Using extremely low initiator concentrations in ionic-liquid radical polymerization produces ultrahigh-molecular-weight polymers at high conversion. Their entanglement forms free-standing, crosslinker-free gels with high stretchability, recyclability, and rapid room-temperature self-healing. Separately, optimized polymers and highly concentrated lithium-salt electrolytes form robust gels that serve as protective interphases on lithium-metal anodes and markedly improve cycling stability.

Growing demand for high-capacity energy storage has drawn increasing attention to rechargeable batteries using lithium-metal anodes. However, the safety and cycling stability of lithium metal remain major challenges, and extensive efforts are being made to address these issues. By optimizing both the composition of the organic electrolyte and the polymer structure, we developed a gel electrolyte consisting of a highly concentrated lithium-salt electrolyte and a newly designed hydrogen-bonding polymer. This gel exhibits exceptionally high mechanical strength compared with previously reported lithium-ion-conducting gel electrolytes. When used as a protective coating on a lithium-metal anode, the gel significantly improves cycling stability. This technology is expected to contribute to the practical realization of next-generation rechargeable lithium batteries.