The Research On The Biomimetic Synthesis And Modification About Nano-lithium Iron Phosphate Cathode Materials

This study adopted alpha amylase (a-amylase) as template, glucose as reducing agent, Fe(NO3)3-9H2O as the iron source, NH4H2PO4 as phosphorus source, LiCO3 as lithium source, successful synthesised the laminated lithium iron phosphate(LiFePO4) anode composite material, and the material had no uniform slit shape mesoporous structure.The a-amylase as template to synthesize the LiFePO4/C-FePO4 composite material with good performance by biomimetic synthesis method. The grain’s specific crystal face of the synthesized composite materials was abnormal developed, as well as the existence of slit shaped mesoporous structure was uniform, thereby reduced the lithium ion diffusion resistance in the process. The test data showed that the discharge capacity of the composite material reached 146.80 mAh ·g-1 under the 0.1 C ratio, after 160 times charging and discharging cycle, the coulomb efficiency was closed to 100%, at the same time, with the increase of cycle number, the discharge capacity was abnormal increased. By explored the influence of different firing temperature, different time, different dosage of reducing agent and different dosage of biological template on LiFePO4/C-FePO4 the cathode composite material’s crystal structure and electrochemical performance, determined the process conditions during the synthesis of composite materials for heat at 700℃ and 8 hours of firing, group allocation ratio was the 0.03 mol LiFePO4 corresponding to 2 g of a-amylase and 2.4 g of glucose.The a-amylase as template to synthesize the LiFePO4/C composite cathode material doped with silver ion by the method of co-precipitation. The a-amylase as a biological template provided the sites where the LiFePO4 crystal particles growth, reduced the interfacial impedance between the electrode and the electrolyte during the charge and discharge process. The silver element with high conductivity and formed new phase with elementaled silver among LiFePO4 grains, increased the transmission path of lithium ion in the LiFePO4 structure, so as to improve the lectronic conductivity rate in the composite and the lithium ion conductive rate in the LiFePO4 structure. The discharge specific capacity of the composite cathode material obtained after doped with silver ions reached 127.91 mAh ·g-1.The a-amylase as template to synthesize the LiFePO4/C composite cathode material with special structure by hydrothermal method and biomimetic synthesis, the microstructure of the composite was the two-dimensional carbon skeleton plate and LiFePO4 crystal phase layered distribution. The plate was micron size and one surface covered by LiFePO4 nano crystal particles with dense lattice fringes, and the other surface without any lattice fringes. Meanwhile, the two-dimensional carbon skeleton plate possessed no uniform slit shape nano-mesoporous structure. The composite showed better electrochemical performance, it’s charge and discharge specific capacity exceeded LiFePO4 theoretical discharge capacity, reached 275.2 mAh ·g-1 and 263.03 mAh ·g-1, respectively.