In Situ Initiator‐Free Self‐Polymerizing Gel Electrolytes Under Ambient Conditions Enabling Sustainable Aqueous Zinc Metal Batteries

Aqueous zinc metal batteries (AZMBs) suffer from dendrite growth and parasitic side reactions, limiting their lifespan and stability. While in situ gel polymer electrolytes (GPEs) form robust electrode-electrolyte interfaces, conventional approaches typically require chemical initiators and crosslinkers that impose harsh conditions, generate byproducts, and result in discontinuous Zn²⁺ conduction pathways. Here, we report that simple mixing of sulfobetaine methacrylate with an aqueous ZnSO₄ solution spontaneously induces self-polymerization, enabling an initiator- and crosslinker-free in situ self-polymerizing GPE under room-temperature and ambient-air conditions without external energy. Zn²⁺ lowers electron density at the vinyl group and induces monomeric aggregates, triggering self-polymerization and rapid formation of a physically crosslinked GPE. The resulting network provides intimate electrode-electrolyte contact and continuous Zn²⁺ conduction channels, achieving a high Zn²⁺ transference number (0.76). Zn||Zn symmetric cells employing this GPE suppress dendrite formation and exhibit stable cycling for over 4100 h and reliable low-temperature (-10°C) operation, significantly outperforming conventional initiator- and crosslinker-based in situ GPEs. Zn||VO₂ full cells also exhibit excellent cycling stability with ∼96% capacity retention. This ZnSO₄-induced in situ self-polymerizing GPE strategy embodies green chemistry principles and enables a high-performance, cost-effective, and sustainable solution to zinc anode challenges, paving the way for next-generation AZMBs.