Research On Performance Of Photo-assisted Rechargeable Vanadium-based Aqueous Zinc-ion Batteries

Rechargeable aqueous zinc ion batteries（ZIBs）are widely used in large-scale energy storage due to their high theoretical capacity(820 m Ah·g^-1 and 5855 m Ah·cm^-3),low redox potential（0.76 V vs.SHE）,high stability,low cost,and high abundance.However,cathode materials with good zinc storage performance are limited.Thus,it is imperative to find suitable cathode materials to prepare battery systems with high energy density,high rate performance and long cycle life.Combing the structural advantages of vanadium oxides and metal organic frameworks（MOFs）in the electrochemical field,new high-performance vanadium-based aqueous zinc ion cathode materials with porous,composite,and micro-nano structures were designed,which showed excellent zinc storage performances.On this basis,an aqueous zinc-ion photo-battery by photo-assisted recharging was prepared.The photo-battery can collect and store energy simultaneously,thus improving the performance of aqueous zinc-ion batteries.The main research contents and results of this thesis are as follows:（1）V₂O₅@C core-shell microcuboids(V₂O_5-x@CCSMs)with oxygen vacancies were prepared devired from MIL-47（V）by high-temperature annealing under air conditions,which show V₂O₅ nanometerization and carbon composite.Profiting from the nano-sized V₂O₅,oxygen vacancy and carbon composite,the V₂O_5-x@CCSMs cathode exhibited superior electrochemical performace,such as a high energy density of 293.4 Wh·kg^-1 at a high power density of 1496.1 W·kg^-1.Moreover,ex-situ XRD showed that the charge-discharge mechanism of V₂O₅ in 3M Zn（CF₃SO₃）₂ is the conversion reaction mechanism of the shrinking nucleus process.（2）Porous melaleuca carbon microcube composites embedded with VO_x（VO_x@PMCs）devired from MIL-47（V）were prepared by using tannic acid（TA）as the protective etchingagent.The nanostructure and carbon composites of VO_x@PMCs can not only increase the active sites of zinc storage and shorten the diffusion path of zinc ions,but also buffer the volume change during the cycle and strengthen the stability of structure.Therefore,the VO_x@PMCs//Zn battery exhibited excellent cycle stability(at 10 A·g^-1 after 1000 cycles still has a high capacity retention rate of 96%)and rate performance(when increasing from 10 A·g^-1 to 20 A·g^-1,the discharge specific capacity hardly decays and the capacity remains stable).（3）The photo-battery with VO_x@PMCs as a photo-cathode was assembled and Xenon lamp was used as light source for assisted recharging.Experimental results showed that light-assisted recharging can greatly increase the reversible specific capacity of the photo-battery,such as at the current density 0.2 A·g^-1,the photo-battery show a discharge specific capacity of468.7 m Ah·g^-1,which is 1.7 times higher than that of non-illumination.photo-assisted recharging provides a new direction for the design of high-performance aqueous ZIBs.