Slurry for forming insulating layer, separator for electrochemical device, method for producing the same, and electrochemical device

Abstract

A slurry for forming an insulating layer of the present invention includes heat-resistant insulating fine particles, a thickening agent, and a dispersion medium. The insulating fine particles are dispersed in the dispersion medium. The slurry for forming an insulating layer has a viscosity of 5 to 500 mPa·s. The proportion of particles with a particle size of 1 μm or less in the insulating fine particles is 30 vol % or more and the proportion of particles with a particles size of 3 μm or more in the insulating fine particles is 10 vol % or less. An electrochemical device of the present invention includes a separator for an electrochemical device of the present invention that is produced using the slurry for forming an electrochemical device of the present invention.

Description

TECHNICAL FIELD[0001]The present invention relates to a slurry for forming an insulating layer suitable for the constituent of a separator for an electrochemical device, a separator for an electrochemical device having an insulating layer formed of the slurry and a method for producing the separator, and an electrochemical device including the separator.BACKGROUND ART[0002]A lithium secondary battery, which is a type of an electrochemical device, is characterized by a high energy density and thus has been widely used as a power source for portable equipment such as a portable telephone and a notebook personal computer. The capacity of the lithium secondary battery is likely to increase further as the performance of the portable equipment becomes higher. For this reason, it is important to ensure the safety of the lithium secondary battery.[0003]In the current lithium secondary battery, e.g., a polyolefin microporous film (microporous film) with a thickness of about 20 to 30 μm is us...

AI Technical Summary

Benefits of technology

[0020]The slurry for forming an insulating layer of the present invention is capable of achieving the uniform dispersion of the insulating fine particles and maintaining the dispersion state stably. The separator for an electrochemical device of the present invention is produced using the slurry for forming an insulating layer of the present invention and thus can have excellent heat resistance. The electrochemical device of the present invention includes the separator for an electrochemical device of the present invention and thus can have high reliability. Moreover, the method for producing a separator for an electrochemical device of the present invention can produce the separator stably and continuously.

Problems solved by technology

Thus, it is hard to say that the margin for safety of the battery is sufficient.

Moreover, the film has been distorted by drawing and may shrink due to residual stress when it is subjected to high temperatures.

If the pores are not sufficiently closed and the current cannot be immediately reduced, the temperature of the battery is easily raised to the shrinkage temperature of the separator, so that an internal short circuit can occur.

Thus, it may be difficult to maintain a stable dispersion state of the fine particles in the slurry.

When the slurry in which the fine particles are agglomerated or settled is applied to the base or the like, the application tends to be not uniform.

Moreover, when the dispersion state of the fine particles in the slurry is particularly unstable, the fine particles are agglomerated or settled in the period of time between the application and drying of the slurry.

This may result in non-uniformity of the surface to which the slurry is applied.

The non-uniform application of the slurry reduces the evenness of the separator produced.

Consequently, in the lithium secondary battery, the ionic conduction is not uniform within the separator, which may cause a deficiency such as a deposition of lithium during charging of the battery particularly at a high current density.

Moreover, if the deposited lithium becomes a dendrite crystal, a short circuit may occur due to the lithium dendrite.

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