Research On The Modification Of Graphite As Anode Material For Low Temperature Li-Ion Battery

Li-ion battery has the advantages of low equivalent weigh, high theoretical capacity, long cycle life, no memory effection and so on. So it can be applied not only in civilian areas, but also in military communications, aerospace and other high-tech fields, thus the performance of li-ion battery has to fit these fields. One of the main factors restricts the use of li-ion battery is its poor performance at low temperature. The main reasons for this phenomenon are the low lithium ion diffusion rate and large charge transfer resistance. In this work the mesophase carbon microbead (MCMB) was modified to investigate the influences of expanding and oxidation effection on the low temperature performance of li-ion battery. Scanning electron microscopy (SEM), X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS) were used to characterize the surface morphology, structural characteristics and resistance of the modified MCMB.Expanded MCMB was prepared to increase the li-ion diffusion coefficient. It was found that the low temperature performance of MCMB had been significantly improved with the increase of expansion. The study of EIS found that the li ion diffusion coefficient of expanded MCMB was three orders magnitude higher than that of unmodified. The capacity of expanded MCMB at -40℃could reach to 38mAhg-1. By heat treated, the capacity of expanded MCMB at -40℃could reach to 101mAhg-1.Oxidate treated MCMB was prepared to change the types and quantities of surface groups, and change the thickness and composition of the solid electrolyte formed on the anode, to increase the conductivity of Solid Electrolyte Interface (SEI). Meanwhile, Oxidation might leads to changes in surface morphology, to form the pore structure and increase the li ion diffusion coefficient. The results showed that after oxidation, the resistance of SEI and the diffusion coefficient increased, but the improvement of low temperature performance was unsatisfied. As a result, just simply surface oxidation treatment couldn't improve the low temperature performance of graphite anodes.