The Preparation And Properties Of Anode Composites For Sodium-Ion Batteries

With the development of economy and society,more and more natural resources have been consumed,resulting in a lot of problems such as resource shortage and environmental pollution.To promote the development of science and technology,it is an important way of scientific advancement to improve the utilization of renewable resources and develop new energy-materials.Lithium-ion batteries?LIBs?have been widely used as energy storage devices owing to their high energy density and long cycling life,and they have been applied commercially.However,lithium resources are relatively limited,so large-scale applications of LIBs has become challenges in terms of their availability.The element of Na is abundant and the price is relatively low.The energy storage of sodium-ion batteries?SIBs?is similar to that of LIBs.Therefore,SIBs have been regarded as a promising substitution for LIBs in a large-scale energy storage system.Most of researches were focused on the cathode materials in SIBs,but it's difficult to apply graphite material to SIBs,so further researches and improvements should be made for anode materials in SIBs.Metals and metal oxides with an advantage of high capacity have a good prospect of application as anodes.Since the radius of Na⁺is larger than that of Li⁺,this kind of materials often undergo large volume changes during charge-discharge process,bringing about structural collapse and severe capacity decay.In this thesis,metals and metal oxides were modified by structural design and combined with carbon to improve structural stability,rates performances and cycling life,thus getting excellent anode materials as SIBs.The detailed contents could be seen as follows:?1?Well ordered mesoporous Fe₂O₃/C composite?denoted as M-Fe₂O₃/C?is prepared by taking mesoporous SiO₂?SBA-15?as a hard template.Fe₂O₃/C composite prepared by a co-impregnation method has a rod-like morphology and well-ordered mesopores.Fe₂O₃ particles dispersed into carbon make up Fe₂O₃/C wall,and those mesoporous channels in M-Fe₂O₃/C composite provide buffer space for the expansion of active material,contributing to contact with electrolyte and helping Na⁺transportation.M-Fe₂O₃/C material has a large surface area that offers active sites,helping Na⁺diffusion.Nano-sized Fe₂O₃ particles reduce the diffusion distance of Na⁺.Carbon as a matrix can not only alleviate large volume changes for Fe₂O₃ particles during charge-discharge,but also enhance the insertion and extraction of Na⁺,contributing to extra capacity for the whole electrode.When comparing with M-Fe₂O₃/C materials in different raw material ratios,M-Fe₂O₃/C-2 anode material with 36.7%?mass ratio?shows the capacity of 272.5 mA h g^-1 after 100 cycles at the current density of 100 mA g^-1?ranging from 0.01 to 3 V?.When cycling300 times under relatively high current density(2000 mA g^-1),M-Fe₂O₃/C-2 anode still has the capacity of 101.9 mA h g^-1,showing its high capacity and superior rate cycling stability.Also this co-impregnation method can be applied in other kinds of raw materials,producing many metal or metal oxides/carbon composites with similar structures,which has a reference meaning for manufacturing materials with special morphology.?2?When using SbCl₃ and ascorbic acid as raw material,antimony materials coated with carbon were prepared after hydrothermal treatment,which were named as Sb₂O₃/Sb@C composite.This composite has a spherical morphology,and Sb₂O₃/Sb materials are dispersed in the core of carbon nanospheres.The diameter of carbon nanospheres are at the range of 400-600 nm and that of Sb₂O₃/Sb particles are 40-60 nm,no obvious agglomeration is observed for the Sb₂O₃/Sb particles.When applying Sb₂O₃/Sb@C composite to SIBs,the injection of antimony materials can enhance the capacity of Sb₂O₃/Sb@C electrode comparing with the pure carbon nanosphere electrode.Such anode exhibits excellent cycling stability and rate performance as well.Especially when working at the current density of 5000 mA g^-1,discharged capacity of 115.5 mA g^-11 can be achieved after cycling 3000 times,which has showed a quite long cycling life and good capacity at high current density.Spherical structures are still maintained from the battery pole piece after cycling 200 times,illustrating a good structural stability for the Sb₂O₃/Sb@C composite.So this composite has a promising application prospect for large-scale energy storage system.