Effect of carbon sources and synthesis conditions on the LiFePO₄/C cathode properties

The sol-gel synthesis and precipitation from dimethyl sulfoxide (DMSO)-water mixture were used to obtain LiFePO4. Sucrose (sucr), citric acid (CA), phthalic acid (phth), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyvinylidene fluoride (PVDF), polyethylene glycol (PEG), polyacrylic acid (PAA) were investigated as carbon precursors. Increasing of the annealing temperature from 600 °C to 800 °C leads to a certain perfection of graphite structure with simultaneous particle size growth. Higher capacities were observed for the materials synthesized at 600 °C. The best results for the sol-gel synthesis were obtained when PVDF was used as a source of carbon coating due to the partial fluorination of LiFePO₄ (discharge capacity of LiFePO₄/C-PVDF was ∼160 and 70 mAh g^-1 at 20 mA g^-1 and 800 mA g^-1 currents, respectively). For nanocrystalline LiFePO₄ obtained by precipitation from DMSO-water mixture the best results were obtained when PEG was used as carbon source (discharge capacity LiFePO4/C-PEG was 158 and 77 mAh g^-1 at 20 mA g^-1 and 800 mA g^-1, respectively).