JP2002097022A - New lithium manganese compound oxide and lithium secondary cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium manganese compound oxide having high capacitance of an active material and provide a method of producing the same, and also provide a lithium secondary cell using the same. SOLUTION: This lithium manganese complex oxide is represented by formula 1: Li1-xMnO2-δ (x represents deficiency amount of lithium, 0<=x<=0.6; δrepresents deficiency amount of oxygen and satisfies 0<=δ<=0.2) and possesses a space group of I41/amd, and lattice constants (a) and (c) satisfy 5.670 Å<a<=5.695 Å and 9.060 Å<=c<=9.170 Å, respectively. A lithium compound is mixed with a manganese compound and this mixture is calcined in low oxygen concentration, and the calcined substance is electrochemically treated to produce the lithium manganese compound oxide. A material for positive electrode of the lithium secondary cell includes this LiMn compound oxide. The lithium secondary cell is provided with a positive electrode formed by this material for positive electrode and a negative electrode containing lithium metals, metal oxides, metal nitrides, and carbon materials or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel lithium manganese composite oxide, and more particularly, to a lithium manganese composite oxide having a specific crystal structure and useful as a positive electrode active material of a lithium secondary battery. And a lithium secondary battery using the same.

[0002]

2. Description of the Related Art In recent years, there has been a strong demand for the development of an electric vehicle having zero emission in order to cope with environmental problems.
As a secondary battery that is a power source for such an electric vehicle,
Among various secondary batteries, lithium secondary batteries having a high charge / discharge voltage and a large charge / discharge capacity are expected. As a conventional positive electrode active material for a lithium secondary battery, LiCoO
_{Although a two-} system material was used, a spinel-structured lithium-manganese composite oxide (LiMn ₂ ) was used as a positive electrode active material for a secondary battery for automobiles from the viewpoints of stability in use environment, price, and reserve amount. Application of O ₄ ) is currently being studied (JP-A-11-171550 and JP-A-11-73962).

[0003]

However, the above-mentioned spinel-structured lithium manganese composite oxide (Li
Mn ₂ O ₄ ) is LiC having an active material capacity of about 100 mAh / g and an active material capacity of about 140 mAh / g.
Since the capacity is not sufficient for the oO ₂ system, the development of a lithium manganese composite oxide-based cathode active material having a higher capacity than the LiCoO ₂ system is desired in order to improve the cruising distance of the electric vehicle. .

The present invention has been made in view of such problems of the prior art, and has as its object to provide a lithium manganese composite oxide having a high active material capacity, a method for producing the same, and a composite oxide. An object of the present invention is to provide a lithium secondary battery using an object.

[0005]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and as a result, have performed electrochemical treatment such as charging and discharging on a predetermined lithium manganese composite oxide to obtain a crystal structure thereof. It has been found that the above problem can be solved by controlling the above, and the present invention has been completed.

That is, the lithium manganese composite oxide of the present invention has the following formula: Li _1-x MnO _2-δ (where x represents the amount of lithium deficiency, 0 ≦ x ≦ 0.6,
[delta] represents an oxygen deficiency, expressed in satisfying 0 ≦ δ ≦ 0.2), space group of the crystal structure can be viewed as _I4 1 / amd, when employing this _I4 1 / amd, a shaft Is characterized in that the lattice constant a satisfies 5.670Å <a ≦ 5.695Å, and the lattice constant c along the c-axis satisfies 9.060Å ≦ c ≦ 9.170Å.

In the method for producing a lithium manganese composite oxide according to the present invention, a lithium compound and a manganese compound are mixed in producing the lithium manganese composite oxide as described above, and the mixture is mixed in an atmosphere having a low oxygen concentration. Firing, and then subjecting the obtained fired product to an electrochemical treatment.

Further, a positive electrode material for a lithium secondary battery according to the present invention is characterized by containing the above-mentioned lithium manganese composite oxide. Furthermore, the lithium secondary battery of the present invention has a positive electrode formed of the positive electrode material for a lithium secondary battery as described above, and at least one selected from the group consisting of a lithium-based metal, a metal oxide, a metal nitride, and a carbon material. 1
It is characterized by having a negative electrode containing various kinds of materials.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the lithium manganese composite oxide of the present invention will be described in detail. In addition, in this specification, "%" shows a mass percentage unless otherwise specified. As described above, the LiMn composite oxide of the present invention has the following formula: Li _1-x MnO _2-δ (where x represents the amount of lithium deficiency, 0 ≦ x ≦ 0.6,
δ indicates the amount of oxygen deficiency and satisfies 0 ≦ δ ≦ 0.2), and the space group of the crystal structure thereof is I 4 ₁ / amd, and a
The lattice constant a of the axis is 5.670６ <a ≦ 5.695Å, c
The lattice constant c of the axis satisfies 9.060 ° ≦ c ≦ 9.170 °.

When the Li deficiency x exceeds 0.6, the discharge capacity
160 mAh / g was not obtained and the O deficiency δ was 0.2
If it exceeds, I4₁/ Amd structure cannot be maintained. Ma
The effect intended by the present invention, typically, 160 mAh
/ G or more of the active material capacity cannot be obtained.
You. As described above, the crystal structure of this LiMn composite oxide
Space group is typically I4 ₁/ Amd.
The composite oxide crystal belongs to a tetragonal system and has a fourfold symmetry axis.
In this case, when the lattice constant a is 5.670 ° or less, the discharge capacity is
The amount of 160 mAh / g cannot be obtained and exceeds 5.695%.
, Sufficient cycle durability characteristics cannot be obtained. Meanwhile, the lattice
If the constant c is less than 9.060 °, sufficient cycle durability
When the temperature exceeds 9.170 °, discharge capacity 16
0 mAh / g cannot be obtained.

In the LiMn composite oxide of the present invention, the diffraction peak intensity ratio y of the plane index (220) to the surface index (101) during X-ray analysis (= diffraction peak intensity of (220) / (101)) Diffraction intensity of 0.9 ≦ y ≦ 1.
8 is preferably satisfied. This intensity ratio is considered to be related to the amount of Li involved in charge and discharge. If the intensity ratio y is less than 0.9, the discharge capacity is 160 mAh / g.
On the other hand, if it exceeds 1.8, sufficient cycle durability may not be obtained, which is not preferable.

Furthermore, in this LiMn composite oxide, the diffraction peak intensity ratio z (= (004) diffraction peak intensity / (101) diffraction peak intensity) between the plane index (004) and (101)) is: It is preferable to satisfy 0.5 ≦ z ≦ 1.0. It is considered that this intensity ratio is also related to the amount of Li. If the intensity ratio y is less than 0.5, a discharge capacity of 160 mAh / g cannot be obtained, while if it exceeds 1.0, sufficient cycle durability may not be obtained, which is not preferable.

The Li deficiency x, lattice constant, peak intensity ratio, and the like in the LiMn composite oxide of the present invention are determined by a predetermined LiMn method as described in detail in the following production method.
It can be controlled by subjecting the composite oxide to an electrochemical treatment such as charge and discharge.

Hereinafter, the method for producing the LiMn composite oxide of the present invention will be described in detail. As described above, in the production method of the present invention, a predetermined lithium compound and a predetermined manganese compound are mixed, and the mixture is fired in an atmosphere having a low oxygen concentration to obtain a fired lithium manganese product. Then, the lithium manganese fired product is subjected to a predetermined electrochemical treatment to obtain a lithium manganese composite oxide represented by the above formula.

Here, the manganese compound which is the lithium source of the intended lithium-manganese composite oxide includes:
Although not particularly limited, electrolytic manganese dioxide,
Chemically synthesized manganese dioxide, dimanganese trioxide, γ-Mn
OOH, manganese carbonate, manganese nitrate, manganese acetate and the like can be used. At this time, the average particle size of the manganese compound powder is preferably 0.1 to 100 μm, and more preferably 20 μm or less.
If the average particle size of the manganese compound is too large, the reaction between the manganese compound and the lithium compound is significantly delayed, and a non-uniform product is easily generated, and the composition may vary.

On the other hand, as a lithium compound as a lithium supply source, lithium carbonate, lithium hydroxide, lithium nitrate, lithium oxide, lithium acetate and the like can be used. Of these, lithium carbonate and lithium hydroxide can be preferably used, and the average particle size in this case is 3 for the same reason as the manganese compound described above.
It is desirable that the thickness be 0 μm or less.

Examples of the low oxygen concentration atmosphere include a gas atmosphere containing almost no oxygen, such as nitrogen, argon, carbon dioxide, and a mixed gas thereof. The oxygen concentration in such an atmosphere is typically 10
The content is preferably controlled to 100 ppm or less and 100 ppm or less.

Further, the firing temperature is typically 1100 ° C. or less, preferably 950 ° C. or less. 1100 ° C
If the temperature exceeds, the product is easily decomposed. The firing time may be 1 to 48 hours, preferably 5 hours.
~ 24 hours. The firing method is not particularly limited, and single-stage firing or multi-stage firing at different firing temperatures as necessary may be performed.

As described above, in the production method of the present invention, the above-mentioned lithium compound and manganese compound are used as essential raw materials, and the method of mixing these is not particularly limited. Other additives can be added. Such additives include carbon-containing compounds,
Preferably, carbon powders such as carbon black and acetylene black, and organic substances such as citric acid can be mentioned. By adding these, the oxygen concentration in the firing atmosphere can be efficiently reduced. The addition amount is typically 0.05 to 10%, preferably 0.1 to 2%. When the addition amount is small, the effect is low, and when the addition amount is large, a by-product is easily generated.
Due to the residual carbon-containing compound added, the desired LiM
The purity of the n composite oxide may decrease.

In this production method, it is preferable that the lithium manganese fired product contains lithium and manganese in an approximately equimolar ratio. By including these in substantially equimolar ratio, the electrochemical treatment of the post-treatment can be effectively performed, and the LiMn composite oxide represented by the above formula can be efficiently obtained. become.

The electrochemical treatment in the production method of the present invention is carried out in order to appropriately control the Li deficiency x, the lattice constant, the peak intensity ratio, etc. of the target LiMn composite oxide. It can be performed by conducting electricity to the lithium manganese fired product. Typically, charge and discharge performed by adjusting the applied voltage under a constant current can be mentioned. In this case, the constant current of about 30 mA / g, which is affected by the size of the fired product, is also used. 0-4.2V
Is preferably employed. The charge / discharge may be performed on the fired product itself, or may be performed on a plate or a rod obtained by molding the fired product with an appropriate binder and performing a heat treatment. If you use things,
Connection during charge / discharge processing can be easily performed.

The above-described LiMn composite oxide of the present invention comprises:
Although it can be used for various applications such as lithium primary batteries, it is particularly useful as a positive electrode active material for lithium secondary batteries. The positive electrode material for a lithium secondary battery of the present invention comprises
It may contain a Mn composite oxide, and may be composed of the LiMn composite oxide. In addition to the unavoidable impurities, a LiNi composite oxide, a LiCo composite oxide and a Li
An additive such as an Fe composite oxide may be included.

Further, as described above, the lithium secondary battery of the present invention comprises a positive electrode formed of the above-described positive electrode material for a lithium secondary battery, and a lithium-based metal, various metal oxides, various metal nitrides and a carbon material. The anode has a high active material capacity, specifically, an active material capacity of 160 mAh / g or more. Here, as the negative electrode, any of the materials used for ordinary non-aqueous electrolyte secondary batteries can be used,
For example, a lithium-based metal such as lithium metal or a lithium alloy, a metal oxide such as SnSiO ₃ , a metal nitride such as LiCoN ₂ , and a carbon material can be used. In the present invention, carbon materials such as coke, natural graphite, artificial graphite, and non-graphitizable carbon can be suitably used.

As the electrolytic solution, a solution prepared by dissolving various lithium salts as an electrolyte in a non-aqueous solvent such as an organic solvent can be used. In this case, the electrolyte is LiCl
O ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₆ , LiC
Conventionally known materials such as F ₃ SO ₃ and Li (CF ₃ SO ₂ ) ₂ N can be used. In addition, examples of the organic solvent include, but are not particularly limited to, carbonates, lactones, and ethers. For example, ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, 1,2-
Solvents such as dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,3-dioxolan, and γ-butyrolactone can be used alone or in combination of two or more. The concentration of the electrolyte dissolved in the non-aqueous solvent or the organic solvent is preferably 0.5 to 2.0 mol / L.

In the lithium secondary battery of the present invention, it is also possible to use an electrolytic medium other than the above-mentioned electrolytic solution, for example, a solid or viscous material in which the above-mentioned electrolyte is uniformly dispersed in a polymer matrix. Alternatively, those impregnated with a non-aqueous solvent can also be used. in this case,
As the polymer matrix, for example, polyethylene oxide, polypropylene oxide, polyacrylonitrile, polyvinylidene fluoride, and the like can be used.

Further, in the lithium secondary battery of the present invention, a separator for preventing a short circuit between the positive electrode and the negative electrode can be provided. As such a separator, a porous sheet of a polymer material such as polyethylene, polypropylene, and cellulose, a nonwoven fabric, and the like are used.

[0027]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. In these examples and comparative examples,
A closed nonaqueous solvent battery cell was prepared using the positive electrode, the negative electrode, and the nonaqueous electrolyte prepared as described below, and evaluated.

[Preparation of Positive Electrode] A powder of lithium hydroxide monohydrate and a powder of dimanganese trioxide are weighed at a predetermined molar ratio.
After these were mixed in a mortar, each of the mixtures was heat-treated at 900 ° C. for 24 hours in an argon atmosphere, cooled, and then the fired product was pulverized using a mortar, and the moles of lithium and manganese contained therein were reduced. LiMn composite oxides (positive electrode active materials) of each example having a ratio of 1: 1 were obtained.

[Preparation of Battery and Measurement of Discharge Capacity] The obtained positive electrode active material of each example, acetylene black as a conductive material, and PTFE powder as a binder were mixed in a weight ratio of 80:
The mixture was mixed at a ratio of 16: 4. This mixture was added at 2 t / cm ²
The resulting molded product was heated at 150 ° C. for 16 hours to obtain a positive electrode.
On the other hand, a disc-shaped lithium metal having a diameter of 12 mm and a reticulated negative electrode current collector made of stainless steel were pressed to form a negative electrode body. As an electrolytic solution, LiPF ₆ was used in a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 1: 1.
Was used at a concentration of 1 mol / liter. A polypropylene film was used as a separator. A SUS thin plate was used as a current collector of the positive electrode, and the positive electrode body and the negative electrode body thus obtained were connected to a lead, and a separator was interposed therebetween to face each other. While holding it with a spring, it was sandwiched between two PTFE plates. Further, the side surfaces of the element were covered with a PTFE plate and sealed to obtain a sealed nonaqueous solvent battery cell. The cell was prepared under an argon atmosphere.

[Control of Lithium Deficiency, Lattice Constant and Peak Intensity Ratio] Using the sealed non-aqueous solvent battery cell obtained as described above, the voltage was set to 4.2 in an ambient atmosphere at 60 ° C.
By charging and discharging at a constant current of 30 mA / g while controlling in the range of V to 2.0 V, the positive electrode active material Li
_By controlling the lithium deficiency x, the lattice constant and the peak intensity ratio in _1-x MnO _2-δ , the LiMn of each Example was controlled.
The composite oxide was prepared into the composite oxide of the present invention. Similarly, charge / discharge was performed using a sample whose lattice constant was controlled by charge / discharge, and the initial discharge capacity was defined as the capacity of the sealed nonaqueous solvent battery cell of each example.

[Evaluation of lattice constant and peak intensity of X-ray diffraction pattern]
The composite oxide was taken out of the cell and subjected to X-ray diffraction measurement. Cu is used as the target and 2θ is 10 ° to 110 °.
The measurement was performed in the range of °. The X-ray diffraction patterns of Examples 1 to 4 and Comparative Example 1 are shown in FIG. Then, using this data, the space group classified by subject modes of atomic arrangement in the crystal as I4 1 _/ amd, determine the lattice constants by performing Rietveld analysis. FIG. 2 shows the relationship between the cell constants and the lattice constants of the a and c axes in Examples 1 to 4 and Comparative Example 1. I4
_From the X-ray diffraction pattern indexed by ₁ / amd,
By dividing the (220) or (004) plane index peak intensity maximum value by the (101) plane index peak intensity maximum value, the (220) / (101) plane index intensity ratio y and (004) / (101) are obtained. The plane index intensity ratio z was determined. FIG.
The surface index intensity ratio y in Examples 1 to 4 and Comparative Example 1
And the relationship between z and capacity.

Example 1 Li _1-x MnO _2-δ (x
= 0) to perform the above-described charge / discharge treatment, and a-axis: 5.
693 °, c-axis: 9.060 °, (220) / (10
1) The surface index intensity ratio y is 1.44, (004) / (10
1) By controlling the plane index intensity ratio z to 0.75, the LiM
An n composite oxide was obtained. The oxygen deficiency δ was 0.02. This composite oxide was evaluated as described above.

Example 2 Li _1-x MnO _2-δ (x
= 0.3), and the a-axis: 5.
686 °, c-axis: 9.097 °, (220) / (10
1) The plane index intensity ratio y is 1.67, (004) / (10
1) By controlling the plane index intensity ratio z to 0.96, the LiM
An n composite oxide was obtained. The oxygen deficiency δ was 0.02. This composite oxide was evaluated as described above.

Example 3 Li _1-x MnO _2-δ (x
= 0.37) to perform the above-mentioned charge / discharge treatment, a-axis:
5.677 °, c-axis: 9.137 °, (220) / (1
01) The plane index intensity ratio y is 0.99, (004) / (10
1) By controlling the plane index intensity ratio z to 0.53, the LiM
An n composite oxide was obtained. The oxygen deficiency δ was 0.02. This composite oxide was evaluated as described above.

Example 4 Li _1-x MnO _2-δ (x
= 0.40) to perform the above charge / discharge treatment, and the a-axis:
5.671 °, c-axis: 9.170 °, (220) / (1
01) The plane index intensity ratio y is 0.90, (004) / (10
1) By controlling the plane index intensity ratio z to 0.56, the LiM
An n composite oxide was obtained. The oxygen deficiency δ was 0.02. This composite oxide was evaluated as described above.

Comparative Example 1 Li _1-x MnO _2-δ (x
= 0.56) to perform the above charge / discharge treatment, and the a-axis:
5.670 °, c-axis: 9.181 °, (220) / (1
01) The plane index intensity ratio y is 0.36, (004) / (10
1) By controlling the plane index intensity ratio z to 0.22, the LiM
An n composite oxide was obtained. The oxygen deficiency δ was 0.02. This composite oxide was evaluated as described above.

Table 1 shows the lattice constants, plane index intensity ratios y and z of the composite oxides of the respective examples, and the capacities of the cells of the respective examples prepared using the respective composite oxides.

[0038]

[Table 1]

From the results in Table 1, it can be seen that Li _1-x MnO _2-δ
In 0 ≦ x ≦ 0.4, 0 ≦ δ ≦ 0.2 (δ>
In the region of 0.2, the crystal structure of Li _1-x MnO _2-δ cannot be maintained. ), And when the space group is I4 ₁ / amd, the lattice constant a of the a-axis is 5.670Å <a ≦ 5.695
格子, c-axis lattice constant c is 9.060Å ≦ c ≦ 9.170
When the X-ray diffraction pattern is indexed by the space group R3m, the (220) / (101) plane index intensity ratio y is 0.9 ≦ y ≦ 1.8 and the (004) / (101) plane Example 1 provided with a positive electrode using a LiMn composite oxide satisfying a condition that an index intensity ratio z satisfies 0.5 ≦ z ≦ 1.0.
Comparative Examples 1 to 4 each having a positive electrode using a LiMn composite oxide that does not satisfy the above conditions.
It can be seen that the capacity is remarkably improved as compared with the lithium secondary battery of No. 4, and that it has a high active material capacity exceeding 160 mAh / g.

[0040]

As described above, according to the present invention, a predetermined lithium manganese composite oxide is subjected to an electrochemical treatment such as charging and discharging to control the crystal structure thereof, and thus a high active material is obtained. Provided are a lithium manganese composite oxide having a capacity, a method for producing the same, and a lithium secondary battery using the composite oxide. The lithium manganese composite oxide of the present invention is a novel manganese composite oxide having a higher capacity than a spinel structure lithium manganese composite oxide or LiCoO ₂ system.
Non-aqueous secondary batteries that use this new composite oxide as a positive electrode active material and a lithium ion conductive non-aqueous electrolyte solution are compact, exhibit high capacity, high performance, And HEV batteries.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction pattern of various lithium manganese composite oxides.

FIG. 2 is a graph showing a relationship between a lattice constant and a cell capacity.

FIG. 3 is a graph showing a relationship between a surface index intensity ratio and a capacity.

Continued on the front page F term (reference) 4G048 AA04 AB01 AB05 AC06 AD06 AE05 5H029 AJ03 AK02 AL01 AL02 AL03 AL06 AL12 AM03 AM04 AM05 AM07 CJ02 CJ08 CJ16 CJ28 DJ17 HJ02 HJ13 5H050 AA08 BA17 CA09 CB01 GA13 GA13 GA12 GA12 GA13

Claims (9)

[Claims] 1. The following formula: Li _1-x MnO _2-δ (where x represents the amount of lithium deficiency, 0 ≦ x ≦ 0.6,
[delta] represents an oxygen deficiency, expressed in satisfying 0 ≦ δ ≦ 0.2), space group of the crystal structure can be viewed as _I4 1 / amd, when employing this _I4 1 / amd, a shaft A lithium-manganese composite oxide characterized by satisfying a lattice constant a of 5.670 ° <a ≦ 5.695 ° and a c-axis lattice constant c of 9.060 ° ≦ c ≦ 9.170 °. 2. The (220) / (101) plane index intensity ratio y
2. The lithium manganese composite oxide according to claim 1, wherein 0.9 ≦ y ≦ 1.8. 3. The (004) / (101) plane index intensity ratio z
3. The lithium manganese composite oxide according to claim 1, wherein 0.5 ≦ z ≦ 1.0. 4. The lithium-manganese composite oxide according to claim 1, wherein the lithium deficiency x is electrochemically controlled. 5. In producing the lithium manganese composite oxide according to any one of claims 1 to 4, a lithium compound and a manganese compound are mixed, and the mixture is fired in an atmosphere having a low oxygen concentration. Next, a method for producing a lithium manganese composite oxide, comprising subjecting the obtained fired product to an electrochemical treatment. 6. The method for producing a lithium manganese composite oxide according to claim 5, wherein lithium and manganese are contained in the calcined product in an approximately equimolar ratio. 7. The method for producing a lithium manganese composite oxide according to claim 6, wherein the electrochemical treatment is charge and discharge performed by adjusting an applied voltage under a constant current. 8. A positive electrode material for a lithium secondary battery, comprising the lithium manganese composite oxide according to any one of claims 1 to 4. 9. A positive electrode formed of the positive electrode material for a lithium secondary battery according to claim 8, and a lithium metal, a metal oxide,
A lithium secondary battery comprising a negative electrode containing at least one selected from the group consisting of metal nitrides and carbon materials.