Sustainable interface regulation enabled by a bismuth solid-state surfactant effect for Zn-free anodes†

Abstract

Due to the highly anisotropic nature of Zn crystalline structures, dendrite formation is a critical challenge for the direct utilization of Zn as a rechargeable battery electrode. This limits the maximum power output and cyclability of batteries, making them unsuitable for demanding applications despite their environmental and economic advantages. Here, we report a self-sustainable surface regulation where both Zn plating and stripping processes on a Bi substrate are modulated by its solid-state surfactant effect. The stable nucleation of Zn covered by Bi surfactants largely reduces the nucleation overpotential and limits the lateral diffusion of newly deposited Zn adatoms, effectively preventing the wild dendrite growth normally present in an unregulated system. In addition, Bi can stay afloat on the Zn plating surface over hundreds of microns, and the resultant plating is smooth with densely packed Zn deposits, making it possible to reach extreme plating capacities (e.g. 115 mA h cm⁻² demonstrated) with minimal dendrite formation in a practical coin cell configuration. The subsequent clean stripping with negligible dead Zn ensures a near-ideal Coulombic efficiency of Zn|Bi half cells over 3000 cycles at an areal capacity of 7 mA h cm⁻². An acidic Zn-free full cell using a Bi anode exhibits over 700 stable cycles at 4 mA h cm⁻² and a high Coulombic efficiency of ∼94.6%. Our results demonstrate that the application of Bi solid-state surfactants can effectively resolve the critical dendrite problem and build high-efficiency Zn-free cell systems.