Tin via Four-Electron Conversion Chemistry for High-Performance Alkaline Batteries

To overcome the intrinsic limitation of low energy density associated with the conventional two-electron reaction of tin anodes, alkaline tin-based four-electron redox chemistry has emerged as a highly promising strategy. While the traditional two-electron Sn/Sn(OH)3− redox couple delivers a limited theoretical specific capacity of 451.6 mAh g−1, the four-electron Sn/Sn(OH)3−/Sn(OH)62− pathway doubles the electron transfer number. This advancement not only elevates the application potential of tin-based batteries but also substantially boosts the theoretical capacity to 903.2 mAh g−1, thereby markedly enhancing the overall energy density. This review systematically deconstructs the key challenges confronting alkaline tin-based four-electron reactions, pinpointing the formation of “dead Sn” induced by kinetic asymmetry and the shuttling of soluble Sn(OH)3− intermediates as the core scientific bottlenecks. Subsequently, it provides a critical examination of the major regulatory strategies developed to achieve stable and reversible Sn/Sn(OH)3−/Sn(OH)62− conversion, encompassing the implementation of ion-selective separators, electrolyte modulation, and current collector modification. Finally, forward-looking perspectives and actionable recommendations are proposed to steer the future development of high-performance four-electron tin-based batteries.