Controllable Preparation And Energy Storage Applications Of Vanadium Based Oxide (Sulfide) Electrode Materials

The extensive use of fossil fuels have resulted in the extinction of the world fossil reservoirs,and brought tremendous change in earth's environment.In view of this,clean renewable energy needs to be developed or optimized in order to replace the current energy which is fossil fuel.However,most sustainable energy resources are greatly dependent on nature conditions(e.g.,wind,sun,etc.)and therefore,efficient energy storage during peak period is vital for providing energy during off-peak periods.Based on the above considerations,it is necessary to develop new energy storage equipment to collect clean energy to meet human requirements for energy and environment.Over the years,lithium-ion batteries(LIBs)have developed into a key power source for broad applications.However,the low abundance and exorbitant cost of lithium resources limit its further applications in large-scale energy storage systems.Therefore,an alternative to lithium must be considered,especially for large-scale energy storage applications in the foreseeable future.The sodium ion battery(SIBs),which has a reaction pattern comparable with that of the LIBs,is one of the promising alternatives because of its low cost and the abundance of sodium resources.Zinc ion batteries(ZIBs)are expected to play an important role in large-scale energy storage systems due to their high safety,great ionic conductivity and high rate performance.Whether SIBs or ZIBs,electrode materials are an important part of them and greatly affect their performance.Therefore,developing electrode materials with outstanding electrochemical performance is imperative but yet remains a major challenge to be overcome.Among many candidates,vanadium-based oxide/sulfide electrode materials have drawn enormous attentions due to their high theoretical capacity,abundant valence states and polycrystalline structure.However,vanadium-based oxide/sulfide have some problems such as sluggish ion diffusion kinetics and low electrical conductivity.Moreover,the large volume expansion of oxide/sulfide results in a poor cycling performance that hinders the practical application of Metal ion battery.Therefore,this thesis focuses on vanadium based oxide/sulfide electrode materials,analyzes the key problems existing in vanadium based oxide/sulfide electrode materials,and aims at developing high-performance vanadium based oxide/sulfide electrode materials for new energy storage devices(SIBs,ZIBs),and promoting its industrialization process.The following four works are the main contents of this thesis:(1)VO₂(R)and VO₂(P)are important components of vanadium-based oxides.Although VO₂(P)has a high room-temperature electronic conductivity of 1.02 S cm^-1,its tunnel structure is unconsolidate.Rutile-type VO₂(R)has a good structural stability due to the six-coordinated[VO₆]octahedron with much shorter V-O bond distance,but its channel space is relatively small limiting the metal ion intercalation capability.Therefore,it is of scientific significance to prepare Nsutite VO₂(denoted as VO₂(N))with both VO₂(R)and VO₂(P)structures through structural regulation.Due to the structural characteristics of VO₂(R)and VO₂(P)and the synergistic effect of VO₂(R)and VO₂(P),the VO₂(N)exhibits better electrochemical performance.In addition,by designing a spindle-like nano-micro composite structure,the VO₂(N)electrode can not only shorten the ion migration distance,but also maintain the stability of the micron structure.Specifically,the fent-shaped VO₂(N)has high capacity(411 m Ah g^-1),excellent rate performance(10.0 A g^-1,106 m Ah g^-1),and excellent cycle stability(10.0 A g^-1,6000 cycles).At the same time,using the electrode preparation of VO₂(N)||NVPOF full cells can deliver a high capacity(0.05 A g^-1,261 m Ah g^-1).(2)Aiming at the problem of structural instability of electrode material in high temperature environment.In this thesis,KV₃O₈ nanoribbon electrode material with stable structure was prepared by simple and efficient method.Benefiting from the large layer spacing and the stability of the nanoribbon structure of KV₃O₈ material,the material exhibits excellent electrochemical properties in high temperature environments.Specifically,the material exhibits a high specific capacity(414 m Ah g^-1 at 0.1 A g^-1).It also features excellent high temperature magnification performance(220 m Ah g^-1 at 20.0 A g^-1).Also,the ex-situ XRD shows that the material can keep the structure stability during the charging and discharging process.(3)In order to solve the problem of volume expansion caused by the sodium storage process of vanadium sulfide,as well as poor cyclic stability.In this thesis,a spherical Cu₃VS₄ electrode material was designed by introducing high conductivity elements and structure optimization.The electronic conductivity of the electrode material is enhanced by the introduction of Cu element.In addition,the designed spherical structure also alleviates the volume expansion of the electrode material during the sodium storage process.Based on this two-effect design,the spherical Cu₃VS₄ electrode showed high sodium storage performance(500 m Ah g^-1 at 0.2 A g^-1).In addition,the Cu₃VS₄ anode also shows excellent long cycle stability(25000 cycles,274 m Ah g^-1)at 20 A g^-1 high rate.For practically application,the high energy density of 171 Wh kg^-1 and extended longevity of Cu₃VS₄//Na₃V₂(PO₄)₂O₂F full batteries can be achieved.Combined with theoretical calculations,it is confirmed that Cu₃VS₄ has large internal pores and stable binding points,which provide applicable channel for ion/electron diffusion.(4)In order to solve the problem of unstable zinc storage performance of vanadium based layered structure materials.In this thesis,we develop a versatile hydrothermal synthesis route to prepare highly crystalline Na₂V₆O₁₆·3H₂O nanobelts.What is more remarkable here is that the high degree of preferred orientation of the Na₂V₆O₁₆·3H₂O results in the formation of ultralong fibrous morphology that enables the construction of free-standing but flexible electrode for ZIBs.Benefiting from the high homogeneity of the nanobelts,it not only increases their contact area with the electrolyte,but also effectively shortens the ion transport distance.Moreover,the prepared free-stranding paper electrode does not contain a resistive binder,thus enhancing the overall material conductivity.The free-stranding paper Na₂V₆O₁₆·3H₂O electrode shows excellent zinc storage performance.Specifically,the free-stranding Na₂V₆O₁₆·3H₂O paper electrode showed excellent long cycle stability(281 and 142 m Ah g^-1are achieved at 2.0 and 5.0 A g^-1 after 5000 cycles,respectively)and rate performance(216 and 167 m Ah g^-1 are achieved at 3.0 A g^-1and 5.0 A g^-1 respectively).