Screening Anionic Groups Within Zwitterionic Additives for Eliminating Hydrogen Evolution and Dendrites in Aqueous Zinc Ion Batteries.

Zwitterionic materials with covalently tethered cations and anions have great potential as electrolyte additives for aqueous Zn-ion batteries (AZIBs) owing to their appealing intrinsic characteristics and merits. However, the impact of cationic and anionic moieties within zwitterions on enhancing the performance of AZIBs remains poorly understood. Herein, three zwitterions, namely carboxybetaine methacrylate (CBMA), sulfobetaine methacrylate (SBMA), and 2-methacryloyloxyethyl phosphorylcholine (MPC), were selected as additives to investigate their different action mechanisms in AZIBs. All three zwitterions have the same quaternary ammonium as the positively charged group, but having different negatively charged segments, i.e., carboxylate, sulfonate, and phosphate for CBMA, SBMA, and MPC, respectively. By systematical electrochemical analysis, these zwitterions all contribute to enhanced cycling life of Zn anode, with MPC having the most pronounced effect, which can be attributed to the synergistic effect of positively quaternary ammonium group and unique negatively phosphate groups. As a result, the Zn//Zn cell with MPC as additive in ZnSO electrolyte exhibits an ultralong lifespan over 5000 h. This work proposes new insights to the future development of multifunctional zwitterionic additives for remarkably stable AZIBs.