Structure Design And Performance Control Of Mesoporous Carbon Supported Nano Tin Oxide Anode Materials

With the increased energy consumption and pollution,the development of efficient,clean and renewable new energy storage devices is urgent.Among all the energy storage devices,lithium-ion batteries(LIBs)have attracted great attention owing to their high energy density and long cycle stability.The characteristics of anode material influence the energy density of LIBs greatly.At present,graphite is mainly used as commercial anode due to its good stability and low cost.However,the low lithium intercalation potential can result in the formation of lithium dendrite,which may induce short circuit of batteries.Besides,the low theoretical capacity of graphite can hardly satisfy people’s demands in high energy storage.As a conversion-type anode material,SnO2 has a moderate lithium intercalation potential ensuring the safety of the battery.Besides,the theoretical specific capacity of SnO2 is 1494 mAh g-1,which is about 4 times of the graphite.However,the coarsening of SnO2 during lithiation/delithiation leads to the pulverization of electrode materials.In this thesis,ordered structure was constructed using nanocrystallized SnO2 with carbon composites to avoid the agglomeration of SnO2,which can improve the electrochemical performance of electrodes.The graphene supporting nano SnO2 electrode(SnO2@rGO/Cl BFEs)was synthesized at low temperature in situ,which improved the traditional electrode material preparation process and inhibited the introduction of non-active binder.The nucleation of Sn2+ on oxygen-containing groups of graphene oxide and subsequent low-temperature heat treatment,then graphene supporting nano SnO2 active materials were directly grown on copper foil collector.By adjusting the amount of SnCl2,the electrode materials with different SnO2 content can be obtained.At the same time,the SnCl2 is used as both tin source and chlorine source,and the product is chlorine modified graphene supporting SnO2.First principles calculations show that chlorine modification promotes the adsorption energy of graphene to SnO2,and improves the conductivity of the composites.When used as anode material of lithium ion battery,the SnO2@rGO/Cl BFEs show a high specific capacity reaches 734 mAh g-1 after 500 cycles.After the rate capabilities,the SnO2@rGO/Cl BFEs delivere a discharge capacity of 559 mAh g-1 after another 1600 cycles.The Orderly stacked graphene supporting nano SnO2 composites(SnO2@OS-rGO)were prepared by ice template method that the adjacent ice crystals grow vertically upward,then the GO sheets are extruded to the crevice of the ice crystals,and arranged orderly along the ice crystals.The strong π-π interaction between ordered graphene which can bind SnO2 effectively and inhibit the coarsening of it.The amount of graphene oxide and citric acid have great influence on the composition and morphology of SnO2@OS-rGO.By optimizng the content of the two,the orderly stacked graphene supporting nano SnO2 composites can be obtained.The electrochemical results show that the discharge capacity of SnO2@OS-rGO increases gradually,finally stabilizes at 1080 mAh g-1 after 500 cycles,which is 200%higher than the initial capacity.The capacity contribution of different voltage ranges and differential voltage curves were used to analyze the capacity increasing behavior.The results show that the increasing capacity comes from the enhancement of conversion reaction of SnO2 and the decomposition of gel polymer membranes.The ordered mesoporous carbon supporting nano SnO2(SnO2@OMC)was designed by using the Fe3O4@OA superstructure as sacrificial template.The geometric confinement of Fe3O4 inhibits the growth of SnO2 to ensure the small size,and oleic acid as carbon source.The ordered mesoporous carbon framework isolates SnO2 nanoparticles in space and inbihites the coarsening of SnO2.Mesoporous alleviates the volume expansion of SnO2 and the three-dimensional interconnected carbon network improves the structural stability of the SnO2@OMC.Finally,the SnO2@OMC shows excellent electrochemical performance.The discharge specific capacity of SnO2@OMC reached 930 mAh g-1 at 0.2 A g-1.Even at a high current density(5 A g-1),SnO2@OMC can release a capacity of 321 mAh g-1 after 1000 cycles.It is found that the SnO2@OMC with large specific surface area generates pseudo capacitance,increases the discharge capacity.Besides,the ordered mesoporous structure shortens the lithium ion transport path,improves the rate performance.