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 Zn2 +, [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.