| IMO promulgated MARPOL 73/78 convention,aiming to improve the environments of marine atmosphere and port by controlling the exhaust emissions of ships.With the rapid expansion of the carrier drive system,the development of green and high-energy power system is the trend of energy-saving and emission-reduction for ships in the future.As an efficient green power system,lithium-ion batteries have been gradually applied in shipping,automobile or other transportation fields.Electrode materials are the focus.Silicon has received intense attention due to the high theoretical capacity as well as their suitable low voltage plateau,and becomes an important anode candidate for high-energy lithium-ion batteries.However,poor cycling stability limits its commercial application owing to its dramatic volumetric shrinking and expanding in the crystal lattice during cycles.In this paper,the material has been designed and optimized reasonably to prepare high-performance Si-containing anodes.In this work,four kinds of Si anode are synthesized via several facile method,and electrochemical mechanisna is also studied in detail.The main research contents and results are as follows:The core-shell Si@Nb2O5 composites are prepared via one-step solvothermal method with Si nanoparticles and NbCl5 as the precursors in ethyl alcohol,and the electrochemical performance of the as-prepared material is investigated.Si@Nb2O5 anode(Si:Nb2O5=7:3 wt%)exhibits a high reversible capacity of 1435.6 mAh g-1 at 5 C.Nb2O5 acts as the "stress buffer layer","ionic conductive layer" and "surface stability layer",coated on the surface of Si,which provides more channels to ensure the rapid diffusion of ions,and acts as an protective layer to reduce the reactivity between Si and electrolyte.Therefore,Si@Nb2O5 exhibits excellent electrochemical property.Based on the research of Si@Nb2O5 composites,Si@Nb2O5/LiNbO3(Li:Nb=3:1)with Nb2O5/LiNbO3 hybrid shell is synthesized via heating treatment.The behavior of electrolyte on the material surface and electrochemical performance of the as-prepared material are investigated.The Li+ diffusion coefficient and electronic conductivity of Si@Nb2O5/LiNbO3 electrode are calculated about 7.68 × 10-13 cm2 s-1,4.13 × 10-6 S cm-1,superior to Si@Nb2O5.LiNbO3 as the fast ionic conductor,co-blends with Nb2O5 to construct a stable solid electrolyte interface film,which makes lithium-insertion behavior controllable,acts as the buffer layer to maintain the structural stability,thereby improves the reversible specific capacity and cycle performance.Combined with the characteristics of Si-C composites,a new strategy is proposed to configure ultra-long-life Si anode by controllable chemical/physical bonding between Si and the matrix.Novel Si nanoparticles anchored in porous rGO/g-C3N4 framework(donated as Si@rGO/g-C3N4)is first synthesized,and the electrochemical performance is investigated.The Li+ diffusion coefficient and electronic conductivity of Si@rGO/g-C3N4 electrode are calculated about 9.30 × 10-14 cm2 s-1,2.18 × 10-6 S cm-1.It is demonstrated that porous g-C3N4 can provide more lithium-ion diffusion pathways to increase Li+ diffusion coefficient,induce possibly N-doping occurring in graphene sheets,leading to rapid charge transfer from rGO to g-C3N4,and thereby change the electronic properties of both.Si@rGO/g-C3N4 anode exhibits the capacity loss of only 0.019%per cycle and ultra-long cycle life of 1000 cycles at 0.5 C.Volume expansion of Si is only 200%in the period,indicating that the formation of Si-N inert nanodomains could efficiently suppress the volume expansion of silicon through confined lithium intercalation behavior.Therefore,the synergic effect of interface bonding and the configuration of 3D porous network ensures an ultra-long cycling life.In this work,moderate interface linkage to configure sandwich Si@C/rGO composite by controllable conjugated polar interaction and functional groups chemical interaction on the interface,where Si NPs are anchored on rGO proposed with PEI as a medium,and the electrochemical performance is investigated.The Li+ diffusion coefficient and electronic conductivity of Si@C/rGO electrode are calculated about 4.08 × 10-14 cm2 s-1,5.59 × 10-5 S cm-1.It is demonstrated that rGO serves as an electron conductor to provide cross-linking electron or ion channels.N-doping effectively promotes the n-type substitution of carbon atoms with graphitic nitrogen,thereby improving the electron transfer across the interface.The first coulombic efficiency is 79.0%.The capacity loss of only 0.103%per cycle at 5 C is achieved,even after 500 cycles.PEI,acts as an electrical/mechanical linking agent,derived to "Electron Bridges" and carbon nanoshell,which play a dominant role in maintaining excellent electrical connectivity and outstanding structural integrity between Si NPs and rGO framework,thereby ensuring the reuse of silicon in subsequent cycles.Therefore,Si@C/rGO anode exhibits ultra-high reversible capacity and excellent C-rates performance due to the synergistic effect of the incorporation of delicate interface control and elaborate structure configuration... |
PDF Full Text Request