Carbon/graphite Composite Materiasl Used For Lithium Ion Batteries

Natural graphite has the performances of good lithium storage and bad compatibility with electrolyte. And it can be modified by using the physical and chemical coating methods in order to improve cycle efficiency. The surface functional groups of natural graphite were changed after being oxidized by H2O2, which could improve the performance of composite graphite.The method of chemical coating with coal-tar pitch was used to ameliorate the performances of natural graphite. The results were measured by X-ray diffraction, scanning electron microscope and galvanostatic charge-discharge cycling techniques. The reversible capacity of coated natural graphite treated at 420℃for 4h kept above 325mAg/h and the first cycle efficiency reached to 90.2%.The oxidized graphite was treated with phenol resin as coating agent to prepare composite anode material, which involves liquid-phenol-impregnation and carbonization process. After researching into the surface morphology, structures, charge-discharge and the electrochemical performances of the oxidized and non-oxidized natural graphite,the conclusions showed that the pyrolysis of resin could coat graphite well and make the surface of graphite more lubricity, which helped to improve the lithium ion insertion/deinsertion performance of natural graphite.By the comparison of the pre-oxidation, carbonization yield, oxygen content and electrochemical performance between the oxidation sample and unoxidation samples, the results proved that the carbonization yield of the composite graphite increased from 90.12% to 93.17%, the oxygen content of graphite increased from 3.7% to 5.8%, which improved the electrochemical performance of the composite graphite.