Polyanionic hydrogel electrolyte enables reversible and durable Zn anode for efficient Zn-based energy storage

Aqueous Zn-ion energy storage systems, which are expected to be integrated into intelligent electronics as a secure power supply, suffer poor reversibility of Zn anodes, predominantly associated with dendritic growth and side reactions. This study introduces a polyanionic strategy to address these formidable issues by developing a hydrogel electrolyte (PACXHE) with carboxyl groups. Notably, the carboxyl groups within the hydrogel structure establish favorable channels to promote the transport of Zn2+ ions. They also expedite the desolvation of hydrated Zn2+ ions, leading to enhanced deposition kinetics. Additionally, these functional groups confine interfacial planar diffusion and promote preferential deposition along the (002) plane of Zn, enabling a smooth surface texture of the Zn anode. This multifaceted regulation successfully achieves the suppression of Zn dendrites and side reactions, thereby enhancing the electrochemical reversibility and service life during plating/stripping cycles. Therefore, such an electrolyte demonstrates a high average Coulombic efficiency of 97.7% for 500 cycles in the Zn||Cu cell and exceptional cyclability with a duration of 480 h at 1 mA cm−2/1 mA h cm−2 in the Zn||Zn cell. Beyond that, the Zn-ion hybrid micro-capacitor employing PACXHE exhibits satisfactory cycling stability, energy density, and practicality for energy storage in flexible, intelligent electronics. The present polyanionic-based hydrogel strategy and the development of PACXHE represent significant advancements in the design of hydrogel electrolytes, paving the way for a more sustainable and efficient future in the energy storage field.