Cation-substituted LiFePO4 prepared from the FeSO4·7H2O waste slag as a potential Li battery cathode material

The purpose of this study is to utilize the huge FeSO4·7H2O waste slag produced by the titanium dioxide industry. FeC2O4·2H2O precursors are synthesized at various pH values by using the waste slag and H2C2O4·2H2O as raw materials, and without any purifying process. ICP analysis confirms that the impurity content of FeC2O4·2H2O increases with the pH value. Crystalline cation-substituted LiFePO4 are prepared from the FeC2O4·2H2O precursors. The cation dopants do not obviously change the structure of LiFePO4, and all the samples are single olivine-type phase and well crystallized. The lattice parameters of LiFePO4 decrease with the increased dopants contents. The dopants limit the size of LiFePO4 nanocrystals, LiFePO4 particles agglomeration and, consequently, improve the electrochemical performance of LiFePO4. The cation-substituted LiFePO4 prepared from the waste slag show much better electrochemical properties than the pure LiFePO4 at high current rates. The optimal pH value for synthesizing FeC2O4·2H2O from the waste slag is about 1.0, with 96.6% iron recovery. The cation-substituted LiFePO4 prepared from this precursor exhibits the best electrochemical properties, which delivers a capacity of 152, 142 and 126 mAh g−1 at 1C, 2C and 5C rate, respectively, and shows excellent cycling performance.