Tuning desolvation kinetics of in-situ weakly solvating polyacetal electrolytes for dendrite-free lithium metal batteries

The host structure of polymers significantly influences ion transport and interfacial stability of electrolytes, dictating battery cycle life and safety for solid-state lithium metal batteries. Despite promising properties of ethylene oxide-based electrolytes, their typical clamp-like coordination geometry leads to crowd solvation sheath and overly strong interactions between Li+ and electrolytes, rendering difficult dissociation of Li+ and unfavorable solid electrolyte interface (SEI). Herein, we explore weakly solvating characteristics of polyacetal electrolytes owing to their alternately changing intervals between –O– coordinating sites in the main chain. Such structural asymmetry leads to unique distorted helical solvation sheath, and can effectively reduce Li+-electrolyte binding and tune Li+ desolvation kinetics in the in-situ formed polymer electrolytes, yielding anion-derived SEI and dendrite-free Li electrodeposition. Combining with photoinitiated cationic ring-opening polymerization, polyacetal electrolytes can be instantly formed within 5 min at the surface of electrode, with high segmental chain motion and well adapted interfaces. Such in-situ polyacetal electrolytes enabled more than 1300-h of stable lithium electrodeposition and prolonged cyclability over 200 cycles in solid-state batteries at ambient temperatures, demonstrating the vital role of molecular structure in changing solvating behavior and Li deposition stability for high-performance electrolytes.