Developing an electro-chemo-mechanically synergistic effect via the cholesteric cellulose crystalline interphase for highly stable flexible zinc metal batteries†

Aqueous zinc-ion batteries (ZIBs) are emerging as a promising energy storage technology for wearable electronics owing to their intrinsic safety, cost-effectiveness, and biocompatibility. Nevertheless, the uncontrolled deposition of the Zn anode can result in rapid short-circuit failure of ZIBs, posing a significant challenge to its practical implementation. Herein, a cholesteric structure cellulose nanocrystal (C-CNC) film that leverages the strong coordination interactions between the Zn²⁺ ions and profuse polar functional groups on sulfonate-grafted cellulose chains was designed as an artificial interphase layer to maintain a delicate balance between the sluggish transfer of Zn²⁺ ions and the faster reduction kinetics, thereby postponing the interfacial deterioration of Zn²⁺. The distinctive cholesteric structure endowed the C-CNC film with exceptional mechanical robustness and functions to re-homogenize the interfacial electric field and distribution of Zn²⁺ ion concentration. Benefitting from the above-mentioned electro-chemo-mechanically synergetic effect, the Zn interphase was stabilized owing to the uniform electrodeposition behavior and suppressed side-reaction. Zn anode modified with C-CNC delivered an ultralong cycling stability of up to 1000 hours and a high reversibility of 99.8% average Coulombic efficiency. Consequently, the C-CNC@Zn//MnO₂ cell demonstrated an excellent capacity retention of 92.0% after 1000 cycles along with desired flexibility. Moreover, a smart wristband was fabricated to demonstrate that the C-CNC films can facilitate further applications of ZIBs in wearable electronics.