JPH11185754A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery using spinnel lithium manganese oxide less in change of capacity caused by charge/discharge cycle as a positive electrode active material by using a specified compound as a lithium contained metal oxide into which lithium can be inserted or from which lithium can be discharged, for a positive electrode. SOLUTION: A spinnel type lithium manganese oxide is used which is represented by a formula, where X and δ are represented by a relation of 0<=X<=0.05 (except a range of 0<=X<=0.02) and a relation of -0.025<=δ<=0.050 (except a range of -0.015<=δ<=0.012), and the average atom value of Mn is in a range of 3.501-3.535 (except a range of 3.505-3.535). It is preferable that the lithium contained metal oxide satisfies a relation of 0<=X<=0.04 or 0.01<=X<=0.055, and a relation of -0.005<=δ<=0.04. Accordingly, a battery having a large charge/discharge capacity and an improved cycle characteristic is obtained. As a result, an inexpensive lithium manganese oxide can be used as the positive electrode material, which leads to provision of a high performance and safe battery.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the improvement of a non-aqueous electrolyte secondary battery, particularly to the improvement of a positive electrode active material, and is intended to improve the charge / discharge capacity and cycle characteristics of the battery.

[0002]

2. Description of the Related Art As a positive electrode active material of a lithium secondary battery,
LiMn ₂ O ₄ which is a composite oxide of manganese and lithium
Has been proposed and research is being actively conducted. Although it has the characteristics of high voltage and high energy density, it has the problem that the charge / discharge cycle life is short, and has not been used as a practical battery. Until now, JP-A-7-
Or the _{Li 1 + X Mn 2-X} O 4 with an excess of lithium as disclosed such as 282,798, JP-A-3-10
8261, LiMn _2-X Co _X O ₄ , LiMn _2-X Cr _X O _{4 by} partially replacing manganese with another metal such as Co or Cr as disclosed in JP-A-3-219571.
To improve the lithium manganese oxide,
Although it has been proposed to improve the cycle characteristics, these reforming methods cause a decrease in the charge / discharge capacity, and thus a lithium manganese oxide having improved cycle characteristics without lowering the charge / discharge capacity has been desired. .

[0003] Spinel lithium manganese oxide (Li
In a battery using Mn ₂ O ₄ ) as a positive electrode active material, the charge / discharge reaction of the positive electrode is represented by the following equation.

[0004]

(Equation 1)

[0005] The spinel lithium manganese oxide has a property that the charge / discharge function is easily lost when the charge / discharge reaction is repeatedly performed. Part of the Mn site is Li
It is possible to improve the deterioration of the charge / discharge function by replacing with metals such as Co and Cr, but there is a drawback that the charge / discharge capacity is reduced. It is hard to say that it is a fundamental improvement method. In view of these circumstances, Japanese Patent Application Laid-Open No. 9-82362 describes M
replacing part of n with a cation having an oxidation number lower than Mn;
By limiting the substitution amount, the number of oxidations of the transition metal in the initial state is limited, and an attempt is being made to simultaneously achieve high charge / discharge capacity and good cycle characteristics. However, according to the results of the examples of the patent, the cycle capacity retention rate decreased to about 90% in 25 cycles, and it is hard to say that the cycle capacity retention rate was improved at a practical level. In addition, the values of the oxidation numbers of specific transition metals in Examples are not described. That is, if only a limited amount of Mn is replaced with a cation having an oxidation number lower than Mn, the actual oxidation number of the transition metal reaches the specified oxidation number (3.50 <a <3.54). It is considered that this did not lead to any fundamental improvement. Therefore, the present inventors diligently studied focusing on the amount of oxygen in the spinel-based lithium manganese oxide, and found that an oxide having oxygen deficiency was generated by the conventional synthesis method. In addition, oxygen deficiency causes a slight increase in initial discharge capacity due to an increase in Mn ³⁺ ions, but causes a decrease in charge / discharge cycle characteristics, and the discharge amount decreases quantitatively with an increase in oxygen deficiency amount. I found that. Based on such knowledge, the present inventors previously filed a patent application for a battery using a spinel-based lithium manganese oxide having oxygen deficiency as a positive electrode material (Japanese Patent Application No. 8-17 / 1990).
No. 6516).

[0006]

SUMMARY OF THE INVENTION The present invention relates to a lithium ion using a spinel-based lithium manganese oxide as a positive electrode active material, while maintaining a high charge / discharge capacity and with little capacity deterioration due to charge / discharge cycles. It is intended to provide a secondary battery.

[0007]

Means for Solving the Problems The present inventors have studied the spinel lithium manganese oxide having oxygen deficiency, and found a substance suitable as a battery cathode material as in the previous application, and achieved the present invention. did. That is, the gist of the present invention is to provide a non-aqueous electrolyte secondary battery using a lithium-containing metal oxide capable of inserting and releasing lithium into a positive electrode, and using a non-aqueous electrolyte containing a lithium solution as an electrolyte. As the lithium-containing metal oxide, general formula (A)

[0008]

Embedded image

Wherein 0 ≦ X ≦ 0.05, −0.025
≤δ≤0.05. ) And the average valence of Mn in the general formula is in the range of 3.501 to 3.535.
0 ≦ X ≦ 0.02, −0.015 ≦ δ ≦ 0.012, and the average valence of Mn is in the range of 3.505 to 3.535). .

The change of oxygen deficiency δ of spinel lithium manganese oxide having oxygen deficiency (LiMn ₂ O ₄ ± δ) by heat treatment conditions and the electrochemical characterization of oxygen deficient lithium manganate are described in J. Am. Elect
rochem. Soc. , Vol. 142, no. 7,
July, 1995. However, there is no clear description about the decrease in cycle characteristics due to oxygen deficiency, and lithium manganate whose electrochemical measurement has been made is not within the scope of the present invention. From the above, it is desirable that the spinel-based lithium manganese oxide having a high initial discharge capacity and excellent cycle characteristics has the X value in the above general formula as small as possible and has no oxygen deficiency δ. That is, an optimized balance between X and δ corresponds to this, so that the values of X and δ need to be bound to each other in order to maintain the balance. Therefore, the present inventors have focused on the fact that the result reflecting both X and δ is the average valence of Mn, and completed the present invention by limiting the range of the average valence of X, δ, and Mn. Reached.

On the other hand, in Japanese Patent Application Laid-Open No. 9-274918, Li
Although the amount of oxygen vacancies present in Mn ₂ O ₄ is specified,
No Li substitution was made on the Mn (16d) site during the synthesis, and the specified Li composition range is a variation range relating to insertion / release of the 8a and 16c sites in the charge / discharge reaction when used as a battery. . Therefore, the average valence of Mn in the initial state before the charge / discharge reaction is less than 3.5, which is outside the scope of the present invention.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The spinel lithium manganese oxide represented by the general formula (A) is produced by firing a mixture of a lithium compound and a manganese compound as a starting material, and has a large initial discharge capacity (initial discharge capacity). Capacity> 12
0 mAh / g) and excellent cycle characteristics (100 mAh / g).
Capacity retention after cycle> 90%, preferably> 93
%) Is obtained. In the present invention, the X, δ values and the average valence of Mn of the general formula (A) to be the positive electrode active material are respectively 0 ≦ X ≦ 0.05 and −0.025 ≦ δ ≦ 0.0.
Although it is defined as 50, 3.501 to 3.535, this range indicates the range of the initial state before lithium is dedoped from the positive electrode active material in the battery system. Outside of this range, it becomes difficult to obtain desired battery characteristics.

Here, when importance is placed on the initial discharge capacity, the lower limit of X is preferably 0.005, and the upper limit of X is preferably 0.04, more preferably 0.02.
Most preferably, it is 0.015. The lower limit of δ is preferably -0.015, more preferably -0.005, and the upper limit of δ is preferably 0.04, more preferably 0.03, and most preferably 0.005. The upper limit of the average valence of Mn is preferably 3.530, and more preferably 3.515. On the other hand, when the capacity retention rate after 100 cycles is emphasized, the lower limit of X is preferably set to 0.1.
01, more preferably 0.02, and the upper limit of X is preferably 0.045, more preferably 0.040. The lower limit of δ is preferably -0.015, more preferably -0.005, most preferably 0.005,
The upper limit of δ is preferably 0.04, more preferably 0.5.
03. The lower limit of the average valence of Mn is preferably 3.503, more preferably 3.505, and most preferably 3.506.

Lithium compound used for this starting material
As Li_TwoCO_Three, LiNO _Three, LiOH, Li
OH ・ H_TwoO, LiCl, CH_ThreeCOOLi, Li_TwoO
Etc., among which LiOH / H_TwoO or LiOH
It is preferable to use Also, as a manganese compound
Is Mn_TwoO_Three, MnO_TwoSuch as manganese oxide, MnC
O_Three, Mn (NO_Three)_TwoSuch as manganese salts
But, among others, γ-MnO_TwoOr Mn_TwoO_ThreeUsing
Is preferable, and Mn in this case is preferable._TwoO_ThreeAs MnCO_Three
Or γ-MnO_TwoPyrolysis
It is preferable to use one prepared by the above method.

Next, in the present invention, the above-mentioned Mn compound and L
Mix i-compound. The mixing may be carried out by a usual method, for example, any method such as dry mixing, wet mixing of both raw materials, suspension of a Mn compound in an aqueous solution of Li salt, or pulverized mixing by a ball mill may be used. The lithium manganese oxide of the present invention can be obtained by performing a special combination of a specific starting material and a specific production method. For example, the following production methods may be mentioned, but are not limited to those obtained by these production methods.

A) Electrolytic manganese dioxide (γ-MnO ₂ )
And lithium hydroxide (LiOH · H ₂ O or LiOH)
Is used as a starting material, and a mixture obtained by mixing Li and Mn at an atomic ratio of preferably 0.500 ≦ Li / Mn ≦ 0.515 is used to obtain an oxygen concentration of 10% or more, preferably 40% or more (normally Pressure or oxygen pressure range 0.4kgf /
in an atmosphere of cm ² or more 10 kgf / cm ² or less), the heating temperature 600 ° C. or higher, preferably at a temperature of 600 ° C. to 850 ° C., preferably heated over 2 hours, 20 ° C. / min or less up to then 500 ° C. or less, preferably Is 10 ° C / min
Hereinafter, more preferably, 0.2 ° C / min to 5 ° C / min.
Method of slow cooling at a low temperature.

B) Dimanganese trioxide (Mn ₂ O ₃ ) obtained by thermally decomposing manganese carbonate and lithium hydroxide (Li)
OH.H ₂ O or LiOH) is mixed at an atomic ratio of Li and Mn of preferably 0.500 ≦ Li / Mn ≦ 0.515.
After calcination at 600C, the temperature is 600C or more, preferably 600C to 8C.
At a heating temperature of 50 ° C., in an atmosphere containing oxygen, preferably, the oxygen concentration is 10% or more, more preferably, the oxygen concentration is 40%.
Above atmosphere (normal pressure or oxygen pressure range 10kgf / cm
² ) or less, and then to 500 ° C or less at 20 ° C /
a method of gradually cooling at a temperature lowering rate of not more than 10 min / min, preferably not more than 10 ° C./min, more preferably 0.2 to 5 ° C./min.

C) After calcining a mixture of Mn ₂ O ₃ and LiOH.H ₂ O or LiOH at a temperature of 400 ° C. to 600 ° C., an atmosphere containing oxygen at a temperature of 600 ° C. or more, preferably 600 ° C. to 850 ° C. Medium, preferably 10% oxygen concentration
After firing in an atmosphere having an oxygen concentration of 40% or more (normal pressure or an oxygen pressure range of 10 kgf / cm ² or less), the temperature is preferably 20 ° C./min or less, preferably 500 ° C. or less.
It is preferably 10 ° C./min or less, more preferably 0.2 ° C./min.
After slowly cooling at a temperature lowering rate of 5 ° C./min to 5 ° C./min,
A method in which the temperature is kept at a constant temperature of 00 ° C. to 500 ° C. in the oxygen atmosphere for one hour or more.

D) Dimanganese trioxide and lithium carbonate, or manganese carbonate and lithium hydroxide, or manganese carbonate and lithium carbonate, preferably in an atomic ratio of Li to Mn of 0.1 to 0.1;
The final heating temperature of the mixture mixed so that 500 ≦ Li / Mn ≦ 0.515 in an atmosphere having an oxygen concentration of 10% or more, preferably 20% or more (normal pressure or an oxygen pressure range of 10 kg / cm ² or less). Is at least 600 ° C., preferably 60
Heating at a temperature of 0 ° C. to 850 ° C., preferably for 2 hours or more,
At that time, the heating rate between the heating temperature of 400 ° C. and the final heating temperature is 40 ° C./hr or less, preferably 20 ° C./hr or less,
More preferably, the temperature is set to 10 ° C / hr or less, 2 ° C / hr or more (including a method in which the entire temperature rising rate falls within this range by a stepwise temperature increasing method), and preferably 20 ° C to 500 ° C or less thereafter. / Min or less, preferably 10 ° C./min
Hereinafter, more preferably, 0.2 ° C / min to 5 ° C / min.
Method of slow cooling at a low temperature. As a cooling method of the sample at this time, rapid cooling is not preferable because oxygen deficiency tends to occur.

E) A non-aqueous solution of a lithium salt and a manganese salt is mixed and co-precipitated by adding a non-aqueous solution of dicarboxylic acid to the mixed solution, and the pH of the co-precipitated solution is adjusted with a non-aqueous basic solvent. A method of obtaining a coprecipitated powder composed of lithium dicarboxylate and manganese dicarboxylate having a controlled precipitation ratio, and calcining the coprecipitated powder. The advantage of the method using this coprecipitation method is twofold. The coprecipitation makes the mixing of the lithium raw material and the manganese raw material uniform, and although the reason is not clear, particularly when coprecipitated with a dicarboxylic acid, A lithium metal-containing oxide in the composition range of the present invention is easily obtained, and as a result, a secondary battery exhibiting both excellent characteristics in both capacity and cycle characteristics is obtained.

The lithium salt used at this time includes:
Examples thereof include lithium nitrate, lithium sulfate, lithium chloride, and lithium acetate. Examples of the manganese salt include manganese nitrate, manganese sulfate, manganese chloride, and manganese acetate. The reason for using a non-aqueous solvent as the precipitation solvent is that, for example, when oxalic acid is used, the produced lithium oxalate is easily soluble in water (solubility: water 19.5 ° C., 8 g / 10
0g). Therefore, any solvent may be used as long as the dicarboxylic acid as a precipitant is easily dissolved and the generated dicarboxylic acid salt is hardly soluble. Preferably, an alcohol such as ethanol is used. The reason is that it is easy to handle,
This is because salts of various metals and oxalic acid as a precipitant are easily dissolved.

The dicarboxylate solution preferably contains as little water as possible to suppress the dissolution of lithium dicarboxylate, but it need not be completely non-aqueous. In this method, the reason for using a dicarboxylic acid (preferably anhydrous) as a precipitant is that most of the metals form fine and hardly soluble salts, and the precipitation operation is controlled (solution temperature, p.
H) is easy. In addition, since all are released as carbon dioxide gas by firing, the operation of removing residual ions can be omitted. Examples of the dicarboxylic acid include oxalic acid, malonic acid, succinic acid, glutaric acid, saturated dicarboxylic acids such as adipic acid, maleic acid, unsaturated dicarboxylic acids such as fumaric acid, and aromatic dicarboxylic acids such as phthalic acid. Particularly preferred is oxalic acid.

In this method, the reason why the non-aqueous basic solvent is used as the pH adjusting solution is that the dissolution of lithium oxalate due to mixing of water does not occur. The precipitation ratio is controlled by adjusting the pH, and the ratio may be appropriately determined depending on the dicarboxylic acid used and the type of the metal to be precipitated. For example, when Li and Mn are charged and coprecipitated using oxalic acid, the pH is preferably in the range of 3 to 9. As the non-aqueous basic solvent, an amine is preferable.
Examples of the amine include ammonia, methylamine, ethylamine, diethylamine, diisopropylamine,
Pyrrolidine, triethylamine, butylamine, dibutylamine, tributylamine, N-methylpyrrolidine,
Cyclohexylamine, 1,4-butanediamine, tetramethylguanidine, arylamine, pyridine and the like are used.

The thus obtained lithium dicarboxylate and manganese dicarboxylate have an atomic ratio of almost Li / M
In the calcination of the coprecipitated powder with n = 1/2, thermal decomposition is performed for several hours to several tens of hours in a temperature range of 100 ° C. to 600 ° C., preferably 350 ° C. to 450 ° C. Next, in an oxidizing atmosphere, at least 600 ° C. and no more than 900 ° C., preferably 700 ° C.
The baking is performed for several hours to several tens of hours in a temperature range of at least 800 ° C. Also in this case, it is preferable to perform slow cooling as a cooling method.

As the negative electrode active material used in combination with the positive electrode composed of the specific spinel-based lithium manganese oxide represented by the general formula (A), usually, the material used for this type of nonaqueous electrolyte secondary battery is used. Both can be used. For example, lithium or a lithium alloy may be used, but a compound that can insert and release lithium with higher safety, for example, a carbon material is preferable. This carbon material is not particularly limited, graphite and, coal-based coke, petroleum-based coke, coal-based pitch carbide, petroleum-based pitch carbide,
Needle coke, pitch coke, phenolic resin,
Carbon materials such as crystalline cellulose and carbon materials partially graphitized thereof, furnace black, acetylene black,
And pitch-based carbon fibers.

As the negative electrode, a negative electrode active material and a binder (binder) formed into a slurry by using a solvent may be applied and dried. As the positive electrode, a slurry obtained by applying a slurry of a positive electrode active material, a binder (binder), and a conductive agent with a solvent, applying the slurry, and then drying can be used. As the binder (binder) for the negative electrode and the positive electrode active material, for example, polyvinylidene fluoride, polytetrafluoroethylene, EP
DM (ethylene-propylene-diene terpolymer),
Examples include, but are not limited to, SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), and fluororubber.

As the conductive agent for the positive electrode, graphite fine particles, carbon black such as acetylene black, and amorphous carbon fine particles such as needle coke are used, but are not limited thereto. As the separator, a microporous polymer film is used, and a separator made of a polyolefin polymer such as nylon, cellulose acetate, nitrocellulose, polysulfone, polyacrylonitrile, polyvinylidene fluoride, polypropylene, polyethylene, and polybutene is used. The chemical and electrochemical stability of the separator is an important factor. In this respect, a polyolefin polymer is desirable, and it is desirable that the battery separator be made of polyethylene from the viewpoint of the self-closing temperature, which is one of the purposes of the battery separator.

In the case of a polyethylene separator, ultrahigh molecular weight polyethylene is preferable from the viewpoint of high-temperature shape retention, and the lower limit of the molecular weight is preferably 500,000, more preferably 1,000,000, and most preferably 1.5 million. On the other hand, the upper limit of the molecular weight is preferably 5,000,000, more preferably 4,000,000, and most preferably 3,000,000. If the molecular weight is too large, the fluidity is too low and the pores of the separator may not be closed when heated. Further, as the electrolyte, for example, a lithium salt as an electrolyte,
An electrolytic solution obtained by dissolving this in an organic solvent is used.

The organic solvent is not particularly restricted but includes, for example, carbonates, ethers, ketones, sulfolane compounds, lactones, nitriles, chlorinated hydrocarbons, ethers, amines and esters. ,
Amides, phosphate compounds and the like can be used. When these representatives are listed, propylene carbonate, ethylene carbonate, vinylene carbonate, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 4-methyl-2-pentanone, 1,2-dimethoxyethane, 1,2 -Diethoxyethane, 1,2-dimethoxyethane, γ-butyrolactone, 1,3-dioxolan, 4-methyl-1,3-dioxolan, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile, benzonitrile, butyronitrile , Valeronitrile, 1,2-dichloroethane, dimethylformamide, dimethylsulfoxide, trimethyl phosphate, triethyl phosphate and the like, alone or in combination of two or more.

As the electrolyte, any of conventionally known electrolytes can be used.
LiClO_Four, LiAsF₆, LiPF₆, LiB
F_Four, LiB (C₆H_Five)_Four, LiCl, LiBr, C
H_ThreeSO _ThreeLi, CF_ThreeSO_ThreeLi or the like is used. Ma
In addition, using not only such a non-aqueous electrolyte but also a solid electrolyte
You may make it.

[0031]

The method of the present invention will be described in more detail with reference to the following examples, which should not be construed as limiting the scope of the invention. Table 1 shows the compositions, discharge capacities, and the like of the lithium manganese oxides obtained in Examples and Comparative Examples of the present invention. EXAMPLE 1 gamma-MnO 24 hours ₂ at 750 ° C., and Mn ₂ O ₃ and LiOH · H ₂ O was obtained by heating in air was used as a starting material, the atomic ratio of lithium and manganese (Li / M
n) was reduced to 1/2. Ethanol was added to this formulation and ground well in a mortar to form a uniform mixture. After heating the obtained mixture at 750 ° C. for 24 hours in the atmosphere, the heating furnace was turned off and the furnace was cooled. At that time, the cooling rate to 450 ° C. was 10 ° C./min.

Example 2 γ-MnO ₂ was added at 750 ° C.
Mn ₂ O ₃ and LiOH.
H ₂ O was used as a starting material and blended such that Li / Mn became 1/2. Ethanol was added to this formulation and ground well in a mortar to form a uniform mixture. The obtained mixture was calcined in air at 500 ° C. for 24 hours. Next, after baking in air at 800 ° C. for 24 hours, the temperature is reduced to 450 ° C. by 0.2 hours.
It was gradually cooled at a rate of ° C / min.

[Embodiment 3] 1 mo determined by a factor
1 / l LiNO_ThreeAnd 1 mol / l Mn (NO _Three)_Two
・ 6H_TwoO / ethanol solution was reduced to 1/2 Li / Mn.
Stir the mixed solution so that 1.5 times
The volume of the oxalic acid ethanol solution was gradually added. This joint
The precipitated solution is stirred for 2 hours and then pH adjusted with triethylamine.
Adjusted to 6.87, stirred for another 3 hours, and allowed to stand
Sinked. After that, the coprecipitated powder is filtered and dried.
(Li_Two(C_TwoO_Four) And Mn (C_TwoO_Four) Of mixed powder)
Prepared. By firing the obtained coprecipitated powder, Li
Mn_TwoO_FourWas synthesized. In addition, the firing conditions are as follows.
Degree: 400 ° C., time: 6 hr, temperature rise / fall rate: 5 ° C./mi
n, pyrolyzed in air, then temperature; 750 ° C, hour
Interval: 24 hr, elevating speed: 5 ° C./min, in air
Perform firing and then cool to 450 ° C at 0.2 ° C / min
After that, hold for 6 hours, and then cool to room temperature at 5 ° C./min.
Was.

Example 4 LiOH.H ₂ O and MnCO
₃ was wet-mixed using a mortar at a ratio of Li / Mn = 1/2, and then the mixture was 450, 500, 550, 6
The temperature was raised stepwise while being kept at 00 ° C. and 12 hours each,
Next, after baking in air at 750 ° C. for 48 hours,
The temperature was gradually cooled to 0.2 ° C. at a rate of 0.2 ° C./min.

Example 5 LiOH.H ₂ O and chemically synthesized manganese dioxide were wet-mixed at a ratio of Li / Mn = 1/2 using a mortar, and the mixture was heated at 500 ° C. and 24 ° C.
It was calcined for hours. Next, after baking in air at 800 ° C. for 24 hours, it was gradually cooled to 450 ° C. at a rate of 0.2 ° C./min.

Example 6 Li ₂ CO ₃ and MnCO ₃ were wet-mixed at a ratio of Li / Mn = 1/2 using a mortar, and the mixture was air-mixed at 450, 500, 550 and 600 in the air.
The temperature was raised stepwise while maintaining the temperature at 12 ° C. for 12 hours, and then calcined at 750 ° C. for 48 hours in the air, and then gradually cooled to 450 ° C. at a rate of 0.2 ° C./min.

[Comparative Example 1] Li ₂ CO ₃ and Mn ₂ O ₃ were wet-mixed using a mortar at a ratio of Li / Mn = 1/2, and the mixture was calcined in the air at 650 ° C. for 24 hours. . Next, after baking in air at 750 ° C. for 24 hours, the heating furnace was turned off and the furnace was cooled. At that time, the cooling rate to 450 ° C. was 10 ° C./min.

Comparative Example 2 LiOH.H ₂ O and γ-Mn
After O ₂ was wet-mixed using a mortar at a ratio of Li / Mn = １ ／, the mixture was calcined at 500 ° C. for 24 hours in the atmosphere. Next, after calcination at 750 ° C. for 24 hours in oxygen, it was quenched (cooling rate: about 50 ° C./min). This was heated again in nitrogen at 575 ° C. for 24 hours, and then rapidly cooled (with a cooling rate of about 50 ° C./min) by extracting a sample from the furnace.

Comparative Example 3 Li ₂ CO ₃ and γ-MnO ₂
Was wet-mixed at a ratio of Li / Mn = 1/2 using a mortar, and the mixture was calcined in the air at 650 ° C. for 24 hours.
Next, after baking in air at 750 ° C. for 24 hours, the heating furnace was turned off and the furnace was cooled. At that time, the cooling rate to 450 ° C. was 10 ° C./min.

Comparative Example 4 LiOH.H ₂ O and γ-Mn
After O ₂ was wet-mixed using a mortar at a ratio of Li / Mn = １ ／, the mixture was calcined at 500 ° C. for 24 hours in the atmosphere. Next, after calcination at 750 ° C. for 24 hours in oxygen, it was quenched (cooling rate: about 50 ° C./min). This was heated again at 550 ° C. for 24 hours in nitrogen, and then rapidly cooled by cooling the sample (with a cooling rate of about 50 ° C./minute) from the furnace.

Comparative Example 5 Li ₂ CO ₃ and MnCO ₃ were wet-mixed at a ratio of Li / Mn = 1/2 using a mortar, and the mixture was calcined at 650 ° C. for 24 hours in the air. Next, after baking in air at 750 ° C. for 24 hours, the heating furnace was turned off and the furnace was cooled. At that time, the cooling rate to 450 ° C. was 10 ° C./min.

Comparative Example 6 γ-MnO ₂ was added at 750 ° C.
Mn ₂ O ₃ and LiOH.
H ₂ O was used as a starting material, and was blended so that the atomic ratio of lithium to manganese was 1: 2. Ethanol was added to this formulation and ground well in a mortar to form a uniform mixture. The resulting mixture was heated at 750 ° C. for 24 hours in an oxygen stream, and then gradually cooled to 450 ° C. at a rate of 0.5 ° C./min.

Comparative Example 7 LiOH.H ₂ O and MnCO
₃ was wet-mixed at a ratio of Li / Mn = 1/2 using a mortar, and the mixture was calcined at 500 ° C. for 24 hours in the atmosphere. Next, after baking in air at 750 ° C. for 24 hours, the heating furnace was turned off and the furnace was cooled. At that time, the cooling rate to 450 ° C. was 10 ° C./min.

Comparative Example 8 LiOH.H ₂ O and γ-Mn
After wet mixing O ₂ at a ratio of Li / Mn = 1/2 using a mortar, the mixture was calcined in the air at 400 ° C. for 6 hours. Next, after baking in air at 750 ° C. for 24 hours,
It was gradually cooled to 0 ° C at a rate of 0.2 ° C / min.

Comparative Example 9 Lithium manganate manufactured by Mitsui Kinzoku Mining Co., Ltd. was used. Comparative Example 10 Lithium manganate manufactured by Nippon Heavy Chemical Industry Co., Ltd. was used.

Comparative Example 11 Li ₂ CO ₃ and Mn ₂ O ₃
Was wet-mixed using a ball mill at a ratio of Li / Mn = 1/2, and the mixture was calcined in the air at 750 ° C. for 24 hours. Next, after baking at 870 ° C. for 24 hours in an oxygen stream, it was gradually cooled to room temperature at a rate of 3 ° C./min.

[Comparative Example 12] CYPRESS FOOT
Lithium manganate manufactured by E Company was used.

Comparative Example 13 Li ₂ CO ₃ and γ-MnO
₂ were wet-mixed using a mortar at a ratio of Li / Mn = 1/2, and the mixture was 450, 500, 550, 6 in air.
The temperature was raised stepwise while being kept at 00 ° C. and 12 hours each,
Next, after baking in air at 750 ° C. for 48 hours,
The temperature was gradually cooled to 0.2 ° C. at a rate of 0.2 ° C./min.

Table 1 shows the compositions of the spinel-based lithium manganese oxides obtained in the above Examples and Comparative Examples, and the initial discharge capacity and capacity retention of batteries using the same as the positive electrode active material. FIG. 2 shows the correlation among the lithium molar ratio (1 + X), δ, the average valence of manganese, the initial discharge capacity, and the cycle characteristics of the lithium manganese oxides obtained in the examples and comparative examples. In FIG. 2, a range surrounded by a thick line and excluding a hatched portion is the scope of the present invention. Also, ● is an example,
X represents a comparative example. The composition analysis values in Examples and Comparative Examples in Table 1 were determined by the following methods.

(Total Li analysis) After vacuum drying at 50 ° C. for 1 hour, a precisely weighed spinel-based lithium manganese oxide was heated and dissolved in a hydrochloric acid solution to prepare a measurement solution. Using an atomic absorption spectrometer, the Li concentration was determined by the calibration curve method, and the Li content per constant weight was calculated.

(Total analysis of Mn: titration by EDTA chelate) After vacuum drying at 50 ° C. for 1 hour, a precisely weighed spinel lithium manganese oxide was heated and dissolved in a hydrochloric acid solution to prepare a measurement solution. The solution was dispensed into a conical beaker with a whole pipette, and a small excess of 0.01 M-E
The DTA solution was added. Then add pure water to make a total volume of 75ml
The pH was adjusted to 10 by adding an appropriate amount of an 8N-NaOH aqueous solution and an ammonia buffer. 100ml pure and total
, And then a BT indicator was dropped. Using a 0.01 M-Mg ion standard solution as a titration solution, titration was performed with a microburette. The point at which the color of the BT indicator changed from blue to red was defined as the end point. From the titration results at this time, the Mn content per constant weight was calculated.

(Iodometry) After vacuum drying at 50 ° C. for 1 hour, a precisely weighed spinel-based lithium manganese oxide was placed in a conical beaker. Next, a small excess of a KI saturated solution and concentrated hydrochloric acid were added in this order to completely dissolve the solution, and then pure water was added to adjust the total volume to 100 ml. Using a 0.1 N sodium thiosulfate solution as a titration solution,
Titration was performed with a microburette. Immediately before the end point, a certain amount of starch solution was added, and the point at which the color of the solution changed from light purple to colorless was regarded as the end point. From the titration result at this time,
The equivalents of Mn ³⁺ and Mn ⁴⁺ per fixed weight were determined.

(Calculation of Mn valence) The Mn of the spinel-based lithium manganese oxide was calculated from the results of the total analysis of Mn by the EDTA chelate titration method and the results of the equivalent analysis of Mn ³⁺ and Mn ⁴⁺ by the iodometry method. The valence was determined. Mn ⁴⁺ , Mn ³⁺ , and Mn ²⁺ were each sample 0.1
It is assumed that k, m, n, and mol exist per g. Then, in the iodometry method,

[0054]

[Number 2] (reaction with ^{Mn 4+) kMn 4+ + 4kI -} → kMnI 2 + kI 2 (2) kI 2 + 2kS 2 O 3 2- → kS 4 O 6 2- + 2kI - (3) by (Mn ^{3+ reaction) mMn 3+ + 3mI - → mMnI} 2 + (1/2) mI 2 (4) (1/2) mI 2 + mS 2 O 3 2- → (1/2) mS 4 O 6 2- + mI - (5 ) (Reaction by Mn ²⁺ ) nMn ⁴⁺ + 2nI ⁻ → nMnI ₂ (6)

Since Mn ²⁺ does not release I ₂ , it does not react with sodium thiosulfate. From the above, a titration value corresponding to (2 k + m) mol is obtained by iodometry. on the other hand,
In the EDTA chelate titration, a titration value corresponding to (k + m + n) mol is obtained. Therefore,

[0056]

Mn valence = 4 × k / (k + m + n) + 3 × m / (k + m + n) + 2 × n / (k + m + n) = (4k + 3m + 2n) / (k + m + n) = 2 + (2k + m) / (k + m + n) = 2 + (result of iodometry) / (result of EDTA chelation) (7)

As can be seen from equation (7), the valence of Mn can be calculated from the results of EDTA chelation and iodometry. (Determination of Oxygen Content) The composition ratio of Li and Mn was calculated from the quantification results of Li and Mn obtained above. In addition, Li
When / Mn is 1/2 or more, the composition of the product is crystallographically

[0058]

Embedded image

Thus, the composition ratio was determined so that the total sum would be 3. When Li / Mn is smaller than 1/2, the composition of the product is crystallographically

[0060]

Embedded image

Thus, the composition ratio is such that the molar amount of Mn is 2
And the atomic weight of Li when X was fixed. The oxygen amount was calculated from the Mn valence obtained from the atomic ratio of Li and Mn using the rule of electrical neutrality. It was confirmed by powder X-ray diffraction that all the samples synthesized in Examples and Comparative Examples were cubic single phases.

The method for producing the battery and the charge / discharge conditions will be described below. The positive electrode active material shown in Table 1, acetylene black as a conductive agent, and polytetrafluoroethylene resin as a binder were mixed at a weight ratio of 75: 20: 5 to prepare a positive electrode mixture. Also, 0.1 g of the positive electrode mixture was
Press molding at 1 ton / cm ^{2 to} 6 mm to form a positive electrode,
A coin-type battery shown in FIG. 1 was produced. In FIG. 1, a porous polypropylene film was placed as a separator 3 on an electrode 1. A lithium plate having a diameter of 16 mm and a thickness of 0.4 mm as the negative electrode 4 was pressure-bonded to a sealing tube 6 provided with a polypropylene gasket 5. 1 as non-aqueous electrolyte
Mol / L lithium perchlorate dissolved in ethylene carbonate and 1,2-dimethoxyethane (50 vol%: 5
(0 vol%) A mixed solution was used and added on the separator 3 and the negative electrode 4. Thereafter, the battery was sealed. The charge / discharge cycle characteristics of these batteries were compared. In addition,
The charge / discharge cycle test in the present example was performed with the charge / discharge current 2
The charging and discharging were performed at a constant current of mA and in a voltage range of 4.35 V to 3.2 V.

[0063]

[Table 1]

In the embodiment of the present invention, the initial discharge capacity is large (initial discharge capacity> 120 mAh / g) and the cycle characteristics are excellent (the capacity retention after 100 cycles is> 90%, preferably> 93%). You can see that. In this embodiment, lithium metal is used as the negative electrode material of the battery. However, similar results are obtained when a lithium alloy or a compound capable of inserting and releasing lithium is used.

[0065]

As described above, when the specific spinel-based lithium manganese oxide according to the present invention is used as the active material of the positive electrode, a battery having a large charge / discharge capacity and improved cycle characteristics can be obtained. As a result, inexpensive lithium manganese oxide can be used as a cathode material, and a high-performance, safe and inexpensive lithium-ion secondary battery can be supplied to a wide range of uses, and its industrial value is great.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a coin-type battery used in an embodiment of the present invention.

FIG. 2 is a correlation diagram of lithium molar ratio (1 + X), δ, average valence of manganese, initial discharge capacity, and cycle characteristics of lithium manganese oxide obtained in Examples and Comparative Examples.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Case 3 Separator 4 Negative electrode 5 Gasket 6 Sealing can ● Example × Comparative example

Claims (5)

[Claims] 1. A non-aqueous electrolyte secondary battery using a lithium-containing metal oxide capable of inserting and releasing lithium into a positive electrode and a non-aqueous electrolyte containing a lithium salt as an electrolyte, wherein the lithium-containing metal oxide is a lithium-containing metal oxide. As a metal oxide, a compound represented by the general formula (A): (Where 0 ≦ X ≦ 0.05, −0.025 ≦ δ ≦ 0.0
Represents 50. ) And a spinel-based lithium manganese oxide having an average valence of Mn in the range of 3.501 to 3.535 (where 0 ≦ X ≦ 0.02, −
0.015 ≦ δ ≦ 0.012 and an average valence of Mn of 3.505 to 3.535) (excluding the range of 3.505 to 3.535). 2. The method according to claim 1, wherein the lithium-containing metal oxide is 0 ≦ X ≦
2. The non-aqueous electrolyte secondary battery according to claim 1, which satisfies 0.04. 3. The method according to claim 1, wherein the lithium-containing metal oxide is 0.01
The non-aqueous electrolyte secondary battery according to claim 1, wherein satisfies ≤ X ≤ 0.05. 4. The method according to claim 1, wherein the lithium-containing metal oxide is -0.0
The non-aqueous electrolyte secondary battery according to claim 1, wherein the following condition is satisfied: 05 ≦ δ ≦ 0.04. 5. The non-aqueous electrolyte secondary battery according to claim 1, wherein the lithium-containing metal oxide has an average valence of Mn of 3.505 to 3.535.