Amorphous Boron Nitride Nanosheet‐based Solid State Electrolytes with High Ionic Conductivity

Amorphous boron nitride nanosheets, with natural electrical insulation, outstanding chemical stability and mechanical properties, are introduced as a matrix to be incorporated with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and polymer polyvinylidene fluoride‐hexafluoropropylene copolymer (PVDF‐HFP), for constructing a novel composite solid‐state electrolyte by a simple solution‐casting method. Amorphous boron nitride nanosheets are produced via a combination method of ball milling and pure water exfoliation. The obtained composite solid‐state electrolyte containing 40% (mass fraction) PVDF‐HFP shows a high lithium ion conductivity (1.936×10‐3 S cm‐1) and lithium ion migration number (0.47), and a wide electrochemical stability window (5V) at room temperature. The LiFePO4/Li based all solid‐state battery, consisting of the composite solid electrolyte (40% PVDF‐HFP), delivers a capacity of 128.1mAh g‐1, a Coulombic efficiency of 99.79% after 500 cycles and a capacity retention rate of 94.5% at 1.0 C and 25 °C. The composite solid electrolyte (40% PVDF‐HFP) can maintain flat and stable stripping/plating plateaus for over 800 hours in symmetrical cells. The morphous boron nitride nanosheets with high lithium ion conductivity are employed to construct solid‐state electrolytes, which is important significant for the development of high energy density, high safety, and long cycle life all‐solid‐state lithium‐ion batteries.