Preparation And Electrochemical Performance Of High-capacity Electrode Materials For The Energy Storage Systems

Along with the rapid development of the economy, there are more and more renewable energy deveice are used, such as the lithium ion battery and supercapacitor. However, the high manufacture cost of their electode materials become a big issue in the corresponding industry. Therefore, the development of low cost electrode mateials becomes the foucs of our research. We used TG, XRD, SEM, Raman, CV, EIS, as well as electrochemical testing method to study the optimized synthesis process of the electrode mateials and the detailed information are listed as following:(1) LiFePO4nanoparticles coated with a carbon layer have been synthesized by a hydrothermal reaction-calcination process, using Fe2O3as an iron source and ascorbic acid as carbon source. The amount of ascorbic acid can have an effect on the structure, phase and carbon amount of the final product. With1g ascorbic acid used in the reaction, the particle sizes of synthesized LiFePO4/C nanocomposites are in a range of220-280nm. When used as cathode materials for the lithium-ion batteries, the as-prepared material shows high capacity and good cycle stability (159mAh/g at0.1C over500cycles), as well as good rate capability.(2) FeSO4was used as the iron source, LiOH as lithium source, P2O5as the phosphorus source, ethylene glycol and water were used as co-solvent for the preparation of the LiFePO4. After hydrothermal reaction at200℃and calcined at700℃, hollow LiFePO4/C nano-composites were obtained. After investigating the reaction conditions on the final product, the reaction mechanism of the LiFePO4/C compostite was illustrated. Electrochemcial perfoamce demonstreated the material can be a good candidate for the lithium ion battery.(3) A simple and convenient Ostwald ripening route to the morphology and phase controlled preparation of cage-like LiFePO4/C microspheres is developed. By selecting appropriate experiment conditions for ripening, the phase of the microspheres can be controlled. The possible formation mechanism for the LiFePO4hierarchical microstructures have been presented in detail. As the cathode material for lithium batteries, the as-prepared LiFePO4/C composite exhibits excellent cycle stability (163mAh/g at0.1C up to100cycles) and good rate capacity (119mAh/g,10C).(4) Self-assembled hierarchical nest-like LiFePO4microstructures from nanoplates have been synthesized by an ethylene glycol-mediated solvothermal route using Li2SO4,Fe(NO3)3·9H2O and P2O5as raw materials. It was found that EG not only played multifold roles in the formation process of such unique LiFePO4hierarchical microstructures, but also acted as carbon source during the heat treatment and forms conductive carbon coating on the surface of the LiFePO4nanoplates. In addition, employing P2O5instead of other phosphorus sources was necessary for the formation of such unique microstructures. The possible formation mechanism for the LiFePO4hierarchical microstructures have been presented in detail. As the cathode material for lithium batteries, the as-prepared LiFePO4architectures exhibit excellent cycle stability (158mAh/g at0.1C up to100cycles) and good rate capacity (120mAh/g,10C). The desirable electrochemical performance can be attributed to such unique microstructure, which could remain structural stability for long-term cycling. Furthermore, the nanoplates as the building blocks can improve the electrochemical reaction kinetics and finally promote the rate performance.(5) A green and efficient method is present to synthesize porous carbon with different morphologies from metal organic framework (MOF) using glucose, resorcinol and formaldehyde as carbon precursors, respecively. Two methods were adopted to introduce the carbon to the MOF. All the carbon precusros were demonstrarted to penetrate into the external surface and/or voids of cubic-shape MOF, then polymerized and carbonized. Meantime, MOF was decomposed into ZnO, which was further reduced by carbon (or CO) into Zn. And Zn would evaporate during the carbonization process, forming a continuous carbon texture. When the synthesized porous carbons were applied as electrode materials for electric double layer capacitor, we found the materiasls can be performance better in a suitable electrolyte.