Towards Highly Stable Sn²⁺ Electrolyte for Aqueous Tin Batteries Using Hydroquinone Antioxidant

Sn redox chemistry in aqueous acidic electrolyte was characterized with high reversibility and kinetics, which is considered as competitive anode material for aqueous batteries. Unfortunately, divalent Sn²⁺ is unstable in aqueous electrolyte. It was revealed that Sn²⁺ is easy to be oxidized to tetravalent Sn⁴⁺ by dissolved oxygen and then forms precipitate through hydrolysis process, leading to serious performance decay. Here, hydroquinone (HQ) was employed as antioxidant to prevent Sn²⁺ oxidation. With addition of HQ, Sn²⁺ electrolyte can maintain transparent and colorless after long-time exposure under air atmosphere, while large amounts of sediment were observed in the electrolyte without HQ. Moreover, HQ can adsorb on electrode surface to regulate Sn deposition and suppress Sn dendrite formation. With the difunctional HQ additive, Sn anode shows a stable cycling performance more than 1500 cycles with a high average coulombic efficiency (CE) of 99.9 %. And the organic||Sn cell shows high cycling stability for 10,000 cycles with 71 % capacity retention. The hydroquinone antioxidant strategy provides a facile and cost-effective way to develop highly stable Sn²⁺-based electrolyte.