A Low-Concentration All-Phosphate Electrolyte for High-Voltage and High-Safety Lithium-Ion Batteries

The majority of safety incidents associated with lithium-ion batteries (LIBs) arise from the utilization of highly volatile and flammable carbonate electrolytes. The adoption of non-flammable all-phosphate-solvent electrolytes could significantly enhance the safety of LIBs. Nevertheless, all-phosphate-solvent electrolytes at low-concentrations (≈1 m) are not compatible with commercial graphite anodes. Herein, we design and synthesize a new six-membered cyclic phosphate (HTP) with intrinsic graphite passivation ability as electrolyte solvent. Conventional tris(2,2,2-trifluoroethyl) phosphate (FTEP) is introduced as co-solvent to regulate the electrolyte solvation structure through solvent-solvent interactions between HTP and FTEP, which facilitates Li⁺ de-solvation and contributes to the formation of a highly robust inorganic-polymeric CEI/SEI. The resulting low-concentration electrolyte with all-phosphate-solvent not only exhibits wide potential window, unmeasurably high flash point, excellent non-flammability and thermal stability, but also promises the 4.5 V graphite||LiNi_0.8Mn_0.1Co_0.1O₂ full-cells to operate stably at extreme temperatures up to 100°C and pass various rigorous safety tests. This work provides new insights into the design of non-flammable electrolytes for high-voltage and high-safety LIBs and are broadly applicable to other batteries.