JPH04294060A - Negative electrode for secondary battery with non-aqueous electrolyte - Google Patents

Abstract

PURPOSE:To provide a negative electrode for non-aqueous electrolyte secondary battery excellent in the charging/discharging cyclic characteristics. CONSTITUTION:A non-aqueous electrolyte secondary battery includes a positive electrode 1 capable of occluding and releasing Li and a negative electrode 4, and a copolymer resin of vinyl chloride and vinyl acetate, which presents good bonding property, is used as a neg. electrode binder of this battery. This suppresses occurrence of insufficient collection of electricity resulting from expansion and contraction of the electrode at charging and discharging, and the negative electrode of a non-aqueous electrolyte secondary battery is obtained and excels in the charging/discharging cyclic characteristics.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a negative electrode for non-aqueous electrolyte secondary batteries.

0002

BACKGROUND OF THE INVENTION Non-aqueous electrolyte secondary batteries using lithium or lithium compounds as negative electrodes are expected to have high voltage and high energy density, and many studies are being conducted on them.

[0003] Until now, positive electrode active materials for non-aqueous electrolyte secondary batteries include LiCoO2, V2O5, Cr2O5, MnO2
, TiS2, MoS2, and other transition metal oxides and chalcogen compounds are known, and these have a layered or tunnel structure, and have a crystal structure in which lithium ions can enter and exit. On the other hand, metallic lithium has been widely studied as a negative electrode active material. However, during charging, lithium precipitates on the lithium surface in a dendritic form, resulting in a reduction in charge/discharge efficiency or in contact with the positive electrode, resulting in an internal short circuit.

0004

[Problems to be Solved by the Invention] As a means to solve such problems, a lithium alloy plate such as lithium-aluminum that can absorb and release lithium while suppressing the dendritic growth of lithium or a lithium alloy plate that can absorb and release lithium is used. Consideration has been made to use metal powders, carbon materials, oxides, and sulfides that can be used as negative electrode active materials. However, when a lithium alloy plate is used, repeated deep charging and discharging causes the electrode to become finer, resulting in a problem with cycle characteristics. In addition, when metal powder, carbon material, oxide, or sulfide is used, electrodes cannot usually be constructed by using them alone, so metal powder, oxide, or sulfide can be used with a conductive agent such as graphite and a binder such as polyethylene. Further, the carbon material also constitutes the electrode together with the binder. As a binder for the negative electrode,
Fluorine resin, which is frequently used as a binder in positive electrodes, promotes decomposition of the electrolyte and reacts with lithium, which is the negative electrode, so polyolefins such as polyethylene are used. However, in all of these methods, expansion and contraction of the electrode occurs as lithium is inserted and released, resulting in poor current collection and poor cycle characteristics, so that sufficient characteristics have not yet been obtained. An object of the present invention is to solve these problems and provide a negative electrode for a non-aqueous electrolyte secondary battery with excellent charge-discharge cycle characteristics.

[0005]

[Means for Solving the Problems] In order to solve the above problems, the negative electrode for a nonaqueous electrolyte secondary battery of the present invention is made of a metal powder, carbon material, sulfide, or oxide that can occlude and release lithium. A copolymer resin of vinyl chloride and vinyl acetate is used as a binder in the negative electrode of a non-aqueous electrolyte secondary battery using as an active material.

[0006]

[Function] With this configuration, the non-aqueous electrolyte secondary battery of the present invention has a negative electrode for a non-aqueous electrolyte secondary battery whose active material is metal powder, carbon material, oxide, or sulfide that can absorb and release lithium. By using a highly binding copolymer resin of vinyl chloride and vinyl acetate as a binder, the current collection in the electrode is maintained sufficiently even after repeated charging and discharging, and the charging and discharging capacity can be increased with a relatively small number of cycles. will no longer decrease,
It becomes possible to construct a negative electrode for a non-aqueous electrolyte secondary battery that has stable battery characteristics.

[0007] As the metal powder that can occlude and desorb lithium, aluminum, tin, lead, indium, and bismuth, which can occlude and desorb lithium relatively easily, are preferable, and as the conductive agent, graphite or carbon is preferable. Black is preferred.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A non-aqueous electrolyte secondary battery according to an embodiment of the present invention will be described in detail below with reference to the drawings.

(Example 1) In this example, aluminum powder capable of inserting and releasing lithium was used as the negative electrode active material, polyvinyl chloride resin was used as the binder, and the content of vinyl chloride was 95 mol%, 85 mol%
, 75 mol %, 65 mol %, and 60 mol % of a battery constructed with a negative electrode using a copolymer resin of vinyl chloride and vinyl acetate will be described. Also shown is a conventional example in which polyethylene is used as a binder.

The negative electrode is made of 300 mesh pass aluminum powder, acetylene black as a conductive agent, and polyvinyl chloride or a copolymer resin of vinyl chloride and vinyl acetate as a binder in a weight ratio of 45:45:10 and 45:45:10.
By mixing at a ratio of 7.5:47.5:5 and press-molding 0.1 g of the obtained negative electrode mixture into a diameter of 17.5 mm at 2 tons/cm2, binding of 10% by weight and 5% by weight was achieved. A negative electrode containing the agent was prepared. LiCoO2 is used as the positive electrode active material,
The positive electrode was made by mixing LiCoO2, acetylene black as a conductive agent, and poly-4-fluoroethylene resin as a binder in a weight ratio of 7:2:1, and the resulting positive electrode mixture was 0.2
g to a diameter of 17.5 mm at a pressure of 2 tons/cm2. In FIG. 1, a molded positive electrode 1 is placed in a case 2. A porous polypropylene film as a separator 3 was placed on the positive electrode 1 . The negative electrode 4 was crimped onto a sealing plate 5 equipped with a polypropylene gasket 6. A propylene carbonate solvent in which 1 mol/l of lithium perchlorate was dissolved was used as a non-aqueous electrolyte, and this was added onto the separator 3 and the negative electrode 4. After that, the battery was sealed.

[0011] A conventional battery using polyethylene as the negative electrode binder was also produced in the same manner as in this example.

As described above, the charge/discharge cycle characteristics of 14 types of batteries were compared. In this example, in order to perform a charge/discharge cycle test on the negative electrode, the battery was constructed under conditions that the battery had a sufficient positive electrode capacity to exclude cycle deterioration due to the positive electrode. The charge/discharge cycle test is performed at a charge/discharge current of 0.5
This was carried out by constant current charging and discharging at mA and a voltage range of 4.0V to 3.0V.

Table 1 shows the initial discharge capacity, the discharge capacity at the 50th cycle, and the capacity retention ratio of the discharge capacity at the 50th cycle relative to the initial discharge capacity.

[0014]

[Table 1]

As shown in Table 1, conventional batteries using negative electrodes containing 5% by weight and 10% by weight of polyethylene as a binder exhibit initial discharge capacities of 6.9mAh and 6.5mAh; The capacity decreases with each cycle, and the discharge capacity retention rate after 50 cycles decreases to about 40%. On the other hand, all of the batteries of this example using a copolymer resin of vinyl chloride and vinyl acetate as the negative electrode binder exhibited a discharge capacity equal to or higher than that of the initial conventional battery, and maintained the discharge capacity after 50 cycles. The cycle characteristics have also been improved, with a cycle rate of over 70%. Binder amount is 5% and 10% by weight
Although the initial discharge capacity of a battery using only polyvinyl chloride resin as the negative electrode binder is slightly larger than that of a battery using a copolymer resin of vinyl chloride and vinyl acetate, the discharge capacity retention rate at the 50th cycle is 5% by weight decreases to 59%, and 10% by weight decreases to 63%. In secondary batteries, since electrodes with high discharge capacity and capacity retention are desired, copolymer resins of vinyl chloride and vinyl acetate are excellent as negative electrode binders. Among them, it has been found that batteries using copolymer resins with a vinyl chloride content of 95 mol % to 65 mol % have high initial discharge capacity and capacity retention rate, and are desirable as negative electrode binders.

As described above, in a battery using aluminum powder as the negative electrode active material, by using a copolymer resin of vinyl chloride and vinyl acetate as the negative electrode binder, a non-aqueous electrolyte secondary battery with excellent cycle characteristics can be created. We confirmed that it can be produced.

In the examples, the combination of aluminum as the metal powder and acetylene black as the conductive agent was explained, but tin, lead, indium, and bismuth powders, which can similarly absorb and release lithium and form an alloy with lithium, are also used. It was confirmed that almost the same effect can be obtained with any combination of graphite and carbon black as the conductive agent.

(Example 2) In this example, a carbon material capable of inserting and releasing lithium was used as the negative electrode active material, polyvinyl chloride was used as the binder, and the content of vinyl chloride was A battery constructed with a negative electrode using a copolymer resin of vinyl chloride and vinyl acetate of 95 mol%, 85 mol%, 75 mol%, 65 mol%, and 60 mol% will be described. Also shown is a conventional example in which polyethylene is used as a binder.

The negative electrode is made of a negative electrode mixture obtained by mixing a carbon material, vinyl chloride as a binder, and a copolymer resin of vinyl chloride and vinyl acetate at a weight ratio of 9:1 and 95:5. .1g to 17.5mm in diameter 2 tons/cm
Negative electrodes containing 10% by weight and 5% by weight of the binder were produced by press molding in Step 2. A positive electrode was produced under the same conditions as in Example 1 using LiCoO2 as the positive electrode active material. The battery was also manufactured under the same conditions as in Example 1.

[0020] A conventional battery using polyethylene as a negative electrode binder was also produced in the same manner as in this example.

As described above, the charge/discharge cycle characteristics of 14 types of batteries were compared. In this example, as in Example 1, a charge/discharge cycle test is performed on the negative electrode, so the battery is constructed under conditions that the battery has a sufficient positive electrode capacity to exclude cycle deterioration due to the positive electrode. The charge/discharge cycle test was performed by constant current charging/discharging at a charge/discharge current of 0.5 mA and a voltage range of 4.1 V to 3.0 V.

Table 2 shows the initial discharge capacity, the discharge capacity at the 50th cycle, and the capacity retention ratio of the discharge capacity at the 50th cycle relative to the initial discharge capacity.

[0023]

[Table 2]

As shown in Table 2, conventional batteries using negative electrodes containing 5% and 10% by weight of polyethylene as a binder exhibited initial discharge capacities of 6.4 mAh and 6.2 mAh, respectively. The capacity decreases with each cycle, and the discharge capacity retention rate after 50 cycles decreases to around 40%. On the other hand, the batteries of this example using a copolymer resin of vinyl chloride and vinyl acetate as the negative electrode binder showed a discharge capacity equal to or higher than that of the initial conventional battery, and also had a discharge capacity after 50 cycles. The cycle characteristics have improved, with a maintenance rate of over 70%. The initial discharge capacity of batteries using polyvinyl chloride resin alone as the negative electrode binder with a binder amount of 5% or 10% by weight is slightly lower than that of batteries using a copolymer resin of vinyl chloride and vinyl acetate. Although it is large, the discharge capacity retention rate at the 50th cycle was 56% for the 5% by weight product, 10%.
The weight percentage decreases to 60%. In secondary batteries, since electrodes with high discharge capacity and capacity retention are desired, copolymer resins of vinyl chloride and vinyl acetate are excellent as negative electrode binders. Among them, it has been found that batteries using copolymer resins with a vinyl chloride content of 95 mol % to 65 mol % have high initial discharge capacity and capacity retention rate, and are desirable as negative electrode binders.

As described above, in a battery using a carbon material as the negative electrode active material, by using a copolymer resin of vinyl chloride and vinyl acetate as the negative electrode binder, a non-aqueous electrolyte secondary with excellent charge/discharge cycle characteristics can be obtained. It was confirmed that batteries could be produced.

[0026] In this example, a carbon material capable of intercalating and releasing lithium was explained as a negative electrode active material, but Fe2O3, which is expected to be a negative electrode active material,
It was confirmed that almost the same effect can be obtained with transition metal oxides such as WO2.

[0027]

[Effects of the Invention] As is clear from the above description of the embodiments,
According to the negative electrode for a non-aqueous electrolyte secondary battery of the present invention, the negative electrode of a non-aqueous electrolyte secondary battery whose active material is a metal powder, carbon material, sulfide, or oxide capable of intercalating and deintercalating lithium. By using a copolymer resin of vinyl chloride and vinyl acetate as an adhesive, it is possible to obtain a negative electrode for a non-aqueous electrolyte secondary battery that has excellent charge-discharge cycle characteristics.

[Brief explanation of drawings]

[Fig. 1] A vertical cross-sectional view of a battery using a negative electrode for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention.

[Explanation of symbols]

1 Positive electrode 2 Case 3 Separator 4 Negative electrode 5 Sealing plate 6 Gasket

Claims (2)

[Claims] 1. A negative electrode for a nonaqueous electrolyte secondary battery whose active material is a metal powder, carbon material, sulfide, or oxide capable of intercalating and deintercalating lithium, wherein vinyl chloride is used as a binder in the negative electrode. A negative electrode for non-aqueous electrolyte secondary batteries using a copolymer resin of and vinyl acetate. Claim 2: The content of vinyl chloride in the copolymer resin of vinyl chloride and vinyl acetate as a binder is from 95 mol% to 65 mol%.
The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, which is mol%.