Dual Li+ Transport Enabled by Bn-Assisted Solid-Polymer-Electrolyte for High-Performance Lithium Batteries

Abstract

Solid-state lithium batteries are expected to revolutionize the future wearable electronics due to their enhanced safety and high energy density; however, the sluggish Li+ kinetics of solid-state electrolyte seriously hampered their practical applications. Herein, we design a solid-polymer-electrolyte (SPE) with the assistance of BN, which exhibits impressive electrochemical properties, i.e., a high ionic conductivity of 0.37 mS cm-1 at 25 °C, a superior Li+ transference number of 0.63, and wide voltage window of 4.8 V. Density functional theory calculations and Raman spectra results reveal that BN not only changes the interaction between Li+ and -CF groups, which enables Li+ hopping easily along polymer segments, but also modifies the Li+ solvation environment from polymer units to aggregated ion pairs, which further accelerates the diffusion rate of Li+. Benefited from these merits, BN-assisted SPE presents superior performance at room temperature: i.e., Li/Li symmetric batteries maintain uniform polarization for more than 600 h at a current density of 0.2 mA cm-2; LiFePO4/Li battery delivers an excellent long cycle stability with a high coulombic efficiency (CE) of 99.7% at 0.5C after 200 cycles; the high-voltage LiNi0.5Co0.2Mn0.3O2/Li system also achieves a superior CE of 99.7%, and what’s more, this system also delivers a high-capacity retention of 90% over 100 cycles, indicating the outstanding antioxidation capability of this BN-assisted SPE. In addition, a bipolar LiFePO4/Li pouch cell with a high-voltage output of 6.41V was achieved and it demonstrates impressive safety during the abuse cutting, well suggesting its great potential in future applications.

Keywords: Li+ transportation kinetics, BN-assisted solid-polymer electrolyte, solvation structure, LITHIUM METAL BATTERY