Journal
RARE METALS
Volume 31, Issue 2, Pages 145-149Publisher
NONFERROUS METALS SOC CHINA
DOI: 10.1007/s12598-012-0480-0
Keywords
lithium ion batteries; LiFePO4; carbon coating; Mn-doping
Funding
- National Science Foundation for Young Scholars [11004032]
- National Natural Science Foundation of China [11074039]
- Fujian Province Science Foundation for Young Scholars [2008F3039]
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Olivine structured LiFePO4/C (lithium iron phosphate) and Mn2+-doped LiFe0.98Mn0.02PO4/C powders were synthesized by the solid-state reaction. The effects of manganese partial substitution and different carbon content coating on the surface of LiFePO4 were considered. The structures and electrochemical properties of the samples were measured by X-ray diffraction (XRD), cyclic voltammetry (CV), charge/discharge tests at different current densities, and electrochemical impedance spectroscopy (EIS). The electrochemical properties of LiFePO4 cathodes with x wt.% carbon coating (x= 3, 7, 11, 15) at gamma =0.2C, 2C (1C= 170 mAh center dot g(-1)) between 2.5 and 4.3 V were investigated. The measured results mean that the LiFePO4 with 7 wt.% carbon coating shows the best rate performance. The discharge capacity of LiFe0.98Mn0.02PO4/C composite is found to be 165 mAh center dot g(-1) at a discharge rate, gamma = 0.2C, and 105 mAh center dot g(-1) at gamma =2C, respectively. After 10 cycles, the discharge capacity has rarely fallen, while that of the pristine LiFePO4/C cathode is 150 mAh center dot g(-1) and 98 mAh center dot g(-1) at gamma=0.2 and 2C, respectively. Compared to the discharge capacities of both electrodes above, the evident improvement of the electrochemical performance is observed, which is ascribed to the enhancement of the electronic conductivity and diffusion kinetics by carbon coating and Mn2+-substitution.
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