In Situ Hybrid Si/F Polymeric Network Electrolyte with Dual Interfacial Stability for High‐Voltage Lithium Metal Batteries

Abstract High‐voltage lithium‐metal batteries (LMBs) are promising for energy storage applications but suffer from poor electrochemical window of solid polymer electrolytes (SPEs), which are difficult to achieve via a single polymeric functionality. Herein, a hybrid Si/F‐based polymeric 3D network is reported bearing polysiloxane backbone with fluorinated pendants to tune the highest occupied molecular orbital (HOMO)/the lowest unoccupied molecular orbital LUMO energies, thermodynamically expanding intrinsic electrochemical window of solid polymer electrolyte (SPE). Meanwhile, the hybrid Si/F functionalities with high fluorine abundance is identified to furnish dual interfacial kinetic stability at both anode and cathode interfaces with stabilized solid electrolyte interface (SEI) and cathode electrolyte interface (CEI), respectively. As a result, stable cycling in solid‐state high‐voltage LMBs is achieved up to an ultrahigh operating voltage of 4.9 V. Furthermore, it shows that in situ blending the Si/F SPE with eutectic electrolytes (EE) to form a non‐flammable gel polymer electrolyte can mitigate parasitic reactions of EE against metallic Li anode and achieve highly reversible charge–discharge cycling from 4.2 to 4.8 V at 25 °C.