Cosolvent-Tailored Hydrous Electrolytes Enable Deep-Cycling and Cryogenic Zn Anodes for Zn-Ion Capacitors

The practical deployment of zinc-ion capacitors (ZICs) is fundamentally constrained by the poor reversibility of zinc anodes, particularly under deep-cycling and cryogenic conditions. Herein, we present a cosolvent engineering strategy that reconstructs the solvation structure of a hydrous organic electrolyte to overcome these limitations. Mechanistic investigations reveal that tetrahydrofuran (THF) acts as a pivotal modulator; while minimally participating in the primary solvation shell, it critically disrupts the anion–solvent network. This reconfiguration promotes the formation of a robust, inorganic-rich solid-electrolyte interphase (SEI) and enables uniform Zn2+ deposition. The optimized electrolyte achieves exceptional anode reversibility, sustaining dendrite-free plating/stripping for over 7000 h and stable operation at an 80% depth of discharge. Zn||Cu asymmetric cell delivered an average Coulombic efficiency of 99.86% over 1100 cycles at 25 °C and maintain stable cycling at −30 °C. Consequently, Zn AC hybrid capacitors attain ultralong lifespans exceeding 20,000 cycles at room temperature and 10,000 cycles at −40 °C with minimal capacity decay. This work establishes a generalizable design principle for electrolyte solvation structure, paving the way for advanced, temperature-resilient zinc-based energy storage.