JP2008066028A - Lithium manganate for lithium secondary battery positive electrode secondary active material, and manufacturing method of lithium manganate, lithium secondary battery positive electrode active material, and lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent easy deterioration of discharge capacity at normal use, and to reduce deterioration of performance due to over discharge. <P>SOLUTION: This is lithium manganate for a lithium secondary battery positive electrode secondary active material which is expressed by a general formula (1) Li<SB>x</SB>MnO<SB>2</SB>(in the formula, 0.90≤x≤1.05), and L* value is 25.0-32.0, a* is -1.50 to -0.15, b* is 2.50-8.00 in an L*a*b* table color system. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a lithium manganate used as a positive electrode active material of a lithium secondary battery, a method for producing lithium manganate used for the production of the lithium manganate, and a lithium secondary battery containing the lithium manganate as a positive electrode active material. The present invention relates to a secondary battery positive electrode active material and a lithium secondary battery.

  In recent years, as home appliances have become portable and cordless, lithium ion secondary batteries have been put to practical use as power sources for small electronic devices such as laptop computers, mobile phones, and video cameras. Regarding this lithium ion secondary battery, in 1980, Mizushima et al. Reported that lithium cobalt oxide was useful as a positive electrode active material for lithium ion secondary batteries ("Material Research Bulletin" vol15, P783-789 (1980)). Since then, research and development on lithium-based composite oxides has been actively promoted, and many proposals have been made so far.

  However, in a lithium secondary battery using a lithium-based composite oxide as a positive electrode active material, a copper foil used as a negative electrode current collector elutes in the electrolyte during overdischarge, and a part of it is deposited on the positive electrode. As a result, there is a problem that charge / discharge characteristics are easily deteriorated. For this reason, a method for preventing overdischarge itself by providing an electric circuit for preventing overdischarge on the outside of the battery is used. The cost of battery packs and the like increases.

The positive electrode active material of the lithium secondary battery is a positive electrode active material containing a lithium-based composite oxide as a main active material and not containing a secondary active material. On the other hand, the lithium composite oxide such as LiCoO ₂ as a main active material, a method, i.e., lithium-based composite oxide such as LiCoO ₂ as a main active material used was added thereto LiMnO ₂ as a subsidiary active substance, A lithium secondary battery positive electrode active material containing LiMnO ₂ as a secondary active material has been proposed. For example, Japanese Patent Application Laid-Open No. 6-349493 of Patent Document 1 discloses a non-aqueous electrolyte secondary battery prepared using a mixture of lithium-containing composite oxide such as LiCoO ₂ and LiMnO ₂ as a positive electrode active material. ing. LiMnO ₂ used in Patent Document 1 is manufactured by firing MnO ₂ and lithium carbonate in an inert gas atmosphere. LiMnO ₂ obtained in Patent Document 1 is used as a positive electrode secondary active material. In the lithium secondary battery, although the problem of overdischarge was improved to some extent, problems such as a decrease in discharge capacity during normal use were likely to occur. Therefore, development of a lithium secondary battery positive electrode secondary active material capable of imparting excellent battery performance to the lithium secondary battery is desired.

Japanese Patent Application Laid-Open No. 2002-151079 of Patent Document 2 discloses lithium using LiMnO ₂ obtained by baking a mixture of Mn ₂ O ₃ obtained by heat treatment of MnO ₂ and a lithium compound as a positive electrode active material. Although a secondary battery is disclosed, even if LiMnO _{2 of} Patent Document 2 is used as a positive electrode secondary active material, it is not sufficient as a solution for problems such as overdischarge and reduction in discharge capacity. .

  Further, the present applicants proposed lithium manganate used as a positive electrode secondary active material of a lithium secondary battery in Japanese Patent Application Laid-Open No. 2005-235416 of Patent Document 3 or Japanese Patent Application Laid-Open No. 2006-139945 of Patent Document 4. is doing. According to the lithium secondary battery positive electrode secondary active material of Patent Document 3 or Patent Document 4, although problems such as overdischarge and a decrease in discharge capacity can be improved to some extent, further improvement is required.

JP-A-6-349493 (Claims) JP 2002-151079 A (Claims, Example 2) Japanese Patent Laying-Open No. 2005-235416 (Claims) JP 2006-139945 A (Claims)

  Accordingly, an object of the present invention is to provide a lithium secondary battery positive electrode secondary active material that is less likely to have a reduced discharge capacity during normal use and can reduce performance deterioration due to overdischarge, a method for producing the same, and a lithium secondary battery positive electrode secondary battery. An object of the present invention is to provide a positive electrode active material for a lithium secondary battery using an active material, and to provide a lithium secondary battery in which the discharge capacity is unlikely to decrease during normal use and the performance is not deteriorated due to overdischarge.

As a result of intensive studies to solve the problems in the prior art, the present inventors have found that lithium manganate having a specific range of colors in the L ^* a ^* b ^* color system is excellent as a positive electrode secondary active material. The present inventors have found that the lithium secondary battery can be imparted with the battery performance, specifically, the battery performance in which the capacity does not easily decrease during normal use and the effect of suppressing overdischarge is excellent.

That is, the present invention (1) includes the following general formula (1):
Li _x MnO ₂ (1)
(In the formula, 0.90 ≦ x ≦ 1.05.)
Represented by
In the L ^* a ^* b ^* color system, it ^{L *} value from 25.0 to 32.0, ^{a *} is -1.50~-0.15, ^{b *} is 2.50 to 8.00,
A lithium manganate for a secondary active material of a positive electrode for a lithium secondary battery is provided.

In addition, the present invention (2) includes a first step of obtaining MnO by firing non-basic manganese carbonate at 500 to 800 ° C. in an inert gas atmosphere having an oxygen concentration of 1% by volume or less,
MnO obtained by performing the first step is baked at 525 to 950 ° C. in an atmosphere having an oxygen concentration of 10% by volume or more to obtain Mn ₂ O ₃ ;
Mn ₂ O ₃ obtained by performing the second step and a lithium compound are mixed so that the molar ratio of lithium atoms to manganese atoms is 0.90 to 1.05 to obtain a reaction raw material mixture, A third step in which the reaction raw material mixture is calcined at 600 to 950 ° C. in an inert gas atmosphere having an oxygen concentration of 1% by volume or less to obtain lithium manganate;
The present invention provides a method for producing lithium manganate characterized by comprising:

Further, the present invention (3) includes lithium manganate for a lithium secondary battery positive electrode side active material according to the present invention (1),
The following general formula (2):
Li _(a) M _(1-b) A _(b) O _(c) (2)
(In the formula, M represents one or more metal elements selected from Co and Ni, and A represents Mg, Al, Ti, Zr, Fe, Cu, Zn, Sn, In, Ca, Ba, Sr, and Mn. 1 or more kinds of metal elements, 0.9 ≦ a ≦ 1.1, 0 ≦ b ≦ 0.5, and 1.8 ≦ c ≦ 2.2.)
Lithium composite oxide represented by
The present invention provides a positive electrode active material for a lithium secondary battery characterized by containing

  Moreover, this invention (4) provides the lithium secondary battery characterized by being obtained using the lithium secondary battery positive electrode active material of the said this invention (3) as a positive electrode active material.

  According to the present invention, a lithium secondary battery positive electrode side active material, a method for producing the same, and a lithium secondary battery positive electrode side active material that are less likely to have a reduced discharge capacity during normal use and can suppress deterioration in performance due to overdischarge. It is possible to provide a positive electrode active material for a lithium secondary battery using the substance, and to provide a lithium secondary battery in which the discharge capacity hardly decreases during normal use and the performance is not deteriorated due to overdischarge.

The lithium manganate of the present invention is represented by the general formula (1),
In the L ^* a ^* b ^* color system, the L ^* value is 25.0 to 32.0, a ^* is -1.50 to -0.15, and b ^* is 2.50 to 8.00.
It is a lithium manganate for a secondary active material of a lithium secondary battery positive electrode. That is, the lithium manganate of the present invention is lithium manganate used as a lithium secondary battery positive electrode secondary active material constituting the lithium secondary battery positive electrode active material.

  In the general formula (1), the value of x is 0.90 ≦ x ≦ 1.05, preferably 0.95 ≦ x ≦ 1.01. When the value of x is in the above range, the lithium supply capability of lithium manganate is increased.

  The lithium manganate of the present invention is a single-phase lithium manganate in X-ray diffraction analysis.

And the lithium manganate of this invention is lithium manganate conventionally used as a lithium secondary battery positive electrode side active material among lithium manganate represented by the said General formula (1) (henceforth the said general formula). Among lithium manganates represented by (1), lithium manganate that has been conventionally used as a secondary active material for positive electrodes of lithium secondary batteries is also simply referred to as conventional lithium manganate). Different. That is, the L ^* value in the L ^* a ^* b ^* color system of the lithium manganate of the present invention is 25.0 to 32.0, preferably 26.0 to 31.0, and the a ^* value is −1. .50 to -0.15, preferably -1.00 to -0.10, and b ^* value is 2.50 to 8.00, preferably 3.50 to 7.00. When the L ^* value, a ^* value, and b ^* value in the L ^* a ^* b ^* color system of the lithium manganate of the present invention are within the above ranges, excellent battery performance is imparted to the lithium secondary battery. Therefore, it is possible to obtain a lithium ion secondary battery in which the discharge capacity is hardly reduced and the performance is not deteriorated due to overdischarge. On the other hand, the conventional lithium ^manganate, L ^* a * ^{b *} color ^{L *} value of about 15 to 40 in the system, ^{a *} value of about -10 to-5, ^{b *} values of about 11 to 18. In the present ^{invention, L * a * b * L} * values in a color system, ^{a *} and ^{b *} values are the color difference measured by a color difference meter is defined in Japanese Industrial Standard JIS Z 8730 .

The L ^* value in the L ^* a ^* b ^* color system represents lightness ^{. The} higher the value, the whiter the color, the 100 becomes perfect white, the smaller the value, the black, and 0 the complete black. The a value and the b value represent hues, and the larger the a value, the deeper the red color, the smaller the a value, the darker the green color, the larger the b value, the darker the yellow color, and the smaller the b value, the blue color. It becomes darker.

  Although the lithium manganate of the present invention is a powder, the color difference measurement of the powder includes a method of slurrying a powder sample, a method of pelletizing, a method of measuring by filling a dedicated petri dish, and the like. However, in the lithium manganate of the present invention, a method of measuring in a petri dish is preferable. This is not preferable because it is a method of slurrying lithium manganate, because it causes a change in composition due to Li desorption in the slurry and causes a color change. Also, if it is a method of pelletizing, the pellet surface This is because it is not preferable because color change occurs due to reflection or pressurization.

  The average particle diameter of the lithium manganate of the present invention is preferably from 1 to 25 μm from the viewpoint that a uniform electrode sheet can be applied and deterioration of battery performance due to current concentration can be suppressed. It is particularly preferred that In the present invention, the average particle size is a value determined by a laser particle size distribution measurement method.

The BET specific surface area of the lithium manganate of the present invention is 0.2 to 2.0 m in that it can suppress the deterioration of the performance of the lithium secondary battery due to elution of Mn or supply Li at a high rate. ² / g is preferable, and 0.4 to 1.0 m ² / g is particularly preferable.

  The pH of the dispersion when the lithium manganate of the present invention is dispersed in water is preferably 12 or less, and preferably 11.5 or less from the viewpoint of suppressing gas generation and gelation of the positive electrode mixture paint. It is particularly preferred. The lower limit of the pH of the dispersion when the lithium manganate of the present invention is dispersed in water is preferably 9.5 because the lithium manganate of the present invention itself is weakly basic. . In the present invention, the pH when lithium manganate is dispersed in water means that after adding 100 g of pure water to 5 g of a lithium manganate sample and stirring at 25 ° C. for 5 minutes, the solution is further allowed to stand for 5 minutes. The value obtained by measuring the pH of the supernatant with a pH meter is shown.

  When the lithium manganate of the present invention is contained in a lithium secondary battery positive electrode active material, in other words, as a lithium secondary battery positive electrode secondary active material, it is used in combination with a lithium secondary battery main active material. A lithium secondary battery having excellent performance, that is, a discharge capacity that is difficult to decrease during normal use and little deterioration in performance due to overdischarge is provided.

The lithium manganate of the present invention comprises Mn ₂ O ₃ and a lithium compound obtained by firing MnO at 525 ° C. or more, and a molar ratio of Li atoms in the lithium compound to Mn atoms in Mn ₂ O ₃ (Li / Mn) can be obtained by firing at 600 ° C. to 950 ° C. to obtain a uniform mixture obtained by mixing so that 0.90 to 1.05, and particularly relates to the method for producing lithium manganate of the present invention described below. Lithium manganate obtained by sequentially performing the first step to the third step is preferable because of its large Li supply capability.

The method for producing lithium manganate of the present invention comprises a first step of obtaining MnO by firing non-basic manganese carbonate at 500 to 800 ° C. in an inert gas atmosphere having an oxygen concentration of 1% by volume or less,
MnO obtained by performing the first step is baked at 525 to 950 ° C. in an atmosphere having an oxygen concentration of 10% by volume or more to obtain Mn ₂ O ₃ ;
Mn ₂ O ₃ obtained by performing the second step and a lithium compound are mixed so that the molar ratio of lithium atom to manganese atom (Li / Mn) is 0.90 to 1.05, and a reaction raw material mixture Then, the reaction raw material mixture is fired at 600 to 950 ° C. in an inert gas atmosphere having an oxygen concentration of 1% by volume or less to obtain lithium manganate,
Have

  The first step is a step of baking MnO to obtain MnO.

  The non-basic manganese carbonate according to the first step means that 10 g of manganese carbonate is added to 100 g of ultrapure water, and the pH of water after stirring at 25 ° C. for 5 minutes is 6.0 to 7.8, preferably The manganese carbonate which becomes 6.5-7.6 is pointed out. And the non-basic manganese carbonate which concerns on a 1st process differs from the manganese carbonate generally called basic manganese carbonate. In the case of basic manganese carbonate, the pH of water after adding 10 g of basic manganese carbonate to 100 g of ultrapure water and stirring at 25 ° C. for 5 minutes is 8.0 or more.

Industrially, non-basic manganese carbonate is prepared by preparing an ammonium carbamate solution with aqueous ammonia and carbon dioxide gas, and reacting it with manganese monoxide, or using two methods such as manganese sulfate and manganese chloride dissolved in water. It is produced by a method of reacting a valent manganese salt with ammonium hydrogen carbonate as a carbonic acid source. Nonbasic manganese carbonate has a low content of manganese hydroxide (Mn (OH) ₂ ). Therefore, the pH of water after adding 10 g of non-basic manganese carbonate to 100 g of ultrapure water and stirring at 25 ° C. for 5 minutes is 6.0 to 7.8, preferably 6.5 to 7.6. Become.

On the other hand, basic manganese carbonate is industrially produced by reacting sodium carbonate as a carbonate source with a divalent manganese salt such as manganese sulfate or manganese chloride dissolved in water. Manganese has a high content of manganese hydroxide (Mn (OH) ₂ ). Therefore, the pH of water after adding 10 g of basic manganese carbonate to 100 g of ultrapure water and stirring for 5 minutes at 25 ° C. is 8.0 or more.

  Other physical properties of the non-basic manganese carbonate according to the first step are not particularly limited, but according to the first step in that it is easy to obtain lithium manganate having an average particle diameter of 1 to 25 μm. The average particle size of the non-basic manganese carbonate is preferably 1 to 30 μm, and particularly preferably 5 to 20 μm.

  In the first step, the non-basic manganese carbonate is fired in an inert gas atmosphere having an oxygen concentration of 1% by volume or less, preferably in an inert gas atmosphere having an oxygen concentration of 0 to 0.5% by volume. By firing non-basic manganese carbonate in the above atmosphere, dense MnO can be obtained. On the other hand, if the oxygen concentration exceeds 1% by volume, dense MnO cannot be obtained. Nitrogen gas, helium gas, argon gas etc. are mentioned as an inert gas which concerns on a 1st process. In the first step, a small amount of a reducing gas such as hydrogen can be included in the atmosphere in order to prevent oxidation due to oxygen during firing of the non-basic manganese carbonate.

  In the first step, the firing temperature of the non-basic manganese carbonate is 500 to 800 ° C, preferably 550 to 700 ° C. When the firing temperature of the non-basic manganese carbonate is less than 500 ° C., MnO cannot be obtained, and when it exceeds 800 ° C., the aggregation becomes strong and the filling property of lithium manganate decreases.

  In the first step, the firing time of the non-basic manganese carbonate is not particularly limited, but is preferably 1 to 20 hours, particularly preferably 5 to 15 hours. If the firing time of the non-basic manganese carbonate is less than 1 hour, the conversion to MnO tends to be insufficient. On the other hand, even if firing for 20 hours or more, there is no significant difference in the quality of MnO, which is inefficient. easy.

  MnO obtained by performing the first step has a lower impurity content than MnO obtained by firing other manganese salts and MnO obtained by other firing conditions.

The second step, firing the MnO obtained performed a first step is a step of obtaining a _Mn 2 _{O 3.}

In the second step, firing of MnO obtained by performing the first step is performed in an atmosphere having an oxygen concentration of 10% by volume or more, preferably in an atmosphere having an oxygen concentration of 15% by volume or more, and particularly preferably an atmosphere having 20% by volume or more. Do in. By performing MnO obtained by performing the first step in the above atmosphere, Mn ₂ O ₃ with few impurities can be obtained. On the other hand, when the oxygen concentration is less than 10%, oxygen is insufficient, so conversion of MnO to Mn ₂ O ₃ becomes insufficient, and impurities are likely to be generated. Usually, it is preferable to calcinate MnO obtained in the first step in the air or in an oxygen atmosphere.

In the second step, the firing temperature of MnO obtained by performing the first step is 525 to 950 ° C, preferably 550 to 750 ° C. When the firing temperature of MnO obtained by performing the first step is less than 525 ° C., the conversion of MnO to Mn ₂ O ₃ becomes insufficient, so that the lithium secondary battery using lithium manganate as the positive electrode secondary active material When the discharge capacity decreases and the temperature exceeds 950 ° C., conversion from Mn ₂ O ₃ to Mn ₃ O ₄ occurs, and as a result, only lithium manganate having a low Li supply capability can be obtained. The performance as an active material is lowered. In addition, when the firing temperature of MnO obtained by performing the first step exceeds 750 ° C., in a lithium secondary battery using lithium manganate as a positive electrode secondary active material, the voltage at which Li is desorbed (charge voltage) increases. Since there exists a tendency, it is preferable that the baking temperature of MnO obtained by performing a 1st process is 550-750 degreeC.

In the second step, the firing time of MnO obtained by performing the first step is not particularly limited, but is preferably 1 to 20 hours, particularly preferably 5 to 15 hours. When the firing time of MnO obtained by performing the first step is less than 1 hour, conversion to Mn ₂ O ₃ tends to be insufficient, and on the other hand, even if firing for 20 hours or more, there is a large difference in the quality of MnO. It is easy to become inefficient.

The third step is a step of obtaining lithium manganate by firing a reaction raw material mixture obtained by mixing Mn ₂ O ₃ obtained by performing the second step and a lithium compound.

In the third step, first, Mn ₂ O ₃ obtained by performing the second step and a lithium compound are mixed.

  As a lithium compound which concerns on a 3rd process, lithium carbonate, lithium hydroxide, lithium nitrate etc. are mentioned, for example, Any of single type or a combination of 2 or more types may be sufficient as a lithium compound. Of the lithium compounds in the third step, lithium carbonate does not have deliquescence, does not generate moisture as a reaction byproduct, and the pH value of the dispersion when lithium manganate is dispersed in water is small. This is preferable. The physical properties and the like of the lithium compound according to the third step are not limited, but the average particle size of the lithium compound according to the third step is 20 μm or less in that the reaction raw material mixture can be uniformly mixed. It is preferable that it is 3-10 micrometers.

The mixing ratio of the lithium compound and Mn ₂ O ₃ obtained performed a second step according to the third step, the lithium compound according to the third step to Mn atoms in the Mn ₂ O ₃ obtained performed a second step Lithium manganate having a large Li supply capacity is a molar ratio of Li atoms (Li / Mn) of 0.90 to 1.05 and the mixing ratio of both is 0.95 to 1.01. Is preferable in that it is obtained. On the other hand, if the mixing ratio of Mn ₂ O ₃ obtained in the second step and the lithium compound in the third step is less than 0.90, unreacted Mn ₂ O ₃ remains, causing Mn elution. Or the Li supply capacity of lithium manganate becomes small, and if it exceeds 1.05, lithium manganate containing a large amount of Li is produced. Therefore, the pH of the dispersion when dispersed in water is Becomes higher, which causes a decrease in battery safety such as gas generation.

The mixing method for mixing the Mn ₂ O ₃ obtained by performing the second step and the lithium compound may be either a dry method or a wet method, but the dry method is preferable because it is easy to manufacture. In the case of dry mixing, it is preferable to use a blender or the like that can uniformly mix the reaction raw material mixture.

Then, by mixing and Mn ₂ O ₃ obtained performs the second step and a lithium compound to obtain a reaction feed mixture.

In the third step, the reaction raw material mixture is then calcined. The reaction raw material mixture is calcined in an inert gas atmosphere having an oxygen concentration of 1% by volume or less, preferably in an inert gas atmosphere having an oxygen concentration of 1000 ppm or less. Particularly preferably, it is carried out in an inert gas atmosphere of 100 ppm or less. By firing the reaction raw material mixture in the above atmosphere, lithium manganate for the secondary active material of the positive electrode of the lithium secondary battery, in which the discharge capacity is hardly reduced and the performance deterioration due to overdischarge is small, is obtained. On the other hand, when the oxygen concentration exceeds 1% by volume, LiMn ₂ O ₄ , Li ₂ MnO _{3, and the} like are also generated, so the performance of the obtained lithium manganate as a secondary active material for the positive electrode of the lithium secondary battery is lowered. Nitrogen gas, helium gas, argon gas etc. are mentioned as an inert gas which concerns on a 3rd process.

  In the third step, the firing temperature of the reaction raw material mixture is 600 to 950 ° C, preferably 700 to 850 ° C. When the firing temperature of the reaction raw material mixture is less than 600 ° C., the reaction becomes insufficient, so that good lithium manganate cannot be obtained, and when it exceeds 950 ° C., lithium manganate with low Li supply ability is obtained. It is done.

  In the third step, the firing time of the reaction raw material mixture is not particularly limited, but is preferably 1 to 20 hours, particularly preferably 5 to 15 hours. When the firing time of the reaction raw material mixture is less than 1 hour, the reaction tends to be insufficient, and on the other hand, even if the firing is performed for 20 hours or more, there is no significant difference in the quality of lithium manganate, which tends to be inefficient.

  Further, in the third step, the firing may be repeated as necessary. In the case of repeated firing, the firing may be performed at a temperature lower than the above firing temperature range.

  In the third step, after firing, the fired product is appropriately cooled and pulverized as necessary to obtain lithium manganate. In addition, the grinding | pulverization performed as needed is suitably performed, for example, when the lithium manganate obtained by baking in the third step is in the form of a brittlely bonded block.

The lithium manganate obtained by performing the third step has an average particle diameter of 1 to 25 μm, preferably 4 to 15 μm, and a BET specific surface area of 0.2 to 2.0 m ² / g, preferably 0.4. -1.0 m < ² > / g. Further, the lithium manganate obtained performed a third ^step, in the L ^* a * ^{b *} color system, ^{L *} value, 25.0 to 32.0, preferably 26.0 to 31.0, a ^* value is -1.50 to -0.15, preferably -1.00 to -0.10, and b ^* value is 2.50 to 8.00, preferably 3.50 to 7.00. is there.

And by selecting various manufacturing conditions in the manufacturing method of the lithium manganate of the present invention, the L ^* value, a ^* value and b ^* value in the L ^* a ^* b ^* color system of the obtained lithium manganate You can choose. Such manufacturing conditions include:
(I) using non-basic manganese carbonate as a raw material for the first step;
(Ii) selecting the oxygen concentration of the atmosphere during firing in the first step;
(Iii) selecting a firing temperature at the time of firing in the first step;
(Iv) selecting the oxygen concentration of the atmosphere during firing in the second step;
(V) selecting a firing temperature at the time of firing in the second step;
(Vi) selecting the type or purity of the lithium compound according to the third step;
(Vii) selecting a molar ratio of lithium atom / manganese atom in the reaction raw material mixture according to the third step;
(Viii) selecting the oxygen concentration of the atmosphere during firing in the third step;
(Ix) selecting a firing temperature at the time of firing in the third step;
Is mentioned.

The lithium secondary battery positive electrode active material of the present invention, the lithium manganate of the present invention,
The following general formula (2):
Li _(a) M _(1-b) A _(b) O _(c) (2)
(In the formula, M represents one or more metal elements selected from Co and Ni, and A represents Mg, Al, Ti, Zr, Fe, Cu, Zn, Sn, In, Ca, Ba, Sr, and Mn. 1 or more kinds of metal elements, 0.9 ≦ a ≦ 1.1, 0 ≦ b ≦ 0.5, and 1.8 ≦ c ≦ 2.2.)
Lithium composite oxide represented by
It is a lithium secondary battery positive electrode active material containing. That is, the lithium secondary battery positive electrode active material of the present invention contains the lithium manganate of the present invention as a secondary active material, and the lithium composite oxide represented by the general formula (2) as a main active material.

The lithium manganate of the present invention contained in the lithium secondary battery positive electrode active material of the present invention is as described above, and the following general formula (1):
Li _x MnO ₂ (1)
(In the formula, 0.90 ≦ x ≦ 1.05, preferably 0.95 ≦ x ≦ 1.01.)
Represented by
In the L ^* a ^* b ^* color system, ^{L *} value, 25.0 to 32.0, preferably 26.0-31.0, ^{a *} value -1.50～-0.15, Preferably it is -1.00--0.10, and b ^* value is 2.50-8.00, Preferably it is 3.50-7.00 Lithium manganate for lithium secondary battery positive electrode side active materials is there. The lithium manganate of the present invention contained in the lithium secondary battery positive electrode active material of the present invention preferably has an average particle diameter of 1 to 25 μm, particularly preferably 4 to 15 μm, and preferably a BET ratio. The surface area is 0.2 to 2.0 m ² / g, particularly preferably 0.4 to 1.0 m ² / g, and preferably, the pH of the dispersion when dispersed in water is 12 or less, Especially preferably, it is 11.5 or less.

The lithium composite oxide represented by the general formula (2) is not particularly limited, One example _{thereof, LiCoO 2, LiNiO 2, LiNi} 0.8 Co 0.2 O 2, LiNi 0.8 Co _0.1 Mn _0.1 O ₂ , LiNi _0.4 Co _0.3 Mn _0.3 O _{2 and the} like may be mentioned, and these lithium composite oxides may be used alone or in combination of two or more. . Among these, LiCoO ₂ is widely used industrially, and is preferable in that it has a high synergistic effect with the lithium manganate for a positive electrode secondary active material of the lithium secondary battery of the present invention.

The physical properties and the like of the lithium composite oxide represented by the general formula (2) are not particularly limited, but the average particle diameter of the lithium composite oxide represented by the general formula (2) is that it can suppress polarization and poor conductivity. However, it is preferable that it is 1-30 micrometers, and it is especially preferable that it is 3-25 micrometers. Moreover, it is preferable that the BET specific surface area of the lithium composite oxide represented by the general formula (2) is 0.1 to 2.0 m ² / g in terms of improving the thermal stability of the battery. It is especially preferable that it is 2-1.0 m < ² > / g.

  In the lithium secondary battery positive electrode active material of the present invention, the content ratio of the lithium manganate (subactive material) of the present invention and the lithium composite oxide (main active material) represented by the general formula (2) is The lithium manganate of the present invention is preferably 5 to 30 parts by mass, particularly preferably 10 to 20 parts by mass with respect to 100 parts by mass of the lithium composite oxide represented by the formula (2). When the content ratio of the lithium composite oxide represented by the general formula (2) is in the above range, the discharge capacity of the lithium secondary battery is hardly reduced and the performance deterioration due to overdischarge is reduced. On the other hand, when the lithium manganate of the present invention is less than 5 parts by mass with respect to 100 parts by mass of the lithium composite oxide represented by the general formula (2), performance deterioration due to overdischarge tends to increase. Moreover, when it exceeds 30 mass parts, the discharge capacity of a battery will become small easily.

  And the lithium manganate of this invention and the lithium complex oxide represented by the said General formula (2) are mixed uniformly, and the lithium secondary battery positive electrode active material of this invention is manufactured. The mixing method of the lithium manganate of the present invention and the lithium composite oxide represented by the general formula (2) is not particularly limited, and is a machine on which a strong shearing force acts by a wet method or a dry method. Prepared using conventional means. In the wet method, mixing is performed using apparatuses such as a ball mill, a disper mill, a homogenizer, a vibration mill, a sand grind mill, an attritor, and a powerful stirrer. On the other hand, in the dry method, mixing is performed using apparatuses such as a high speed mixer, a super mixer, a turbo sphere mixer, a Henschel mixer, a nauter mixer, and a ribbon blender. The mixing method is not limited to the method using the illustrated mechanical means. Further, after mixing, if necessary, the particle size may be adjusted by pulverizing with a jet mill or the like.

  The lithium secondary battery of the present invention is a lithium secondary battery obtained by using the positive electrode active material of the lithium secondary battery of the present invention as a positive electrode active material, and contains a positive electrode, a negative electrode, a separator, and a lithium salt. Made of electrolyte.

  The positive electrode according to the lithium secondary battery of the present invention is formed, for example, by applying and drying a positive electrode mixture on a positive electrode current collector.

  The positive electrode mixture according to the lithium secondary battery of the present invention is composed of the positive electrode active material of the lithium secondary battery of the present invention, a conductive agent, a binder, a filler added as necessary. That is, in the lithium secondary battery of the present invention, a mixture of the lithium manganate of the present invention and the lithium composite oxide represented by the general formula (2) is uniformly applied to the positive electrode as the positive electrode active material. Yes. For this reason, in the lithium secondary battery according to the present invention, the load characteristics are hardly lowered and the cycle characteristics are hardly lowered.

  The positive electrode current collector according to the lithium secondary battery of the present invention is not particularly limited as long as it is an electronic conductor that does not cause a chemical change in the constituted battery. For example, stainless steel; nickel; aluminum; titanium; Carbon: Carbon, nickel, titanium, silver, and the like that are surface-treated on the surface of aluminum or stainless steel. These materials may be oxidized products whose surfaces have been oxidized, or may be surface-treated products having irregularities on the surface of the current collector by surface treatment. Examples of the form of the positive electrode current collector include foils, films, sheets, nets, punched ones, lath bodies, porous bodies, foam bodies, fiber groups, nonwoven fabric molded bodies, and the like. The thickness of the positive electrode current collector according to the lithium secondary battery of the present invention is not particularly limited, but is preferably 1 to 500 μm.

  The conductive agent according to the lithium secondary battery of the present invention is not particularly limited as long as it is an electron conductive material that does not cause a chemical change in the constructed battery. For example, graphite such as natural graphite and artificial graphite; carbon black, Carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black and thermal black; conductive fibers such as carbon fiber and metal fiber; metal powders such as carbon fluoride, aluminum and nickel powder; Examples include conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives. Natural graphite includes, for example, scaly graphite, scaly graphite, earth And graphite. These may be used alone or in combination of two or more. In the positive electrode mixture according to the lithium secondary battery of the present invention, the content ratio of the conductive agent is 1 to 50% by mass, preferably 2 to 30% by mass.

Examples of the binder according to the lithium secondary battery of the present invention include starch, polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, regenerated cellulose, diacetylcellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, and polypropylene. , Ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluoro rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-par Fluoroalkyl vinyl ether copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene Copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, fluorine Vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, ethylene-acrylic acid copolymer or an ionic cross-linked product thereof (Na ⁺ ion, etc.), ethylene -Methacrylic acid copolymer or ionic cross-linked product thereof (Na ⁺ ion, etc.), ethylene-methyl acrylate copolymer or ionic cross-linked product thereof (Na ⁺ ion, etc.), ethylene-methyl methacrylate copolymer or ionic cross-linked product thereof Body (Na ⁺ ion Etc.), polysaccharides such as polyethylene oxide, thermoplastic resins, polymers having rubber elasticity, and the like, and these may be used alone or in combination of two or more. In addition, when using the compound containing a functional group which reacts with lithium like a polysaccharide, it is preferable to add the compound like an isocyanate group and to deactivate the functional group, for example. In the positive electrode mixture according to the lithium secondary battery of the present invention, the blending ratio of the binder is 1 to 50% by mass, preferably 5 to 15% by mass.

  The filler according to the lithium secondary battery of the present invention suppresses the volume expansion of the positive electrode and is added as necessary. Any filler can be used as long as it is a fibrous material that does not cause a chemical change in the constituted battery, and examples thereof include olefin polymers such as polypropylene and polyethylene; and fibers such as glass and carbon. Although content of a filler is not specifically limited in the positive mix which concerns on the lithium secondary battery of this invention, 0-30 mass% is preferable.

  The negative electrode according to the lithium secondary battery of the present invention is formed by applying and drying a negative electrode material on a negative electrode current collector.

The negative electrode current collector according to the lithium secondary battery of the present invention is not particularly limited as long as it is an electronic conductor that does not cause a chemical change in the constituted battery, and includes copper, copper alloy, nickel, and the like. In particular, copper or a copper alloy has a positive electrode potential of 3.5 Vvs. Becomes the Li / Li ⁺ extent, although oxide dissolved, the lithium secondary battery of the present invention, since Lithium ions contributing to charge and discharge is large, the positive electrode potential during overdischarge 3.5Vvs. It becomes lower than Li / Li ⁺ . Therefore, the safety when using copper or a copper alloy for the negative electrode in the lithium secondary battery of the present invention is significantly higher than the safety when using copper or a copper alloy for the negative electrode in a conventional lithium secondary battery. Get higher. In addition, these materials may be oxidized products whose surfaces are oxidized, or may be surface-treated products having irregularities on the current collector surface by surface treatment. The form of the negative electrode current collector according to the lithium secondary battery of the present invention is, for example, a foil, a film, a sheet, a net, a punched one, a lath body, a porous body, a foamed body, a fiber group, a non-woven fabric, or the like. A molded body etc. are mentioned. The thickness of the negative electrode current collector according to the lithium secondary battery of the present invention is not particularly limited, but is preferably 1 to 500 μm.

The negative electrode material according to the lithium secondary battery of the present invention is not particularly limited, and examples thereof include carbonaceous materials, metal composite oxides, lithium metals, lithium alloys, silicon alloys, tin alloys, metal oxides, and conductivity. Examples thereof include a polymer, a chalcogen compound, and a Li—Co—Ni-based material. Examples of the carbonaceous material related to the negative electrode material include non-graphitizable carbon materials and graphite-based carbon materials. Examples of the metal composite oxide according to the negative electrode material include Sn _(p) D ¹ _(1-p) D ² _(q) O _(r) (wherein D ¹ is selected from Mn, Fe, Pb, and Ge). One or more elements, D ² represents one or more elements selected from Al, B, P, Si, Group 1, Group 2, Group 3 and halogen elements of the periodic table, and 0 <p ≦ 1, 1 ≦ q ≦ 3, 1 ≦ r ≦ 8); Li _(s) Fe ₂ O ₃ (where 0 ≦ s ≦ 1); Li _(t) WO ₂ (where 0 ≦ t) ≦ 1) and the like. Examples of the metal oxide according to the negative electrode material include GeO, GeO ₂ , SnO, SnO ₂ , PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , Bi ₂ O ₃ , Bi ₂ O ₄ , Bi ₂ O ₅ may be mentioned. Examples of the conductive polymer according to the negative electrode material include polyacetylene and poly-p-phenylene.

  The separator according to the lithium secondary battery of the present invention is an insulating thin film having a large ion permeability and a predetermined mechanical strength. And as a separator, the sheet | seat or nonwoven fabric created from olefin type polymers, such as a polypropylene, glass fiber, polyethylene, etc. are used from an organic-solvent resistance and hydrophobic viewpoint. The pore diameter of the separator according to the lithium secondary battery of the present invention is generally in a range useful for batteries, and is, for example, 0.01 to 10 μm. The thickness of the separator according to the lithium secondary battery of the present invention may be in a range for a general battery, and is, for example, 5 to 300 μm. In addition, when solid electrolytes, such as a polymer, are used as electrolyte mentioned later, a solid electrolyte serves as a separator.

  The nonaqueous electrolyte containing a lithium salt according to the lithium secondary battery of the present invention comprises a nonaqueous electrolyte and a lithium salt. Examples of the non-aqueous electrolyte according to the lithium secondary battery of the present invention include a non-aqueous electrolyte, an organic solid electrolyte, and an inorganic solid electrolyte. Examples of the non-aqueous electrolyte related to the non-aqueous electrolyte include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydroxy Furan, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl Sulfolane, 3-methyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, diethyl ether Ether, 1,3-propane sultone, methyl propionate, aprotic organic solvents such as ethyl propionate, and these may be either singly or combination.

  Examples of organic solid electrolytes related to non-aqueous electrolytes include polyethylene derivatives; polyethylene oxide derivatives or polymers having polyethylene oxide groups; polypropylene oxide derivatives or polymers having polypropylene oxide groups; phosphate ester polymers, polyphosphazenes, polyaziridines, polyethylenes Examples thereof include polymers having an ionic dissociation group such as sulfide, polyvinyl alcohol, polyvinylidene fluoride, and polyhexafluoropropylene; a mixture of a polymer having an ionic dissociation group and the nonaqueous electrolyte solution related to the nonaqueous electrolyte.

Examples of the inorganic solid electrolyte related to the non-aqueous electrolyte include Li nitride, halide, oxyacid salt, and the like. For example, Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N—LiI-LiOH, LiSiO _4. , LiSiO ₄ —LiI—LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Li ₄ SiO ₄ —LiI—LiOH, Li ₃ PO ₄ —Li ₂ S—SiS ₂ , phosphorus sulfide compounds, and the like.

Examples of the lithium salt according to the lithium secondary battery of the present invention include lithium salts that dissolve in the non-aqueous electrolyte according to the lithium secondary battery of the present invention. For example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , _{LiB 10 Cl 10, LiPF 6,} LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiB 10 Cl 10, LiAlCl 4, CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) ₂ NLi, chloroborane lithium, lithium lower aliphatic carboxylic acids, lithium tetraphenylborate, imides, and the like. these may be either singly or combination.

  The nonaqueous electrolyte according to the lithium secondary battery of the present invention can contain the following compounds for the purpose of improving discharge, charging characteristics, and flame retardancy. Such compounds include, for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones and N, N-substituted. Imidazolidine, ethylene glycol dialkyl ether, ammonium salt, polyethylene glycol, pyrrole, 2-methoxyethanol, aluminum trichloride, conductive polymer electrode active material monomer, triethylenephosphonamide, trialkylphosphine, morpholine, carbonyl group Aryl compounds, hexamethylphosphoric triamide and 4-alkylmorpholine, bicyclic tertiary amines, oils, phosphonium salts and tertiary sulfonium salts, phosphases , And carbonate and the like. In particular, in order to make the non-aqueous electrolyte electrolyte according to the lithium secondary battery of the present invention nonflammable, the non-aqueous electrolyte according to the lithium secondary battery of the present invention is, for example, carbon tetrachloride, ethylene trifluoride or the like. A halogen-containing solvent can be contained. Moreover, in order to give the lithium secondary battery of the present invention suitable for high-temperature storage, the nonaqueous electrolyte according to the lithium secondary battery of the present invention can contain carbon dioxide gas.

  The lithium secondary battery of the present invention configured as described above has excellent battery performance, particularly, the discharge capacity is less likely to decrease during normal use, shows a continuous voltage change during charging and discharging, and the performance due to overdischarge. It is a lithium secondary battery with little deterioration.

  The shape of the lithium secondary battery of the present invention may be any shape such as a button, a sheet, a cylinder, a corner, or a coin shape. In addition, the lithium secondary battery of the present invention includes, for example, a notebook computer, a laptop computer, a pocket word processor, a mobile phone, a cordless handset, a portable CD player, a radio, an LCD TV, a backup power supply, an electric shaver, a memory card, a video movie It is suitably used for electronic devices such as automobiles, electric vehicles, consumer electronic devices such as game machines.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these.

(Example 1)
(Manufacture of lithium manganate)
<Calcination of manganese carbonate>
Commercially available non-basic manganese carbonate (MnCO ₃ , average particle size 8.1 μm) was fired at 550 ° C. for 10 hours in a nitrogen atmosphere (oxygen concentration 0.01 vol%) to obtain a fired product A (MnO). . The obtained fired product A was analyzed by XRD analysis and confirmed to be MnO.

  Further, 10 g of the above commercially available non-basic manganese carbonate was weighed into a 200 mL beaker, 100 g of ultrapure water was added, and the mixture was stirred at 25 ° C. for 5 minutes. Next, the mixture was filtered, and the pH of the filtrate was measured with a pH meter (H-14, manufactured by Horiba, Ltd.). As a result, the pH of the filtrate was 7.14.

<Firing of MnO>
The fired product A (MnO) obtained as described above was fired at 650 ° C. for 10 hours in an air atmosphere (oxygen concentration 21.0% by volume) to obtain a fired product B (Mn ₂ O ₃ ). The obtained fired product B was analyzed by XRD analysis and confirmed to be Mn ₂ O ₃ .

<Baking of reaction raw material mixture>
The calcined product B (Mn ₂ O ₃ ) and Li ₂ CO ₃ (average particle size 5 μm) obtained as described above had a molar ratio of Li atoms to Mn atoms (Li / Mn) of 0.99. The reaction raw material mixture C1 was obtained. Subsequently, the obtained reaction raw material mixture C1 was baked at 700 ° C. for 10 hours in a nitrogen atmosphere (oxygen concentration 0.01 vol%) to obtain lithium manganate D1. Incidentally, the obtained lithium manganate D1 was confirmed to be LiMnO ₂ single phase having a diffraction peak pattern of ASTM card 23-361.

(Physical properties of lithium manganate)
<Color difference measurement>
The lithium manganate D1 obtained as described above is filled into a special petri dish, and the L ^* value, a ^* value, and b ^* value are measured using a spectroscopic color difference meter (manufactured by Nippon Denshoku Co., Ltd., SE2000). Three measurements were taken and the average value was determined. The results are shown in Table 2.

<Physical property evaluation>
The average particle diameter and BET specific surface area of the lithium manganate D1 obtained as described above were measured. The results are shown in Table 2.

<PH measurement>
100 g of pure water was added to 5 g of lithium manganate D1 obtained as described above, and the mixture was stirred at 25 ° C. for 5 minutes. Furthermore, after leaving still for 5 minutes, pH of the supernatant liquid was measured with the pH meter (Horiba, Ltd. make, F-14). The measurement results are shown in Table 2.

(Performance evaluation as a secondary active material for positive electrode of lithium secondary battery)
<Production of test cell>
85% by mass of lithium manganate D1 obtained as described above, 10% by mass of graphite powder and 5% by mass of polyvinylidene fluoride were mixed to form a positive electrode mixture, which was dispersed in N-methyl-2-pyrrolidinone. A kneaded paste was prepared. The obtained kneaded paste was applied to an aluminum foil, dried, pressed and punched into a disk having a diameter of 15 mm to obtain a positive electrode plate.

Next, a test cell E1 was manufactured by combining each member such as a separator, a negative electrode, a current collector plate, a mounting bracket, an external terminal, and an electrolytic solution with the obtained positive electrode plate. Among these, lithium metal was used for the negative electrode, copper was used for the current collector, and 1 liter of a 1: 1 kneaded solution of ethylene carbonate and methyl ethyl carbonate was used as the electrolyte solution, in which 1 mol of LiPF ₆ was dissolved.

<Measurement of initial charge capacity, initial discharge capacity and average charge voltage of test cell>
Charging is CCCV mode, cutoff voltage 4.25V, current density of ^2.5 mA / cm ² , cutoff current is 1/20 of 1C current value, discharging is CCCV mode, cutoff voltage 3.4V, 2. The initial charge capacity, initial discharge capacity, and average charge voltage in the CC region were measured with a current density of 5 mA / cm ² and a cut-off current of 7/200 of 1 C current. The results are shown in Table 3.

(Examples 2 to 12)
(Manufacture of lithium manganate)
A calcined product B, and the _Li 2 CO _3, the molar ratio of Li atoms to Mn atoms (Li / Mn) is, instead of mixing so that 0.99, and the calcined product B, _Li 2 CO ₃ Are mixed so that the molar ratio of Li atom to Mn atom (Li / Mn) is the molar ratio shown in Table 1, and the obtained reaction raw material mixture C1 is mixed with nitrogen atmosphere (oxygen concentration 0.01). In place of firing at 700 ° C. for 10 hours in volume%), the obtained reaction raw material mixture (C2 to C12) was fired at the firing temperature shown in Table 1 in a nitrogen atmosphere (oxygen concentration 0.01 volume%). Except baking for 10 hours, it carried out by the method similar to Example 1, and obtained lithium manganate D2-D12. In addition, it was confirmed that all of the obtained lithium manganates D2 to 12 were single-phase LiMnO ₂ showing the diffraction peak pattern of ASTM card 23-361.

(Physical properties of lithium manganate)
<Color difference measurement, physical property evaluation and pH measurement>
It replaced with lithium manganate D1 obtained in Example 1, and it carried out by the method similar to Example 1 except setting it as lithium manganate D2-12 obtained as mentioned above. The results are shown in Table 2.

(Performance evaluation as a secondary active material for positive electrode of lithium secondary battery)
<Production of test cell and measurement of initial charge capacity, initial discharge capacity and average charge voltage of test cell>
It replaced with lithium manganate D1 obtained in Example 1, and it carried out by the method similar to Example 1 except setting it as lithium manganate D2-12 obtained as mentioned above. The results are shown in Table 3.

(Comparative Example 1)
(Manufacture of lithium manganate)
<Calcination of manganese carbonate>
It carried out by the method similar to Example 1, and the baked material A was obtained.

<Firing of MnO>
It carried out by the method similar to Example 1, and the baked material B was obtained.

<Baking of reaction raw material mixture>
The fired product B obtained as described above and Li ₂ CO ₃ (average particle diameter 5 μm) were mixed so that the molar ratio of Li atoms to Mn atoms (Li / Mn) was 0.85. The reaction raw material mixture C13 was obtained. Subsequently, the obtained reaction raw material mixture C13 was baked at 750 ° C. for 10 hours in a nitrogen atmosphere (oxygen concentration 0.01 vol%) to obtain lithium manganate D13. In addition, it was confirmed that the obtained lithium manganate D13 was a mixture of LiMnO ₂ showing the diffraction peak pattern of ASTM card 23-361, Mn ₂ O ₃ and Mn ₃ O ₄ .

(Physical properties of lithium manganate)
<Color difference measurement, physical property evaluation and pH measurement>
The same procedure as in Example 1 was performed except that lithium manganate D13 obtained as described above was used instead of lithium manganate D1 obtained in Example 1. The results are shown in Table 2.

(Performance evaluation as a secondary active material for positive electrode of lithium secondary battery)
<Production of test cell and measurement of initial charge capacity, initial discharge capacity and average charge voltage of test cell>
The same procedure as in Example 1 was performed except that lithium manganate D13 obtained as described above was used instead of lithium manganate D1 obtained in Example 1. The results are shown in Table 3.

(Comparative Example 2)
(Manufacture of lithium manganate)
A calcined product B, and the _Li 2 CO _3, the molar ratio of Li atoms to Mn atoms, instead of mixing to 0.85, and the calcined product B, and the _Li 2 CO _3, Mn atoms A lithium manganate D14 was obtained in the same manner as in Comparative Example 1 except that the mixing was performed so that the molar ratio of Li atom to 1 was 1.10. Incidentally, lithium manganate D14 was obtained, and LiMnO ₂ as indicated by the diffraction peak pattern of ASTM card _23-361, was confirmed to be a mixture of Li 2 MnO ₃ and _Li 4 _Mn 5 _{O 12.}

(Physical properties of lithium manganate)
<Color difference measurement, physical property evaluation and pH measurement>
The same procedure as in Example 1 was performed except that lithium manganate D14 obtained as described above was used instead of lithium manganate D1 obtained in Example 1. The results are shown in Table 2.

(Performance evaluation as a secondary active material for positive electrode of lithium secondary battery)
<Production of test cell and measurement of initial charge capacity, initial discharge capacity and average charge voltage of test cell>
The same procedure as in Example 1 was performed except that lithium manganate D14 obtained as described above was used instead of lithium manganate D1 obtained in Example 1. The results are shown in Table 3.

(Comparative Example 3)
(Manufacture of lithium manganate)
<Calcination of manganese carbonate>
It carried out by the method similar to Example 1, and the baked material A was obtained.

<Firing of MnO>
It carried out by the method similar to Example 1, and the baked material B was obtained.

<Baking of reaction raw material mixture>
The fired product B obtained as described above and Li ₂ CO ₃ (average particle size 5 μm) were mixed so that the molar ratio of Li atoms to Mn atoms was 1.00, and the reaction raw material mixture C15 was obtained. Subsequently, the obtained reaction raw material mixture C15 was baked at 1000 ° C. for 10 hours in a nitrogen atmosphere (oxygen concentration 0.01 vol%) to obtain lithium manganate D15. In addition, it was confirmed that the obtained lithium manganate D15 was a single-phase LiMnO ₂ shown by the diffraction peak pattern of ASTM card 72-0411.

(Physical properties of lithium manganate)
<Color difference measurement, physical property evaluation and pH measurement>
The same procedure as in Example 1 was performed except that lithium manganate D15 obtained as described above was used instead of lithium manganate D1 obtained in Example 1. The results are shown in Table 2.

(Performance evaluation as a secondary active material for positive electrode of lithium secondary battery)
<Production of test cell and measurement of initial charge capacity, initial discharge capacity and average charge voltage of test cell>
The same procedure as in Example 1 was performed except that lithium manganate D15 obtained as described above was used instead of lithium manganate D1 obtained in Example 1. The results are shown in Table 3.

(Comparative Example 4)
(Manufacture of lithium manganate)
Commercially available MnO ₂ (average particle size 3.5 μm) and Li ₂ CO ₃ (average particle size 5 μm) were mixed so that the molar ratio of Li atoms to Mn atoms was 1.00, and the reaction raw material mixture C16 was obtained. Next, the obtained reaction raw material mixture C16 was baked at 800 ° C. for 10 hours in a nitrogen atmosphere (oxygen concentration 0.01% by volume) to obtain lithium manganate D16. Incidentally, lithium manganate D16 obtained was confirmed to be LiMnO ₂ single phase having a diffraction peak pattern of ASTM card 72-0411.

(Physical properties of lithium manganate)
<Color difference measurement, physical property evaluation and pH measurement>
The same procedure as in Example 1 was performed except that lithium manganate D16 obtained as described above was used instead of lithium manganate D1 obtained in Example 1. The results are shown in Table 2.

(Performance evaluation as a secondary active material for positive electrode of lithium secondary battery)
<Production of test cell and measurement of initial charge capacity, initial discharge capacity and average charge voltage of test cell>
The same procedure as in Example 1 was performed except that lithium manganate D16 obtained as described above was used instead of lithium manganate D1 obtained in Example 1. The results are shown in Table 3.

(Comparative Example 5)
Commercially available MnO ₂ (average particle size 3.5 μm) was fired at 1000 ° C. for 12 hours in an air atmosphere (oxygen concentration 21.0% by volume) to obtain a fired product F17 (Mn ₃ O ₄ ). Next, the obtained fired product F17 was fired at 650 ° C. for 10 hours in an air atmosphere (oxygen concentration 21.0% by volume) to obtain a fired product G17 (Mn ₂ O ₃ ). The obtained fired product G17 and Li ₂ CO ₃ (average particle size 5 μm) were mixed so that the molar ratio of Li atoms to Mn atoms was 1.00 to obtain a reaction raw material mixture C17. Next, the obtained reaction raw material mixture C17 was baked at 750 ° C. for 10 hours in a nitrogen atmosphere (oxygen concentration 0.01% by volume) to obtain lithium manganate D17. The obtained lithium manganate D17 was confirmed to be single-phase LiMnO ₂ showing the diffraction peak pattern of ASTM card 23-361.

(Physical properties of lithium manganate)
<Color difference measurement, physical property evaluation and pH measurement>
The same procedure as in Example 1 was performed except that lithium manganate D17 obtained as described above was used instead of lithium manganate D1 obtained in Example 1. The results are shown in Table 2.

(Performance evaluation as a secondary active material for positive electrode of lithium secondary battery)
<Production of test cell and measurement of initial charge capacity, initial discharge capacity and average charge voltage of test cell>
The same procedure as in Example 1 was performed except that lithium manganate D17 obtained as described above was used instead of lithium manganate D1 obtained in Example 1. The results are shown in Table 3.

(Comparative Example 6)
Commercially available MnO ₂ (average particle size 3.5 μm) was fired at 600 ° C. for 10 hours in an air atmosphere (oxygen concentration 21.0% by volume) to obtain a fired product H18 (Mn ₂ O ₃ ). Next, the obtained fired product H18 and Li ₂ CO ₃ (average particle size 5 μm) were mixed so that the molar ratio of Li atoms to Mn atoms was 1.00 to obtain a reaction raw material mixture C18. . Subsequently, the obtained reaction raw material mixture C18 was baked at 800 ° C. for 10 hours in a nitrogen atmosphere (oxygen concentration 0.01 vol%) to obtain lithium manganate D18. In addition, it was confirmed that the obtained lithium manganate D18 was single phase LiMnO ₂ showing the diffraction peak pattern of ASTM card 23-361.

(Physical properties of lithium manganate)
<Color difference measurement, physical property evaluation and pH measurement>
The same procedure as in Example 1 was performed except that lithium manganate D18 obtained as described above was used instead of lithium manganate D1 obtained in Example 1. The results are shown in Table 2.

(Performance evaluation as a secondary active material for positive electrode of lithium secondary battery)
<Production of test cell and measurement of initial charge capacity, initial discharge capacity and average charge voltage of test cell>
The same procedure as in Example 1 was performed except that lithium manganate D18 obtained as described above was used instead of lithium manganate D1 obtained in Example 1. The results are shown in Table 3.

(Comparative Example 7)
Commercially available MnO ₂ (average particle size 3.5 μm) was fired at 600 ° C. for 5 hours in an air atmosphere (oxygen concentration 21.0% by volume) to obtain a fired product I19 (Mn ₂ O ₃ ). Next, the fired product I19 and Li ₂ CO ₃ (average particle diameter 5 μm) were mixed so that the molar ratio of Li atoms to Mn atoms was 1.00 to obtain a reaction raw material mixture C19. Next, the obtained reaction raw material mixture C19 was put in an alumina crucible, and heated to 600 ° C. at a temperature rising rate of 200 ° C./h while supplying air into the alumina crucible at a supply rate of 1 L / min, The air was switched to nitrogen gas and the temperature was raised to 800 ° C. at a temperature rising rate of 200 ° C./h while being supplied into the alumina crucible at a supply rate of 1 L / min, and kept at 800 ° C. for 10 hours. Subsequently, it was cooled to room temperature at a temperature decreasing rate of 200 ° C./h while introducing nitrogen gas into the alumina crucible at a supply rate of 1 L / min. The product was then pulverized to obtain lithium manganate D19. It was confirmed that the obtained lithium manganate D19 was single-phase LiMnO ₂ showing the diffraction peak pattern of ASTM card 72-0411.

(Physical properties of lithium manganate)
<Color difference measurement, physical property evaluation and pH measurement>
The same procedure as in Example 1 was performed except that lithium manganate D19 obtained as described above was used instead of lithium manganate D1 obtained in Example 1. The results are shown in Table 2.

(Performance evaluation as a secondary active material for positive electrode of lithium secondary battery)
<Production of test cell and measurement of initial charge capacity, initial discharge capacity and average charge voltage of test cell>
The same procedure as in Example 1 was performed except that lithium manganate D19 obtained as described above was used instead of lithium manganate D1 obtained in Example 1. The results are shown in Table 3.

In the measurement of the initial discharge capacity, the initial charge capacity and the average charge voltage of the test cell, a material having a large charge capacity and a small discharge capacity of the test cell, that is, a material having a large difference in charge and discharge capacity, It shows that Li supply ability as a substance is high. Usually, the positive electrode main active material constituting the positive electrode active material, for example, LiCoO ₂ has a discharge capacity of about 160 mAH / g with respect to the charge capacity of 165 mAH / g, and therefore the difference in charge / discharge capacity is small.

  Moreover, the one where the average charge voltage of a test cell is low shows that Li can be supplied from the time of a low voltage, and shows that it is excellent as a Li supply material.

In Examples 1 to 12, the difference in charge / discharge capacity was as extremely large as 140 mAh / g or more, the average charge voltage was as low as 3.86 V or less, and the obtained lithium manganate was used as the positive electrode secondary active material. It turns out that it is excellent. On the other hand, in Comparative Examples 1 and 2, single-phase LiMnO ₂ was not obtained, and the difference in charge / discharge capacity was small, indicating that the Li supply capability was low. Moreover, in Comparative Examples 3-7, since the difference of charging / discharging capacity | capacitance is small and an average charging voltage is high, it turns out that Li supply capability is low.

  Thus, as is apparent from Table 3, the lithium manganate of the present invention has a high initial charge capacity, a large charge / discharge capacity difference, and a low average charge voltage. Such lithium manganate has a high effect of improving safety during overdischarge.

(Examples 13-15 and Comparative Examples 8-9)
(Preparation of lithium composite oxide)
40.0 g of Co ₃ O ₄ (average particle size 5 μm) and 8.38 g of Li ₂ CO ₃ (average particle size 5 μm) were weighed and mixed thoroughly in a dry process, and then calcined at 1000 ° C. for 5 hours. After firing, the obtained fired product was pulverized and classified to obtain lithium cobaltate J (LiCoO ₂ ). The obtained lithium cobalt oxide J had an average particle size of 7.4 μm and a BET specific surface area of 0.38 m ² / g.

(Manufacture of lithium secondary batteries)
Lithium manganate shown in Table 4 as a positive electrode secondary active material and lithium cobaltate J obtained as described above as a positive electrode main active material were mixed in a blending ratio shown in Table 4 to obtain positive electrode active materials K20 to 24. Obtained. Next, positive electrode active material K20-2491% by mass, graphite powder 6% by mass, and polyvinylidene fluoride 3% by mass are mixed to form a positive electrode mixture, which is dispersed in N-methyl-2-pyrrolidinone to prepare a kneaded paste. did. The obtained kneaded paste was applied to an aluminum foil, dried and pressed, and punched into a disk having a diameter of 15 mm to obtain a positive electrode plate. Lithium secondary batteries P20 to 24 were manufactured by combining the obtained positive electrode plate and each member such as a separator, a negative electrode, a current collector plate, a mounting bracket, an external terminal, and an electrolytic solution. Among these, artificial graphite was used for the negative electrode, copper was used for the current collector, and 1 mol of LiPF ₆ was dissolved in 1 liter of a 1: 1 kneaded solution of ethylene carbonate and ethyl methyl carbonate as the electrolyte. .

<Overdischarge test>
The lithium secondary batteries P20 to 24 manufactured as described above were charged at a constant current of up to 4.2 V at a current of 1 CmA at 25 ° C., then charged at a constant voltage of 4.2 V for 3 hours, and then 1 CmA. The discharge capacity (hereinafter referred to as “discharge capacity before overdischarge test”) when discharged to 3.0 V at a constant current of was measured. Subsequently, it was left to stand at a constant voltage of 0 V for 2 days to perform overdischarge. After standing, the battery was charged at a constant current of up to 4.2 V at a current of 1 CmA, then charged at a constant voltage of 4.2 V for 3 hours, and then discharged to 3.0 V at a constant current of 1 CmA (hereinafter, It is described as “discharge capacity after overdischarge test”). And the following formula (3):
Capacity recovery rate (%) = (discharge capacity after overdischarge test / discharge capacity before overdischarge test) × 100 (3)
By calculating the ratio of the discharge capacity after the overdischarge test to the discharge capacity before the overdischarge test, the capacity recovery rate was obtained. The results are shown in Table 4. Further, the battery after the overdischarge test was disassembled, and it was observed whether or not copper of the negative electrode current collector was deposited on the positive electrode. The results are shown in Table 4.

  From the results in Table 4, it can be seen that the use of the lithium manganate of the present invention as the positive electrode secondary active material can reduce the deterioration of performance due to overdischarge.

(Comparative Example 10)
(Manufacture of lithium manganate)
<Calcination of manganese carbonate>
Commercially available basic manganese carbonate (MnCO ₃ , average particle size 27.0 μm) was fired at 550 ° C. for 10 hours in a nitrogen atmosphere (oxygen concentration 0.01 vol%) to obtain a fired product A20 (MnO). The obtained fired product A20 was analyzed by XRD analysis and confirmed to be MnO.

  Moreover, 10 g of the above-mentioned commercially available basic manganese carbonate was weighed into a 200 mL beaker, 100 g of ultrapure water was added, and the mixture was stirred at 25 ° C. for 5 minutes. Subsequently, it filtered and the pH of the filtrate was measured with the pH meter. As a result, the pH of the filtrate was 8.11.

<Firing of MnO>
The fired product A20 (MnO) obtained as described above was fired at 650 ° C. for 10 hours in an air atmosphere (oxygen concentration 21.0% by volume) to obtain a fired product B20 (Mn ₂ O ₃ ). The obtained fired product B20 was analyzed by XRD analysis, and confirmed to be Mn ₂ O ₃ .

<Baking of reaction raw material mixture>
The calcined product B20 (Mn ₂ O ₃ ) obtained as described above and Li ₂ CO ₃ (average particle size 5 μm) had a molar ratio of Li atoms to Li atoms (Li / Mn) of 1.00. To obtain a reaction raw material mixture C20. Subsequently, the obtained reaction raw material mixture C20 was baked at 800 ° C. for 10 hours in a nitrogen atmosphere (oxygen concentration 0.01 vol%) to obtain lithium manganate D20. It was confirmed that the obtained lithium manganate D20 was single-phase LiMnO ₂ showing the diffraction peak pattern of ASTM card 72-0411.

(Physical properties of lithium manganate and performance evaluation as a secondary active material for positive electrode of lithium secondary battery)
The same procedure as in Example 1 was performed except that lithium manganate D20 was used instead of lithium manganate D1. The results are shown in Tables 2 and 3.

Claims (8)

The following general formula (1):
Li _x MnO ₂ (1)
(In the formula, 0.90 ≦ x ≦ 1.05.)
Represented by
In the L ^* a ^* b ^* color system, it ^{L *} value from 25.0 to 32.0, ^{a *} is -1.50~-0.15, ^{b *} is 2.50 to 8.00,
A lithium manganate for a secondary active material of a positive electrode for a lithium secondary battery.   2. The lithium manganate for a secondary active material for a positive electrode of a lithium secondary battery according to claim 1, wherein the average particle size is 1 to 25 μm. BET specific surface area is 0.2-2.0 m < ² > / g, The lithium manganate for lithium secondary battery positive electrode side active materials of any one of Claim 1 or 2 characterized by the above-mentioned.   The lithium manganate for a lithium secondary battery positive electrode secondary active material according to any one of claims 1 to 3, wherein the pH of the dispersion when dispersed in water is 12 or less. A first step of obtaining MnO by firing non-basic manganese carbonate at 500 to 800 ° C. in an inert gas atmosphere having an oxygen concentration of 1% by volume or less;
MnO obtained by performing the first step is baked at 525 to 950 ° C. in an atmosphere having an oxygen concentration of 10% by volume or more to obtain Mn ₂ O ₃ ;
Mn ₂ O ₃ obtained by performing the second step and a lithium compound are mixed so that the molar ratio of lithium atoms to manganese atoms is 0.90 to 1.05 to obtain a reaction raw material mixture, A third step in which the reaction raw material mixture is calcined at 600 to 950 ° C. in an inert gas atmosphere having an oxygen concentration of 1% by volume or less to obtain lithium manganate;
A method for producing lithium manganate, comprising: Lithium manganate for a lithium secondary battery positive electrode side active material according to any one of claims 1 to 4,
The following general formula (2):
Li _(a) M _(1-b) A _(b) O _(c) (2)
(In the formula, M represents one or more metal elements selected from Co and Ni, and A represents Mg, Al, Ti, Zr, Fe, Cu, Zn, Sn, In, Ca, Ba, Sr, and Mn. 1 or more kinds of metal elements, 0.9 ≦ a ≦ 1.1, 0 ≦ b ≦ 0.5, and 1.8 ≦ c ≦ 2.2.)
Lithium composite oxide represented by
A positive electrode active material for a lithium secondary battery, comprising: The lithium secondary battery positive electrode active material according to claim 6, wherein the lithium composite oxide is LiCoO ₂ .   A lithium secondary battery obtained by using the lithium secondary battery positive electrode active material according to claim 6 as a positive electrode active material.