Configurational Entropy Engineering in Electrolyte Solvation Sheaths for Durable Aqueous Zinc-Ion Batteries

The stability of metal anodes in aqueous batteries is governed by the solvation environment of charge carriers, yet electrolyte design remains largely empirical. Here we establish a thermodynamic framework for electrolyte engineering based on the principle that maximizing configurational entropy within the solvation sheath thermodynamically favors water-lean coordination structures. Using Zn²⁺ as a model system, we demonstrate that strategic combination of solvents with complementary donor numbers (DN) and dielectric constants (ε), specifically DMSO (high DN, high ε) and DMAc (moderate DN, moderate-ε with N-donor functionality), creates a diverse ensemble of solvation configurations, increasing configurational entropy by ΔS ≈ X J mol^-1 K^-1 (validated by ITC). This entropy gain lowers the Gibbs free energy of water-deficient solvation complexes by ΔG ≈ Y kJ mol^-1, fundamentally suppressing water activity. Concurrently, the orthogonal decomposition chemistries of DMSO and DMAc generate a gradient solid-electrolyte interphase with organic-rich outer and inorganic-rich inner layers. The resulting Zn anodes achieve exceptional durability (>3100 h at 1 mA cm^-2) and enable pouch cells retaining 60.2% capacity after 480 cycles. This entropy-centric design principle transforms electrolyte engineering from trial-and-error to thermodynamically guided materials discovery, with implications beyond zinc batteries to other metal anodes facing similar solvation challenges.