| Lithium ion battery is a new kind of high-energy secondary battery which developed quickly for the system features with high working voltage, high specific energy, wide working temperature range, stable discharge, small volume, light quality and the advantages of no memory effect. The applications of lithium ion battery in vehicles and energy storage put forward higher requirements, including higher energy density, long cycle life and lower cost of the preparation etc. Among them the key to improve the energy density is to improve the electrode materials’ specific capacity. At present the mainstream cathode materials of the research and development, their theoretical specific capacity are lower than 350 m Ah/g, which means to improve the overall capacity of the battery, we have to focus on improving the anode materials’ specific capacity.Silicon due to its high theoretical specific capacity of 3579 mAh/g(Li15Si4) has been considered to be the most potential of a new generation of high-performance lithium-ion battery anode materials. In addition, Si has the advantages of lower intercalated-li potential(lower than 0.5 V Li/Li +), abundant and clean/environmental protection. However, silicon has huge volume expansion(400%) in the process of the intercalated-li, accompanying with very strong mechanical stress leads to the collapse of material, which cause to electrode structure instability and hence the cycle stability decline. In addition, its low conductivity is also the main reason that limits its development. The main method to solve the problem: 1) reduce the size or dimension of Si; 2) Si/M composite; 3) porous structure material. This work mainly focuses on the porous silicon carbon composite material, and we also explored the effect of different Si /carbon on the electrochemical properties. The main research work is as follows:1. Silicon carbon composite material related research. In this part mainly includes: 1) preparation of composite material; 2) The material performance characterization and electrochemical testing methods, including several kinds of characterization of the instrument and the commonly used method is introduced in the battery test. 3)Screening of raw materials, including screening of silicon /carbon sources and explore effect of oxidation treatment on the properties of silicon powder.2. Porous silicon carbon composite material. Through embedded SiO2 particles in advance, and removing them to get porous Si/C composite. The silica powder, sugar, carbon black were introduced into silicon slurry and then stirring 3 hours. By using the method of spray drying, the spherical particle was got. After carbonization and hydrofluoric acid, porous Si/C composite material was obtained. Due to the larger specific surface area, porous structure will need more adhesive and conductive agent. In order to improve structural stability and also electrochemical stability without sacrifice of active materials, various conducting agents were used to bridge the porous Si-C composites, including zero-dimensional(0D), one-dimensional(1D) and two-dimensional(2D) systems. VGCF and RGO can be a good bridge between porous silicon carbon particles, and porous structure can be well ease the volume expansion, thus improve the cycle stability of the battery materials.3. Through embedding different size silica particles to form different size pores in the Si/C composite. Research results show that the composite with smaller pores has a better electrochemical property, the main reason is that the smaller holes can be evenly dispersed near the silicon particles, thus in the process of silicon intercalated-li the smaller pores can ease silicon particles’ volume expansion and extend the cycle stability. |
PDF Full Text Request