Hexagonal boron nitride inducing anionic trapping in polyethylene oxide based solid polymer electrolyte for lithium dendrite inhibition

Here we prepare the hexagonal boron nitride (h-BN)-polyethylene oxide composite polymer electrolyte via a convenient casting method, which reflects high mechanical strength. Meanwhile, the electrochemical properties (electrochemical window and lithium ion transference number) are enhanced but the ionic conductivity of h-BN composite electrolyte is decreased after adding h-BN. Density functional theory (DFT) calculations results show that a stronger binding effect is observed in TFSI- and BN, compared to that between Li+ and BN. Molecular dynamics (MD) simulations are also utilized to study the mechanism behind the enhanced Li ionic diffusion by h-BN addition. Li+ diffusion in PEO/LiTFSI/BN is lower than that in PEO/LiTFSI system, but the diffusion of TFSI- exhibits a more significant decline rate in the presence of BN. It indicates that the presence of BN suppresses anion motion and enhance selectivity in Li+ transport. Thus, the PEO/LiTFSI/h-BN composite electrolyte exhibits higher Li ion conductivity but lower anionic diffusivity than PEO/LiTFSI system. Hence the h-BN composite polymer electrolyte in a Li/Li symmetric battery reflects long cycling of 430 h at 0.2 mA cm-2. The Li metal/LiFePO4 full battery with PEO/LiTFSI/h-BN composite electrolyte also works efficiently for long-term cycling (140 cycles) than filler-free PEO based electrolyte (39 cycles).