Bond-length engineering unlocks ultrahigh-DOD aqueous zinc batteries with relaxed solvation shell

Aqueous Zn-ion battery development is challenged by H₂O-induced side reactions and dendrite growth. Interface protective engineering and electrolyte additive including high-concentration salts or organic co-solvents can reduce H₂O molecules, but often at the expense of cost, ionic conductivity, and safety. An approach that mitigates H₂O damage without compromising the merits of aqueous electrolytes is highly desired. Herein, we propose an intrinsic tuning strategy to strengthen the intramolecular O–H bond and elongate the Zn²⁺–O (H₂O) bond length by utilizing electronic and steric hindrance effects, thereby inherently reducing the H₂O reactivity and constructing a relaxed solvation shell. Using ascorbic acid (AA) as a proof-of-concept additive, this bond-length engineering is verified to facilitate Zn²⁺ desolvation and raise the H₂O reduction barrier, leading to even Zn electrodeposition together with inhibition of detrimental side reactions. Therefore, the Zn anode achieves stable cycling for over 380 h under ultrahigh depth of discharge (DOD) of 86.1% together with high current density and areal capacity (100 mA/mAh cm⁻²). Full Zn/NaV₃O₈·1.5H₂O cell also presents remarkably enhanced cycling stability, demonstrating the practicality of this approach for high-performance AZIB.