| Summary: | 碩士 === 國立臺南大學 === 材料科學系碩士班 === 102 === Recently, graphite is one of the common commercial anode materials used in lithium ion batteries (LIBs). However, after several charging and discharging cycles, the charge capacity of LIBs will decay quickly owing to the structure of graphite electrode was destroyed. Therefore, surface modification of graphite is an important issue for LIBs. In this study, we employ three methods, e.g. metal-catalyst-free chemical vapor deposition (MFC-CVD), acid-treatment and CO2 etching, to modify surface structures of graphite (Small Mesophase Graphite Powder-SMGP) . The characterization of the pristine graphite and treated ones were conducted by SEM、TEM、Raman、XRD、BET and TGA. For the applications in LIBs, we compared the electrochemical performances of treated and untreated graphite electrodes using SBR+CMC and PVDF binder systems. For MFC-CVD, we find that numerous nano-scale carbon spheres were generated between graphite particles displaying a better channel or pathway for accessing Li+ or electron transportation. Furthermore, we find that the content of nanoscale carbon spheres depicts a linear correlationship with the combustion temperatures of surface-modified SMGPs determined by TGA. For LIBs application, we found that the charge capacity of first cycle increasing about 19% comparing with the untreated SMGP. When SMGP was treated by various concentrations of ammonium persulfate (APS) solutions, the oxygenated functional groups generated and display a higher capacity at first cycle in LIBs. However, the fading of LIB capacity are quickly than that of untreated SMGP. Finally, The CO2-treated SMGP display higher roughness than that of untreated one proved by BET measurements and larger IG/ID ratio in Raman spectra. Increasing roughness of SMGP could increase the capacity in SBR+CMC system for the first ten cycles. In addition, the irreversible capacity of the first cycle in LIBs is lower 1.2% than that of untreated SMGP.
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