Electrochemical Properties Of Carbon Prepared By Pyrolysis Of Polymer Materials Used As Liyhium-ion Battery Anode

Lithium-ion batteries are widely used as a power source in portable consumerelectronic equipment, electric vehicles, space technology, and defense industry due toits high energy density, high operating voltage, long cycle life, no memory effect, andso on. One of the key factors determining the performance of the lithium-ion battery isthe choice of anode materials. Graphitic carbons are the mainstay of anode materialsfor commercialized lithium ion batteries because of their high conductivity, excellentcycle stability, and low cost. However, graphite anode has a limited theoreticalcapacity （LiC₆,372mAh/g）. In addition, the operating voltage close to that of Li/Li+often leads to a plating of metallic lithium on the graphite surface, which will run arisk of metallic lithium dendrite growth on the electrode surface that causes securityproblems.Non-graphitic carbons are mainly composed of graphitic fragments andamorphous region due to incomplete graphitization reaction. Non-graphitic carbon hasan isotropic structure, and presents a relatively large number of lithium ions insertionsites on the electrode surface which lead a much higher reversible capacity thangraphite. Despite of that, non-graphitic carbon materials prepared from pyrolysis oforganic compounds usually suffer from low electrical conductivities due to their poorgraphitization degree and large voltage hysteresisIn the thesiss, carbon materials prepared by pyrolysis of polymeric metalphthalocyanine deliver high reversible capacity, excellent cycle stability and rateperformance. Most importantly, the improvement of initial coulomb efficiency andthe reduction of voltage hysteresis have been achieved. The contents are as follows:1. A novel C/Co composite with Co nanoparticles embedded in carbon matrix issynthesized firstly by pyrolysis of polymeric cobalt phthalocyanine （PcCo） at700℃in argon atmosphere. This composite is investigated as an anode material for lithiumion batteries, indicating high tap density and excellent electrochemical performance.The C/Co electrode can retain a higher reversible capacity of over600mAh/g at acurrent of50mA/g after40cycles and shows better rate capability and less hysteresisin comparison to carbon not containing Co. The significant improvement is attributedto the Co nanoparticles grown in-situ reaction with catalytic activity and highelectrical conductivity.2. A C/Co-Fe composite has been synthesized by pyrolysis of the polymer （cobaltphthalocyanine-iron phthalocyanine）. As an anode material, the C/Co-Fe compositeexhibits a high reversible capacity of about550mAh/g after90cycles between0.005～3.5V at a current of100mA/g. Moreover, the C/Co-Fe composite has a marked reduction in voltage hysteresis of battery and a10%increase in initialcoulomb efficiency compared to pure carbon anode material.