Preparation And Properties Of Zinc Stannate And Carbon Materials Composites For Anode Materials For Lithium Ion Batteries

Zinc stannate represents two kinds of compound?ZnSnO₃ and Zn₂SnO₄?.It has been widely used in the fields of gas sensing,nanogenerator,photo-catalysis and solar cells due to its stable chemical and physical properties.In addition,zinc stannate possesses high electrical conductivity and excellent electron mobility compared with binary metallic oxides.Also,the theoretical capacity of ZnSnO₃ and Zn₂SnO₄ is 1320 mA h g^-1 and 1494 mA h g^-11 respectively.Therefore,zinc stannate can be an alternative candidate for anode materials of lithium ion batteries?LIBs?.However,there is an unavoidable problem-the loss of cyclic performance due to the pulverization and agglomeration during the charge-discharge process.At present,the main means to deal with this problem are preparing zinc stannate with different morphologies such as hollow spheres and hollow cubes and synthesizing different three-dimensional composites.As for the preparation process of negative electrodes of LIBs,the common method is to coat the slurry made with active materials,binders and conductive agent on copper foil or aluminium foil.This mechanical combination cannot help to release or retard the volume change and pressure during the charge-discharge processes,which accounts for the pulverization and agglomeration of active materials.As a result,fabricating free-binder,preparing freestanding and flexible electrodes is a great way to tackle these problems.This thesis mainly studies zinc stannate as anode materials of lithium-ion batteries including the preparation of ZnSnO₃-rGAs and Zn₂SnO₄-carbon cloth their electrodes'electrochemical properties.In addition,this work focuses on the crystalline structure of‘orthorhombic perovskite ZnSnO₃'.The main contents and conclusions of this thesis are as follows:First,3D porous ZnSnO₃-rGAs with large specific area,excellent mechanical properties and electronical conductivity was prepared by the hydrothermal method.The electrochemical performance of ZnSnO₃-rGA electrodes has been largely improved.After 200 charge-discharge cycles at the current density of 100 mA/g,it still delivered a capacity of 780 mA h/g while ZnSnO₃ electrodes only delivered 190 mA h/g.Second,it was proved through XRD and SAED patterns of the as-prepared zinc stannate?ZnSnO₃?that the orthorhombic perovskite ZnSnO₃ did not exist and was a mixture of the spinel Zn₂SnO₄ and SnO₂.Third,the Zn₂SnO₄-carbon cloth composites were obtained by a combine pre-functionalization and hydrothermal method with plate-like and octahedron-like Zn₂SnO₄ uniformly dispersed on the surface of carbon cloth.The Zn₂SnO₄-carbon cloth composites electrodes were directly assembled after cutting the flexible composites as the negative electrodes without conductive agent or binder.It was found that the cyclic stability and reversible capacity of the flexible electrodes were greatly improved.After 50 charge-discharge cycles at the current density of 100 mA/g,it still delivered a capacity of 1510 mA h/g.In addition,the preparation method can largely simply traditional process of assembling batteries and realizes the light weight of lithium-ion batteries.