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 CO₂-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.