A facile route to modify ferrous phosphate and its use as an iron-containing resource for LiFePO4 via a polyol process

Novel Synthesis of 3D Mesoporous FePO4 from Electroflocculation of Iron Filings as a Precursor of High-Performance LiFePO4/C Cathode for Lithium-Ion Batteries

This study presents an economic and environmentally friendly method for the synthesis of microspherical FePO₄·2H₂O precursors with secondary nanostructures by the electroflocculation of low-cost iron fillers in a hot solution. The morphology and crystalline shape of the precursors were adjusted by gradient co-precipitation of pH conditions. The effect of precursor structure and morphology on the electrochemical performance of the synthesized LiFePO₄/C was investigated. Electrochemical analysis showed that the assembly of FePO₄·2H₂O submicron spherical particles from primary nanoparticles and nanorods resulted in LiFePO₄/C exhibiting excellent multiplicity and cycling performance with first discharge capacities at 0.2C, 1C, 5C, and 10C of 162.8, 134.7, 85.5, and 47.7 mAh·g^-1, respectively, and the capacity of LiFePO₄/C was maintained at 85.5% after 300 cycles at 1C. The significant improvement in the electrochemical performance of LiFePO₄/C was attributed to the enhanced Li⁺ diffusion rate and the crystallinity of LiFePO₄/C. Thus, this work shows a new three-dimensional mesoporous FePO₄ synthesized from the iron flake electroflocculation as a precursor for high-performance LiFePO₄/C cathodes for lithium-ion batteries.

Phosphate Recovery from Aqueous Solutions via Vivianite Crystallization: Interference of FeII Oxidation at Different DO Concentrations and pHs

Vivianite (Fe₃(PO₄)₂·8H₂O) crystallization has attracted increasing attention as a promising approach for removing and recovering P from wastewaters. However, Fe^II is susceptible to oxygen with its oxidation inevitably influencing the crystallization of vivianite. In this study, the profile of vivianite crystallization in the presence of dissolved oxygen (DO) was investigated at pHs 5-7 in a continuous stirred-tank reactor. It is found that the influence of DO on vivianite crystallization was highly pH-related. At pH 5, the low rate of Fe^II oxidation at all of the investigated DO of 0-5 mg/L and the low degree of vivianite supersaturation resulted in slow crystallization with the product being highly crystalline vivianite, but the P removal efficiency was only 30-40%. The removal of P from the solution was substantially more effective (to >90%) in the DO-removed reactors at pH 6 and 7, whereas the efficiencies of P removal and especially recovery decreased by 10-20% when Fe^II oxidation became more severe at DO concentrations >2.5 mg/L (except at pH 6 with 2.5 mg/L DO). The elevated degree of vivianite supersaturation and enhanced rate and extent of Fe^II oxidation at the higher pHs led to decreases in the size and homogeneity of the products. At the same pH, amorphous ferric oxyhydroxide (AFO)─the product of Fe^II oxidation and Fe^III hydrolysis─interferes with vivianite crystallization with the induction of aggregation of crystal fines by AFO, leading to increases in the size of the obtained solids.

Controlled Hydrothermal/Solvothermal Synthesis of High-Performance LiFePO4 for Li-Ion Batteries

The sluggish Li-ion diffusivity in LiFePO₄ , a famous cathode material, relies heavily on the employment of a broad spectrum of modifications to accelerate the slow kinetics, including size and orientation control, coating with electron-conducting layer, aliovalent ion doping, and defect control. These strategies are generally implemented by employing the hydrothermal/solvothermal synthesis, as reflected by the hundreds of publications on hydrothermal/solvothermal synthesis in recent years. However, LiFePO₄ is far from the level of controllable preparation, due to the lack of the understanding of the relations between the synthesis condition and the nucleation-and-growth of LiFePO₄ . In this paper, the recent progress in controlled hydrothermal/solvothermal synthesis of LiFePO₄ is first summarized, before an insight into the relations between the synthesis condition and the nucleation-and-growth of LiFePO₄ is obtained. Thereafter, a review over surface decoration, lattice substitution, and defect control is provided. Moreover, new research directions and future trends are also discussed.