Non-flammable long chain phosphate ester based electrolyte via competitive solventized structures for high-performance lithium metal batteries

Abstract

Safety remains a persistent challenge for high-energy–density lithium metal batteries (LMBs). The development of safe and non-flammable electrolytes is especially important in harsh conditions such as high temperatures. Herein, a flame-retardant, low-cost and thermally stable long chain phosphate ester based (tributyl phosphate, TBP) electrolyte is reported, which can effectively enhance the cycling stability of highly loaded high-nickel LMBs with high safety through co-solvation strategy. The interfacial compatibility between TBP and electrode is effectively improved using a short-chain ether (glycol dimethyl ether, DME), and a specially competitive solvation structure is further constructed using lithium borate difluorooxalate (LiDFOB) to form the stable and inorganic-rich electrode interphases. Benefiting from the presence of the cathode electrolyte interphase (CEI) and solid electrolyte interphase (SEI) enriched with LiF and LixPOyFz, the electrolyte demonstrates excellent cycling stability assembled using a 50 μm lithium foil anode in combination with a high loading NMC811 (15.4 mg cm−2) cathode, with 88% capacity retention after 120 cycles. Furthermore, the electrolyte exhibits excellent high-temperature characteristics when used in a 1-Ah pouch cell (N/P = 0.26), and higher thermal runaway temperature (238 °C) in the ARC (accelerating rate calorimeter) demonstrating high safety. This novel electrolyte adopts long-chain phosphate as the main solvent for the first time, and would provide a new idea for the development of extremely high safety and high-temperature electrolytes.