Thermodynamically and Physically Stable Dendrite-Free Li Interface with Layered Boron Nitride Separators

The development of promising separator candidates, offering both great physical rigidity and high thermal resistance, is still a global challenge to guarantee high-performance electrochemical cells. Freestanding hexagonal boron nitride (h-BN) separators are developed using strategically combined synthetic steps with liquid and thermal expansion exfoliation methods, which can simply fabricate the largely yielded h-BN nanosheets. The as-prepared freestanding h-BN nanosheet separator presents better ionic conductivity than commercial polymer separators and further provides excellent stability of Li ion cells by suppressing the protruding dendritic Li growth during cycles on the electrodes, as well as the high thermal and electrochemical stabilities of h-BN nanosheet separators even after the aging process at high temperatures of 80–120 °C. Furthermore, lithium titanate (LTO) batteries with the freestanding h-BN separators maintain an outstanding reversible Coulombic efficiency of ∼99% after 600 cycles, as well as high cycling retention, indicating the significant improvement in battery performance compared to the LTO batteries with commercial polymer separators. Thus, the freestanding h-BN separators may provide a new strategic way for the efficient storage of charge in next-generation rechargeable batteries and high-safety energy storage applications.