Synthesis And Properties Of Electrode Materials For Lithium Ion Batteries

With the rapid consuming of fossil energy, global warming, environmental pollution, and the political crisis and war which caused by the energy crisis, energy has been one of the most hot topic in the 21st century. As a result, funding some new energy and energy storage materials, to current counties governments and science & research circle, became one of the emergent tasks. Due to the high operation voltage, high specific energy and low self-discharge, lithium-ion batteries have aroused wide concern. So, build on the predecessors’excellent researches, we did some researches as follows:1. On the basis of predecessors’researches about simple binary transition metals compounds (such as transition metals oxides, sulfids) as anode materials for lithium ion batteries, we used FeSO4@(NH4)2SO4·6H2O, oleic acid, NaOH and CH3CH2OH as raw materials, synthesized a-FeOOH nano-rods though LSS(liquid-solid-solution) method and hydrothermal reaction. Using IR(Infrared ray)、XRD (X-ray diffraction)、HRTEM (high resolution transmission electronmicroscope)、SEM(scanning electron microscopy)、SAEDs (Selected Area Electron Diffractions) and charge-discharge tested the properties and the electrochemical performance of the material as lithium ion batteries anode. Moreover, based on the results of XRD、SAEDs and HRTEM, which tested at different charge/discharge stage, we deduced the mechanism of a-FeOOH as anode materials for Li-ion batteries. The results showed that a-FeOOH and the transition metals oxides had the similar mechanism, the OH- of a-FeOOH does not affect the insertion and remotion of Li ion in the material. The mechanism is described as follow:The first discharge:a-FeOOH+3Li++3e-→Fe+LiOH+Li2OThe following circles:2/3Fe+Li2O(?)1/3Fe2O3+2Li++2e-These results are excellent supplements to the transition metals compounds as anode materials for lithium ion batteries.2. On the base of research 1, useing KMnO4 and cetyl trimethylammonium bromide (CTAB) as raw materials, we synthesized y-MnOOH nanowires by hydrothermal reaction. HR、XRD、HRTEM、SEM、SAEDs and charge-discharge were used to inspect the properties and the electrochemical performance of the material as anode materials for lithium ion batteries. Moreover, based on the results of XRD、SAEDs and HRTEM which tested at different charge/discharge stage, we deduced the mechanism of y-MnOOH as anode materials for Li-ion batteries. The results showed the reaction mechanism is similarity to that of a-FeOOH:The first discharge:y-MnOOH+3Li++3e-→Mn+Li2O+LiOHThe following circles:Li2O+3/4 Mn (?)2Li++1/4 Mn3O4+2e-These results proved the mechanism of the transition metal hydroxyl compound as lithium ion batteries anode is universality.3. To overcome the conflict between high-rate performance and high tap densinty of newly lithium ion batteries cathode material LiFePO4, by using Fe(NO3)3·9H2O, sodium dodecylsulfate (SDS) and H3PO4 as raw materials, though hydrothermal reaction, we synthesized "micro-nano structure" FePO4·2H2O quasi-microspheres (secondary structure) which build by nano-plates (primary structure). Then, by lithiating the FePO4·2H2O quasi-microspheres via rheological phase reaction, we synthesized the "micro-nano structure" LiFePO4/C composite which composed of nanoplates with 30 nm thickness and 150 nm length, and even coated thin carbon. We used XRD、TG (Thermogravimetric)、HRTEM、SEM、EDX(Energy Dispersive X-Ray Fluoresence Spectrometer)、Raman spectrum to explore the electrochemical properties of the material as cathode materials for lithium ion batteries, and the results revealed the "micro-nano structure" LiFePO4/C exhibited excellent high-rate capability, with discharge capacities reaching 116,96 and 75 mAh g-1 at 10 C,20 C and 30 C current rates, respectively. Furthermore, the LiFePO4/C material had a relative high tap density (1.4 g cm-3).4. Based on the work 3, we optimized the parameters of synthesizing FePO4·2H2O via hydrothermal reaction. And the parameters of lithization time and temperature during the rheological phase reaction also discussed. Finally, we get the optimization condition to synthesizing the "micro-nano structure" LiFePO4/C.5. To simplify the processes of research 3 and increase the feasibility of industrial application, using the same materials, though water bathe method and rheological phase reaction lithition, we synthesized microsphere LiFePO4/C composite which composed of nanoplates. This material delivered discharge capacity about 162 mAh/g、155 mAh/g、137 mAh/g、102 mAh/g and 97 mAh/g when charged/discharged with rates of 0.1 C、0.5C 1C、5C and IOC. Moreover, this LiFePO4/C has a relative high tap density about 1.4 g cm-3 So, this microsphere LiFePO4/C with hierachical nanoplates would have good application future.