The use of various dicarboxylic acids as a carbon source for the preparation of LiFePO4/C composite

Olivine-type LiFePO4 composite powders with carbon were synthesized by freeze drying and subsequent thermal annealing. The main purpose of the research is to explore how various dicarboxylic acids as carbon sources influence the electrochemical properties of the resulting composites. Three dicarboxylic acids (oxalic, malonic, and adipic) were used as a carbon source. The synthesis was followed by X-ray powder diffraction, scanning electron microscopy, particle-size analysis, and electrochemical experiments. It is shown that the amount of the in situ formed carbon depends on the thermal behaviour of the acids in inert atmosphere rather than on their carbon content. Cyclic voltammetry experiments and galvanostatic cycling illustrate the behaviour of different powders: the powder obtained with oxalic acid yields the highest discharge capacity at small currents, while the one obtained with adipic acid shows better high-current response. Malonic acid has turned out to be a poor carbon source and it consequently yields powder with poor electrochemical performance.