A Diprotic Acid Additive Simultaneously Enables Stable Anode/Cathode Interfaces and Regulated Solvation Structure for High‐Performance Aqueous Zinc‐Ion Batteries

The large‐scale application of aqueous zinc‐ion batteries (AZIBs) is impeded by critical challenges, including uncontrolled zinc dendrite growth, severe parasitic side reactions, and hydrogen evolution reaction. To address these issues, we introduce a versatile diprotic acid, malonic acid (Mal), as a functional electrolyte additive. Combined experimental and theoretical results, we propose a new “etching‐adsorption‐deposition” mechanism, where Mal and its protons synergistically form a dendrite‐free, (101)‐oriented Zn anode. Concurrently, Mal participates in the Zn 2+ solvation sheath, effectively inhibiting water activity and hydrogen evolution reaction. These synergistic effects endow it with outstanding electrochemical stability, the Zn//Zn cell exhibits ultra‐long cycle stability over 4700 h at 5 mA cm −2 and 1 mAh cm −2 . Furthermore, the Zn//Cu cell delivers a significantly improved reversibility with an average Coulombic efficiency (CE) of 99.86% after 2000 cycles at 5 mA cm −2 and 1 mAh cm −2 . Surprisingly, Mal molecules exhibit a strong affinity for the V 2 O 5 cathode, forming a protective layer that mitigates vanadium dissolution and suppresses parasitic by‐products. The Zn//V 2 O 5 full cell consequently demonstrates excellent cycling performance, with 98.25% capacity retention after 1000 cycles at 1 A g −1 . Notably, its stability extends to extreme conditions, as it also maintains 64.5% capacity retention after 5000 cycles at 10 A g −1 .