Uncovering the Function of a Five-Membered Heterocyclic Solvent-Based Electrolyte for Graphite Anode at Subzero Temperature

Ethylene carbonate (EC) is taken as the essential electrolyte component in lithium-ion batteries (LIBs) due to its high permittivity and film-forming ability. However, its high melting point (36.4 degrees C) and strong solvation energy severely hinder Li+ transportation and Li+ desolvation process under low temperatures, resulting in capacity loss and even Li plating on graphite anode. Herein, a five-membered heterocyclic compound isoxazole (IZ), similar to EC molecule, is well-formulated to substitute EC for low-temperature operation of graphite anode. It is revealed that IZ with dispersed charge distribution exhibits a weaker solvation ability than EC with highly polar carbonyl group, which induces relatively more anions into the solvation sheath to form contact ion pairs and aggregates. The tamed electrolyte not only exhibits high ionic conductivities over wide-temperature range but also generates an inorganic-rich interphase with low activation barrier for smooth Li+ ions threading. This enables graphite anode with an impressive reversible capacity of 263 mAh g(-1) at the low temperature of -30 degrees C (a room-temperature retention of as high as 71.5%), nearly twice higher than graphite with EC-based electrolyte. This study provides an alternative electrolyte recipe to relieve the anxiety of LIBs operated under harsh conditions.