Response Surface Optimization for Process Parameters of LiFePO4/C Preparation by Carbothermal Reduction Technology

A statistically based optimization strategy is used to optimize the carbothermal reduction technology for the synthesis of LiFePO4/C using LiOH, FePO4 and sucrose as raw materials. The experimental data for fitting the response are collected by the central composite rotatable design (CCD). A second order model for the discharge capacity of LiFePO4/C is expressed as a function of sintering temperature, sintering time and carbon content. The effects of individual variables and their interactions are studied by a statistical analysis (ANOVA). The results show that the linear effects and the quadratic effects of sintering temperature, carbon content and the interactions among these variables are statistically significant, while those effects of sintering time are insignificant. Response surface plots for spatial representation of the model illustrate that the discharge capacity depends on sintering temperature and carbon content more than sintering time. The model obtained gives the optimized reaction parameters of sintering temperature at 652.0 °C, carbon content of 34.33 g·mol−1 and 8.48 h sintering time, corresponding to a discharge capacity of 150.8 mA·h·g−1. The confirmatory test with these optimum parameters gives the discharge capacity of 147.2 and 105.1 mA·h·g−1 at 0.5 and 5 C, respectively.