A Low‐Acidity Chloride Electrolyte Enables Exceptional Reversibility and Stability in Aqueous Tin Metal Batteries.

Tin (Sn) metal has emerged as a promising anode for aqueous batteries, due to its high capacity, non‐toxicity, and cost‐effectiveness. However, Sn metal has often been coupled with strong and corrosive sulfuric acids (2–3 M), leading to severe electrode corrosion and hydrogen evolution issues. Although high efficiency and long cycling were reported, the results were achieved using high currents to kinetically mask electrode‐electrolyte side reactions. Herein, we introduce a low‐acidity tin chloride electrolyte (pH=1.09) as a more viable option, which eliminates the need of strong acids and enables a reversible dendrite‐free Sn plating chemistry. Remarkably, the plating efficiency approaches unity (99.97 %) under standard testing conditions (1 mA cm−2 for 1 mAh cm−2), which maintains high at 99.23–99.93 % across various aggressive conditions, including low current (0.1–0.25 mA cm−2), high capacity (5–10 mAh cm−2), and extended resting time (24–72 hours). The battery calendar life is further prolonged to 3064 hours, significantly surpassing literature reports. Additionally, we presented an effective method to mitigate the potential Sn2+ oxidization issue on the cathode, demonstrating long‐cycling Sn||LiMn2O4 hybrid batteries. This work offers critical insights for developing highly reversible Sn metal batteries. [ABSTRACT FROM AUTHOR]