HEC/PAM hydrogel electrolyte toward regulating the surface of zinc negative electrode for inhibited dendrite in zinc-ion batteries

The inhomogeneous plating/stripping of zinc and side reactions originating from the dissolution of the cathode material in water lead to the poor stability of zinc anode, which inevitably limits the practical application of zinc-based aqueous batteries. Therefore, a novel hydrogel electrolyte made of hydroxyethyl cellulose/polyacrylamide (HEC/PAM) with a 3D network-like structure is synthesized by radical polymerization and cross-linking reinforcement. Thanks to the porous crosslinked network and massive hydrophilic groups, the electrolyte has high ion conductivity of 3.17 × 10^–2 S cm⁻² and decomposition voltage of 2.6431 V. The ion conductive hydrophilic groups facilitate the interfacial compatibility of the electrode with the electrolyte and stabilize zinc plating/stripping, which suppresses the formation of zinc dendrites. Meanwhile, the hydrogel electrolyte effectively alleviates the dissolution of the positive electrode and the occurrence of side reactions, and subsequently improves the stability of the electrode. As a result, the assembled Zn–Zn symmetric cell with HEC/PAM hydrogel electrolyte is stable without short circuit and rapid increase of overvoltage at 5 mA cm⁻². The polarization voltage of the assembled Zn–Cu half-cell is 59.2 mV and initial coulomb efficiency reaches 94.3%. The assembled Zn–V₂O₅·nH₂O/CNT full cell delivers an excellent cycling stability of 186.9 mAh g⁻¹ at 0.5 A g⁻¹ after 500 cycles with a high-capacity retention of 92.5% (only 52.1% in aqueous system). The new idea is provided for further development of functional hydrogel electrolytes in zinc-ion batteries.