Insights into phosphorus doping on the structure and electrochemical performance of Li2FeSiO4/C nano-composites

Li2FeSiO4 is one of the most promising cathode materials for lithium ion batteries due to its high theoretical capacity. However, the low electrical conductivity and low lithium-ion diffusion coefficient restrict its practical applications. Hetero-ion doping distinctly affect the crystal and electrochemical properties of Li2FeSiO4 based materials. Herein, phosphorus (P) doped Li2FeSiO4/C nano-composites (Li1.95FeSi0.95P0.05O4/C, abbreviated as LFSPC) and Li2FeSiO4/C nano-composites (LFSC) were synthesized and investigated as cathode material for lithium ion batteries. XRD and XPS analyses indicate that P has been doped in the crystal Li2FeSiO4. SEM results prove that the particle size of LFSPC is smaller than that of LFSC. These features make LFSPC exhibit better electrochemical performance over LFSC. The discharge capacity of LFSPC at 0.1C is as high as 218.1 mAh/g, higher than that of LFSC (144.0 mAh/g). The capacity retention ratio for LFSPC after 200 cycles at 1C is 85 %, higher than that of LFSC (78 %). In addition, LFSPC deliver larger rate performance, lower charge transfer resistance and larger lithium-ion diffusion coefficient.