Opportunities and Challenges of Aqueous Tin Batteries for Future Energy Storage.

Aqueous tin batteries are promising because tin offers high volumetric capacity, sluggish hydrogen-evolution kinetics, relatively isotropic deposition, and two- or four-electron redox chemistry. However, dendrite-resistant growth alone does not ensure reversibility. Hydrolysis, oxygen-induced oxidation, corrosion, kinetic asymmetry, soluble Sn2+ intermediates, incomplete stripping, particle detachment, pore blockage, and crossover can all disrupt the tin redox cycle. This review summarizes the fundamental chemistry of acidic Sn2+/Sn and alkaline Sn4+/Sn2+/Sn systems and examines the conditional advantages, coupled failure mechanisms, materials strategies, and chemical compatibility of representative full cells. It also proposes practical benchmarking criteria based on tin inventory conservation, species confinement, electrochemical recoverability, and realistic utilization conditions to distinguish genuine reversibility from performance masked by shallow cycling, excess tin inventory, or large electrolyte volumes. Future progress requires coordinated control of tin speciation, deposition, intermediate confinement, charge-carrier transport, and cathode compatibility. The key objective is to keep every tin species spatially confined and electrochemically recoverable throughout deep, prolonged cycling.