Synthesis Of CoSnO₃-based Nanocomposites And Their Applications In Lithium-air Batteries

Recently,the deterioration of global climate and the growing shortage of fossil resources have become the major challenges which mankind must be faced with and overcome.Therefore,the needs to developa novel clean energy which can satisfy the increasing demands and the related energy storage and conversion technologies are becoming more and more urgent.Rechargeable Lithium-Air Batteries(Li-Air batteries,LABs),possess the ultra-high theoretical energy density which multi-times bigger than the conventional Lithium-Ion Batteries(LIBs),as well as can be comparable with the gasoline,have drawn much attention and become the most promising candidate for the next generation energy conversion sources.However,to realize the practical application,there are several problems must be solved,including the stabilities of electrolyte and electrodes,poor cycle ability and high overpotantials during the charge/discharge process.The latest research indicates that exploiting an efficient cathode catalyst material is one of the key to process the solvent.In recent years,Due to its lower price and outstanding performance,transition metal oxides-based materials have attracted intense interestof research.In this thesis,we have used chemical synthesis route to synthesize CoSno3 nanomaterials.And based on the previous preparation of CoSno3,CoSno3@rGO and CoSno3@Ruo2 composites were also been synthesized successfully.A systematic study of CoSno3 and CoSno3-based composites ascathode catalytic materials for LABs have been investigated.The main results were showed below:1.Synthesis of CoSno3 nanocube with solid and hollow structureWith CoCl2 and SnCl4 as the raw materials,sodium citrate as the stabilizer,the precursor CoSn(OH)6 have been synthesized by using a simple chemical co-precipitation method in alkaline environment.And then after the thermal treatment,we obtained the final products CoSnO3 solid nanocube.By adjusting theaddition of NaOH,the morphology of obtained products can change from solid nanocube to hollow nanocube and size distribution of the nanoparticles is uniform.By using the as-prepared CoSnO3 solid and hollow nanocubes as cathode catalyst materials for LABs,the results of the electrochemical performance indicated that both prepared CoSnO3 nanocubes showed a better electrochemical performance compared with traditional carbon material KB under a limited specific capacity test system.Using CoSnO3 with solid and hollow nanocube structure as cathode materials have greatly reduced the overpotential about 380 mV and 460 mV,respectively.And They could also be processed stably for 40 cycles and 100 cycles at the current density of 200 mA g-1 with fixed specific capacity of 1000 mAh g-1.Due to its high specific surface area which could largely improve the contact area between the electrolyte and the catalyst materials,hollow CoSnO3 nanocube showed more efficient catalytic activity than solid structure.2.Synthesis of CoSnO3@rGO nanocompositesThe synthesized graphite oxide(GO)by chemical route contain numerous oxygen-contain functional groups are always negatively charged.Thus,based on the previous synthesized hollow CoSnO3 nanocube,we have used cationic surfactant CTAB to assist the fabrication the CoSnO3@rGO nanocomposites.After the thermal reduction,the final products CoSnO3@rGO nanocomposites were obtained.Because of the good electrical conductivity of rGO,greatly increasing the speed of electron transport and Li-ion transport between the electrolyte and discharge products Li2O2 which lead to the fast transformation ofproducts during the charge-discharge process.Meanwhile,the large specific surface area of rGO could also provide more reactive sites for the formation and decomposion of discharge products Li2O2.The final electrochemical performance showed that the OER catalytic activity and cycle performance of CoSnO3@rGO has been enhanced when compared with pure CoSnO3.3.Synthesis of CoSnO3@RuO2 nanocompositesBased on the previous synthesized hollow CoSnO3 nanocube,a simple one-step hydrothermal process has used to synthesize CoSnO3@RuO2 nanocomposites.Through the contrast between the CoSnO3@RuO2 nanocomposites and single CoSnO3 materials,we have found a great improvement of the electrochemical performance.It could be ascribed to the novel structure of the composite which consisted of tiny RuO2 nanoparticles distributing on the surface of CoSnO3 nanocube uniformly.The synergistic effect between the RuO2 nanoparticles and CoSnO3 nanocube largely increased the OER and ORR catalytic activity.