Study On Structure And Interface Design And Preparation Of High Capacity Silicon-based Anode Materials

With the development of high-energy density lithium-ion batteries,the high specific energy anodes are urgently required.The silicon-based anodes have high specific capacity,which are recognized as the next-generation anode for lithium-ion battery.However,the volume effect of silicon-based anodes leads to the structural and interfacial instability during cycling,which results in the limited cycling life.Additionally,the silicon-based anodes still face the technical challenges,such as high-cost and low-areal capacity.To improve the structural and interfacial stability,we systematically studied the structural design and construction of Si/C composites,the construction of polymer artificial interfaces,and the relationship between the structure and electrochemical performance,as well as the mechanism of the polymer coating on the interface chemistry.And the preparation methods of low-cost silicon anodes and the design and construction of high-area-capacity silicon electrodes were explored.The construction of a sandwich-like structural Si/C composite using the electrostatic self-assembly and the pyrolysis characteristics of melamine was carried out,and the relationship between the structure and electrochemical properties was analyzed.Structural characterization shows that silicon nanoparticles are uniformly encapsulated in a two-dimensional nitrogen-doped carbon sheets.The NRC/Si-1 shows the outstanding electrochemical performance.It maintains a high reversible capacity of 1000 m Ah/g after300 cycles at 2 A/g,which is due to the sandwich-like structure of the two-dimensional nitrogen-dopped carbon materials,enhancing the structural stability and improving the ion-electron transport kinetics.The influence of the interlayer structure on the electrochemical performance of silicon-carbon composites was studied,and the effect of the interlayer structure on the lithium ion diffusion kinetics and structural stability was analyzed.Results showed that the Ti O₂/Ti₅Si₃interlayer in the silicon-carbon composite not only effectively improves the structural stability,but also accelerates the lithium ions diffusion.The Ti O₂/Ti₅Si₃heterogeneous interlayer significantly improves the cycling performance of the silicon-carbon composite.The T-Si@C composite maintains a high reversible capacity of 876m Ah/g after 2800 cycles at 500 m A/g.The influence of the molecular layer deposited polyurea coating on the electrochemical performance and the interface chemistry of the silicon anodes were studied,and the compatibility of the polyurea coating with silicon particles of different particle sizes and different electrolytes was explored.Results showed that the～3 nm polyurea coating greatly improves the cycling stability and rate performance.Interface analysis shows that the polyurea coating can significantly reduce the decomposition of lithium salt and promote the formation of a stable thinner Li F-rich SEI interface.Simultaneously,the polyurea coating shows good adaptability to large-size silicon particles and ether-based electrolytes.The effect of the Zincone coating constructed by molecular layer deposition on the electrochemical performance and interface chemistry of silicon anodes were studied,and the evolution mechanism of Zincone coating during charge-discharge process was explored.Results showed that the～3 nm Zincone coating significantly improve the electrochemical cycling stability.Elemental analysis shows that the zinc element in the Zincone coating transformed into metallic Zn or Li_xZn alloy,accelerating the ion-electron transport dynamics in the silicon electrode.The interfacial chemistry analysis shows that Zincone coating can effectively reduce the decomposition of lithium salt and promote the formation of a Li F-rich SEI interface.The preparation of low-cost silicon anodes by using cheap waste glass as a precursor was studied.The relationship between structure and electrochemical performance was explored.The prepared silicon anode was composed of the cross-linked ultra-thin silicon nanosheets and contains a large number of mesoporous structures.Benefited from structural feature,the silicon anode shows the good electrochemical performance.More importantly,this study provides an effective way for the recycling of wasted glass.Extrusion-type 3D-printing was used to controllably construct the high areal capacity silicon-graphene free-standing electrodes,and the influence of electrode structure on electrochemical performance was explored.Results showed that the reserved space in the 3D printed grid electrode can alleviate the volume change and enhance the structural stability of the electrode,and the graphene conductive network in the electrode can provide a good electron-ion transportation channel.Electrochemical tests show that the 3D printed electrode exhibits a very high area specific capacity,and the area capacity is still as high as 8.5 m Ah/cm²after 70 cycles.The preparation of the low-cost Si/G@C composite using industrial silicon was studied,and the high-loading performance and the applications in full batteries were explored.Results showed that the silicon particles in the composite are fixed in a carbon skeleton composed of graphite and pyrolytic carbon,which greatly improves the structural stability of the silicon anode.Electrochemical tests showed that the composite material exhibits the good cycling stability and high-loading performance.In addition,the composites are successfully applied in full-cells,showing great application prospects.