Impact of incorporation of chromium on electrochemical properties of LiFePO₄/C for Li-ion batteries

LiFe_0.95Cr_0.05PO₄/C was successfully synthesized by one-step solid-state reaction using a single mode microwave reactor. The effect of incorporation of chromium on LiFePO₄ lattice parameters was systematically investigated by X-ray diffraction. Surface analysis was done by scanning electron microscopy and transmission electron microscopy. The ratio of amorphous to graphitic carbon was determined from Raman spectroscopic data. The influence of chromium incorporation on electrochemical properties was studied by recording charge/discharge cycles combined with electrochemical impedance spectroscopy (EIS) and cyclic voltammetry. It was found that Cr incorporation significantly enhanced the electrochemical performance of LiFePO₄ at all current densities up to 10 C. LiFe_0.95Cr_0.05PO₄/C prepared exhibited the best performance with an initial specific discharge capacity of 157.7, 144.8, 138.3, 131.0, 124.1 and 111.1 mAh·g⁻¹ at 0.1 C, 0.5 C, 1.0 C, 2.0 C, 5 C and 10 C, respectively. The doped sample displayed excellent capacity retention, which was substantially superior than that of pristine LiFePO₄/C at a higher current rate.