Electrochemical properties of LiFePO4/C synthesized by mechanical activation using sucrose as carbon source

Abstract

Olivine lithium iron phosphate (LiFePO4) is attracting much attention as a safe, low cost and high capacity cathode material for lithium batteries, especially for applications in electric and hybrid-electric vehicles. In the present work, carbon-coated LiFePO4 (LiFePO4/C) materials are synthesized from lithium carbonate, ferrous oxalate, ammonium dihydrogen phosphate, and sucrose (varying content) as starting materials, by the process of mechanical activation followed by thermal treatment. A uniform, in situ coating of carbon surrounding the crystals of LiFePO4 is achieved by the pyrolysis of sucrose during the thermal treatment. The structural properties of LiFePO4/C are characterized by X-ray diffraction, and the morphological characteristics are studied by electron microscopy methods. Phase-pure particles of approximately 100 nm size and a homogeneous particle size distribution are obtained with 6 wt% carbon content. The electrochemical properties are evaluated at room temperature by cyclic voltammetry and charge-discharge performance in coin cells fabricated with lithium metal anode, LiFePO4/C cathode, and 1 M LiPF6 in ethylene carbonate (EC)/dimethyl carbonate (DMC) electrolyte. LiFePO4/C containing 6 wt% of carbon exhibits high discharge capacity of 165 mAh/g (corresponding to 97% of theoretical capacity) at 0.1 C-rate and 145 mAh/g at 1 C-rate. Good rate capability and stable cycle performance are realized for lithium cells employing LiFePO4/C prepared by adding the cheap and easily available sucrose as carbon source during the synthesis of LiFePO4.