JP2002167220A - Lithium manganese compound oxide, cathode material for lithium secondary battery, cathode for lithium secondary battery, lithium secondary battery and manufacturing method for lithium manganese compound oxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the initial discharge capacitance characteristics of a cathode active substance comprised of a lithium manganese compound oxide useful for a cathode material for a lithium secondary battery. SOLUTION: The peak strength ratio (A/B) of the lithium manganese compound oxide between the strength A of diffraction peak (a) observed at 15.4±1.0 deg. and the strength B of diffraction peak (b) observed at 18.3±1.0 deg. by the following measuring conditions (X-ray source: CuKα1 line (CuKα1=1.5406 Å); Diverging slit: 0.25 deg.; Scattering slit: 0.25 deg.; Receiving slit: 0.15 mm; and Step width: 0.020 deg.) of powder X-ray diffraction is expressed as 0.05<=A/B. The half-value width of the diffraction peak b is 0.20 deg. or more and 2 deg. or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lithium-manganese composite oxide, and a positive electrode material for a lithium secondary battery, a positive electrode for a lithium secondary battery, and a lithium secondary battery using the same. The present invention also relates to a method for producing a lithium manganese composite oxide.

[0002]

2. Description of the Related Art In recent years, as portable electronic devices have become smaller and lighter, a secondary battery having a high output and a high energy density has been demanded as a power source thereof. In addition, a secondary battery having the above characteristics is also required as a power source for an automobile. In particular, lithium secondary batteries meet the above requirements,
Its development is occurring rapidly.

As a positive electrode active material of a lithium secondary battery,
LiCoO_Two, LiNiO_Two, LiMnO_Two, LiMn_TwoO
_FourAnd other lithium composite oxides have been proposed and
Have been done. Especially mainly composed of lithium and manganese
Complex oxide (hereinafter referred to as “lithium-manganese complex oxide”
May be written), Mn is compared with Co or Ni
It is attracting attention because of its large reserves and low cost. So
Among them, monoclinic, orthorhombic, and hexagonal
LiMnO with structure_Two(Hereinafter, “layered lithium manganese
Complex oxides) have a spinel structure
LiMn having _TwoO_FourBecause the theoretical capacity is large compared to
Attention has been paid.

As a layered lithium manganese composite oxide,
Several reports have been made. J. Electroche
m. Soc. Vol. 145 (1999) p. 3217
Describes that lithium orthohydroxide is mixed with trimanganese tetraoxide and calcined in an inert gas atmosphere to produce an orthorhombic lithium manganese composite oxide. But,
This orthorhombic lithium manganese composite oxide has a problem that the initial discharge capacity is small.

[0005] Also, Electrochemical
and Solid-State Letters, Vo
l. 1 (1998) p. 13, and Solid Sta
te Ionics, Vol. 130 (2000) p.
In step 53, manganese (III) nitrate and aluminum nitrate are coprecipitated to form a precursor, and lithium hydroxide is mixed with the precursor, freeze-dried in liquid nitrogen, and calcined in an inert gas atmosphere. It is described to produce a crystalline lithium manganese composite oxide.

[0006] Further, J.I. Power Source
s, Vol. 81 (1999) p. No. 406 describes a method for producing a monoclinic lithium manganese composite oxide in which lithium carbonate, chromium oxide, and dimanganese trioxide are mixed in a solid phase and baking and crushing are repeated at 1000 ° C. for 24 hours. Although these monoclinic lithium manganese composite oxides have an increased initial discharge capacity as compared with the orthorhombic lithium manganese composite oxide, they are still not practically sufficient.

[0007] The above-mentioned method uses industrial manganese (III) nitrate, which is difficult to obtain and is expensive, as well as the use of methods such as flash freezing with liquid nitrogen and repeated firing at high temperatures for a long time. However, none of these methods is still satisfactory as an industrial production method due to problems on the surface. Further, the layered lithium manganese composite oxide belonging to the orthorhombic or monoclinic system has a large difference between the initial charge capacity and the initial discharge capacity (hereinafter sometimes referred to as “irreversible capacity”), and the initial efficiency (initial efficiency). (Discharge capacity / initial charge capacity) is low. In addition, there is a problem that the discharge capacity characteristics (hereinafter, sometimes referred to as “rate characteristics”) obtained when the discharge current density is increased are low.

[0008]

An object of the present invention is to improve the initial discharge capacity characteristics of a positive electrode active material comprising a lithium manganese composite oxide useful as a positive electrode material for a lithium secondary battery.

[0009]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that a lithium manganese composite oxide having a crystal structure in which an orthorhombic lithium manganese composite oxide is mixed in a monoclinic lithium manganese composite oxide. The rate characteristics are improved by using a material, and further, such a lithium manganese composite oxide is easily obtained by uniformly mixing a lithium source and a manganese source and firing the mixture at a relatively low temperature. And found that the present invention was completed.

The gist of the present invention resides in the following (1) to (20). (1) 15.4 ± by powder X-ray diffraction under the following measurement conditions
Intensity A of diffraction peak a observed at 1.0 ° and 18.3
The peak intensity ratio (A / B) of the diffraction peak b observed at ± 1.0 ° to the intensity B is

[0011]

## EQU2 ## 0.05 ≦ A / B, and the half width of the diffraction peak b is 0.20 ° or more.
° or less, a lithium manganese composite oxide.

[0012]

[Table 2] [Measurement conditions] X-ray source: CuKα ₁ ray (CuKα ₁ = 1.5406 °) Divergence slit: 0.25 ° Scattering slit: 0.25 ° Light receiving slit: 0.15 mm Step width: 0.020 ° (2) The lithium manganese composite oxide according to (1), wherein the value of the peak intensity ratio A / B is 20 or less. (3) In the above (1) or (2), wherein part of the Mn site of the lithium manganese composite oxide is substituted with another metal element, and part of the Li site is substituted with another metal element. The lithium manganese composite oxide according to the above. (4) Part of the Mn site of the lithium manganese composite oxide is Al, Ti, V, Cr, Fe, Li, Co, Ni,
Cu, Zn, Mg, Ga, Zr, Nb, Mo, Pd, S
i, Sn, Ta, W, Ru, As, Te, Re and Ge
The lithium manganese composite oxide according to any one of the above (1) to (3), which is substituted with at least one metal element selected from the group consisting of: (5) Part of the Li site of the lithium manganese composite oxide is K, Na, Ba, Mg, Ca, Zn, Cu, Ga,
Mn, Pb, La, Ce, Nd, Y, Cs, Rb, T
1, Au, Sr, Eu, Ag, Ac, Bi, Hg and P
The lithium-manganese composite oxide according to the above (3), which is substituted with at least one metal element selected from the group consisting of u. (6) A metal having a smaller ionic radius in valence when a part of the Mn site of the lithium manganese composite oxide is contained in the lithium manganese composite oxide than the ionic radius of Mn (the ionic radius of Mn ³⁺ ). The ionic radius in the valence when the element is replaced by the element (M1) and a part of the Li site is contained in the lithium manganese composite oxide is larger than the ionic radius of Li (the ionic radius of Li ⁺ ). The lithium manganese composite oxide according to the above (3), which is substituted with a metal element (M2). (7) The metal element (M1) is Al, Ti, V, Cr, F
e, Co, Ni, Ga, Nb, Mo, Pd, Si, T
The lithium-manganese composite oxide according to (6), which is at least one selected from the group consisting of a, W, Ru, As, Te, Re, and Ge. (8) When the metal element (M2) is K, Na, Ba, Ca, C
u, Pb, La, Ce, Nd, Y, Cs, Rb, Tl,
(6) which is at least one selected from the group consisting of Au, Sr, Eu, Ag, Ac, Bi, Hg and Pu.
The lithium manganese composite oxide according to the above. (9) In a method for producing a lithium manganese composite oxide having a layered structure by firing a mixture of a lithium source and a manganese source, the lithium source and the manganese source are uniformly mixed. And then firing at 600-1200 ° C.
(8) The method for producing a lithium manganese composite oxide according to any one of (8). (10) The method for producing a lithium manganese composite oxide according to (9), wherein the lithium manganese composite oxide is fired at 650 to 880 ° C. (11) The above (9) in which lithium and an element source other than manganese are uniformly mixed together with the lithium source and the manganese source.
Or the method for producing a lithium manganese composite oxide according to (10). (12) The method for producing a lithium manganese composite oxide according to any one of (9) to (11), wherein the uniform mixing is performed by a wet method. (13) The above (9) to (9) using a water-soluble lithium source.
(12) The method for producing a lithium manganese composite oxide according to any one of (12). (14) The method for producing a lithium manganese composite oxide according to any one of the above (9) to (13), wherein the mixture is subjected to spray drying and then firing. (15) The method for producing a lithium manganese composite oxide according to any one of the above (9) to (14), wherein a part of the firing step is performed in an inert gas atmosphere. (16) The method for producing a lithium manganese composite oxide according to any one of the above (9) to (15), wherein firing is performed in an oxygen-containing atmosphere and then firing in an inert gas atmosphere. (17) The above (9) to sintering in an inert gas atmosphere
(14) The method for producing a lithium manganese composite oxide according to any one of (14). (18) A positive electrode material for a lithium secondary battery, comprising the lithium manganese composite oxide according to any one of the above (1) to (8). (19) A positive electrode for a lithium secondary battery, comprising the positive electrode material for a lithium secondary battery according to (18) and a binder. (20) A lithium secondary battery including the positive electrode according to (19), a negative electrode, and an electrolyte layer.

Conventionally, when a layered lithium manganese composite oxide belonging to a monoclinic system is used, the discharge capacity, rate characteristics, and initial efficiency are more improved as a positive electrode active material than when an orthorhombic system is used. It was known to be excellent. Therefore, if a positive electrode active material in which the lithium manganese composite oxide belonging to the orthorhombic system is mixed with the layered lithium manganese composite oxide belonging to the monoclinic system is synthesized, the performance is expected to decrease. However, the lithium manganese of the present invention exhibits a specific peak intensity ratio and a half-value width indicating that the layered lithium manganese composite oxide belonging to the monoclinic system and the layered lithium manganese composite oxide belonging to the orthorhombic system are mixed. It is not at all foreseeable that the composite oxide can exhibit excellent battery performance from the above conventional prediction.

Incidentally, Solid State Ioni
cs Vol. 130 (2000) p. 53
There is a description suggesting that the orthorhombic lithium manganese composite oxide and the monoclinic lithium manganese composite oxide are mixed in the range where the amount of Al substitution is small, but firing at a high temperature of 950 ° C. Extremely large, XR
D does not satisfy the parameter range. Also, the battery characteristics have not been evaluated.

Japanese Patent Application Laid-Open No.
No. 317226 is disclosed. First, a partially substituted sodium-manganese composite oxide is synthesized from sodium, manganese, and an element obtained by partially replacing manganese, and most of Na ions in n-hexanol are synthesized by an ion exchange method. Is not industrially suitable because a method of synthesizing a lithium-manganese composite oxide by exchanging with Li ions is used. Also, there is no disclosure of detailed XRD data.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. In the lithium manganese composite oxide of the present invention, the intensity A (peak height) of a diffraction peak a observed at 15.4 ± 1.0 ° in powder X-ray diffraction under the following measurement conditions is 18.3 ± 1.
The peak intensity ratio (A / B) to the intensity B (peak height) of the diffraction peak b observed at 1.0 ° is 0.05 or more, and the half width of the diffraction peak b is 0.20 °. A lithium manganese composite oxide having a layered structure of 2 ° or less (hereinafter sometimes referred to as “layered lithium manganese composite oxide”).

[0017]

[Table 3] [Measurement conditions] X-ray source: CuKα ₁ ray (CuKα ₁ = 1.5406 °) Divergence slit: 0.25 ° Scattering slit: 0.25 ° Light receiving slit: 0.15 mm Step width: 0.020 ° The diffraction peak a is a diffraction peak observed at 15.4 ± 1.0 ° and is assigned to the (010) diffraction plane of the layered lithium manganese composite oxide belonging to the orthorhombic system. The diffraction peak b is a diffraction peak observed at 18.3 ± 1.0 ° and is assigned to the (001) diffraction plane of the layered lithium manganese composite oxide belonging to the monoclinic system. Therefore, it can be seen that these peak intensity ratios A / B are parameters that correspond to the mixing ratio of those belonging to the orthorhombic system and those belonging to the monoclinic system.

The value of A / B is preferably 0.1 or more, more preferably 0.15 or more. A /
The value of B is usually 20 or less, preferably 10 or less, more preferably 5 or less, and most preferably 3 or less. If the range of the peak intensity ratio A / B is too small, the properties of the monoclinic system are largely reflected, and if it is too large, the properties of the orthorhombic system are largely reflected, and in any case, the effects of the present invention are hardly obtained.

The half width of peak b is preferably 1.0 ° or less, more preferably 0.5 ° or less. Peak b
If the half width of is too small, the crystallite size becomes too large, which adversely affects the rate characteristics.If it is too large, there is a problem in the stability of the crystal when charging and discharging are repeated, and the cycle characteristics are likely to be adversely affected. . In the powder X-ray analysis, the measured values greatly differ depending on the X-ray source, divergence slit, scattering slit, light receiving slit, and step width. Therefore, in the present invention, the values are determined as described above.

It is not clear why the discharge capacity characteristics are improved by satisfying the above conditions, but by using a material exhibiting X-ray diffraction such that monoclinic and orthorhombic are mixed, There is a possibility that the lithium concentration gradient in the domain size and discharge is improved. Also, the half width is considered to be related to the domain size. As the lithium-manganese composite oxide of the present invention, a lithium-manganese composite oxide in which a part of the manganese site is substituted by another metal element, a lithium-manganese composite oxide in which a part of the lithium site is substituted by another metal element, and Using a lithium manganese composite oxide in which part of the manganese site is replaced with another metal element and part of the lithium site is replaced with another metal element improves cycle characteristics at high temperatures and reduces irreversible capacity. This is preferable for improving initial efficiency and improving rate characteristics.

Other metal elements which partially replace the manganese site include Al, Ti, V, Cr, Fe, Li, C
o, Ni, Cu, Zn, Mg, Ga, Zr, Nb, M
o, Pd, Si, Sn, Ta, W, Ru, As, Te,
Re and Ge. Other metal elements that partially replace the lithium site include K, Na, Ba,
Mg, Ca, Zn, Cu, Ga, Mn, Pb, La, C
e, Nd, Y, Cs, Rb, Tl, Au, Sr, Eu,
Ag, Ac, Bi, Hg, and Pu.

Further, in the above case, the valence in a state where a part of the Mn site of the lithium manganese composite oxide is contained in the lithium manganese composite oxide is determined by the ionic radius of Mn (the ionic radius of Mn ³⁺ ). Are substituted by a metal element (M1) having a small ionic radius, and a part of the Li site is contained in the lithium-manganese composite oxide in accordance with the ionic radius of Li (ionic radius of Li ⁺ ). Element with a large ionic radius (M
The lithium manganese composite oxide substituted in 2) is more preferable.

As the metal element having an ionic radius smaller than that of Mn, preferably, Al, Ti, V, Cr, Fe, C
o, Ni, Ga, Nb, Mo, Pd, Si, Ta, W,
Ru, As, Te, Re and Ge are mentioned, Al, Ti, V, Cr, Fe, Co and Ni are more preferred, and Al, Cr, Fe, Co and Ni are particularly preferred. The Mn site may be substituted with one of the above metal elements, or may be substituted with two or more metal elements.

As the metal element having an ionic radius larger than that of Li, preferably, K, Na, Ba, Ca, Cu, P
b, La, Ce, Nd, Y, Cs, Rb, Tl, Au,
Sr, Eu, Ag, Ac, Bi, Hg and Pu, and more preferably K, Na, Ba, Ca, Cu, P
b, La, Ce, Nd, Y and Cs, particularly preferably K, Na, Ba and Ca. The Li site may be substituted with one of the above metal elements, or may be substituted with two or more metal elements.

In the case of manganese sites, the substitution ratio of the other metal elements is usually 70 mol% or less of Mn, preferably 60 mol% or less, more preferably 30 mol% or less, and usually 2.5 mol% or less. % Or more. In the case of a lithium site, it is at least 2.5 mol%, preferably at least 5 mol%, and usually at most 30 mol%, preferably at most 20 mol% of Li. If the substitution ratio is too small, the effect of improving the high-temperature cycle may not be sufficient, and if it is too large, the capacity of the battery may decrease.

In the present specification, the ionic radius is defined as
It represents the radius when the ion is regarded as a sphere, and is Shanno
n and Prewitt are the values arranged based on the actual measurement (Ac
taCrystallor. , B25, P925 (19
69)) and those obtained by Shannon with improvements (Acta Crystallor., A32, P75).
1 (1976)). (Chemical Handbook, edited by The Chemical Society of Japan, Basic Edition, 4th revised edition, Maruzen Co., Ltd., PII-725
(1999)) The ionic radius as a reference in the present invention is based on the above value, and is based on the ionic radius (r
(Li ⁺ )) is 0.90 °, the ionic radius of manganese ions (r (Mn ³⁺ )) is 0.79 °, the ionic radius of cobalt ions (r (Co ³⁺ )) is 0.69 °, and the ions of nickel ions are The radius (r (Ni ³⁺ )) is set to 0.70 °, and the value of the ion radius ratio (r (Li ⁺ ) / r (Mn ³⁺ )) of Mn ion to Li ion of the lithium manganese composite oxide is 1.139. , The ion radius ratio (r (Li ⁺ ) / r (Co) of Co ions and Li ions of a composite oxide containing lithium and cobalt as main components (hereinafter sometimes referred to as “lithium-cobalt composite oxide”) ³⁺ )) is 1.30
4. The ion radius ratio (r (Li ⁺ ) / r (r) of Ni ions and Li ions of a composite oxide containing lithium and nickel as main components (hereinafter sometimes referred to as “lithium-nickel composite oxide”). Ni ³⁺ )) was calculated to be 1.286.

Mn ion of lithium manganese composite oxide
And the ion radius ratio of Li ions (r (Li⁺) / R (Mn
³⁺)) Is 1.139, whereas lithium
Positive electrode active material of lithium secondary battery as well as gun complex oxide
Lithium cobalt composite oxide used as
Ionic radius ratio (r (L (L
i ⁺) / R (Co³⁺)) Is 1.304,
Ion and lithium ion in the case of uranium nickel composite oxide
Ion radius ratio (r (Li⁺) / R (Ni³⁺))The value of the
Is 1.286.

The ionic radius ratio of the lithium-manganese composite oxide is determined by adjusting the ionic radius of the lithium-cobalt composite oxide or the lithium-nickel composite oxide free of the above-mentioned problems (large irreversible capacity, low initial efficiency, low rate characteristics). To approach the ratio means that part of the Mn site of the lithium manganese composite oxide is replaced with a metal element having an ionic radius smaller than Mn, and part of the Li site is replaced with a metal element having an ionic radius larger than Li. That is, the irreversible capacity can be reduced, the initial efficiency can be improved, and the rate characteristics can be improved.

In the method in which the raw materials are mixed and fired, unless Cr or Al is replaced with Mn sites and fired at a high temperature,
It has been difficult to synthesize a layered lithium-manganese composite oxide in which a layered lithium-manganese composite oxide belonging to a monoclinic system and a layered lithium-manganese composite oxide belonging to an orthorhombic system are mixed. In addition, when firing at high temperature, the initial efficiency tends to decrease. However, as described above, part of the Mn site of the lithium manganese composite oxide is replaced with a metal element having a smaller ionic radius than Mn ion, and part of the Li site is replaced with a metal element having a larger ionic radius than Li ion. By the method of mixing and firing the raw materials,
By lower temperature firing, it is possible to synthesize a layered lithium manganese composite oxide in which a monoclinic layered lithium manganese composite oxide and an orthorhombic layered lithium manganese composite oxide are mixed, and the initial efficiency is further improved. I do. Therefore, when a lithium manganese composite oxide is synthesized by a method of mixing and firing the raw materials, a part of the Mn site of the lithium manganese composite oxide is replaced with a metal element having an ionic radius smaller than that of Mn ions, and the Li site Part of L
It is preferable to substitute with a metal element having a larger ionic radius than i ion.

The average particle size of the primary particles of the lithium manganese composite oxide in the present invention is usually at least 0.01 μm, preferably at least 0.02 μm, and is usually at most 50 μm, preferably at most 30 μm. When the average particle size is too small, when used as a positive electrode active material of a lithium secondary battery, a side reaction with an electrolyte may be induced, and when too large, diffusion of lithium between the active material and the electrolyte is inhibited,
Problems may occur in use at high current densities.
There is no particular limitation on the shape of the primary particles. The average particle size of the secondary particles of the lithium manganese composite oxide is usually 0.1 μm or more, preferably 0.2 μm or more, and usually 100 μm or more.
μm or less, preferably 60 μm or less. If the average particle size is too small, handling is difficult, and if it is too large, it becomes difficult to prepare a coated electrode.

The shape of the secondary particles is not particularly limited. The specific surface area of the obtained lithium manganese composite oxide is usually 0.1.
05M ² / g or more, preferably 0.1 m ² / g or more, and usually 100 m ² / g or less, preferably 50 m ² /
g or less. If the specific surface area is too small, diffusion of Li between the active material and the electrolytic solution is hindered, while if it is too large, a side reaction with the electrolytic solution may be induced.

The layered lithium manganese composite oxide of the present invention can be produced as follows. That is, it can be obtained by a method in which a lithium source and a manganese source are uniformly mixed and then fired. In order to further improve the battery characteristics such as the cycle characteristics at high temperatures, it is possible to further mix the other element sources evenly and then to fire. There is no particular limitation on the method of uniformly mixing, and examples thereof include dry mixing, ball mill pulverization, and wet pulverization, with wet pulverization being preferred. In the case of dry mixing, it may be difficult to mix uniformly. For example, if the Li source is not mixed uniformly, a different phase that does not act as a positive electrode active material, such as Li ₂ MnO ₃ or Mn ₃ O _4, may appear and deteriorate battery characteristics. There is.

The method of wet grinding is not particularly limited.
Conventional methods such as a Dyno mill and a pearl mill can be used. The dispersion medium is not particularly limited, and water, an organic solvent such as alcohol, and a mixture thereof can be used, but water is preferred from the viewpoint of the drying step. The slurry or the solution obtained by the wet pulverization can be fired after being dried. The method for drying is not particularly limited, but spray drying is preferred. The method of spray drying is not particularly limited, and is conventionally used.
Spray drying using a disk, a two-fluid nozzle or the like can be performed.

As a firing method, a method of firing in an inert gas atmosphere may be mentioned. As the inert gas, nitrogen,
Examples include argon and helium. As the firing atmosphere, part of the firing step is preferably performed in an inert gas atmosphere, and it is particularly preferable that firing is performed in an oxygen-containing atmosphere and then in an inert gas atmosphere. Batteries using lithium manganese composite oxide fired in an inert gas atmosphere after firing in an oxygen-containing atmosphere, and batteries using lithium manganese composite oxide fired in another firing atmosphere as an active material As compared with the above, the initial efficiency and the rate characteristics are improved.

The firing temperature is generally 350 ° C. or higher and 12
00 ° C or less, especially 600 ° C or more and 1000 ° C or less
To obtain the specific layered lithium manganese composite oxide
In order to do this, it is necessary to carry out at a relatively low temperature of
Very preferred. Using a temperature of 880 ° C. or higher
It may be difficult to obtain lithium manganese composite oxide
Above 880 ° C, the primary particle size becomes too large
This is because there is a tendency. Thus, generally lower
It is preferable to perform firing at a temperature, but as described above,
Part of the Mn site of the titanium-manganese composite oxide is Mn
Ionic radius (Mn ³⁺Lithium ion)
The valence in the state of being contained in the gun complex oxide
Substituted with a metal element (M1) having a small on-radius,
In addition, a part of the Li site has an ionic radius of Li (Li⁺of
(Ion radius) contained in lithium manganese composite oxide
Sources with large ionic radii in the charged state in the charged state
Lithium manganese composite oxidation substituted with element (M2)
When firing the product, firing at a high temperature of 880 ° C or higher
To obtain the desired lithium-manganese composite oxide
It is possible to On the other hand, generally firing at low temperature
Although it is preferable that the crystal structure is too low,
Normally, the temperature is set to 650 ° C. or more because it is difficult to grow sufficiently.
You.

The baking time is usually from 1 hour to 72 hours, preferably from 2 hours to 50 hours. If the firing time is too short, the effect of firing cannot be sufficiently obtained, and if it is too long, it is difficult to recognize a difference in effect. The oxygen concentration during firing, especially after reaching the maximum temperature, is usually 10,000
It is preferably at most ppm, more preferably at most 1000 ppm.

As a lithium source, Li ₂ CO ₃ , LiN
Inorganic acid salts such as O ₃ , hydroxides such as LiOH, LiOH · H ₂ O, halides such as LiCl and LiI, oxides such as Li ₂ O, CH ₃ COOLi, lithium dicarboxylate,
Organic acid salts such as fatty acid lithium, and alkyl lithium such as butyl lithium are exemplified. In particular, when wet grinding is used, it is preferable to use a water-soluble salt such as a hydroxide as the lithium source.

Examples of the manganese source include manganese oxide, manganese oxyhydroxide, manganese carbonate and the like. As the manganese oxide, a compound in which the valence of Mn is trivalent is preferable. For example, Mn ₂ O ₃ or The America
n Menalogist Vol. 50 (196
5) γ-Mn ₂ O ₃ described on page 1296 can be mentioned. Although a small amount of water may be added to these compounds, it is preferable that the amount of the added compound is small because a large amount of the compound decreases the yield after firing. As the manganese oxide, a manganese oxide in which a part of the Mn site is substituted with the other metal element can be used. As manganese oxyhydroxide,
A material in which the Mn site and / or the H site are substituted with the above other metal element can also be used. As the manganese oxide or manganese oxyhydroxide substituted with these other metal elements, those substituted with a plurality of metal elements can be used.

The source of the other element is not particularly limited, and various oxides, hydroxides, inorganic acid salts, carbonates, organic acid salts,
Ammonium salts can be used as appropriate. Examples of the other metal element include the above-described various elements that can substitute a part of a manganese site or a part of a lithium site. The layered lithium manganese composite oxide of the present invention can be used as a positive electrode material for a lithium secondary battery. This positive electrode material can be used as a positive electrode of a lithium secondary battery.

The positive electrode material for a lithium secondary battery comprises the above layer
Contains lithium-manganese composite oxide,
May be contained as an active material. this
Other positive electrode materials include spinel-type lithium
Gun complex oxide, LiNiO _TwoLithium nickel like
Composite oxide, LiCoO_TwoLithium cobalt like
A composite oxide or the like can be used. Preferably, the other
Spinel-type lithium manganese composite oxidation as cathode material
And / or lithium nickel composite oxide is used.
The spinel-type lithium manganese composite oxide,
Titanium nickel composite oxide, lithium cobalt composite oxidation
Compounds such as products can be produced by a conventionally known method.
May have a small amount of oxygen deficiency, non-stoichiometric
Manganese sites, nickel sites and cobalt sites
And the lithium site is replaced by another element
Is also good.

The positive electrode for a lithium secondary battery of the present invention usually contains the above positive electrode material and a binder. Preferably,
A conductive agent is contained together with the layered lithium manganese composite oxide and the binder. As the binder, for example, polyvinylidene fluoride, polytetrafluoroethylene,
Various polymers such as EPDM (ethylene-propylene-diene terpolymer), SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), and fluororubber are exemplified. Examples of the conductive agent include fine particles of graphite, carbon black such as acetylene black, and fine particles of amorphous carbon such as needle coke.
The contents of the active material, the binder, and the conductive agent in the positive electrode are generally about 20 to 90% by weight, about 10 to 50% by weight, and about 1 to 20% by weight, respectively. The positive electrode can be obtained by applying and drying a slurry containing the above-described material on a current collector such as Al metal.

The positive electrode can be used in a lithium secondary battery in combination with a negative electrode and an electrolyte layer. As the active material used for the negative electrode, any of the materials usually used for this type of lithium secondary battery can be used. For example, a carbon-based material favorably used as a negative electrode agent of a lithium ion battery can be used. Also, lithium metal, Al, Si, Sn, Pb, In, Bi, S
lithium alloy with b, Ag, etc., 2 against lithium metal
MoO ₂ , WO ₂ , Ti capable of reversibly doping and undoping lithium at a relatively low potential such as V or lower.
Transition metal oxides or sulfides such as S ₂ and TiO _2, as well as amorphous tin composite oxides and lithium nitrides can be used. As the carbon-based material, it is possible to use natural graphite, artificial graphite, and resin compositions such as coal-based and petroleum-based cokes and pitches, phenolic resins, and various celluloses at high temperatures. It is. Further, a composite of two or more of these carbon-based materials or a composite of two or more of the above-described non-carbon-based materials and carbon-based materials can also be used. The use of the above-mentioned negative electrode active material is not particularly limited, but natural graphite, artificial graphite, and even those obtained by using an amorphous carbon material alone or in combination with pitch coke as a raw material are preferably used. Can be The negative electrode usually contains the active material and a binder. As the binder, the same material as that for the positive electrode can be used.
Also, the same method as that for the positive electrode can be used for the production.

The electrolyte layer is usually composed of an ion conductor made of an electrolyte and a separator. When using a separator, usually a microporous polymer film is used, nylon, cellulose acetate, nitrocellulose, polysulfone, polyacrylonitrile, polyvinylidene fluoride, polypropylene, polyethylene, those made of polyolefin polymers such as polybutene Used. The chemical and electrochemical stability of the separator is an important factor. In this respect, a polyolefin-based polymer is preferable, and it is preferable that the battery is made of polyethylene from the viewpoint of the self-closing temperature, which is one of the purposes of the battery separator.

In the case of a polyethylene separator, ultrahigh molecular weight polyethylene is preferable from the viewpoint of high-temperature shape retention, and the lower limit of the molecular weight is preferably 500,000, more preferably 1,000,000, and most preferably 1.5 million. On the other hand, the upper limit of the molecular weight is preferably 5,000,000, more preferably 4,000,000, and most preferably 3,000,000. If the molecular weight is too small, the blocking property becomes too high and there is a problem in use at a high temperature. If the molecular weight is too large, the fluidity is too low and the pores of the separator may not be blocked when heated.

As the ionic conductor in the lithium secondary battery of the present invention, for example, known organic electrolytes, polymer solid electrolytes, gel electrolytes, inorganic solid electrolytes and the like can be used. Is preferred. The organic electrolyte is composed of an organic solvent and a solute. The organic solvent is not particularly limited, for example, carbonates, cyclic ethers, ketones, sulfolane compounds,
Lactones, nitriles, chlorinated hydrocarbons, ethers, amines, esters, amides, phosphate compounds and the like can be used. Specific examples of these representatives include propylene carbonate, ethylene carbonate, vinylene carbonate, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-
Dioxane, 4-methyl-2-pentanone, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, 1,3-dioxolan, 4-methyl-1,
3-dioxolane, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile,
Benzonitrile, butyronitrile, valeronitrile,
Examples thereof include 1,2-dichloroethane, dimethylformamide, dimethylsulfoxide, trimethyl phosphate, triethyl phosphate, and the like, and a single solvent or a mixture of two or more solvents can be used.

The solute to be dissolved in this solvent is not particularly limited, but any of the conventionally known ones can be used, and LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiPF
BF ₄ , LiB (C ₆ H ₅ ) ₄ , LiCl, LiBr, CH
₃ SO ₃ Li, include lithium salts such as CF ₃ SO ₃ Li, can be used at least one or more of these.

When a polymer solid electrolyte is used, any known polymer can be used. In particular, a polymer having high ionic conductivity with respect to lithium ions is preferably used. Polypropylene oxide, polyethyleneimine and the like are preferably used, and the polymer can be used as a gel electrolyte by adding the above solvent together with the above solute.

When an inorganic solid electrolyte is used, a known crystalline or amorphous solid electrolyte can be used for the inorganic substance. Examples of the crystalline solid electrolyte include Li
I, Li ₃ N, Li _{1 + x} M _x Ti _2-x (PO ₄ ) ₃ (where M
= At least one selected from the group consisting of Al, Sc, Y and La), Li _0.5-3x RE _{0.5 + x} TiO ₃ (where R
E = La, Pr, Nd and Sm), and the amorphous solid electrolyte is, for example, 4.9LiI-34.1Li ₂ O-61.
_{B 2 O 5, 33.3Li 2 O} -66.7SiO oxide such as ₂ glass or 0.45LiI-0.37Li ₂ S-0.26
_{B 2 S 3, 0.30LiI-0.42Li} 2 S-0.28SiS 2 sulfide glass etc. and the like. At least one of these
More than one species can be used.

[0049]

The present invention will be described in more detail with reference to the following examples. In the following examples, “parts” means “parts by weight”. Example 1 Dimanganese (III) trioxide 20.0 was added to 63.5 parts of water.
Parts, 12.05 parts of lithium hydroxide monohydrate, and 2.14 parts of dichromium (III) trioxide were crushed for 2 hours using zirconia beads having a diameter of 0.5 mm to form a slurry, and sprayed at a drying temperature of 86 ° C. Drying was performed. This powder is placed under a stream of nitrogen 8
The firing was performed at 50 ° C. for 10 hours.

Next, the obtained lithium manganese composite oxide was subjected to powder X-ray diffraction (XRD) measurement under the following measurement conditions.

[0051]

[Table 4] [Measurement conditions] X-ray source: CuKα ₁ ray (CuKα ₁ = 1.5406 °) Divergence slit: 0.25 ° Scattering slit: 0.25 ° Light receiving slit: 0.15 mm Step width: 0.020 ° FIG. 1 shows the results of the powder XRD measurement. Further, the intensity A of the diffraction peak a observed at 15.4 ± 1.0 ° and the intensity B of the diffraction peak b observed at 18.3 ± 1.0 °, and the diffraction obtained from the above measurement results. Table 1 shows the half width of the peak b.

A battery was prepared using the lithium manganese composite oxide, and the initial discharge capacity was measured. The voltage range was 4.35V to 2.0V. First, both the charging current density and the discharging current density were measured at 0.2 mA / cm ² , and the values were defined as C1 and D1, respectively. Thereafter, a constant charge current density at 0.5 mA / cm ^2, discharge current density was subjected to the allowed by eight measurements increased from 0.2 mA / cm ² until 11 mA / cm ^2, discharge current density 1.0 mA / cm
The value at ² was taken as D2. Finally, the charge current density and the discharge current density were both measured again at 0.2 mA / cm ² , and the discharge capacity at that time was defined as D3. Table 1 shows these results.

The battery was prepared as follows. 75% by weight of positive electrode material, 20% of acetylene black
% By weight, polytetrafluoroethylene resin weighed at a ratio of 5% by weight, and thoroughly mixed in a mortar to form a thin sheet.
Punched with a 9 mmφ punch. At this time, the total weight was adjusted to be about 8 mmg each. This was pressed against an Al expanded metal to form a positive electrode. Next, with respect to the positive electrode manufactured as described above, a battery cell was assembled using a 0.5-mm-thick Li metal as a counter electrode. That is, a porous polypropylene film was placed as a separator on the positive electrode, and the negative electrode was pressed on a porous can fitted with a polypropylene gasket. 1 mol / l LiPF as non-aqueous electrolyte
Using a mixed solution of ethylene carbonate and diethyl carbonate (50 vol%: 50 vol%) in which No. 6 was dissolved, this was added onto the separator and the negative electrode. Thereafter, the battery was sealed to form a lithium secondary battery (button type). Example 2 A lithium-manganese composite oxide was produced and evaluated in the same manner as in Example 1 except that the calcination was performed at 800 ° C. for 10 hours under a nitrogen stream. The results are shown in FIG. 2 and Table 1. Example 3 A lithium-manganese composite oxide was produced and evaluated in the same manner as in Example 1 except that the firing was performed at 800 ° C. for 20 hours under a nitrogen stream. The results are shown in FIG. Example 4 A lithium-manganese composite oxide was produced and evaluated in the same manner as in Example 1, except that calcination was performed at 750 ° C. for 15 hours under a nitrogen stream. The results are shown in FIG. Comparative Example 1 A lithium-manganese composite oxide was produced and evaluated in the same manner as in Example 1, except that the firing was performed at 900 ° C. for 10 hours under a nitrogen stream. The results are shown in FIG. Example 5 5.00 g of dimanganese (III) trioxide, 2.66 g of lithium hydroxide monohydrate, 0.18 g of sodium carbonate, and 0.20 g of aluminum oxyhydroxide (III) were uniformly mixed in an appropriate amount of ethanol. The mixture was mortar mixed for at least 30 minutes, dried at 150 ° C. for 3 hours under reduced pressure, pelletized, calcined at 600 ° C. for 5 hours in an oxygen-containing atmosphere, and the resulting pellets were pulverized and further nitrogen The firing was performed at 700 ° C. for 24 hours in an atmosphere.

The lithium manganese composite oxide was evaluated in the same manner as in Example 1 except that the lithium manganese composite oxide was produced by the above method. The results are shown in FIG.
It is shown in FIG. Example 6 5.00 g of dimanganese (III) trioxide, 2.66 g of lithium hydroxide monohydrate, 0.18 g of sodium carbonate, and 0.20 g of aluminum oxyhydroxide (III) were uniformly mixed in an appropriate amount of ethanol. The mixture was mortar mixed for at least 30 minutes, dried at 150 ° C. for 3 hours under reduced pressure, pelletized, calcined at 600 ° C. for 5 hours in an oxygen-containing atmosphere, and the resulting pellets were pulverized and further nitrogen The firing was performed at 900 ° C. for 24 hours in an atmosphere.

The lithium manganese composite oxide was evaluated in the same manner as in Example 1 except that the lithium manganese composite oxide was produced by the above method. The results are shown in FIG.
It is shown in FIG. Example 7 Dimanganese (III) trioxide (5.00 g), lithium hydroxide monohydrate (2.39 g), and sodium carbonate (0.34 g) were mortar-mixed in an appropriate amount of ethanol for at least 30 minutes until the whole became homogeneous, followed by mixing. After drying the powder under reduced pressure at 150 ° C. for 3 hours,
Pellets were formed and fired in an oxygen-containing atmosphere at 600 ° C. for 5 hours. The obtained pellets were pulverized, and further fired in a nitrogen atmosphere at 900 ° C. for 24 hours.

The lithium manganese composite oxide was evaluated in the same manner as in Example 1 except that the lithium manganese composite oxide was produced by the above method. The results are shown in FIG.
It is shown in FIG. Example 8 Dimanganese (III) trioxide 5.00 g, lithium hydroxide monohydrate 2.95 g, aluminum oxyhydroxide (I
II) 0.42 g was mixed in an appropriate amount of ethanol in a mortar for at least 30 minutes until the whole became uniform, and the mixed powder was reduced under reduced pressure for 15 minutes.
After drying at 0 ° C. for 3 hours, pellets were formed, and baked in an oxygen-containing atmosphere at 600 ° C. for 5 hours.

The lithium manganese composite oxide was evaluated in the same manner as in Example 1 except that the lithium manganese composite oxide was produced by the above method. The results are shown in FIG.
It is shown in FIG.

[0058]

[Table 5]

[0059]

[Table 6] (In Tables 1 and 2, the unit of the half width is represented by “°” and the unit of the capacity is represented by “mAh / g.”) From the results of Tables 1 and 2, the layered lithium of the present invention is shown. It can be seen that the manganese composite oxide shows a high discharge capacity, improves the rate characteristics, and reduces the irreversible capacity.

[0060]

According to the present invention, the battery characteristics of a positive electrode active material comprising a layered lithium-manganese composite oxide useful as a positive electrode material for a lithium secondary battery can be improved.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction result of a layered lithium manganese composite oxide produced in Example 1.

FIG. 2 is an X-ray diffraction result of the layered lithium manganese composite oxide produced in Example 2.

FIG. 3 is an X-ray diffraction result of the layered lithium manganese composite oxide produced in Example 3.

FIG. 4 is an X-ray diffraction result of the layered lithium manganese composite oxide produced in Example 4.

FIG. 5 is an X-ray diffraction result of the layered lithium manganese composite oxide produced in Comparative Example 1.

FIG. 6 is an X-ray diffraction result of the layered lithium manganese composite oxide produced in Example 5.

FIG. 7 is an X-ray diffraction result of the layered lithium manganese composite oxide produced in Example 6.

FIG. 8 is an X-ray diffraction result of the layered lithium manganese composite oxide produced in Example 7.

FIG. 9 is an X-ray diffraction result of the layered lithium manganese composite oxide produced in Example 8.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Koji Shima 1000 Kamoshita-cho, Aoba-ku, Yokohama-shi, Kanagawa Prefecture Inside Mitsubishi Chemical Co., Ltd. F term (reference) 4G048 AA04 AA05 AB01 AB05 AC06 AD06 AE05 5H029 AJ03 AK03 AK07 AK08 AK16 AL06 AL12 AM03 AM04 AM05 AM07 AM12 AM14 AM16 EJ04 EJ12 HJ13 HJ14 5H050 AA02 BA17 CA09 CB07 EA09 GA10 EA09 HA10 EA09

Claims (20)

[Claims] 1. X-ray powder diffraction under the following measurement conditions:
Intensity A of diffraction peak a observed at 4 ± 1.0 ° and 1
The peak intensity ratio (A / B) of the diffraction peak b observed at 8.3 ± 1.0 ° to the intensity B (A / B) is 0.05 ≦ A / B, and the half width of the diffraction peak b is Is 0.20 ° or more 2
° or less, a lithium manganese composite oxide. [Table 1] [Measurement conditions] X-ray source: CuKα ₁ ray (CuKα ₁ = 1.5406 °) Divergence slit: 0.25 ° Scattering slit: 0.25 ° Light receiving slit: 0.15 mm Step width: 0.020 ° 2. The lithium manganese composite oxide according to claim 1, wherein the value of the peak intensity ratio A / B is 20 or less. 3. The lithium manganese composite oxide, wherein a part of the Mn site is replaced by another metal element, and a part of the Li site is replaced by another metal element. 3. The lithium manganese composite oxide according to 1 or 2. 4. A method according to claim 1, wherein part of the Mn site of the lithium manganese composite oxide is Al, Ti, V, Cr, Fe, Li, C
o, Ni, Cu, Zn, Mg, Ga, Zr, Nb, M
o, Pd, Si, Sn, Ta, W, Ru, As, Te,
4. The method according to claim 1, wherein said metal is substituted with at least one metal element selected from the group consisting of Re and Ge.
4. The lithium manganese composite oxide according to any one of the above. 5. A method according to claim 1, wherein part of the Li site of the lithium manganese composite oxide is K, Na, Ba, Mg, Ca, Zn, or C.
u, Ga, Mn, Pb, La, Ce, Nd, Y, Cs,
Rb, Tl, Au, Sr, Eu, Ag, Ac, Bi, H
The lithium manganese composite oxide according to claim 3, wherein the lithium manganese composite oxide is substituted with at least one metal element selected from the group consisting of g and Pu. 6. A part of the Mn site of the lithium manganese composite oxide has an ionic radius of Mn (an ionic radius of Mn ³⁺ ).
The metal element (M1) having a smaller ionic radius in the valence when contained in the lithium-manganese composite oxide is more substituted, and a part of the Li site has an ionic radius of Li (an ionic radius of Li ⁺ ). 4. The lithium-manganese composite oxide according to claim 3, wherein the lithium-manganese composite oxide is substituted with a metal element (M2) having a larger ionic radius in valence when contained in the lithium-manganese composite oxide. 7. The method according to claim 1, wherein the metal element (M1) is Al, Ti, V,
Cr, Fe, Co, Ni, Ga, Nb, Mo, Pd, S
The lithium manganese composite oxide according to claim 6, wherein the lithium manganese composite oxide is at least one selected from the group consisting of i, Ta, W, Ru, As, Te, Re, and Ge. 8. The method according to claim 8, wherein the metal element (M2) is K, Na, Ba,
Ca, Cu, Pb, La, Ce, Nd, Y, Cs, R
b, Tl, Au, Sr, Eu, Ag, Ac, Bi, Hg
The lithium manganese composite oxide according to claim 6, wherein the lithium manganese composite oxide is at least one selected from the group consisting of Li and Pu. 9. A method for producing a lithium manganese composite oxide having a layered structure by firing a mixture of a lithium source and a manganese source, wherein the lithium source and the manganese source are uniformly mixed. The method for producing a lithium manganese composite oxide according to any one of claims 1 to 8, wherein the mixture is calcined at 600 to 1200 ° C. 10. The method for producing a lithium manganese composite oxide according to claim 9, wherein the firing is performed at 650 to 880 ° C. 11. The method for producing a lithium-manganese composite oxide according to claim 9, wherein lithium and an element source other than manganese are uniformly mixed together with the lithium source and the manganese source. 12. The method according to claim 9, wherein the uniform mixing is performed by a wet method.
2. The method for producing a lithium manganese composite oxide according to any one of 1. 13. The method for producing a lithium manganese composite oxide according to claim 9, wherein a water-soluble lithium source is used. 14. The method for producing a lithium manganese composite oxide according to claim 9, wherein after mixing, spray drying is performed and then firing is performed. 15. The method for producing a lithium manganese composite oxide according to claim 9, wherein a part of the firing step is performed in an inert gas atmosphere. 16. The method for producing a lithium manganese composite oxide according to claim 9, wherein after firing in an oxygen-containing atmosphere, firing is performed in an inert gas atmosphere. 17. The method for producing a lithium manganese composite oxide according to claim 9, wherein the firing is performed in an inert gas atmosphere. 18. A positive electrode material for a lithium secondary battery, comprising the lithium manganese composite oxide according to claim 1. Description: 19. A positive electrode for a lithium secondary battery, comprising the positive electrode material for a lithium secondary battery according to claim 18 and a binder. 20. A positive electrode according to claim 19, a negative electrode,
A lithium secondary battery having an electrolyte layer.