Inhibition of Sn(Ⅱ) disproportionation for durable tin-metal aqueous batteries

Tin (Sn) electrochemistry in alkaline electrolytes offers a negative potential and intrinsic HER resistance, yet the instability of the Sn(II) state causes active material loss and rapid battery failure. Herein, we identify Sn(II) self-disproportionation into inert Sn(OH) 6 2− and dead Sn 0 as the key degradation mechanism and propose a hydroxy-bridge-disrupting (HBD) electrolyte to stabilize the Sn/Sn(OH) 3 − redox couple. The HBD strategy disaggregates hydroxy-bridged Sn(OH) 3 − (Sn–(μ-OH)–Sn) into stable Sn(OH) 3 − monomers, increasing the disproportionation energy barrier. Scanning electrochemical microscopy and molecular dynamics simulations further confirm uniform nucleation and layer-by-layer deposition. Consequently, the Sn anode achieves a high Coulombic efficiency of 99.8% and over 1,400 h of cycling. Without dendrites and dead Sn, a new prototype of Sn//Fe flow battery delivers a power density of 409.6 mW cm −2 and a lifespan exceeding 1,900 cycles. This work elucidates the failure mechanism of alkaline Sn electrochemistry and presents economically viable strategies to advance Sn-based aqueous batteries.