A multi-functional electrolyte additive for fast-charging and flame-retardant lithium-ion batteries

Abstract

Lithium-ion batteries (LIBs) are extensively used in electric vehicles and portable electronics due to their high energy density. However, conventional carbonate electrolytes suffer from potential Li plating at high current density and high flammability, which hinder their fast charging capability. Herein, a multi-functional electrolyte additive, namely ethoxy(pentafluoro)cyclotriphosphazene (PFPN), is explored to realize extreme fast charging of graphite‖LiFePO₄ (LFP) cells with enhanced safety. The addition of PFPN into the baseline electrolyte comprising 1 M lithium bisfluorosulfonimide salt (LiFSI) in 1,3-dioxolane not only enhances the bulk ionic conductivity but also promotes the generation of a robust and ionic-conductive solid electrolyte interphase, hence enabling superior fast-charging performance of LIBs. In addition, the PFPN additive improves the nonflammability of electrolytes and inhibits the corrosion of Al foil caused by the LiFSI salt. As a result, graphite anodes deliver reversible capacities of 314.2 mA h g⁻¹ and 164.4 mA h g⁻¹ at 20C and 50C, respectively. Furthermore, the graphite‖LFP full pouch cells maintain a reversible capacity of 127.9 mA h g⁻¹ and a high capacity retention of 99.68% over 500 cycles under 1C. This work provides a viable pathway to designing fast-charging electrolytes with remarkable cycling stability and excellent flame retardancy.