Preparation And Potassium Storage Properties Of Micro Nanostructured Vanadate

As a mature energy storage technology,lithium-ion batteries（LIBs）have been wildly used in portable electronic devices and gradually applied on new energy vehicles.However,the development of LIBs is limited by problems such as resource shortage and rising cost,which urges researchers to study and develop alternative energy storage devices.The energy storage mechanism of K-ion batteries（KIBs）is similar to LIBs,and metal potassium has the advantages of rich reserves and easy access.However,the relatively large radius of K⁺cause the low-capacity retention rate and poor rate performance of KIBs.The development of cathode materials that can quickly and stably insert/extract K⁺is the key to promoting the commercialization of KIBs.In recent years,vanadate has attracted extensive attention because of its high theoretical capacity,diverse structures and valence states and high electrochemical activity.Among them,sodium vanadate materials are widely studied as cathode materials in LIBs,sodium-ion batteries（SIBs）and aqueous zinc-ion batteries（AZIBs）,but less in KIBs.Therefore,two common sodium vanadate materials(β-Na_0.33V₂O₅andδ-Na_xV₂O₅)are selected as cathode materials of KIBs to explore their potassium storage performance.Then inspired byδ-Na_xV₂O₅ as the cathode material of KIBs,potassium vanadate material containing potassium source(δ-K_0.5V₂O₅)was directly synthesized by conventional method,and it was optimized to further improve its electrochemical performance.The specific research work is as follows:（1）Preparation and electrochemical properties ofβ-Na_0.33V₂O₅andδ-Na_xV₂O₅materials.β-Na_0.33V₂O₅andδ-Na_xV₂O₅ are two common cathode materials.The crystal structure ofβ-Na_0.33V₂O₅is tunnel structure,and the crystal structure ofδ-Na_xV₂O₅material is layered structure.In order to explore the potassium storage properties of the two materials,a series of electrochemical performance tests were carried out.The test results show that the potassium storage performance ofδ-Na_xV₂O₅is better than that ofβ-Na_0.33V₂O₅,becauseδ-Na_xV₂O₅ has relatively large interlayer distance and diffusion path,and can fully accommodate large K⁺ions,which improves its cycle stability to a certain extent.（2）Preparation and electrochemical properties ofδ-K_0.5V₂O₅and K_0.5V₂O₅/CNTs materials.Inspired by materialδ-Na_xV₂O₅,stable materialδ-K_0.5V₂O₅ was synthesized directly by conventional methods,and its electrochemical properties were analyzed.It was found that the electrochemical properties of pureδ-K_0.5V₂O₅ material were similar to that ofδ-Na_xV₂O₅material,which still needed to be further optimized.Here we choose to combineδ-K_0.5V₂O₅with carbon materials for optimization.Combined with the one-dimensional structure ofδ-K_0.5V₂O₅ material,it is compounded with common CNTs to make a flexible KIBs cathode material.Electrochemical study demonstrates that this K_0.5V₂O₅/CNTs electrode could exhibit a reversible discharge capacity of～90m Ah g^-1 at 50 m A g^-1,and the capacity retention rate is 88.8%after 100 cycles.In addition,a full K ion battery composed of the K_0.5V₂O₅/CNTs film cathode and hard carbon anode exhibit a discharge capacity of 68 m Ah g^-1 at 50 m A g^-1 with a high-capacity retention of>80%after 80 cycles.Furthermore,based on the flexible K_0.5V₂O₅/CNTs film electrode,a cable-shaped flexible full KIB is fabricated and shows good electrochemical performance and flexibility.