Integrated Design for in Situ Ultra‐Stable Gel Polymer Electrolyte Network Enables Long‐Cycling and High‐Voltage Lithium Metal Batteries

In situ polymerized electrolytes are considered as promising candidates for next‐generation lithium metal batteries (LMBs) due to their conformal interface contact and compatibility with existing battery manufacturing processes. However, their application in LMBs is hindered by dendrite growth, a narrow electrochemical stability window, and low thermal stability. By constructing a cross‐linked network via in situ copolymerization of 1,3‐dioxolane (DOL) and S,S,S‐triglycidyl isocyanurate (S,S,S‐TGIC), the resulting TPDOL‐based gel polymer electrolyte (GPE) effectively suppresses interfacial side reactions and significantly enhances oxidation stability. In addition, the electronegative nitrogen atoms on S,S,S‐TGIC weaken ether‐Li + coordination, lowering the desolvation energy barrier and promoting uniform lithium deposition. Consequently, the resulting GPE delivers a high ionic conductivity of 1.66 × 10 −3 S cm −1 and a wide electrochemical stability window of 5.7 V. The Li||Li symmetric cell achieves ultra‐long cycling stability exceeding 2200 h at 1 mA cm −2 . When coupled with high‐voltage LiNi 0.8 Co 0 .1 Mn 0.1 O 2 (NCM811) cathodes, the full cell retains 86.7% capacity after 200 cycles at 1 C. Even with a high NCM811 loading of 7.1 mg cm −2 , the cell achieves a stable initial discharge capacity of 155.4 mAh g −1 . This polymer design strategy demonstrates significant promise for the development of high‐energy‐density LMBs.