Preparation And Electrochemical Performance Of Tin Dioxide-based Anode Materials

Lithium-ion batteries?LIBs?have captured enormous attention in the field of energy storage owing to their high energy density,long lifespan and environmental benignity.With the increasing demand for next-generation LIBs,electrode materials with high specific capacity,long cycling stability and extraordinary rate capability are highly desired.Among the available anode materials for LIBs,SnO₂ has been perceived as a promising candidate due to its high theoretical capacity as well as appropriate working potential.Unfortunately,its practical application is limited by the large initial irreversible capacity loss and huge volume variation during the lithium insertion/extraction process.Two effective strategies have been proposed to address the aforementioned issues of SnO₂ anodes.One strategy is to fabricate SnO₂ with unique structures,such as nanowires,nanotubes and nanospheres.The other strategy is to employ conformal carbon coatings.The two strategies can effectively buffer the volume variation during the lithium insertion/extraction process and improve the cyclic stability of SnO₂materials.In addition,the introduction of transition metals or transition metal oxides is also an effective strategy to improve the electrochemical performance of SnO₂materials,which can improve the reversibility of the conversion reaction of SnO₂ to Sn,thereby reducing the initial irreversible capacity loss.Based on the above ideas,SnO₂@C nanotubes and C@SnO₂@V₂O₃nanocomposites were synthesized using the template method.The morphology and structure of the synthesized materials were characterized in detail using modern testing methods.Then they were used as anode materials for LIBs and tested for electrochemical performance.The main research results of this thesis are as follows:?1?The MnOOH nanowires are used as sacrificial template to prepare SnO₂nanotubes by an oxalate-assisted“redox etching and precipitating”route.MnOOH is gradually consumed while SnO2 is preferentially deposited on the preformed SnO2shell.And the reaction conditions of this method are easy to reach,so it is more advantageous than the general template method.Through a series of characterizations and analysis,the"redox etching and precipitating"mechanism proposed in this thesis is confirmed.?2?To improve the electronic conductivity and structural stability,the SnO₂nanotubes are further coated with a thin carbon layer to obtain SnO₂@C nanotubes.When evaluated as anode materials for LIBs in the voltage range of 0.01-2.5 V,the SnO₂@C nanotubes demonstrate an excellent electrochemical performance,which can maintain a reversible capacity of 663 mAh g^-1 at the current density of 500mA g^-1 after 100 cycles and still provide a specific capacity of 711 mAh g^-1 at a high current density of 4000 mA g^-1.?3?The V₆O₁₃ nanosheets were synthesized by a simple hydrothermal method.And then Sn²⁺ions were assembled on the surface of V₆O₁₃ nanosheets with the help of PVP.Next,mismatched coordination reactions occured between Sn²⁺ions and terephthalic acid.Sn-precursor@V₆O₁₃ nanocomposites were then obtained.After calcination in hydrogen,the Sn-precursors were carbonized to form carbon-confined SnO₂ nanoparticles,and the V₆O₁₃ nanosheets were reduced to V₂O₃ nanosheets.Finally,C@SnO₂@V₂O₃ nanocomposites were obtained.?4?When evaluated as anode materials for LIBs in the voltage range of0.01-3.0 V,the C@SnO₂@V₂O₃ nanocomposites exhibit excellent cycling stability with a discharge capacity of 1125 mAh g^-1 at the current density of 1000 mA g^-1 after500 cycles and superior rate capability with a discharge capacity of 573 mAh g^-1 at a high current density of 5000 mA g^-1.