Highly dispersed and functionalized boron nitride nanosheets contribute to ultra-stable long-life all-solid-state batteries

Abstract

Composite polymer electrolytes (CPEs) are considered the most promising all-solid-state battery (ASSB) electrolytes. However, they are limited by their low ionic conductivity and poor stability with Li metal. Herein, highly dispersed and surface-functionalized active boron nitride nanosheets (BNNSs) were prepared using the boric acid assisted ball milling method, and only a small amount of addition (3%) could significantly improve the physical and electrochemical properties of CPEs. The uniform dispersion of BNNSs forms fast lithium-ion transport pathways, significantly improving the ionic conductivity (6.7 × 10⁻⁶ S cm⁻¹ at 30 °C, 2.77 × 10⁻⁴ S cm⁻¹ at 50 °C). The excellent thermal conductivity of BNNSs avoids the space-charge region accumulation caused by the agglomeration of inorganic fillers, weakens the growth of lithium dendrites, enhances the interface stability, and optimizes the thermal management of the batteries. In addition, improving mechanical properties reduces the risk of short circuits and extends the service life. The LFP/CPE-BNNS/Li battery was optimized by systematically increasing Li⁺ diffusion, widening the electrochemical stability window, and enhancing interface stability and delivers excellent rate performance (88.7 mA h g⁻¹ at a rate of 2.0C) and perfect cycle stability (160.1 mA h g⁻¹ after 200 cycles at 0.5C and 60 °C with a capacity degradation rate of 0.009% per cycle). Therefore, the CPE-BNNSs created by us would open a new avenue to improve the performance of ASSBs.