Battery separator with Z-direction stability

Abstract

A battery separator is a microporous membrane. The membrane has a major volume of a thermoplastic polymer and a minor volume of an inert particulate filler. The filler is dispersed throughout the polymer. The membrane exhibits a maximum Z-direction compression of 95% of the original membrane thickness. Alternatively, the battery separator is a microporous membrane having a TMA compression curve with a first substantially horizontal slope between ambient temperature and 125° C., a second substantially horizontal slope at greater than 225° C. The curve of the first slope has a lower % compression than the curve of the second slope. The curve of the second slope is not less than 5% compression. The TMA compression curve is graphed so that the Y-axis represents % compression from original thickness and the X-axis represents temperature.

Description

BACKGROUND OF THE INVENTION [0001] The use of microporous membranes as battery separators is known. For example, microporous membranes are used as battery separators in lithium-ion batteries. Such separators may be single layered or multi-layered thin films made of polyolefins. These separators often have a ‘shut-down’ property such that when the temperature of the battery reaches a predetermined temperature, the pores of the membrane close and thereby prevent the flow of ions between the electrodes of the battery. Increasing temperature in the battery may be caused by internal shorting, i.e., physical contact of the anode and cathode. The physical contact may be caused by, for example, physical damage to the battery, damage to the separator during battery manufacture, dendrite growth, excessive charging, and the like. As such, the separator, a thin (e.g., typically about 8-25 microns thickness) microporous membrane, must have good dimensional stability. [0002] Dimensional stability...

AI Technical Summary

Problems solved by technology

Increasing temperature in the battery may be caused by internal shorting, i.e., physical contact of the anode and cathode.

The physical contact may be caused by, for example, physical damage to the battery, damage to the separator during battery manufacture, dendrite growth, excessive charging, and the like.

To date, nothing has been done to improve the Z-direction dimensional stability of these battery separators.

As they move closer to one another, the risk of physical contact increases.

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