Partially crosslinked adhesive-supported porous film for battery separator and its use

Abstract

A partially crosslinked adhesive-supported porous film for battery separator, which in producing a battery, can effectively produce a battery as an electrode / separator laminate in which an electrode and a separator are temporarily bonded to each other without causing mutual slip movement between the electrode and the separator and which after producing a battery, functions itself as a separator having a small heat shrinkage factor even at high temperatures, and a process of producing a battery using such a partially crosslinked adhesive-supported porous film. The partially crosslinked adhesive-supported porous film for battery separator, includes a porous film substrate having supported thereon a partially crosslinked adhesive that is partially crosslinked by preparing a reactive polymer having a functional group in the molecule and capable of being crosslinked upon reaction with a polyfunctional compound having reactivity with the functional group and then reacting the reactive polymer with a polyfunctional compound.

Description

[0001] The present invention relates to a partially crosslinked adhesive-supported porous film that is not only useful for production of batteries but also able to contribute to safety during use of the thus produced batteries, and a process of producing batteries utilizing the same.DESCRIPTION OF THE RELATED ART[0002] Conventionally, a method of producing batteries has been known in which a positive electrode and a negative electrode are laminated while sandwiching a separator between the electrodes for the purpose of preventing a short circuit therebetween, or a positive (or negative) electrode, a separator, a negative (or positive) electrode, and a separator are laminated in this order; the laminate is wound up to form an electrode / separator laminate; the electrode / separator laminate is charged into a battery container; and an electrolyte liquid is then pouring into the battery container, following by sealing, as described in, for example, JP-A-09-161814 and JP-A-11-329439.[0003]...

AI Technical Summary

Benefits of technology

[0022] Especially, in a porous film having supported thereon a partially crosslinked adhesive obtained from a reactive polymer whose glass transition temperature is the normal temperature or higher, since the partially crosslinked adhesive does not have tackiness at the normal temperature, even when the partially crosslinked adhesive-supported porous film is overlaid or wound up, it does not cause blocking. Further, for example, in the case where the porous film having a partially crosslinked adhesive supported thereon is guided into a winding machine and laminated on an electrode to obtain a laminate, the porous film is free from the matter that it is adhered on a roll guide and taken up by the roll guide.

[0055] The electrode / porous film laminate according to the present invention can be suitably used for the production of batteries. That is, the electrode / porous film laminate is charged into a battery container, and an electrolyte liquid having a polyfunctional compound dissolved therein is poured into the battery container and reacted with the unreacted functional group of the reactive polymer in the partially crosslinked adhesive in the electrode / porous film laminate to further crosslink the reactive polymer, whereby the electrode is bonded to and integrated with the porous film. Thus, it is possible to obtain a battery having an electrode / separator junction body in which not only the porous film functions as a separator, but also this separate is firmly bonded to the electrode.

Problems solved by technology

However, in such a method of producing batteries, the electrode and the separator are liable to cause mutual slip movement during custody or delivery of the electrode / separator laminate.

As a result, problems involved such that the productivity of batteries is low and that inferior goods are liable to occur.

Further, according to the thus obtained batteries, the electrode blisters or shrinks during the use, whereby adhesiveness between the electrode and the separator becomes worse, leading to reduction in battery characteristics, or an internal short circuit occurs, whereby the battery causes heat generation and temperature rise, leading to even possibility of causing breakage.

However, such a method involved problems such that not only the steps are complicated, but also the quality of the resulting products becomes hardly stable, and bonding between the electrode and the separator is not sufficient (see, for example, JP-A-10-172606).

However, such a battery separator made of a porous film obtained by stretching in a high ratio markedly shrinks under a high-temperature environment such as the case where the battery causes an abnormal temperature rise by an internal short circuit, etc., and according to circumstances, there is a problem such that the battery separator does not function as a diaphragm between electrodes.

However, contrary to the above-described method, this method does not employ stretching, and therefore, the resulting porous film involves a problem such that the strength is not sufficient.

When the film thickness is less than 3 .mu.m, the strength is insufficient so that in the case where the porous film substrate is used as the separator in the battery, an internal short circuit may possibly occur.

On the other hand, when it exceeds 100 .mu.m, a distance between the electrodes is too large so that an internal resistance becomes excessive.

When the proportion of the polyfunctional compound is less than 0.1 parts by weight based on 100 parts by weight of the reactive polymer supported on the porous film, crosslinking of the reactive polymer with the polyfunctional compound is insufficient, and in the resulting electrode / separator junction body, it is impossible to obtain firm bonding between the electrode and the separator.

On the other hand, when the proportion of the polyfunctional compound is more than 20 parts by weight based on 100 parts by weight of the reactive polymer, the adhesive after crosslinking is too hard so that adhesiveness between the separator and the electrode may possibly be hindered.