A safer organic cathode material with overheating self-protection function for lithium batteries

Abstract

Rechargeable lithium batteries (LBs) have been widely applied in portable devices, electric vehicles (EVs) and grid energy storage systems due to their higher energy density, long cycle life and lack of memory effect. However, if operated improperly such as thermal impact, mechanical damage or short-circuiting, it will cause the vast heat accumulation of LBs, finally fires or explosions. Here, we report a novel concept that the temperature-sensitive conductive polymer-based materials (P3OT@CNT and P3BT@CNT nanocomposites) as cathode materials with intrinsic overheating self-protection function enabled by removing active anions can mitigate the safety concern of LBs. In normal operation conditions, both P3OT@CNT and P3BT@CNT display a better electrochemical performance compared with the reported anion-active cathode materials. More importantly, the thermal dedoping of electroactive PF6- from P3OT or P3BT matrix when the battery temperature reaches to a given high temperature can provide overheating self-protection for LBs, avoiding the occurrence of thermal runaway. During the charging process, the thermal dedoping of PF6- causes the battery voltage to not rise, namely the loss of charging function. This abnormal voltage signal can offer an early warning of battery overheating, allowing timely handling and preventing the occur of thermal runaway of battery. When discharged, the battery can be rapidly switched off with delivering little capacity, avoiding the continuous heat accumulation and preventing battery from thermal runaway. This work provides a new thermal protection strategy for safer LBs, utilizing the intrinsic overheating protection function of cathode materials without introducing extra thermal protection elements to battery.