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Small Scale Preparation of Silicon/Graphite/Carbon Anode Material for Lithium Ion Batteries and Elec

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Tutor: YinGePing
School: Harbin Institute of Technology
Course: Chemical Engineering and Technology
Keywords: Li-ion battery,Si/Graphite/C composite material,temperature field,negative plate
CLC: TM912
Type: Master's thesis
Year:  2012
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As a kind of anode material of lithium-ion battery, silicon will be wildly utilized by its high specific capacity. However, a high volume expansion can have a serious impact on the cycle stability of the silicon material while the silicon and lithium are alloying/de-alloying. Therefore, the silicon anode material is not practical.This dissertation summarizes the recent researches and the industrialization of silicon-based anode material. In this dissertation, an optimized craft of sintering100g more Si/Graphite/C composite is studied for the enlargement of the material manufacture. Based on materials obtained, the negative plate craft and the design parameters of high-capacity battery are studied an optimized via physical and electrochemical measurements.A suitable range for sintering material and a well argon flow were optimized through researching for the temperature field of tube furnace heating zone. Under these conditions,100g Si/Graphite/C material was sintered, which had fine electrochemical property and batches stability. The material showed a initial coulombic efficiency of85%, a reversible specific capacity of664mAh g-1after60cycles, a retention rate of70%and a relative range between batches of12%for4batches in their initial reversible specific capacity.The material obtained was used as the active substance of anode and the negative foil process was studied and optimized from four factors as followed, anode coating thickness, charge-discharge system, heat treatment and electrolyte additives. The battery cycle stability was improved under a changed charge-discharge system in the first two cycles, which showed a initial reversible specific capacity of1038mAh g-1, a reversible specific capacity of796mAh g-1after30cycles and a retention rate of77%. For thick anode plates, heat treatment enhanced their cycle stability.After6h heat treatment, anode plates with3mg material showed a reversible specific capacity of548mAh g-1after45cycles and a retention rate of85%. Vinylene carbonate joined only improved the cycle stability a little but decreased the reversible specific capacity a lot.The design parameters of high-capacity LiCoO2-Si/graphite/C523450lithium-ion battery were studied and optimized. The high capacity batteries showed a initial reversible capacity of978mAh, a discharge capacity of664mAh g-1after20cycles and a retention rate of91%. There were no obvious charge and discharge platforms during charging and discharging of the batteries and only such two relatively flat districts of voltage change existed that3.5-3.3V in discharge and3.6-3.7V in charge, respectively. Compared with the graphite anode batteries under the same specifications, batteries above showed higher capacities before the13th cycle, but after that they were caught up a little at the aspects of discharge capacities. Therefore, their cycle stabilities needs be improved by further researches.
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