Boron Nitride Nanosheet/ionic Liquid-based Crosslinked Composite Polymer Electrolyte

The key issue in limiting the development of high energy density lithium metal batteries is the uncontrolled lithium dendrite growth,while the highly safe polymer electrolyte（PE）can replace the liquid electrolyte to inhibit the growth of lithium dendrites.Crosslinked polymer electrolytes（CPE）and composite polymer electrolytes are two of the most promising electrolytes in PE.However,there is the trade-off effect between the ionic conductivity and mechanical strength of the crosslinked polymer electrolyte（CPE）,and the agglomeration effect of the composite filler of the composite polymer electrolyte,which seriously hinders the development of the safe lithium metal battery（LMB）.Here,a novel crosslinked composite polymer electrolyte（CCPE）with the combination of confined ionic liquid（IL）polymer network structure and uniformly dispersed boron nitride nanosheet（BNNS）is reported.The CCPE consist of UV（ultraviolet）-cured vinyl IL/ethylene glycol dimethacrylate（EGDMA）（acting as the crosslinked matrix）,homogeneously dispersed 2D BNNS（as the nanofiller）and ILbased electrolyte（as ion sources）.This UV-curable CCPE is formed on electrode via in-situ crosslinking of a precursor solution in a rapid and solvent-free step,and the assembly process of LMBs and interfacial contact/adhesion are maximum optimized.The critical point of this CCPE is that a facile channel for Li⁺transfer and a robust skeleton for confining IL and strengthening interface are simultaneously achieved via the introduction of network structure and 2D BNNS in PE.The main research contents of this paper are as follows:（1）Analysis of the electrochemical properties of CCPE.Compared with pure CPE,CCPE doped with BNNS has high ionic conductivity(room temperature ionic conductivity reaches 2.7×10^-4 S cm^-1),high lithium ion transferance number（0.67）,wide electrochemical window（5.5 V）,and there is a stable interface between CCPE and lithium metal.（2）Analysis of the relevant battery performance of the CCPE assembled LiFePO₄|Li battery.Compared with LiFePO₄|CPE|Li battery,LiFePO₄|CCPE|Li battery incorporating2.0 wt%BNNS has been significantly improved in charge and discharge cycle stability and rate performance.This study provides an efficient and simple method to prepare a CCPE that can effectively inhibit the growth of lithium dendrites,and promotes the development of high energy density lithium metal battery energy storage systems.