Dendrite-Free Zinc Ion Hybrid Supercapacitors with ZnCl₂-Modified Lignocellulose Hydrogel Electrolyte for Modulating Zinc Ion Solvation and Directed Deposition

Chargeable–dischargeable zinc–ion hybrid supercapacitors (ZHSCs) face significant challenges regarding low coulombic efficiency and short cycle life, primarily due to water-induced side reactions and uncontrolled zinc anode dendrite growth. Herein, a Zn-friendly hydrogel electrolyte is developed using ZnCl₂-modified lignocellulose (LC), which effectively facilitates the coordination of Zn²⁺ with −OH by disrupting the strong hydrogen bonding between the LC chains, exposing more −OH binding sites, and thus modulating the deposition behavior and interfacial chemistry of Zn on the Zn electrode. Experimental results and theoretical calculations demonstrate that the formed solvated Zn²⁺ effectively suppresses the undesirable hydrogen evolution reactions (HER). Meanwhile, the abundant −OH groups in LC affect the adsorption conformation of solvated Zn²⁺. This promotes a directed deposition (0 0 2) process that prevents dendrite growth and facilitates the directed deposition with rapid reaction kinetics at the zinc electrode. As a result, the Zn//Zn symmetric cell demonstrates high reversibility in deposition/stripping behavior with a cycle life exceeding 2800 h. Notably, the assembled Zn//ZnCl₂+LC//AC full cell achieves exceptional cycling stability over 11 000 cycles, while the Zn//NVO full cell maintains stable cycling performance for over 3500 cycles.