Microenvironment Regulation via Synergistic Chain Topology and Weakly Coordinating Chemistry for Ultra‐Stable High‐Voltage Lithium Metal Batteries

Abstract In situ polymerized polyether electrolytes offer superior interfacial contact in lithium metal batteries (LMBs) but suffer from insufficient oxidative stability and uncontrollable interfacial reactions at high voltages. Herein, these limitations are addressed through microenvironment regulation, synergistically integrating chain topology control and weakly coordinating chemistry. A novel poly(ester‐alt‐ether) copolymer electrolyte (PMDGE) is synthesized through in situ copolymerization of 4‐methyl‐1, 3‐dioxane and glutaric anhydride. The extended methyl‐branched alkyl chains and weakly coordinating ester groups intrinsically lower the highest occupied molecular orbital (HOMO) energy of the polymer and weaken Li + ‐polymer interactions, significantly promoting anion participation in the Li + solvation sheath. Crucially, this molecular engineering drives the formation of dual inorganic‐rich interphases: a LiF/Li x BO y F z ‐enriched solid electrolyte interphase effectively suppresses dendrites, while a LiF‐dominant cathode electrolyte interphase mitigates oxidative decomposition. Consequently, PMDGE exhibits an expanded electrochemical window (5.2 V), a high lithium‐ion transference number (0.58), and enables ultra‐stable Li plating/stripping (>1200 h). Remarkably, Li|PMDGE|LiFePO 4 cell demonstrates unprecedented cycling stability, retaining 96.3% capacity after 10000 cycles at 2 C. Furthermore, Li|PMDGE|LiCoO 2 cell maintains 80.2% capacity after 1200 cycles at a cut‐off voltage of 4.45 V. This work demonstrates molecular solvation engineering through polymer structure design as a powerful paradigm for designing high‐performance polymer electrolytes in high‐voltage LMBs.