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 Sn 2+ ions in aqueous acidic electrolytes. Owing to its abundant sulfonate and hydroxyl functional groups, LSC coordinates with Sn 2+ 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 Sn 2+ 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.