Multidentate ether modifies solvation structure in nonflammable phosphate electrolytes for wide-temperature lithium-ion batteries

Conventional carbonate electrolytes cannot meet the requirements for lithium-ion batteries (LIBs) with wide temperature range and high safety. Diethyl ethylphosphonate (DEEP) has excellent flame retardancy and a wide temperature range (-83 to 198 °C), which holds promise for developing a non-flammable electrolyte for wide-temperature application in LIBs. However, its limited compatibility with graphite electrodes and slow ionic transport capability must be addressed. Herein, we introduce diethylene glycol dimethyl ether (DEGDME) to reconfigure the solvation structure of DEEP-based electrolyte and enhance its ion transport capacity. The film-forming additives enable the electrolyte to preserve 98% capacity retention after 150 cycles for Li||Graphite cells. The non-flammable DEEP-based electrolytes modified with DEGDME enable improved low-temperature performance with achieving 71% 50th-cycle retention of Graphite||LiFePO4 cells at -20 °C. This work introduces a new strategy for designing non-flammable phosphate electrolytes, enabling the reliable and safe application of LIBs across a wide temperature range. Diethyl ethylphosphonate (DEEP) is a promising candidate for developing non- flammable electrolytes for wide-temperature application in Li-ion batteries, but low compatibility with graphite electrodes and slow ionic transport hinder its implementation. Here, the authors show that incorporating diethylene glycol dimethyl ether into a DEEP-based electrolyte enhances ion transport and improves low-temperature performance in graphite-based cells.