Doping effects on the crystal structure and electrochemical performance of LiFePO₄/C

LiFe_0.98M_0.02PO₄/C (M = Mg, Ni, Co, Sr) composite materials were prepared by solid-state synthesis method using Fe₂O₃ as one of the starting materials. The structures and electrochemical performance of samples were carried out by means of XRD, SEM, TEM, and constant-current charge-discharge method. The results showed that the ion doping did not change the crystal structure and morphology of LiFePO₄. Unit-cell volume gradually increased, which was good for embedding and disembedding of Li⁺, and improving conductivity and charge-discharge performance. The electrical conductivity of powders was increased by carbon coating and ion doping. The initial discharge capacity of Ni²⁺-doped sample reached 156.6 mA·h/g and 149.4 mA·h/g at 0.2C and 1C rate. After 30 cycles, the capacity retention rate was still 98.8% and 97.2%.