Cost-effective Materials For The Potassium-ion Batteries

Grid-scale energy storage systems?ESSs?have been more and more important because of growing environmental pollution and energy crisis.Among various electrochemical energy storage devices,Lithium-ion batteries?LIBs?have been considered the one of the most promising storage application because of their high gravimetric and volumetric energy densities.However,the resources distribution and cost problems of LIBs would limit their development in the future.Benefiting from wide resources distribution in the world and low cost,potassium-ion batteries?PIBs?have attracted increasing attention as one important alternative to LIBs.PIBs are just at the infancy stage,materials that have been studied for electrodes of PIBs are rather limited at present and there is no report of the full PIBs.The research of PIBs'anode electrode mainly concentrated on the carbonaceous material in the organic electrolyte,and the cathode materials research mainly concentrated in the aqueous electrolyte,the voltage window is limited.The purpose of this thesis is to synthesize Prussian blue cathode material by wet-chemical method,to study its electrochemical performance in organic electrolyte for PIBs,and to demonstrate the full PIBs for the first time.At the same time,nitrogen-doped carbon nanotubes were prepared by template method,and the effect of nitrogen doping on the electrochemical properties of negative electrode was revealed.This is of great significance for the future research and commercial application of PIBs electrode materials.The main contents are summarized as follows:?1?In this thesis,the development of the secondary ion batteries,PIBs storage mechanism and compositions are detailly reviewed.And we summarizes the process of cathode and anode materials of PIBs'with a brief analysis and introduction according to the classification and storage mechanism.The research prospects and ideas of this thesis also are put forward.At the same time,the experimental regents and equipment for this thesis are summarized,and the experimental methods and test methods used in this thesis are described in detail.?2?In this thesis,low cost Prussian blue nanoparticles were synthesized as the cathode electrode by a mild wet-chemical method,and the electrochemical performance of PIBs in organic electrolyte was tested.The energy storage mechanism was analyzed by ex situ XRD,Raman and XPS characterizations.Finally,we for the first time demonstrate the high-performance full PIBs with commercial Super P anode.The experimental result shows,Prussian blue as PIBs cathode material delivered a capacity of 74.5 mAh/g at rate of 50 mA/g and shows excellent cycalibility with capacity retention over 98%after 50 cycles.It also showed great rate capability with the capacities of 56.1 and 46.1 mAh/g at rates of 200 and 300 mAh/g,respectively,and a very small capacity decay rate of⁰.09%per cycle after 150 cycles.The C-coordicated Fe ^III/Fe ^II couple has been confirmed to be the redox-active site and thus responsible for K⁺storage.?3?In this thesis,low cost polypyrrole nanofibers were fabricated by a facile template method,and different nitrogen-doped carbon nanotubes NCFN650,NCFN950,NCFN1100 were obtained by carbonized polypyrrole at 650?,950?and 1100?,respectively.The experimental result shows,NCFN650 as the PIBs anode clearly manifest the best cycling and rate performance.It delivers reversible capacity of 248.1 mAh/g at the rate of 25 mA/g after 100 cycles.It also shows the best long cycling stability and reversible capacity compared to all reported carbon materials of PIBs anode at high rates.The comparison of theoretical calculation between NCFN650,NCFN950 and NCFN1100 shows that the nitrogen doping can enhance the capacitive contribution on the surface of the carbon material,and effectively improve the capacity retention and cycle stability at high current density.