Synthesis And Electrochemical Performance Of Cu₂Mo₆S₈and Fe（M）S₂（M=Cu,Mo）

Cathode material of lithium-ion battery was accounted for more than30percent of the cost in lithium-ion battery industry. LiCoO₂, LiMn₂O₄arewidely used as lithium-ion battery cathode materials, but their hightemperature performance and technical indicators still can not meet therequirements of high-power lithium-ion battery. Finding new cathodematerials with superior electrochemical performance become very important.This dissertation emphasizes on Chevrel phase compound Cu₂Mo₆S₈cathodematerials possessed excellent structure and superior performance. Thesynthesis, electrochemical behavior and kinetics of lithiuminsertion-exlraction process of Chevrel phase compound Cu₂Mo₆S₈cathodematerials were studied in detail. Then the doping of pyrite were studied, too．The Chevrel Phases （CPs） materials Cu₂Mo₆S₈used in lithium-ionbatteries were synthesized by molten salt method. X-ray diffraction, scanningelectron microscope, charge-discharge test, cyclic voltammetry and EIS are used to investigate the structural properties and electrochemical performancesof the sample. The results show that Cu₂Mo₆S₈is Chevrel phase and hasuniformly distribution of gain size. Determined the best operating voltagerange of the material is1-3.2V. Kinetics of lithium insertion-exlractionprocess of Chevrel phase compound Cu₂Mo₆S₈cathode materials werestudied by AC impedance method.Li/Cu₂Mo₆S₈battery charge-discharge test results show that: Thematerial first discharge capacity increased with the rise of the chargingvoltage,but the cycle performance experienced a first increased and thendecreased with the rise of the charging voltage, the best operating voltagerange of the material is1-3.2V. Materials exist a1.1V voltage platform in thefirst discharge process which disappear in the follow cycles,which is thereason of the high capacity of first discharge. We learn from the materialcycle-efficiency curve that there are some obstacles in Chevrel phaseCu₂Mo₆S₈material in the exlraction process of lithium ion,while it’s easy forthe insertion process of lithium ion. The electrochemical characteristic showsgood charge and discharge performance with an energy density of at least100mAh/g for the first twenty-five cycles in the potential range between3.2and1V. The voltammetric cycle curve of the material has a relativelysymmetrical redox peaks which indicates the material has good redox reversibility. The resuls of AC impedance test with Li/Cu₂Mo₆S₈batteryshown that Chevrel phase Cu₂Mo₆S₈materials formed passivation filmunder high lithium intercalation voltage,which contribute to the high capacityof the materials.Pyrite cathode materials were modified by doping multiple componentsCu or Mo. The results indicated that FeS₂cycle capacity had greatlyimproved by elemental metals doping. However, its impact on the ambienttemperature cycling capacity fading of pyrite is not obvious. The metaldoping did not significantly affect lithium ion insertion-exlraction mechanismin the FeS₂,but the first discharge capacity of the material was greatlyimproved, which then improve the cycle specific capacity of FeS₂. It showedan enhancement of the first discharge capacity with addition of5wt％Cu and3wt％Mo respectively at0.1C-rate ingiving540mAh/g and490.5mAh/g.The cycle performance was also enhanced with the metals added. FeS₂with3wt％Mo delivered a reversible capacity of215.8mAh/g （66％of its capacityin the2rd cycle） after50cycles．...