JPH10241667A - Electrode active substance for nonaqueous battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode active substance for lithium-iron based nonaqueous battery which not only has its charge/ discharge reversibility but is provided with its high discharge capacity. SOLUTION: A mixed crystalline phase of a lithium-iron complex oxide α-LiFeO2 having a crystal structure of space group Fm3m and lithium-iron complex oxide β-LiFe5 O6 having a crystal structure of space group Fd3m, comprising a lithium-iron complex oxide of 0.1<=z<=0.7 in mole ratio z (Li/Fe) between lithium(Li) and iron (Fe) as an electrode active substance for nonaqueous battery.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode active material for a non-aqueous battery, and more particularly, to a lithium electrode suitable as an electrode active material for a lithium secondary battery using a non-aqueous electrolyte such as an organic electrolyte. The present invention relates to an iron composite oxide.

[0002]

2. Description of the Related Art Conventionally, lithium cobalt oxide (LiCoO ₂ ) has been used as a general material as a positive electrode active material of a non-aqueous battery using such a non-aqueous electrolyte, for example, a lithium secondary battery. However, as an alternative material due to problems such as cost and resources, iron (Fe), which is rich in resources, is
Are attracting attention as positive electrode active materials.

As an example using iron (Fe) as a positive electrode active material, for example, Japanese Patent Application Laid-Open No. 8-78019 discloses a BET
The specific surface area produced by the method is 0.5 to 20.5 m ² / g
A lithium iron composite oxide Li _x F
eO _y (0 <x ≦ 1.5, 1.8 <y <2.2) is disclosed. This Li _x FeO _y material is made of lithium carbonate (L
i ₂ CO ₃ ) and ferric oxide (Fe ₂ O ₃ ) in a molar ratio of 1: 1.
And heat-treated in the air, and pulverized to a specific particle size (specific surface area) to use, thereby obtaining a battery having a large discharge capacity.

[0004] Japanese Patent Application Laid-Open No. 7-134886 also discloses
Li _x F as lithium cathode composite oxide
eO _y (1.25 ≦ x ≦ 5.05, 1.8 ≦ y ≦ 4.02
5) is disclosed. According to this, Li _x FeO
_y is obtained by specifying the molar ratio of lithium to iron (Li / Fe), mixing the raw materials, and baking the mixture at a temperature of 500 to 900 ° C. By using this as a positive electrode active material, a battery having a large discharge capacity is obtained. Is obtained.

Further, Japanese Patent Application Laid-Open No. 5-62679 discloses that
Lithium iron composite oxide β-LiFeO as positive electrode active material
_A technique for obtaining a battery having a large discharge capacity by using No. ₂ is disclosed. According to this, β-LiFeO ₂
The calcined product containing as a main component has a molar ratio of lithium to iron (Li
/ Fe) is set to 0.8 to 1.2, and the raw materials are mixed.
It is obtained by firing at a specific temperature of 00 ° C., and a high discharge capacity is obtained.

Japanese Patent Application Laid-Open No. 8-124600 discloses that
As a positive electrode active material, in X-ray diffraction, plane spacing is 4.8 ± 0.3
Compositional formula LiFeO ₂ having angstrom peak
A technique for obtaining a battery having a large discharge capacity by using the composite oxide given by (1) is disclosed. According to this, the element M (M: an element other than lithium, which can be a monovalent or divalent cation) is a MFeO having a layered structure.
It is said that a high discharge capacity can be obtained by using a complex oxide LiFeO ₂ obtained by performing ion exchange reaction of a type ₂ compound in a lithium molten salt and replacing it with lithium.

Further, Japanese Patent Application Laid-Open No. 5-275079 discloses a technique in which iron oxide, particularly α-Fe ₂ O _3, which is immersed and treated in a solution of an organic lithium compound, is used as a negative electrode active material. This publication discloses Japanese Patent Application Laid-Open No. 3-1120.
There is disclosed a technique for obtaining a battery having better cycle characteristics than using ferric oxide (Fe ₂ O ₃ ) disclosed in Japanese Patent Publication No. 70 as a negative electrode active material.

[0008]

However, the above-mentioned Japanese Patent Application Laid-Open No. 8-78019 or Japanese Patent Application Laid-Open No.
Although the molar ratio (Li / Fe) in the starting material is specified in the one disclosed in Japanese Patent No. 4986, the discharge capacity is not always satisfactory even with the electrodes disclosed thereby.

The lithium-iron composite oxides disclosed in JP-A-5-62679, JP-A-8-124600, and JP-A-5-275079 alleged that a high discharge capacity was obtained. Some iron composite oxides have various crystal structures. Not only the molar ratio (Li / Fe) of lithium (Li) and iron (Fe) but also the lithium iron composite oxide The crystal structure is different, and it is presumed that the crystal structure strongly relates to the discharge capacity as the electrode active material.

As a means for synthesizing the lithium iron composite oxide, various methods have been proposed, such as an ion exchange reaction in a molten salt and a lithium insertion reaction in a solution of an organic lithium compound, in addition to a usual solid phase reaction. However, since the crystal structure formed differs depending on the synthesis means employed, it is presumed that the choice of the synthesis means is also an important key.

An object of the present invention is to provide a lithium-iron-based composite oxide having not only a reversible charge / discharge but also a high discharge capacity as an electrode active material used for a non-aqueous battery such as a lithium secondary battery. To provide things.

[0012]

In order to achieve this object, an electrode active material for a non-aqueous battery according to the present invention has a space group of Fm3m.
Α-LiFeO, a lithium-iron composite oxide having a crystal structure of
₂ and a mixed crystal phase of lithium-iron composite oxide β-LiFe ₅ O ₈ having a crystal structure of space group Fd3m, wherein the molar ratio z (Li / Fe) of lithium (Li) and iron (Fe) is The gist of the invention is to include a lithium iron composite oxide satisfying 0.1 ≦ z ≦ 0.7.

In this case, "Fm3m" or "Fd
"3 m" indicates a space group represented by an international symbol based on the Herman-Morgan symbol. Space group Fm3
Lithium iron composite oxide α-LiFe having a crystal structure of m
O ₂ (JCPDS Powder Diffraction File, 17-0938)
It has a rock salt type (NaCl type) structure, and the space group F
Lithium iron composite oxide β-Li having a crystal structure of d3m
Fe ₅ O ₈ (JCPDS Powder Diffraction File, 17-0114)
Has a spinel structure. Both of these crystals have a cubic close-packed (ccp) oxygen ion lattice, and the ratio of the metal ion lithium ion (Li ⁺ ) and iron ion (Fe ³⁺ ) between the lattices. And the way of arrangement is different.

That is, in α-LiFeO ₂ , lithium ions (Li ⁺ ) and iron ions (Fe ³⁺ ) are octahedral sites at a ratio represented by the composition formula [Li ⁺ ₂ Fe ³⁺ ₂ ] _oct O _4. (Oct), and lithium ions (Li ⁺ ) and iron ions (Fe ³⁺ ) are irregularly arranged. β-LiFe
_{In 5} O ₈ , the composition formula (Fe ³⁺ ) _tet [Li ⁺ _0.5 Fe ³⁺ _1.5 ]
_At a rate represented by _oct O ₄ , lithium ions (Li ⁺ ) and iron ions (Fe ³⁺ ) are distributed at tetrahedral sites (tet) or octahedral sites (oct), and α-LiFeO ₂
In the same manner as described above, the lithium ions (L
i ⁺ ) and iron ions (Fe ³⁺ ) are irregularly arranged.

In this case, although the amount of oxygen cannot be specified, the electrode active material for a non-aqueous battery according to the present invention, which is composed of a mixed crystal phase of α-LiFeO ₂ and β-LiFe ₅ O ₈ , ie, lithium The composition formula of the iron composite oxide is
Li ⁺ _z Fe ³⁺ O _p is assumed to be close to (0.1 ≦ z ≦ 0.7), also is charge compensation deficiency of the lithium-ion (Li ⁺⁾ is the increase in iron ions (Fe ³⁺⁾ This suggests that an empty site (vacancy) through which lithium ions (Li ⁺ ) can diffuse is formed.

Further, α-LiFeO ₂ and β-LiFe ₅ O ₈
Is not known, but each composition formula is α
-LiFeO ₂ is Li ⁺ _x Fe ^{3 +} O _{2-(1-x) / 2} (x <1)
Where β-LiFe ₅ O ₈ is Li ⁺ _m Fe ³⁺ O
It is estimated that _{8 / 5- (1 / 5-m) / 2} (m <1/5). Therefore, the composition formula Li ⁺ _z Fe ³⁺ of the lithium iron composite oxide which is the electrode active material for a non-aqueous battery according to the present invention.
O range of values of p for _p is at least, 2- (1-x) /
2>p> 8 / 5- (1 / 5-m) / 2.

Here, when “□” is an empty octahedral site and the lithium iron composite oxide α-LiFeO _{2 is represented} by a composition formula, [Li ⁺ _{8x / 3 (1 + x / 3)} Fe ³⁺ _{8 / 3 (1 + x / 3)} □
_{4 (1-x) / 3} (1 + x / 3)] is expressed as _oct O _4, if indicated lithium iron composite oxides β-LiFe ₅ O ₈ by the composition formula, (Fe ³⁺⁾
_tet [Li ⁺ _{8m / 3 (1 + m / 3)} Fe ³⁺ _{5 (1-m / 5) / 3 (1 + m / 3)} □
₅ becomes _{(1/5-m) /} 3 (1 + m / 3)] can be expressed as _oct O _4.

From this, the lithium iron composite oxide α-L
4 (1-x) / 3 (1 + x / 3) for iFeO ₂
Empty octahedral sites are formed irregularly at a ratio of 5 (1 / 5-m) / 3 (1 + m / 3) in the case of the lithium iron composite oxide β-LiFe ₅ O ₈ . Empty octahedral sites will be formed irregularly in a proportion.
By forming an empty site in this manner, α-L
It is presumed that the crystal lattices of iFeO ₂ and β-LiFe ₅ O ₈ expand.

Meanwhile, it the range of values of z of a non-aqueous battery electrode active material according to the present invention Li ⁺ _z Fe ³⁺ O _p is 0.1 ≦ z ≦ 0.7, as described above It is desirable. This is because when the value of z becomes smaller than 0.1, Li ⁺ _m
The main phase is Fe ³⁺ O _{8 / 5- (1 / 5-m) / 2} , and the value of z is 0.7.
Since the becomes larger than _{^{Li + x Fe 3+ O 2- (}} 1-x) / 2 is the main phase, not obtained a synergistic effect as a mixed crystal phase In either case, the lithium secondary battery of this This is because a sufficient battery capacity cannot be obtained even if it is applied to the above. As an electrode active material for a non-aqueous battery capable of obtaining a particularly good discharge capacity when applied to a lithium secondary battery, lithium (Li) and iron (Fe) in a mixed crystal phase are used.
Having a molar ratio z (Li / Fe) of about z = 0.3 to 0.5.

Further, the electrode active material for a non-aqueous battery according to the present invention has a crystal structure of space group Fm3m.
β-LiFe with eO ₂ and crystal structure of space group Fd3m
Comparing the diffraction peaks in X-ray diffraction with ₅ O ₈ ,
The diffraction peak of β-LiFe ₅ O ₈ is relatively broad (the width of the diffraction line is widened). That is, the electrode active material for a non-aqueous battery according to the present invention includes α-LiFeO ₂ and α-LiFeO ₂ , which have higher crystallinity than β-LiFe ₅ O _8.
It is mainly composed of a mixed crystal phase with β-LiFe ₅ O ₈ having lower crystallinity than O ₂ , in other words, a mixed crystal phase composed of two substances having different crystallinities. Among them, the β-LiFe ₅ O ₈ phase having a high amorphous property and a small crystallite size was obtained because the mixed crystal phase was synthesized by a molten salt treatment method at a relatively low temperature of 200 to 300 ° C. It is inferred that this is the case.

Since the insertion / desorption reaction as an electrode active material is nothing but the ingress and egress of lithium ions (Li ⁺ ) through the surface of the electrode active material, in addition to the disorder of the lattice within the crystal lattice, the crystallite size It is presumed that the effect of the above is also working effectively. That is, since lithium ions (Li ⁺ ) can easily enter and exit from the crystallite surface, the interfacial reaction resistance between the electrolyte and the electrode active material is reduced, and the polarization is reduced. An electrode active material that maintains a high capacity is configured. β-LiFe ₅
In O ₈ , since the diffraction line became broader toward the higher angle, the crystal lattice due to the formation of vacancies, irregularities in the arrangement of lithium ions (Li ⁺ ), iron ions (Fe ³⁺ ), and vacancies, etc. It is presumed that the disturbance is increased.

According to the electrode active material for a non-aqueous battery having the above structure, the lattice expansion, the lattice expansion, and the crystal structure of the lithium iron composite oxide α-LiFeO ₂ and the lithium iron composite oxide β-LiFe ₅ O ₈ respectively. In addition to the formation of vacancies, disordered crystal lattices such as lithium ions (Li ⁺ ), iron ions (Fe ³⁺ ) and irregularities in the arrangement of vacancies are introduced, and both have a cubic close-packed oxygen ion lattice. The coexistence promotes the disorder of the lattice in each crystal lattice and significantly increases. Therefore, lithium ion (Li
⁺ ) Diffusion paths are formed. This allows
Lithium ions (Li ⁺ ) can be easily inserted or desorbed with a valence change of Fe ³⁺ → Fe ²⁺ or Fe ²⁺ → Fe ³⁺ . This lithium ion (L
Reversible discharge / charge becomes possible by the insertion / desorption of i ⁺ ), which contributes to realization of good cycle characteristics and high discharge capacity.

The lithium iron composite oxide β-LiFe ₅
O ₈ has a relatively broad diffraction peak as compared with the lithium iron composite oxide α-LiFeO ₂ , so that particularly large lattice disorder is introduced into its crystal structure and its crystallite size is also small. Therefore, lithium ions (Li ⁺ ) can be more easily inserted and desorbed, and high capacity and reversible charge / discharge under a high current density can be achieved.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described specifically with reference to examples. First, electrode active materials for nonaqueous batteries were produced by a molten salt treatment method, a solid-phase reaction method, and an ion exchange method as Examples and Comparative Examples. Tables 1 and 2 collectively show production conditions and reaction products of Examples 1 to 8 of the present invention and Comparative Examples 1 to 12 of comparative products.

[0025]

[Table 1]

[0026]

[Table 2]

Example 1 Lithium nitrate (LiNO ₃ )
And lithium hydroxide monohydrate (LiOH.H ₂ O)
After mixing at a molar ratio of 1:39, α-type iron oxyhydroxide (α-FeOOH) was further added thereto such that the molar ratio (Li / Fe) of lithium (Li) and iron (Fe) became 30. Mixed. All commercially available reagents were used as the raw material powders. This mixed powder was placed in a Pyrex glass beaker and, in an electric furnace filled with nitrogen gas, a temperature of 200 ° C. slightly higher than 186 ° C., which is the eutectic point of lithium eutectic salt (LiNO ₃ —LiOH.H ₂ O). Heat treatment was carried out at a low temperature for 8 hours. After cooling, a lump-shaped sample was obtained in the beaker by melting.

A brown reaction product (lithium iron composite oxide) was observed at the bottom of the sample. Since most of the bulk sample was a molten and solidified lithium salt, it was washed with a large amount of ion-exchanged water and filtered to separate only a brown reaction product. This was dried in a dryer at 120 ° C. for 24 hours, and crushed to obtain a brown powdery reaction product.

Example 2 α-form iron oxyhydroxide (α-
FeOOH) and lithium salt (LiNO ₃ -LiOH · H
_A sample was prepared in the same manner as in Example 1 except that the heating temperature of the mixed powder of ₂ O) was set to 260 ° C., and a powdery reaction product was obtained.

Example 3 The procedure was carried out except that ferrous oxalate dihydrate (FeC ₂ O ₄ .2H ₂ O) was used instead of α-form iron oxyhydroxide (α-FeOOH) as a raw material. A sample was prepared in the same manner as in Example 1 to obtain a powdery reaction product.

Example 4 Ferrous oxalate dihydrate (FeC ₂ O ₄ .2H ₂ O) was used in place of α-form iron oxyhydroxide (α-FeOOH) as a raw material. A sample was prepared in the same manner as in Example 1 except that the heating temperature of the mixed powder of (LiNO ₃ -LiOH · H ₂ O) was set to 260 ° C., to obtain a powdery reaction product. (Examples 5 to 8) The reaction products obtained in Example 1 were used as samples.

Comparative Example 1 A sample was prepared in the same manner as in Example 1 except that α-type iron sesquioxide (α-Fe ₂ O ₃ ) was used as a raw material, and a powdery reaction product was prepared. I got Comparative Example 2 As a raw material, α-type iron sesquioxide (α-Fe
₂ O ₃ ) and a lithium salt (LiNO ₃ -LiO)
A sample was prepared in the same manner as in Example 1 except that the heating temperature of the mixed powder of H.H ₂ O) was set to 260 ° C., to obtain a powdery reaction product.

(Comparative Example 3) As a raw material, α-type iron sesquioxide (α-Fe ₂ O ₃ ) was used, and a lithium salt (LiN
The heating temperature of the mixed powder of O ₃ —LiOH · H ₂ O) is 300
A sample was prepared in the same manner as in Example 1 except that the temperature was changed to ° C, and a powdery reaction product was obtained.

Comparative Example 4 As a raw material, γ-type iron oxyhydroxide (α-FeOOH) was used, and lithium nitrate (Li
NO ₃ ) and lithium hydroxide monohydrate (LiOH · H ₂ O)
And lithium nitrate (LiNO ₃ ) in place of the lithium salt mixed at a molar ratio of 61:39, and the heating temperature of the mixed powder was raised to 255 ° C., which is the melting point of lithium nitrate (LiNO ₃ ). Except that it was 300 ° C,
A sample was prepared in the same manner as in Example 1 to obtain a powdery reaction product.

Comparative Example 5 Lithium Carbonate (Li ₂ CO ₃ )
And α-type iron sesquioxide (α-Fe ₂ O ₃ ) were mixed at a molar ratio of 1: 5, and uniaxially pressed at a pressure of 200 kgf / cm ² using a mold having a diameter of φ25 mm. It was molded to produce a molded body having a thickness of about 10 mm. Using a tubular atmosphere furnace at 900 ° C. in an air flow of 100 cc / min.
And crushed for 24 hours at a high temperature to prepare a sample, thereby obtaining a powdery reaction product.

Comparative Example 6 Lithium Carbonate (Li ₂ CO ₃ )
And γ-type iron sesquioxide (γ-Fe ₂ O ₃ ) are mixed at a molar ratio of 1: 1 and uniaxially pressed at a pressure of 200 kgf / cm ² using a mold having a diameter of 18 mm. It was molded to produce a molded body having a thickness of about 5 mm. Using a tubular atmosphere furnace,
This was fired at a high temperature of 640 ° C. for 8 hours in an air stream of 100 cc / min, and crushed to prepare a sample, thereby obtaining a powdery reaction product.

Comparative Example 7 Lithium Carbonate (Li ₂ CO ₃ )
And α-type iron sesquioxide (α-Fe ₂ O ₃ ) were mixed in a molar ratio of 1: 1 and the calcination temperature was set to 540 ° C. in the same manner as in Comparative Example 6. Was prepared to obtain a powdery reaction product.

Comparative Example 8 Sodium Oxalate (Na ₂ C ₂ O)
₄ ) and ferrous oxalate dihydrate (FeC ₂ O ₄ .2H ₂ O) were mixed at a molar ratio of 1: 2, and a pressure of 200 kgf / cm ² was used using a mold having a diameter of 25 mm. To form a molded body having a thickness of about 10 mm. Using a tubular atmosphere furnace, in an air flow of 100 cc / min, 600
After pyrolysis / firing at a temperature of 20 ° C. for 20 hours, the product was crushed, molded again, and then baked again at a temperature of 650 ° C. for 20 hours to obtain a powder α-NaFeO ₂ .

Next, an ion exchange reaction of Na → Li was attempted in a molten lithium salt (LiNO ₃ ) using the α-NaFeO ₂ as a host material. The molar ratio of lithium (Li) and sodium (Na) (α-NaFeO ₂ )
/ Na) is 30 so that lithium nitrate (LiNO
₃ ) was added and mixed, and an ion exchange reaction was performed at 300 ° C. for 8 hours in the same manner as in Example 1 to prepare a sample, thereby obtaining a reaction product.

Comparative Example 9 Commercially available reagent β-NaFeO ₂
Comparative Example 8 except that an ion exchange reaction of Na → Li was performed in a lithium molten salt (LiNO ₃ ) using
A sample was prepared in the same manner as described above to obtain a reaction product. (Comparative Examples 10 to 12) As Comparative Examples 10 to 12, α-iron sesquioxide (α-Fe ₂ O ₃ ) which is a commercially available reagent,
γ-type iron sesquioxide (γ-Fe ₂ O ₃ ) and triiron tetroxide (F
e ₃ O ₄ ) was used as is.

Next, with respect to the reaction products of the product of the present invention and the comparative product, a powder X-ray diffraction pattern of the produced phase was obtained by using a powder X-ray diffractometer (Rigaku Denki RAD-B, using CuKα ray). The composition of each reaction product was examined by inductively coupled plasma (ICP) emission spectroscopy. The characteristics of the reaction product, such as the crystal system, space group, lattice constant, and Li / Fe molar ratio, of the reaction product were identified based on the results. These characteristics are collectively shown in Tables 3 and 4 and described.

[0042]

[Table 3]

[0043]

[Table 4]

Of the materials shown in Table 3, powder X of Example 1
The line diffraction pattern is shown in FIG. In this figure, the horizontal axis indicates the diffraction angle, and the vertical axis indicates the intensity of each diffraction line. In the figure, (hkl) ^* and (hkl) indicate the space group Fm3, respectively.
m and the surface index of the space group Fd3m. First, the diffraction angle at which a diffraction peak is observed for the plane index (hkl) ^* of the space group Fm3m is spread between 10 and 70 °, but the diffraction peak of (111) ^* is approximately 43 ° and about 43 °. A diffraction peak of (200) ^* is observed around ゜, and a diffraction peak of (220) ^* is observed around 63 °. The powder X-ray diffraction pattern shown in this figure is based on the JCPDS Powder Diffracti
It is consistent with that of on File 17-0938. This allows
It was confirmed that the generated phase contained lithium-iron composite oxide α-LiFeO ₂ having a crystal structure of space group Fm3m.

Next, the surface index (hkl) of the space group Fd3m
The diffraction angle at which a peak is observed is broadly spread between 10 and 70 °, but is close to about 30 ° (22
0), a (311) diffraction peak near about 35 °, a (400) diffraction peak near about 43 °,
A diffraction peak of (511) is found around 57 °, and a diffraction peak of (440) is found near 63 °. The broad X-ray powder diffraction pattern shown in this figure is JCPDS Powder D
It matches the one in iffraction File 17-0114. Accordingly, it was confirmed that the generated phase contained the lithium iron composite oxide β-LiFe ₅ O ₈ having a crystal structure of the space group Fd3m.

When the lattice constant a of α-LiFeO ₂ having a relatively sharp diffraction peak was determined,
4.177 angstroms, and a =
It was found to be significantly larger than 4.158 Å.

Further, the content of lithium (Li) and iron (Fe) of the reaction product of Example 1 was examined by inductively coupled plasma (ICP) emission spectroscopy.
The weight percentages were 2.60% and 54.9%, respectively. The molar ratio (Li / Fe) between lithium (Li) and iron (Fe) was 0.38.

The X-ray powder diffraction pattern of the reaction product of Example 2 was almost the same as that of Example 1, except that α-LiFeO ₂
And a mixed crystal phase of β-LiFe ₅ O ₈ . The molar ratio of lithium (Li) and iron (Fe) (Li /
Fe) is 0.36, and α-Li in the mixed crystal is
The lattice constant of FeO ₂ was a = 4.185.

The powder X-ray diffraction pattern of the reaction product of Example 3 was almost the same as that of Example 1, and α-LiFe
It was confirmed that it was a mixed crystal phase of O ₂ and β-LiFe ₅ O ₈ . The molar ratio of lithium (Li) to iron (Fe) (L
i / Fe) is 0.46, and α-
The lattice constant of LiFeO ₂ was a = 4.176.

The powder X-ray diffraction pattern of the reaction product of Example 4 was also substantially similar to that of Example 1, and α-LiFe
It was confirmed that it was a mixed crystal phase of O ₂ and β-LiFe ₅ O ₈ . The molar ratio of lithium (Li) to iron (Fe) (L
i / Fe) is 0.47, and α-
The lattice constant of LiFeO ₂ was a = 4.179. The fifth to eighth embodiments are the same as the first embodiment, and a description thereof will be omitted.

The powder X-ray diffraction pattern of the reaction product of Comparative Example 1 shows a cubic crystal having a crystal structure of space group Fm3m in addition to the diffraction peak due to the unreacted raw material (α-Fe ₂ O ₃ ). The diffraction pattern of the system due to α-LiFeO ₂ was obtained. When the lattice constant of this α-LiFeO ₂ was examined, a = 4.174. In addition, lithium (L
The molar ratio (Li / Fe) between i) and iron (Fe) is 0.2
8, unreacted α-type iron sesquioxide (α-Fe ₂ O ₃ )
, The proportion of lithium (Li) was insufficient.

The powder X-ray diffraction pattern of the reaction product of Comparative Example 2 was found to be a diffraction pattern of a cubic α-LiFeO ₂ having a crystal structure in the space group Fm3m. The lattice constant is a = 4.17
1 and the molar ratio of lithium (Li) to iron (Fe) (Li / Fe) was 0.82.

The powder X-ray diffraction pattern of the reaction product of Comparative Example 3 showed that the product phases were α-LiFeO ₂ and a trace amount of β-LiF
It was found that this was a lithium iron composite oxide composed of a mixed crystal phase of e ₅ O ₈ . The lattice constant of α-LiFeO _{2 as} the main phase was a = 4.172, and the molar ratio (Li / Fe) between lithium (Li) and iron (Fe) was 0.80.

The powder X-ray diffraction pattern of the reaction product of Comparative Example 4 showed that the produced phase was a cubic β-LiFe ₅ O ₈ having a crystal structure of the space group Fd3m. The lattice constant was a = 8.353, and the molar ratio (Li / Fe) between lithium (Li) and iron (Fe) was 0.06. The powder X-ray diffraction pattern of the reaction product of Comparative Example 5 was
The generated phase was a cubic α-LiFe ₅ O ₈ having a crystal structure of the space group P4132. The lattice constant is a = 8.33
The molar ratio of lithium (Li) to iron (Fe) (Li / Fe) was 0.20.

The powder X-ray diffraction pattern of the reaction product of Comparative Example 6 was a cubic α-LiFeO ₂ having a crystallographic structure in a space group of Fm3m. The lattice constant is a = 4.
156, and the molar ratio (Li / Fe) between lithium (Li) and iron (Fe) was 0.96. The powder X-ray diffraction pattern of the reaction product of Comparative Example 7 shows that the generated phase is in the space group.
Tetragonal γ-LiF having a crystal structure of I 4 ₁ / amd
eO ₂ . The lattice constant is a = 4.055, c = 8.
742, and the molar ratio of lithium (Li) to iron (Fe) (Li / Fe) was 0.94.

The powder X-ray diffraction pattern of the reaction product of Comparative Example 8 was a trigonal layered rock-salt type-LiFeO ₂ having a generated phase having a crystal structure in the space group R-3m. The lattice constant is a = 2.961, c = 14.67, and the molar ratio (Li / Fe) between lithium (Li) and iron (Fe) is:
It was 0.85. The powder X-ray diffraction pattern of the reaction product of Comparative Example 9 was orthorhombic-LiFeO ₂ whose generated phase had a crystal structure of the space group Pna21. The lattice constant is a
= 5.499, b = 6.407, c = 5.064,
The molar ratio of lithium (Li) to iron (Fe) (Li / F
e) was 0.76.

The powder X-ray diffraction pattern of Comparative Example 10 shows a trigonal α-Fe ₂ O ₃ having a crystal structure of space group R-3c.
Met. The lattice constants are a = 5.037 and c = 13.76.
Met. The powder X-ray diffraction pattern of Comparative Example 11 shows a cubic γ-Fe ₂ O ₃ having a crystal structure of space group P4132.
Met. The lattice constant was a = 8.348. The powder X-ray diffraction pattern of Comparative Example 12 was cubic Fe ₃ O ₄ having a crystal structure of the space group Fd3m. The lattice constant was a = 8.396.

(Trial Production of Lithium Secondary Battery) Next, a test cell of a lithium secondary battery was assembled using the reaction products and reagents of Examples 1 to 8 and Comparative Examples 1 to 12 as positive electrode active materials. This will be described with reference to FIG. First, the positive electrode mixture 12 used for the test cell 10 will be described. The positive electrode mixture 12 is composed of a reaction product (α-LiFeO ₂ and β
-Life ₅ as a mixed crystal phase etc.) to the conductive material of the O ₈ and polyvinylidene fluoride as acetylene black and a binder, the reaction products: acetylene black: polyvinylidene fluoride = 90: 5 were mixed in a weight ratio of 5 And N-methyl-2-pyrrolidone to the mixed powder, mixed powder: N
Methyl 2-pyrrolidone = 100: 45 was added and kneaded to form a paste.

And a thickness 0.1 having a hole diameter of φ20 mm.
This paste was applied on a 50 μm-thick aluminum foil (positive electrode current collector plate 14) using a stencil of 2 mm 2.
After drying sufficiently, the positive electrode mixture on this aluminum foil
Heating and pressurization was performed at a temperature of 0 ° C. at a pressure of 1500 kgf / cm ² , and the substrates were brought into close contact. Then, a positive electrode was punched out with a punch having a diameter of 15 mm. As a result, about 10 mg of a reaction product or a reagent as a positive electrode active material was applied to the positive electrode.

Next, the negative electrode 16 is made of metallic lithium (Li) having a thickness of 1 mm punched with a punch having a diameter of 15 mm. As the separator 18, a polyethylene microporous membrane was used. As an electrolytic solution, 1 mol of propylene carbonate (PC) and 1 mol of organic solvent of dimethoxyethane (DME) mixed in a volume ratio of 1: 1 were mixed. LiPF ₆ electrolyte dissolved (1M-LiPF ₆ /
(PC + DME). Reference numeral 20 denotes a positive terminal, 2
2 is a negative electrode terminal and 24 is an insulator.

Next, the characteristics of the lithium secondary battery were evaluated and will be described. In this characteristic evaluation, the battery cell 10 was attached to a charge / discharge test apparatus, and 4.2 to 1.5 V
(Example 5 is 4.2 to 1.2 V, and Example 6 is 4.2 to 1.0 V.
V, Comparative Example 9 is 0.1 m in a voltage range of 4.5 to 1.5 V).
A constant current charge / discharge of A / cm ² (Example 7: 0.5 mA / cm ² , Example 8: 1.0 mA / cm ² ) was carried out and the discharge capacity per 1 g of the positive electrode active material was examined. It is. Tables 3 and 4 described above also show the characteristics of the main reaction products of Examples 1 to 8 and Comparative Examples 1 to 12, as well as the battery characteristics of each of them.

FIG. 3 shows a charge / discharge curve and FIG. 4 shows a cycle characteristic of the lithium secondary battery manufactured using Example 1. The charge / discharge curve shown in FIG. 3 is obtained by plotting the capacity (mAh / g) on the horizontal axis and the voltage (V) on the vertical axis. Charge and discharge alternate between 1.5 and 4.2 V. It is shown that this has been done repeatedly. This proved that the reversibility of charge and discharge was sufficient.

The cycle characteristics shown in FIG. 4 are obtained by plotting the number of cycles on the horizontal axis and the discharge capacity on the vertical axis.
It shows the discharge capacity when charging and discharging are repeated in the range of 5 to 4.2V. According to this, the discharge capacity becomes 130 over the first to tenth cycles.
~ 140 mAh / g, almost stable results (average 13
1 mAh / g). As a result, it was found that a discharge capacity much larger than that of the conventional one (about 20 mAh / g) was repeatedly obtained.

Regarding the battery characteristics of the lithium secondary battery manufactured using Example 2, the discharge capacity was 130 mAh / g.
In addition to showing a considerably larger discharge capacity than the conventional one, it was also found that the reversibility of charge and discharge was sufficient. Regarding the battery characteristics of the lithium secondary battery manufactured by using Example 3, the discharge capacity was 128 mAh / g, which was significantly larger than that of the conventional battery, and the reversibility of charge and discharge was sufficient. There was found.

Regarding the battery characteristics of the lithium secondary battery manufactured using Example 4, the discharge capacity was 128 mAh / g.
In addition to showing a considerably larger discharge capacity than the conventional one, it was also found that the reversibility of charge and discharge was sufficient. The battery characteristics of the lithium secondary battery manufactured using Example 5 were as follows:
The voltage range of 4.2 to 1.2 V was examined. The discharge capacity was 148 mAh / g, which was much larger than the conventional one, and the reversibility of charge and discharge was sufficient. It has been found.

The battery characteristics of the lithium secondary battery manufactured using Example 6 were obtained by examining the battery characteristics in a voltage range of 4.2 to 1.0 V. The discharge capacity was 259 m.
Ah / g, a discharge capacity considerably larger than that of the conventional one, and reversibility of charge and discharge was found to be sufficient.

The battery characteristics of the lithium secondary battery manufactured using Example 7 were obtained by examining the battery characteristics at a charge / discharge current of 0.5 mA / cm ^2.
8 mAh / g. The battery characteristics of the lithium secondary battery manufactured using Example 8 were such that the charge / discharge current was 1.0 mA /
When the battery characteristics were examined in terms of cm ² , the discharge capacity was 70 mAh / g. According to those of Examples 7 and 8, it was found that even when the current density was increased to a practical level, the discharge capacity was considerably larger than that of the conventional one. It was also found that the reversibility of charge and discharge was extremely high.

Using Comparative Examples 1 to 12, the battery characteristics were examined in the same manner as in Example 1. The results were as follows. The battery characteristics of the lithium secondary batteries manufactured using Comparative Examples 1 to 3 were as follows: discharge capacity was 41 mAh / g and 52 mAh, respectively.
/ G, 58 mAh / g, and a very large discharge capacity could not be obtained. From the results of Comparative Examples 1 to 3, α-L
iFeO ₂ only or lithium (L
It was found that when the molar ratio (Li / Fe) between i) and iron (Fe) was close to 1 and α-LiFeO ₂ was the main phase, a very large discharge capacity could not be obtained.

The battery characteristics of the lithium secondary battery manufactured using Comparative Example 4 were as follows. The discharge capacity was 67 mAh / g, and it was found that a very large discharge capacity could not be obtained. From this result, the molar ratio of lithium (Li) and iron (Fe) (Li / Fe) is close to 0, if consisting only of β-LiFe ₅ O ₈ is that not too large discharge capacity can be obtained all right.

As for the battery characteristics of the lithium secondary battery manufactured using Comparative Example 5, the discharge capacity was 16 mAh / g, and it was found that only the same capacity as that of the conventional battery could be obtained. From these results, it can be seen that the space group is P 4132 and α-LiFe ₅ O ₈ in which the molar ratio (Li / Fe) between lithium (Li) and iron (Fe) is the stoichiometric ratio (0.2). It was found that a large discharge capacity could not be obtained.

As for the battery characteristics of the lithium secondary battery manufactured using Comparative Example 6, the discharge capacity was 12 mAh / g, and it was found that only the same capacity as that of the conventional battery could be obtained. From these results, it can be seen that the composition is composed of only α-LiFeO ₂ and has a molar ratio of lithium (Li) to iron (Fe) (Li / Fe).
It was found that when the stoichiometric ratio was almost the stoichiometric ratio (1), a very large discharge capacity could not be obtained.

The battery characteristics of the lithium secondary batteries produced using Comparative Examples 7 to 9 were as follows: the discharge capacity was 10 mAh /
g, 15 mAh / g, and 43 mAh / g, indicating that only the same capacity as the conventional one can be obtained. From the results of Comparative Examples 7 to 9, the space groups were different and α-LiF
It was found that in the case of a lithium iron composite oxide having a crystal structure different from that of eO ₂ or β-LiFe ₅ O ₈ , a very large discharge capacity could not be obtained.

The battery characteristics of the lithium secondary batteries prepared using Comparative Examples 10 to 12 (commercially available reagents) were as follows: discharge capacity was 26 mAh / g, 26 mAh / g, and 13 mAh / g, respectively.
It was found that only the same capacity as that of the conventional device could be obtained.

From the above results, it is clear that the electrode active material of this example achieved a considerably large discharge capacity as compared with the comparative example (conventional one). In this case, the molar ratio between lithium (Li) and iron (Fe) is such that the molar ratio z (Li / Fe) is z = 0.3 to from the comparison between the product of the present invention and the comparative product.
A value of about 0.5 is particularly desirable, but at least 0.1 is necessary because it is necessary to introduce vacancies in the crystal structure and disorder of the crystal lattice such as irregularities in the arrangement of lithium ions, iron ions and vacancies. It is required that ≦ z ≦ 0.7.

The positive electrode active material, which is a reaction product, has a lattice expansion and voids formed in the crystal structures of the lithium iron composite oxide α-LiFeO ₂ and the lithium iron composite oxide β-LiFe ₅ O _8. , lithium ion (Li ^+), iron ions (Fe ³⁺⁾ and lithium as disorder of the crystal lattice can be introduced irregularities such arrays of holes (Li) and iron (F
e) and the molar ratio z (Li / Fe) with 0.1 ≦ z ≦ 0.7, and both coexist with a cubic close-packed oxygen ion lattice. Turbulence is encouraged and will increase significantly.

With these features, lithium ion (L
i ⁺ ) is formed, so that Fe ³⁺ → Fe ²⁺ ,
Alternatively, lithium ions (Li ⁺ ) can be easily inserted or ^{removed with} a valence change of Fe ²⁺ → Fe ³⁺ . Further, a lithium iron composite oxide β-LiFe
₅ O ₈ has a relatively broad diffraction peak as compared with the lithium-iron composite oxide α-LiFeO ₂ , so that particularly large lattice disorder is introduced into its crystal structure, and its crystallite size also increases. small. From these facts, insertion / desorption of lithium ions (Li ⁺ ) is made easier, so that reversible discharge / charge becomes possible, which contributes to realization of good cycle characteristics and high discharge capacity.

According to this example, the reaction product was 20
Since it is obtained after heat treatment in a relatively low temperature range of 0 to 300 ° C., corrosion of a reaction vessel and an electric furnace can be reduced, so that manufacturing equipment can be used for a long time. It will be possible to reduce production costs.

The present invention is not limited to the above-described embodiments, and can be applied to various batteries without departing from the gist of the present invention. For example, in the above embodiment, only the case where the electrode active material according to the present embodiment is used as the positive electrode active material of a lithium secondary battery has been described as an example, but the electrode active material according to the present embodiment is a primary battery, a secondary battery, Alternatively, the present invention can be applied to a non-aqueous battery regardless of whether it is a positive electrode or a negative electrode.

[0079]

The electrode active material for a non-aqueous battery according to the present invention is a lithium iron composite oxide α having a crystal structure of space group Fm3m.
-LiFeO ₂ and a mixed crystal phase of a lithium iron composite oxide β-LiFe ₅ O ₈ having a crystal structure of a space group Fd3m, and a molar ratio z (L) of lithium (Li) and iron (Fe)
(i / Fe) is mainly composed of a lithium iron composite oxide in which 0.1 ≦ z ≦ 0.7. In addition, lithium ion insertion / desorption reactions occur through disorder of the crystal lattice introduced into the crystal structure, whereby an electrode active material having reversibility of charge / discharge and high discharge capacity can be obtained. .

In addition to the reversibility of charge / discharge, a high charge / discharge capacity is ensured.
It is expected to be applied to communication office equipment such as personal computers and mobile phones, or to electric vehicle power supplies for which demand is expected in the near future.

[Brief description of the drawings]

FIG. 1 is a view showing an X-ray diffraction pattern for analyzing a crystal structure of a reaction product of Example 1 which is a product of the present invention.

FIG. 2 is a cross-sectional view showing a configuration of a battery cell of a lithium secondary battery for testing battery characteristics of the product of the present invention.

FIG. 3 is a diagram showing charge / discharge characteristics of a lithium secondary battery using the reaction product of Example 1 as a positive electrode active material.

FIG. 4 is a view showing cycle characteristics of a lithium secondary battery using the reaction product of Example 1 as a positive electrode active material.

Claims (1)

[Claims] 1. A mixed crystal phase of a lithium iron composite oxide α-LiFeO ₂ having a crystal structure of a space group Fm3m and a lithium iron composite oxide β-LiFe ₅ O ₈ having a crystal structure of a space group Fd3m. , Lithium (Li) and iron (Fe)
A lithium iron composite oxide having a molar ratio z (Li / Fe) of 0.1 ≦ z ≦ 0.7 with the electrode active material for a non-aqueous battery.