Highly Conductive and Stable Composite Polymer Electrolyte with Boron Nitride Nanotubes for All‐Solid‐State Lithium Metal Batteries

Abstract All‐solid‐state lithium metal batteries (ASSLMBs) have emerged as the most promising next‐generation energy storage devices. However, the unsatisfactory ionic conductivity of solid electrolytes at room temperature has impeded the advancement of solid‐state batteries. In this work, a multifunctional composite solid electrolyte (CSE) is developed by incorporating boron nitride nanotubes (BNNTs) into polyvinylidene fluoride‐hexafluoropropylene (PVDF‐HFP). BNNTs, with a high aspect ratio, trigger the dissociation of Li salts, thus generating a greater population of mobile Li + , and establishing long‐distance Li + transport pathways. PVDF‐HFP/BNNT exhibits a high ionic conductivity of 8.0 × 10 −4 S cm −1 at room temperature and a Li + transference number of 0.60. Moreover, a Li//Li symmetric cell based on PVDF‐HFP/BNNT demonstrates robust cyclic performance for 3400 h at a current density of 0.2 mA cm −2 . The ASSLMB formed from the assembly of PVDF‐HFP/BNNT with LiFePO 4 and Li exhibits a capacity retention of 93.2% after 850 cycles at 0.5C and 25 °C. The high‐voltage all‐solid‐state LiCoO 2 /Li cell based on PVDF‐HFP/BNNT also exhibits excellent cyclic performance, maintaining a capacity retention of 96.4% after 400 cycles at 1C and 25 °C. Furthermore, the introduction of BNNTs is shown to enhance the thermal conductivity and flame retardancy of the CSE.