Regulating Zn Deposition Manner by Confining the Reactivity of Free Water in the Electric Double Layer

Aqueous Zn ion batteries (AZIBs) are promising candidates of next-generation energy storage devices with high safety and theoretical capacity. However, the irreversibility of metallic Zn anode, attributed to dendrite growth and water decomposition, severely limits the cycling durability of AZIBs and restricts their further development. Herein, a facile surface engineering strategy is put forward to tackle the issue of poor reversibility of the Zn anode. Benzotriazole (BTA) is employed as a functional additive of ZnSO₄ electrolyte to confine the reactivity of free water situated in the electric double layer (EDL). Experimental results and theoretical simulation reveal that BTA can preferiencially adsorb onto the Zn surface to uniform Zn²⁺ ion distribution and alleviate H₂O-involved side reactions like hydrogen evolution, and surface passivation. Consequently, in BTA-modulated aqueous electrolyte, the lifespan of the Zn anode is extended from 170 h-1092 h at 1 mA cm^-2/1 mAh cm^-2. The reversibility improvement of Zn anode also benefits the cycling durability of full devices including supercapacitors and batteries. Zn||I₂ batteries assembled in as-designed electrolyte witness only 11.3 % capacity decay over 17000 cycles at 1 A g^-1, far outstripping that observed in ZnSO₄ counterpart (~4675 cycles). The design criteria proposed in this study offers a new concept for the development of regulation additives that confine the reactivity of free water in the electric double layer.