.6M LiOH / 3wt
% H ₂ O ₂ aqueous solution 180ml and 0.6M KOH / 3wt
20 ml of a 20% aqueous solution of H ₂ O ₂ was mixed to prepare 200 ml of an aqueous solution of hydroxide H ₂ O ₂ . The aqueous nitrate solution and the aqueous hydroxide H ₂ O ₂ solution are mixed to form a mixed solution, and the mixture is reacted for 5 minutes with vigorous stirring using a stirrer piece to obtain a composition formula (Li _0.9 K _0.1 ) _0.6 Mn _0.95 Ni _0.05 O ₂・ 0.5
A composite oxide precursor having a layered rock salt structure represented by H ₂ O was precipitated. Next, this precursor is placed in a container lined with Teflon together with the mixed solution after deposition, and aged at room temperature and various temperatures in the range of 50 ° C. to 200 ° C. for 2 days as in the case of the above-mentioned precipitation aging method A. , Followed by filtration, washing with water,
By drying, various lithium manganese composite oxides were obtained. And these were made into the lithium manganese composite oxide by the precipitation aging method C.

<Lithium-manganese composite oxide by solid-phase reaction method A> A lithium-manganese composite oxide produced by a conventional solid-phase reaction method and compared with the one obtained by the above-mentioned precipitation ripening method,
This is a lithium manganese composite oxide having a spinel structure in which none of the Li sites are substituted. Mn ₂ O ₃ and Li
OH was sufficiently mixed using an automatic mortar so that the molar ratio of Mn: Li was 2: 1.02, and this mixture was
It was manufactured by firing in air at a temperature of 800 ° C. for 6 hours. This lithium manganese composite oxide has a spinel structure represented by a composition formula LiMn ₂ O ₄ .

<Lithium-manganese composite oxide by solid-phase reaction method B> In order to compare with the above-mentioned one by the precipitation aging method, a lithium-manganese composite oxide was produced by a conventional solid-phase reaction method, and a part of the Mn site was replaced with Ni. It is a lithium manganese composite oxide having a spinel structure. Mn ₂ O ₃ , Ni (OH) ₂ and Li
OH and Mn: Ni: Li in a molar ratio of 1.95: 0.
05: 1 to 1.8: 0.2: 1, and the various mixtures were mixed in air at 800 ° C. for 6 hours.
By firing for hours, various compositions were manufactured.
Incidentally, the mixing ratio is Mn: Ni: Li = 1.9: 0.
A mixture obtained by sintering a mixture of 1: 1.02 has a composition formula of L
and has a spinel structure lithium manganese composite oxide represented by iMn _1.9 Ni _{0 .1} O _4.

<Lithium manganese composite by precipitation aging method>
Crystal structure of oxide> produced by the above-mentioned precipitation aging method A
For various lithium manganese composite oxides with different aging temperatures
By conducting X-ray diffraction analysis, the crystal structure
It was confirmed. When the aging temperature is room temperature, the spinel structure L
iMn_TwoO_FourIs almost never generated. Aging temperature is 5
At 0 ° C., the spinel structure LiMn_TwoO_FourOther than
Layered rock salt structure Li_0.6MnO_Two・ 0.5H_TwoO remains
are doing. If the aging temperature is 200 ° C,
Structure LiMn_TwoO_FourIn addition, the layered rock salt structure LiMnO _Two
Is a by-product. On the other hand, the aging temperature is 70 ° C.
In the range of 150 ° C., the spinel structure LiMn_TwoO_FourSimply
It was confirmed that they were in one phase.

Similarly, X-ray diffraction analysis was performed on various lithium manganese composite oxides produced by the above-mentioned precipitation ripening method B and having different ripening temperatures to confirm their crystal structures. Mn (NO ₃ ) ₂ aqueous solution and 0.3M N
The i (NO ₃ ) ₂ aqueous solution was mixed with a molar ratio of Mn: Ni of 19: 1.
In the case of a lithium manganese composite oxide produced from an aqueous solution mixed such that the ripening temperature is room temperature, the spinel structure LiMn _1.9 Ni _0.1 O ₄
Is almost never generated. Those having an aging temperature of 50 ° C. have an unreacted layered rock salt structure Li _0.6 Mn _0.95 Ni _0.05 O _{2 .0.4 in} addition to the spinel structure LiMn _1.9 Ni _0.1 O _4.
H ₂ O remains. Unlike the case of precipitation aging method A,
Those having an aging temperature in the range of 70 ° C. to 200 ° C. have a single phase of spinel structure LiMn _1.9 Ni _0.1 O ₄ , and even when the sintering temperature is 200 ° C., the layered rock salt structure LiMn _0.95
It was confirmed that Ni _0.05 O ₂ was not produced as a by-product. It is considered that the reason why the result at the aging temperature of 200 ° C. is different from that in the case of the precipitation aging method A is that Mn ⁴⁺ is generated by Ni substitution and the spinel structure is stabilized as described above.

Mn (NO_Three)_TwoAqueous solution and 0.3M Ni
(NO_Three)_TwoThe aqueous solution was converted to Mn: Ni at a molar ratio of 18: 2.
Precipitation produced from using mixed aqueous solutions
Regarding the lithium manganese composite oxide of the ripening method B,
It was confirmed that similar results were obtained. In addition, generate
In the spinel structure, the composition formula is LiMn._1.8Ni_0.2O
_FourWas represented by Furthermore, according to the precipitation aging method C
Lithium manganese composite oxide
The same result as in the case of B was obtained, and the spinel structure in this case was obtained.
Is made of the composition formula Li_0.9K_0.1Mn_1.8Ni_0.2O_Fourso
Was represented.

For reference, a lithium manganese composite oxide obtained by the precipitation aging method A, wherein the aging temperature is room temperature, 5
FIG. 1 shows a diffraction chart of X-ray diffraction analysis at 0 ° C., 80 ° C., 120 ° C., and 200 ° C. Further, the lithium manganese composite oxide obtained by the precipitation aging method B,
An Mn (NO ₃ ) ₂ aqueous solution and a 0.3 M Ni (NO ₃ ) ₂ aqueous solution are produced from an aqueous solution obtained by mixing Mn: Ni at a molar ratio of 19: 1, and the ripening temperature is 80%.
FIG. 2 shows a diffraction chart of X-ray diffraction analysis at 200 ° C. and 200 ° C. In FIG. 1, the hatched diffraction peak is the diffraction peak of the spinel structure LiMn ₂ O ₄ . Further, in the precipitation aging methods A to C, the relationship between the aging temperature and the composition and crystal structure of the lithium composite oxide to be produced was evaluated by examining typical aging temperatures of 50 ° C. and 80 ° C.
Table 1 below shows the results for the cases of 200C and 200C.

[0051]

[Table 1]

Next, the spinel-structured lithium manganese composite oxide obtained by the precipitation aging method A and the precipitation aging method B, and the spinel-structured lithium manganese composite oxide obtained by the solid-state reaction method A and the solid-state reaction method B And Mn
A comparison was made of the change in the value of the lattice constant due to the change in the substitution ratio of Ni at the site. FIG. 3 shows the result. A spinel-structured lithium manganese composite oxide in which the Mn site is not substituted and a part of which is substituted by Ni has a composition formula of Li
It can be generalized to Mn _2-y Ni _y O ₄ , and the value of y in this composition formula can be used as the substitution ratio. About the thing by the precipitation aging method, and also about the thing by the solid phase reaction method,
As the substitution ratio y increases, the value of the lattice constant a decreases linearly. Further, it is clear that the value of the lattice constant a does not differ depending on the manufacturing method. Therefore, from this, the precipitation ripening method adopted by the production method of the present invention is the same as the conventional solid-phase reaction method in which the treatment is performed at a high temperature of 500 ° C. or higher, despite performing a relatively low temperature treatment of 100 ° C. or lower. Furthermore, it can be confirmed that a lithium-manganese composite oxide having a spinel structure having good crystallinity can be produced.

<Evaluation as Positive Electrode Active Material> A coin-type lithium secondary battery using a lithium manganese composite oxide prepared by the above-described precipitation ripening method and a lithium manganese composite oxide prepared by a solid phase reaction method as a positive electrode active material and metallic lithium as a negative electrode was used. A secondary battery was manufactured. A charge / discharge cycle test was performed on each lithium secondary battery, the initial discharge capacity and the capacity retention were confirmed, and the lithium manganese composite oxide was used as a positive electrode active material of a lithium manganese composite oxide by a precipitation aging method employed in the production method of the present invention. The performance was evaluated.

In the positive electrode of the coin-type lithium secondary battery, 70 parts by weight of the respective lithium manganese composite oxide powder, 25 parts by weight of acetylene black as a conductive material, and 5 parts by weight of polyvinylidene fluoride as a binder were used. The mixture was partially mixed, press-molded at a pressure of ² t / cm ² , and then heat-treated at a temperature of 200 ° C. in a vacuum to produce the film. The non-aqueous electrolyte contains LiPF ₆ in a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 1: 1.
M dissolved at a concentration of M was used.

The conditions of the charge / discharge cycle test performed on each of the manufactured lithium secondary batteries were as follows: at a temperature of 60 ° C., a current density of 1 mA / cm ² , a charge to a final voltage of 4.2 V, and a 10-minute pause. And then a current density of 1 mA /
After discharging to a final voltage of 3.0 V in cm ² , a step of resting for 10 minutes was defined as one cycle, and this cycle was repeated 50 times or more. The discharge capacity per unit weight of the positive electrode active material and the capacity retention rate after 50 cycles (discharge capacity at 50th cycle / initial discharge capacity) of each battery were determined. Table 2 below shows an example of this result. Table 2 shows the secondary batteries using the lithium manganese composite oxide prepared by the precipitation aging method with aging temperatures of 80 ° C and 200 ° C. In the case of the precipitation ripening method B and the solid-phase reaction method B, only those in which the substitution ratio of Mn sites by Ni, that is, the value of y in the composition formula is 0.1 are listed.

[0056]

[Table 2]

As can be seen from Table 2, there is a large difference in the initial discharge capacity and the capacity retention between the secondary battery using the solid-state reaction method and the secondary battery using the precipitation aging method. However, it can be confirmed that the lithium manganese composite oxide obtained by the precipitation aging method can be a good positive electrode active material. In addition, the replacement of the Mn site by Ni and the replacement of the Li site by K lowers the initial discharge capacity but increases the capacity retention rate, and becomes a positive electrode active material that can constitute a more practical secondary battery with good cycle characteristics. It can be confirmed that it is obtained. Regarding the effect of this substitution, no special difference is found between the solid phase reaction method and the precipitation ripening method.

However, the aging temperature by the precipitation aging method A is 20
Those having a temperature of 0 ° C. have been aged at a temperature outside the preferred aging temperature in the production method of the present invention, and have a layered rock salt structure LiMn in the produced lithium manganese composite oxide.
O ₂ phase is by-produced. Therefore, the capacity retention rate after 50 cycles is a low value of 75%. Therefore, from this, in order to produce a lithium manganese composite oxide that can constitute a secondary battery having good cycle characteristics,
It can be confirmed that it is desirable to ripen in the above preferable ripening temperature range.

Next, in order to confirm that the precipitation aging method, which is the production method of the present invention, can produce a lithium manganese composite oxide which is more excellent in the uniformity of the composition of the whole crystal as compared with the solid phase reaction method. A charge / discharge characteristic curve of a secondary battery using a lithium manganese composite oxide according to each method as a positive electrode active material was prepared. One of the secondary batteries to be compared is a secondary battery using an aging temperature of 80 ° C. by the above-mentioned precipitation aging method B, and the other is a secondary battery using an aging temperature by the solid phase reaction method B. is there. The lithium manganese composite oxide used had an overall composition of LiMn _1.9 Ni _0.1
It has a spinel structure represented by O ₄ . FIG. 4 shows the charge / discharge characteristic curves of the two.

As can be seen from FIG. 4, in the case of the solid-state reaction method, the voltage between the terminals of the battery changes stepwise over time on both the charging side and the discharging side. On the other hand, according to the precipitation aging method, the voltage between the terminals of the battery changes linearly on both the charging side and the discharging side. In the case of the solid-phase reaction method, it is difficult to mix the starting materials in an extremely uniform state, and it is more difficult to add a material serving as a substitution element source. Therefore, in the case of the solid-phase reaction method, Ni as a substitution element is segregated in the crystal, and the crystal undergoes a phase transition with charge / discharge, and the charge / discharge characteristic curve changes stepwise. It is considered to be. In contrast, in the case of the precipitation aging method that changes linearly,
It is considered that a phenomenon such as Ni segregation did not occur. That is, since the precipitation step of the production method of the present invention is a reaction in a liquid phase, the mixed state of the starting materials can be made extremely uniform. From these results, it can be confirmed that the production method of the present invention is a method that can easily produce a lithium manganese composite oxide having more excellent composition uniformity of the whole crystal.

[0061]

The method for producing a lithium-manganese composite oxide for a lithium secondary battery positive electrode active material according to the present invention comprises a nitrate aqueous solution serving as a manganese source or another element source capable of replacing manganese and manganese sites; And an aqueous solution of a hydroxide serving as a source of an alkali metal element capable of replacing a lithium site with a H ₂ O ₂ aqueous solution of a hydroxide, and performing a solution reaction to precipitate a composite oxide precursor having a layered rock salt structure; An aging step in which the body is kept at a relatively low temperature for aging and the crystal structure is changed from a layered rock salt structure to a spinel structure.

By adopting such a constitution, the production method of the present invention can produce a spinel-structured lithium manganese composite oxide having excellent uniformity in the composition of the whole crystal at a relatively low temperature and at a low cost. This is a method that can be easily manufactured.

[Brief description of the drawings]

FIG. 1 shows an X-ray diffraction chart of a lithium manganese composite oxide produced by a precipitation aging method that is a production method of the present invention.

FIG. 2 shows an X-ray diffraction chart of a lithium manganese composite oxide produced by a precipitation aging method, which is a production method of the present invention, in which a part of Mn sites has been substituted by Ni.

FIG. 3 shows a lithium manganese composite oxide produced by a precipitation ripening method and a solid phase reaction method.
The change of the lattice constant with respect to the change of the substitution ratio of Mn site by Ni is shown.

FIG. 4 shows a charge / discharge characteristic curve of a lithium manganese composite oxide produced by a precipitation ripening method and a solid phase reaction method, in which a part of the Mn site is substituted by Ni.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01M 4/58 H01M 4/58 10/40 10/40 Z F-term (Reference) 4G002 AA06 AA10 AB02 AE05 4G048 AA04 AB02 AC06 AD06 AE07 5H003 AA08 BA00 BA03 BB01 BB04 BB05 BC06 BD00 BD01 BD03 5H014 AA02 BB01 BB05 BB06 BB08 CC01 EE08 EE10 5H029 AJ14 AK03 AK19 AL01 AL06 AL12 AM03 AM04 AM05 AM07

Claims (8)

[Claims] 1. Me (NO ₃ ) _m (Me is Mn, Ni, C
a nitrate aqueous solution in which at least one selected from the group consisting of o, Cr, Fe, Al, and Ti and containing at least Mn, where m is a value corresponding to the valency of Me, is dissolved in water; At least one member selected from the group consisting of at least L
hydroxides containing i) was dissolved in aqueous solution of H ₂ O ₂ H ₂ O ₂
An aqueous solution is mixed to form a mixed solution, and a composition formula A _x MeO ₂ .nH ₂ O (0 <x ≦ 1, 0.1 ≦ n ≦
A precipitation step of precipitating a composite oxide precursor having a layered rock salt structure represented by 1), and aging the composite oxide precursor in the mixed solution after deposition, represented by a composition formula AMe ₂ O ₄ A method for producing a lithium manganese composite oxide for a lithium secondary battery positive electrode active material, comprising: an aging step of obtaining a lithium manganese composite oxide having a spinel structure. 2. The method according to claim 1, wherein the Me comprises only Mn and the A
Is composed only of Li, and the composite oxide precursor has a composition formula of Li _x MnO ₂ .nH ₂ O
The lithium manganese composite oxide is represented by a composition formula LiMn ₂ O ₄ , and the aging temperature in the aging step is higher than 50 ° C. and lower than 200 ° C. 2. Method for producing lithium manganese composite oxide for substances. 3. The method according to claim 1, wherein A comprises only Li, and the nitrate aqueous solution contains Mn (NO ₃ ) ₂ and Me ′ (NO ₃ ).
_{m ′} (Me ′ is at least one selected from Ni, Co, Cr, Fe, Al and Ti, m ′ is a value corresponding to the valence of Me ′) and the molar ratio between Mn and Me ′ is 2- y: y is prepared by dissolving so that the composite oxide precursor has a composition formula of Li _x Mn _{1-y / 2} Me ′ _{y / 2}
O ₂ · nH ₂ O, wherein the lithium manganese composite oxide is represented by a composition formula LiMn _2-y Me ′ _y O ₄ , wherein the aging temperature in the aging step is higher than 50 ° C. and lower than 300 ° C. Item 4. The method for producing a lithium manganese composite oxide for a lithium secondary battery positive electrode active material according to Item 1. However, 0 <y ≦
0.5. 4. The Me comprises only Mn, and the aqueous solution of hydroxide H ₂ O ₂ comprises LiOH and A′OH (A ′).
Is prepared by dissolving at least one selected from alkali metals excluding Li) such that the molar ratio of Li and A ′ is 1-z: z, and the composite oxide precursor has a composition formula (Li _1-z A ' _z ) _x MnO
₂ · nH ₂ O, and the lithium manganese composite oxide is represented by a composition formula Li _1-z A ′ _z Mn ₂ O ₄ , and the aging temperature in the aging step is higher than 50 ° C. and lower than 200 ° C. A method for producing a lithium manganese composite oxide for a lithium secondary battery positive electrode active material according to claim 1. However, 0 <z
≦ 0.3. 5. The method according to claim 1, wherein the nitrate aqueous solution contains Mn (NO_Three)_TwoWhen
Me '(NO_Three)_{m '}(Me ′ is Ni, Co, Cr, Fe,
At least one selected from Al and Ti, m 'is a valence of Me'
And the molar ratio between Mn and Me ′ is 2-y: y and
The hydroxide H is prepared by dissolving_TwoO_TwoThe aqueous solution is LiOH and A'OH (A '
Is one or more selected from alkali metals except Li) and
Li was dissolved so that the molar ratio of Li and A ′ became 1-z: z.
The composite oxide precursor is prepared by the composition formula (Li_1-zA '_z)_xMn
_{1-y / 2}Me '_{y / 2}O_Two・ NH _TwoO, and said lithium
Mumanganese composite oxide has the composition formula Li_1-zA '_zMn_{2- y}M
e '_yO_FourThe aging temperature of the aging step is higher than 50 ° C.
2. The lithium secondary battery according to claim 1, wherein the temperature is lower than 300 ° C.
Of Lithium-Manganese Composite Oxide for Pond Positive Electrode Active Material
Law. However, 0 <y ≦ 0.5 and 0 <z ≦ 0.3. 6. The method for producing a lithium manganese composite oxide for a lithium secondary battery positive electrode active material according to claim 3, wherein Me ′ is Ni. 7. The method for producing a lithium manganese composite oxide for a lithium secondary battery positive electrode active material according to claim 4, wherein A ′ is K. 8. The method according to claim 8, wherein Me ′ is Ni and A ′ is K
The method for producing a lithium-manganese composite oxide for a positive electrode active material for a lithium secondary battery according to claim 5.