Preparation And Properties Study Of Vanadium-based Cathode Materials For Zinc Ion Batteries

Aqueous zinc ion batteries（ZIBs）have great application prospects in the field of energy storage because of its high security,high performance,and relatively low cost.Among a variety of cathode materials being studied at present,vanadium-based materials enable multi electron transfer and provide high specific capacity,so they have great application potential and have attracted more and more researchers’attention.Researchers can study from many aspects due to the rich variety of vanadium-based materials.As the cathode material for zinc ion batteries,vanadium-based materials still have many problems to be solved,such as the relatively poor conductivity,unstable structure,and low cycles life.This paper takes vanadium-based materials as the research object.Three vanadium-based compounds with different crystal structures are prepared by adjusting the structure,composition and morphology of the materials.Different conductive materials were introduced to form composite electrode materials,and a systematic study was carried out.The research results are as follows.（NH4）2V10O25·8H2O（NHVO）nanobelts with a thickness of about 14 nm were prepared by hydrothermal method.NHVO was mixed with Ti3C2Tx nanosheets.NHVO/Ti3C2Tx hybrid film were prepared by simple vacuum filtration method.In the hybrid film,due to the good conductivity and dispersion of Ti3C2Tx nanosheets,NHVO/Ti3C2Tx hybrid film can be directly used as a self-supporting electrode.Ti3C2Tx nanosheet can effectively contact with NHVO nanobelts,providing continuous electronic conduction path for NHVO,thereby promoting electronic transmission.Ti3C2Tx can also be used as binder for NHVO nanobelts to stabilize the structural changes of electrodes during charging and discharging,which is beneficial to the improvement of cycle performance.NHVO/Ti3C2Tx hybrid electrode showed good electrochemical performance.Among them,when the amount of Ti3C2Tx nanosheet is 30%,the discharge specific capacity of NHVO/Ti3C2Tx-30%composite electrode reaches 514.7 m Ah g^-1 at 0.1 A g^-1 current density.When the current density increases to 5 A g^-1,the specific discharge capacity is 135.1 m Ah g^-1.After 6000 cycles,the capacity remained at 84.2%of the initial capacity at 5 A g^-1.Ultra thin V2O5·1.6H2O nanobelts with a thickness of 2 nm were prepared by hydrothermal method using orthorhombic V2O5 as precursor.CNTs were mixed with V2O5·1.6H2O nanobelts.V2O5/CNTs hybrid material were prepared by vacuum filtration method.The introduction of structural water can expand the layer spacing of V2O5 and stabilize the interlayer structure.The addition of CNTs can improve the conductivity of the electrode.At the same time,CNTs can build an interpenetrating network structure with V2O5·1.6H2O to improve the ion diffusion channel.It is found that the specific capacity of V2O5/CNTs-30%electrode at 0.1 A g^-1 is 485.8m Ah g^-1.When the current density increases to 5.0 A g^-1,the specific capacity is355.6 m Ah g^-1,and the capacity retention rate is 73%.Even at 50 A g^-1,the specific capacity is still 137.6 m Ah g^-1,indicating that the electrode has good rate performance.The capacity retention rate is 91.9%after 2500 cycles at 5.0 A g^-1.In addition,V2O5/CNTs-30%hybrid electrode not only has high mass specific capacity,but also shows high volume specific capacity of 937.3 m Ah cm^-3 at 0.1 A g^-1.Using ammonia vanadate as precursor and PVP as carbon source,V2O3@C materials were prepared by one-step high temperature pyrolysis method.In the process of high temperature pyrolysis,ammonia vanadate is decomposed to form V2O3,and PVP is carbonized at the same time.In the composite of V2O3@C,the average size of V2O3 nanoparticles is about 5 nm.V2O3 nanoparticles are surrounded by amorphous carbon,forming a fast electron conduction path.At the same time,amorphous carbon can prevent the agglomeration of nanoparticles,and alleviates the volume change.Next,The V2O3 is converted into high valence V10O24·12H2O（VOH）by the electrochemical pre-oxidation method.The result show that the composites displayed excellent electrochemical properties.At 0.2 A g^-1,the specific capacity is up to 454.1 m Ah g^-1.It also has excellent rate performance.When the discharge current increases to 5.0 A g^-1,the capacity can still be maintained at 383.3 m Ah g^-1.At 50 A g^-1,the capacity can still maintain 176.5m Ah g^-1.The cycle results show that the capacity retention rate is as high as 86%at50 A g^-1 after 10000 cycles,showing good cycle performance.The pre-oxidation mechanism of the V2O3@C material also is studied.It was found that V2O3@C was transformed into VOH@C after pre-oxidation.VOH has a double-layer V2O5structure similar to the intercalation of water molecules.Compared with the traditional V2O5 powder structure,the intercalation of water molecules increases the layer spacing,and contributes to structural stability.Study on zinc ions storage mechanism of VOH@C electrode,reveals that zinc ions can reversibly（de）intercalation in VOH@C electrode.