Hierarchical Ligand Solvation Directs Organic-Templated Growth of Ordered ZnF₂ Toward Ultrastable Zn Metal Anode

Uncontrolled decomposition of BF₄ ^- anions in aqueous Zn(BF₄)₂ electrolytes tends to generate irregular and loose ZnF₂ precipitates, which aggravate parasitic side reactions and fail to protect the Zn anode. To circumvent this issue, a gradient solvation structure of Zn^{2 +}, [Zn(H₂O)_2.5(NMA)_2.1(CPL)_0.9]²⁺(BF₄ ^-)_0.5, is rationally constructed in a deep eutectic electrolyte by leveraging the hierarchical ligand binding energy sequence H₂O < N-methylacetamide (NMA) < ε-caprolactam (CPL) < BF₄ ^-. Beyond suppressing water reactivity, the tailored desolvation pathway can direct the stepwise decomposition of BF₄ ^- and concurrently trigger ring-opening polymerization of CPL at the interface. The in situ grown poly-CPL chains serve as a templating matrix that guides the ordered assembly of ZnF₂ nuclei into a compact, uniform organic-inorganic hybrid solid electrolyte interphase (SEI). Such a distinctive SEI architecture integrates high ionic conductivity from ZnF₂ nanodomains with mechanical flexibility from the polymer network, effectively protects the Zn anode from electrolyte corrosion and dendrite proliferation. Consequently, the symmetric Zn||Zn cell achieves a 100-fold improvement in cycling lifespan, sustaining stable operation for over 6200 h at 1 mA cm^-2. Meanwhile, the Coulombic efficiency is significantly boosted from 88.5% to 99.4%. This work provides a new paradigm for interface engineering through ligand binding energy regulation.