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Lithium-ion battery anode material capacitance Preparation and Properties

Author: FangJie
Tutor: WangZhiXing
School: Central South University
Course: Electrochemical Engineering
Keywords: lithium ion capacitor-battery the composite anode materials low temperature pyrolysis capacitance performance electrochemical lithiation/delithiation performance
CLC: TM912
Type: Master's thesis
Year: 2010
Downloads: 280
Quote: 2
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Abstract


Lithium ion capacitor-batteries have been the new research field for power source in recent years due to large energy density and high power density. It is very important to develop a new anode material with electrochemical lithiation/delithiation performance and capacitance performance for lithium ion capacitor-battery.In this thesis, the CMS/actived carbon composite anode materials with different mass ratio were prepared by physical mixing. Electrochemical performances of CMS/actived carbon composites materials in different electrolyte LiPF6-EC/DMC/EMC, LiTFSI-EmimTFSI and LiTFSI-PP13TFSI were investigated. The new composite anode materials for lithium ion capacitor-battery were synthesized by pitch coating CMS at low temperature, and properties of the new anode composites materials were researched in detail.The results showed that CMS/actived carbon anode composites have electrochemical lithiation/delithiation and capacitive properties in the LiPF6-EC/DMC/EMC electrolyte, and the increase of the content of activated carbon in the composite materials caused a more obvious capacitive property. The composite materials of CMS and AC with a mass ratio of 8:2 show excellent electrochemical performance. The first charge capacity and the first charge and discharge efficiency are 297.9 mAh·g-1 and 52.18% at 0.1C. The capacity provided by activated carbon is 93 F·g-1. Performance of high current for composite materials was improved compared with the pure CMS. The charge time of the composite materials is 3 times as long as the pure CMS at current of 4 A·g-1. The charge capacity of the composite material increases 30 mAh·g-1 and the potential of charge plateau decreases 0.35 V.The first charge/discharge efficiency of the composite materials was improved in the ionic liquid electrolyte of LiTFSI-EmimTFSI and LiTFSI-PP13TFSI compared with that in organic electrolyte. But electrochemical polarization and impedance increase and cycle ability become worse in the ionic liquid electrolyte. Electrochemical performance of the composite materials was improved when added 10% PC in LiTFSI-EmimTFSI. The first charge/discharge capacity of composite material of CMS and AC with a mass ratio of 8:2 are 318.7 and 319.2 mAh·g-1 with almost no capacity fading after 20 cycles.The lithium diffusion coefficient of CMS and composite materials in the different electrolyte are studied by chronoamperometry measurements. The results indicate that the lithium ion diffusion coefficient of composite materials is much greater than that of pure CMS.The new composite anode materials for lithium ion capacitor-battery were prepared by pitch coating CMS at low temperatures. The results show that properties of the new anode composites are mainly affected by content of pitch and pyrolysis temperature. The composite material of CMS and AC with a mass ratio of 7:3, synthesized at 650℃show best performance. The specific surface area is 151.05m2·g-1. The average pore size is about 7.16nm. The initial charge and discharge capacity of the new composites are 461.7 and 767.2 mAh·g-1 repectively, and 286.7 mAh·g-1 charge capacity, namely 375.3 F·g-1, is obtained in the voltage ranges 0.25 to 3 V. The cycle ability is excellent, and the capacity retention is about 98.9% after 50 cycles. Charge time and capacity of the new composite materials are 83.5 seconds and 92.8 mAh·g-1 at current of 4 A·g-1. Therefore, the new anode composite material is a promising negative electrode material for lithium ion capacitor-battery.

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