Synthesis Of Nano-lifepo₄ Via Hydrothermal Stripping

Olivine-structured lithium iron phosphate is the most promising cathode material for Li-ion dynamic batteries. The solution reaction method for synthesis of LiFePO₄ is the current research focus, and the nano-sized materials and modification of LiFePO₄, which are the important ways to enhance the electrochemical performance, becomes a major research field.The controlling of morphology and practical size is the key to enhance the performance of LiFePO₄, and this can be resolved by setting up an advanced solution reaction method. Herein, we describe a new method based on hydrothermal stripping technique according to coupling principle, and have successfully improved it to synthesize nano-LiFePO₄. The samples were directly synthesized by cation exchange between organic phase, which prepared with industrial FeSO₄·7H₂O and naphthenic acid, and aqueous prepared with H₃PO₄ and LiOH. The measurement results of XRD, FTIR and TEM show that the samples prepared by this method are the regular nanoparticles with single phase and uniform distribution.In this paper, the principle and some factors influencing LiFePO₄ synthesized by stripping iron (II)-loaded naphthenic acid-isooctanol system with LiH₂PO4 solution were studied in detail. The extraction percentage of Fe in different conditions was measured in order to obtain the optimal experimental condition. Some possible factors, such as the molar ratio of Li⁺/PO₄^3- in water, pH value, the amount of surfactant and reducing agent, the ratio of organic and water phase, the stripping temperature and time, stirring speed, lithium-ion source and so on, which influenced on microstructure, constitute, morphology and practical size, were investigated. The results indicated that the most significant factors are the molar ratio of Li⁺/PO₄^3-, pH value, addition of reducing agent and stripping temperature. The spherical and rod-like crystals of LiFePO₄ in the size range of 20nm-200nm were synthesized by controlling stripping conditions.Compared with other methods, such as hydrothermal synthesis, the hydrothermal stripping is a facile, fast, energy, low consumption of drugs and green synthesis (organic and water phases could be recycled) method, and more suitable for industrial production. Through contrasting the samples'performances, it was showed that the LiFePO₄ prepared by hydrothermal stripping is unique microstructure, regular morphology, smaller practical size and uniform distribution, and these lay the foundation for improving the electrochemical properties of materials.The necessary modification of materials is also the key technical measure to enhance the performance of cathode material. This paper showed some modifications including metal ion doping, carbon coating, silver coating, calcined and so on. The characterization results showed that the modification did not alter the crystal structure and morphology. The enhanced electrochemical performance of LiFePO₄ will be the focus of future work.