Flame Retardant Polyurethane‐Based Semi‐Interpenetrating Network Electrolyte with Continuous Ion Channel for High‐Voltage Lithium‐Metal Batteries

Abstract High‐nickel cathode materials is known to have high specific capacity but poor stability and safety due to nickel diffusion. While Al‐doped high‐nickel cathode (NCMA) particles exhibit enhanced stability, their durability under high‐charge cut‐off voltages remains uncertain. Herein, a polymer electrolyte with semi‐interpenetrating network (SIPN) structure is designed for high‐voltage lithium‐metal battery application. The matrix of the polymer electrolyte is composed of a CO 2 ‐derived thermoplastic polyurethane (TPU) and an in situ polymerized polyacrylonitrile (PAN), where the PAN provides strength and the TPU offers excellent high‐voltage resistance and abundant ion‐complexing sites. With the assistance of additives, the PAN‐TPU‐based electrolyte performs excellent flame retardancy, wide electrochemical stability window (>5.1 V) and can lead to stable organic–inorganic hybrid cathode‐electrolyte interface during cycling. The Li‖PAN‐TPU/TEP‐E‖Li cell lasts over 3400 h at 0.2 mA cm −2 . With the construction of well‐connected ion pathway by incorporating of the TPU as binder for cathode and in situ forming the PAN‐TPU‐based electrolyte. The NCMA@TPU‖PAN‐TPU/triethyl phosphate‐based electrolyte (TEP‐E)‖Li cell shows outstanding performances, which maintains a capacity of 186 mAh g −1 at a 4.3 V charging cut‐off voltage, retaining 82% capacity after 300 cycles at 0.5 C. Even at a 4.5 V cut‐off voltage, it retains 78% capacity after 200 cycles at 0.5 C.