Positive‐Temperature‐Coefficient Graphite Anode as a Thermal Runaway Firewall to Improve the Safety of LiCoO2/Graphite Batteries under Abusive Conditions

Abstract

A positive‐temperature‐coefficient graphite anode as a thermal runaway firewall of LiCoO2/graphite lithium‐ion batteries (LIBs) is prepared by introducing thermally sensitive polymer microspheres (TSPMs) into the anode to improve battery safety under abusive conditions. The TSPMs are composed of an acrylonitrile and acrylate copolymer shell and a cyclopentane hydrocarbon core. Due to the thermally sensitive properties of TSPMs, the graphite anode swells under abusive conditions, and the electric connection of active materials and current collector can be cut off. Thus, the resistance of LIBs is increased to solve the thermal runaway and safety problems before the temperature of LIBs approaches explosion limit. The TSPMs with a size distribution of 4–20 μm and an initial foaming temperature of 95–110 °C exhibit excellent stability and foaming properties. Compared with the batteries without TSPMs, under abusive conditions including overcharge at 1 C/10 V, thermal shock from 20 to 130 °C, and external short circuit with a resistance of ≈80 mΩ, the batteries with TSPMs effectively mitigate thermal runaway. In addition, TSPMs do not show obvious influences on the conventional performances of LIBs, indicating that adding TSPMs into graphite anodes is a promising method to improve the safety of LIBs under abusive conditions.