Preparation And Study On Anode Materials Of Lithium-ion Batteries

In this paper, the influences of the different modification methods (oxidized bynitric acid, coated by pitch and complex modified) for the performances of naturegraphite as anode materials for Lithium-ion battery were discussed deeply. Inmicrocosmic, the change of crystal structure was researched. In macroscopic, theimprovement of electrochemiscal performance was detected. The different testingskills were used to test electrochemiscal performance of modified graphitematerials strictly. In order to receive the better graphite anode materials, whichhave high specific capacity, low irreversible capacity, and better stability ofrecirculation, high rate charge and discharge.The results indicated that:First, oxidized by nitric acid didn't charge plate-sheet structure of naturalgraphite. The defect structure for surface of natural graphite was wiped off bynitric acid oxidized. Meanwhile, some crack or dent structure and nanometer-micropore was formed at the flank of natural graphite. It was used to enhance thecapacity for storing lithium-ion, the oxygenated group was formed at the crystalinterface of nature graphite where is apt to decomposing electrolyte. Wettingbetween electrode and electrolyte was improved. Interface impedance of naturegraphite was reduced. Second, the surface of nature graphite was coated byamorphous carbon, which came from pitch decomposition. It was used toimprove circulate performance of natural graphite. Flake-step of no-orientationamorphous carbon became bigger than that of natural graphite. Resistance forlithium-ion scattering was decreased. Finaly, compared with the natural graphite,the irreversible capacity of complex modified graphite was decreased from81.1mAh·g^-1 to 41.3mAh·g^-1. Capacity retention after 50 cycles was increasedfrom 55.4％to 97.7％. And cycle capacity of first was increased, from 290.8mAh·g^-1 to 359.8mAh·g^-1. The ratio of the capacity charged at 2C and that chargedat 0.5C raised from 72.1％for natural graphite to 89.6％. And the ratio of thecapacity charged at 3C and the capacity charged at 0.5C raised form 70.2％for natural graphite to 86.7％.Above all, the best complex modification for nature graphite as lithium-ionbattery anode was that: milling time should be 45min, oxidized temperature bynitric acid should be 60℃, coated content of pitch should be 9％, heat treatmenttemperature should be 850℃.