Optimization of titanium and vanadium co-doping in LiFePO4/C using response surface methodology

A statistically based optimization strategy is used to optimize the amount of titanium and vanadium that is co-doped in LiFePO4/C. Experimental data for fitting the response were collected using a central composite rotatable design. A second-order model that represents the discharge capacity of co-doped LiFePO4/C was expressed as a function of amount of doping titanium and vanadium. The effect of individual variables and their interactions was studied by statistical analysis of variance. The linear and quadratic effects and interactions of the amount of doping titanium and vanadium were statistically significant. Response surface plots, the spatial representations of the model, show that the discharge capacity depends more on the amount of doping vanadium than titanium. The obtained model reveals that the optimized amounts of doping titanium and vanadium are 0.03 and 0.07, respectively, which results in a theoretical discharge capacity of 144.8 mAh g(-1) at 10 C. Confirmatory tests for the optimized LiV0.07Ti0.03Fe0.9PO4/C show a discharge capacity of 144.1 mAh g(-1) with a capacity retention ratio of similar to 100 % after 100 cycles at 10 C. The optimized LiV0.07Ti0.03PO4/C exhibits a good rate performance and cycle stability because of the enhancement of electronic conductivity and reaction reversibility through the vanadium and titanium co-doping.