Study Of Carbon Anode Materials For Li-Ion Battery

Pyrolysis carbon was made from phenolic resin, pitch and glucose by hightemperature solid state method in this thesis, and the preparation parameters werestudied furthermore. To improve the initial coulombic efficiency, hard carbon wascoated with pitch-pyrolyzed carbon by high temperature solid state method and thesynthesis parameters were optimized. Graphite/hard carbon and MCMB/hard carboncomposites were prepared by mechanical mixing of hard carbon to enhance the ratepabalitibility of graphite and MCMB. The enhanced rate capability and initialcoulombic efficiency were gained by changing doping proportions.Phenolic resin-pyrolyzed carbon was prepared by high temperature solid statemethod and the results showed that the highest initial coulombic efficiency of 58% wasobtained at 900℃, while the highest reversible capacity of 180mAh/g was exhibited at700℃. Pitch-pyrolyzed carbon showed that highest lithium extraction capacity of400mAh/g was obtained at 600℃with the initial coulombic efficiency of 63%.Meanwhile, the best cycling performance of pitch-pyrolyzed carbon was gained at900℃. Glucose-pyrolyzed carbon was prepared by hydrothermal and high temperaturesolid state method. The results showed that the pyrolyzed carbon exhibited betterperformance by high temperature solid state method, which delivered a reversiblecapacity of 290mAh/g and a coulombic efficiency of 50%.Hard carbon/pitch-pyrolyzed carbon composite was prepared by high temperaturesolid state method at 900℃. The results showed that the hard carbon/pitch-pyrolyzedcarbon composite exhibited improved initial coulombic efficiency. It was found thatthe highest initial coulombic efficiency was obtained by sample with the ratio of hardcarbon: pitch=2:1, which was enhanced by 15% and reached 70%. Meanwhile, thereversible capacity was enhanced by 20mAh/g. The best cycling performance wasobtained after pyrolyzing for 1h. It was found that hard carbon revealed good cyclingperformance at large current density, and the hard carbon/pyrolyzed carbon compositefurther maintained rate capability of hard carbon.Graphite/hard carbon and MCMB/hard carbon composites were prepared bymechanical mixing the samples of graphite and hard carbon or MCMB and hard. Theresults showed that the rate capability of graphite and MCMB were improvedapparently by hard carbon mixing, but the initial efficiency was decreased. When theratio of graphite (or MCMB): hard carbon=2:1, i.e. the initial efficiency ofgraphite/hard carbon was 71%, 10% lower than that of graphite; the initial efficiencyof MCMB/hard carbon was 78%, 2% lower than that of MCMB. And the ratecapability of graphite and MCMB were improved apparently by hard carbon mixing.