Molecular brush-based ultrathin polymer electrolytes with stable interfaces for high-voltage large-areal-capacity lithium metal batteries

Abstract

Polymer electrolytes hold great promise for long-cycling lithium metal batteries, but their unsatisfactory ionic conductivities and unstable interfacial contacts with electrodes greatly limit their practical applications under high cut-off voltage and large areal capacity conditions. Herein, a super-structured multifunctional molecular brush, BC-g-P(CCMA-co-TFEMA) (BC = bacterial cellulose; CCMA = (2-oxo-1,3-dioxolan-4-yl) methyl methacrylate; TFEMA = 2,2,2-trifluoroethyl methacrylate), has been designed to develop an ultrathin polymer electrolyte with superior ionic conductivity and stable electrolyte/electrode interfaces. The cyclic carbonate group in CCMA can weaken the binding of solvents and anions with lithium ions, thereby enhancing ionic transport. Meanwhile, the fluorine-containing group in TFEMA is beneficial for simultaneously constructing LiF-rich electrolyte/anode and electrolyte/cathode interfaces with enhanced stability. Moreover, the robust BC backbone provides the polymer electrolyte with outstanding mechanical properties. With such polymer electrolytes, a remarkable capacity retention of 83% has been demonstrated for Li/LiFePO₄ cells at 1C after 1000 cycles. Remarkably, the solid-state full cell with a high-loading LiNi_0.8Mn_0.1Co_0.1O₂ cathode delivers a high discharge specific capacity of 204 mA h g⁻¹ for more than 400 cycles at a high cut-off voltage of 4.5 V. This work provides a novel design principle for advanced electrolytes of high-voltage and large-areal-capacity lithium metal batteries.