Novel Energy Source Materials-Study On The Electerode Materials For Electrochemical Capacitor And Lithium Ion Battery

On account of high potential window, large energy density, long cycle life, low self discharge rate and green environmental conservation, lithium ion battery has attracted much attention and applied widely in portable electric instruments at present, which is developing towards the fields of space technology, national defense industry, electronic vehicle and uninterrupted power supply. The key of lithium ion battery is the successful exploitation of insertion electrode materials, and nowadays the main attack has reformed techniques, decreased costs and improved on performances. Electrochemical capacitor is a new type of energy storage equipments with high power characteristics and good cycle life. It can be used as not only the backup power sources for computers and all kinds of electric instruments, but also the driving power systems for electric vehicle combined with lithium ion batteries. Therefore, electrochemical capacitor is also one of the hotspots in new type of chemical energy sources studies.In this thesis, we have reviewed the newest development in research of electrode materials of both lithium ion battery and electrochemical capacitor devices, prepared relevant electrode materials and explored their applications in these two kinds of devices in detail. The micro-structures and morphologies of these materials were investigated by XRD, SEM, TEM , IR measurements. The electrochemical performances have been evaluated by galvanostatic charge-discharge, cyclic voltammetry (CV) and electrochemical impedance spectra (EIS). The charge-storage capability of the electrodes materials has been discussed mostly. The main content is the following:We have proposed a new strategy to synthesize a series of zeolite-based metal hydroxides or oxides by a liquid-precipitated method, which used the super-stable Y zeolite as the template, and applied these materials in the electrochemical capacitor fields. Particular discussions were conducted on the zeolite-based composite materials of anisotropy morphology, electrochemical capacitive characteristics, electrochemical reaction mechanism and electrode dynamics performances. The results have shown that the pored compound has a highly dispersed morphology in three-dimensional space and a loosely packed microstructure in the nanometer scale. The special microstructure can accommodate the electroactive speciesnot only on the surface but also in the solid bulk, which is very helpful for making full use of the electroactive sites to take place the faradic reaction, and contributed to the excellent capacitive characteristics. For example, the composite of Co(OH)2/USY (28 wt% loading Co(OH)2) shows the specific capacitance of 958 F/g, even more than the capacitive behavior of hydrous RuC?2 in the acid medium, and approximately 98% of the theoretical value. The new strategy has opened the great potential fields of the zeolite materials, and obtained the best electrochemical capacitive values of supercapacitors.A new low-temperature synthetic route has been developed and demonstrated for the production of spinel LiMn2O4 and doped LiMn2O4 as cathode materials for lithium ion batteries. Primary efforts have been focused on exploring the relationships among the synthesis conditions, structural changes, and the electrochemical performances. Based on the role of glucose, we have initially proposed the reaction mechanism. Combined with the existing results, we have finally concluded that both glucose and reactive temperature played very critical roles in the formation of preferable spinel LiM^CV And the optimized reactive parameter is at 200°C with the presence of glucose. The hydrothermal synthesized spinels have shown better cyclability compared with those by annealing process. On the other hand, the doped spinel oxides are better than the pure spinel ones on the electrochemical performance, and Al3+, F* co-substituted spinels had the best combination of initial capacity and capacity retention among all these samples, having the initial capacity of 115 mAh/g and maintained more than 90% of the initial value at the 50th cycle. This hydrothermal procedure is a simple, efficient, good-performance, environmentally friendly method to synthesis ofIn view of the insulative behavior of zeolite material, it decreased the electric conductivity of the composite to some content and held back the applications in the energy storage fields. Combined with the active carbon of good characteristics, an asymmetric electrochemical capacitor using zeolite-based composite and active carbon (AC) as positive and negative electrode, respectively, has been designed. For example, as the Co(OH)2/USY composite, the results showed that the asymmetric supercapacitor has excellent capacitance of 110 F/g, which is the highest value of the metal hydroxides or oxides in the aqueous solution. The corresponding potential window has increased from 0.45 to 1.5 V. All these profit fromusing the active carbon as the negative electrode materials with large surface and proper pore distribution, which ensure the zeolite-based composite proceed with the faradic reaction in the larger applied potential range. The hybrid supercapacitor exhibits improved power and energy performances by the increased potential window, particularly in the larger current density. As for the Ni(OH)2/USY composite, the increased window potential is less than Co(OH)2/USY, ranging from 0.45 V to 0.9 V. The electrochemical impedance spectra indicate that the charge transfer resistance is large, which is difficult for storage of charges in the low potential, and the conductivity of Ni(0H)2 is less than that of the Co(OH)2, attributed to the limited potential increasing.