Cu‐MOF Functionalized Hydroxyapatite/Bacterial Cellulose Composite Separator Enabling Dendrite‐Free Fast Charging and Enhanced Thermal Safety for High‐Loading Graphite Anode

Abstract

Fast charging of high‐loading graphite anodes in lithium‐ion batteries (LIBs) is hampered by sluggish Li+ ion transport kinetics, leading to detrimental Li dendrite formation and safety hazards. Herein, a copper‐based metal‐organic framework (Cu‐MOF) functionalized hydroxyapatite/bacterial cellulose (Cu‐MOF@HB) composite nanofibers separator is designed to address these critical challenges. The hierarchical porous structure of the Cu‐MOF@HB separator enhances electrolyte wettability and adsorption. Density functional theory (DFT) calculation reveals that abundant open metal sites within the Cu‐MOF promote PF6− anion immobilization via Lewis acid‐base interactions, effectively increasing the Li+ ion transference number and facilitating faster Li+ ion migration within the separator. Consequently, the Cu‐MOF@HB separator effectively mitigates concentration polarization at the graphite anode/separator interfaces, suppressing Li dendrite formation and improving Coulombic efficiency. This significantly improves fast‐charging performance in high‐loading LiFePO4 (15.5 mg cm−2)||graphite (7.5 mg cm−2) batteries, achieving 79% capacity retention after 600 cycles at 3 C, compared to only 16% with a conventional polypropylene (PP) separator. Critically, the Cu‐MOF@HB separator also exhibits exceptional thermal stability and flame retardancy, enhancing battery safety. This work highlights the significant potential of interfacial engineering of separators, particularly through the incorporation of functional MOFs and thermally stable inorganic nanofibers, for achieving safe and high‐performance fast‐charging LIBs.