The Electrochemical Performance Of Silicon Oxide Composites Research

The electrochemical performance of SiO was investigated with galvanostatic charge-discharge cycling. The Electrochemical impedance spectroscopy (EIS) in a frequency range from 0.5MHz to 0.001Hz was conducted on SiO electrode. Different equivalent circuits were proposed for fitting the experimental results, which obtained at different voltages. According to the fitting, the kinetic of Li-ion insertion at SiO and its evolution property of surface/interface during the first discharging operation were discussed.Based on the modification of anode materials, composite material was prepared to enhance the first charge-discharge efficiency and improve the cycle performance by various methods in this dissertation. Meanwhile, the composite effects were investigated by XRD, SEM, EIS, EDS and galvanostatic discharge-charge.Silver particles were distributed on the surface of SiO powder and SiO electrode film by electroless deposition. Compared with SiO, SiO/Ag composite electrode had higher columbic efficiency, higher specific capacity and excellent cyclability. The measurement of EIS shows that the charge-transfer resistance decreases and the diffusion coefficient of lithium ion increased evidently with Ag additives, which could be attributed to good electronic conductivity of Ag.The presence of Li₂CO₃ favors the formation of more compact and conductive SEI, as a result, initial irreversibility was significantly reduced; in addition, high reversible specific capacities and good cycle performance can obtained for cobalt oxides. SiO_x/CoO and SiO/Li₂CO₃ composite materials were prepared by mechanical ball-milling. The structures of the obtained materials were characterized by XRD, and SEM of three samples after 20 cycles were also given. The results from galvanostatic discharge-charge show that the composite samples have larger initial reversible capacities and better cycle performance than pure SiO. Also, a schematic diagram showing the buffer effects of Li₂CO₃ addition and the mechanism of improving electrochemical performance by adding Li₂CO₃ are put forward.Amorphous carbon coated SiO material was synthesized by dip-pyrolyzed method. Results from galvanostatic discharge-charge indicate that carbon is in favor of enhancing the first charge-discharge efficiency and improving the cycle performance of SiO electrode. EIS show that the charge-transfer resistance decreases and the diffusion coefficient of lithium ions increases after amorphous carbon coating. SiO/MWNTs anode was prepared by mixing SiO particles with Multi-Walled carbon nanotubes as conductive agent. The results show that the SiO/(20%)MWNTs composite anode shows a initial specific reversible capacity of 1463.9 mAh·g^-1, much higher than 582.3 mAh·g^-1 for SiO/(20%)AB. The results of SEM and EIS confirm that the excellent cycle performance is attribute to the perfect flexibility and good electric conductivity of MWNTs network, while SiO/AB has larger interparticle contact resistance, which is resulted from the crumbling and conduction network breakage.