Super Electrolyte-Philic Boron Nitride Nanotube Membranes as Highly Robust Separators for Lithium Batteries

Abstract

The widespread deployment of lithium ion (Li+) batteries with increasing energy density entails a worsening safety concern. Among many contributing factors, the typical polymer separators are plagued with poor thermal stability,limited mechanical strength and lower Li+ transference number, and are prone to catastrophic failure when subjected to local thermalor mechanical stress (e.g., pierced by lithium dendrites). Herein, we report an all-inorganicnonwoven boron nitride nanotube membrane featuring exceptional chemical stability, thermal stability, fire resistance and mechanical flexibility. The resulting membranes show superior wettability to electrolyte to endow excellent Li+ transport properties with the lowest ionic resistance and the highest Li+ transference number (0.86) when compared with all commercial separators. They can thus function as highly robust separators for Li/Li symmetriccells with ultralow overpotential (8.5 mV) and exceptional reversibility for repeated lithium plating/stripping cycles for over 8000 hours, and for practical LiFePO4/Li cell with unusually high temperature stability. Our study defines a unique class of super electrolyte-philic ceramic separators with favorable mechanical strength, thermal stability and ion transfer properties for advanced lithium batteries.