Nitrogen-doped-carbon coated lithium iron phosphate cathode material with high performance for lithium-ion batteries

Highlights: • LiFePO₄ coated with N-doped carbon was successfully synthesized via one-step solid state method. • Ionic liquids was served as carbon and nitrogen sources, which formed uniformly graphitizing carbon layers. • NC-LiFePO₄ shows better rate capability and higher capacity than C-LiFePO₄. - Abstract: LiFePO₄ coated with nitrogen-doped carbon (NC-LiFePO₄) is successfully synthesized via a simple and efficient solid state method by using nitrogen-containing ionic liquid (IL) as nitrogen source. The uniformly coated N-doped carbon layers on the particles are examined by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray (EDS). The nitrogen-doped carbon layers on the particle surface can increase the electronic conductivity of LiFePO₄, resulting in higher capacity and more superior rate capability compared with the one coated with undoped carbon (C-LiFePO₄). The specific discharge capacities of NC-LiFePO₄ are 160.1 mA h g⁻¹ at 0.1 C and as high as 124.5 mA h g⁻¹ at 10 C, while they are 149.1 mA h g⁻¹ at 0.1 C and 95.7 mA h g⁻¹ at 10 C for C-LiFePO₄. The method reported in this paper is very effective in electronic conductivity improvement of LiFePO₄ and can be easily applied to the synthesis of other cathode materials