Preparation And Properties Of Silicon-carbon Anode Materials For Lithium Ion Batteries

In recent years,with the support of the state,the field of new energy vehicles has developed rapidly,and new requirements for the performance of lithium-ion batteries have also been put forward.Energy density has become one of the key factors in the development of electric vehicles.The energy density of lithium-ion batteries It mainly depends on the positive and negative materials of the lithium ion battery.The actual specific capacity of the positive electrode material is about 160 m Ah/g.In order to improve the energy density of the lithium ion battery,we can focus on the improvement of the capacity of the negative electrode material.Silicon-based materials have high theoretical specific capacity(4200m Ah / g),suitable lithium insertion potential,and environmental protection,cheap,etc.,is considered to be a key material that is expected to replace graphite as the next generation of lithium-ion batteries;but silicon-based anode materials A large volume expansion(~320%)occurs during the intercalation process,causing the substrate to be broken and pulverized,and the electrode performance is deteriorated.At the same time,silicon is a semiconductor,the electron conductivity is low,and the rate performance is low.Adverse factors hinder the development of silicon-based anode materials.In order to solve these problems,the researchers improved the electrical properties of silicon-based anode materials by means of electrode material modification and electrolyte modification.The research directions are mainly in the following fields: material nano-crystallization,silicon/carbon composite,silicon/alloy composite,Directions such as silicon oxide.In order to improve the electrical properties of silicon anode materials,silica-carbon composites were prepared by ball milling-pyrolysis method and spray drying method.The effects of preparation process on the structure and properties of the materials were studied.X-ray diffraction,scanning electron microscopy,charge-discharge cycles were studied.Testing,cyclic voltammetry and other analytical testing methods to characterize and modify silicon-carbon composites.We prepared the silicon-carbon composite by ball milling-pyrolysis method,and determined the optimal preparation process: nano-silicon,graphite,asphalt with a mass ratio of 1:5:3,ball milling for 3h under nitrogen atmosphere,950 °C nitrogen Under high temperature pyrolysis,heat preservation for 3h,to obtain the desired silicon carbon composite material.The silicon-carbon anode material was cycled 100 times at a current density of 200 m A/g,and its capacity was stabilized at 577 m Ah/g,the capacity retention rate was 82.55%,and the first charge-discharge efficiency was 83.81%.Has the best performance.We used spray drying method to prepare spherical silicon-carbon anode materials,and verified the influence of mixing method on material properties through experiments,and obtained the best mixing method.By comparing the carbon source content of different pyrolysis carbon sources,the material properties were compared.The effect is that when the ratio of nano-silicon,graphite and PVP is 1:5:3,the initial charge-discharge efficiency of the negative electrode material is 82.04%.At the current density of 200 m Ah/g,the capacity retention rate is 70.38%.Performance,and this material exhibits relatively excellent rate performance.At current densities of 50 m A/g,200 m A/g,500 m A/g,and 1000 m A/g,the material specific capacity is 997 m Ah/g,816 m Ah/g,618 m Ah/g and 414 m Ah/g.