A non-woven fabric base material for a lithium ion secondary battery separator composed mainly of a polyethylene terephthalate fiber, characterized in that the non-woven fabric base material comprises a polyethylene terephthalate binder fiber and a crystallized polyethylene terephthalate fiber, and the content of a polyethylene terephthalate binder fiber having a fiber length of 2.5 mm or less is 10 to 60 mass %.

Provided is a method for producing a porous polyimide film with which it is possible to suppress the occurrence of curling in the polyimide-fine particle composite film obtained by firing the unfired composite film. The method for producing a porous polyimide film of the present invention includes, in the following order: forming an unfired composite film using a varnish that contains a resin including polyamide acid and/or polyimide, fine particles, and a solvent; immersing the unfired composite film in a solvent including water; firing the unfired composite film to obtain a polyimide-fine particle composite film; and removing the fine particles from the polyimide-fine particle composite film.

Provided herein are a porous film, a separator including the same, an electrochemical device including the separator, and a method of preparing the porous film. The porous film includes first cellulose nanofibers which is impregnated with a carbonate-based solvent-containing electrolyte solution and has a reaction heat of 150 J/g or less at a temperature ranging from about 30° C. to about 300° C., as measured by differential scanning calorimetry (DSC).

Provided are separators for use in an electrochemical cell comprising (a) an inorganic oxide and (b) an organic polymer, wherein the inorganic oxide comprises organic substituents. Also provided are electrochemical cells comprising such separators.

Disclosed herein are novel or improved microporous battery separator membranes, separators, batteries including such separators, methods of making such membranes, separators, and/or batteries, and/or methods of using such membranes, separators and/or batteries. Further disclosed are laminated multilayer polyolefin membranes with exterior layers comprising one or more polyethylenes, which exterior layers are designed to provide an exterior surface that has a low pin removal force. Further disclosed are battery separator membranes having increased electrolyte absorption capacity at the separator/electrode interface region, which may improve cycling. Further disclosed are battery separator membranes having improved adhesion to any number of coatings. Also described are battery separator membranes having a tunable thermal shutdown where the onset temperature of thermal shutdown may be raised or lowered and the rate of thermal shutdown may be changed or increased. Also disclosed are multilayer battery separator membranes having enhanced web handling performance during manufacturing processes and coating operations.

It is an object of the present invention to provide a nonwoven fabric having mechanical strength which is hardly cut and broken by an external force, and a separator for electrochemical devices using the nonwoven fabric.

The inventive nonwoven fabric has a sum of tensile strengths by zero-span per basis weight in the machine direction and the cross-machine direction of 6.5N/50 mm or more. Thus, the strength of the constituent fibers of this nonwoven fabric against an external force is high, and this nonwoven fabric has mechanical strength which is hardly cut and broken by an external force.

The separator for electrochemical devices of the present invention is composed of this nonwoven fabric.

A paper suitable for use as a separator or thermal or fire insulation for use in or with electrochemical cells, and an electrochemical cell comprising the same, the paper having 90 to 99 weight percent aramid fibrous pulp comprising aramid polymer fibrils and 1 to 10 weight percent polyvinylpyrrolidone present as a coating on the surface of the fibers, the paper having a thickness of 10 to 40 micrometers and a tensile strength of at least 15 megapascals or greater.

In accordance with at least selected embodiments, a battery separator or separator membrane comprises one or more co-extruded multi-microlayer membranes optionally laminated or adhered to another polymer membrane. The separators described herein may provide improved strength, for example, improved puncture strength, particularly at a certain thickness, and may exhibit improved shutdown and/or a reduced propensity to split.

A lithium secondary battery comprising a cathode, an anode, an elastic polymer protective layer disposed between the cathode and the anode, and a working electrolyte, wherein the elastic polymer protective layer comprises a high-elasticity polymer having a thickness from 2 nm to 100 μm, a lithium ion conductivity from 10.sup.−8 S/cm to 5×10.sup.−2 S/cm at room temperature, and a fully recoverable tensile elastic strain from 2% to 1,000% when measured without any additive dispersed therein and wherein the high-elasticity polymer comprises at least a crosslinked polymer network of chains from at least one polymer containing carboxylic and/or hydroxyl groups or from at least one polymer that is water-soluble prior to crosslinking.

Provided is a separator that includes a matrix including a polyolefin having a weight average molecular weight (M.sub.w) of 250,000 to 450,000 and a molecular weight distribution (M.sub.w/M.sub.n) of 3 to 7; and a silane-modified polyolefin crosslinked in the matrix, and a method of manufacturing the same.