Achieving stable and dendrite-free Zn metal batteries by water-confinement hydrogel electrolytes

Aqueous zinc metal batteries (ZMBs) are one of the most promising grid-scale renewable energy storage batteries. However, the practical application of ZMBs is limited by uncontrollable Zn dendrites and parasitic side reactions at the anode interface. Herein, a unique water-confinement hydrogel electrolyte (TONFC/PAM) was constructed by carboxyl-rich nanocellulose (TONFC) and acid amide-rich polyacrylamide (PAM). The parasitic side reactions were effectively suppressed due to limiting the movement of water in the designed hydrogel electrolyte. Meanwhile, the electrostatic interactions with the electron-rich group (–COOH and–CONH₂) established fast Zn²⁺ ion transport channels in the electrolyte, enabling an excellent ionic conductivity (30.23 mS cm⁻¹) and horizontal deposition of Zn metal. As a result, the Zn∣∣Zn cells and Zn∣∣Cu cells with TONFC/ PAM electrolyte achieve a long cycling life of over 1,400 h at 1 mA cm⁻² and a high average coulombic efficiency of 99.4%, respectively. More importantly, the Zn∣∣MnO₂ full cells can stably run for 1,000 cycles with a high capacity (∼150 mAh g⁻¹) at a current density of 2 A g⁻¹. These results show that TONFC/PAM is a suitable hydrogel electrolyte for ZMBs, which presents attractive opportunities for future research on ZMBs.