Influence of bio-derived agar addition on the electrochemical performance of LiFePO4 cathode powders for Li-ion batteries

Olivine structured LiFePO4 cathode materials were successfully synthesized via a newly developed eco-friendly sol-gel process. In this study, bio-derived natural agar powders were used as chelating agents as well as carbon sources for the first time. The impacts of different agar concentrations (3 wt%-12 wt%) and calcination temperatures (400 degrees C-700 degrees C) on the structural and electrochemical properties of LiFePO4/C powder were investigated in detail. XRD analysis showed that as the concentration of agar reached 6 wt%, a LiFePO4 phase was obtained in N-2 atmosphere with 700 degrees C heating for 8 h. Moreover, increasing the agar concentration to 12 wt% significantly lowered the calcination temperature to 500 degrees C for the formation of LiFePO4 phase. Particle size distribution spectra also revealed that addition of up to 12 wt% agar concentration reduced the particle sizes of the as-prepared LiFePO4 powder. LiFePO4 powder synthesized with 12 wt% agar concentration at 600 degrees C exhibited an initial specific discharge capacity of 147 mA h/g at C/10 rate and maintained 146 mA h/g at the end of 50th cycle in 2-4.2 V window, indicating excellent capacity retention. The analysis of electrochemical impedance spectra and CV test indicated that the charge transfer resistance and potential difference were effectively reduced.