Spherical Sn Deposition Enabled by Lignosulfonate for Stable Aqueous Sn Metal Batteries

Aqueous Sn metal batteries are promising candidates for sustainable energy storage owing to their intrinsic safety and cost-effectiveness. Nevertheless, their practical deployment remains challenging due to vigorous Sn dendrite growth, hydrogen evolution reactions and poor interfacial stability. Herein, we report a bio-derived and environmentally benign electrolyte additive, lignosulfonic acid calcium salt (LSC), to regulate both solvation chemistry and interfacial behavior of Sn²⁺ ions in aqueous acidic electrolytes. Owing to its abundant sulfonate and hydroxyl functional groups, LSC coordinates with Sn²⁺ ions and regulates solvation structure. In addition, spectroscopic analyses such as FT-IR and Raman reveal a strong interfacial adsorption of LSC on Sn surfaces. This dual regulation suppresses hydrogen evolution reaction, homogenizes Sn²⁺ flux and induces uniform, spherical Sn deposition with preferential low-index crystal orientation. Opernado X-ray imaging confirms dendrite-free Sn plating even at high areal capacities. Consequently, Sn/Cu asymmetric cell employing LSC delivers exceptional cycling stability, maintaining a high Coulombic efficiency of 99.84% for over 1600 cycles even under harsh conditions of 10 mA cm^-2 with a capacity of 1 mAh cm^-2. This work highlights a sustainable and effective strategy for stabilizing aqueous Sn metal batteries through synergistic solvation and interfacial engineering using biomass-derived additives.