Safety Test Methods Simulating Internal Short Circuit and the Mechanism for Safety Improvement of Li-ion Batteries by Heat Resistant Separators

Abstract

It is widely recognized that heat-resistant separators improve the safety of lithium-ion batteries. However, it is not clear how the separator contributes to battery safety, or how much heat resistance is required. The state of separators when a short circuit occurs in batteries was simulated and the following tests were conducted. As a first test, the edges of the separator were restrained, and hot air was applied only to a limited part of the specimen. For the second test, a model battery system was constructed and electrical heat generation during the early stage of a short circuit was observed. In these tests, several types of separators were compared with respect to the extent of damage and electrical heat generation. The separators that gave good results during nail penetration tests showed limited damage and electrical heat generation during the previously discussed tests. The heat resistance of a separator should be discussed with regard to whether it can maintain the separator function during electrical heat generation via short circuit.