Harnessing Cation–Anion Synergistic Effect for High‐Performance Aqueous Zinc‐Ion Batteries

ABSTRACT Aqueous zinc‐ion batteries (AZIBs) are promising for large‐scale energy storage due to environmental friendliness, inherent safety, and low cost. However, the practical deployment of AZIBs is hindered by notorious side reactions at the zinc (Zn) anode, which seriously deteriorate the battery stability and reversibility. Here, we propose guanidine sulfate (GS) as an electrolyte additive, leveraging a cation–anion synergistic mechanism to jointly inhibit side reactions. Both theoretical and experimental results confirm that the guanidine cation (CH 6 N 3 + ) preferentially adsorbs on the Zn anode surface, providing an electrostatic shielding effect that promotes uniform Zn deposition. Concurrently, the sulfate anion (SO 4 2– ) contributes to the formation of a robust solid electrolyte interface (SEI), effectively inhibiting dendrite growth and enhancing interfacial stability. Consequently, Zn||Cu asymmetric cells with GS deliver a high Coulombic efficiency of 99.6% over 1200 cycles, while Zn||Zn symmetric cells exhibit an extended lifespan exceeding 500 h at various current densities. Furthermore, the Zn||O d ‐NVO·nH 2 O full cells demonstrate outstanding cycling stability, retaining over 90% of initial capacity after 2000 cycles at current densities of 2 and 5 A g −1 . This research provides a viable electrolyte design strategy leveraging cation–anion synergy, offering new insights into electrolyte modulation and advancing the performance of AZIBs.