Surface-modified boron nitride as a filler to achieve high thermal stability of polymer solid-state lithium-metal batteries

Abstract

Solid polymer electrolytes with low density, low cost, and excellent processability have been the ideal choice for researchers. However, their thermal stability and mechanical properties are so inadequate that it is difficult for them to withstand a sufficiently high temperature and to effectively suppress Li dendrites. PEO cannot inhibit dendrite growth by itself, particularly when the battery is operated at a higher temperature (>80 °C) and the mechanical properties of PEO are significantly reduced. At high temperatures, the growth of lithium dendrites is an important factor affecting the cycle life of Li-metal batteries. Therefore, polymer electrolytes with high mechanical strength and excellent thermal stability can overcome the problems associated with Li-metal anodes and realize the application of rechargeable Li batteries in high-temperature situations. Herein, we prepared a polyethylene oxide (PEO) composite polymer electrolyte (CPE) with thermal stability and high mechanical strength via the modification of hexagonal boron nitride nanosheets (h-BNNS). The surface modification of h-BN enhanced the interface interaction between h-BNs and improved the thermal conductivity, thereby greatly enhancing the thermal stability of the battery. At the same time, the surface modification of h-BN enlarged the effective specific surface area of the filler, promoting the interaction with the Lewis acid–base of the anion, and helping the dissociation of Li salts to release more Li⁺ ions. This type of “One Sagittal Two Piercing” effect enabled the Li/LiFePO₄ full battery with PEO/LiTFSI/SiO₂@BNNS (PLSB) composite electrolyte to perform long-term cycles (900 cycles). Even when the battery was operated at a temperature as high as 150 °C, it could cycle stably for more than 1000 cycles at a rate of 2C, making the lithium metal battery suitable for operation at higher temperatures.