Synthesis and characterization of PVDF-coated cotton-derived hard carbon for anode of Li-ion batteries

A carbonized cotton that is coated by pyrocarbon of Polyvinylidene Fluoride (PVDF) (HC/P) was synthesized by a facile method. Its microstructure and electrochemical performances as anode for Li-ion batteries were characterized by X-Ray Diffraction (XRD), Raman, X-ray photoelectron spectrometer (XPS), Scanning Electron Microscope (SEM), and other means. It is found that coating process does not affect the phase structure but influences the morphology, specific area, and electrochemical performances. HC/P series have abundant pores with diameter of 2 to 5 nm and small-size particles; thus, they have much more lithium storage position or charge/discharge capacity than pristine hard carbon (HC). Besides, Cyclic Voltammetry (CV) curves of HC/P-2 proved that the irreversible side reactions of Li+ with surface functional groups were reduced, which can explain the advancement of initial coulomb efficiency. Among three HC/P samples, HC/P-2 owns the best electrochemical performances. It delivered 520 mAh/g under current density of 20 mA/g and kept 95.9% retention rates of capacity after 100 cycles under 200 mA/g of current density.