The micro–nano-structured FePO4·2H2O was prepared from mixed solution of FeSO4 oxidized in diluted H3PO4 with H2O2 and NaOH solution in the turbulent flow cycle state at 90 °C. The resulting products were characterized by thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Constant current charge/discharge tests were adopted to investigate the electrochemical performance and the rate capability (from 0.1C to 5C) of the carbon-coated LiFePO4 composite materials prepared from the micro–nano-structured FePO4. The carbon-coated LiFePO4 composite materials deliver a high specific discharge capacity of 153.7 mAh·g–1, exhibit excellent cycle performance with 98.6% of the capacity retained after 30 cycles. This study demonstrates that the turbulent flow cycle method may be an economical and effective method for industrial production of fine and uniform micro–nano-structured FePO4·2H2O particles for LiFePO4 cathode materials for Li-ion batteries.
Yangming Xu,Lanbin Wang,Wenjie Xie,Yu Chen,Keshuo Zhang,Yaguang Du
Copper slag (CS) contains a high content of valuable iron, the stockpile of CS occupies a large amount of land and leads to a waste of secondary resources. This study proposed producing battery-grade FePO 4 ·2H 2 O from CS through selective leaching, synthesis, and purification. The combined acid leaching/evaporation method was used to leach out Fe and inhibit Si from fayalite selectively, and then FePO 4 ·2H 2 O was formed by adding Na 2 HPO 4 ·12H 2 O without extra pH adjustment. The purity of FePO 4 ·2H 2 O obtained by using a reactor heated for 5 h at 180 ℃ with an HCl concentration of 2.5 M was 99.47 %, and the impurities were all by the industry standard for battery-grade FePO 4 ·2H 2 O (HG/T 4701–2021). The LiFePO 4 /C material was further synthesized and tested for battery performance. Under the test current of 0.1C, the charging-specific capacity of the battery in the first week was 175.8 mAh/g, and the discharge-specific ability was 159.3 mAh/g, which was close to the theoretical specific capacity and effective. Life cycle assessment (LCA) indicated that for each 1 kg of iron phosphate produced, the carbon emission of this study was reduced by 4.71 kg CO 2 eq compared with the traditional technology.
With the large-scale application of LiFePO 4 batteries in electric vehicles and energy storage, the recycling of spent LiFePO 4 cathode materials is receiving increasing attention. Hydrometallurgical derived full-component separation strategy has been verified as the most capable recycling process for LiFePO 4 cathode. During which, complete elements (i.e., Li, Fe and P) are dissolved into a solution of excessive acidic leachate, and subsequently separated to obtain battery-grade FePO 4 ·2H 2 O and lithium salt, enabling high element recovery rates of up to 100 %. However, the use of excessive leaching agent leads to high acidity of the leaching solution (pH < 0.8), which brings a necessary of pH regulation prior to the regeneration of FePO 4 ·2H 2 O, markedly complicating the succedent separation and purification. In this investigation, a practical method for directly regenerating FePO 4 ·2H 2 O from H 2 SO 4 -based full-component leaching solution is proposed. In this process, H 2 SO 4 as leaching agent is used to digest LiFePO 4 completely, and then Fe and P are premeditatedly recovered from the extremely acidic filtrate (pH < 0.8) as FePO 4 ·2H 2 O via direct precipitation without any pH regulator. Consequently, there are no extra impurities affecting the recovery of Fe and P during regeneration. The regeneration behavior of FePO 4 ·2H 2 O under extremely acidic condition are investigated and the growth mechanism is also clarified by monitoring the overall microstructure and phase evolutions. The results demonstrate that the above regeneration is found to be an exponential growth process driven by the quantity of nucleation site, and meanwhile influenced by the dissolution-reprecipitation equilibrium of amorphous iron phosphate. Specifically, the process can be accelerated by introducing FePO 4 ·2H 2 O or amorphous iron phosphate to increase the nucleation sites. Additionally, the primary nanosheet size of regenerated FePO 4 ·2H 2 O causes a smaller primary particle size of the corresponding LiFePO 4 /C material, contributing to its better physical and electrochemical properties. This work provides a guidance for the direct regeneration of FePO 4 ·2H 2 O from excessive acidic leachate and has potential industrial applications.
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