Preparation And Characterization Of Molybdenum Compound Oxide Modified Graphite Anode Materials

Graphite is used as an anode material at the beginning of lithium ion batteries investigation.The graphite electrode has many advantages,such as high power density,high electronic conductivity,low self-discharge rate,and long cycling life time.However lithium dendrites/moss forms on the surface of graphite,due to the uneven distribution of charge builded up on the surface,finally rendering incidents because of internal shortcuts triggered by the lithium dendrites.Resolving these problems and exploring new anode materials with higher cycling rate stability,higher safety performance,and longer cycling life time have become the goal of investigators.Two kinds of molybdenum-based materials were tested as anode materials for lithium ion battery in this investigation.The materials were synthesized by ball-mill mixing,spray drying,and then sintering in nitrogen atmosphere to obtain the anode material.The physical properties of the composites were characterized by SEM.XRD.cycle voltammetry,and AC impedance.The coulombic efficiency,oxidation-reduction potential,and Li+ion transition coefficient were measured.In chapter 3,the lithium molybdate/carbon was prepared by means of ball milling and spray drying.Organic ammonium salt was used as surfactant to disperse lithium molybdate into carbon.Materials were prepared with different lithium molybdate to carbon ratios.They were characterized by methods mentioned previously.The results show that composite material with 10%content of organic ammonium salt and 20%of lithium molybdate behavior the best.The first specific discharge capacity of material reached 655mAh/g.The material calcined at 400? has the highest first charge-discharge efficiency of 69.6%.The best material still remained a specific capacity of 350mAh/g after 50 charge-discharge cycles.At a charge-discharge rate of 500mA/g,the material has a specific capacity of 350mAh/g,which displays excellent rate capacity.The future work aimed at reducing capacity fading of the material.This work is still in progressing in the investigation group.In chapter 4,the magnesium molybdate/carbon composite material was prepared by the same method as that in chapter 3.The influences of surfactant,calcination temperatures,the content of magnesium molybdate,and LiOH on electric properties of the materials were investigated.The results show that the material prepared with poly ethylene glycol as surfactant,doped with 7%of LiOH,and calcined at 400 ?with a magnesium molybdate loading of 25wt%(relative to MgMo04)has the highest specific discharge/charge capacity(discharge 544.8mAh/g,charge 349.3mAh/g).After 70 discharge/charge cycles,the material still remained a specific capacity of 340mAh/g(about 97%of the primary specific capacity).At a charge-discharge rate of 500mA/g,the material reached a specific capacity of 150mAh/g.