Self-cleaning all-fluorinated nonflammable electrolyte for high-voltage and high-temperature Li||NCM811 batteries

Abstract

All-fluorinated electrolytes with high oxidation stability and favorable flame-retardant property are promising electrolytes for high-voltage Li metal batteries. However, conventional all-fluorinated electrolytes consisting of fluoroethylene carbonate (FEC) and LiPF₆ suffer from grievous decompositions at elevated temperature, which generates reactive species (such as HF and PF₅) and seriously damages interfacial structures of electrodes. Herein, we develop a self-cleaning all-fluorinated nonflammable electrolyte, which employes ethoxy(pentafluoro)cyclotriphosphazene (PFPN) to stabilize PF₆⁻ via intermolecular interactions, restrain the generation of HF, prevent the decomposition of FEC and enhance thermostability of the electrolyte. The strong interactions between PFPN and other components regulate the solvation structures, and bring more PF₆⁻ anions into the primary solvation shell of Li⁺ to construct solid electrolyte interphases (SEIs) and cathode-electrolyte interphases (CEIs), which leads to the fabrication of robust LiF-rich SEIs/CEIs. Benefiting from the above advantages, the designed electrolyte possesses excellent high-temperature interface compatibility with Li metal anodes and NCM811 cathodes, which endows Li||NCM811 batteries with significantly enhanced cycling stability at 60 °C and high cut-off voltage of 4.5 V. This work provides rational design of highly stable electrolytes for Li metal batteries capable of withstanding aggressive operating conditions.