Synthesis and Characterization of (1-x)Li2FeSiO4 • xLi3PO4/C as a Cathode Material for Lithium Ion Batteries

(1-x)Li2FeSiO4 center dot xLi(3)PO(4)/C, i.e. Li-2 Fei_(x)lpSi(1-x)O(4)/C, are proposed as a novel cathode material for lithium ion batteries. (1-x)Li2FeSiO4 center dot xLi(3)PO(4)/C composites are prepared by a citric acid assisted sal-gel method. A complete solid solution can be formed for any value of x if the calcination temperature is high enough. However, the coexistence of Li2FeSiO4-rich and Li3PO4-rich phases is confirmed when the calcination temperature is 700 degrees C and x is higher than 0.1 and lower than 0.9. The discharge capacity declines with an increase in x when the current density is low, which is due to the reduction in the number of Fe2+/Fe3+ redox couples. When the applied current density is high enough (1 C or higher), Li-2.05Fe(0.95) P0.05 SiO0.95O4 has the highest discharge capacity and capacity retention because of its best crystallinity, lowest charge transfer resistance and highest lithium ion diffusion coefficient. Lower calcination temperature leads to better pore size distribution, higher carbon content and smaller particle size, resulting in better electrochemical performance. The carbon network wraps and connects the Li(2.05)Peo(0.95)P(0.05)Si(0.95)O(4) particles when the calcination temperature is 700 degrees C, and it has a hierarchically porous structure. These features are of great benefit to its electrochemical performance.