The Research Of Building And Energy Storage Mechanism For Potassium-based Batteries

With the increasing demand for advanced battery technology that can achieve high energy power density,high safety,low-cost,long cycle life,and large-scale energy storage.Therefore,it is imperative to develop the next generation of non-lithium rechargeable battery technology.Potassium reserves are abundant,and the standard reducing hydrogen potential is close to lithium,which not only meets the low-cost requirement but also solves the problem of low energy density.In addition,the Stokes radius of potassium ions in the electrolyte has high ionic conductivity,which makes the potassium ion battery have ultra-high rate performance.Therefore,potassium ion battery technology is considered to be one of the potential candidates for advanced battery technology.However,there can be too many problems at this stage that hinder the development of potassium ion batteries.For example:the radius of potassium ions is relatively large.In the process of deintercalation potassium ions from the host,the release of structural stress causes serious volume expansion,electrode powdering and shedding,and ultimately resulting in a sharp decline in specific capacity and charge and discharge platform;lack of long-term stability,suitable The positive and negative electrode materials of the charging and discharging platform,etc.This paper designed a series of high performance of non-aqueous potassium ion battery and environmental friendly,low cost,high safety of aqueous potassium ion battery energy storage system.The in-situ or ex-situ X-ray diffraction(XRD)and the first principles calculation investigate the electrode reaction mechanism during the charge and discharge.The details are as follows:(1)In Chapter 2,Molybdenum Selenide(MoSe₂)shows the advantages of high conductivity and stable sandwich structure.MoSe₂/N-C was prepared by in-situ carbon coating technique.We first compared the performance of the MoSe₂/N-C electrode in the electrolyte of difluorosulfimide salt and potassium hexafluorophosphate.The results show that the electrode has the best electrochemical performance in 1M KFSI/EMC electrolyte.Also,in-situ XRD,ex-situ Raman,and TEM were used to analyze the electrode structure durong charge and discharge.The results show that the discharge product component of MoSe₂/N-C in the potassium ion battery system is mainly K₅Se₃,and the charge product includes MoSe₂,Mo₁₅Se₁₉,and elemental Se.This new electrolyte and proposed reaction mechanism will provide the direction and ideas for the fabrication and design of new anode materials for potassium ion batteries in the future.(2)In Chapter 3,3M KFSI/DME electrolyte at high pressures above 4V,corrosion of the collector and the decomposition of the electrolyte.the development of electrodes with a suitable platform(when the cathode is coupled with a high platform anode,the cathode potential is pulled lower,thus avoiding electrolytic decomposition and current collector corrosion),high capacity,ultra-stable anode material is critical.As potassium ion battery anode,FeSe₂ shows stable cycling performance in the half cell.In addition,the reaction mechanism of FeSe₂ was investigated by first-principles calculations,in situ X-ray diffraction and non-in situ transmission electron microscopy.It was found that the irreversible electrochemical reconstruction of FeSe₂ will be transformed into Fe₃Se₄ during the first charge and discharge process.This work demonstrates a basic understanding of the mechanism of potassium storage in FeSe₂.Besides,FeSe₂ mixed with activated carbon cathode matching of potassium ion hybrid capacitor,the hybrid capacitor can provide 230 Wh kg^-1 and 920 W kg^-1 energy density and power density.(3)In Chapter 4,we report a new method to catalyze g-C₃N₄ to produce multistage structure high nitrogen-doped micron spheres(CMSs)for potassium ion battery anode by adjusting the different temperatures.Compared with traditional carbon nanomaterials,CMSs have rich internal structures,which not only provide additional active sites and better electron transport but also alleviate the volume dilation caused by potassium ion displacement.CMSs have been used as anode material for potassium ion batteries for more than 12 months with stable operation at low current density.CMSs anodes also exhibit durable cycling properties,after 10,000 stable cycles at high current densities.It is worth noting that the CMSs anode can be coupled with the organic positive PCTDA to form a reverse potassium ion hybrid capacitor.The hybrid capacitor can output high energy density and power density,141 Wh kg^-1 and 4382 W kg^-1,respectively.Considering the rich microstructure of CMSs and its easy synthesis method,this study describes the advantages of using CMSs over other electrode materials in battery applications.(4)In Chapter 5,the aqueous potassium ion battery is a competitive candidate to replace the lithium-based battery due to its inherent high safety and low production cost.Organic materials are abundant and inexpensive,which meets the requirements of large-scale energy storage and low cost.Secondly,the structure of organic materials is diverse,and the dischaege potential of organic materials can be adjusted by adjusting the functional groups.Besides,organic electrodes have the advantages of environmental degradability and sustainability,which is of great significance for reducing the carbon footprint.Therefore,in this chapter,we first reported an all-organic aqueous potassium dual-ion battery consisting of organic polytriphenylamine as the cathode,organic3,4,9,10-perylene tetracarboxylic diimine as anode and 21 M KFSI aqueous solution as the electrolyte.Under the 500 mA g^-1 current density,can show the long cycle stability of the 900 times.Also,the working mechanism of the aqueous potassium dual-ion battery was revealed by X-ray spectroscopy and scanning electron microscopy:during charge and discharge,FSI^-can react with nitrogen atoms in the cathode of polyaniline,while K⁺can react with C=O bond in the anode of PTCDI.(5)The lack of cathode materials with ultra-long cycle stability and a high discharge platform seriously hinders the development of aqueous potassium ion batteries.In Chapter 6,here we report an in situ cation exchange chemistry by modification of an electrolyte(0.2 M Fe(CF₃SO₃)₃ with 21 M,KCF₃SO₃ electrolyte),involving Fereplacing Mn on the surface of an Mn-based Prussian blue anemone(KMF),which prevents the dissolution of Mn²⁺and the multiphase transition during charge and discharge.The cathode modified by the modified electrolyte shows excellent electrochemical performance.High discharge capacity,excellent capacity retention,and long cycle stability demonstrate the results of in situ cationic substitute on strategy.By organic PTCDI with the modified KMF cathode anode coupling,build the aqueous potassium ion battery.It can delivers energy density 92 Wh kg^-1 and high capacity.Therefore,in situ cationic substitution strategy can be a perfect technique for the construction of long-term cycling stability of aqueous potassium ion battery cathodes.