JP2932516B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a structure of a cylindrical nonaqueous electrolyte secondary battery having an electrode structure in which a positive electrode and a negative electrode are spirally wound via a separator. Things.

[Conventional technology]

In recent years, there has been a remarkable increase in the performance and miniaturization of electronic devices such as video cameras and headphone stereos, and there is also a demand for improved heavy load characteristics and higher capacity of the secondary batteries that power these electronic devices. It is getting stronger. As a secondary battery, a lead secondary battery and a nickel-cadmium battery have been conventionally used. In addition, non-aqueous electrolyte secondary batteries using materials capable of doping and undoping lithium metal, lithium alloys, or lithium ions as negative electrode active material materials are being actively developed as being capable of obtaining high energy density. I have. Among them, in particular, a cylindrical spiral non-aqueous electrolyte secondary battery (hereinafter, referred to as a spiral electrode) in which a positive electrode electrode and a negative electrode electrode are spirally wound via a separator to increase the electrode area.
Spiral type non-aqueous electrolyte secondary batteries) have recently attracted attention as being capable of rapid charging and discharging. However, this battery has a problem in that an internal short circuit is likely to occur due to the fact that the electrode material at both ends in the width direction of the strip electrode breaks through the separator. This type of electrode often uses a slurry in which an active material or an electrode mixture is dispersed in a solvent,
It is applied to the entire surface of the belt-shaped current collector, dried, and then compression-molded by a roller press, and cut into a predetermined width. The electrode obtained by this method is manufactured by cutting the electrode. The cut ends are steep, which easily breaks through the separator and easily causes an internal short circuit.

[Problems to be solved by the invention]

An object of the present invention is to improve the structure of both ends in the width direction of an electrode obtained by coating a belt-shaped current collector with an active material or an electrode mixture, and to provide a spiral nonaqueous electrolyte secondary solution which does not cause the above-described problems. It is to provide a battery.

[Means for solving the problem]

The non-aqueous electrolyte secondary battery of the present invention is a spiral non-aqueous electrolyte secondary battery having an electrode structure in which a positive electrode and a negative electrode are spirally wound via a separator, and The at least one electrode is formed of a band-shaped current collector cut to a predetermined width in advance, and a layer of an active material or an electrode mixture that covers the band-shaped current collector except for both ends in the width direction. I do. Here, at both ends in the width direction of the current collector, the width of a portion that is not covered with the layer of the active material or the electrode mixture is preferably 0.05 times or less the width of the strip-shaped current collector.

INDUSTRIAL APPLICABILITY The present invention can be applied to a battery using an electrode in which a band-shaped current collector is coated with a layer of an active material or an electrode mixture. For example, a negative electrode in which a calcined organic polymer or pitch coke is pulverized and coated on a current collector, or a positive electrode in which a current collector is coated with lithium manganese oxide or lithium cobalt oxide is used. As the electrolyte according to the present invention, for example, a non-aqueous electrolyte obtained by dissolving a lithium salt as an electrolyte in an organic solvent (non-aqueous solvent) is used. Here, examples of the organic solvent include, but are not particularly limited to, propylene carbonate, ethylene carbonate, 1.2-dimethoxyethane, 1.2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 1.3-dioxolan, 4-
A single solvent such as methyl-1.3-dioxolan, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile, or a mixture of two or more thereof can be used. As the electrolyte, any of those conventionally known can be used, for example, LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiB
(C ₆ H ₅ ) ₄ , LiCl, LiBr, CH ₃ SO ₃ Li, CF ₃ SO ₃ Li and the like.

[Action]

An internal short circuit can be prevented by coating the active material or the electrode mixture while leaving both ends in the width direction of the current collector.

〔Example〕

FIG. 3 is a cross-sectional view schematically showing the structure of the spiral nonaqueous electrolyte secondary battery according to the present invention.

Hereinafter, examples and comparative examples will be described with reference to FIG.

Example 1 A battery was manufactured using LiCoO ₂ as a positive electrode active material and needle coke as a negative electrode active material. 90 parts by weight of the crushed needle coke and 10 parts by weight of polyvinylidene fluoride as a binder were mixed to prepare a negative electrode mixture. Then, this negative electrode mixture was dispersed in a solvent N-methylpyrrolidone to form a slurry (paste). Next, the negative electrode mixture slurry was applied to both sides of a 10 μm thick copper foil strip-shaped negative electrode current collector cut to a width of 34.5 mm, leaving 0.5 mm from both ends thereof, and dried.

After drying, it was compression-molded by a roller press machine to obtain a belt-shaped negative electrode 2. In the strip-shaped negative electrode 2, the negative electrode mixture is formed on both surfaces of the negative electrode current collector with substantially the same thickness,
The sum of these film thicknesses was about 175 μm.

Next, the positive electrode was produced as follows. Lithium carbonate 1
Mixing molar and cobalt 1 mole carbonate, to give a 5 hours firing LiCoO ₂ of powdery and in 900 ° C. in air, used as a positive electrode active material, earthenware pots by this LiCoO ₂ 91 weight conductive material graphite 6 Parts by weight, polyvinylidene fluoride 3 as binder
Parts by weight were added and mixed to obtain a positive electrode mixture. Then, this positive electrode mixture was dispersed in a solvent N-methylpyrrolidone to obtain a slurry (paste). Next, this positive electrode mixture slurry was applied to both surfaces of a 20 μm-thick strip-shaped aluminum foil positive electrode current collector cut to a width of 33.5 mm, leaving 0.5 mm from both ends thereof, and dried. After drying, it was compression-molded by a roller press machine to obtain a belt-shaped positive electrode 1. In this strip-shaped positive electrode 1, the positive electrode mixture is formed on both surfaces of the positive electrode current collector with substantially the same film thickness, and the sum of these film thicknesses is about 175.
μm. Then, a strip-shaped positive electrode 1, a strip-shaped negative electrode 2, and a separator 3 made of a microporous polypropylene film having a thickness of 25 μm are laminated in the order of the negative electrode 2, the separator 3, the positive electrode 1, and the separator 3. A wound body was made by spirally winding a large number of times. The wound body made as described above was housed in a nickel-plated iron battery can 5 having an inner diameter of 13.3 mm, as shown in FIG.
Then, one end of an aluminum positive electrode lead was attached to the positive electrode 1 and the other end was welded to the explosion-proof valve 8 to collect the current of the positive electrode 1. To collect the current of the negative electrode 2, one end of a nickel negative electrode lead was attached to the negative electrode 2, and the other end was welded to the battery can 5. Into this battery can 5, an electrolyte obtained by mixing propylene carbonate 1.2-dimethoxyethane in which lithium hexafluorophosphate 1 mol / dissolved was injected. Next, the insulating plate 4 was disposed in the battery can 5 so as to face the upper and lower surfaces of the wound body. Finally, the battery can 5 and the battery lid 7 were caulked via an insulating sealing gasket 6 to seal the battery lid 7. As described above, a spiral nonaqueous electrolyte secondary battery having a diameter of 13.8 mm and a height of 42 mm was produced.

Example 2 When preparing a negative electrode and a positive electrode, the mixture slurry was applied to both surfaces of the current collector except for 1 mm from both ends of the current collector,
Otherwise, the procedure of Example 1 was followed to fabricate a battery.

Example 3 When preparing a negative electrode and a positive electrode, the mixture slurry was applied to both surfaces of the current collector except for 1.8 mm from both ends of the current collector, and a battery was prepared in the same manner as in Example 1 except for the above.

Comparative Example 1 The negative electrode was formed by applying and drying a negative electrode mixture slurry on the entire surface of the current collector, and compression-molding the slurry by a roller press.
Cut to 34.5mm width. The positive electrode was prepared by applying and drying a positive electrode mixture slurry on the entire surface of the current collector, compression-molding the slurry by a roller press, and then cutting the slurry to a width of 33.5 mm. Otherwise, a battery was fabricated in the same manner as in Example 1.

Comparative Example 2 A negative electrode was prepared by applying and drying a negative electrode mixture slurry on the entire surface of a current collector cut to a width of 34.5 mm, and compression-molding the slurry with a roller press. The positive electrode was formed by applying and drying a positive electrode mixture slurry on the entire surface of a current collector cut to a width of 33.5 mm, and compressing and molding the slurry with a roller press. Otherwise, a battery was fabricated in the same manner as in Example 1.

When the cross sections of the positive and negative electrode strip electrodes obtained in the examples and comparative examples were observed with a microscope, the following results were obtained. FIG. 1 is a diagram schematically showing a cross section of an electrode obtained in Examples 1, 2, and 3. FIG. 2A is a diagram schematically illustrating a cross section of the electrode obtained in Comparative Example 1, and FIG. 2B is a diagram schematically illustrating a cross section of the electrode obtained in Comparative Example 2. As shown by the above results, the electrode obtained in the example is applied with the mixture slurry on the band-shaped current collector cut into a predetermined width in advance, so that the end face in the width direction has a rounded band, Have been taken. On the other hand, in the electrode obtained in Comparative Example 1, the mixture slurry was applied to the belt-shaped current collector, dried, and then cut into a predetermined electrode width. In addition, although the electrode obtained in Comparative Example 2 has a corner at the end face in the width direction, as shown in FIG. 2B, there is no current collector at both ends of the electrode.

The batteries of Examples 1, 2, 3 and Comparative Examples 1, 2 were respectively
A 50 charge / discharge cycle was performed in which each of them was charged with a current of 190 mA at an upper limit voltage of 4.1 V for 3 hours, and then discharged with a constant resistance of 160 Ω to a discharge end voltage of 2.9 V.
Perform 30 cycles, charge again under the above conditions, and then
The battery was left to stand for a few days, and the occurrence rate of the battery whose open-circuit voltage dropped to 3.9 V or less was examined as an internal short-circuited product. Further, among these batteries, those having no internal short circuit were discharged under the above-mentioned conditions, and their capacities were also examined. Table 1 shows the results.

As can be seen from this table, the battery of Comparative Example 1 has an extremely high incidence of internally short-circuited products. When the internal short-circuited battery was disassembled and examined, it was observed that the electrode mixture at both ends of the electrode partially broke through the separator. In the battery of Comparative Example 2, an internally short-circuited product was also generated. When the battery with the internally short-circuited was disassembled and examined, the electrode mixture at both ends of the electrode fell off from the electrode, and this broke through the separator. Was observed.

In the batteries of Examples 1, 2, and 3, no internal short-circuit product was generated.
Therefore, it is considered that the effect of not covering both ends of the current collector with the electrode mixture is great. Further, regarding the discharge capacity, as compared with Examples 1, 2, and 3, the discharge capacity decreases as the width of the portion of the current collector that is not covered with the electrode mixture increases.
In Example 3 in which the width of the portion not covered with the electrode mixture at both ends was 0.05 times or more the width of the current collector, compared to Comparative Example 1 in which the entire surface of the current collector was covered with the electrode mixture, Discharge capacity is 10
% Or less, which is not preferable. Note that, as shown in the above examples, for both the positive electrode and the negative electrode, it is preferable that both ends of the current collector are not covered with the active material or the electrode mixture, but either one of the positive electrode and the negative electrode However, it goes without saying that the above is effective for preventing an internal short circuit.

〔The invention's effect〕

According to the present invention, in a spiral nonaqueous electrolyte secondary battery,
It has become possible to prevent internal short circuit of the battery, which is one of the problems. As a result, a secondary battery having high energy density and excellent rapid charge / discharge cycle characteristics can be provided, and its industrial value is great.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a strip-shaped electrode of an example, FIGS. 2A and 2B are schematic cross-sectional views of a strip-shaped electrode of a comparative example, and FIG. 3 is a spiral nonaqueous electrolyte secondary solution of the present invention. FIG. 2 is a schematic cross-sectional view illustrating a structure of a battery. 1 and 2A and B, reference numeral 10 denotes a current collector, and reference numeral 20 denotes an electrode mixture. In FIG. 3, 1 is a positive electrode, 2 is a negative electrode, 3 is a separator,
Reference numeral 5 denotes a battery can.

Claims (2)

(57) [Claims] In a cylindrical non-aqueous electrolyte secondary battery having an electrode structure in which positive and negative electrode strips are spirally wound with a separator interposed therebetween, at least one of the electrode strips is predetermined. A band-shaped current collector cut to a width of, and a layer of the active material or the electrode mixture that covers the band-shaped current collector except for both ends in the width direction, and the layer of the active material or the electrode mixture. Characterized in that both end portions have a curved surface configuration. 2. The width of both ends in the width direction of the strip-shaped current collector, which is not covered with the active material or the electrode mixture, is 0.05 times or less of the width of the strip-shaped current collector. 2. The cylindrical non-aqueous electrolyte secondary battery according to claim 1.