The Controllable Construction Of Carbon-based Anode Materials And Their Mechanism For Potassium Ion Energy Storage Devices

Benefiting from potassium resources with abundant reserves and low prices,potassium ion energy storage devices,as new energy storage technologies,have attracted extensive attention.So far,they mainly involve potassium ion batteries（PIBs）and potassium ion hybrid capacitors（PIHCs）.However,it is easy to result in some problems such as large volume expansion and diffusion resistance during the potassium/depotassium process due to the large ionic radius of potassium ion（K⁺）.These intractable issues hinder the applications of potassium ion energy storage technologies.Anode materials are of great significance to safety and cycling life.Therefore,it is necessary to design and prepare reasonable anode materials to improve the corresponding electrochemical performances of potassium storage.To date,carbon-based materials have attracted a lot of attention due to their extensive sources,low cost,non-toxicity and structural stability.Nonetheless,unimproved carbon-based materials still have shortcomings such as smaller interlayer distance,a few active sites and smaller contact area with the electrolyte,which brings about their unsatisfactory electrochemical performances.Thus,it is necessary to adopt some strategies to regulate the structure of carbon-based materials for enhancing their performances.In this thesis,the structure of carbon-based materials was regulated by focusing on controllable pore-size construction and nitrogen-doping strategies to achieve performances improvement.And then,the dual-carbon confinement strategy was used to deal with the obvious volume expansion of antimony（Sb）in the course of potassiation.Detailed research contents are as follows:（1）Three-dimensional（3D）nitrogen doped porous carbon flake framework（NPCF）was constructed by sodium chloride template and pyrolysis method as the anode materials of PIBs.The NPCF owned high porosity,high content of pyridinic N/pyrrolic N and larger interlayer distance.After being tested,the NPCF anode delivered a high specific capacity of 326.3 m Ah g^-1at a current density of 50 m A g^-1 and represented long cycle life of 10000 cycles at a current density of 5000 m A g^-1.Moreover,the kinetic analysis affirmed that the capacitive-controlled effects play a leading role in the potassium storage process.Consequently,equipped with activate carbon（AC）as cathode material and NPCF as anode material,the assembled PIHCs achieved an energy density of 65.8 Wh kg^-1 and 30 Wh kg^-1at 100 m A g^-1and 5000 m A g^-1,respectively.Accordingly,the NPCF anode processes the potential for practical application.（2）Nitrogen-doped mesoporous carbon spheres（MCS）with uniform pore sizes were synthesized by a silica hard-template method and utilized as anode materials for potassium storage.The effects of calcination temperature and pore size on the electrochemical performances of the MCS anode were investigated.The experimental results illustrated that the pyrolysis temperature of 900°C and the pore diameter of 7 nm were the optimal conditions.The optimized MCS-7-900 processed larger interlayer spacing,larger specific surface area,abundant mesoporous structures and nitrogen-doped active sites,helping to promote K-ion migration and diffusion.Benefiting from structural characteristics mentioned above,the MCS-7-900 electrode achieved a high rate capacity(107.9 m Ah g^-1 at 5000 m A g^-1)and stably brought about 3600cycles at 1000 m A g^-1.According to electrochemical reaction kinetic analysis,the capacitive-controlled effects played a dominant role in the total storage process.The better reversibility of the potassium storage process was demonstrated by using the ex-situ XRD technique.Additionally,the full cell equipped MCS-7-900 as anode material was successfully constructed and exhibited better electrochemical performances.（3）Based on this dual-carbon confinement strategy,rGO wrapped Sb/MCS-22-900composite（Sb/MCS-22-900@rGO）was prepared by combining mesoporous carbon spheres with the pore diameter of 22 nm（MCS-22-900）and reduced graphene oxide（rGO）.Sb/MCS-22-900@rGO not only used abundant mesopores of MCS to confine Sb,but also utilized rGO with the large specific surface area to wrap the Sb/MCS-22-900 as a confinement layer.In view of the synergistic effects of dual-carbon confinement,the Sb/MCS-22-900@rGO anode realized advantageous rate capability(341.9 m Ah g^-1 at 1000 m A g^-1)and better cycling stability(508.8 m Ah g^-1 after 50 cycles at 50 m A g^-1).The stepwise reaction of Sb with K⁺was revealed by cyclic voltammetry（CV）,galvanostatic charge-discharge test technique（GCD）and ex-situ XRD methods.Combined with various testing techniques,it was verified that Sb/MCS-22-900@rGO had better potassium storage kinetics.Furthermore,the anode material was also applied to the full cell which exhibits high rate specific capacities.Therefore,the Sb/MCS-22-900@rGO also owns the potential for practical applications.