Engineered heat dissipation and current distribution boron nitride-graphene layer coated on polypropylene separator for high performance lithium metal battery

Li metal as a battery anode has been intensively studied because of its high gravimetric capacity (3860 mAh g⁻¹), a low standard electrode potential (−3.04 vs. SHE), a reasonable electronic conductivity and low density. However, lithium metal suffers from a continuous Li dendrite growth upon charge-discharge cycling, delivering a poor coulombic efficiency and consequently its early failure. Here, engineered bilayer separators demonstrate that a boron nitride-graphene (BN_xGr_y) layer coated on one side of polypropylene (PP) membrane remarkably reduces the polarization and impedance, and significantly improve the performance and stability of Li/Cu half-cells. Moreover, Li/LiFePO₄ full cell with the modified BN₅₀Gr₅₀/PP separator presents a remarkably stable 1000 charge-discharge cycles with a specific capacity of 114 mAh g⁻¹ at 1C-rate. The superiority of the modified separator is orginated from an effective synergistic effect between physico-chemical properties of Gr (reducing local current density) and BN (dissipating local heat) and its enhanced structural and mechanical stability.