JPH10177860A - Positive electrode material for lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure charging/discharging cycle durability so as to provide a positive electrode material for suppressing the reduction of a charging/ discharging capacity by introducing lithium ions in the mangan site made of lithium mangan composite oxide having a spinel crystal structure and substituting fluorine for all or a part of oxygen deficiency. SOLUTION: A material having a composition represented by an expression is used. In the expression, x is 0.0133<=x<=0.3333; y is 0<y<=0.2; z is 0.01<=z<=0; z<=y. By introducing lithium ions, a charging/discharging cycle characteristic is improved. Following the introduction of lithium ions, a mangan ion valency number is charged, and the disadvantage of the reduction of an initial charging/ discharging capacity is prevented by providing oxygen deficiency in a crystal grid. The weakening of a crystal structure caused by the oxygen deficiency is prevented by introducing fluorine. This positive electrode material is applied to a lithium secondary battery for communication office equipment such as a personal computer or a portable telephone set and thus an energy density is increased and the need for a long life can be satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a positive electrode material for a lithium secondary battery, and more particularly to a positive electrode material for a lithium secondary battery, which is a lithium-manganese composite oxide having a spinel-type crystal structure. .

[0002]

2. Description of the Related Art In recent years, attention has been paid to lithium secondary batteries because of their high charge / discharge voltage and large charge / discharge capacity. And high energy density, small size
Because it can be reduced in weight, it is also expected to be used as communication office equipment such as personal computers and mobile phones, or in the near future as a power source for electric vehicles.

As a cathode material of this lithium secondary battery, lithium cobalt oxide (LiCoO) has been used.
₂ ) Instead of materials, lithium manganate (L), which is a lithium-manganese composite oxide having a spinel-type crystal structure, is used.
iMn ₂ O ₄ ) -based compounds are promising.

In particular, among LiMn ₂ O ₄ compounds, as shown by the composition formula Li _{1 + X} Mn _2-X O ₄ (0 <x <0.03), Li ions are very slightly substituted on Mn sites. Attention has been paid to the fact that those introduced improve the cycle durability of charge and discharge (Y. Gao and JKDahn, J. Electroche
m. Soc., 143 , 100 (1996)). The cause of the cycle durability improvement is that the Mn site is partially replaced with Li,
It is considered that the change in crystal lattice due to charge / discharge, that is, desorption / insertion of Li ions is reduced.

On the other hand, LiMn ₂ O ₄ compounds in which oxygen is partially substituted with fluorine (F) are disclosed in JP-A-7-254.
No. 403 discloses this. This is the composition formula Li _X
Mn ₂ O _4-a F _b (where 0 <x ≦ 1.02, a ≦ 0.0
5, 0.01 ≦ b <0.1). It is assumed that self-discharge in a charged state is suppressed and a discharge capacity, particularly a discharge capacity under a high temperature condition, is ensured.

[0006]

However, the former example, that is, L of a spinel structure with a slight excess of Li
i _{1 + x} Mn _2-x O ₄ has a serious problem that the discharge capacity is reduced. In this case, the cation configuration of Li _{1 + x} Mn _2-x O ₄ is expressed as (Li) _8a [Li _x Mn _2-x ] _16d O ₄ . Eight four-coordinate tetrahedral sites (8
Li ion is located at (a site). Further, Mn was added to 16 hexacoordinate octahedral sites (16d sites) of this crystal lattice.
Ion and the excess L partially substituted for this Mn ion
i ion is located.

That is, since excess Li is located at the 16d site, the average valence of Mn ions increases to 3.5 or more. The charge and discharge of Li _{1 + x} Mn _2-x O ₄ with respect to Li metal is as follows:
Because of the oxidation-reduction reaction between Mn ³⁺ and Mn ^4+, an increase in the average valence of Mn ions leads to a decrease in the charge / discharge capacity of the battery, particularly the initial charge / discharge capacity.

FIG. 1 shows the relationship between the excess Li amount and the theoretical capacity (mAh / g). In this figure, Li _{1 + x}
When focusing on the sample of Mn _2-x O ₄ (material c), excess L
It can be seen that the theoretical capacity decreases linearly as the i amount x increases. When the value of the excess Li amount x is x = 0.03, Li
The theoretical capacity of the _{1 + x} Mn _2-x O ₄ sample is about 9 for the sample with x = 0.
Reduce to 2%.

Conventionally, this reduction in capacity has been tolerated in order to improve durability. However, a decrease in capacity impairs the feature of the lithium secondary battery that it has a high energy density. This is a significant problem when considering its application to portable electronic devices or power sources for electric vehicles.

On the other hand, the latter example, that is, when the fluorine-oxygen partially substituted with a _{Li x Mn 2 O 4-a} F b is, M
Li is not substituted into the n-site. Therefore, in the case of this material, the initial charge / discharge capacity does not decrease, but the discharge capacity greatly decreases when charge / discharge is repeated,
There is a problem that the charge / discharge cycle durability is not sufficient. Further, it is said that it is difficult to replace oxygen in the spinel structure with fluorine by a normal solid-state reaction method.

The problem to be solved by the present invention is to provide a positive electrode material for a lithium secondary battery capable of securing a high energy density by suppressing a decrease in the charge / discharge capacity while securing cycle durability of charge / discharge. To provide.

[0012]

In order to achieve this object, a cathode material for a lithium secondary battery according to the present invention is a lithium-manganese composite oxide having a spinel type crystal structure, and has a composition formula of Li _{1+ x} Mn _2-x O _4-y F _Z (where x is 0.0
133 ≦ x ≦ 0.3333, y is 0 <y ≦ 0.2, and z is 0.01 ≦ z ≦ 0.2, and z ≦ y. Is what you do.

In the above composition of Li _{1 + x} Mn _2-x O _4-y F _Z , oxygen is deficient in order to suppress an increase in the valence of manganese ions due to excess lithium. (When z = 0) B) Replace oxygen with fluorine. (When y = z) C) A part of oxygen is replaced by fluorine, and oxygen is also deficient. (If z <y). But,
If the oxygen deficiency is excessive in the case of A), the spinel structure becomes unstable, and the cycle durability is further reduced. Therefore, it is desirable to replace all or part of the oxygen vacancy with fluorine as in the cases B) and C).

The excess Li amount x and the theoretical capacity (mA) shown in FIG.
Explaining the relationship with h / g), the above case A) is represented by a straight line of the material a: Li _{1 + x} Mn _2-x O _4-x , and the case B) is the material b: Li _{1 + x} Mn represented by a straight line of _{2-x O 4-x F} x. Case C) corresponds to a shaded region between the straight line of the material a and the straight line of the material b. Where the theoretical capacity C _theo (mAh
/ g) and the excess Li amount x are given by the following equation (1). In Equation 1, mw (x) is the molecular weight of the sample, and F is the Faraday constant (9.6485 × 10 ⁴ C / mo).
1).

[0015]

(Equation 1)

As can be seen from the theoretical equation (1), Li _{1 + x}
In the sample of Mn _2-x O _4-x F _x , the decrease in capacity was measured as Li _{1 + x} Mn.
In the best case of _2-x O ₄ can be reduced to about 1/3. Therefore, the positive electrode material according to the present invention has a high capacity almost the same as a conventional product. Further, the durability is greatly improved as compared with the case of the LiMn ₂ O ₄ positive electrode.

Next, the range of the excess Li amount x of Li _{1 + x} Mn _2-x O _4-y F _Z will be described. The relationship between the capacity C (n) at the nth cycle and the initial capacity C _{0 in} the durability test is given by the following _equation (2).
It is expressed like the equation shown in FIG.

[0018]

(Equation 2)

Here, α is the capacity retention rate per cycle. Conversely, from this equation, in order to maintain a capacity of 60% of the initial capacity after 100 cycles of charge and discharge, the capacity retention rate per cycle is α = 0.94949.
Becomes FIG. 2 shows the relationship between α and x for Li _{1 + x} Mn _2-x O ₄ .

In FIG. 2, the capacity retention rate α increases with an increase in the excess Li amount x, but x ≧ 0.0133 in order to maintain practically necessary durability. This relationship was substantially the same for Li _{1 + x} Mn _2-x O _4-y F _Z.

On the other hand, when x = 0.333, Li _{1 + x} Mn _2-x
All Mn ions of O ₄ become +4, and a sample cannot be synthesized even if Li is introduced in excess. That is, in the region [A] of FIG. 2, the capacity is greatly reduced by the number of cycles, and it is difficult to use in practical use. In the area [B] in FIG.
The initial volume decreases to about 96% of the pure sample,
Capacity can be maintained up to 00-300 cycles. In the region [C] of FIG. 2, the initial capacity decreases to 96% or less,
A positive electrode exhibiting stable characteristics over a long period of 300 cycles or more can be obtained. The present invention corresponds to the regions [B] and [C] in FIG.

Note that Japanese Patent Application Laid-Open No. 7-25 is cited as a prior art.
No. 4403 discloses Li _{1 + x} Mn _2-x O
_4-y F _Z when expressed as, 0 ≦ x ≦ 0.0132 (2
(Corresponding to the region [A] in FIG. 3). It is clear that in this region, the excess Li amount x is too small and the durability is not sufficiently improved.

When a part of oxygen is deficiently substituted or replaced with F, the long-range interaction between Mn ions via oxygen is significantly weakened. Therefore, even if charging and discharging are repeated,
It is possible to provide a positive electrode material for a lithium secondary battery having a crystal structure that does not easily change and is more excellent in durability.

In the above composition formula Li _{1 + x} Mn _2-x O _4-y F _Z , 0 <y ≦ 0.2 and 0.01 ≦ z ≦ 0.2. z <
At 0.01, a sufficient effect by F substitution cannot be obtained. When 0.2 ≦ z, F does not replace oxygen, and LiF is precipitated as an impurity.

The crystal structure of Li _{1 + x} Mn _2-x O _4-y F _Z is preferably a cubic spinel structure. When the oxygen deficiency yz is increased, the crystal structure changes to tetragonal in the vicinity of yz = 0.07. When the tetragonal phase appears in the positive electrode material, the charge / discharge voltage decreases. Therefore, to maintain the cubic spinel structure even when oxygen vacancies are introduced, y-
z is preferably smaller than 0.07.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described specifically with reference to examples. _First , the composition formula Li _{1 + x} Mn _2-x O _4-y F _z
The synthesis of the above materials will be described. For the synthesis of this material, first, a LiMn ₂ O ₄ material was synthesized. Powders of lithium carbonate (Li ₂ CO ₃ ) and manganese dioxide (MnO ₂ ) were used as raw materials. 3.505 g of Li ₂ CO ₃ and 16.495
g of MnO ₂ was mixed in a planetary ball mill using ethanol as a solvent. After drying this mixed powder, it was formed into pellets and calcined three times in a still atmosphere at 700 ° C. for 8 hours. Then, the pellet is sufficiently pulverized to obtain LiMn ₂
To give the O ₄ of the material.

Next, this LiMn ₂ O ₄ powder material 24.6
To 89 g, 0.182 g of lithium fluoride (LiF) and 0.129 g of lithium carbonate (Li ₂ CO ₃ ) were added and mixed well. The mixed powder was press-formed again into a pellet, heat-treated in an oxygen stream at 650 ° C. for 12 hours, and gradually cooled in a furnace to room temperature. According to the composition analysis, this sample was Li
_1. was ₀₅ Mn _1.95 O _3.95 F _0.05. This is called “Sample 1 of the present example”.

In the same manner, Li _1.02 Mn _1.98
O _3.98 F _0.02 (Sample 2 of this example), Li _1.1 Mn _1.9 O
_3.9 F _0.1 (Sample 3 of this example), Li _1.15 Mn _1.85 O _3.85
F _0.15 (Sample 4 of this example), Li _1.2 Mn _1.8 O _3.8 F _0.2
(Sample 5 of this example), Li _1.05 Mn _1.95 O _3.96 F
_0.04 (sample 6 of this example), Li _1.05 Mn _1.95 O _3.97 F
_0.03 (Sample 7 of the present example) and Li _1.05 Mn _1.95 O _3.99
F _0.01 (sample 8 of this example) was obtained.

The mixed powder molded product of the sample 1 of the present embodiment was
50 ° C., quenched from a 20% O ₂ -Ar atmosphere to obtain Li _1.05
Mn _1.95 O _3.95 F _0.04 (Example 9) and sample 7 of Example 7 were quenched from 650 ° C. and 15% O ₂ -Ar atmosphere to obtain Li _1.05 Mn _1.95 O _3.95 F _0.03 (Example 9). Sample 10) was changed to 650 ° C., 10% O
_After quenching from the ₂ -Ar atmosphere, Li _1.05 Mn _1.95 O _3.95 F
_0.01 (Example 11 of this example) was obtained.

Next, a comparative sample was synthesized by the following method. Comparative Example Sample C1 (Li _1.05 Mn _1.95 O ₄ )
To 24.613 g of Mn ₂ O ₄ powder, lithium carbonate (Li ₂ CO 3) was added.
₃ ) Add 0.387 g and mix well.
It was obtained by heating in an oxygen stream for an hour and then gradually cooling in a furnace to room temperature. Further, this sample was subjected to 650 ° C., 10% O ₂ -Ar
The mixture was rapidly cooled from the atmosphere to obtain Li _1.05 Mn _1.95 O _3.95 (Comparative Sample C2). Table 1 shows the compositions of the sample 1-11 of the example and the samples C1 and C2 of the comparative example and the amounts of the respective raw materials necessary for the synthesis.

[0031]

[Table 1]

In the above synthesis, lithium carbonate and lithium fluoride were used as raw materials. However, the same applies when lithium nitrate, lithium acetate, lithium hydroxide or the like is used as a lithium source and ammonium fluoride or the like is used as a fluorine source. A sample is obtained.

Next, the characteristics of the lithium secondary battery as a positive electrode material were evaluated. The samples used were Sample 1-11 of this example, Samples C1 and C2 of Comparative Example, and LiMn used as a raw material.
₂ O ₄ (standard sample S1).

First, the structure of the lithium secondary battery will be described. As the positive electrode of the lithium secondary battery, a mixture of 90 wt% of each sample obtained as described above and 10 wt% of the conductive binder was used. One metal lithium foil having a thickness of 0.4 mm was used for the negative electrode. A polypropylene nonwoven fabric was used for the separator provided between the positive electrode and the negative electrode.
The electrolyte in the lithium secondary battery is a 1N LiPF ₆ solution, and the solvent is a 1: 1 mixture of ethylene carbonate and diethyl carbonate.

The charge and discharge conditions for measuring the initial discharge characteristics and cycle characteristics of this lithium secondary battery will be described. First, charge each lithium secondary battery up to 4.5 V at 1 mA / cm ²
Was charged at a constant current. After that, when the voltage reaches 4.5V,
Constant voltage charging was performed at this voltage. The total of the above charging times was 2 hours. Then, immediately after completion of the charging, discharging was started. The discharge was performed at a constant current of 1 mA / cm ² , and the discharge was terminated when the voltage reached 3.5 V. Immediately after that, charging was started again. The above was regarded as one cycle.

FIG. 3 shows sample 1 of the present embodiment and sample C of the comparative example.
1 shows the initial discharge characteristics of a lithium secondary battery using positive electrodes 1, C2 and standard sample S1, respectively. As compared with the standard sample S1, it can be seen that the initial discharge capacity of the lithium secondary batteries using the sample 1 of the present example and the samples C1 and C2 of the comparative examples is reduced. The decrease in the initial discharge capacity is shown in Comparative Sample C1
Is the largest, followed by Sample 1 of the present example and Sample C2 of the comparative example.
It was in order. These behaviors were as expected in FIG. In the figures, the comparative sample C2 is 0.2 V, the comparative sample C1 is 0.4 V, the standard sample S1 is 0.6 V, and the data is shifted in the vertical axis direction for easy comparison.

FIG. 4 shows sample 1 of the present embodiment and sample C of the comparative example.
1 shows the discharge cycle characteristics of a lithium secondary battery using positive electrodes 1, C2 and standard sample S1 as positive electrodes. The vertical axis shows the discharge capacity (mAh /
g). The horizontal axis represents the number of times charge / discharge was repeated, that is, the number of cycles (times). Although the standard sample S1 has a high initial discharge capacity, the discharge capacity sharply decreases when the cycle is repeated.

In the comparative sample C1, the decrease in the discharge capacity due to the repetition of the cycle is small, but the initial discharge capacity is greatly reduced. On the other hand, the sample of this example 1 and the sample of comparative example C2
In the lithium secondary battery using, the decrease in the initial discharge capacity is not as remarkable as C1. It can be seen that in the sample 1 of the present example, the decrease in the discharge capacity due to repetition of charge and discharge is small.

In order to examine the effect of the amount of fluorine substitution,
FIG. 5 shows charge / discharge cycle characteristics of the lithium secondary battery using the sample 1-5 of the example and the sample C1 of the comparative example as a positive electrode.
For Li _1.02 Mn _1.98 O _3.98 F _{0.02 of the} sample 2 of the present example,
The excess Li amount and F substitution amount are insufficient, and after 100 cycles, the capacity is reduced to about 90% of the initial capacity.
However, it maintains a larger discharge capacity than the comparative sample C1.

On the other hand, Li _1.05 M
n _1.95 O _3.95 F _0.05 , Li _1.1 Mn _1.9
O _3.9 F _0.1 , Li _1.15 Mn _1.85 O _3.85 F
It was confirmed that when the excess Li amount and the F replacement amount increased in the order of _0.15 and Li _1.2 Mn _1.8 O _3.8 F _0.2 of Sample 5, the initial discharge capacity was reduced, but the cycle characteristics were significantly improved. In particular, Li _1.15 Mn _{1.85 of} Sample 4 of the present example.
O _3.85 F _0.15 and Li _1.2 Mn _1.8 O _3.8 F
_{At 0.2} , the initial discharge capacity was inferior to the comparative sample C1, but hardly deteriorated even after 100 cycles.

Next, the effect of the amount of fluorine substitution was examined while keeping the composition ratio of Li and Mn constant and eliminating the loss of anions. As is clear from FIGS. 3 to 5, the high capacity and the cycle durability at a high level were both satisfied in the sample 1 of the present embodiment.
Was _{(Li 1.05 Mn 1.95 O 3.95 F} 0. 05). Therefore, while maintaining the ratio of cations (Li: Mn = 1.05: 1.95) and the total sum of anions (4-y + z = 4) constant, a sample with a different F content (Sample 6- 8) was synthesized. FIG.
The charge / discharge cycle characteristics of a lithium secondary battery using Samples 1 and 6-8 of this example and Comparative sample C1 as positive electrodes are shown below. The vertical axis is the discharge capacity (mAh / g). The horizontal axis represents the number of repetitions of the charge / discharge capacity, that is, the number of cycles (times).

Sample 1 of the present example has a high initial capacity and a small decrease in discharge capacity due to repetition of cycles. As the amount of fluorine is reduced in the order of Samples 6, 7, and 8 of the present example and Sample C1 of Comparative Example, the initial capacity decreases sequentially, and it can be seen that the decrease in discharge capacity due to repetition of charge and discharge is almost the same. In other words, it has been clarified that high capacity and cycle durability can both be achieved by substituting fluorine without deficiency of anions.

Further, the effect of the amount of fluorine substitution was examined while keeping the composition ratio of Li and Mn and the amount of oxygen constant. That is, while keeping the ratio of cations (Li: Mn = 1.05: 1.95) and the oxygen amount (3.95) constant, a sample (Sample 9-11 in this example) in which the amount of F substitution was changed was used. Synthesized. FIG. 7 shows the charge / discharge cycle characteristics of the lithium secondary batteries using the positive electrode samples of Examples 1 and 9-11 and Comparative Examples C1 and C2. The vertical axis is the discharge capacity (mAh / g). The horizontal axis represents the number of times charge / discharge was repeated, that is, the number of cycles (times).

The sample 1 of this example has a high initial discharge capacity and a small decrease in capacity due to repetition of the cycle. When the amount of fluorine is reduced in the order of Samples 9, 10, and 11 of the present example and Comparative Example Sample C1 while the amount of oxygen is kept constant, the initial discharge capacity increases sequentially, but the discharge capacity decreases remarkably due to repeated charging and discharging. It turns out that it becomes.

In particular, the cycle characteristics of Samples 1 and 4-6 of this example were better than those of Sample 9-11 of this example and Comparative sample C1. This indicates that Samples 1 and 6-8 of the present example, in which the anion sites are completely filled, have more stable crystal structures than Samples 9-11 of the present Example having a defective site and Comparative Sample C1. It is considered to mean.

Further, both the sample 1-11 of the present embodiment and the comparative samples C1 and C2 had a cubic spinel structure at room temperature.
Excessive oxygen deficiency turns the sample into a tetragon at room temperature. The appearance of the tetragonal system lowers the charge / discharge voltage. Therefore, it is desirable that the battery has a cubic spinel structure in the operating temperature range of the battery or at least at room temperature.

The above results can be summarized as follows: lithium manganate-based material having a spinel crystal structure: composition formula LiMnO ₄
When Li is substituted and introduced into the Mn site, the charge / discharge cycle characteristics are improved, but the initial discharge capacity is reduced. It is effective to provide oxygen vacancies in the crystal lattice in order to avoid the decrease in the initial discharge capacity. However, if fluorine (F) is further introduced into the oxygen vacancies, the charge / discharge cycle characteristics are further improved. It was confirmed that the material would be highly practical.

Although the embodiment has been described above, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the gist of the present invention. For example, in the above embodiment, the method of partial substitution of oxygen in the crystal lattice was used to introduce fluorine (F) into the crystal lattice, but instead, oxygen deficiency was provided in the crystal lattice. In part or all of the missing part,
Of course, it is also good to introduce the method.

Although the introduction of excess Li into the Mn site and the introduction of F into the crystal lattice are performed simultaneously using lithium fluoride (LiF), these may be performed by different methods. Then, the Li replacement amount and the F introduction amount can be determined to be appropriate amounts, respectively, and the initial discharge capacity and the charge / discharge cycle characteristics can be adjusted to more appropriate characteristics.

[0050]

The positive electrode material for a lithium secondary battery according to the present invention has an improved charge / discharge cycle characteristic by introducing lithium ions into the manganese site of a lithium-manganese composite oxide having a spinel-type crystal structure. The disadvantage that the manganese valency changes with the introduction of ions and the initial discharge capacity decreases is avoided by providing oxygen vacancies in the crystal lattice, and the crystal structure becomes weaker with the oxygen vacancies. The disadvantage was solved by introducing fluorine.

Therefore, according to the positive electrode material for a lithium secondary battery of the present invention, a high initial charge / discharge capacity is secured, and a stable state of the spinel type crystal structure is maintained to improve the charge / discharge cycle characteristics, that is, the cycle durability. It also contributes to. As a positive electrode material for lithium secondary batteries for communication office equipment such as personal computers and mobile phones, which are expected to spread in the future, or as a positive electrode material for lithium secondary batteries as electric vehicle power supplies, for which demand is expected in the near future If applied, it can sufficiently meet the needs of high energy density and long life.

[Brief description of the drawings]

FIG. 1 shows the theoretical capacity and excess Li amount x in comparison between a Li _{1 + x} Mn _2-x O _4-y F _z material according to the present invention and a conventional Li _{1 + x} Mn _2-x O ₄ material and the like. FIG.

FIG. 2 is a diagram showing the relationship between the capacity retention ratio per charge / discharge cycle of the Li _{1 + x} Mn _2-x O ₄ material shown in FIG. 1 and the excess Li amount x.

FIG. 3 is a diagram showing the initial discharge characteristics of a lithium secondary battery using Sample 1 of the present Example, Samples C1 and C2 of Comparative Example, and Standard Sample S1 as a positive electrode material. In the figure, for ease of comparison, the comparative sample C2 is 0.2 V, the comparative sample C1 is 0.4 V, the standard sample S1 is 0.6 V, and the data is shifted in the vertical axis direction.

FIG. 4 is a diagram showing charge / discharge cycle characteristics of a lithium secondary battery using the sample of the present example 1, the samples of comparative examples C1, C2, and the standard sample S1 as positive electrodes.

FIG. 5 is a diagram showing charge / discharge cycle characteristics of a lithium secondary battery using the sample 1-5 of the example and the sample C1 of the comparative example as positive electrodes.

FIG. 6 shows samples 1 and 6-8 of the present example and comparative sample C1.
FIG. 3 is a diagram showing charge / discharge cycle characteristics of a lithium secondary battery having a positive electrode as a positive electrode.

FIG. 7 shows Samples 1 and 9 to 11 of the present invention and Sample C of Comparative Example.
FIG. 1 is a diagram showing charge / discharge cycle characteristics of a lithium secondary battery having C2 as a positive electrode.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tatsuya Hatanaka 41-Cho, Yokomichi, Nagakute-cho, Aichi-gun, Aichi Prefecture Inside Toyota Central Research Laboratory Co., Ltd. 41, Yokomichi, Toyota Central Research Laboratory Co., Ltd. (72) Inventor Tatsumi Hioki 41, Okucho, Yoji, Nagakute-cho, Aichi-gun, Aichi Prefecture 1 Toyota Toyota Central Research Laboratory Co., Ltd.

Claims (1)

[Claims] 1. A composite oxide of lithium and manganese having a spinel type crystal structure, wherein the composition formula is Li _{1 + X} Mn _2-X O
_4-y F _Z (where x is 0.0133 ≦ x ≦ 0.3333, y
Is 0 <y ≦ 0.2, and z is 0.01 ≦ z ≦ 0.2, and z ≦ y).