Study On Surfactant Assisted Synthesis Of Lithium Iron Phosphate

This paper studied the supermolecular template assisted synthesis of lithium iron phosphate (LFP) in the alcohol-water system, with the surfactant sodium dodecyl sulfonate (SDS) as template. And for the first time, long-range ordered lamellar nanostructured lithium iron phosphate precursor and ordered layered nano-lithium iron phosphate polycrystalline powders were synthesized. At both high and low temperature alcohol-water system, the influence of reaction temperature, concentration of reactants, concentration of surfactant, the ratio of alcohol and water and other conditions were investigated on the structure and morphology of the product.Long-range ordered lamellar nanostructured lithium iron phosphate precursor (Pre-LFP) was synthesized at low temperature alcohol-water system. The repeat periodicity of lamellar nanostructure is 2.96nm. After sintered, the precursor transformed into crystal phase of lithium iron phosphate. There are some pore structure similar to lamellar nanostructure of clay, graphite in sintered precursor. The sintered precursor The optimum synthesis process of Pre-LFP as follows: the volume ratio of ethanol to water is 1:1, concentration of surfactant is 0.025g/mL, molar ratio of reactants Li: P (H3PO4) : Fe = 2:1:1, temperature is 115℃and reaction time is 24h. Additionally, when the volume ratio of ethanol to water is 1:1, the concentration of surfactant is 0.05g/mL, molar ratio of reactants Li: P [(NH4)2HPO4]: Fe = 1:1:1, temperature is 115℃and reaction time is 24h, ordered layered nano-lithium iron phosphate polycrystalline powders were synthesized. The thickness of layer is 20～40nm. FTIR spectra of LFP and Pre-LFP showed obvious C-H vibration absorption peaks, which indicated that both LFP and Pre-LFP formed a nano-composite with surfactant template.Well-crystalline lithium iron phosphate was synthesized at high temperature alcohol-water system. It is found that the high concentration of reactants lead to remarkable refinement of particles, while low concentration of reactants corresponded to good dispersion and regular morphology. The increasing volume ratio of alcohol to water could inhibit the generation of impurity LiFePO4(OH). However, at high temperature alcohol-water system, any results of long-range ordered lamellar nanostructure did not appear.Finally, the paper made comparisons of factors between high and low temperature alcohol-water system with surfactant assisted, also discussed the synthesis process of lithium iron phosphate and mechanism of supermolecular template at alcohol-water system. The surfactant sodium dodecyl sulfonate supermolecular template not only improved the regularity of particulate morphology, but also induced synthesis of both long-range ordered lamellar nanostructured lithium iron phosphate precursor and ordered layered nano-lithium iron phosphate polycrystalline powder. This synthesis system and method extended the application of nanotechnology in synthesizing electrode materials.