Non-Flammable Polymer Electrolyte with Fast Ion Conductivity for High-Safety Li Batteries

The safety and ionic conductivity of solid polymer electrolytes have hindered their large-scale application. Tetrabromobisphenol A (TBBA) is regarded as an efficient flame retardant for polymers. However, the -OH group of TBBA is active during electrochemical process and results in the sacrifice of capacity in battery cycling. Herein, a new organic filler, TBBA-dichlorobutane (TD) is generated by replacing the H of -OH in TBBA using the 1,4-dichlorobutane through copolymerization modification. The electrochemical stability of TD has been improved, which facilitates the generation of the solid electrolyte interphase (SEI) layer of LiBr, improving interface ionic conductivity. Meanwhile, the addition of TD significantly reduces the crystallinity of polyacrylonitrile (PAN), improving the ionic conductivity of the electrolyte. Furthermore, the electrochemical mechanism has been characterized by in-situ Raman and Fourier transform infrared (FT-IR) spectra, revealing the high stability and fast ion transfer ability of electrolytes. From the theoretical calculation (density functional theory (DFT), COMSOL, and molecular dynamics (MD)), the priority combination between lithium-ion and the bromine in PAN-TD (P-TD), as well as uniform lithium-ion flux, can be certified. Therefore, the LiFePO4//Li battery exhibits a specific capacity of 157 mA h g−1 at 0.5 C and maintains 154 mA h g−1 after 100 cycles. At the same time, the safety properties have been improved by the formation of the carbon layer and the capture of free radicals through bromine, exhibiting an oxygen index as high as 29%.