Cation-substituted LiFePO_4 prepared from the FeSO_(4.7)H_2O waste slag as apotential Li battery cathode material

摘要

The purpose of this study is to utilize the huge FeSO_(4.7)H_2O waste slag produced by the titanium dioxide industry. FeC_2O_(4.2)H_2O precursors are synthesized at various pH values by using the waste slag and H_2 C_2O_(4.2)H_2O as raw materials, and without any purifying process. ICP analysis confirms that the impurity content of FeC_2O_(4.2)H_2O increases with the pH value. Crystalline cation-substituted LiFePO_4 are prepared from the FeC_2O_(4.2)H_2O precursors. The cation dopants do not obviously change the structure of LiFePO_4, and all the samples are single olivine-type phase and well crystallized. The lattice parameters of LiFePO_4 decrease with the increased dopants contents. The dopants limit the size of LiFePO_4 nanocrystals, LiFePO_4 particles agglomeration and, consequently, improve the electrochemical performance of LiFePO_4. The cation-substituted LiFePO_4 prepared from the waste slag show much better electrochemical properties than the pure LiFePO_4 at high current rates. The optimal pH value for synthesizing FeC_2O_(4.2)H_2O from the waste slag is about 1.0, with 96.6% iron recovery. The cation-substituted LiFePO_4 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.