Hexagonal BN-Mediated Highly Improved Li Transfer Kinetics for High-Performance All-Solid-State Lithium Metal Batteries

All-solid-state lithium metal batteries based on solid polymer electrolytes (SPEs) have long aroused the curiosity of scientists and engineers worldwide due to their superior electrochemical stability, security, and easy manufacturing into any required flexible film forms. However, developing and improving efficient SPEs with high Li-ion transference number and excellent mechanical strength still remains a challenging issue to enhance the high rate performance and stability by suppressing Li dendrite growth. In this study, on the basis of the Lewis acid-base theory, a homodispersed and self-standing SPE is designed and developed by introducing nanostructured hexagonal boron nitride as an efficient polymer matrix support using a facile straightforward loading approach on hydrophilic SiO₂. The optimized SPE sample exhibits a high ionic conductivity of 0.916 mS cm^-1 at 25 °C, an improved Li-ion transference number of 0.641, and a good electrochemical stability (>5 V versus Li/Li⁺), as well as superior thermal stability and an improved mechanical modulus (16.8 MPa). Moreover, the Li|BN-50|Li symmetric cell exhibits highly reversible Li plating/stripping behavior characteristics over 700 h with a low overpotential of 20 mV at 0.1 mA cm^-2, indicating excellent Li dendrite inhibition ability. Furthermore, it is also demonstrated that the Li|BN-50|Ni_0.8Co_0.15Al_0.05O₂ cell delivers a high discharge capacity of 155.7 mA h g^-1 at 0.2 C and retains 82.2% of its initial specific capacity after 300 cycles.