Constructing flame-retardant gel polymer electrolytes via multiscale free radical annihilating agents for Ni-rich lithium batteries

Abstract

Parasitic multiscale free radical reactions of electrolytes not only deteriorate battery performance but also cause a fire hazard. Therefore, fundamentally blocking free radical reactions is a smart strategy for simultaneous improvement. Herein, a multiscale free radical annihilating agent hexachlorocyclotriphosphazene cross-linked tannic acid microsphere (HT) is unprecedentedly applied to polyethylene glycol diacrylate based in-situ constructed polymer electrolytes (PEGGPE@HT), which significantly annihilates free radicals from electrolytes at high-voltage and high temperature. The electrochemical stability of PEGGPE@HT is improved to 4.5 V (Li/Li+). The capacity retention rate of the LiNi0.8Mn0.1Co0.1O2 (NCM811)//Li cell is increased to 85.3% after 200 cycles at 1 C and that of the LiFePO4//Li cell is up to 96.4% after 400 cycles at 1 C by the presence of HT. Moreover, the effectiveness of this strategy has also been further validated in the NCM811//Graphite pouch full cell and high loading NCM811//ultra-thin Li cell. Furthermore, benefiting from the annihilation of phosphorus radicals generated from HT at high temperatures, the PEGGPE@HT shows good flame retardancy and endows the pouch cell with excellent fire safety. Additionally, the pouch cell also features excellent mechanical abuse resistance. This facile synthesis is compatible with the existing battery industry process, which renders great potential for PEGGPE@HT to construct competitive LIBs with high energy density and high safety in large-scale applications.