Organic Small Molecules Intercalated Vanadium Oxide As A Positive Electrode Material For Aqueous Zinc-ion Batteries

The intermittent energy resources,such as solar and wind,need to be transformed tostable chemical energy and stored to reuse.The aqueous zinc-ion batteries（ZIBs）based on the anode of zinc metal and neutral aqueous electrolyte have gained widespread attention,which were applied in energy storage system due to several advantages of zinc,including of great abundancy,low redox potential and high chemical stability.Layered vanadium oxide was extensively utilized as cathode in ZIBs because of abundant valence state of vanadium.However,the drawbacks of low specific capacities and sluggish reaction kinetics limited the practical application of vanadium oxide in ZIBs.In order to solve above disadvantages,in this paper we prepared the small organic molecules intercalated vanadium oxide as energy storage materials through chemical pre-intercalation strategy.The intercalation of organics improved the electrochemical performance of ZIBs and the main research contents are as follows:（1）The organic dye molecules,methyl orange and methylene blue,intercalated vanadium oxygen hydrates were successfully prepared by one-step hydrothermal reaction,which were applied as the cathode materials in ZIBs.After the insertion of organic dye molecules,the morphology of vanadium oxygen hydrate was transferred to nanosheet structure and the interlayer spacing was also changed compared to pure vanadium oxygen hydrate（VOH）.So that the organic dye molecules intercalated VOH exhibited better electrochemical performance than VOH,reaching higher specific capacities of 293,311 m Ah g^-1 at 0.3 A g^-1 respectively.In the long-term cycling performance at 3 A g^-1,the methyl orange and methylene blue intercalated VOH displayed better specific capacities than VOH.In addition,the methyl orange intercalated VOH has over 100%capacity retention after 1000 cycles.Otherwise,the intercalation of organic dye molecules could expedite the reaction kinetics,such as electrochemical resistance,diffusion coefficient of Zn²⁺and pseudo-capacitance ratio.After the intercalation of organics,a repulsion between Zn²⁺and organics was generated,which could weaken the electrostatic interaction between Zn²⁺and the vanadate layers based on theoretical calculation,resulting the change of binding energy from-6.39e V to-4.63 e V between Zn²⁺and vanadate.（2）In this work,the thiourea molecules as intercalant were inserted into the interlayer spacing of vanadium oxygen hydrates based on the perspective of amidogen in organics could connect with vanadate by H-bond and the conclusion of the structure and functional atom in organics might influence the electrochemical performance of vanadium oxygen hydrates.In the exist of sulphur atom and H-bond generated by double amidogen made the thiourea intercalated VOH exhibiting excellent electrochemical performance,arriving at a high specific capacity of 420 m Ah g^-1 at 0.1 A g^-1.When the current density increased to 2A g^-1,the specific capacity still kept at 323 m Ah g^-1.At the maximum of 5 A g^-1,the thiourea intercalated VOH could exhibit a specific capacity of 269 m Ah g^-1 and long life-span stability with 84%capacity retention over 10000 cycles.In addition,all aspects of electrochemical performance of thiourea intercalated VOH was best compared to thioacetamide and urea pre-insertion strategy,illustrating both the double amidogen and the sulphur atom could facilitate the electrochemical reaction.