Electrodeposition And Electrochemical Performance Of 3D Porous Nickel Supported Silicon/tin-based Composite Anodes For Lithium-ion Batteries

Silicon/tin-based materials with extremely high capacity are the most promosing subsititues of commercialized carbonaceous materials in order to meet the demand of next-generation high-performance lithium ion batteries,which provides high capacity,high rate capability and good cyclibility.However,the electrode will pulverize due to the volume effect of active material Si/Sn during lithiation/delithiation processes,which leads to obvious capacity fading and cyclability deterioration.Current solutions such as preparing nanostructured materials or composite materials are highly depedent of equipments and are always complicated,which are difficult to be utilized in large scale.Fabricating Si/Sn-based anode materials by electrodeposition technique is easy,controlabe and less dependent of equipments,what`s more,it can avoid the usage of conductive addtives and polymer binders,which is a good method with low cost.Though,there have been several critical issues await to be addressed.First,it is difficult to increase the deposition amount.Second,the adhesive strength between the electrodeposited materials and current collector is poor.Third,it is quite easy for the electrodeposited materials to peel off from current collector during cycling.Therefore,to investigate a useful method which could increase the deposition amount,reinforce the adhesive force between electrodeposited materials and current collector,and accommodate the great volume change of Si/Sn during cycling is of great significance to promote large-scale applications of Si/Sn-based anode materials fabricated by electrodeposition technique.Based on the above-mentioned strategy,this thesis mainly introduced the preparation of 3D porous Si-O-C/Ni and Sn-O-C/Ni composite film anode by a two-step electrodeposition method,which aimed at improving the cycling performance of electrodeposited composite anode by means of 3D highly porous dendritic structures.Meanwhile,the fabrication techniques,as well as chemical compositions and mechanism of lithiation/delithiation reactions of Si-O-C/Ni and Sn-O-C/Ni composite anode were investigated systematically.The main content of this thesis are as follows:1.The 3D porous nickel electrode was electrodeposited from inorganic plating solution containg NH₄Cl and NiCl₂·6H₂O using hydrogen dynamic template method.The electrodeposition parameter was determined with a current density of 3.0 A cm^-2 and electrodepsotion time of 60 s,which could ensure the formation of size-fitted pores with an average diameter of 5?m.The phase compositions and chemical constitutions are characterized with XRD and XPS,which indicated that the major composition was nickel,but there were Ni₂O₃ and NiCl₂ on the surface of 3D porous nickel.Furthermore,the CV measurement and galvanostatic charge/discharge tests also verified the existence of Ni₂O₃.2.The 3D porous Si-O-C/Ni composite thick film anode material was electrodeposited from organic electrolyte containing SiCl₄ with a passed charge of 10 coulombs using porous nickel as current collector.The FETEM and XPS analysis of the as-prepared electrode demonstated that the Si-O-C composite was composed of amorphous SiO_x and amorphous decomposition products of organic electrolyte comprised of elemental C and O.It was due to the effective accommodation effect of highly porous dendritic structures and amorphous decomposition products of organic electrolyte towards Si that ensured the execellent cycling performance and rate capability of the electrode.In addition,the comparative analysis of the surface morphologies of electrodes at different cycles elucidated the mechanism of capacity fading and electrode material degradation.3.The Sn-O-C composite was electrodeposited onto 3D porous nickel current collector from organic electrolyte containing SnCl₂ with a passed charge of 0.25 coulombs to construct a porous Sn-O-C/Ni composite thin film anode.The FESEM and XPS analysis demonstrated that Sn nanocrystals were dispersed in amorphous decomposition products of organic electrolyte comprised of elemental C and O.The execellent cyclability of the electrode was attributed to the effective accommodation effect of micro/nano-scale spacings between nickel dendrites and amorphous decomposition products of organic electrolyte towards Sn.The interfacial resistence of the electrode increased with the cycle number,which was attested by the EIS measurement of the electrode at different cycles upon reaching fully delithiated state.Moreover,the irrevisible volume change became more obvious as the lithiation/delithiation reactions increased also provided evidence for the capacity fading and material degradation of the electrodeposited Sn-O-C/Ni composite thim film anode.