JP2003217589A - Lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium secondary battery which is superior in cycle characteristics at high temperature, while its positive electrode active material is lithium manganate of a spinel structure. <P>SOLUTION: This is a lithium secondary battery of which the positive electrode active material is lithium manganate having a spinel structure. The concentration of sodium in the lithium manganate is 50-5000 ppm. And the concentration of sodium in the lithium manganate is 50-50,000 ppm and the concentration of boron is 10 ppm or more. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a lithium secondary battery using lithium manganate as a positive electrode active material and having excellent high temperature cycle characteristics.

[0002]

2. Description of the Related Art In recent years, portable electronic devices such as mobile phones, VTRs, and notebook personal computers have been rapidly reduced in size and weight. As a power source battery, a lithium transition element composite oxide is used as a positive electrode active material. A secondary battery using a carbonaceous material as a negative electrode active material and an organic electrolytic solution obtained by dissolving a Li ion electrolyte in an organic solvent as an electrolytic solution has been used.

Such a battery is generally called a lithium secondary battery or a lithium ion battery, has a large energy density, and has a unit cell voltage of about 4V.
Due to its high degree of features, not only the portable electronic device but also an electric vehicle (hereinafter referred to as “EV”), which has been widely popularized as a low-pollution vehicle due to recent environmental problems. Or as a motor drive power source for a hybrid electric vehicle (hereinafter referred to as “HEV”).

In such a lithium secondary battery
Indicates its battery capacity and charge / discharge cycle characteristics (hereinafter
"Kuru characteristics". ) Indicates the material characteristics of the positive electrode active material used.
It largely depends on gender. Here, as the positive electrode active material
The lithium transition element composite oxide used as
Physically, lithium cobalt oxide (LiCoO ₂) And Ni
Lithium Kerate (LiNiO₂), Lithium manganate
(LiMn₂O_Four) And the like (for example, Patent Document 1)
~ 5).

[0005]

[Patent Document 1] Japanese Patent Laid-Open No. 2001-180939

[Patent Document 2] JP-A-7-272765

[Patent Document 3] Japanese Patent Laid-Open No. 2000-231921

[Patent Document 4] Japanese Unexamined Patent Publication No. 11-171551

[Patent Document 5] JP 2001-48547 A

[0006]

Among such positive electrode active materials, lithium manganate spinel (stoichiometric composition: LiMn ₂ O ₄ ) is inexpensive as a raw material, has a large output density, and has a high potential. However, there is a problem in that it is difficult to obtain good cycle characteristics because the discharge capacity gradually decreases with repeated charge / discharge cycles especially at high temperatures.

This is because in the case of a lithium secondary battery produced by using a LiPF ₆ based electrolytic solution as an electrolytic solution, hydrogen fluoride (HF) is generated in the system under high temperature conditions, which causes lithium manganate spinel. Therefore, it is considered that a part of Mn is eluted in the electrolytic solution. That is, it is considered that under high temperature conditions, the positive electrode active material is deteriorated and the negative electrode active material is adversely affected, so that the cycle characteristics of the battery are deteriorated.

The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to provide cycle characteristics at high temperature even when the positive electrode active material is lithium manganate spinel. To provide an excellent lithium secondary battery.

[0009]

Means for Solving the Problems That is, according to the present invention, a lithium secondary battery in which the positive electrode active material is lithium manganate having a spinel structure, wherein the lithium manganate has a sodium concentration of 50 to 5000 ppm. There is provided a lithium secondary battery characterized by the above. This is the first invention. Furthermore, according to the present invention, the positive electrode active material is a lithium secondary battery in which lithium manganate having a spinel structure is used, and the sodium concentration of the lithium manganate is 50 to 50,000 ppm and the boron concentration is 10 ppm or more. A featured lithium secondary battery is provided. This is the second invention.

In the first aspect of the invention, it is preferable that the lithium manganate is synthesized using lithium carbonate having a sodium concentration of 30 ppm or more and manganese dioxide having a sodium concentration of 50 ppm or more.

In the first invention, the sodium concentration of lithium carbonate is preferably 100 ppm or more, and the sodium concentration of manganese dioxide is 400 p or less.
It is preferably at least pm.

In the first aspect of the invention, it is preferable that lithium manganate is synthesized using lithium carbonate having a sodium concentration of 30 ppm or more and manganese carbonate having a sodium concentration of 35 ppm or more.

In the first invention, the sodium concentration of lithium carbonate is preferably 100 ppm or more, and the sodium concentration of manganese carbonate is 100 pp.
It is preferably m or more.

In the first invention, the sodium concentration of lithium manganate is more preferably 500 to 4000 ppm, particularly preferably 1000 to 3000 ppm.

In the first invention, the aluminum (Al) concentration of lithium manganate is 10 to 30000.
ppm and / or boron (B) concentration is 10 to 4000 pp
m and / or vanadium (V) concentration is 10 to 4000 p
pm is preferable, and the aluminum concentration is 10 to 10.
The concentration is more preferably 20000 ppm, the boron concentration is more preferably 10 to 2000 ppm, and the vanadium (V) concentration is 10 to 2000 pp.
More preferably m.

In the first invention, the Li / Mn ratio of lithium manganate is preferably more than 0.5,
Further, a part of the transition element Mn in lithium manganate (LiMn ₂ O ₄ ) contains Ti, and in addition, Li, Fe,
Ni, Mg, Zn, B, Al, Co, Cr, Si, S
n, P, V, Sb, Nb, Ta, composed of one or more elements selected from the group consisting of Mo and W, LiM formed by substituted in two or more kinds of elements _Z Mn _2-Z O ₄ (provided that, It is preferable that M is a substitution element and Z is a substitution amount) as a positive electrode active material.

In the first invention, it is preferable that the lattice constant of lithium manganate is 8.23 angstroms or less, and further that the lattice constant is 8.22 angstroms or less.

Further, in the first invention, lithium manganate is mixed with a salt and / or oxide mixture of each element adjusted to a predetermined ratio in an oxidizing atmosphere at 650 to 1000 ° C.
It is preferable that it is obtained by firing in the range of 5 to 50 hours. The firing is more preferably performed twice or more, and it is preferable that the firing temperature be successively increased each time the firing is repeated.

In the second invention, the boron concentration is 40
It is preferably 00 ppm or less.

In the second invention, it is preferable that the lithium manganate has an aluminum concentration of 10 to 30000 ppm and / or a vanadium concentration of 10 to 4000 ppm.

In the second invention, the aluminum concentration is more preferably 10 to 20000 ppm.

In the second invention, the Li / Mn ratio of lithium manganate is preferably more than 0.5,
Further, a part of the transition element Mn in lithium manganate (LiMn ₂ O ₄ ) contains Ti, and in addition, Li, Fe,
Ni, Mg, Zn, B, Al, Co, Cr, Si, S
n, P, V, Sb, Nb, Ta, composed of one or more elements selected from the group consisting of Mo and W, LiM formed by substituted in two or more kinds of elements _Z Mn _2-Z O ₄ (provided that, It is preferable that M is a substitution element and Z is a substitution amount) as a positive electrode active material.

In the second invention, the lattice constant of lithium manganate is preferably 8.23 angstroms or less, and further preferably the lattice constant is 8.22 angstroms or less.

Further, in the second invention, lithium manganate is mixed with a salt and / or oxide mixture of each element adjusted to a predetermined ratio in an oxidizing atmosphere at 650 to 1000 ° C.
It is preferable that it is obtained by firing in the range of 5 to 50 hours. The firing is more preferably performed twice or more, and it is preferable that the firing temperature be successively increased each time the firing is repeated.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention (first invention and second invention) will be described, but the present invention is not limited to the following embodiments. It should be understood that changes and improvements in design can be appropriately made based on the ordinary knowledge of those skilled in the art without departing from the spirit of the invention.

The first invention relates to a lithium secondary battery in which the positive electrode active material is lithium manganate having a spinel structure, and the sodium concentration of lithium manganate is 50 to 50.
It is characterized by being 5000 ppm, and has excellent cycle characteristics at high temperatures. Note that ppm
Indicates a weight ratio. The details will be described below.

When the lithium secondary battery is used under high temperature conditions, hydrogen fluoride is inevitably generated, and Mn is easily eluted from the positive electrode active material lithium manganate, so that the capacity of the positive electrode active material is increased. Is deteriorated, and problems such as deterioration of cycle characteristics tend to occur. However, since lithium manganate used in the lithium secondary battery of the first invention contains sodium at a predetermined concentration, the amount of Mn eluted from lithium manganate is reduced even under high temperature conditions. It Therefore, the lithium secondary battery of the first aspect of the present invention has a high efficiency of Li ⁺ insertion and desorption, and can suppress a decrease in the capacity of the positive electrode active material itself, and thus has excellent high-temperature cycle characteristics.

When the sodium concentration of lithium manganate is less than 50 ppm, it is not preferable because the effect of improving the high temperature cycle characteristics is not sufficient.
If it exceeds 00 ppm, it may adversely affect the battery characteristics, which is not preferable. From the viewpoint of providing a lithium secondary battery having a high efficiency of Li ⁺ insertion / extraction and excellent high temperature cycle characteristics, the sodium concentration of lithium manganate is 500 to 4
000 ppm is preferable, and 1000 to 300
More preferably, it is 0 ppm.

In the first aspect of the invention, lithium manganate used as the positive electrode active material is lithium carbonate having a sodium concentration of 30 ppm or more and 50 p
It is preferably synthesized using manganese dioxide of pm or more, and has a sodium concentration of 100 p each.
More preferably, it was synthesized using lithium carbonate of pm or more and manganese dioxide of 400 ppm or more, and was synthesized using lithium carbonate of which sodium concentration was 150 ppm or more and manganese dioxide of 1000 ppm or more, respectively. It is particularly preferable that it is one. The use of lithium carbonate having a sodium concentration of less than 30 ppm and manganese dioxide having a sodium concentration of less than 50 ppm is not preferable because the synthesized lithium manganate has a sodium concentration of less than 50 ppm.

The upper limit of the sodium concentration of lithium carbonate and manganese dioxide used in the first invention is not particularly limited, but the sodium concentration of the obtained lithium manganate is the manganese in the first invention. From the viewpoint of not exceeding the upper limit of 5000 ppm of the sodium concentration of lithium oxide, the sodium concentration of lithium carbonate is 245
00 ppm or less, and the sodium concentration of manganese dioxide may be 5000 ppm or less. Note that these upper limit values are numerical values determined on the assumption that other materials used at the same time do not contain sodium,
There may be some variation depending on the situation.

On the other hand, in the first invention, the lithium manganate used as the positive electrode active material is lithium carbonate having a sodium concentration of 30 ppm or more and 35 p
It is preferably synthesized using manganese carbonate of pm or more, and the sodium concentration is 100 pp for each.
More preferably, it was synthesized using lithium carbonate of m or more and manganese carbonate of 100 ppm or more, and was synthesized using lithium carbonate of which sodium concentration was 150 ppm or more and manganese carbonate of 750 ppm or more, respectively. It is particularly preferable that it is one. When synthesized using lithium carbonate having a sodium concentration of less than 30 ppm and manganese carbonate having a sodium concentration of less than 35 ppm, the lithium concentration of lithium manganate obtained is less than 50 ppm, which is not preferable.

The upper limit of the sodium concentration of lithium carbonate and manganese carbonate used in the first invention is not particularly limited, but the sodium concentration of the obtained lithium manganate is the manganese of the first invention. From the viewpoint of not exceeding the upper limit of 5000 ppm of the sodium concentration of lithium oxide, the sodium concentration of lithium carbonate is 2450.
It may be 0 ppm or less, and the sodium concentration of manganese carbonate may be 3500 ppm or less. It should be noted that these upper limit values are numerical values determined on the assumption that sodium is not contained in other materials used at the same time, and may vary to some extent depending on the situation.

In order to make lithium manganate used as the positive electrode active material have a predetermined sodium concentration, as described above, Li containing a proper amount of sodium is used.
In addition to a method of preparing both raw materials and a raw material of Mn and using them, a method of using a raw material containing sodium at a high concentration in only one of the Li raw material and the Mn raw material, and a low concentration of sodium The method of synthesizing lithium manganate, which is the above, and adding sodium to it can be mentioned. Whichever method is used, it is possible to keep the sodium concentration of lithium manganate finally used within a predetermined range.

However, in the lithium secondary battery produced by using the lithium manganate prepared by the above method, the improvement in high temperature cycle characteristics tends to be not remarkable. Although the reason why such a tendency is observed is not clear, the improvement of high temperature cycle characteristics, that is, the effect of effectively suppressing the generation of hydrogen fluoride depends on the distribution state of the sodium element in the crystal of lithium manganate. It is presumed that it depends. Therefore, as indicated above,
In the lithium secondary battery of the first invention, since lithium manganate obtained by using both the Li raw material and the Mn raw material containing an appropriate amount of sodium is used, the high temperature cycle characteristics are more excellent. There is.

In the lithium secondary battery of the first invention, the lithium manganate used as the positive electrode active material contains aluminum (A
1) and / or boron (B) are preferably contained. It is preferable that the lithium manganate contains aluminum and / or boron because the high temperature cycle characteristics of the lithium secondary battery are further improved. The aluminum concentration of lithium manganate is preferably 10 to 30,000 ppm, more preferably 10 to 20,000 ppm. If it is less than 10 ppm, the effect of including aluminum may not be exhibited, and 3000
If it is more than 0 ppm, the effect of further improving the high temperature cycle characteristics of the lithium secondary battery is not recognized, and aluminum is wastefully used. The boron concentration of lithium manganate is preferably 10 to 4000 ppm,
More preferably, it is 10 to 2000 ppm. 10
If it is less than ppm, the effect of including boron may not be exhibited, and if it is more than 4000 ppm, sintering of particles of lithium manganate progresses and becomes hard, and a crushing step is required, resulting in high manufacturing cost. There is.

The vanadium concentration of lithium manganate is preferably 10 to 4000 ppm, and 1
More preferably, it is 0 to 2000 ppm. 10p
If it is less than pm, the effect of incorporating vanadium may not be exhibited, and if it is more than 4000 ppm, the sintering of lithium manganate particles progresses to be hard as in the case of boron, and a crushing step is required. However, the manufacturing cost may increase.

In the lithium secondary battery of the first invention, lithium manganate having a spinel structure is used as the positive electrode active material. The stoichiometric composition of lithium manganate is represented by LiMn ₂ O ₄ , but in the first invention, it is not limited to such a stoichiometric composition, and a part of the transition element Mn contains Ti. , Li, Fe,
Ni, Mg, Zn, B, Al, Co, Cr, Si, S
n, P, V, Sb, Nb, Ta, composed of one or more elements selected from the group consisting of Mo and W, LiM formed by substituted in two or more kinds of elements _Z Mn _2-Z O ₄ (provided that, M is a substitution element, and Z is a substitution amount.) Is also preferably used.
Here, as a matter of course, the spinel structure includes a cubic system as a crystal system.

When the element substitution as described above is performed, the Li / Mn ratio (molar ratio) becomes (1 + Z) / (2-Z) in the case of excess Li in which Mn is replaced by Li, When substituted with a substitution element M other than Li, 1 /
(2-Z), so L is always L in any case.
The i / Mn ratio is> 0.5.

In the first invention, as described above, Li
It is preferable to use lithium manganate having an / Mn ratio of more than 0.5. As a result, the crystal structure is further stabilized as compared with the case where a stoichiometric composition is used, and thus a battery having excellent high temperature cycle characteristics can be obtained.

The substitution element M is theoretically
Li is +1, and Fe, Mn, Ni, Mg, and Zn are +2.
Valence, B, Al, Co, Cr are +3 valence, Si, Ti, Sn
Is +4 valence, P, V, Sb, Nb, Ta is +5 valence, Mo,
W becomes an ion with a valence of +6 and is an element that forms a solid solution in LiMn ₂ O ₄ , but with respect to Co and Sn, in the case of a valence of +2, F
e, Sb, and Ti are +3 valences, Mn is +3 valences, +4 valences, Cr is +4 valences, +
It may be hexavalent. Therefore, the various substitution elements M may exist in a state having mixed valences, and the amount of oxygen does not necessarily have to be 4 as represented by the theoretical chemical composition, and the crystal structure It may be deficient or excessively present within the range for maintaining.

In the lithium secondary battery of the first invention, the lattice constant of lithium manganate having a spinel structure used as a positive electrode active material is preferably 8.23 angstroms or less, and 8.22 angstroms or less. More preferably. If it is larger than 8.23 angstrom, improvement in high temperature cycle characteristics may not be observed. When the lithium secondary battery is repeatedly charged and discharged, lithium ions are repeatedly desorbed from the lithium manganate crystal lattice and inserted into the crystal lattice, which causes the crystal volume to repeatedly expand and contract. The structure easily deteriorates (breaks easily). At this time, the larger the lattice constant of the crystal is, the larger the volume change of the crystal is, and thus the crystal structure is more likely to be deteriorated.

Next, a method for synthesizing the lithium manganate having the above-mentioned thermal characteristics will be described. As the synthesis raw material, a salt and / or an oxide of each element (including the substituting element M when element substitution is performed) is used. The salt of each element is not particularly limited, but it is preferable to use an inexpensive salt having a suitable purity as a raw material. In addition, it is preferable to use carbonates, hydroxides, and organic acid salts that do not generate harmful decomposition gas during heating or firing. However, nitrates, hydrochlorides, sulfates and the like can also be used.
The Li raw material is usually Li ₂ which is an oxide.
O is difficult to handle because it has a strong hygroscopic property, and therefore a chemically stable carbonate is preferably used.

As described above, it is preferable to use the synthetic raw material (lithium carbonate, manganese dioxide, manganese carbonate, etc.) containing sodium at a predetermined concentration in the first invention. It is also possible to obtain these synthetic raw materials by adding a sodium source to a highly purified compound, but to synthesize a relatively inexpensive compound in which sodium as an impurity is inevitably mixed. It can also be used as a raw material. It is preferable to use such a synthetic raw material from the viewpoint of reducing the manufacturing cost of the lithium secondary battery.

A mixture of such synthetic raw materials in a predetermined ratio is first fired in an oxidizing atmosphere at 650 ° C. to 1000 ° C. for 5 hours to 50 hours. Here, the oxidizing atmosphere generally means an atmosphere having an oxygen partial pressure that causes an in-furnace sample to undergo an oxidation reaction, and specifically, an atmospheric atmosphere, an oxygen atmosphere and the like are applicable.

After the first firing, the composition uniformity is not always good, but the Li / Mn ratio>
When 0.5 is satisfied, that is, M with respect to stoichiometric composition
When elemental substitution of n is carried out, particularly in a composition with excess Li formed by substituting a part of Mn by Li, Ti, Mg, etc., one exhibiting predetermined thermal characteristics can be obtained even by firing once. It was confirmed experimentally that it would be easier. The reason for this is not clear, but it is presumed that the addition of the substitutional element M stabilizes the crystal structure.

As described above, with some compositions, it is possible to synthesize lithium manganate exhibiting predetermined thermal characteristics even by one-time firing, but a synthesis condition that is more independent of composition is established. Therefore, it is preferable to perform the firing twice or more.

The number of firings largely depends on the firing temperature and the firing time. When the firing temperature is low and / or the firing time is short, a large number of firings are required. Further, depending on the type of the substitution element M, from the viewpoint of uniform composition,
It may be preferable to increase the number of firings. In this case, it is considered that it is difficult to form a phase atmosphere suitable for crystal growth by adding the substitution element M.

However, since increasing the number of firings means that the production process is lengthened accordingly, it is preferable to keep the number of firings to a necessary minimum. The sample obtained by performing such firing a plurality of times has a sharper peak shape on the XRD chart than the sample obtained by performing the firing once. It can be confirmed that the improvement has been achieved.

The firing temperature is less than 600 ° C., and /
Or, when the firing time is less than 5 hours, X of the fired product
In the RD chart, a peak showing the residual of the raw material, for example, when lithium carbonate (Li ₂ CO ₃ ) is used as the lithium source, a peak of Li ₂ CO ₃ is observed and a single-phase product cannot be obtained. On the other hand, when the firing temperature is higher than 1000 ° C. and / or the firing time is longer than 50 hours, a high-temperature phase is generated in addition to the target crystal system compound, and a single-phase product cannot be obtained.

Further, when the firing is performed twice or more, it is preferable that the firing temperature in the next step is successively higher than the firing temperature in the previous step. For example, in the case of the second firing, the product obtained when the synthesis is performed with the second firing temperature being equal to or higher than the first firing temperature is a product obtained by using the conditions of the second firing temperature and the second firing time. The peak shape on the XRD chart protrudes sharper than the
The crystallinity can be improved.

The lithium manganate described above has a stable crystal structure and effectively suppresses the elution of Mn. Therefore, the lithium secondary manganese oxide according to the first aspect of the present invention which uses this as a positive electrode active material. Batteries have been particularly improved in high temperature cycle characteristics. Such improvement in high-temperature cycle characteristics is particularly remarkable in a large-capacity battery using a large amount of electrode active material, and therefore its application can be, for example, an EV or HEV motor drive power source. However, the first invention can be naturally applied to a small capacity battery such as a coin battery.

As the other member (material) for forming the lithium secondary battery of the first invention using the above-mentioned lithium manganate as the positive electrode active material, various conventionally known materials can be used. . For example, as the negative electrode active material, an amorphous carbonaceous material such as soft carbon or hard carbon, or a highly graphitized carbon material such as artificial graphite or natural graphite can be used. Above all, it is preferable to use a highly graphitized carbon material having a large lithium capacity.

Examples of the organic solvent used in the non-aqueous electrolytic solution include carbonate ester solvents such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC) and propylene carbonate (PC), γ-butyrolactone, and tetrahydrofuran. A single solvent or a mixed solvent such as acetonitrile is preferably used.

Examples of the electrolyte include lithium complex fluoride compounds such as lithium hexafluorophosphate (LiPF ₆ ) and lithium borofluoride (LiBF ₄ ), or lithium halides such as lithium perchlorate (LiClO ₄ ). One kind or two or more kinds are dissolved in the solvent and used. In particular, it is preferable to use LiPF ₆ which does not easily undergo oxidative decomposition and has high conductivity of the non-aqueous electrolyte.

The battery structure is a coin type battery in which a separator is placed between a plate-shaped positive electrode active material and a negative electrode active material and an electrolyte solution is filled in, or a positive electrode active material is applied to the surface of a metal foil. Cylindrical type or box type using an electrode body formed by winding or laminating a positive electrode plate formed by processing and a negative electrode plate formed by similarly applying a negative electrode active material on the surface of a metal foil with a separator interposed therebetween. Various batteries can be mentioned.

A second invention relates to a lithium secondary battery in which the positive electrode active material is lithium manganate having a spinel structure, and the sodium concentration of lithium manganate is 50 to 50%.
It is characterized in that it is 50,000 ppm and the boron concentration is 10 ppm or more, and it has excellent cycle characteristics at high temperatures. The details will be described below.

As described above, when the lithium secondary battery is used under high temperature conditions, hydrogen fluoride is unavoidably generated, and lithium manganate, which is the positive electrode active material, is used to generate M.
Since n easily elutes, the capacity of the positive electrode active material decreases, which tends to cause problems such as deterioration in cycle characteristics. However, since lithium manganate used in the lithium secondary battery of the second invention contains sodium at a predetermined concentration and boron at a predetermined concentration, lithium manganate under high temperature conditions is The Mn elution amount of is reduced. Therefore, the lithium secondary battery of the second invention is excellent in high-temperature cycle characteristics because it has a high efficiency of Li ⁺ insertion and desorption and can suppress the capacity decrease of the positive electrode active material itself. Second
In the invention described above, since boron is contained together with sodium, it becomes possible to obtain excellent high temperature characteristics in a wide range (50 to 50,000 ppm) of sodium concentration.

When the sodium concentration of lithium manganate is less than 50 ppm, it is not preferable because the effect of improving the high temperature cycle characteristics is not sufficient.
If it exceeds 000 ppm, it may adversely affect the battery characteristics, which is not preferable. When the boron concentration is less than 10 ppm, the high temperature cycle characteristics cannot be improved when the sodium concentration is high, which is not preferable.

Further, in the second invention, it is preferable that the boron concentration of lithium manganate is 4000 ppm or less. If it is more than 4000 ppm, sintering of particles of lithium manganate progresses and becomes hard,
A crushing process is required, which may increase the manufacturing cost.

In order to make the lithium manganate used as the positive electrode active material have a predetermined sodium concentration and a predetermined boron concentration, both the Li raw material and the Mn raw material containing appropriate amounts of sodium are used, and the boron-containing substance is added to the raw material. (B
₂ O ₃ etc.), a method in which sodium is contained at a high concentration in only one of the Li raw material and the Mn raw material, and a boron-containing substance (B ₂ O ₃ etc.) is mixed with this. , And a method of synthesizing lithium manganate having a low concentration of sodium, adding sodium to this, and further mixing a boron-containing substance (B ₂ O ₃ or the like), and the like. Whichever method is used, it is possible to keep the sodium concentration of lithium manganate finally used within a predetermined range.

However, in the lithium secondary battery produced by using the lithium manganate prepared by the above method, the improvement in high temperature cycle characteristics tends to be not remarkable. Although the reason why such a tendency is observed is not clear, the improvement of high temperature cycle characteristics, that is, the effect of effectively suppressing the generation of hydrogen fluoride depends on the distribution state of the sodium element in the crystal of lithium manganate. It is presumed that it depends. Therefore, as shown above,
In the lithium secondary battery of the second invention, both raw materials of Li and Mn containing sodium in an appropriate amount are used, and a boron-containing substance (B ₂ O ₃ etc.) is mixed with the raw material. Since it uses lithium manganate, it has more excellent high-temperature cycle characteristics.

In the lithium secondary battery of the second invention, the lithium manganate used as the positive electrode active material contains aluminum (Al) and vanadium (V) as well as sodium and boron as described above. It is preferably included. It is preferable that the lithium manganate contains aluminum and / or vanadium because the high temperature cycle characteristics of the lithium secondary battery are further improved. Aluminum concentration of lithium manganate is 10
Is preferably about 30,000 ppm, and is about 10 to 20
More preferably, it is 000 ppm. When it is less than 10 ppm, the effect containing aluminum may not be exhibited, and when it is more than 30,000 ppm,
Since the effect of further improving the high temperature cycle characteristics of the lithium secondary battery is not recognized, aluminum is wastefully used. The vanadium concentration of lithium manganate is 10-4
It is preferably 000 ppm. If it is less than 10 ppm, the effect containing vanadium may not be expressed, and if it is more than 4000 ppm, as in the case of vanadium, sintering of particles of lithium manganate progresses and becomes hard, A crushing process is required, which may increase the manufacturing cost.

In the lithium secondary battery of the second invention, lithium manganate having a spinel structure is used as the positive electrode active material. The stoichiometric composition of lithium manganate is represented by LiMn ₂ O ₄ , but the second invention is not limited to such a stoichiometric composition, and a part of the transition element Mn contains Ti. , Li, Fe,
Ni, Mg, Zn, B, Al, Co, Cr, Si, S
n, P, V, Sb, Nb, Ta, composed of one or more elements selected from the group consisting of Mo and W, LiM formed by substituted in two or more kinds of elements _Z Mn _2-Z O ₄ (provided that, M is a substitution element, and Z is a substitution amount.) Is also preferably used.
Here, as a matter of course, the spinel structure includes a cubic system as a crystal system.

When the element substitution as described above is performed, the Li / Mn ratio (molar ratio) becomes (1 + Z) / (2-Z) in the case of excess Li in which Mn is replaced by Li, When substituted with a substitution element M other than Li, 1 /
(2-Z), so L is always L in any case.
The i / Mn ratio is> 0.5.

In the second invention, as described above, Li
It is preferable to use lithium manganate having an / Mn ratio of more than 0.5. As a result, the crystal structure is further stabilized as compared with the case where a stoichiometric composition is used, and thus a battery having excellent high temperature cycle characteristics can be obtained.

The substitution element M is theoretically
Li is +1, and Fe, Mn, Ni, Mg, and Zn are +2.
Valence, B, Al, Co, Cr are +3 valence, Si, Ti, Sn
Is +4 valence, P, V, Sb, Nb, Ta is +5 valence, Mo,
W becomes an ion with a valence of +6 and is an element that forms a solid solution in LiMn ₂ O ₄ , but with respect to Co and Sn, in the case of a valence of +2, F
e, Sb, and Ti are +3 valences, Mn is +3 valences, +4 valences, Cr is +4 valences, +
It may be hexavalent. Therefore, the various substitution elements M may exist in a state having mixed valences, and the amount of oxygen does not necessarily have to be 4 as represented by the theoretical chemical composition, and the crystal structure It may be deficient or excessively present within the range for maintaining.

In the lithium secondary battery of the second invention, the lattice constant of lithium manganate having a spinel structure, which is used as a positive electrode active material, is preferably 8.23 angstroms or less, and 8.22 angstroms or less. More preferably. If it is larger than 8.23 angstrom, improvement in high temperature cycle characteristics may not be observed. When the lithium secondary battery is repeatedly charged and discharged, lithium ions are repeatedly desorbed from the lithium manganate crystal lattice and inserted into the crystal lattice, which causes the crystal volume to repeatedly expand and contract. The structure easily deteriorates (breaks easily). At this time, the larger the lattice constant of the crystal is, the larger the volume change of the crystal is, and thus the crystal structure is more likely to be deteriorated.

Next, a method for synthesizing the lithium manganate having the above-mentioned thermal characteristics will be described. As the synthesis raw material, a salt and / or an oxide of each element (including the substituting element M when element substitution is performed) is used. The salt of each element is not particularly limited, but it is preferable to use an inexpensive salt having a suitable purity as a raw material. In addition, it is preferable to use carbonates, hydroxides, and organic acid salts that do not generate harmful decomposition gas during heating or firing. However, nitrates, hydrochlorides, sulfates and the like can also be used.
The Li raw material is usually Li ₂ which is an oxide.
O is difficult to handle because it has a strong hygroscopic property, and therefore a chemically stable carbonate is preferably used. B ₂ O ₃ is preferably used as the boron raw material.

Here, in the second invention, it is preferable to use a synthetic raw material (lithium carbonate, manganese dioxide, manganese carbonate, etc.) containing sodium at a predetermined concentration. Although it is possible to obtain these synthetic raw materials by adding a sodium source to a highly purified compound, a relatively inexpensive compound in which sodium as an impurity is inevitably mixed is used as a synthetic raw material. Can also be used as It is preferable to use such a synthetic raw material from the viewpoint of reducing the manufacturing cost of the lithium secondary battery.

A mixture of such synthetic raw materials in a predetermined ratio is first fired in an oxidizing atmosphere at 650 ° C. to 1000 ° C. for 5 hours to 50 hours. Here, the oxidizing atmosphere generally means an atmosphere having an oxygen partial pressure that causes an in-furnace sample to undergo an oxidation reaction, and specifically, an atmospheric atmosphere, an oxygen atmosphere and the like are applicable.

After the first firing, the composition uniformity is not always good, but the Li / Mn ratio>
When 0.5 is satisfied, that is, M with respect to the stoichiometric composition
When elemental substitution of n is carried out, particularly in a composition with excess Li formed by substituting a part of Mn by Li, Ti, Mg, etc., one exhibiting predetermined thermal characteristics can be obtained even by firing once. It was confirmed experimentally that it would be easier. The reason for this is not clear, but it is presumed that the addition of the substitutional element M stabilizes the crystal structure.

As described above, with some compositions, it is possible to synthesize lithium manganate exhibiting predetermined thermal characteristics even by one-time firing, but a synthesis condition that is more independent of composition is established. Therefore, it is preferable to perform firing twice or more.

The number of firings largely depends on the firing temperature and the firing time. When the firing temperature is low and / or the firing time is short, a large number of firings are required. Further, depending on the type of the substitution element M, from the viewpoint of uniform composition,
It may be preferable to increase the number of firings. In this case, it is considered that it is difficult to form a phase atmosphere suitable for crystal growth by adding the substitution element M.

However, increasing the number of firings means lengthening the production process accordingly, so it is preferable to keep the number of firings to the necessary minimum. The sample obtained by performing such firing a plurality of times has a sharper peak shape on the XRD chart than the sample obtained by performing the firing once. It can be confirmed that the improvement has been achieved.

The firing temperature is less than 600 ° C., and /
Or, when the firing time is less than 5 hours, X of the fired product
In the RD chart, a peak showing the residual of the raw material, for example, when lithium carbonate (Li ₂ CO ₃ ) is used as the lithium source, a peak of Li ₂ CO ₃ is observed and a single-phase product cannot be obtained. On the other hand, when the firing temperature is higher than 1000 ° C. and / or the firing time is longer than 50 hours, a high-temperature phase is generated in addition to the target crystal system compound, and a single-phase product cannot be obtained.

When the firing is performed twice or more, it is preferable that the firing temperature in the next step is successively higher than the firing temperature in the previous step. For example, in the case of the second firing, the product obtained when the synthesis is performed with the second firing temperature being equal to or higher than the first firing temperature is a product obtained by using the conditions of the second firing temperature and the second firing time. The peak shape on the XRD chart protrudes sharper than the
The crystallinity can be improved.

Since the lithium manganate described above has a stable crystal structure and effectively suppresses the elution of Mn, it is used as a positive electrode active material in the lithium secondary battery according to the second invention. Batteries have been particularly improved in high temperature cycle characteristics. Such improvement in high-temperature cycle characteristics is particularly remarkable in a large-capacity battery using a large amount of electrode active material, and therefore its application can be, for example, an EV or HEV motor drive power source. However, the second invention can be naturally applied to a small capacity battery such as a coin battery.

As the other member (material) for forming the lithium secondary battery of the second invention using the above-mentioned lithium manganate as the positive electrode active material, various conventionally known materials can be used. . For example, as the negative electrode active material, an amorphous carbonaceous material such as soft carbon or hard carbon, or a highly graphitized carbon material such as artificial graphite or natural graphite can be used. Above all, it is preferable to use a highly graphitized carbon material having a large lithium capacity.

Examples of the organic solvent used in the non-aqueous electrolytic solution include carbonic acid ester solvents such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC) and propylene carbonate (PC), γ-butyrolactone and tetrahydrofuran. A single solvent or a mixed solvent such as acetonitrile is preferably used.

Examples of the electrolyte include lithium complex fluoride compounds such as lithium hexafluorophosphate (LiPF ₆ ) and lithium borofluoride (LiBF ₄ ), or lithium halides such as lithium perchlorate (LiClO ₄ ). One kind or two or more kinds are dissolved in the solvent and used. In particular, it is preferable to use LiPF ₆ which does not easily undergo oxidative decomposition and has high conductivity of the non-aqueous electrolyte.

The battery structure is a coin-type battery in which a separator is placed between a plate-shaped positive electrode active material and a negative electrode active material and filled with an electrolytic solution, or a surface of a metal foil is coated with the positive electrode active material. Cylindrical type or box type using an electrode body formed by winding or laminating a positive electrode plate formed by processing and a negative electrode plate formed by similarly applying a negative electrode active material on the surface of a metal foil with a separator interposed therebetween. Various batteries can be mentioned.

[0082]

EXAMPLES Hereinafter, the present invention (first invention and second invention) will be specifically described by way of examples, but the present invention is not limited to these examples. (Synthesis of lithium manganate) Li ₂ C as a starting material
Using O ₃ , MnO ₂ or MnCO ₃ , LiMn ₂ O
Each was weighed and mixed so as to have a composition of ₄ . Then, it was baked in an oxidizing atmosphere at 800 ° C. for 24 hours to synthesize lithium manganate (Examples 1 to 12, Comparative Examples 1 to 4). The starting materials Li ₂ CO ₃ , MnO ₂
Alternatively, MnCO ₃ and Na of the obtained LiMn ₂ O ₄
The concentration (ppm) was quantified by plasma induced emission spectroscopy (ICP). The results are shown in Tables 1 and 2.

[0083]

[Table 1]

[0084]

[Table 2]

Further, as starting materials, Li ₂ CO ₃ and Mn are used.
Using O ₂ or MnCO ₃ , each was weighed so as to have a composition of LiMn ₂ O ₄ , and further, Al ₂ O ₃ or B ₂ O ₃
Was mixed in a predetermined amount. Then, in an oxidizing atmosphere, 800 ° C.,
It was calcined for 24 hours to synthesize lithium manganate (Examples 13 to 41, Comparative Examples 5 to 8). For Examples 25 to 28, the amount of Li ₂ CO _{3 and the} amount of MnO ₂ were adjusted during synthesis to change the lattice constant. The concentrations (ppm) of Na, Al and B of the obtained LiMn ₂ O ₄ were quantified by plasma induced emission analysis (ICP). In addition, Example 1
Regarding 5, 21, 25 to 28, the lattice constant was also measured by the following method. The results are shown in Table 3. In addition, Examples 1-40 and Comparative Examples 1-4 are Examples and Comparative Examples of the first invention, and Example 41 and Comparative Examples 5-8 are Examples and Comparative Example of the second invention.

[0086]

[Table 3]

(Measurement Method of Lattice Constant) Using a “powder X-ray diffractometer RINT” manufactured by Rigaku Denki Co., Ltd., X-ray diffraction measurement was performed under the following conditions. The X-ray diffraction pattern of the obtained positive electrode active material was measured by "RINT2" manufactured by Rigaku Denki Co., Ltd.
000 series application software WPP
F program ”was used for analysis to determine the lattice constant of the positive electrode active material. At the time of measurement, ZnO was used as an internal standard substance.

X-ray diffraction measurement conditions: X-ray source: CuKα ray Tube voltage and tube current: 50kV, 300mA Divergence slit: 0.5 deg Scattering slit: 0.5 deg Light receiving slit: 0.15mm Step: 0.02 ° Counting time: 0.5 sec Scanning range: 10-120 °

(Lithium manganate immersion treatment in electrolytic solution)
5 g each of the synthesized lithium manganate (Examples 1 to 41 and Comparative Examples 1 to 8) was mixed with ethylene carbonate (EC) and diethyl carbonate (DEC) in an equal volume ratio (1: 1).
1m of LiPF ₆ as an electrolyte in the organic solvent mixed in
20m prepared by dissolving to a concentration of ol / l
It was immersed in an electrolytic solution at 80 ° C. for 400 hours. Next, each sample (lithium manganate) was separated from the electrolytic solution by a filter paper filter, and washed with ethylene carbonate (EC) in this order, a mixed organic solvent of ethylene carbonate (EC) and diethyl carbonate (DEC).

In addition, plasma induced emission analysis (IC
Pn was used to quantify the Mn eluted in the electrolytic solution (Mn elution amount (%)). The results are shown in Table 4 (Mn source is MnO ₂ or MnCO ₃ , containing sodium) and Table 5 (Mn source is Mn
O ₂ , containing sodium, containing aluminum or boron),
Table 6 (Mn source contains MnCO ₃ , sodium, aluminum or boron), Table 7 (Mn source contains MnO ₂ , sodium, aluminum or boron, lattice constant changed)
Shown in. In addition, the Mn elution amount (%) is shown in Examples 1 to 6, Examples 13 to 15, Examples 19 to 21, and Examples 25 to 3.
1, Example 35 to 37, Example 41, Comparative Example 2 and Comparative Examples 5 to 8 are Examples 7 to 12 and Example 16 when the Mn elution amount (mass) of Comparative Example 1 is 100%. ~ 1
8, Examples 22 to 24, Examples 32 to 34, and Example 38
˜40 and Comparative Example 4 are relative values when the Mn elution amount (mass) of Comparative Example 3 is 100%.

(Production of Battery) Using the above-mentioned lithium manganate (Examples 1 to 41 and Comparative Examples 1 to 8) as a positive electrode active material, acetylene black powder as a conduction aid and polyvinylidene fluoride as a binder were used. A positive electrode material was prepared by adding and mixing in a mass ratio of 50: 2: 3. 0.02 g of the positive electrode material has a diameter of 20 m at a pressure of 300 kg / cm ^2.
A positive electrode was obtained by press-molding into a disk shape of mφ. Next, ethylene carbonate (EC) and diethyl carbonate (D
EC) in an organic solvent mixed in an equal volume ratio (1: 1),
A coin cell was prepared using an electrolyte prepared by dissolving LiPF ₆ as an electrolyte to a concentration of 1 mol / l, a negative electrode made of carbon, a separator separating the positive electrode and the negative electrode, and the positive electrode prepared as described above. (Example 1
~ 41, Comparative Examples 1-8).

(Evaluation of High-Temperature Cycle Characteristics) The coin cells (Examples 1 to 41, Comparative Examples 1 to 8) thus prepared were heated to an internal temperature of 60 ° C.
Installed in a constant temperature bath of 1C, depending on the capacity of the positive electrode active material, 1C
The battery was charged to 4.1 V at a constant rate current and a constant voltage. Next, similarly, charging / discharging for discharging up to 2.5 V at a constant current of 1 C rate was set as one cycle, 100 cycles were performed, and the cycle efficiency (%) after 100 cycles was calculated. The results are shown in Tables 4-7. The “cycle efficiency (%)” is a numerical value obtained by dividing the discharge capacity after 100 cycles by the initial discharge capacity.

[0093]

[Table 4]

[0094]

[Table 5]

[0095]

[Table 6]

[0096]

[Table 7]

(Discussion) In the first invention, the higher the sodium concentration of lithium manganate, the more M in the electrolytic solution.
It was found that the n elution amount was suppressed and the progress of destruction of the crystal structure was suppressed. Then, it was found that the inclusion of aluminum or boron further suppressed the elution amount of Mn in the electrolytic solution, and further suppressed the progress of destruction of the crystal structure. Either aluminum or boron may be contained as in this embodiment, but even if aluminum and boron are contained at the same time, the elution of Mn into the electrolytic solution is effectively suppressed. Further, in Comparative Examples 2 and 4, it was found that although the Mn elution amount was the smallest, the cycle efficiency also tended to decrease. That is,
It has been clarified that the sodium concentration of lithium manganate is preferably within an appropriate numerical range in terms of cycle characteristics. Even when boron is replaced by vanadium, these effects are almost the same as in the case of boron.

Therefore, it can be confirmed that the lithium secondary battery of the first invention using lithium manganate having a sodium concentration within a predetermined numerical range as the positive electrode active material has excellent high temperature cycle characteristics. Further, it was confirmed that when the aluminum concentration and / or the boron concentration and / or the vanadium concentration were set within a predetermined numerical range, the high temperature cycle characteristics were further excellent.

In addition, it can be seen from Table 7 that the smaller the lattice constant, the smaller the amount of Mn eluted and the better the cycle efficiency. In the present embodiment, MnO ₂ is used as the Mn source of the raw material, but similarly, when MnCO ₃ is used, the smaller the lattice constant is, the more the cycle characteristics are improved. Even when boron is replaced by vanadium, the same effect as that of boron can be obtained.

As is clear from the results shown in Table 5, the second
In the invention of No. 4, when Example 41 and Comparative Example 5 are compared, even if the sodium concentration is as large as about 50,000 ppm, if the boron concentration is a predetermined value (10 ppm or more), the cycle characteristics are good due to the presence of boron. I can say.
On the other hand, when the sodium concentration is larger than 50,000 ppm, it can be said that the cycle efficiency is better with boron, but it is not so good as compared with the sodium concentration and the boron concentration within the predetermined ranges. However, it can be said that Comparative Example 7 is better than Comparative Example 6 due to the effect of boron. Further, looking at Comparative Example 8, the cycle characteristics are poor because the sodium concentration is outside the predetermined range, even though the boron concentration is within the predetermined range. From these results, it is considered that there is some interaction between sodium and boron, and it was found that the cycle efficiency is improved when the concentrations of sodium and boron are within the concentration range specified by the second invention.

[0101]

As described above, in the lithium secondary battery of the first invention, since the sodium concentration of lithium manganate having a spinel structure used as the positive electrode active material is within a predetermined numerical range, the electrolytic solution The elution of Mn into the inside is effectively suppressed, and the high temperature cycle characteristics are excellent. The lithium secondary battery of the second invention is
Since the sodium concentration and the boron concentration of the lithium manganate having a spinel structure used as the positive electrode active material are within the predetermined numerical range, the lithium manganate has a characteristic that the high temperature cycle characteristic is excellent due to the interaction between sodium and boron.

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Claims (31)

[Claims] 1. A lithium secondary battery in which the positive electrode active material is lithium manganate having a spinel structure, and the sodium concentration of the lithium manganate is 50 to 50.
Lithium secondary battery, which is 00 ppm. 2. The lithium secondary battery according to claim 1, wherein the lithium manganate is synthesized by using lithium carbonate having a sodium concentration of 30 ppm or more and manganese dioxide having a sodium concentration of 50 ppm or more. . 3. The lithium carbonate has a sodium concentration of 1
The lithium secondary battery according to claim 2, wherein the content is 00 ppm or more. 4. The lithium secondary battery according to claim 2, wherein the sodium concentration of the manganese dioxide is 400 ppm or more. 5. The lithium secondary battery according to claim 1, wherein the lithium manganate is synthesized using lithium carbonate having a sodium concentration of 30 ppm or more and manganese carbonate having a sodium concentration of 35 ppm or more. . 6. The lithium carbonate has a sodium concentration of 1
The lithium secondary battery according to claim 5, which has a content of 00 ppm or more. 7. The manganese carbonate has a sodium concentration of 1
The lithium secondary battery according to claim 5, which has a content of 00 ppm or more. 8. The lithium secondary battery according to claim 1, wherein the lithium manganate has a sodium concentration of 500 to 4000 ppm. 9. The lithium secondary battery according to claim 1, wherein the sodium concentration of the lithium manganate is 1000 to 3000 ppm. 10. The lithium manganate has an aluminum concentration of 10 to 30000 ppm and / or a boron concentration of 10 to 4000 ppm and / or a vanadium concentration of 1.
It is 0-4000 ppm, The lithium secondary battery as described in any one of Claims 1-9. 11. The aluminum concentration is 10 to 200.
It is 00 ppm, The lithium secondary battery of Claim 10. 12. The boron concentration is 10 to 2000 ppm.
The lithium secondary battery according to claim 10, which is 13. The vanadium concentration is 10 to 2000.
It is ppm, The lithium secondary battery of Claim 10. 14. Li / Mn of the lithium manganate
The lithium secondary battery according to any one of claims 1 to 13, wherein the ratio is more than 0.5. 15. The lithium manganate (LiMn ₂
Part of the transition element Mn in O ₄ ) contains Ti, and in addition, Li, Fe, Ni, Mg, Zn, B, Al, Co,
Cr, Si, Sn, P, V, Sb, Nb, Ta, composed of one or more elements selected from the group consisting of Mo and W, formed by substitution in two or more kinds of elements LiM _Z Mn _2-Z O
The lithium secondary battery according to any one of claims 1 to 14, wherein ₄ (wherein M represents a substitution element and Z represents a substitution amount) is used as a positive electrode active material. 16. The lithium secondary battery according to claim 1, wherein the lithium manganate has a lattice constant of 8.23 angstroms or less. 17. The lithium secondary battery according to claim 16, wherein the lattice constant of the lithium manganate is 8.22 angstroms or less. 18. A mixture of salts and / or oxides of the respective elements in which the lithium manganate is adjusted to a predetermined ratio is fired in an oxidizing atmosphere at 650 to 1000 ° C. for 5 to 50 hours. The lithium secondary battery according to any one of claims 1 to 17, which is obtained. 19. The lithium secondary battery according to claim 18, wherein the lithium manganate is obtained by performing the firing twice or more. 20. The lithium secondary battery according to claim 19, wherein the lithium manganate is obtained by sequentially increasing the firing temperature each time the firing is repeated. 21. A lithium secondary battery in which the positive electrode active material is lithium manganate having a spinel structure, wherein the sodium concentration of the lithium manganate is 50 to 50.
A lithium secondary battery having a concentration of 000 ppm and a boron concentration of 10 ppm or more. 22. The lithium secondary battery according to claim 21, wherein the boron concentration is 4000 ppm or less. 23. The aluminum concentration of lithium manganate is 10 to 30000 ppm and / or the vanadium concentration is 10 to 4000 ppm.
2. The lithium secondary battery described in 2. 24. The aluminum concentration is 10 to 200.
The lithium secondary battery according to claim 23, which has a concentration of 00 ppm. 25. Li / Mn of the lithium manganate
The lithium secondary battery according to any one of claims 21 to 24, which has a ratio of more than 0.5. 26. The lithium manganate (LiMn ₂
Part of the transition element Mn in O ₄ ) contains Ti, and in addition, Li, Fe, Ni, Mg, Zn, B, Al, Co,
Cr, Si, Sn, P, V, Sb, Nb, Ta, composed of one or more elements selected from the group consisting of Mo and W, formed by substitution in two or more kinds of elements LiM _Z Mn _2-Z O
The lithium secondary battery according to any one of claims 21 to 25, wherein ₄ (wherein M represents a substitution element and Z represents a substitution amount) is used as a positive electrode active material. 27. The lithium-manganese oxide having a lattice constant of 8.23 angstroms or less.
The lithium secondary battery according to any one of 1. 28. The lithium secondary battery according to claim 27, wherein the lattice constant of the lithium manganate is 8.22 angstroms or less. 29. A mixture of salts and / or oxides of the respective elements, in which the lithium manganate is adjusted to a predetermined ratio, is fired in an oxidizing atmosphere at 650 to 1000 ° C. for 5 to 50 hours. The lithium secondary battery according to any one of claims 21 to 28, which is obtained. 30. The lithium secondary battery according to claim 29, wherein the lithium manganate is obtained by performing the firing twice or more. 31. The lithium secondary battery according to claim 30, wherein the lithium manganate is obtained by sequentially increasing the firing temperature each time the firing is repeated.