Synergistic interfacial chemistry enabled by a multifunctional zwitterionic polymer additive for highly reversible Zn metal anodes.

Aqueous zinc ion batteries have attracted considerable interest because of their affordability and enhanced safety features. However, several key challenges like uncontrollable Zn dendrites, hydrogen evolution and corrosion side-reactions hinder their practical application. Herein, carboxymethyl chitosan (CMCS), a cost-effective zwitterionic electrolyte additive, is proposed to stabilize the Zn anodes. The concurrently owned NH cations and COO anions endow the CMCS molecule with a preferential adsorption ability, achieving reversible adsorption on the anode/electrolyte interface driven by the electric field, thereby leading to uniform and dendrite-free Zn deposition. Additionally, the adsorption layer of CMCS molecule is beneficial for effective water molecule repelling and side-reaction suppression. Consequently, an optimized 0.3 g L CMCS additive actualizes extended lifespan of 800 h in the symmetric Zn//Zn cells at the test condition of 1 mA cm, 1 mAh cm. An average Coulombic efficiency of 98.75 % is achieved, which is much superior to the case in the benchmark ZnSO electrolyte. To illustrate the feasibility of the CMCS-contained electrolyte, Zn//VO full batteries were assembled and exhibits enhanced electrochemical performance. This study highlights the zwitterionic polymer as a versatile platform for advancing electrolyte design, paving the way for practical next-generation energy storage.