Synthesis and electrochemical properties of olivine LiFePO <SUB>4</SUB> as a cathode material prepared by mechanical alloying

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• Kim, Cheol Woo
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• Jeong, Woon Tae
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• Lee, Kyung Sub

Abstract

Pure olivine LiFePO ₄ and LiFePO ₄/C composite powders are synthesized by using mechanical alloying (MA) and subsequent firing. The powder properties and the electrochemical characteristics of the prepared samples are investigated in comparison with those of a sample obtained by the conventional solid-state reaction. The olivine LiFePO ₄ prepared by MA shows a maximum discharge capacity of 135 mA h g ^-1 at the C/20 rate (8.5 mA g ^-1) when fired at a relatively low temperature of 600 °C. A LiFePO ₄/C composite compound prepared by the MA process under optimum firing conditions has a high capacity of 156 mA h g ^-1 at the C/20 rate, i.e. 92% of the theoretical capacity. The composite also displays a better rate capability, a higher charge-discharge capacity and a more stable cycle-life than when produced by the conventional solid-state method. The improved electrode performance of MA samples originates mainly from very fine particles of sub-micron size and with a rough surface morphology. These powder characteristics increases the surface area of LiFePO ₄ particles and maximizes the contact area with the conductor additive, which results in enhanced electronic conductivity. Consequently, the MA technique offers a promising synthetic process to overcome the disadvantages of olivine-type LiFePO ₄ and LiFePO ₄/C composite cathode materials for rechargeable lithium batteries.