JPH0773884A - Secondary battery - Google Patents

Abstract

PURPOSE:To synthesize lithium-containing manganese composite oxide for a positive electrode material, excellent in a cycle characteristics by mixing manganese dioxide including each specific quantity of Mn and MnO2 with a lithium compound, followed by a heat treatment at a specific temperature. CONSTITUTION:Manganese dioxide having a ratio b/a of 1.53 or more, where (a) represents the Mn content and (b) represents the MnO2 content, is prepared. The resultant manganese dioxide of high purity can be obtained by oxidizing synthetic MnCO3. The manganese dioxide is mixed with a lithium compound such as Li2CO3, LiNO3 or LiOH in a molar ratio of about 1:0.25. The resultant mixture is subjected to a heat treatment at 500 deg.C or higher, e.g. at about 750 deg.C, thus composing LiMn2O4. Use of the resultant lithium-containing manganese composite oxide of spinel crystal structure as a positive electrode active material can improve a cycle characteristic of a non-aqueous electrolyte secondary battery so as to realize a high energy density at a low cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improving the performance of a non-aqueous electrolyte secondary battery.

[0002]

2. Description of the Related Art As electronic devices are becoming smaller and lighter, there is a growing demand for high energy density secondary batteries as their power sources. In order to meet the demand, non-aqueous electrolyte secondary batteries have been attempted to be put into practical use because of their high potential as high energy density batteries. Above all, a non-aqueous electrolyte secondary battery using metallic lithium for the negative electrode and a lithium-containing manganese composite oxide for the positive electrode seemed to be quite promising. However, there is a problem in practical cycle life because the metallic lithium negative electrode becomes powdered by repeated charge and discharge and its performance is significantly deteriorated, and metallic lithium deposits on dendrites and causes an internal short circuit. Practical application is difficult. Therefore, in recent years, a non-aqueous electrolyte secondary battery has been under development, in which a carbon electrode that utilizes the inflow / outflow of lithium ions into / from carbon is used as the negative electrode instead of the lithium metal negative electrode. This battery was named by the present inventors as a lithium ion secondary battery, and was named in 1990 (Magazine Prog.
less in Batteries & Solar
Cells, Vol. 9, P.I. 209) for the first time, typically LiCoO ₂ is used for the positive electrode material, and a carbonaceous material is used for the negative electrode. At present, the battery industry and academic societies are calling it the next-generation rechargeable battery "lithium-ion rechargeable battery" and are drawing attention. In fact, 200 Wh /
A small amount of lithium ion secondary batteries having an energy density of about 1 have already been put into practical use. The energy density of the existing nickel-cadmium battery is 100 to 150 Wh / l, and the energy density of the lithium ion secondary battery is much higher than that of the existing battery. Another feature of lithium-ion secondary batteries is their long life. The carbon negative electrode is extremely charged because lithium ions are doped into carbon in the electrode during charging, and lithium ions are undoped from the carbon during discharging, and the carbon itself does not undergo a large change in crystal structure during charge / discharge, which is extremely high. Stable charge / discharge characteristics are exhibited, the characteristic deterioration due to charge / discharge is small, and specifically, the charge / discharge can be repeated 1000 times or more. However, the biggest drawback is that it is very expensive compared to existing batteries. LiCoO _{2 as the} positive electrode material
In the above lithium ion battery using a carbonaceous material for the negative electrode, since expensive cobalt and a special carbon material are used, the raw material cost becomes extremely high. The existing nickel-cadmium battery has an energy density of 100-150W.
Although it is h / l, the material cost is relatively low. Therefore, lithium-ion batteries are also inexpensive materials (for example, LiMn
_{If 2} O ₄ ) is used as a positive electrode active material and an energy density of about 200 Wh / l can be achieved, a lithium ion secondary battery will be used for a wide range of applications instead of the existing nickel cadmium battery. In addition to the lithium cobalt composite oxide (LiCoO ₂ ), lithium nickel composite oxide (LiNiO ₂ ) and spinel-type lithium manganese composite oxide (LiM) can be used as a positive electrode material that can be combined with a carbon negative electrode to form a lithium ion battery.
n ₂ O ₄ ) and LiMn _{2 in} terms of an inexpensive material.
O ₄ is attractive. However, only by replacing LiMn ₂ O ₄ with LiCoO ₂ as a positive electrode material, an energy density of about 170 Wh / l can be achieved. Until now, the carbonaceous material suitable for the carbon negative electrode of the lithium-ion secondary battery has been a carbon material obtained by thermal decomposition of various organic compounds or carbonization by firing, and the thermal history temperature is adjusted to adjust the carbon material. It is said that the conditions are important, carbonization is not sufficient if the heat history temperature is too low, and it is said that the temperature is at least 800 ° C or higher. Further, the upper limit of the heat history temperature is more important, and crystal growth occurs at a temperature of 2400 ° C or higher. It was said that the battery characteristics would be significantly impaired if it proceeded too much. In other words, a carbon material with good performance is considered to be a pseudo-graphite material having a certain degree of disordered structure, and in a highly crystalline graphite material, the electrolytic solution decomposes on the graphite surface, and the intercalation reaction of lithium ions is difficult to proceed. Was reported. However, the result of the most recent research is that if an appropriate electrolyte is selected, it is even flatter to use a more graphitized carbon material that has been heat treated at 2400 ° C or higher, or graphite itself as the negative electrode carbon material. It has been found that the lithium ion secondary battery has a high discharge voltage (Japanese Patent Publication No. 4-115457). Therefore, if a graphite material is used as the negative electrode material, inexpensive LiM can be used as the positive electrode material.
Even if n ₂ O ₄ is used, the energy density is 200
There is a possibility that the lithium ion secondary battery will exceed Wh / l. However, although the lithium-ion secondary battery using a carbon material for the negative electrode should have good cycle characteristics, the lithium-ion secondary battery using LiMn ₂ O ₄ as the positive electrode material does not always have good cycle characteristics. I found out. In the most typical conventional synthesis method of spinel-type lithium-containing manganese composite oxide LiMn ₂ O ₄ , commercially available manganese dioxide is used as a manganese compound, and a lithium salt such as lithium carbonate or lithium nitrate is mixed with the manganese dioxide. Synthesized by firing at 600 to 800 ° C.
Manganese dioxide is produced in large quantities for use in dry batteries, and electrolytic manganese dioxide (EMD) and chemically synthesized manganese dioxide (CMD) are commercially available at high prices as high-purity products, so inexpensive LiMn ₂ O ₄ is produced. Above, it can be said that it is a convenient material as a synthetic starting material. However, the lithium ion secondary battery using LiMn ₂ O ₄ prepared by the conventional method has a short cycle life, and the battery capacity deteriorates to almost half of the initial capacity after 50 to 100 cycles of charging and discharging. I will end up. The cause of this deterioration is not clear,
The lithium ion secondary battery using LiCoO ₂ has excellent cycle characteristics, and the cause is LiM of the positive electrode material.
It is almost clear that it is related to n ₂ O ₄ . In order to improve the cycle characteristics, it has been assumed that LiMn ₂ O ₄ crystals may collapse during charge / discharge cycles, and therefore Mn was used for the purpose of increasing crystal stability.
A part of various elements other than Mn (eg Co, C
(R, Ni, Ta, Zn, etc.) has been proposed as a lithium-containing manganese composite oxide (Japanese Patent Publication No. 4-141954).
However, it has not reached the practical cycle life (300 to 500 cycles).

[0003]

DISCLOSURE OF THE INVENTION The present invention improves the cycle characteristics of a non-aqueous electrolyte secondary battery in which a lithium-containing composite oxide having a spinel type crystal structure is mainly used as a positive electrode active material and a carbon material is used as a negative electrode active material. In particular, the present invention intends to provide a lithium-containing manganese composite oxide which is a positive electrode material having good cycle characteristics.

[0004]

As a means for solving the problem, manganese dioxide having a high purity is used as a starting material for synthesizing a lithium-containing manganese composite oxide. Specifically, a lithium compound (lithium hydroxide, lithium oxide, lithium salt, etc.) is added to manganese dioxide having a ratio (b / a) of Mn content (a) and MnO ₂ content (b) of 1.53 or more. Are mixed and heat-treated at a temperature of 500 ° C. or higher to synthesize.

[0005]

According to the most typical conventional method of synthesizing LiMn ₂ O ₄ , manganese dioxide is used as a manganese compound, lithium carbonate is mixed with this, and the mixture is calcined at 600 to 800 ° C. to synthesize. Manganese dioxide is manufactured for use in dry batteries, and electrolytic manganese dioxide (EMD) and chemically synthesized manganese dioxide (CMD) are commercially available as high-purity products. However, even with these high-purity manganese dioxides, the Mn content is 60.3 to 61.3% (theoretical value: 63.19%), and the ratio of the Mn content (a) to the MnO ₂ content (b). (B
/ A) is 1.53 (theoretical value: 1.582) or less.
By the way, EMD manufactured by Mitsui Kinzoku Co., Ltd. (TAD-I, TSV, etc.)
Then, a = 60.3%, b = 92.2%, and b / a = 1.
529, and CMD (FARADISER) manufactured by Cedema
-M), a = 61.3%, b = 91.7%, and b / a
= 1.496. Especially b / a is 9 against the theoretical value
6.7% or less means that 3.3 out of Mn contained.
% Means that mixed in MnO ₂ in other oxidation states rather than MnO _{2 (Mn} 2 _{O 3,} etc.). The inventor
MnO ₂ is specially synthesized to have various b / a values.
₂ was prepared, and LiMn ₂ synthesized using this as a starting material
A lithium ion secondary battery was prepared using O ₄ as an active material,
It has been found that the cycle characteristics vary greatly depending on the b / a value of MnO ₂ which is a starting material for LiMn ₂ O ₄ synthesis. That is, it was found that a battery using LiMn ₂ O ₄ synthesized from MnO _{2 with} b / a ≧ 1.53 had very good cycle characteristics. LiMn ₂ O
No. ₄ is a cubic crystal structure having a spinel structure. In a battery using this as a positive electrode active material, L
The i ions are extracted, and Li again enters the crystal due to discharge. After repeating the charge and discharge cycle, LiMn ₂
It is known that when O ₄ is examined by x-ray diffraction, the crystallinity decreases. Although the reason for the improvement of the cycle characteristics according to the present invention is not clear, L synthesized from MnO ₂ having a higher purity is used.
It is considered that iMn ₂ O ₄ has a higher purity, has less crystal distortion caused by the presence of impurities, has increased crystal stability, and is significantly improved in charge / discharge cycle characteristics.

[0006]

The present invention will be described in more detail with reference to the following examples. First, as starting materials for synthesizing the positive electrode active material LiMn ₂ O ₄ , MnO ₂ samples (A) to (G) were prepared as follows.

Synthesis of MnCO ₃ MnSO ₄ and (NH ₄ ) ₂ CO at the same concentration of 3 mol / l
₃ was charged in a reaction vessel in parallel at a dropping rate of 150 cc / h, kept at a reaction temperature of 5 ° C. or lower, and reacted for 6 hours to synthesize MnCO ₃ (X) having an average particle diameter of 0.008 mm. In the synthesis of small particle size MnCO ₃ having an average particle size of 0.008 mm, the most important point is to keep the reaction temperature at 5 ° C. or lower, and the small particle size MnCO ₃ is efficiently oxidized in the oxidation step to obtain high purity. Suitable for the synthesis of various MnO ₂ .

Synthesis of high-purity MnO ₂ (1) The above MnCO ₃ (X) was added to a NaOH solution while blowing nitrogen gas, reacted at a temperature of 40 ° C. for 2 hours to obtain Mn (OH) ₂ , and the blowing gas was changed. The N ₂ is replaced with air and maintained for 2 hours, and the reaction product is filtered and dried. 300 g of dried matter and 3 liters of distilled water were put into the reaction vessel again,
Air was introduced at a flow rate of 300 liters / h, Cl ₂ gas was introduced at a flow rate of 60 liters / h, and the mixture was stirred at 50 ° C. for 5 hours, filtered and dried, and 3 mol / l of HNO ₃ 900c was added to 300 g thereof.
c was added, and the mixture was stirred at 90 ° C. for 1 h, filtered, washed with water and dried to obtain a MnO ₂ sample (A). (2) Furthermore, 300 g of MnO ₂ sample (A) and Mn (NO
₃ ) ₂ 180 g was added to a 0.5 mol / l HNO ₃ solution and kept at 80 ° C., 72 g of NaClO ₃ was added under stirring for 15 minutes, and after addition, reacted at 80 ° C. for 3 hours,
It was filtered, washed with water and dried to obtain a MnO ₂ sample (B). (3) The MnCO ₃ (X) was heated at 600 ° C. for 20 hours to be Mn ₂ O _3, and 0.6 g per 1 g of Mn ₂ O ₃
The operation of adding 13N-HNO ₃ in a proportion of cc and thermally decomposing at 280 ° C. was repeated 3 times to obtain a β-type MnO ₂ sample (C) having extremely fine particles of about 0.001 mm.

High Purification of Commercial Manganese Dioxide MMD (TAD-I) manufactured by Mitsui Kinzoku Co., Ltd.
After heat treatment for an hour, the heat-treated product is placed in a porcelain container, 13N-HNO ₃ is added at a rate of 0.8 cc per 1 g of the heat-treated product, and the mixture is placed in an electric furnace and heated to 280 ° C. Then, heat treatment was performed to obtain a high-purity β-MnO ₂ sample (D). The above MnO ₂ of (A) to (D) is JI.
The Mn content (a) and the MnO ₂ content (b) were measured based on the S analysis method, and the b / a value was obtained for each MnO ₂ sample. The results are shown in Table 1. The MnO ₂ of (A) to (D) prepared for this example are all highly pure with a b / a value of 1.535 or more.

Synthesis of LiMn ₂ O ₄ Each of the above manganese dioxide (MnO ₂ ) was well mixed with lithium carbonate (Li ₂ CO ₃ ) at a ratio of 1 mol: 0.25 mol, and this was mixed in air. After heat treatment at 750 ° C. for 48 hours (However, as a result of preliminary experiments, it was confirmed that sufficient battery capacity could not be obtained at a heat treatment temperature of 500 ° C. or less), and M
Starting from the nO ₂ sample (A), LiMn ₂ O
₄ (A) in the same manner as MnO ₂ samples (B), (C),
Starting from (D), LiMn ₂ O ₄ (B),
(C) and (D) were adjusted respectively.

A specific battery of the present invention will be described with reference to FIG. A battery element which is a power generation element for carrying out the present invention was prepared as follows. First 2800
Mesocarbon microbeads (BE
90 parts by weight of T ratio surface area = 0.8 m ² / g, d ₀₀₂ = 3.37 Å), and polyvinylidene fluoride (PV
DF) 10 parts by weight is added, and the solvent is N-methyl-2-
Wet-mix with pyrrolidone to form a slurry (paste form). Then, this slurry has a thickness of 0.01 m as a collector.
m was uniformly applied to both sides of the copper foil, dried, and then pressure-molded with a roller press to form a strip-shaped negative electrode (1). LiMn ₂ O ₄ (A) to (D) prepared as described above were each added with acetylene black 3 as a conductive agent in 88 parts by weight.
Part by weight and 4 parts by weight of graphite are mixed with 5 parts by weight of polyvinylidene fluoride as a binder and wet mixed with a solvent N-methyl-2-pyrrolidone to form a paste. Next, this paste is uniformly applied to both sides of a 0.02 mm-thick aluminum foil which will be a positive electrode current collector, and after being dried and pressure-molded by a roller press machine, a strip-shaped positive electrode (2) is prepared.
Subsequently, the negative electrode (1) and the positive electrode (2) are wound into a roll with a porous polypropylene separator (3) sandwiched between them to form a battery element with a wound body having an average outer diameter of 15.7 mm. Next, a nickel-plated iron battery can (4)
An insulating plate (5) is installed on the bottom of the battery to accommodate the battery element. The negative electrode lead (6) taken out from the battery element was welded to the bottom of the battery can, and ethylene carbonate (EC) and diethyl carbonate (DE) were used as electrolyte in the battery can.
Lithium perchlorate dissolved in the mixed solvent of C) at a rate of 1 mol / liter is injected. Then, the insulating plate (5) is installed also on the upper part of the battery element, the gasket (7) is fitted, and the explosion-proof valve (8) is installed inside the battery as shown in FIG. The positive electrode lead (9) taken out from the battery element is welded before injecting the electrolytic solution into this explosion-proof valve. A closure lid (10) serving as a positive electrode external terminal is placed on the explosion-proof valve, the edge of the battery can is caulked, and the battery structure shown in FIG. 3 has an outer diameter of 16.5.
Batteries (A) to (D) having a size of 65 mm and a height of 65 mm were prepared.
Battery (A) is a battery using LiMn ₂ O ₄ (A) as a positive electrode active material, and batteries (B), (C) and (D) are used.
Are batteries in which LiMn ₂ O ₄ (B), (C), and (D) are used as positive electrode active materials, respectively.

[0012]

Comparative Example The method of synthesizing MnO ₂ carried out in the examples is not a general one, and is a few method for obtaining high-purity MnO ₂ . In the usual method, MnO ₂ having the same level of b / a value as that of currently commercially available manganese dioxide is synthesized.
In this comparative example, the same level of b / a as that of commercially available manganese dioxide was used.
Of MnO ₂ having
A battery having n ₂ O ₄ as a positive electrode was prepared and compared with the battery in the example. Also, commercially available electrolytic manganese dioxide and chemically synthesized manganese dioxide were used as starting materials for LiMn ₂
A battery having O ₄ as a positive electrode was also prepared and compared with the battery in the example.

Synthesis of MnCO ₃ (1) MnSO ₄ and (NH ₄ ) at the same concentration of 3 mol / l
₂ CO ₃ was charged in the reaction vessel in parallel at a dropping rate of 150 cc / h, the reaction temperature was maintained at about 20 ° C., and the reaction was allowed to proceed for 6 hours. MnCO ₃ (Y) having an average particle size of 0.040 mm
Was synthesized.

Synthesis of MnO ₂ (1) The above MnCO ₃ (Y) was added to the NaOH solution while blowing nitrogen gas, reacted at a temperature of 40 ° C. for 2 hours to make Mn (OH) ₂ , and the blowing gas was N ₂ The mixture is replaced with air for 2 hours, and the reaction product is filtered and dried. 300 g of dried matter and 3 liters of distilled water were put into the reaction vessel again,
Air was introduced at a flow rate of 300 liters / h, Cl ₂ gas was introduced at a flow rate of 60 liters / h, and the mixture was stirred at 50 ° C. for 5 hours, filtered and dried, and 3 mol / l of HNO ₃ 900c was added to 300 g thereof.
c was added, and the mixture was stirred at 90 ° C. for 1 h, filtered, washed with water and dried to obtain a MnO ₂ sample (E). (2) Furthermore, 300 g of MnO ₂ sample (E) and Mn (NO
₃ ) ₂ 180 g was added to a 0.5 mol / l HNO ₃ solution and kept at 80 ° C., 72 g of NaClO ₃ was added under stirring for 15 minutes, and after addition, reacted at 80 ° C. for 3 hours,
It was filtered, washed with water and dried to obtain a MnO ₂ sample (F).

Commercially available manganese dioxide for dry batteries MMD (TAD-I) (G) manufactured by Mitsui Kinzoku and CMD (Faradizer M) (H) manufactured by Cedema were prepared. As in the case of the embodiment, MnO ₂ of (E) to (H) is also JIS
The Mn content rate (a) and the MnO ₂ content rate (b) were measured on the basis of the analysis method described in 1 above, and the b / a value was obtained for each MnO ₂ sample. The results are shown in Table 2.

Synthesis of LiMn ₂ O _{4 As} in the case of the example, the above manganese dioxide (Mn 2
O ₂ ) was also well mixed with lithium carbonate (Li ₂ CO ₃ ) at a ratio of 1 mol: 0.25 mol, and this was mixed in air for 750
After heat treatment at 48 ° C. for 48 hours, the MnO ₂ sample (A) was used as a starting material for (LiMn ₂ O ₄ (E), and similarly MnO ₂ samples (F), (G), and (H) were used as starting materials. _Two
O ₄ (F), (G) and (H) were adjusted respectively.

Using the adjusted LiMn ₂ O ₄ (E) to (H) as active materials, a strip-shaped positive electrode (2b) is prepared in exactly the same manner as in the examples. The same negative electrode (1) and positive electrode (2b) as those produced in the examples were wound into a roll with a porous polypropylene separator (3) sandwiched therebetween, and a wound body having an average outer diameter of 15.7 mm was used as a battery element. And the outer diameter of 16.5 m in the same battery structure as shown in FIG.
Batteries (E) to (H) having m and a height of 65 mm were prepared. The battery (E) is a battery using LiMn ₂ O ₄ (E) as a positive electrode active material, and the batteries (F), (G), (H) are also LiMn ₂ O ₄ (F), (G), ( H) is a positive electrode active material.

Test Results Batteries (A) thus prepared in Examples and Comparative Examples
(H) indicates that the charging voltage is 4.2 after the aging period of 12 hours has passed for the purpose of stabilizing the inside of the battery.
The battery was set to V, charged for 8 hours in each case, and discharged for all batteries by a constant current discharge of 800 mA to a final voltage of 3.0 V to perform a charge / discharge cycle test.
As a result, the discharge capacity at the time of 10 cycles was about 910 mAh for both the battery according to the example and the battery according to the comparative example.
Is obtained, and the energy density is about 240 Wh / l. This value is more than 1.5 times that of the existing nickel-cadmium battery, and even 15% for the lithium-ion secondary battery using cobalt currently in practical use.
It is superior. However, as shown in FIG. 1, the batteries (E), (F), (G), and (H) according to the comparative examples have considerably deteriorated capacities with the charge / discharge cycles. Each battery is different only in the positive electrode active material used, and the positive electrode active material (LiMn ₂ O ₄ ) is greatly related to the deterioration of the capacity with the cycle. All of the LiMn ₂ O ₄ differ in the MnO _{2 of} the starting material, and are synthesized by the same method. Therefore, the LiMn ₂ O ₄ is greatly influenced by the MnO ₂ of the starting material, which is good or bad as a positive electrode active material. Will be there. Therefore, the ratio (b / a) of the Mn content rate (a) and the MnO ₂ content rate (b) in each MnO ₂ that is the starting material of the positive electrode material and the cycle life of each battery (here, the capacity is 50% of the initial capacity). %, The lifespan is defined as the number of cycles to reach 100%, and as shown in FIG. 2, LiMn ₂ O ₄ synthesized from MnO ₂ with b / a ≧ 1.53 as a starting material is used as an active material. The battery (A,
B, C and D) have very good cycle characteristics. For example, the energy density of the battery (D) is 240 Wh / l or more, and the cycle life (however, the number of cycles until reaching 50% of the initial capacity) exceeds 400 cycles, which is a lithium-ion secondary battery that can be sufficiently put into practical use. Can be said.
Although the reason for the improvement in cycle characteristics according to the present invention is not clear,
LiMn ₂ O ₄ synthesized from higher-purity MnO ₂ has higher purity, has less crystal distortion caused by the presence of impurities, increases crystal stability, and significantly improves charge-discharge cycle characteristics. It is considered to be seen. The present invention is not limited to the synthesis of LiMn ₂ O ₄ simply, and a part of Mn of LiMn ₂ O ₄ may be Mn.
It is naturally applicable to the synthesis of a lithium-containing manganese composite oxide having a spinel type crystal structure which is replaced with an element other than. In addition, in this embodiment, Li was used as the lithium compound.
LiMn ₂ O ₄ was synthesized using ₂ CO ₃ , but the present invention is not limited to this, and other lithium salts and various lithium compounds such as lithium hydroxide and lithium oxide can of course be used. is there.

[0019]

The lithium ion secondary battery using the lithium-containing manganese composite oxide as the positive electrode active material had the shortcoming that the cycle life thereof was short, but the Mn content (a) and the MnO ₂ content were the main problems. The ratio (b / a) to (b) is 1.
Manganese dioxide of 53 or more and a lithium compound (lithium hydroxide, lithium oxide, lithium salt, etc.) are mixed,
In a lithium ion secondary battery using a lithium-containing manganese composite oxide of spinel type crystal structure synthesized by heat treatment at 500 ° C. as a positive electrode active material, cycle characteristics are significantly improved. As a result, a lithium ion secondary battery with an energy density sufficiently higher than that of existing secondary batteries can be made at a low material cost, and a long-life, high-capacity secondary battery can be provided for a wide range of applications. The target value is great.

[Brief description of drawings]

[Fig. 1] Cycle characteristic diagram of prototype battery

FIG. 2 Relationship between cycle life and MnO2 / Mn

FIG. 3 is a schematic cross-sectional view showing the structures of batteries in Examples and Comparative Examples.

[Explanation of symbols]

1 is a negative electrode, 2 is a positive electrode, 3 is a separator, 4 is a battery can, 5
Is an insulating plate, 6 is a negative electrode lead, 7 is a gasket, 8 is an explosion-proof valve, 9 is a negative electrode lead, and 10 is a closing lid.

Claims (2)

[Claims] 1. A Mn content (a) and a MnO ₂ content (b).
With manganese dioxide having a ratio (b / a) of 1.53 or more to lithium compounds (Li ₂ CO ₃ , LiNO ₃ , LiO
H) and the like and mixed by heat treatment at a temperature of 500 ° C. or more to synthesize a lithium-containing manganese composite oxide having a spinel type crystal structure. 2. A non-aqueous electrolyte secondary battery, wherein the lithium-containing manganese composite oxide having the spinel type crystal structure according to claim 1 is used as a positive electrode active material.