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The Study of Electrochemical Performance of Li3V2（PO4）3under Multi Electron Exchange Condition

Author: ZhangJiaoLong
Tutor: DaiChangSong
School: Harbin Institute of Technology
Course: Chemical Engineering and Technology
Keywords: lithium ion battery Li3V2（PO4）3 carbon-coating doping lithium-ioncapacitor battery
CLC: TM912
Type: Master's thesis
Year: 2013
Downloads: 2
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Abstract


Monoclinic Li3V2（PO4）3has been considered as highly promising cathodematerial for high power lithium ion batteries, due to its high operating voltage, highreversible capacity and good safety performance. But it has low electronicconductivity and poor cycling performance under three electron exchange condition（conresponding to the operating potential range of3.04.8V）, which limit its furtherapplication in power batteries. In response to above deficiencies, carbon coating, Zn2+doping and PB composite materials were studied.Li3V2（PO4）3/C was synthetized using sucrose, carbon black, carbon nanotubes（CNT） and graphite as carbon sources. Results showed that carbon sources had a greatimpact on the morphology and electrochemical performance of Li3V2（PO4）3/C.Compared with other samples, the Li3V2（PO4）3/C synthetized with sucrose as carbonsource have optimum electrochemical performance under different electron exchangeconditions. When the upper cut-off voltage were limited to4.3V,4.6V and4.8V, theinitial discharge capacities at0.2C rates were120.3mAh·g-1,148.2mAh·g-1and161.0mAh·g-1, respectively. The comparative study of structural evolution uponcycling showed that cycling processes as well as the operating potential regions had asignificant impact on the structure of Li3V2（PO4）3. The crystallinity loss and theirreversible expansion of crystal plane interspace and unit cell volume occurred,accompanied with the cycling, and the extent of these phenomena is enlarged whenthe upper limit potentials are extended.Zn2+doping was studied on the basis of using sucrose as carbon source. Studiesshowed that Zn2+doping on the V bit could effectively improve structural stability ofLi3V2（PO4）3/C composite materials in cycling process. A small amount of Zn2+dopinghad no effect on the lattice structure of materials, but when the amount of dopinggetting larger, Zn-related miscellaneous phases would be generated in process ofsynthetizing material. Amoung all the Li3V2-2/3xZnx（PO4）3/C materials,Li3V1.97Zn0.05（PO4）3/C had excellent electrochemical performance under differenteletron exchange conditions. In the potential range of3.04.3V, its initial dischargecapacity was131.2mAh·g-1under0.2C, and122.6mAh·g-1under1C, the capacityretention was99.3%after50cycles. In the potential range of3.04.8V, the initialdischarge was183.4mAh·g-1under0.2C,93.1%of the theoretical capacity.Li3V1.97Zn0.05（PO4）3/C and PB composite electrode materials were prepared bymechanical mixing and the lithium-ion capacitor was studied on the basis of carbon-coating （using sucrose as carbon source） and Zn2+doping. Studies showed thatPB has good electronic conductivity, as well as the characteristic of capacitance,which could make it act as active material upon cycling. Electrochemical tests showedthat, the better high rate performance of Li3V1.97Zn0.05（PO4）3/C and PB compositeelectrode materials could be obtained, accompanied with the increase of PB content.When charged at20C and discharged at1C, the composite material with10wt%PB（PB10） shows the best performance, the initial discharge capacity of PB10was107.3mAh·g-1, and discharge capacity of110.9mAh·g-1could be obtained after200cycles,namely, there was no loss of capacity; when charged at1C and discharged at1C, itsinitial discharge capacity was108.7mAh·g-1, and the capacity retention was98.7%after200cycles.

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CLC: > Industrial Technology > Electrotechnical > Independent power supply technology (direct power) > Battery
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