Weakly coordinating cationic polymer electrolytes for fast-charging solid-state lithium-metal batteries

Despite the growing interest in fast-charging solid-state lithium (Li)-metal batteries (SSLMBs), their practical implementation has yet to be achieved, primarily due to an incomplete understanding of the disparate and often conflicting requirements of the bulk electrolyte and the electrode-electrolyte interphase. Here, we present a weakly coordinating cationic polymer electrolyte (WCPE) specifically designed to regulate the Li+ coordination structure, thereby enabling fast-charging SSLMBs. The WCPE comprises an imidazolium-based polycationic matrix combined with a succinonitrile (SN)-based high-concentration electrolyte. Unlike conventional neutral polymer matrices, the polycationic matrix in the WCPE competes with Li+ for interactions with SN, weakening the original coordination between SN and Li+. This modulation of SN–Li+ interaction improves both Li+ conductivity of the WCPE (σLi+ = 1.29 mS cm−1) and redox kinetics at the electrode-electrolyte interphase. Consequently, SSLMB cells (comprising LiFePO4 cathodes and Li-metal anodes) with the WCPE achieve fast-charging capability (reaching over 80% state of charge within 10 min), outperforming those of previously reported polymer electrolyte-based SSLMBs.