Preparation Of Silicon/Carbon Composite And Their Application As Anode Of Lithium-ion Batteries

Lithium-ion batteries?LIBs?are a kind of high-efficiency electrochemical energy storage device,and they have been used widely in portable electronic devices such as mobile phone,laptop,digital camera,etc.In addition,emerging electric vehicles and smart power grids in recent years make their application more expansive and promising.Along with the rapid development of these fields,there is an urgent need to improve the energy density,power density,safety performance and cycle life of LIBs.The performance improvement of LIBs need the continuous development of cathode,anode,separator and electrolyte.Silicon?Si?own high theoretical specific capacity(3579 mAh g^-1,almost10 times higher than graphite),suitable working potential,abundant resource and good environment compatibility,which make it is regarded as the most promising anode material for next-generation LIBs.However,the violent volume expansion of Si during lithiation brings many problems and prevents their practical application.Designing nanostructures and compositing with other materials can effectively restrain the volume variation of Si and improve their electrochemical profermance.In this dissertation,we attempt to utilize Si nanomaterials compositing with carbon-based materials,preparing kinds of Si/C composite and explore their application as anode of LIBs,main contents are shown as following:1.Nanoporous silicon derived from natural palygorskite as anode of LIBs.We utilize natural clay with abundant resource as precursor containing Si and fabricate nanoporous Si by magnesiothermic reduction,then prepare Si/C composite through carbon coating.When used as anode of LIBs,the Si/C composite show an initial reversible capacity above 1300mAh g^-1,and the specific capacity maintains above 1000 mAh g^-1 after 200 cycles at the current density of 200 mA g^-1,displaying excellent cycling performance.2.Carbon-coated Si nanoparticles/reduced graphene oxide multilayer anchored to nanostructured current collector as lithium-ion battery anode.We design a kind of nano current collector with three-dimensional network structure,and anchor Si nanoparticles under the synergy protection of reduced graphene oxide?rGO?and amorphous carbon onto the nano current collector,acquiring Si/rGO/C electrode without binder and conductive additive.The Si/rGO/C electrodes show superior cyclability and rate performance.When tested at the current density of 2.0 A g^-1,the electrode displays a specific capacity above 800 mAh g^-1 after 350 cycles,at a higer current density of 8.0 A g^-1,its reversible capacity maintains at 739mAh g^-1,approaching 2 times of theoretical capacity of graphite anode.3.Interfacial modification of a lightweight carbon foam current collector for high-energy density Si/LCO lithium-ion batteries.We design a kind of lightweight,inexpensive three-dimensional carbonaceous current collector,through modifying the interface between carbon current collector and silicon active layer with thin titanium layer,we acquire Si electrode without binder and conductive additive with excellent electrochemical performance.The Si electrodes show high specific capacity about 1300 mAh g^-1after 1000 cycles at the current density of 2.0 A g^-1,average decay rate for per cycle is only 0.009%.At a higher current density of 8.0 A g^-1,its reversible capacity still maintains above 1000 mAh g^-1.When paired with commercial LiCoO₂?LCO?cathode to assemble a Si/LCO full cell,it can maintain stable cyclability over 200 rounds,corresponding energy density reaches up to 479.5 Wh kg^-1,equal to 1.43 times of the graphite/LCO system.