An artificial cathode-electrolyte interphase with flame retardant capability enabled by an organophosphorus compound for lithium metal batteries

Abstract

Lithium metal batteries (LMBs) have attracted much attention in recent years due to their low redox potential and superior theoretical capacity (∼3860 mA h g⁻¹). However, the highly reactive lithium metal with flammable electrolytes has posed enormous challenges associated with inconsistent cycling stability and safety concerns. Herein, a flame-retardant artificial cathode-electrolyte interphase (A-CEI) enabled by an organophosphorus compound is proposed for LMBs. The successful incorporation of dimethyl methylphosphonate (DMMP) into poly(vinylidenefluoride-co-hexafluoropropylene) not only provides a reliable CEI layer (<10 nm) with LiF during cycling, but also suppresses fire by a radical scavenging mechanism with heat barriers. The A-CEI cell reduces capacity decay from 21% to 9.4% on cycling and consistently achieves a high coulombic efficiency of ∼99.6%. During the flame test, multiple ignitions were attempted, but any flames were extinguished within 1 s, suggesting superior flame-retardant properties of the A-CEI. It also revealed a strong thermal stability up to 280 °C. This study provides an efficient and facile way to simultaneously address the key challenges of LMBs for practical applications.