Insight into Sulfur-Containing Zwitter-Molecule Boosting Zn Anode: from Electrolytes to Electrodes

Numerous organic electrolytes additives have been reported to improve Zn anode performance in aqueous Zn metal batteries (AZMBs). However, the modification mechanism needs to be further revealed in consideration of different environments for electrolytes and electrodes during the charge-discharge process. Herein, sulfur-containing zwitter-molecule (methionine, Met) is used as an additive for ZnSO₄ electrolytes. In electrolytes, Met reduces the H₂O coordination number and facilitates the desolvation process by virtue of functional groups (─COOH, ─NH₂, C─S─C), accelerating Zn²⁺ transference kinetics and decreasing the amount of active water. On electrodes, Met prefers to adsorb on Zn (002) plane and further transforms into a zincophilic protective layer containing C─SO_x─C through an in situ electrochemical oxidization, suppressing H₂ evolution/corrosion reactions and guiding dendrite-free Zn deposition. By using Met-containing ZnSO₄ electrolytes, the Zn//Zn cells show superior cycling performance under 30 mA cm^-2/30 mA h cm^-2. Moreover, the full cells Zn//NH₄V₄O₁₀ full cells using the modified electrolytes exhibit good performance at temperatures from -8 to 60 °C. Notably, a high energy density of 105.30 W h kg^-1 can be delivered using a low N/P ratio of 1.2, showing a promising prospect of Met electrolytes additives for practical use.