Reversible Lithium And Zinc Storage Of Vanadium Based Nanocomposites

With the increasing depletion of fossil resources,renewable sources cannot supply the stable power because of periodicity.Thus,batteries as energy conversion devices become important.To obtain high-performance batteries,it is essential to develop electrode materials.Among various electrode materials,vanadium based compounds due to their rich valence and diverse structures,are widely used in energy storage devices.However,such materials usually face the poor electronic conductivity or low ion diffusion coefficient.Therefore,in this thesis,intercalation-typed vanadium based compounds are used as the research object,and their microstructure/size and surface coating are adjusted to explore the application in various energy storage devices including lithium-ion batteries,lithium-ion capacitors,and zinc-ion batteries.The specific research contents are as follows:(1)Li3VO4 nanoparticles in N-doped carbon with porous structure as an advanced anode material for lithium-ion batteries.Melamine,owing to low cost,high nitrogen content and easy adsorption on metal oxides,is selected as nitrogen source.It reacts with citric acid to form supermolecular aggregates.During the carbonization of aggregates,Li3VO4 particles are limited to tens of nanometers and uniformly distribute in porous N-doped carbon(LVO-m/c).Compared with uncoated-Li3VO4,LVO-m/c has better electrochemical performances.After 1000 cycles at 4 A g-1,the specific capacity of LVO-m/c can maintain at 236.6 mAh g-1 When the current density increases to 10 A g-1,the specific capacity stabilizes at 199.9 mAh g-1.Smaller charge transfer resistance and the electrode reaction controlled by capacitive behavior,account for its excellent rate performance.When matched with LiCoO2,the energy density of the assembled full cell can achieve to 94.06 Wh kg-1 at a power density of 3.9 kW kg-1.(2)Hierarchically porous Li3VO4/C nanocomposite as an advanced anode material for high-performance lithium-ion capacitors.Hierarchically porous Li3VO4/C nanocomposites(hp-LVO/C)are designed via solvothermal reaction followed with annealing.The center of the composite is a large hole,and the surrounding walls are filled with mesopores,which effectively shortens charge transfer path,improves the contact area with electrolyte,and increases active sites.Combing with carbon enhances the electronic conductivity of Li3VO4.At 2 A g-1,the lithium-storage capacity of hp-LVO/C is 304 mAh g-1,higher than mesoporous Li3VO4/C.Electrochemical kinetic analysis shows that the capacitor contribution to total specific capacity is?80%at 0.7 mV s-1,indicating the fast electrochemical reaction rates in hp-LVO/C.Pairing hp-LVO/C with mesoporous carbon,the obtained lithium-ion hybrid capacitor can generate an energy density of 105 Wh kg-1 at 188 W kg-1.When the power density increases to 9.3 kW kg-1,the energy density can still maintain at 62 Wh kg-1.(3)Zinc-storage properties of layer-structured VS2/rGO nanocomposites as a cathode material.The composite of VS2 nanosheets and reduced graphene oxide(VS2/rGO)is synthesized and its cycling performance in electrolyte Zn(CH3COO)2 is more stable than in ZnSO4 and Zn(BF4)2.After 400 cycles at 1 A g-1,the specific capacity can maintain at 84.2 mAh g-1.This result can be attributed to the fact that cathode VS2/rGO remains stable in Zn(CH3COO)2,avoiding the capacity loss arising from dissolution.At the same time,anode zinc foil in Zn(CH3COO)2 forms relatively flat zinc deposition,improving the reversibility of zinc stripping/plating.(4)Zinc-storage properties of N-doped V2O5 nanobelts as a cathode material.N-doped V2O5 nanobelts are designed via introducing element nitrogen into V2O5.The obtained product buffers the structural change caused by the insertion/desertion of Zn2+,shortens charge transport path and increases active sites.Thus,its electrochemical performance is improved.After 1000 cycles at 5 A g-1,the specific capacity of N-doped V2O5 nanobelts is 184.7 mAh g-1,higher than V2O5.When the current density raises to 10 A g-1,and the cycle number increases to 3000,its specific capacity can stabilize at 111.1 mAh g-1.Small interface charge transfer resistance indicates a high electrochemical reaction rate in N-doped V2O5 nanobelts.