Enhanced electrochemical properties of LiFePO4 by Mo-substitution and graphitic carbon-coating via a facile and fast microwave-assisted solid-state reaction

Abstract

A composite cathode material for lithium ion battery applications, Mo-doped LiFePO₄/C, is obtained through a facile and fast microwave-assisted synthesis method. Rietveld analysis of LiFePO₄-based structural models using synchrotron X-ray diffraction data shows that Mo-ions substitute onto the Fe sites and displace Fe-ions to the Li sites. Supervalent Mo⁶⁺ doping can act to introduce Li ion vacancies due to the charge compensation effect and therefore facilitate lithium ion diffusion during charging/discharging. Transmission electron microscope images demonstrate that the pure and doped LiFePO₄ nanoparticles were uniformly covered by an approximately 5 nm thin layer of graphitic carbon. Amorphous carbon on the graphitic carbon-coated pure and doped LiFePO₄ particles forms a three-dimensional (3D) conductive carbon network, effectively improving the conductivity of these materials. The combined effects of Mo-doping and the 3D carbon network dramatically enhance the electrochemical performance of these LiFePO₄ cathodes. In particular, Mo-doped LiFePO₄/C delivers a reversible capacity of 162 mA h g⁻¹ at a current of 0.5 C and shows enhanced capacity retention compared to that of undoped LiFePO₄/C. Moreover, the electrode exhibits excellent rate capability, with an associated high discharge capacity and good electrochemical reversibility.