Developing “Polymer-in-Salt” High Voltage Electrolyte Based on Composite Lithium Salts for Solid-State Li Metal Batteries

The stringent demands for lithium salts make the design of “polymer-in-salt” type solid electrolyte restricted since it was proposed in 1993. Herein, a novel polymer-in-salt solid electrolyte is developed via a supramolecular strategy based on poly(methyl vinyl ether-alt-maleic anhydride) (PME) and novel single-ion lithiated polyvinyl formal (LiPVFM)/lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) composite salts (Dual-Li). Hydroxyl of LiPVFM in Dual-Li forms a strong hydrogen bond with the carboxylic acid group generated by the partial ring-opening reaction of maleic anhydride in PME. Meanwhile, PME with abundant carbonyl enables the improved LiTFSI coordination in the polymer/salt composites. As a result, the greatly enhanced mutual solubility of PME and Dual-Li is of importance to build a “polymer-in-salt” solid electrolyte (PISE), which exhibits high ionic conductivity of 3.57 × 10 –4 S cm –1 , wide electrochemical window beyond 5 V, and superior lithium-ion transference number of 0.62 at 25 °C as well as excellent interfacial compatibility with electrodes. The as-assembled LiCoO 2 ||Li solid batteries present prominent high-voltage cyclability with 89.2% capacity retention in 225 cycles. Furthermore, LiNi 0.7 Mn 0.2 Co 0.1 O 2 ||Li pouch cells exhibit remarkable safety even under harsh conditions. The study offers a promising strategy to address the high voltage compatibility and interfacial issues using PISE in solid-state batteries.