Electrochemical Performances of Li-Ion Batteries Based on LiFePO₄ Cathodes Supported by Bio-Sourced Activated Carbon from Millet Cob (MC) or Water Hyacinth (WH)

The electrochemical performances of Li-ion batteries based on LiFePO4(LFP) cathode supported by bio sourced activated carbon obtained from Millet Cob (MC) or Water Hyacinth (WH) were determined. The carbons were obtained by combustion prior to drying the raw materials of WH and MC, followed by steps of various chemical cleanings, were activated at the following different mass ratios of potassium hydroxide (KOH) and WH or MC respectively: KOH/WH 1:1, 2:1, and 5:1, and KOH/MC 1:1, 2:1, and 5:1.The physics properties (X-ray diffraction patterns, BET surface area, micropore and mesopore volume, conductivity, etc. ) and electrochemical performances (specific capacity, discharge at various current rates, electrochemical impedance measurement, etc.) were determined. The electrochemical performances of coin cells based on cathodes composed of 85% LiFePO4, 8% of these activated carbons, and 7% polyvinylidene fluoride (PVDF) as a binder, with lithium metal as the anode were studied. Cycling tests and the discharge at different current rates of these cells based on the LiFePO4/C cathodes supported by the various activated carbons were achieved. It was found that the coulombic efficiency, the specific capacity and the discharge at different current densities of these cells were interesting for Li-ion batteries applications. It was shown that their Coulombic efficiency was at least 99% and was very close to that of the cell based on LFP/commercial graphite cathode. The specific capacity of the cells was correlated to the KOH/WH et KOH/MC. Overall, the electrochemical performances of cells based on LFP/MC and LFP/WH were correlated to the physics properties of the activated carbons of MC and WH. Their performances were also compared to those of cells based on LFP/graphite. It was found that cells based on activated carbon obtained from WH exhibited better performances than those from MC. For a given current rate and the same number of cycles, the specific capacity of the cells based on activated carbons of WH is very close to that based on graphite.