Structure Design And Properties Of Silicon Anode For Lithium-ion Battery

Lithium-ion battery has obtained the most common application through the long-term development.With the upgrading of portable electronic devices caused by the technological innovation and pure electric vehicle development trends,the requirements for high energy density and cycle performance of commercial lithium-ion battery are gradually increased.As the most critical part of lithium-ion battery,the lithium storage capacity and electrochemical stability of electrode materials directly determines the external output performance of the battery.The development of cathode material is hampered by their limited types,therefore the exploitation and modification of novel anode materials have become the focus attention of research workers.The silicon material is one of the anode materials which have been found to possess ultra-high lithium storage capacity.The maximum theoretical specific capacity is more than 12 times higher than that of the commercial graphite anode.However,the lithium intercalation reaction of the silicon anode is accompanied by severe volume expansion,material pulverization,rapid capacity attenuation and other defects,which greatly hindered its practical application.Therefore,the modification of the silicon anode,especially the measures to maintain the stability of the electrode structure during cycling needed to beextensively studied.In this thesis,a simple layered structure designed and Cu₂O coating treatment were investigated to improve the cycling stability and capacity retention rate of the silicon anode material.The first part of this work started with the direction of the integral structure of the electrode assembly,which attempted to introduce the intermediate layer between the silicon active material and the current collector to achieve the supporting and stress buffering during the process of silicon material volume changes to maintain integral structure stability of the electrode and then guaranted the electrochemical reaction proceeds continuously and reversibly.The second part of this work was focused on the directly coating on the silicon electrode material.This coating not onlybuffered the stress but also enhanced the efficiency of electron transport,and supressed the side reaction between the silicon material and the electrolytic solution.The detail experimental results and conlusions are as follows:?1?The titanium dioxide nanotube arrays were grown directly on the titanium substrate by simple anodic oxidation,in which the titanium plate acted as a current collector and the titanium dioxide nanotube arrays served as an intermediate support layer.The mixed slurry of the silicon material,the conductive agent and the binder was applied to titanium dioxide nanotube arrays by a conventional coating method so as to form a double-layer structure electrode.The galvanostatic charge/discharge test results indicated that the initial discharge specific capacity of the double-layer electrode was 3748.1 mAh/g at a current density of 500 mA/g.After 120 cycles the capacity was finally naintained as 1201.2mAh/g.In contrast,the pristine silicon electrode'capacity decayed rapidly,and ultimately decreased to 110mAh/g.The electrode morphology analysis before and after the charge/discharge cycling showed that the electrode structure did not show any obvious damage after the introduction of the support layer,while the pristine silicon electrode displayed a lot of cracks and pulverization.These results indicate that the enhancement of the discharge capacity and cycling performance of the double-layer sturcyure silicon electrode mainly come from the effective suppression of the big volume changes,and the maintaing of structural integrity.?2?The silicon material coated with cuprous oxide nanoparticles was fabricated by one step thermal reduction and co-stirring.Phase analysis and microscopic morphological characterization,show that thecuprous oxide formed by the reduction reaction on the surface of the nano-silica particles were gradually aggregated to form a 10 nm coating layer.The electrochemical performance test indicated that the silicon electrode coated with cuprous oxide showed improved cycling stability and specific capacity.After 80 charge/discharge cycling with a current density of 300mA/g,the specific capacity was 827.5mAh/g.And after the introduction of double-layer electrode stucture,the capacity retention rate has been further improved and eventually stabilized at 994.8mAh/g.The above results show that the cuprous oxide coating is beneficial to the cycling performance of silicon material.The materials coting combined with the double-layer electrode structure introduction,can jointly improve the electrochemical properties of the of the silicon anode materials.