Different sulfur modified carbon coated lithium iron silicate (Li 2 FeSiO 4 /C) composites were prepared by sol-gel precursor and solid-state reaction using 1-dodecanethiol as a sulfur source material. The effects of sucrose amount, sulfur content, sintering temperature and sintering time on crystal structure, surface morphology and electrochemical performance of sulfur modified Li 2 FeSiO 4 /C composites were investigated through orthogonal design experiments. The results of the orthogonal investigation indicated that the significance of the influence on the capacity performance followed the decreasing order as sulfur doping content > sucrose content > sintering temperature > sintering time. The optimized conditions were determined to be: sucrose content of 70%, sulfur doping content of 10%, sintering temperature at 600°C for 7 h.
A series of different vanadium modified carbon coated lithium iron silicate (Li2Fe1-xVxSiO4/C) composites were prepared by sol-gel precursor and solid-state reaction using ammonium metavanadate (NH4VO3) as a vanadium source material. The effects of vanadium content, sucrose amount, sol-gel time and type of carboxylate acid on crystal structure, surface morphology, elemental composition and electrochemical performance of Li2Fe1-xVxSiO4/C composites were investigated through orthogonal design experiments. The initial discharge capacity of the nominal 35% vanadium modified Li2FeSiO4/C, prepared under the optimized conditions (sucrose amount of 80% and sol-gel time of 2 h using citric acid as a pH regulator), reached as high as 216.7 mAh/g (corresponding to 1.30 moles per formula unit) at 0.1C and room temperature. The composite exhibited a mixed Pmn21 and P21 phase with the coexistences of metallic iron (Fe) and lithium silicate (Li2SiO3) as the main impure phases.
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