Salting-Out Effect Realizing High-Strength and Dendrite-Inhibiting Cellulose Hydrogel Electrolyte for Durable Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries are limited by poor Zn stripping/plating reversibility. Not only can hydrogel electrolytes address this issue, but also they are suitable for constructing flexible batteries. However, there exists a contradiction between the mechanical strength and the ionic conductivity for hydrogel electrolytes. Herein, high-concentration kosmotropic ions are introduced into the cellulose hydrogel electrolyte to take advantage of the salting-out effect. This can significantly improve both the mechanical strength and ionic conductivity. Additionally, the obtained cellulose hydrogel electrolyte (denoted as Con-CMC) has strong adhesion, a wide electrochemical stability window, and good water retaining ability. The Con-CMC is also found to accelerate the desolvation process, improve Zn deposition kinetics, promote Zn deposition along the (002) plane, and suppress parasitic reactions. Accordingly, the Zn/Zn cell with Con-CMC demonstrates dendrite-free behavior with prolonged lifespan and can endure extremely large areal capacity of 25 mAh cm–2. The Con-CMC also enables a large average Coulombic efficiency of 99.54% over 500 cycles for the Zn/Cu cell. Furthermore, the assembled pouch-type Zn/polyaniline full battery provides great rate capability, superior cyclability (even with limited Zn anode excess), a slow self-discharge rate, and outstanding affordability to external forces. Overall, this work extends our knowledge of the rational design of hydrogel electrolytes.