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 Zn²⁺ 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 V₂O₅ cathode, forming a protective layer that mitigates vanadium dissolution and suppresses parasitic by-products. The Zn//V₂O₅ 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.