Coordination Regulation Enabling Deep Eutectic Electrolyte for Fast-Charging High-Voltage Lithium Metal Batteries.

The safety and cycle stability of lithium metal batteries (LMBs) under conditions of high cut-off voltage and fast charging put forward higher requirements for electrolytes. Here, a sulfonate-based deep eutectic electrolyte (DEE) resulting from the eutectic effect between solid sultone and lithium bis(trifluoromethanesulfonyl)imide without any other additives is reported. The intermolecular coordination effect triggers this eutectic phenomenon, as evidenced with nuclear magnetic resonance, and thus the electrochemical behavior of the DEE can be controlled by jointly regulating the coordination effects of F···H and Li···O intermolecular interactions. The DEE with a properly coordinated environment of Li presents a low motion barrier and a high transport rate of localized Li, leading to a 10 C fast-charging LiFePO||Li battery with a capacity retention of 95.1% after 500 cycles. Meanwhile, the strengthened α-H···F coordination broadens the electrochemical stability window of the DEE, thus enabling the cycle stability of high-capacity and high-voltage cathode materials in LMBs, e.g., a cycle stability at 4.5 V in the LiNiCoMnO||Li battery with a capacity retention of 81.0% after 500 cycles, and an excellent compatibility in 4.5 V LiCoO||Li and 4.8 V LiMnNiCoO||Li batteries. The practical applicability of the carefully designed DEE is underscored through successful implementation in pouch cells.