Study On Synthesis And Characteristics Of Anode Material Of Lithium-ion Battery

Silicon is promising anode material of Li-ion rechargeable batteries, with high theorical capacity about 4200 mAh/g, ten times higher than the common graphite anode material (372 mAh/g). However, as anode material of Li-ion rechargeable batteries, silicon will experience some 400% volume expansion during cycling due to the lithiaon. Volume expansion will lead to fracture and capacity will decrease as result. To solve this problem, various structures, including hollow silicon sphere, silicon nanowire, silicon-carbon composite material, has been studied.In this paper, hollow silicon sphere was chosen as the object of research firstly. Silicon was fabricated through magnesiothermic reduction, using silica as precursor. During magnesiothermic reduction procedure, reaction system had been adjusted several times and finally settled as that a stainless steel box with silica powder in it and a stainless steel copple with magnesium powder in it were placed in a vacuum quartz tube separately. The final sample was identified as crystalline silicon.To fabricate samples with hollow sphere structure well preserved, silica precursor was coated with carbon via hydrothermal method. During magnesiothermic reduction, SiC was synthesized in the reaction between carbon and silicon. With SiC acting as supporting matrix, Si-SiC composite with well preserved hollow sphere structure was fabricated. The structure of final sample was characterized by SEM and TEM. It has large BET surface area of 150.33 m2/g and pores with diameter around 12.9 nm according to Nitrogen absorption-desorption test. XRD, XPS and TG-DSC were all performed to identify the structure and composition of the Si-SiC composites.During synthesis of hollow silicon sphere and Si-SiC composite, the silica precursor was also considered as anode material. It turned out that silica anode material exhibited better performance than silicon anode material. Silica with different structure was tested as anode material, among which hollow silica sphere with carbon coating and silica-carbon bicontinuous composite sphere had best electrochemical performance. Compared to silicon anode material, silica anode material had better cycling performance. Silica-carbon bicontinuous composite sphere anode material exhibited increasing capacity as the cycle went on.Li4-Ti5O12 is typical anode material with good cycling performance. During lithiation and delithiation, the volume of Li4Ti5O12 hardly changed. The electric potential vs Li+/Li is as high as 1.5 V, which can significantly avoid the decomposition of electrolyte. In this paper, Li4Ti5O12 was prepared via high temperature solid-state method and some of the sample was calcined in air and the other was calcined under N2 atmosphere. Without carbon coating, Li4Ti5O12 calcined in air showed better electrochemical performance. The initial charge and discharge capacity were 132.9 mAh/g and 151.7 mAh/g respectively, with good charge-discharge voltage plateau.