Thermal Runaway Inhibition of Lithium-Ion Batteries Employing Thermal-Driven Phosphazene Based Electrolytes

Abstract

Organic electrolyte is a threat to the safe operation for Ni-rich lithium ion batteries due to its flammability and high voltage cycle instability. Exploring advanced battery electrlytes with high safety and high voltage cyclability is of great significance to the development of electrical vehicles and grid energy storage. Herein, a multi-functional electrolyte additive, ethoxy-(pentafluoro)-cyclotriphosphazene, for high-safety and high-energy pouch-type LiNi_0.8Mn_0.1Co_0.1O₂|graphite (NMC811|Gr) cells is explored. It combined the structure of non-flammable cyclophosphazene with fluorine, with a good electrochemical compatibility. The high efficiency of the flame retardant produced properties that can not be achieved using “normal” fluorine-based flame retardants for thermal runaway inhibition. Moreover, the phosphazene (C₂H₅F₅N₃OP₃)-based electrolyte (FPEele) endowed an NCM811|Gr pouch cell with extraordinary safety (thermal runaway trigger temperature increased by +41.7 °C, and its highest temperature is decreased by ─205.7 °C) and electrochemical performance (4.5 V high-voltage cycling, 81.7% capacity retention after 200 cycles). The capacity fading and thermal safety of the battery are simultaneously improved based on the additive engineering. In fact, the phosphazene-based additive contained F, P, and N atoms, which stabilized the electrode interface and synergistically suppressed combustion during battery failure. Thus, such a work can provide a new ideal for designing a multi-functional electrolyte.