Suppression of chlorine evolution reaction enabled by water chemistry in nonaqueous electrolyte for highly stable...

Nonaqueous electrolytes have garnered significant attention due to their wide electrochemical stability window (ESW) and high reversibility. However, the application of nonaqueous electrolytes is limited by the crucial challenge of sluggish reaction kinetics due to the high viscosity and low ionic conductivity. Herein, we found that the ZnCl₂-Dimethyl sulfoxide (DMSO) electrolyte system exhibited a narrow ESW of only 1.45 V due to the severe chlorine evolution reaction (ClER). To address this issue, we further demonstrated that the introduction of trace water in ZnCl₂-DMSO electrolyte could effectively inhibit the ClER, thus extend the ESW to 2.28 V. This improvement is ascribed to the reconstruction of Zn²⁺ solvation sheath and the substitution of coordinated DMSO molecules with H₂O molecules to form Cl^-- and H₂O-dominated Zn²⁺ solvation structures. Furthermore, the introduction of trace H₂O enhances ion transport kinetics and synergistically induces DMSO decomposition to guide the in-situ formation of a Cl-rich organic-inorganic hybrid solid electrolyte interphase (SEI). As a result, the Zn//Cu asymmetric cell with this electrolyte achieves a high average Coulombic efficiency (ACE) of 99.5% for 1100 cycles at 2.0 mA cm^-2 and 1.0 mAh cm^-2. The Zn//Zn symmetrical cell also demonstrates stable operation for 3350 h at 2.0 mA cm^-2 and 1.0 mAh cm^-2. Impressively, the assembled Zn//activated carbon (AC) hybrid capacitor with this electrolyte can be cycled stably within a voltage range of 0.01-2.0 V, exhibiting 91.5% capacity retention after 40,000 cycles at 5.0 A g^-1. This work provides new insights into uncovering the ClER origin in nonaqueous ZnCl₂ electrolytes and inhibits ClER with H₂O chemistry to achieve highly stable Zn anode for high voltage zinc-ion hybrid capacitors.