Study On The Preparation And Performance Of Graphene-based Silicon-carbon Anode Materials For Lithium-ion Batteries

Lithium ion battery is the most promising energy storage devices due to its excellent electrochemical performance and environmental friendly.The main factor limiting the development of lithium ion battery is electrode material.Silicon has the highest theoretical capacity,low potential for lithium insertion and extraction,as well as abundant resourse and low cost.However,the practical utilization of Si as anode material is hindered by its huge volume changes/shrinkage during the lithium-ion insertion and extraction process,cause the pulverization of materials as well as activity materials falling from the electrode.In addition,the low electric conductivity of pristine Si and the difficulty in the formation of stable solid-electrolyte interphase(SEI)films have also restrained the commercialization of Si anode materials.In this paper,silicon and graphene are combined to prepare graphene based silicon/carbon composites,which can effectively inhibit the volume expansion of silicon according to the flexibility of graphene,improve the electric conductivity of silicon and ionic transport of lithium ions,and thus enhance the electrochemical properties of silicon.The experimental results are summarized as follows:1.Study of self-standing carbon coated silicon/reduced graphene oxide(C@Si/rGO)film to synergetic protect the silicon as high-performance anode material.Firstly,polydiallyl dimethy lammonium chloride(PDDA)are used as coating carbon precursor to charging the Si particles with electropositive properties.Then,self-standing C@Si/rGO film electrode are prepared by electrostatic assembly PDDA@Si with graphene oxide after pyrolysis(500?,Ar).The PDDA was converted to an inner amorphous carbon layer and tightly anchor on the graphene sheets.The electrode material presents a flexible self-supporting structure,which can alleviate the volume expansion of silicon particle during the lithium ion insertion/extraction,ensure good electrical contact between silicon particle and reduced graphene.Thus the self-standing C@Si/rGO film electrode show a high reversible capacity of 1002 mAhg-1 over 100 cycles at 0.2A g-1 and exhibited much better rate capability for lithium-ion batteries.2.Study of self-assembly encapsulation of Si in N-doped reduced graphene oxide as lithium ion battery anode.We utilized hydrothermal process to prepare a highly dispersed silicon/nitrogen doped reduced graphene oxide(Si/N-doped rGO)by electrostatic self-assembly of Si particles and GO via surface modification of Si particles with(3-Aminopropyl)triethoxysilane(APTES).Three different nitrogen configurations(pyridinic N,pyrrolic N,and graphitic N)were confirmed,introducing abundant vacancies and defects to facilitate the Li ions diffusion,and improve the electron conductivity and electrochemical activity of Si/N-doped graphene composite.Therefore,the Si/N-doped rGO composite material shows an excellent electrochemical performance,retaining a high reversible capacity of 1391 mAhg-1 over 100 cycles at 0.2A g-1.3.Study of self-assembly encapsulation of Si in N,S-co-doped reduced graphene oxide(Si/N,S co-doped rGO)as lithium ion battery anode.Finally,highly dispersed silicon/nitrogen,sulfur co-doped reduced graphene oxide(Si/N,S co-doped rGO)were also fabricated by use thiourea both as nitrogen and sulfur source.The rGO nanosheets presented many large voids in the Si/N,S co-doped rGO composite due to the introduction of sulfur atoms,which could alleviate the volume expansion of silicon during the electrochemical process.On the other hand,nitrogen,sulfur doped in graphene structure could improve the diffusion of lithium ion.Thus,the Si/N,S co-doped rGO exhibits high capacity retention,which displayed a high reversible capacity of 1570 mAhg-1 over 65 cycles at 0.2A g-1 with high capacity retain of 90.6%.