JP3536944B2 - Non-aqueous electrolyte battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nonaqueous electrolyte battery, and more particularly to a positive electrode active material thereof.

[0002]

2. Description of the Related Art In recent years, active materials having an operating voltage of about 4 V for higher energy density and batteries using a carbon material for a negative electrode for longer life have attracted attention. Even when a carbon material is used for the negative electrode for prolonging the life, it is difficult to obtain a high energy density battery unless the operating voltage of the positive electrode is high, so that LiCoO ₂ or LiNi
An oxide having a layered structure represented by LiMO ₂ , such as O ₂ , or an oxide having a spinel structure represented by LiM ₂ O ₄ , such as LiMn ₂ O ₄ , has been proposed and has already been partially put into practical use.

[0003]

The above-mentioned α-Na
It is known that an oxide having an FeO ₂ structure or an oxide having a spinel structure is self-discharged at the end of charging due to decomposition of an electrolyte solution or reaction with mixed water at the end of charging. ing. For example, decomposition of the electrolytic solution generates gas, which causes swelling of the battery and an increase in internal resistance of the battery, causing a problem that the device is damaged or that sufficient characteristics cannot be obtained.

Further, a product obtained by decomposing the alkali-containing oxide by moisture as described above is strongly alkaline, and decomposes the electrolytic solution and the binder to cause a reduction in charge / discharge efficiency and capacity due to cycles. The reaction of forming a strong alkali by water is irreversible, and once the reaction with water occurs, the strong alkali component cannot be removed by simple water removal. In addition, in order to solve this problem, it is necessary to perform sufficient moisture management. However, in order to solve this problem, it is necessary to perform the battery assembly process in a dry air atmosphere, which leads to an increase in cost.

On the other hand, the above-mentioned positive electrode active materials usually have poor electron conductivity, and it has been necessary to add a conductive agent such as carbon black in addition to the positive electrode active material. Therefore,
There is also a problem that the active material packing density of the electrode cannot be increased and the capacity per unit weight and unit volume decreases.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems.
An object of the present invention is to provide a long-life non-aqueous electrolyte battery having excellent storage characteristics and high energy density.

As a result of intensive studies on the above problems, as a means for solving the problems, the surface of the center layer compound capable of reversibly occluding and releasing an alkali metal is made to be inert to an electrolytic solution or moisture and to have an electron conductivity. It has been found that the above problem can be solved by using an active material covered with a compound forming a surface layer having ion conductivity. However, the surface layer and the central layer compound described in the present specification are different from those in which the compounds are simply brought into contact with each other, for example, by mixing.

In the present invention, the compound capable of reversibly storing and releasing an alkali metal is at least α-NaFe.
An oxide having an O ₂ structure or a spinel structure, specifically, an oxide having an α-NaFeO ₂ structure or a spinel structure, such as LiNiO ₂ , LiCoO ₂ , Li
Examples thereof include, but are not limited to, Ni _1-x Co _x O ₂ and LiMn ₂ O ₄ .

The compound forming the surface layer is a metal oxide, a metal composite oxide, a boride, a carbide, a nitride, a silicide,
A metal or alloy, specifically, a metal oxide forming a surface layer, CoO, Cr
O ₂ , Fe ₃ O ₄ , Fe ₂ O ₃ , In ₂ O ₃ , Ir
O ₂ , MnO ₂ , Mn ₂ O ₃ , MoO ₂ , NbO, Nb
O ₂ , OsO ₂ , PtO ₂ , ReO ₂ , ReO ₃ , Ru
O ₂ , LiTiO ₂ , TiO, Ti ₂ O ₃ , Ti
₃ O ₅ , Ti ₃ O ₇ , Ti ₄ O ₇ , Ti ₅ O ₉ , W
O ₂ , W ₁₈ O ₄₉ , V ₂ O ₃ , V ₄ O ₇ , V ₅ O ₉ , V ₆
O ₁₁ , V ₇ O ₁₃ , V ₈ O ₁₅ , VO ₂ , V ₆ O _13, etc. are borides such as CrB ₂ , HfB ₂ , MoB, NbB, Tb
aB, TiB ₂ , ZrB ₂ etc. are B ₄ C,
HfC, MoC, NbC, SiC, TaC, TiC, U
C, VC, WC, ZrC, etc. are BN, Nb as nitrides.
N, TaN, TiN, VN, ZrN, etc. may be MoSi ₂ , NbSi ₂ , TaSi, TiSi ₂ , VS
i ₂ , WSi _2, etc. are Ag as a single metal or alloy,
Examples include, but are not limited to, Al, Au, Cu, Ni, Ti, and SUS.

The method of forming the positive electrode active material into a central layer and one or more surface layers includes a method of baking the surface by firing, a method of chemically treating the active material surface, and a method of electrochemically depositing the active material surface. Examples thereof include, but are not limited to, a method of coating the surface by vapor deposition, a method of applying mechanical energy to the fine powder to cause a strong surface fusion to the compound serving as the central layer, and the like.

[0011]

In the positive electrode active material of the present invention, a compound different from the active material is formed on the surface of an active material capable of reversibly storing and releasing an alkali metal. That is, since the active surface of the active material is covered with a compound different from the active material, a direct reaction with the electrolytic solution and the water mixed in the electrolytic solution is suppressed, and as a result, self-discharge is suppressed. Further, since the decomposition of the electrolyte solution that occurs at the end of charging is also suppressed, the battery does not swell due to gas generation, and the internal resistance of the battery does not increase. Therefore, it is possible to prevent the device from being damaged when this battery is used, and to obtain stable characteristics. Further, since strongly alkaline decomposition products generated by the reaction with water are also suppressed, decomposition of the electrolytic solution and the binder is suppressed, and as a result, the charge / discharge capacity is large, and the charge / discharge efficiency and cycle characteristics are improved.

Further, by disposing an electron conductive compound on the surface, the electron conductivity between particles is improved. Therefore, the amount of the conductive agent to be added can be reduced or eliminated, and the capacity per unit weight and unit volume is improved.

[0013]

Embodiments of the present invention will be described below.

(Example 1) As a synthesis of a compound to be a central layer of a positive electrode active material, a case of LiNiO ₂ which is a lithium composite oxide having a layered structure is taken as an example. LiOH ・ H
₂₀ and NiCO ₃ at a Li: Ni molar ratio of 1.03:
Weigh and mix to 1.00, in oxygen at 750 ° C
For 20 hours. After firing, mechanical energy was applied to 5% by weight of the IrO ₂ fine powder to fuse with the surface of the center layer compound to obtain a positive electrode active material. I was added to the surface of the obtained positive electrode active material.
An rO ₂ layer was confirmed.

Using this positive electrode active material, a coin-type lithium secondary battery was prototyped as follows. The positive electrode active material, acetylene black and polytetrafluoroethylene powder were mixed at a weight ratio of 80: 16: 4, and toluene was added and kneaded sufficiently. This is 0.8mm thick by roller press
Into a sheet. This roller press was performed in the atmosphere. The filling rate of this positive electrode sheet was 34%. Next, this sheet was punched out into a circle having a diameter of 16 mm and heat-treated at 200 ° C. for 15 hours under reduced pressure to obtain a positive electrode 1. The positive electrode 1 was used by being pressed against a positive electrode can 4 provided with a positive electrode current collector 6.
The negative electrode 2 is made of a 0.3 mm thick lithium foil having a diameter of 15 mm.
And pressed to the negative electrode can 5 via the negative electrode current collector 7 for use. 1 m of LiPF _{6 in} a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 1: 1
ol / l dissolved electrolytic solution was used, and a microporous polypropylene membrane was used for the separator 3. 20 mm in diameter and 1.6 m in thickness using the above-mentioned positive electrode, negative electrode, electrolyte and separator.
m was manufactured. This battery is A1
And

Example 2 A positive electrode active material, acetylene black and polytetrafluoroethylene powder were mixed in a weight ratio of 9%.
A battery was fabricated in the same manner as in Example 1 except that the mixture was 4: 2: 4. This battery is designated as A2. The filling rate of the positive electrode sheet used in this battery was 53%.

Example 3 A battery was fabricated in the same manner as in Example 1 except that after firing, the IrO ₂ fine powder was fused instead of applying mechanical energy to fuse the TiB ₂ fine powder. On the surface of the obtained positive electrode active material, TiB ₂
Layers were identified. This battery is designated as A3.

Example 4 A battery was fabricated in the same manner as in Example 1 except that after sintering, instead of fusing IrO ₂ fine powder by applying mechanical energy, fusing fine TiC powder was used. A TiC layer was confirmed on the surface of the obtained positive electrode active material. This battery is designated as A4.

Example 5 A battery was produced in the same manner as in Example 1 except that after baking, the IrO ₂ fine powder was fused with a TiN fine powder instead of being fused by applying mechanical energy. A TiN layer was confirmed on the surface of the obtained positive electrode active material. This battery is designated as A5.

Example 6 A battery was fabricated in the same manner as in Example 1 except that after baking, instead of fusing IrO ₂ fine powder by applying mechanical energy, fusing TiSi ₂ fine powder. On the surface of the obtained positive electrode active material, TiS
i _2-layer has been confirmed. This battery is designated as A6.

Example 7 Instead of fusing IrO ₂ fine powder by applying mechanical energy after firing, instead of adding 5% by weight of Fe ₃ O ₄ before firing the active material, except that it is baked on the LiNiO ₂ surface. A battery was manufactured in the same manner as in Example 1. An Fe ₃ O ₄ layer was confirmed on the surface of the obtained positive electrode active material. This battery is designated as A7.

Example 8 A battery was fabricated in the same manner as in Example 1 except that gold was deposited after firing the active material instead of fusing IrO ₂ fine powder after application of mechanical energy after firing. . Au is applied to the surface of the obtained positive electrode active material.
Layers were identified. This battery is designated as A9.

Comparative Example 1 A battery was manufactured in the same manner as in Example 1 except that the untreated cathode active material was used after firing. The filling rate of the positive electrode sheet used in this battery was 35%.
was.

The batteries A1 to A9,
A charge / discharge cycle test was performed using B1. The test conditions were a charging current of 3 mA, a charge termination voltage, and a power cycle test. The test conditions were a charging current of 3 mA and a charging end voltage of 4.
The discharge current was 2 V, the discharge current was 3 mA, and the discharge end voltage was 3.0 V.
Further, the battery was stored in a charged state at room temperature for 30 days, and its capacity retention and battery swelling were measured.

Table 1 shows the results of the charge / discharge test and the capacity retention of these batteries.

[0026]

[Table 1]

As can be seen from Table 1, the battery A according to the present invention
1 to A9 are superior in the capacity retention after storage for 30 days compared to the comparative battery B1. That is, since the active surface of the active material is covered with a compound different from the active material, it can be seen that direct reaction with the electrolytic solution and the water mixed in the electrolytic solution was suppressed. In addition, since no swelling of the battery was observed after storage for 30 days, decomposition of the electrolytic solution at the end of charging was suppressed, indicating that no gas was generated. Also, batteries A1 to
A9 has a larger initial charge / discharge capacity than the comparative battery B1,
The charge and discharge efficiency is also excellent. Further, the decrease in capacity after 10 cycles was small. In other words, it is considered that the strongly alkaline decomposition products generated by the reaction with water are suppressed, and the decomposition of the electrolytic solution and the binder is suppressed. As a result, the charge / discharge capacity is increased, and the charge / discharge efficiency and cycle characteristics are improved.

When A1, A2, and B1 are compared, it is found that the filling rate is improved, and as a result, the charge / discharge capacity is increased. In other words, it is understood that the surface layer assists the electron conduction between the particles, sufficient characteristics can be obtained without the conductive agent, and the capacity per unit volume is improved.

The present invention is not limited to the starting materials, production methods, positive electrodes, negative electrodes, electrolytes, separators, and battery shapes of the active materials described in the above embodiments. Further, the present invention is also applicable to a device using a carbon material for the negative electrode, a device using a solid electrolyte instead of an electrolyte or a separator, and the like.

[0030]

Since the present invention is configured as described above, it is possible to provide a non-aqueous electrolyte battery having excellent storage characteristics, a large energy density, and a long life.

[Brief description of the drawings]

FIG. 1 is a sectional view of a coin-type lithium secondary battery according to Embodiment 1 of the present invention.

[Explanation of symbols]

1 positive electrode 2 Negative electrode 3 separator 4 Positive electrode can 5 Negative electrode can 6 positive electrode current collector 7 Negative electrode current collector 8 Insulation packing

Continuation of front page (56) References JP-A-4-328258 (JP, A) JP-A-6-150928 (JP, A) JP-A-6-111819 (JP, A) JP-A-6-168721 (JP) JP-A-7-235292 (JP, A) JP-A-8-138670 (JP, A) JP-A-8-171935 (JP, A) JP-A-7-288127 (JP, A) 8-102332 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01M 4/00-4/62 H01M 10/40

Claims (8)

(57) [Claims] 1. A positive electrode active material comprising a central layer composed of a compound capable of reversibly inserting and extracting an alkali metal and a surface layer composed of at least one compound different from the compound constituting the central layer. A non-aqueous electrolyte battery, characterized in that the compound forming the surface layer,
Non-aqueous electrolyte batteries that are borides. 2. A positive electrode active material comprising a central layer composed of a compound capable of reversibly storing and releasing an alkali metal and a surface layer composed of at least one compound different from the compound constituting the central layer. A non-aqueous electrolyte battery, characterized in that the compound forming the surface layer,
Non-aqueous electrolyte battery that is carbide. 3. A positive electrode active material comprising a central layer composed of a compound capable of reversibly inserting and extracting an alkali metal and a surface layer composed of at least one compound different from the compound constituting the central layer. A non-aqueous electrolyte battery, characterized in that the compound forming the surface layer,
Non-aqueous electrolyte battery which is a nitride. 4. A positive electrode active material comprising a central layer composed of a compound capable of reversibly inserting and extracting an alkali metal and a surface layer composed of at least one compound different from the compound constituting the central layer. A non-aqueous electrolyte battery, characterized in that the compound forming the surface layer,
Non-aqueous electrolyte batteries that are silicides. 5. The non-aqueous solution according to claim 1, wherein the compound capable of reversibly storing and releasing the alkali metal is an oxide having an α-NaFeO ₂ structure or an oxide having a spinel structure. Electrolyte battery. 6. The non-aqueous electrolyte battery according to claim 5, wherein the oxide having the α-NaFeO ₂ structure is LiCoO ₂ . 7. The non-aqueous electrolyte battery according to claim 5, wherein the oxide having the α-NaFeO ₂ structure is LiNiO ₂ . 8. The method according to claim 1, wherein the oxide having a spinel structure is L
The nonaqueous electrolyte battery according to claim 5 wherein the iMn ₂ O _4.