Chemical reaction characteristics, structural transformation and electrochemical performances of new cathode LiVPO(4)F/C synthesized by a novel one-step method for lithium ion batteries

A new cathode LiVPO(4)F/C with a high working voltage of around 4.2 V was synthesized by a novel one-step method. The color of the solution turns green, which implies that V(2)O(5) is successfully reduced to V(3+). The reaction thermodynamics indicates that LiVPO(4)F/C is formed when the sintering temperature is higher than 650 °C, while the accompanying impurity phase Li(3)V(2)(PO(4))(3)/C is also generated. The reaction kinetics proves that the reaction is third order and the activated energy is 208.9 kJ mol(−1). X-ray photoelectron spectra imply that the components of LiVPO(4)F/C prepared at 800 °C (LVPF800) are in their appropriate valence. LVPF800 is composed of micron secondary particles aggregating from nano subglobose. The structural transformation shows that the V : P : F ratio in LVPF800 is close to 1 : 1 : 1. The reason behind generation of impurity Li(3)V(2)(PO(4))(3) at a high temperature of 850 °C is demonstrated directly, which is mainly due to the volatilization of VF(3). The electrochemical performances of the cathode are related to the crystallite content of LiVPO(4)F/C and Li(3)V(2)(PO(4))(3)/C. The specific capacities at 0.2 and 5C of LVPF800 are as high as 139.3 and 116.5 mA h g(−1). Electrochemical analysis reveals that LVPF800 possesses an excellent reversibility in the extraction and insertion process and minimum charge transfer resistance.