Cation Group-Driven Dual-Track Regulation Enables Dendrite-Free and Low-Temperature Zn-Ion Hybrid Supercapacitors

Despite their promising potential, the advancement of zinc-ion hybrid supercapacitors (ZHSCs) is significantly impeded by sluggish zinc-ion migration, parasitic side reactions, and dendrite growth, challenges that are exacerbated under low-temperature conditions. Current research predominantly focuses on zinc ions, while the critical role of anions in mediating these degradation pathways has been largely overlooked. Herein, we present a "cation group-driven dual-track regulation" strategy by engineering a cationic hydrogel electrolyte composed of poly(acryloyloxyethyl trimethyl ammonium chloride) (PDAC) and ZnCl₂. The immobilized quaternary ammonium groups (─N⁺(CH₃)₃) electrostatically confine Cl^‒ anions, thereby creating highly efficient Zn²⁺-selective migration channels and suppressing competing side reactions. Simultaneously, these cationic groups adsorb onto high-energy zinc crystal facets, guiding (002)-oriented Zn deposition and effectively inhibiting dendrite growth. The optimized PDAC-based electrolyte delivers a high ionic conductivity of 5.3 mS cm^-1 at -50°C, a Zn²⁺ transference number of 0.87, and exceptional average reversibility of Zn plating/stripping (98%) in Zn||Cu cells down to -40°C. Moreover, PDAC-optimized ZHSCs demonstrate outstanding cyclability over 20 000 at -40°C (95.2% capacity retention). This work establishes a generalizable electrolyte design paradigm that concurrently addresses kinetic and interfacial limitations, paving the way for dendrite-free, high-performance Zn-based energy storage systems operable under low-temperature conditions.