JP2000090923A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode material having 5 V solid phase redox potential comprising spinel structure manganese iron lithium base composite oxide capable of controlling expansion and contraction by using Fe as a replacing element of Mn. SOLUTION: In a secondary battery comprising a positive active material, a negative active material, and a nonaqueous electrolyte containing a lithium salt, the positive active material is spinel structure manganese iron lithium composite oxide having a lattice constant (a) of 8.19-8.28 Å, represented by general formula, Li[Fe1/2+xMeyMn3/2-x-y]O4 (wherein 0<x, 0<y, x+y=<=1/2, Me is one or two or more of Cr, Co, and Al). The positive active material is prepared in such a way that at least one of a Cr source compound, a Co source compound, and an Al source compound is added to a mixture containing LiOH, MnOOH (manganite), and FeOOH (goethite), the mixed powder is pressed to form a pellet, the pellet is preliminarily baked in the air at 250-600 deg.C for 2-12 hours, the preliminarily baked material is crushed, the crushed powder is molded in a pellet again, then the pellet is heated in the air at 700-850 deg.C for 2-24 hours as main baking.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a positive electrode active material comprising a composite oxide suitable as a positive electrode material for a lithium ion secondary battery, in particular, an all solid state lithium ion battery, a method for producing the same, and a method for producing the same. The present invention relates to a lithium ion secondary battery in which a negative electrode active material made of a material is combined.

[0002]

2. Description of the Related Art As a positive electrode active material of a lithium secondary battery,
A 4V discharge reaction with a practical discharge capacity has been confirmed.
Materials include LiCoO_Two, LiNiO_Two , LiM
n_Two O _FourAre known. What
Even, LiMn_TwoO_Four Is a resource-rich and inexpensive man
Significant reduction in cathode cost due to use of cancer compound as raw material
It is drawing attention as a possible material. However, LiMn_Two 
O_FourIs a positive electrode active material, LiMn_TwoO_FourCrystal structure
The diffusion rate of Li ions during fabrication is slow, and the internal resistance of the battery is low.
Increase in operating voltage during discharge,
Of the manganese in the crystal.
The compound dissolves in the electrolyte and the reversibility of the electrode is lost.
Has disadvantages.

For this reason, LiMn_TwoO_FourOne of the Mn atoms
LiMn whose part is replaced by another atom X _(2-y)X_y O
_FourAttempts have been made to use as a positive electrode active material. example
For example, Japanese Patent Application Laid-Open No. 4-87268 discloses Li_x Mn
_(2-y)Fe_yO_Four(However, 0 <x, 0 <y <2)
Of spinel type structure or spinel-like structure
Lithium using lithium manganese iron composite oxide as a positive electrode active material
Battery is described. This battery has an iron content
0 <y <2 is possible, and 0.1 <y <≦ 1
Is stated to be particularly preferred.

However, only a substance produced by mixing manganese dioxide and an oxide or salt of iron and heat-treating it in an atmosphere containing oxygen at a temperature of 450 ° C. or more can be used in a high voltage region of an operating voltage of 3 V or more. It is described that the discharge capacity is large, the internal resistance of the battery is remarkably improved, and large-current discharge is easy. Those which do not satisfy the above manufacturing conditions do not exhibit the expected effect. As a specific example, L
Only the one manufactured at a molar ratio of i: Mn: Fe = 1: 1.6: 0.4 is described, but no specific disclosure is made about a positive electrode material of 0.4 <y.

Japanese Patent Application Laid-Open No. Hei 7-122299 discloses a general formula Li _{1 + x} Mn _{(2-y) AZ} O ₄ (provided that -1.0
<X <1.7, 0 <y <1.2, 0.02 <z <1.
No. 0) describes a lithium battery using a lithium-containing manganese composite oxide having a spinel structure as a positive electrode active material. In this formula, A is a metal cation and N
i, Co, Cu, Fe, Ti, Cr, V, Zr, Nb,
Numerous elements such as Ru, S, Ge, Ga, Sb, and Te are mentioned, and 0.02 <z <1.0. More preferably, the amount of the metal cation added to manganese is It is less than 20%, 0.02 <z <0.4 is preferable, and y = z is not preferable.

It is disclosed that this positive electrode active material can be obtained by subjecting a lithium salt and a manganese salt or a manganese oxide to a solid phase reaction at a high temperature in the presence of a metal oxide or a salt thereof as a dopant. . That is, when lithium carbonate and manganese dioxide are used as raw materials, the firing temperature is 350 ° C. to 900 ° C., preferably 350 ° C. to 500 ° C., and the firing time is 8 hours to 48 hours. When lithium nitrate having a low melting point is used as the lithium salt, the firing temperature is from 300 ° C to 900 ° C, preferably from 300 ° C to 500 ° C. The manganese oxide, λ-MnO _2, electrolytically prepared MnO _2,
It is stated that chemically prepared MnO ₂ and mixtures thereof can be used. However, as described above, more preferably, 0.02 <z <0.4, and in the case where the cation is Fe, the Examples
Only _0.95 Mn _1.7 Fe _0.2 O ₄ is shown, but only _0.15 Mn _1.7 Fe _0.2 O ₄ .
No specific disclosure is made of a material using a positive electrode material of 4 <z.

[0007] Japanese Patent Laid-Open No. 8-298115, the general formula _{Li X Mn (2-y)} M y O 4 ( where, 1 ≦ x ≦ 2.
1, 0.45 <y <0.60, M is Ni, Co, F
e, Zn) describes a positive electrode active material for a lithium battery having a cubic spinel structure with a lattice constant of 8.190 angstroms or less. Then, as a method of synthesizing the positive electrode material when Ni is selected as M, the value of y is set to 0.
If it exceeds 2, it is difficult to substitute Mn for Ni, and NiO always remained as an impurity. This trend was independent of the type of starting material. As described above, it was found that a pure spinel structure could not be obtained when the amount of Mn to Ni exceeds 0.2, but as a result of various examinations of the starting materials and synthesis conditions, lithium nitrate as a starting material, Solid-state reaction method using manganese carbonate and nickel nitrate (calcination temperature:
Only when 750 to 850 ° C. was employed, it was found that when the treatment of pressurization and re-firing was repeated, LiMn _1.6 Ni _0.4 O ₄ was obtained even when the value of y was as large as 0.4. It is disclosed that a pure cathode active material of the above general formula cannot be obtained unless specific synthesis conditions are used.

[0008] Japanese Patent Application Laid-Open No. 10-188894 describes
General formula LiMn_(2-y)M_yO_Four(However, 0 <y ≦ 1.
0 and M are represented by Fe, Co, Ni, Cu, Zn, etc.)
A solid secondary battery using a positive electrode active material is described.
When 0 <y ≦ 1.0, the spinel structure is stable
Although it is described as preferable, particularly, 0 <y ≦
It is stated that it is preferably 0.2. Soshi
The positive electrode active material may be a lithium salt (for example, Li_Two
CO_Three , Li_TwoNO_Three, LiOH, etc.), manganese compounds
(For example, Mn_ThreeO_Four, MnO_TwoEtc.), compounds of M (oxidation
Substances, hydroxides, carbonates, nitrates, etc.)
It is obtained by heat treatment at a temperature. "
As a specific example, “Li_TwoCO_Three , Mn_TwoO
_Three , Fe_Two O _ThreeIn a 1: 1.5: 0.5 molar ratio,
LiMn fired at 750 ° C for 8 hours in air_1.5Fe
_0.5O_Four Was synthesized. Is disclosed.

Further, in the literature, the general formula Li [Me _0.5
It has been reported that a composite oxide of [Mn _1.5 ] O ₄ (Me: Cr, Ni, Cu) exhibits a solid-state redox potential of approximately 5 V due to a cubic densely packed oxygen arrangement linked to tetravalent manganese ions (“ Solid State Ioni
cs "81, 162, 1995," J. Electro
chem. Soc. 144, 205, 1997,
"J. Electrochem. Soc." 144, L
205, 1997).

[0010]

In recent years, research and development of lithium ion batteries have been actively carried out, and the lithium ion battery is shifting to a growth period. Among these new batteries, the one that works quietly as the positive and negative electrodes is called the lithium insertion material. The battery functional material does not function as a single material, but the compatible materials are always paired (battery), and exhibit a power storage / power generation function by appropriately changing the chemical composition from time to time. When batteries are evaluated on a common scale, the concept of energy density is often used. Material development for high energy density batteries
A material having a large storage capacity per unit volume (or unit weight) may be skillfully combined to achieve a high battery voltage and a light weight.

A lithium ion-containing transition metal oxide used as a positive electrode material of a lithium ion battery has a capacity of 1 cm ³
It is possible to store more than 1 Ah in the volume. Chalcogenides such as sulfides and selenides are disadvantageous as battery materials because the size of the anions constituting the solid matrix is bulky and the storage capacity is less than half that of oxides. In addition, sulfides and selenides have a stronger covalent bond than oxides, and the operating voltage of a battery when combined with lithium is usually lower than that of oxides. Therefore, when considering a positive electrode material for a high energy density battery, it is limited to a transition metal dioxide (containing lithium ions).

On the other hand, the negative electrode material of the lithium ion battery is
The closer the operating voltage is to the lithium metal negative electrode, the better. A transition metal oxide having a low operating voltage can be used, but when a material having an operating voltage close to that of lithium metal is considered, a structure of an sp element is obtained from the electronic structure of lithium. Among these, the negative electrode material using the compound formation of graphite and lithium composed only of carbon (lithium-graphite intercalation compound) has a storage capacity per unit volume, which is inferior to lithium metal negative electrode It is interesting and attractive in terms of operating voltage, dimensional stability and property stability.

In considering electrode materials for lithium ion batteries, particularly important factors are electrode shape and dimensional stability. From this viewpoint, the formula □ C ₆ + xLi → Li _X C ₆ (0 ≦ x ≦
A comparison between a graphite negative electrode based on 1) and a lithium metal negative electrode shows that the charge / discharge capacity of 1 Ah is now considered. In the case of a lithium metal negative electrode, the volume of the negative electrode disappears by 0.49 cm ³ during discharging, Since the same volume is newly generated at the time of charging, a significant change in the negative electrode volume occurs.

On the other hand, in the case of the LiC ₆ negative electrode, the volume of LiC ₆ is 1.34 cm ³ at a storage capacity of 1 Ah, and the volume when this is discharged to graphite is 1.19 cm ³ .
In other words, the negative volume change is 0.15 per Ah
cm ³ , which is much smaller than that of lithium metal. In addition, the graphite has a strong carbon-carbon covalent bond and a layered structure, and is rich in electrode form and dimensional stability. As described above, the graphite negative electrode expands in volume by about 10% during charging and contracts during discharging. Therefore, a positive electrode suitable for this negative electrode is LiNi.
O ₂ , LiAl _1/4 Ni _3/4 O ₂ , LiCo _1/4 Ni
It is a lithium insertion material such as _3/4 O ₂ or Li [Li _X Mn _{2 -X} ] O _4, whose volume shrinks during charging and expands during discharging. In particular, when considering solid-state batteries such as polymer batteries, which are expected as next-generation lithium batteries, and solid-state lithium-ion batteries such as semi-solid batteries using a gel electrolyte, the development of a new cathode material having such characteristics is particularly desired. .

Iron is the most valuable resource, environment and cost.
LiCoO _Two LiF with the same structure as
eO_TwoAttempts have been made to synthesize as a positive electrode material
Is LiMn_TwoO_FourIs a complex oxide with a spinel structure of Mn
Is a redox
LiMn_Two O
_FourIf you can achieve excellent battery characteristics that cannot be obtained with
Significantly lowers the manufacturing cost of
Co-friendly batteries can be provided.

[0016] In each of the above patent documents, a part of Mn is replaced by another.
Lithium alloy consisting of spinel double oxide substituted with metal
Cathode materials for on-batteries are shown, for example, Li
[Fe _1/2Mn_3/2] O_FourMaterial shows a two-step reaction,
Cycles at 4-5V, but still has problems with electrolyte stability
There is a title. In addition, for the positive electrode materials described in each patent document,
In each case, batteries are manufactured by a specific synthesis method.
A pure single-phase substance of the above composition
, But especially those that substitute for Mn.
When Fe is selected as the positive electrode material, a positive electrode material of 0.5 <y is simply used.
Phase synthesis is very difficult, and each patent document
Method of obtaining a substance like the above, characteristics of the obtained substance, etc.
Is not disclosed. Therefore, the substitution element of Mn
That can control expansion and contraction using Fe
Manufacture of manganese iron lithium-based composite oxide with flannel type structure
Pure single-phase cubic densely packed oxygen arrangement with high Fe substitution
5V solid phase reddish
Battery properties that are extremely useful as cathode materials with
Be expected.

[0017]

SUMMARY OF THE INVENTION The present invention provides a positive electrode active material,
In a secondary battery comprising a negative electrode active material and a nonaqueous electrolyte containing a lithium salt, the positive electrode active material has a general formula Li [Fe
_{1/2 + x Me y Mn} 3/2-x -y] O 4 ( where 0 <
x, 0 <y, x + y ≦ 1/2, Me is Cr, Co, A
l alone or in combination of two or more)
A lithium ion secondary battery characterized by a lithium manganese iron composite oxide having a spinel structure of 8.19 to 8.28 angstroms. The present invention also provides, in particular, the formula Li [Li _1/3 Ti _5/3 ] O as a negative electrode active material.
₄ is a non-aqueous electrolyte lithium-ion secondary battery using the lithium-titanium composite oxide shown in ₄ . Also, the present invention
In particular, when the positive electrode active material of the above general formula and the negative electrode active material of the above formula are combined and the operating voltage using the solid electrolyte is 3.5 V
The above is an all-solid-state lithium ion secondary battery.

Further, the present invention provides the above-mentioned cathode material,
LiOH, MnOOH (manganite), FeOOH
A raw material powder obtained by adding at least one of a compound of a Cr source, a compound of a Co source, and a compound of an Al source to a mixture containing (getite) is pressed into pellets, and is heated at 250 to 600 ° C. in air for 2 to 12 hours. Preliminarily calcined by heating, the preliminarily calcined material is pulverized and formed into pellets again, and 700 to
This is a method for producing a positive electrode material for a lithium ion secondary battery comprising a manganese iron lithium-based composite oxide having a spinel structure, which is heated at 850 ° C. for 2 to 24 hours and subjected to main firing. As the compound of the Cr source, the compound of the Co source, and the compound of the Al source, oxides, hydroxides, carbonates, nitrates and the like can be used. For example, as the Cr source, Cr ₂ O
₃ , Co (OH) ₂ as Co source and Al as Al source
By mixing (OH) ₃ with the raw material powder, Cr, C
General formula Li [Fe _{1/2 +} containing at least one of o and Al
_{x Me y Mn 3/2-} x-y] O 4 ( however, 0 <x, 0 <
y, x + y ≦ 1/2, Me is Cr, Co. (Single or two or more types of Al) can be obtained.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The positive electrode active material of the present invention has a general formula L
i [Fe_{1/2 + x}Me_yMn_{3 / 2-xy}] O _Four(However,
0 <x, 0 <y, x + y ≦ 1/2, Me is Cr, C
o, Al alone or in combination of two or more)
a = 8.19 to 8.28 angstroms of spinel type
It is a structure manganese iron lithium-based composite oxide, and Mn is
Fe, a large amount of Cr, Co, Al
Singly or two or more of
Positive electrode producing a redox potential of about 5 V with a spinel structure of
It is possible to realize the substance.

A specific example of the composition of the lithium manganese iron composite oxide of the present invention is, for example, Li [Fe _0.6 Co _0.3 M
_{n 1.1] O 4, Li [} Fe 0.5 Cr 0.25 Mn 1.25] O
₄ , Li [Fe _0.5 Al _0.25 Mn _1.25 ] O ₄ . Characteristics of spinel structure manganese oxide, the starting materials, the firing temperature is large to be governed by synthetic methods such as baking time, Fe ₂ O ₃ and Li, Mn,
It is necessary to produce a pure (single-phase) composite oxide containing no Fe oxide or the like, and the desired properties of the positive electrode material shown in the prior art are obtained for the first time by a specific production method.

In the present invention, LiOH is used as the Li source, and Mn is used as the Li source.
MnOOH (manganite) as a source and F as an iron source
A raw material powder obtained by adding at least one of a compound of a Cr source, a compound of a Co source, and a compound of an Al source to a mixture containing eOOH (goethite) is pressed into pellets, and first, the pellets are formed in air.
Preheat at 0 to 600 ° C for 2 to 12 hours and calcine. 2
When the temperature is lower than 50 ° C, the reaction becomes only a dehydration reaction,
If it is higher, the reaction becomes heterogeneous, and Li ₂ MnO ₃ , Li
It is not preferable because an impurity phase such as FeO ₂ is mixed. The powder after the calcination is a predetermined cubic microcrystal. The heating time is set to 2 to 12 hours suitable for obtaining predetermined cubic crystallites in relation to the temperature.

The calcined pellets are made into powder by a suitable pulverizing means, the powder is formed into pellets again, and heated in air at 700 to 850 ° C. for 2 to 24 hours, followed by main firing. If the temperature is lower than 700 ° C., the crystal does not grow sufficiently. 85
If the temperature is higher than 0 ° C., Li ₂ Mn ₂ O ₄ , Li ₂ MnO ₃ , L
Separates into iFeO ₂ etc. The heating time is 2 to 2 suitable for growing a predetermined cubic crystal depending on the temperature.
4 hours. At the time of the above synthesis, Fe, Cr, Co, Al
Is fixed in a trivalent state, and the lattice constant is a = 8.19-
8.28.

Li [Fe _1/2 Mn _3/2 ] O ₄ showed clear oxidation peaks at about 4.2 V and 5.1 V by voltammetric measurement, and reduced to 3.9 V and 4.9 V. A peak is observed. Also, by X-ray diffraction (XRD), LiMn ₂ O ₄ (a = 8.24 angstroms)
It has a larger lattice constant a = 8.27 angstroms. General formula Li [Fe _{1/2 + x} Mn _{3 / 2-x} ] O
As the value of x of ₄ increases, the lattice constant a increases. At x = 1/4, the lattice constant a becomes 8.28 angstroms.

The topotactic reaction of Li [Fe _1/2 Mn _3/2 ] O ₄ is represented by the following formula based on the results of experiments.
At 4.05V,

[0025]

[Equation 1] Li [Fe _1/2 Mn _3/2 ] O ₄ → ← Li _1/2 [Fe _1/2 Mn _3/2 ] O ₄ + (1/2) Li + + (1/2) e -(Fd3m; a = 8.27A) (Fd3m; a = 8.17A)

At 5.00 V,

[0027]

[Equation 2] Li _1/2 [Fe _1/2 Mn _3/2 ] O ₄ → ← □ [Fe _1/2 Mn _3/2 ] O ₄ + (1/2) Li + + (1/2) e -(Fd3m; a = 8.17A) (Fd3m; a = 8.07A)

From the above equation, the formula Li [Fe _1/2 Mn
_When a positive electrode for a lithium ion battery is operated, the composite oxide of _3/2 ] O ₄ has a two-stage reaction of 74 mAh / g at 4.0 V and 74 mAh / g at 5 V, for a total of 148 mAh / g.
g of discharge capacity can be obtained.

The present invention uses the formula Li [Fe_1/2 Mn_3/2] O
_Four Me to control the two-step reaction of the complex oxide of
To form a solid solution of one or more elements of Cr, Co, and Al,
The general formula Li [Fe_{1/2 + x} Me_yMn_{3 / 2-xy}] O_Four
 Succeeded in synthesizing a novel single-phase composite oxide
This achieves a reaction in the 5V region.
You. The formula Li [Fe_1/2 Mn_3/2 ] O_Four Complex oxide of C
When one or more elements of o, Cr and Al are dissolved,
The pressure is 4.8-5.2V in all cases,
The area disappears and its capacity rises to the area of about 5V,
A capacity of 100 mAh / g or more is obtained. Other than the above two
As a method of controlling the reaction of the stage, the formula Li [FeMn] O
_Four It is conceivable to synthesize a composite oxide of
Synthesis is theoretically unstable and difficult to synthesize.
The highest Fe content that has hitherto been successful is Li [Fe
_0.75Mn_1.25] O_FourUp to.

[0030] general formula _{Li [Fe 1/2 + x} Me y Mn
_3/2-x-y] for the value of _{O 4} of x, theoretically x
The upper limit becomes 1/2 since 4V disappears and all become 5V when == 1/2. However, the larger the value of x, the more difficult it is to produce a single-phase composite oxide. 1
/ 4, and a preferable value of y is 1/4 or more.
However, when Al is dissolved, the value of x exceeds 1/4 and F
It has been found that it is possible to contain e in production. For example, a composite oxide close to a single phase of Li [Fe _0.8 Al _0.2 Mn] O ₄ can be synthesized. Al is 5V
Is an element suitable for slightly increasing the operating voltage of the insertion material and adjusting the stability of the insertion material during operation and the degree of expansion and contraction.

The cathode material of the present invention is mixed with a conductive agent such as acetylene black and a binder such as polyvinyl fluoride and applied to a current collector such as aluminum, stainless steel and titanium as in a normal battery. can do. As the negative electrode active material, lithium, an alloy such as a Li-Al alloy, a Li-Sn alloy, a Li-Mg alloy, an intercalating material capable of absorbing lithium ions such as carbon and tin oxide can be used. As the electrolyte, propylene carbonate, an electrolyte solution obtained by adding a lithium salt to an organic solvent such as ethylene carbonate, a polypropylene oxide derivative, an organic solid electrolyte such as a polyethylene oxide derivative, a nitride of Li,
Known substances such as inorganic solid electrolytes such as halides and oxyacid salts can be used. Using the positive electrode material of the present invention,
5V with constant current charge / discharge characteristics and graphite as negative electrode active material
Grade non-aqueous electrolyte lithium ion battery can be provided.

Also, lithium titanate or lithium titanate may be used.
A mixed crystal in which titanium and rutile titanium oxide coexist is used as the negative electrode active material.
Although it is known to be a substance, in particular,
Strain-free insert with no change in lattice size before and after the reaction
The formula Li [Li _1/3Ti_5/3] O_FourIndicated by
Combined lithium-titanium composite oxide as negative electrode
Then, using a solid electrolyte, all solid lithium of 3.5V class
An ion battery can be realized. The general formula Li [Li_XTi
_2-X ] O_Four , Except in x = 1/3, in humid air
It is difficult to use because it generates heat by reaction. LiTiO_Four
Is highly reactive with water and cannot be used. The formula Li [Li
_1/3 Ti_5/3 ] O_FourIs, for example, TiO._Two
(Anatase) and LiOH / H_TwoO2 mixture with nitrogen stream
Can be prepared by heating at 800 ° C for 12 hours in
You.

Comparative Experimental Examples LiOH, MnOOH (manganite), FeOOH
(Goethite) mixture (Li: Mn: Fe = 2: 1:
(Molar ratio of 3) was pressed into pellets (diameter 23 mm, thickness 5 mm), which were preheated in air at 550 ° C. for 15 hours and calcined. The state after the calcination at 550 ° C. was a microcrystalline state in which the crystal had not grown sufficiently but had a desired cubic diffraction profile despite broad diffraction lines in the powder X-ray diffraction method. The pre-calcined material is pulverized, formed into pellets again, and finally fired in air at 750 ° C. for 15 hours.
i [Fe _1/2 Mn _3/2 ] O ₄ was prepared. The reaction product was ground and analyzed by XRD. In a similar manner, FeO
Instead of OH, Cr ₂ O ₃ , Co (OH) ₂ , Ni (O
H) ₂ and CuO as raw materials, respectively, and Li [Me _1/2 M
A sample was prepared for n _3/2 ] O ₄ (Me: Cr, Co, Ni, Cu).

Samples were stored on blue silica gel in a desiccator before use. When producing an electrode for cyclic voltammetry, the above reaction product 80 w / o
% (% By weight), 10 w / o of acetylene black and 10 w / o% of polyvinylidene fluoride (PVDF) are dissolved in an N-methyl-2-pyrrolidone (NMP) solution and applied to an aluminum plate (15 × 20 mm ² ). And dried in vacuum at 150 ° C. for 12 hours. Two porous diaphragms (battery guard 2500) were used as separators. An electrolytic solution obtained by dissolving 1 mol of LiPF6 in ethylene carbonate (EC) / diethyl carbonate (DEC) (1/1 by volume) was used.

The open-circuit terminal voltage of the initial battery is as follows:
3.0-3.5V. When the battery was scanned upward at a scanning speed of 0.2 mV / s, distinct oxidation peaks were observed at about 4.2 V and 5.1 V, and reduction peaks were observed at 3.9 V and 4.9 V when cycled back to 3 V. Was. The respective midpoint voltage between the oxidation and reduction peaks is 4.05
V and 5.00V. The redox peak at 4.05V appears to be a single redox peak. Table 1 shows the structural data and electrochemical redox properties of each sample measured between 3.0 and 5.2V. As can be seen from this table, Me = Fe, Cr, Ni, Co, Cu
When synthesized as i [Me _1/2 1Mn _3/2 ] O ₄ , a redox level of about 4.8 to 5.2 V is generated without exception.

[0036]

[Table 1] Lattice constant Redox level * Mea / A E <4.5V E> 4.5V .. Fe 8.269 4.05V 5.00V Cr 8.217 ca. 4.09V ca. 4.9V Co 8.152 ca. 4.0V ca. 5.0V (?) Ni 8.188 ca. 3.95V 4.75V Cu 8.210 3.98 & 4.15V 4.90V

*: Oxidation and reduction peaks obtained by observing a Li [Me _1/2 Mn _3/2 ] O ₄ cell at a scanning rate of 0.2 mV / s between 3.0 and 5.2 V by cyclic voltammetry. Is an estimated value from the intermediate voltage.

[0038]

Example, except that a mixture of Co (OH) ₂ in Example 1 starting mixture in the same manner as above Comparative Experiment _{Li [Fe 0.6 Co 0.3 Mn 1.1} ]
O ₄ was prepared. The lattice constant is a = 8.21 angstroms, there is a slight flat portion (about 15 mAh / g) at 4 V, the operating voltage is 4.8-5.15 V, and the charge / discharge capacity is 90-110 mAh / g (theoretical). 130 mAh /
g). It was confirmed that a value exceeding 90 mAh / g was obtained by solid solution of Co.

Example 2 Li [Fe _0.5 Cr _0.25 Mn _1.25 ] O ₄ was prepared in the same manner as in the comparative example except that the raw material mixture was mixed with Cr ₂ O _3.
Was prepared. The lattice constant is a = 8.25 angstroms, and a little flat portion at 4 V (about 25-30 mAh / g)
The operating voltage is 4.8-5.1 V, and the charge / discharge capacity is 75-90 mAh / g (theoretically 110 mAh / g).
Met. It was confirmed that a value exceeding 75 mAh / g was obtained by solid solution of Cr.

Example 3 Li [Fe _0.5 Al _0.25 Mn _1.25 ] was prepared in the same manner as in the comparative example except that Al (OH) ₃ was mixed in the raw material mixture.
O ₄ was prepared. The solution of Al did not change the capacity of 5 V, and the capacity of 4 V was halved.

[0041]

According to the battery of the present invention, the energy density can be improved by further developing a cathode material for lithium ion batteries using Fe and Mn which are inexpensive and have very little concern about environmental problems and realize the use of a 5 V region. Therefore, it is suitable not only for normal use but also as a large lithium ion battery for electric vehicles. In particular, by selecting a non-strained insertion material made of a lithium-titanium composite oxide represented by the formula Li [Li _1/3 Ti _5/3 ] O ₄ as a negative electrode, all-solid lithium having a high operating voltage can be obtained. An ion battery can be realized.

Claims (4)

[Claims] 1. A positive electrode active material, negative electrode active material, a secondary battery comprising a nonaqueous electrolyte containing a lithium salt, the positive electrode active material has the general formula _{Li [Fe 1/2 + x} Me y Mn 3
_{/ 2−xy} ] O ₄ (where 0 <x, 0 <y, x + y ≦
(1/2, Me is Cr, Co, Al alone or in combination of two or more). It is characterized by being a spinel-type manganese iron lithium-based composite oxide having a lattice constant a = 8.19 to 8.28 angstroms. Lithium ion secondary battery. 2. The method according to claim 1, wherein the negative electrode active material has the formula Li [Li _1/3 T
The lithium ion secondary battery according to claim 1, which is a lithium-titanium composite oxide represented by _i5 / ₃ ] _O4 . 3. An operating voltage of 3.5 V using a solid electrolyte.
The all-solid-state lithium-ion secondary battery according to claim 2, wherein: 4. A raw material powder comprising a mixture containing LiOH, MnOOH (manganite), and FeOOH (geetite) to which at least one of a Cr source compound, a Co source compound, and an Al source compound has been added is pressed and pelletized. And in the air 2
Pre-calcining by heating at 50 to 600 ° C. for 2 to 12 hours, pulverizing the pre-calcined material, forming it again into pellets,
A method for producing a positive electrode material for a lithium ion secondary battery comprising a manganese iron lithium-based composite oxide having a spinel structure, which is heated at 700 to 850 ° C. for 2 to 24 hours in air to perform main firing.