Fundamental Research On Continuous Supercritical Hydrothermal Synthesis Of Lithium Iron Phosphate

As a rapid and efficient preparation technology, continuous supercritical hydrothermal synthesis technology plays an important role in the field of micro and nano particle preparation. Compared with the traditional preparation of micro-nano-particles, continuous supercritical hydrothermal process has many advantages such as short reaction time, controllable process parameters, product properties uniform, and environmental friendly. In this paper, lithium iron phosphate nanoparticles were prepared by a continuous supercritical hydrothermal synthesis process, the effects of different process parameters on product properties were investigated, and the effects of process parameters on the crystallization kinetics of products were analyzed. The main contents and conclusions are as follows:(1) A continuous supercritical hydrothermal synthesis system was constructed. LiFePO4pure spherical particles and the LiFexM1-xPO4(M=Cu, Mn and Mg. x=0.05,0.1and0.3) samples doping with different metal cations was successfully prepared.(2) The effects of temperature, pressure, feed rate, feed concentration, and Fe2+protection method on purity, crystallinity and particle size of LiFePO4product was studied. The particles of different preparation conditions were characterized by XRD, particle size distribution, scanning Characterization electron microscope, and materials were tested by cyclic voltammetry and AC impedance electrochemical methods.C3) Experimental results showed that the product particles simultaneously with the high crystal quality and uniform particle size distribution characteristics when at the condition is temperature of390℃, pressure of25MPa, the raw material liquid Li+concentration of0.06mol/L, a feed rate of20mL/min with ascorbic acid protection. The above condition was chosen as optimum preparation condition for further study. The particle obtained under the conditions of a average size of700nm, the particle morphology was uniformly dispersed, the particles were spherical particlese with wrinkles. After20laps cyclic voltammetry test, the redox potential difference is always maintained at0.203V, which show the material has a reliable lithium deintercalation reversibility and cycling stability.(4) The impact of temperature, pressure, concentration of raw materials and feed rate on the crystallization process of LiFePO4particles in supercritical hydrothermal synthesis was examined by using MSMPR crystallization model. The dynamic relationship between nucleation rate B and the growth rate G at different experimental conditions was built. Experimental results showed that the growth of LiFePO4particles was "The size independent growth" under the experimental conditions of continuous supercritical hydrothermal synthesis,. At high temperature, low pressure, high concentration and high raw material feed rate, the product with a high crystal growth rate, more prone to large particles.