Highly reversible tin redox chemistry for stable anode-free acidic proton battery

Non-toxic metallic tin (Sn) possesses high hydrogen overpotential and environmental friendliness, which is favorable for high-performance aqueous batteries. However, the large particle size and irregular deposition morphology of Sn in acidic electrolyte dramatically decrease cycle stability. Here, we demonstrated that the inherent root for above issues is the high exchange current density of Sn/Sn2+ in acidic electrolyte, and two effective approaches were presented (gelatin additives and methanesulfonic acid-based electrolyte). In particular, the methanesulfonic-acid-based electrolyte with unique complexing environment not only improves uniformity of deposited Sn but also suppresses the hydrogen evolution, conferring Sn/Sn2+ with high average Coulombic efficiency of 99.95%. The assembled anode-free organic/Sn battery with lean electrolyte can exert unprecedented stability more than 4,000 cycles. Moreover, a scale-up anode-free battery with 23 mAh capacity sustained more than 1,000 cycles. The findings provide universal strategies to improve the stability of the Sn cycle, marking a solid step toward the practical application.