A Study Of Silicon/Carbon Material As Anode Electrode Of Lithium-ion Battery

Nowadays,with the rapid development of industrialization and informatization,people put forward high demand for new energy device.Green and high-efficient devices such as electric vehicles become the most important part of future development.Lithium-ion batteries have become one of the research hotspots because of their high energy density and green sustainable development characteristics.Silicon anode is one of the best alternatives to replace graphite anode(372 mAh g-1)because of its high theoretical capacity(4200 mAh g-1).However,the shortcomings of silicon anode exist such as poor conductivity,unstable SEI film,especially as high as 400%volume expansion,which greatly limits the application of silicon in commercial lithium-ion batteries.The purpose of this thesis is to release the huge volume change,improve the conductivity and stabilize SEI film while keeping a high theoretical capacity of silicon anode.For this purpose,we use carbon-based materials as the matrix or coating materials to keep the advantages of silicon anode electrode while solve the problems as-mentioned above.The experimental scheme is listed as follows:(1)The nano-Si and expanded graphit or other carbon matrix are combined to form micro-particle by spraying drying.Then,the final composite anode materials were prepared by decomposition of acetylene.We also study the morphology and electrochemical properties of expanded graphite and Si at different ratios.It is indicated that 50%expanded graphite/Si/carbon materials and graphene oxide/Si/carbon materials have better cycling performance.(2)More negative charges are attached onto the surface of SiO2 by adsorbing poly(diallyldimethylammonium chloride)and poly(4-styrenesulfonic acid),then copper ions are attracted onto the surface of SiO2 by electrostatic attraction principle.Subsequently,copper is reduced and deposited on SiO2 by borane dimethylamine complex.SiO2 is reduced to Si by magnesium-thermal reaction after the deposition of carbon layer on SiO2@Cu.Lastly,the litchi core-shell Si@C anode material is obtained by removing the excess impurities such as Cu and MgO.Compared with Si@C material without copper,litchi-type Si@C anode has obvious improvement in structure,cycle,coulomb efficiency and impedance.