Cu substrate as bi-directional kinetic promoter for high-efficiency four-electron Sn aqueous batteries

Abstract

Aqueous batteries utilizing four-electron tin (Sn) anodes are promising candidates for grid-scale energy storage due to their intrinsic safety and high energy density. However, carbon-based anode substrates exhibit non-uniform Sn deposition and sluggish [Sn(OH)6]2-/Sn kinetics, limiting voltage efficiency. Here, we employ a copper (Cu) anode substrate that delivers bi-directional kinetic enhancement through Cu-Sn interfacial chemistry. Surfacesensitive analyses unveil an in-situ formation of a Cu6Sn5 alloy interphase during plating and a surface-bound Sn(OH)x intermediate during oxidation. Benefiting from this strong Cu-Sn affinity, the Cu substrate eliminates the nucleation voltage spike on charge and reduces the second-step discharge overpotential by ~300 mV at 1 mA cm -2 , yielding a near-single-plateau voltage profile for this four-electron redox. As a result, the round-trip efficiency of Sn-Ni full cells rises from 70% to 80%, sustained for > 200 cycles with improved rate capability. This study underscores the importance of substrate engineering in achieving high efficiency and offers guiding principles for interface-driven optimization in multi-electron aqueous batteries toward practical, long-duration energy storage.