Japan Atomic Energy Research Institute

Yuasa Battery Co., Ltd.

Keizi Senoo

Takanobu Sugo

Sueo Machi

Isao Ishigaki

Kazuo Murata

Shiro Tanso

Toshio Okada

A method of producing a hydrophilic membrane from a polyethylene base film by first irradiating the film with ionizing radiation in air or an oxygen atmosphere and then grafting acrylic acid and/or methacrylic acid onto the irradiated film at low temperatures.

Method of producing a hydrophilic membrane from a polyethylene base film

A novel process for the production of a separator for use in a cell to prevent the short-circuiting of positive active material and negative active material comprises irradiating a polyolefin film 150 .mu.m or less thick with ionizing radiation at a dose rate of 5.times.10.sup.4 -10.sup.7 rads/sec. to give a total dose of 1 Mrad or more, contacting the irradiated film with an aqueous solution of a terminally unsaturated monomer such as acrylic acid, methacrylic acid and the like at a temperature of 10.degree. C.-60.degree. C. to thereby cause grafting of the monomer onto the polyolefin film before the grafted polymer film is treated with an aqueous alkaline solution to finally obtain the separator for use in a cell, which is substantially improved in that it shows low electrical resistance and is excellent both in its acid resistance and mechanical strength.

Process for production of separators for use in cells

There is disclosed a novel cell separator made of a grafted membrane comprising a polyethylene film which is graft-copolymerized with a monomer having an ion exchange group, characterized in that said membrane has an area which is not grafted at all or an area of low degree grafting. By making use of this membrane, a small size and thin cell having excellent performance as well as satisfactory mechanical strength can be produced at low cost with great advantages.

Cell separator and cell

A method of producing a dimensionally stable battery separator characterized by grafting acrylic acid and/or methacrylic acid onto a polyethylene film, treating the resulting membrane with an aqueous alkaline solution, and drying the treated membrane under application of tension.

Method of producing a dimensionally stable battery separator

A battery separator composed of a composite sheet of film to which a monomer having a hydrophilic or electrolytic group is grafted is disclosed. Said film consists of a first polymeric layer containing a substance capable of catching a metal ion dissolved from a positive or negative active material and a second polymeric layer integrally bonded to either one or both sides of the first polymeric layer and which contains no such substance or contains it in a smaller amount that that contained in said first polymeric layer. Also disclosed is a method of producing a battery separator by irradiating such composite sheet of film with ionizing radiation and immersing the irradiated film in a solution of a monomer containing a hydrophilic or electrolytic group or bringing it into contact with the monomer solution to thereby graft the monomer to the film.

Growing community of inventors

Takasaki, Japan

Keizi Senoo