The Preparation,Performance,and Application Investigation Of Cathode Materials For Potassium-ion Batteries

With the rapid development of industry,the global energy demand is increasing day by day,while the supply of traditional fossil fuels is facing the challenges derived from the climate,environment and resources issues.Thus,the clean renewable energies are expected to replace the fossil fuels,solving the global energy crisis,while the integration of renewable energy into grid is highly dependent on the large-scale energy storage system.Unfortunately,traditional lithium-ion batteries cannot meet the requirements of large-scale energy storage systems,due to their high cost and less safety.The development of low-cost and high-efficiency novel ion-batteries is of great significance for the utilization of the clean renewable energy.Recently,the successful demonstration of electrochemical K-storage process in graphite has aroused the attention on potassium-ion battery.Due to its abundant resources and low cost,potassium-ion battery is considered as one of the most promising secondary batteries to realize large-scale energy storage.Since the graphite anode has been successfully used in potassium-ion batteries,the research focus of potassium-ion battery is to design suitable cathodes.Generally,cathodes undergo ion embedding reaction.However,the significantly larger radius of the K ion causes greater structural changes and distortions in the host structure upon insertion and removal,which often results in short cycle life and,in particular,poor rate capability of the cathode material.Thus,the development of cathode material with low cost,high capacity and cycle stability has far-reaching significance and research value for the practical application of the real potassium-ion battery.This thesis mainly focuses on the cathode materials with large interlayer spacing and large framework structures,exploring their K-storage performance and working mechanism as well as the potential methods to improve their electrochemical performance.The research mainly focuses on the following aspects:1.Reconstruction of the?-V₂O₅ with compact interlayer space to create abundant active sites and diffusion channels for K ion,thus improving the capacity and rate performance of vanadium oxide.In detail,to unlock the compact structure of?-V₂O₅ for the diffusion of K ion,single-crystalline bilayered?-K_0.51V₂O₅ nanobelts?KVO?with a large interlayered structure and optimized growth orientation was synthesized by using a scalable,facile,and low-cost chemical preintercalation method.Due to the large interlayered structure and the unique 1D morphology along the[010]orientation,the KVO deliver high capacity and rate capability.The combined analysis of ex situ XRD and XPS reveals that the?-K_0.51V₂O₅transforms reversibly into a new phase upon K-ion deintercalation and intercalation.More importantly,a rocking-chair potassium ion full cell with KVO as the cathode material and graphite as the anode material was demonstrated,exhibiting a high energy density(238 Wh kg^-1)and a high power density(5480 W kg^-1).2.Construction of Prussian blue based integrated electrode with double conductive layer to improve the rate and cycle performance of Prussian blue in potassium-ion battery.In detail,using rusty stainless-steel meshes as solid-state iron sources and conductive substrates,we devise a facile method of fabricating flexible binder-free electrodes via transformation of the corrosion layer of rusty stainless-steel meshes into compact stack layers of Prussian blue nanocubes.Moreover,to further enhance conductivity and improve the structural stability of electrodes,a unique reduced graphite oxide coated structure has been designed.As a result,the as-prepared electrode delivers high rate capability and outstanding cycle stability.More importantly,the proposed method opens new avenues for the reuse of rusty stainless steel toward new value-added applications,which are of great importance to assist the efforts to build a resource-sustainable and environmentally friendly society.3.Development of Prussian blue based integrated flexible electrode to achieve flexible potassium-ion battery.In detail,based on the cyanotype process,a cheap,simple and controllable method for the preparation of Prussian blue was developed.Prussian blue has high crystallinity and highly dispersed nanometer block morphology,showing excellent positive electrode performance of potassium ion batteries.On the basis of the cyanotype process,a new strategy for the preparation of photographic pattern electrode with lightweight,mechanically stable structure was proposed,which realized the growth of high crystalline Prussian blue on the flexible substrates of xuan paper.Based on this flexible electrode,a flexible potassium-ion battery with high energy density(232 Wh kg^-1)was constructed,verifying its application prospect in flexible energy storage devices.