JPH05151949A - Multilayer separator for battery - Google Patents

Abstract

PURPOSE:To provide a multilayer separator of consolidated structure, wherein the man-hours for battery assembly is reduced and the quality and reliability are enhanced. CONSTITUTION:A multilayer separator for battery is formed from a laminate of polyolefin type fine porous film 2 and polyolefin type nonwoven cloth 3 and is yielded through the heating/pressurizing process with a temperature lower than the melting point of the nonwoven cloth component material and the film of a laminate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in battery separators, particularly multilayer separators.

[0002]

2. Description of the Related Art For example, in a non-aqueous electrolyte secondary battery, an internal short circuit is caused by a so-called dendrite in which lithium is deposited in a dendritic form on the negative electrode during charging.
It was a cause of deterioration of charge / discharge cycle characteristics. As a countermeasure against this, in recent years, a configuration in which a lithium alloy is used to suppress the growth of dendrites is often used for the negative electrode, but this is not perfect, and in addition to the original liquid retaining non-woven fabric separator, In many cases, a structure in which a microporous thin film capable of suppressing passage of dendrites is provided in the battery, mainly on the negative electrode side, is used. Further, two-layer type and three-layer type separators are often used, such as a structure in which a non-woven fabric separator is further provided on the negative electrode side with an emphasis on the liquid holding property on the negative electrode side.

However, as the number of separators increases, the number of assembling steps increases, which complicates the manufacturing process and causes a structural error such as an error in the number of sheets or a positional deviation, which adversely affects the cycle performance and leak performance of the battery. Was affecting.

As a countermeasure against this, various attempts have been made to integrate different kinds of separators, and a part of the separators is heat-treated.
It is integrated by being tossed or formed by melt-injecting different kinds of separator materials on the main separator. However, according to these methods, the original physical properties of the separator material,
That is, in many cases, the basis weight, the porosity, the air permeability, the liquid retaining property, etc. are largely changed, and the battery performance is deteriorated.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a multi-layer separator that solves the problems of increased assembly man-hours and reduced quality.

[0006]

The multilayer separator of the present invention comprises a laminate of a polyolefin microporous thin film and a polyolefin non-woven fabric, the laminate having a melting point lower than that of the thin film and the non-woven fabric constituent material. It was heated and pressurized at a temperature.

[0007]

The multi-layer separator according to the present invention is different from the conventional multi-layer separator in that it is heated and pressed at a temperature below the melting point of the separator constituent material when integrated, so that the individual separators are separated. It is possible to prevent deterioration of battery performance by integrating the constituent materials while maintaining their original physical properties.

[0008]

EXAMPLES Examples of the present invention will be described in detail below.

FIG. 1 is a perspective view of the separator of the present invention, and FIG. 2 shows an example of a method of manufacturing the separator of the present invention.

In FIG. 1, a separator 1 of the present invention comprises a microporous membrane 2 made of polypropylene and having a thickness of about 0.03 mm.
The microporous membrane 2 and the non-woven fabric layer 3 are made of a laminate with a polypropylene non-woven fabric layer 3 having a thickness of about 0.20 mm, and are heated and pressed at a temperature not higher than the melting point of polypropylene. The diameter of the separator 1 of the present invention is 20 mm.

Next, referring to FIG. 2, a method of manufacturing the separator of the present invention will be described. On the microporous thin film 2 placed on the separator mounting table 4, a thin polypropylene film not subjected to calendaring treatment is used. Several pieces of cloth 5 are stacked, and the temperature (100 to 12) lower than the melting point of polypropylene (about 170 ° C) is used.
While heating at 0 ° C.), the non-woven fabric layer 3 is formed by passing between the special rollers 6 and pressurizing it to a predetermined thickness, and the non-woven fabric layer 3 and the microporous thin film 2 are integrated, This is punched to a predetermined size by using a punching device 7 to obtain a separator 1A of the present invention.

FIG. 3 shows a flat non-aqueous electrolyte secondary battery prepared by using this separator 1A. Reference numeral 8 denotes a positive electrode, which is obtained by mixing 80% by weight of manganese dioxide as an active material with 10% by weight of acetylene black as a conductive agent and 10% by weight of a fluororesin as a binder, followed by pressure molding, a diameter of 18 mm, A molded body having a thickness of 1.0 mm was prepared and heat-treated, and is pressed against the positive electrode can 9. 10
Is a negative electrode, and a lithium-aluminum alloy plate having a diameter of 18 mm and a thickness of 1.0 mm is used as a negative electrode can 11 made of stainless steel.
It is crimped to. The electrolyte used was a mixed solvent of propylene carbonate and dimethoxyethane in which 1 mol / l of lithium perchlorate was dissolved. 1A is a multi-layer separator which is the gist of the present invention, and 12 is an insulating packing. The battery has a diameter of 25 mm and a height of about 3 mm. This battery is designated as A '.

Next, the following separators and batteries were prepared as comparative examples.

A comparative separator 1B is obtained by simply superposing a polypropylene microporous membrane and a polypropylene non-woven fabric. A battery produced using this comparative separator 1B in the same manner as in the example is designated as B '.

A comparative separator 1C is prepared by injecting melted polypropylene on a microporous film made of polypropylene to form a nonwoven fabric layer by fusion. A battery prepared in the same manner as in the example using this comparative separator 1C was C ′.
And

As shown in FIG. 4, a polypropylene microporous membrane 2 and a polypropylene non-woven fabric 3 are superposed and heat-sealed in a diamond pattern 13 to form a comparative separator 1D. To do. A battery prepared in the same manner as in the example using this comparative separator 1D is designated as D '.

Table 1 shows a comparison of the assembly man-hours of the prototype batteries A'to D ', and Table 2 shows a comparison of the constitutional defects of the separators.

[0018]

[Table 1]

[0019]

[Table 2]

It can be seen from Table 1 that the battery using the multi-layered separator in which the different kinds of separators are integrated can reduce the number of assembling steps as compared with the multi-layered separator in which the different kinds of separators are simply stacked. .. This is due to the reduction of man-hours in the separator mounting process.

Further, it can be seen from Table 2 that the multi-layer type separator in which different kinds of separators are integrated has a great effect in preventing the constitutional defect. As the contents of the configuration failure, it was confirmed that the number of separators was wrong, the microporous membrane and the non-woven fabric were misaligned, and the biting into the packing was defective.

Next, the prototype batteries A'-D 'were heated at a temperature of 60.degree.
Table 3 shows the results of examining the leakage resistance at the time of storage for 90 days under conditions of high temperature and high humidity with a humidity of 90%.

[0023]

[Table 3]

It can be seen from Table 3 that the multi-layered separator in which different kinds of separators are integrated improves the battery performance as compared with the multi-layered separator in which different kinds of separators are simply stacked.

From the above results, it was confirmed that by assembling the separator, the number of assembling steps can be reduced and the quality can be improved.

This is because, in the case of a multi-layer type separator in which different kinds of separators are integrated, the occurrence of fluffing of fibers due to separation work of non-woven fabrics and the like, and the occurrence of dents in the packing due to the displacement of the separators are eliminated. Is.

Next, the charge / discharge cycle characteristics of the prototype batteries A'-D 'were compared. Conditions are charging current 3m
At A, the end-of-charge voltage is 3.5 V, and the discharge is 3
It was 4 hours at mA. The result is shown in FIG.

From the above, it can be seen that the performances of the comparative batteries C'and D'are lower than those of the comparative battery B ', whereas the performance of the battery A'of the present invention is not deteriorated at all.

The reason for this will be considered below.

Table 4 shows a comparison of the air permeation resistance (Galley value) and the electrolytic solution retention rate (jab immersion / unit area) of the separators 1A to 1D (values are average values of n = 10). Shown in.

[0031]

[Table 4]

Compared to the comparative separator 1B, the separator 1A of the present invention shows almost no change in permeation resistance and liquid retention, whereas the comparative separators 1C and 1D have deteriorated characteristics. The separator 1C is obtained by injecting a melt of polypropylene resin on the surface of a microporous film and injecting it into a fibrous shape.
This was welded and laminated over the entire contact surface while it was still in the melt-adhesive state. Therefore, it is considered that the fine pore structure of the microporous thin film was partially blocked by the molten fiber.

On the other hand, in the case of the separator 1D, as shown in FIG. 4, the microporous thin film 1 and the non-woven fabric 2 are diamond-patterned.
The sheet is laminated with a heat seal 13 and naturally, the lattice portion has the fine pore structure and the porosity of the non-woven fabric destroyed or altered.

As described above, the separators 1C and 1D have a factor of impairing the battery performance, whereas in the case of the separator 1A of the present invention, a polypropylene nonwoven fabric layer is laminated on the microporous thin film, Even though it is heated at a low temperature, it is calendered through a special roller to a predetermined thickness, and the bonding surface is not in a molten state, so the physical properties originally possessed by the microporous thin film and nonwoven fabric are impaired. Without being integrated, it does not cause deterioration of battery performance. The separation test of the integrated separator showed that the contact surface of the separator of the present invention was clean, but in the separator 1C, some non-woven fabric fibers remained on the surface of the microporous membrane, and the separator 1D showed almost no separation. It was welded as much as possible.

In addition to the above comparative examples, a rolling and mechanical integration under a large mechanical load, and a simple lamination and punching to a predetermined size were also examined. Was small, and the surface of the non-woven fabric was not fluffed by pressure, wettability was lowered, and liquid retention was significantly lowered. Further, incomplete integration resulted in defective peeling. On the other hand, with respect to the latter as well, peeling defects frequently occurred, and it was practically impossible as an integrated separator.

As described above, the multilayer separator of the present invention is
It can be integrated without impairing the original properties of the separator, reducing man-hours and improving quality and reliability.

In this embodiment, the effect was confirmed with a non-aqueous electrolyte secondary battery, but a flat primary battery, a prismatic battery, a cylindrical battery, or an aqueous solution battery using a multilayer separator is used. It can be widely applied to.

Further, in the present embodiment, an example in which the same kind of constituent material is used as the microporous thin film and the non-woven fabric which constitute the multilayer separator is shown, but the present invention is also applied to the multilayer separator made of different constituent materials. It goes without saying that you can do it. However, it is more effective when the multilayer separator is formed of the same kind of constituent material.

In addition, the manufacturing method in the embodiment is merely an example, and does not define the scope of the claims.

[0040]

The battery separator according to the present invention comprises a laminate of a polyolefin microporous thin film and a polyolefin non-woven fabric, and is heated and pressed at a temperature lower than the melting points of the thin film and the non-woven fabric constituent material of the laminate. In addition, since it is integrated, it is possible to reduce the man-hours at the time of battery assembly, and because it maintains the original properties of the separator, it also has a great effect on the improvement of quality and reliability. Yes, its industrial value is extremely large.

[Brief description of drawings]

FIG. 1 is a perspective view of a multilayer separator of the present invention.

FIG. 2 is an example of a method for producing the multilayer separator of the present invention.

FIG. 3 is a vertical cross-sectional view of a flat battery prepared by using the multilayer separator of the present invention.

FIG. 4 is a perspective view of a separator integrated by a heat seal.

FIG. 5 is a comparison diagram of cycle characteristics of prototype batteries.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Separator 2 Microporous membrane 3 Nonwoven fabric 4 Loading table 5 Thin cloth 6 Roller 7 Punching device 8 Positive electrode 9 Positive electrode can 10 Negative electrode 11 Negative electrode can 12 Insulation packing 13 Heat seal part 1A Present invention separator 1B-1D Comparison Separator A'Battery made using the separator of the present invention B'-D 'Battery made using the comparative separator

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiyuki Kumasaka 2-18 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd.

Claims (2)

[Claims] 1. A laminate comprising a polyolefin-based microporous thin film and a polyolefin-based nonwoven fabric, wherein the laminate is heated and pressed at a temperature lower than the melting points of the thin film and the nonwoven fabric constituent material. Multilayer separator for batteries. 2. The multilayer separator for a battery according to claim 1, wherein the thin film constituent material and the non-woven fabric constituent material are the same.