Amphoteric Polymer Strategy with Buffer-Adsorption Mechanism for Long-Life Aqueous Zinc Ion Batteries

Water-based secondary batteries with multivalent metals anode provide a promising option for energy storage with low cost and high security. However, the electrochemical performance of aqueous Zinc ion batteries (AZIBs) is mainly restricted by problems such as poor reversibility and hydrogen evolution. Herein, an "amphoteric polymer strategy" with buffer-adsorption mechanism for AZIBs is proposed by introducing poly-L-Glutamic Acid (PGA) into the electrolyte. Amphoteric polymer enriched functional carboxyl and amino groups confer high compatibility of the Zn metal anodes as well as the relative stability of the bulk electrolyte pH simultaneously. Partial PGA molecules distributed in bulk electrolyte dynamically dissociate to stabilize pH and correspondingly slow down the generation of inert components, while others specifically adsorbed on zinc foil can relieve electrochemical corrosion and induce dendrite-free uniform Zn deposition. Consequently, long-term cycling stability (>1650 h) and high levels of reversibility (Coulombic efficiency>99.5%) of Zn anode are harvested in 2 m ZnSO4 electrolyte with only 0.5 wt% of PGA. In addition, when coupled with Zn0.25V2O5(ZVO) cathode, the full cell exhibits higher capacity retention and less pH fluctuation. This work reveals a novel buffer-adsorption mechanism offered by amphoteric functional polymer, and provides a new additive design principle for rechargeable AZIBs.