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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 32, Number 12
BKCSDE 32(12)
December 20, 2011 

Structural and Electrochemical Properties of Li2Mn0.5Fe0.5SiO4/C Cathode Nanocomposite
Youngmin Chung, Seungho Yu, Min Seob Song, Sung-Soo Kim,*, Won Il Cho *
Lithium manganese iron silicate, Polyanion system, Cathode, Physical blending, Lithium-ion battery
The Li2Mn0.5Fe0.5SiO4 silicate was prepared by blending of Li2MnSiO4 and Li2FeSiO4 precursors with same molar ratio. The one of the silicates of Li2MnSiO4 is known as high capacitive up to ~330 mAh/g due to 2 mole electron exchange, and the other of Li2FeSiO4 has identical structure with Li2MnSiO4 and shows stable cycle with less capacity of ~170 mAh/g. The major drawback of silicate family is low electronic conductivity (3 orders of magnitude lower than LiFePO4). To overcome this disadvantage, carbon composite of the silicate compound was prepared by sucrose mixing with silicate precursors and heat-treated in reducing atmosphere. The crystal structure and physical morphology of Li2Mn0.5Fe0.5SiO4 was investigated by X-ray diffraction, scanning electron microscopy, and high resolution transmission electron microscopy. The Li2Mn0.5Fe0.5SiO4 / C nanocomposite has a maximum discharge capacity of 200 mAh/g, and 63% of its discharge capacity is retained after the tenth cycles. We have realized that more than 1 mole of electrons are exchanged in Li2Mn0.5Fe0.5SiO4. We have observed that Li2Mn0.5Fe0.5SiO4 is unstable structure upon first delithiation with structural collapse. High temperature cell performance result shows high capacity of discharge capacity (244 mAh/g) but it had poor capacity retention (50%) due to the accelerated structural degradation and related reaction.
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