JP2001325960A - Lithium secondary cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary cell using lithium-manganese compound oxide like LiMn2O4 having a long-life at high temperature for a positive electrode active material by improving the positive electrode. SOLUTION: The lithium secondary cell mainly structured by a positive electrode containing lithium-manganese compound oxide in at least a part of positive electrode active material, a negative electrode composed of materials which can store and discharge lithium reversibly, nonaqueous electrolyte which dissolves lithium salt in organic solvent, the positive electrode contains one or more additional agents selected from metaaluminate or metasilicate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery utilizing reversible occlusion and release phenomena of lithium ions, and using a lithium manganese composite oxide as a positive electrode active material, a lithium secondary battery having excellent high temperature characteristics. Battery.

[0002]

2. Description of the Related Art Lithium secondary batteries that utilize the insertion and extraction of lithium ions have high voltage and high energy density, and have become practical in the fields of information equipment and communication equipment as personal computers and mobile phones have become smaller. Has spread, and has spread widely to the general public. On the other hand, the development of electric vehicles has been rushed due to environmental problems and resource problems, and the use of this lithium secondary battery as a power source for electric vehicles is being studied.

As a positive electrode active material of these lithium secondary batteries, LiCoO 2 is used as a material capable of forming a 4V class battery.
Lithium transition metal composite oxides such as ₂ , LiNiO ₂ and LiMn ₂ O ₄ are known. When a lithium secondary battery is used as a power source for an electric vehicle, a large amount of active material must be used. Therefore, among the positive electrode active materials, lithium such as LiMn ₂ O _4, which has abundant resources and low material cost, is used. Manganese composite oxides are advantageous.

However, in a lithium secondary battery using a lithium manganese composite oxide such as LiMn ₂ O ₄ as a positive electrode active material, it is known that manganese elutes from the active material at a high temperature, and the battery life at high temperatures is particularly short. Have been. On the other hand, in order to stabilize the crystal structure of LiMn ₂ O _{4 having} a spinel structure and reduce the elution of manganese, a method of partially replacing manganese sites with lithium (Y. Gao and JR Dah
n, J. Electrochem. Soc., 143, 100 (1996), etc.)
Or a method of substituting with another metal (Japanese Unexamined Patent Application Publication No.
Etc.) have been proposed. However, the effect of improving the high-temperature characteristics of LiMn ₂ O _{4 having} a spinel structure was not sufficient. Further, in order to further improve the high-temperature characteristics, a surface treatment is performed by subjecting a lithium manganese composite oxide in which a part of a manganese site is substituted with another metal to a heat treatment with a boron compound as disclosed in Japanese Patent Application Laid-Open No. Hei 10-241682. A method of applying has been proposed.

[0005]

However, the above conventional method improves the high-temperature life of a lithium secondary battery using a lithium manganese composite oxide such as LiMn ₂ O ₄ as a positive electrode active material, but it still has an effect of the improvement. Is not enough. In the method disclosed in Japanese Patent Application Laid-Open No. Hei 10-241682, heat treatment is required, which causes a rise in raw material costs.

The present invention has been made in view of the above-mentioned conventional problems. By improving a positive electrode, a lithium manganese composite oxide such as LiMn ₂ O _{4 having} a long high-temperature life is used as a positive electrode active material. It is intended to provide a secondary battery.

[0007]

According to the present invention, there is provided a positive electrode comprising a lithium manganese composite oxide in at least a part of a positive electrode active material, a negative electrode comprising a substance capable of reversibly storing and releasing lithium,
In a lithium secondary battery including a nonaqueous electrolyte in which a lithium salt is dissolved in an organic solvent as a main component, the positive electrode may include one or more additives selected from metaaluminates and metasilicates. It is a feature of the lithium secondary battery.

The most remarkable point in the present invention is that
The positive electrode is a metaaluminate (AlO) _Two ^-Salt) or metasilicon
Acid salt (SiO_Three ^2-Salt).
That is.

According to the present invention, by adding one or more salts selected from metaaluminates and metasilicates to a positive electrode containing a lithium manganese composite oxide, the lithium manganese composite oxide and the electrolyte, especially at a high temperature, are added. The reaction with manganese can be suppressed, whereby the elution of manganese therefrom can be reduced, and the life at high temperatures can be improved.

Next, as in the second aspect of the invention, the metaaluminate and the metasilicate are preferably an alkali metal salt or an alkaline earth metal salt. Further, as in the third aspect of the present invention, the positive electrode comprises the metaaluminate and the metasilicate in an amount of 0.1% based on the weight of the positive electrode active material.
It is preferable to contain 1 to 10% by weight.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, typical embodiments of the lithium secondary battery of the present invention will be described. The secondary battery of the present invention is mainly composed of a positive electrode and a negative electrode capable of reversibly storing and releasing lithium ions, and a non-aqueous electrolyte in which a lithium salt is dissolved in an organic solvent. The positive electrode is prepared by mixing a positive electrode active material, at least one additive selected from metaaluminates or metasilicates, a conductive material and a binder, and adding an appropriate solvent to form a paste-like positive electrode mixture. Use what was done. Then, this can be applied to the surface of a current collector made of a metal foil such as aluminum, dried and, if necessary, compressed to increase the electrode density.

[0012] The positive electrode active material contains at least one lithium manganese composite oxide. As an example of the lithium manganese composite oxide, LiMn ₂ O ₄ having a spinel structure can be given. In addition, LiMn ₂ O having a spinel structure
₄ is not limited to the stoichiometric _{composition, Li 1 + x Mn 2-} x O 4 a part of manganese site was replaced with _{lithium, LiMn 2-y M y O} 4 obtained by substituting other metals M, Li _{1 + x} Mn _2-xy MyO ₄ substituted with lithium and another metal M can be used. Further, if necessary, LiCoO ₂ , LiNi
O _{2 and the} like can be mixed and used as a positive electrode active material.

The metaaluminate or metasilicate, which is an additive to the positive electrode, which is a feature of the present invention, is mixed well with the positive electrode active material in advance, and then mixed with a conductive material, a binder, and a solvent to form a positive electrode mixture. It can be. In this case, in order to remove impurities such as moisture in the positive electrode active material, a positive electrode active material mixed with metaaluminate or metasilicate is used for 600 minutes.
There is no problem even if heat treatment such as drying is performed at a temperature of not more than ° C.
Metaaluminate or metasilicate is preferably an alkali metal salt or an alkaline earth metal salt because of its low cost advantage. Examples of these are LiAlO ₂ , NaAlO ₂ , Ba (AlO ₂ ) ₂ , L
i ₂ SiO _{3 and the} like can be mentioned.

It is desirable that the total amount of metaaluminate or metasilicate added to the positive electrode be 0.1% by weight or more and 10% by weight or less based on the weight of the positive electrode active material. This is because when the total amount of metaaluminate and metasilicate is less than 0.1% by weight, a sufficient effect of suppressing the elution of manganese from the positive electrode active material cannot be obtained, and thus the lithium secondary battery constituted has This is because a sufficient improvement effect of the high-temperature life cannot be obtained, and when it exceeds 10% by weight, the battery capacity of the configured lithium secondary battery is greatly reduced. It is more preferable that the practical addition ratio be 1% by weight or more and 5% by weight or less.

The conductive material is used to ensure the electrical conductivity of the positive electrode. For example, one or a mixture of two or more powdered carbon materials such as carbon black, acetylene black, and graphite is used. be able to. The binder is
It plays the role of anchoring a solid material such as an active material in the positive electrode mixture, for example, polytetrafluoroethylene,
Fluororesin such as polyvinylidene fluoride and fluoro rubber,
Thermoplastic resins such as polypropylene and polyethylene can be used. Further, in order to obtain a paste-like positive electrode mixture, an organic solvent such as N-methyl-2-pyrrolidone can be used as a solvent.

As the negative electrode, metallic lithium and lithium alloy can be used. However, when these are used, there is a problem of dendrite precipitation. Instead of these, as in the case of the positive electrode, a binder is mixed with a negative electrode active material capable of occluding and releasing lithium ions reversibly. The negative electrode mixture formed into a paste by adding a solvent can be formed by applying and drying the surface of a metal foil current collector such as copper and compressing it to increase the electrode density as necessary.

In this case, as the negative electrode active material, for example, an organic compound fired body such as natural graphite, artificial graphite, and phenol resin, and a powdered carbon material such as coke can be used. In this case, a fluorine-containing resin such as polyvinylidene fluoride or the like is used as the negative electrode binder similarly to the positive electrode, and N-methyl- is used as a solvent for dispersing these active materials and the binder.
An organic solvent such as 2-pyrrolidone can be used.

The separator provided between the positive electrode and the negative electrode is for separating the positive electrode and the negative electrode and holding the electrolytic solution. For example, a thin microporous film such as polyethylene or polypropylene can be used. . As the non-aqueous electrolyte, a solution in which a lithium salt is dissolved in an organic solvent may be used.

The lithium salt is dissociated by dissolving in an organic solvent and forms lithium ions in the electrolyte. Lithium salts that can be used include LiPF ₆ , Li
BF ₄ , LiClO ₄ , LiCF ₃ SO ₃ , LiAsF ₆ ,
LiN (CF ₃ SO ₂ ) ₂ and LiN (C ₂ F ₅ SO ₂ ) ₂ . These lithium salts may be used alone, or two or more of these lithium salts may be used in combination. Among these lithium salts,
Considering that it has high electrochemical stability and high ionic conductivity, it is preferable to use LiPF ₆ .

An aprotic organic solvent is used as the organic solvent for dissolving the lithium salt. For example, a mixed solvent of one or more of cyclic carbonate, chain carbonate, cyclic ester, cyclic ether or chain ether can be used. Examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate. Examples of the chain carbonate include dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. Examples of the cyclic ester include gamma butyl. Examples of lactone, gamma barrel lactone and the like, examples of cyclic ethers include tetrahydrofuran and 2-methyltetrahydrofuran, and examples of chain ethers include dimethoxyethane and ethylene glycol dimethyl ether.

The lithium secondary battery of the present invention constituted as described above as a main constituent element can have various shapes such as a coin type, a card type, a cylindrical type, and a stacked type. Regardless of the shape, the separator is narrowed between the positive electrode and the negative electrode to form an electrode body, and the space between the positive electrode current collector and the negative electrode current collector to the positive electrode terminal and the negative electrode terminal leading to the outside is used for current collection. Connect using lead wires, etc.
This electrode body is impregnated with the above non-aqueous electrolyte, and the battery case is sealed to complete the battery.

[0022]

EXAMPLE Based on the above embodiment, 18650 was actually
A cylindrical lithium secondary battery having a die size was manufactured, and a high-temperature cycle test at an ambient temperature of 60 ° C. was performed. Hereinafter, these contents will be described.

Example 1 A lithium secondary battery of Example 1 has a spinel structure of Li _1.1 Mn _1.8 as a positive electrode active material.
Ni _0.1 O ₄ was used. The Li _1.1 Mn _1.8 Ni _0.1
O ₄ is composed of Li ₂ CO ₃ , MnO ₂ and NiO at 11: 36: 2.
The mixture was synthesized by heating at 850 ° C. Li _1.1 Mn _1.8 Ni _0.1 O ₄
And LiAlO ₂ were mixed well at a weight ratio of 95: 5, and then vacuum dried at 200 ° C. Then, 10 parts of graphite powder as a conductive material were added to 86 parts by weight of the mixture.
Parts by weight, polyvinylidene fluoride (PVd
F) was mixed in an amount of 4 parts by weight, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added as a solvent to obtain a paste-like positive electrode mixture.

Next, this positive electrode mixture was applied to both sides of a 20 μm-thick aluminum foil current collector at a thickness of 100 μm per side.
, And vacuum-dried at 200 ° C., and the density was increased to 65 μm per side by a roll press to produce a positive electrode. The area of this positive electrode was 243 cm.
^{And 2} .

As the negative electrode active material, spherical artificial graphite MCMB2 was used.
5-28 (manufactured by Osaka Gas Chemicals) was used. First, 5 parts by weight of PVdF as a binder was added to 95 parts by weight of the spherical artificial graphite.
Parts by weight were mixed and an appropriate amount of NMP was added as a solvent to obtain a paste-like negative electrode mixture. Next, this negative electrode mixture was applied in a thickness of 60 μm per side of a copper foil current collector having a thickness of 10 μm, dried in vacuum at 120 ° C., and then increased in density to a thickness of 40 μm per side by a roll press. To produce a negative electrode. The area of the negative electrode was 280 cm ² .

The above positive electrode was heated at 200 ° C.
After vacuum drying again at 0 ° C., in a dry room at a dew point of −40 ° C., the positive electrode and the negative electrode were wound facing each other via a separator made of a 25 μm-thick polyethylene microporous membrane,
A roll-shaped electrode body was formed. This electrode body was prepared by mixing ethylene carbonate and diethyl carbonate at a volume ratio of 3:
7 was sealed in a 18650 type battery case together with a non-aqueous electrolytic solution in which LiPF ₆ was dissolved as an electrolyte to a concentration of 1 M in the mixed organic solvent mixed in 7 to complete a lithium secondary battery. This lithium secondary battery was used as the lithium secondary battery of Example 1.

(Embodiment 2) The lithium secondary battery of Embodiment 2 is different from the lithium secondary battery of Embodiment 1 in that LiAl
It is a mixture of NaAlO ₂ in the positive electrode instead of O ₂ .
The addition ratio and other battery configurations were the same as those of the lithium secondary battery of Example 1.

(Embodiment 3) The lithium secondary battery of Embodiment 3 is different from the lithium secondary battery of Embodiment 1 in that LiAl
It is obtained by mixing Ba (AlO ₂ ) ₂ in the positive electrode instead of O ₂ . The addition ratio and other battery configurations were the same as those of the lithium secondary battery of Example 1.

(Embodiment 4) The lithium secondary battery of Embodiment 4 is different from the lithium secondary battery of Embodiment 1 in that LiAl
It is a mixture of Li ₂ SiO ₃ in the positive electrode instead of O ₂ . The addition ratio and other battery configurations were the same as those of the lithium secondary battery of Example 1.

(Examples 5 to 7) In the lithium secondary batteries of Examples 1 to 4, after mixing the positive electrode active material and metaaluminate or metasilicate, at 200 ° C. to remove adsorbed moisture. Was vacuum dried. This drying temperature is
In Examples 5 to 7, a mixture of a positive electrode active material and a metaaluminate or metasilicate is used at a temperature of 200 ° C.
Heat treatment was performed at a temperature higher than the above, and the effect on battery characteristics was examined.

That is, the lithium secondary battery of the fifth embodiment is similar to the lithium secondary battery of the first embodiment in that the Li _1.1 M
n _1.8 Ni _0.1 O ₄ and LiAlO ₂ in a weight ratio of 95:
5 and mixed well. Thereafter, the mixture was heat-treated in air at 500 ° C. for 10 hours. This Li _1.1 M
except that the heat-treated n _1.8 Ni _0.1 mixture of O ₄ and LiAlO ₂ were the same as in the preparation method of the lithium secondary battery of Example 1.

The lithium secondary battery of Example 6 is the same as the lithium secondary battery of Example 5, except that Ba (AlO ₂ ) ₂ is mixed in the positive electrode instead of LiAlO ₂ . The addition ratio and other battery configurations were the same as those of the lithium secondary battery of Example 1. The lithium secondary battery of the seventh embodiment is the same as the lithium secondary battery of the fifth embodiment except that
_In this example, Li ₂ SiO ₃ was mixed in the positive electrode instead of ₂ .
The addition ratio and other battery configurations were the same as those of the lithium secondary battery of Example 1.

Comparative Example 1 The lithium secondary battery of Comparative Example 1 is different from the lithium secondary batteries of Examples 1 to 7 above.
This is a lithium secondary battery manufactured using a positive electrode mixture into which neither metaaluminate nor metasilicate is added. Other battery configurations were the same as the lithium secondary battery of Example 1.

Comparative Example 2 The lithium secondary battery of Comparative Example 2 is the same as the lithium secondary battery of Example 1 except that
In this case, lithium metaborate (LiBO ₂ ) is mixed with the positive electrode in place of O ₂ . The addition ratio and other battery configurations were the same as those of the lithium secondary battery of Example 1.

Comparative Example 3 The lithium secondary battery of Comparative Example 3
The pond was made of Li as in the lithium secondary battery of Comparative Example 2. _1.1M
n_1.8Ni_0.1O_FourAnd LiBO_Two95: 5 by weight
And mixed well. Then, in the air of 500 ℃
The mixture was heat treated for 10 hours. This Li_1.1Mn
_1.8Ni_0.1O_FourAnd LiBO_TwoHeat treatment of the mixture
The external battery configuration was the same as that of the lithium secondary battery of Comparative Example 2.
did.

<High Temperature Cycle Test> Each of the lithium secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 3 was subjected to a high temperature cycle test. First, each battery was charged and discharged under the following conditions in an environment of 25 ° C. A constant current constant voltage for charging at a constant current of 1.1 mA / cm ² up to a charging end voltage of 4.2 V and charging at a constant voltage after reaching 4.2 V so that the total charging time becomes 2.5 hours. After charging, after charging, 0.33 mA up to the discharge end voltage 3.0 V
/ Constant current discharge at a constant current with a current density of 5 cm / cm ²
A cycle was performed.

After that, each battery was subjected to a high-temperature cycle test at 60 ° C. Charge end voltage is 4.2
V, the discharge end voltage is 3.0 V, and 1.1 mA / cm ²
100 cycles of charging and discharging were performed at a constant current having a current density of. It should be noted that charging and discharging were suspended for 10 minutes after charging and discharging were completed. The ratio between the discharge capacity at the 100th cycle and the discharge capacity at the first cycle in a cycle test in an environment at 60 ° C. was defined as a capacity retention ratio. That is, [capacity retention rate] = [discharge capacity at 100th cycle]
/ [Discharge capacity at first cycle] × 100 (%).
As a result of the high-temperature cycle test, the capacity retention rates of the lithium secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 3 are shown in Table 1 below.

[0038]

[Table 1]

As is clear from Table 1 above, Example 1 in which either a metaaluminate or a metasilicate was added.
It can be seen that the lithium secondary batteries of Nos. To 4 have a larger capacity retention ratio than the lithium secondary batteries of Comparative Example 1 to which they are not added, and show good high-temperature cycle characteristics.
Further, as is apparent from Comparative Examples 2 and 3, when lithium metaborate is added, heat treatment after the addition is necessary. In contrast, the lithium secondary battery of this embodiment to which either a metaaluminate or a metasilicate was added,
It can be seen that heat treatment after the addition is not required and the cost is advantageous. Further, the lithium secondary battery of this embodiment to which either a metaaluminate or a metasilicate is added,
As is clear from Examples 5 to 7, it is understood that good high-temperature cycle characteristics can be obtained even if heat treatment is performed after addition as necessary. From these results, it can be confirmed that the lithium secondary battery of the present invention is a low-cost lithium secondary battery having excellent high-temperature cycle characteristics.

<Quantification of Manganese Deposition on Negative Electrode> 60 ° C.
The negative electrodes of the lithium secondary batteries of Example 1 and Comparative Example 1 in the discharged state after 100 cycles of the cycle test were taken out, washed well with diethyl carbonate, and then washed with IC.
The amount of manganese deposited per unit weight of the negative electrode material was determined by P emission analysis. The results are listed in Table 2.

[0041]

[Table 2]

From the results shown in Table 2, the lithium secondary battery of the present invention shows that the reaction between the lithium manganese composite oxide, which is the positive electrode active material, and the electrolyte is caused by the action of metaaluminate or metasilicate added to the positive electrode. It can be confirmed that the high-temperature cycle life was improved because the dissolution of manganese from the lithium manganese composite oxide was suppressed by suppressing manganese.

[0043]

As described above, according to the present invention, a lithium secondary battery using a lithium manganese composite oxide such as LiMn ₂ O _{4 having} a long life at high temperature as a positive electrode active material is provided by improving a positive electrode. can do.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yasuhito Kondo 41-1, Oku-cho, Yokomichi, Nagakute-cho, Aichi-gun, Aichi Prefecture F-term in Toyota Central R & D Laboratories Co., Ltd. 5H029 AJ01 AK03 AL06 AL12 AM03 AM04 AM05 AM07 EJ11 HJ01 5H050 AA05 BA17 CA08 CA09 CB08 CB12 DA02 DA09 EA22 EA24 HA01

Claims (3)

[Claims] 1. A positive electrode comprising a lithium manganese composite oxide in at least a part of a positive electrode active material, a negative electrode comprising a material capable of reversibly storing and releasing lithium, and a non-aqueous electrolytic solution in which a lithium salt is dissolved in an organic solvent. In a lithium secondary battery comprising a liquid as a main component, the above-mentioned positive electrode contains one or more additives selected from metaaluminate and metasilicate.
A lithium secondary battery comprising at least one species. 2. The lithium secondary battery according to claim 1, wherein the metaaluminate and the metasilicate are an alkali metal salt or an alkaline earth metal salt. 3. The method according to claim 1, wherein the positive electrode is
A lithium secondary battery comprising the metaaluminate and the metasilicate in an amount of 0.1 to 10% by weight based on the weight of the positive electrode active material.