Resin composition, separator for non-aqueous electrolyte secondary battery and production method therefor, and non-aqueous electrolyte secondary battery

Abstract

The present invention provides a resin composition comprising the following resin (a) and filler particles. The use of this composition makes it possible to obtain a separator having excellent heat resistance. Resin (a): a copolymer comprising a structural unit represented by a formula (1) and a structural unit represented by a formula (2), ##STR00001##
wherein M.sup.n+ represents a metal ion, and n represents the valence thereof, ##STR00002##

Claims

1. A separator for a non-aqueous electrolyte secondary battery, the separator comprising a filler layer comprising the following resin (a) and filler particles, and a separator substrate for a non-aqueous electrolyte secondary battery; resin (a): a copolymer comprising a structural unit represented by a formula (1) and a structural unit represented by a formula (2): ##STR00008## wherein M.sup.n+ represents a metal ion, and n represents the valence thereof; ##STR00009##

2. The separator according to claim 1, wherein the separator substrate for a non-aqueous electrolyte secondary battery is a porous membrane of polyolefin.

3. A method for producing a separator for a non-aqueous electrolyte secondary battery, the method comprising a step of applying a resin composition comprising the following resin (a) and filler particles to a surface of a separator substrate; resin (a): a copolymer comprising a structural unit represented by a formula (1) and a structural unit represented by a formula (2): ##STR00010## wherein M.sup.n+ represents a metal ion, and n represents the valence thereof; ##STR00011##

4. The production method according to claim 3, further comprising a step of drying the resultant applied product.

5. The production method according to claim 3, wherein the separator substrate for a non-aqueous electrolyte secondary battery is a porous membrane of polyolefin.

6. A non-aqueous electrolyte secondary battery comprising the separator according to claim 1.

Description

(PRODUCTION EXAMPLE 1) PRODUCTION OF SUBSTRATE POROUS FILM

(1) Seventy parts by weight of ultra-high molecular weight polyethylene powder (340M, produced by Mitsui Chemicals, Inc.), 30 parts by weight of polyethylene wax (FNP-0115, produced by NIPPON SEIRO CO., LTD.) having a weight average molecular weight of 1000, 0.4 parts by weight of an antioxidant (IRGANOX (registered trademark) 1010, produced by Ciba Specialty Chemicals), 0.1 parts by weight of an antioxidant (IRGAFOS (registered trademark) P168, produced by Ciba Specialty Chemicals), and 1.3 parts by weight of sodium stearate were mixed, and to the resulting mixture, calcium carbonate (produced by MARUO CALCIUM CO., LTD.) having an average particle size of 0.1 μm was added so as to be 38% by volume with respect to the whole volume of the resulting mixture. These materials were mixed as powder by a Henschel mixer, and then melt-kneaded by a twin-screw kneader to obtain a polyolefin resin composition. The polyolefin resin composition was rolled with a pair of roller whose surface temperature was 150° C. to prepare a sheet. The sheet was immersed in an aqueous hydrochloride solution (hydrochloric acid 4 mole/L, nonionic surfactant 0.5% by weight) to remove calcium carbonate, subsequently stretched by 6 times at 105° C., and subjected to a corona treatment at 50 W/(m.sup.2/minute) to obtain a substrate porous film (thickness 16.6 μm) made of a polyethylene porous membrane.

(EXAMPLE 1) PRODUCTION OF RESIN COMPOSITION AND SEPARATOR

(2) One hundred parts by weight of alumina fine particles (“AKP3000” (trade name) produced by Sumitomo Chemical Co., Ltd.), 3 parts by weight (as a resin solid content) of 20% by weight aqueous solution (neutralized with an aqueous sodium hydroxide solution, degree of neutralization 1) of ISOBAM (registered trademark) 306 (produced by KURARAY CO., LTD., weight average molecular weight 80000 to 90000), and 82 parts by weight of isopropyl alcohol were mixed, and to the resulting mixture, water was added so that a solid content was 20% by weight, and the resulting mixture was stirred and mixed by Ultra-High Speed Multi-use Mixing System (TK ROBOMIX (registered trademark), manufactured by PRIMIX Corporation). The resulting mixture was dispersed and mixed with a high pressure homogenizer (Star Burst (registered trademark), manufactured by Sugino Machine Limited) to obtain the resin composition of the present invention as a uniform slurry. The resin composition was uniformly applied to one side of the substrate porous film obtained in Production Example 1 with a gravure coater, and the resin composition applied was dried at 60° C. to obtain a separator for a non-aqueous electrolyte secondary battery.

(3) The weight per unit area of the resin composition of the obtained separator was 9.83 g/m.sup.2 (ISOBAM (registered trademark) 306: 0.29 g/m.sup.2, alumina: 9.54 g/m.sup.2). The properties of the separator are as follows.

(4) (1) Dimension retention: 97% in machine direction (MD) and 91% in transverse direction (TD)

(5) (2) Air permeability: 89 seconds/100 cc

(6) The term “degree of neutralization of 1” in neutralization of ISOBAM (registered trademark) 306 indicates that the resin (a) contained in the resulting aqueous solution is substantially consisting of the structural unit (1) and the structural unit (2), and Mn.sup.+ in the structural unit (1) is Na.sup.+.

COMPARATIVE EXAMPLE 1

(7) A separator for a non-aqueous electrolyte secondary battery was obtained in the same manner as in Example 1 except for using 3 parts by weight of polyvinyl alcohol (produced by Wako Pure Chemical Industries, Ltd., Wako first class, average degree of polymerization 3100 to 3900, degree of saponification 86 to 90% by mole) in place of ISOBAM (registered trademark) 306.

(8) The weight per unit area of the resin composition of the obtained separator was 11.05 g/m.sup.2 (polyvinyl alcohol: 0.32 g/m.sup.2, alumina: 10.73 g/m.sup.2). The properties of the separator are as follows.

(9) (1) Dimension retention: 30% in machine direction (MD) and 46% in transverse direction (TD)

(10) (2) Air permeability: 113 seconds/100 cc

(11) It can be said that when the separator has higher dimension retention, the separator has excellent heat resistance. Further, it can be said that when the separator has a lower value of air permeability, the separator has better ion permeability and excellent load characteristics.

INDUSTRIAL APPLICABILITY

(12) When the resin composition of the present invention is used as a resin composition for a surface treatment of a separator substrate for a non-aqueous electrolyte secondary battery, a separator having excellent heat resistance is obtained. A non-aqueous electrolyte secondary battery including such a separator is excellent in safety.