Controlled Synthesis Of Vanadium-based Oxide Nanomaterials And Their Application And Research In Aqueous Zinc Ion Batteries

As fossil fuels continue to be consumed and the greenhouse effect progressively worsens,there is an increasing demand for efficient energy storage and conversion devices.Aqueous electrolytes offer many technical advantages over organic electrolytes,which pose substantial safety risks,such as high safety,low price and ease of manufacture,and are expected to be used in the development of the next generation of green rechargeable batteries.Among the many aqueous rechargeable monovalent/multivalent metal ion batteries,aqueous zinc ion batteries(AZIBs)are one of the most popular devices.However,the electrostatic repulsion of Zn2+ in their system is high and Zn2+ is highly hydrated in the aqueous electrolyte.The resistance to movement of hydrated Zn2+ between layers and in space is considerable,resulting in sluggish electrochemical kinetics.The large radius of the hydrated ions(4.3 ?)and the need for large diffusion channels are fundamental bottlenecks to further promote the practical application of AZIBs.Among the many cathode materials available,layered vanadium-based cathode materials have received a lot of attention due to their open crystal structure which can provide a convenient channel for Zn2+ to move through.However,the problems of poor cycling capacity and stability due to the unstable layer structure and low electronic conductivity cannot be ignored.This thesis addresses the problems of vanadium-based oxides as cathode materials for aqueous zinc ion batteries,using a simple hydrothermal method to synthesise ultra-thin layered vanadium-based oxides,investigating the effect of crystalline water on vanadium oxide,constructing positively charged vanadium-based nanomaterials through surface modification and the introduction of metal elements,using charged vanadium oxide materials to anchor organic molecules or preparing heterojunction materials,and studying in detail the electrochemical properties and charging and discharging mechanisms of this series of materials The electrochemical performance and charging/discharging mechanism of the aqueous zinc ion battery as the positive electrode.The thesis consists of five main sections as follows:1.Layered hydrated V6O13·2.72H2O ultrathin nanoribbons were synthesized by a simple hydrothermal method using ethanol as the reducing agent and used as an aqueous zinc ion battery cathode material to compare the effect of interlayer crystalline water on the electrochemical performance.The unique ultra-thin nanoribbon structure of the hydrated vanadium oxide shortens the diffusion path and the presence of crystalline water widens the interlayer spacing in the(200)direction.The capacity retention rate was still 94.0%after 1000 cycles and 85.2%after 2000 cycles.The diffusion and storage mechanisms of Zn2+ have also been investigated in depth in combination with various in-situ and non-in-situ tests.2.In order to introduce a positive charge in the V6O13·2.72H2O nanoribbon,the V6O13·2.72H2O nanoribbon was covered with positively charged dopamine hydrochloride(PDA).The composites of VO2 and amorphous nitrogen-doped carbon(VO2@NC)were obtained by calcination.with higher electrical conductivity and a faster Zn2+ diffusion kinetics due to less structural change in the amorphous structure during ion diffusion,the VO2@NC composites exhibited excellent electrochemical properties,including a high reversible capacity of 435.4 mAh·g-1 at a current density of 1.0 A·g-1 and a capacity retention of 96.3%after 100 cycles.Even after 2,500 long cycles at a high current density of 10 A·g-1,a capacity retention of 99.7%was achieved.In addition,VO2@NC has an energy density of 238.0 Wh·kg-1 and a power density of 7.0 kW·kg-1.Therefore,the use of VO2@NC as the AZIB cathode will achieve high initial discharge specific capacity and stable cycling performance at high current densities.3.The introduction of metal ions is also a way to make oxides positively charged.Using V6O13·2.72H2O nanoribbons as a template,a series of nanomaterials with domain-limited metals were successfully synthesized by a one-step hydrothermal method,and the effect of interlayer spacing on the electrochemical properties was investigated.The effects of domainlimited different metals and domain-limited different metal contents on the interlayer spacing of vanadium oxide were systematically investigated to reveal the two-carrier co-embedding mechanism of domain-limited metal ions in the nanoribbons.The obtained Al2.65V6O13·2.72H2O as the anode of AZIBs achieves an initial capacity of up to 571.7 mAh·g1 at a current density of 1.0 A·g-1.Even at a high current density of 5.0 A·g-1,the initial capacity still reaches 205.7 mAh·g-1,and the capacity retention rate is up to 89.2%after 2000 cycles.The nanoribbon domain-limited metal ions can stabilise the layered structure and effectively control the interlayer spacing,providing a larger diffusion channel for Zn2+ embedding and exfoliation without changing the vanadium oxide morphology.The right amount of metal ions also gives the vanadium oxide better ionic conductivity.Among other things,water molecules also play a role in improving the ion dynamics.4.The A1350DMF cathode material is obtained by replacing part of the crystalline water in Al2.65V6O13·2.72H2O and using electrostatic adsorption with Al3+ in the layer spacing to anchor the polar organic molecule DMF exactly in the oxide layer spacing.the presence of Al3+ allows the structure to be left undamaged during the removal of the crystalline water.In general,Zn2+ interacts with the highly polar carbonyl(C=O)group in the DMF.However,the presence of the highly polar C=O group makes it difficult for Zn2+ to interact with the DMF any further due to the presence of the highly polar C=O group which shows a stronger electrostatic attraction to the Al3+ between the layers during charging/discharging compared to water molecules,and this weak interaction will allow Zn2+ to embed more freely in the layers of vanadium oxide for delamination.The initial discharge capacity of the Zn//A1350DMF cell was 279.2 mAh·g-1 at 0.5 A·g-1 and the capacity retention after 50,100,200 and 300 cycles was 67%,52%,35%and 25%,respectively.The average discharge specific capacity was 430.56,363.94,257.92,196.22,150.58 and 84.7 mAh·g-1 at current densities of 0.1,0.2,0.5,1.0,2.0 and 5.0 A·g-1,respectively.when the current density was suddenly restored from 5.0 A·g-1 to 0.05 A·g-1,the Zn//Al350DMF cell was able to recover its average discharge capacity to 418.84 mAh·g-1,demonstrating the better multiplicative performance of the Zn//A1350DMF cell.This work provides a feasible idea for the introduction of vanadium oxide into organic molecules.5.The vanadium oxide Co3V2O8 corresponds to a ternary transition metal oxide formed by coupling a transition metal oxide(cobalt oxide)with vanadium elements.The synergistic effect of the multi-component can enhance electrical/ionic conductivity,reversible capacity,mechanical stability and improve electrochemical activity.The in-situ growth of MnO2 nanosheets can be achieved by using the low valence metal ions(Co2+ and V4+)on the surface of Co3V2O8 to obtain the heterojunction material Co3V2O8@MnO2.This structure can effectively mitigate the volume shrinkage/expansion of the material during the charging/discharging process,and to a certain extent reduce the irreversible structural dissolution and side reactions.The homogeneous growth of MnO2 nanosheets provides sufficient reaction sites for the electrolyte and the heterojunction electrode material itself has advantages in terms of high electronic conductivity.Due to the unique hollow and heterojunction structure,the Co3V2O8@MnO2 cathode exhibits a relatively high discharge specific capacity(245.4 mAh·g-1 at 100 mA·g-1),which is stable at around 140.0 mAh·g-1 after 300 cycles at a current density of 300 mA·g-1.Combined with non-in situ tests,the diffusion and storage mechanisms of Zn2+ were explored and investigated,demonstrating the feasibility of the material as an anode material for AZIBs.