| In the fast-paced modern society,the demand for fast charging capacity of portable electronic products and electric vehicles is increasing rapidly,and the rate performance of energy storage system becomes more and more important.Lithium ion battery as the representative of alkali metal ion battery has been one of the most promising energy storage devices due to its high energy density.Based on the previous research of alkali metal ion battery,the development of electrode materials with high rate performance and long cycle life could effectively alleviate the requirements of social development for energy storage system.Carbon materials with low price,friendly environment,adjustable composition,and high electronic conductivity can be widely used as electrode materials or additive.Carbon materials with different structures exhibit different characteristics when they are used as electrodes:the one-dimensional carbon nanofibers or carbon nanotubes have excellent electron transport capability and ion diffusion capability due to their high aspect ratio.Based their special microstructure,graphene with two-dimensional structure and new-type carbon with three-dimensional structure can effectively improve the electrochemical properties of electrode materials,such as specific capacity,rate performance and cycling stable performance.In this paper,based on the advantages of carbon materials,the electrode materials with high electron/ion conductivity were designed to realize lithium ion battery,potassium ion battery and dual carbon battery with high rate performance.At the same time,the reaction mechanism of the electrode materials was investigated by scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray photoelectron spectroscopy(XPS),X-ray diffraction(XRD),Raman diffraction(Raman).(1)In Chapter 3,in order to improve the rate performance and cycle stability of lithium ion battery,Fe S-hollow core-shell structure with ultrathin carbon coated composite(H-Fe S@C)were synthesized and used as anode electrodes of LIBs.The ultra-thin carbon matrix wrapped on the surface of Fe S can enhance the electric conductivity and protect the electrode,while the hollow structure can adjust large volume expansion during cycling.In addition,carbon materials as additives can increase the conductivity of electrode materials,provide accessible channels for ion transport,and improve the rate performance.The experimental results show that the electrode material show high reversible capacity after ultra long cycle(reversible capacity of 100mA h g-1 after 100 K cycles at 80000 mA g-1)and high rate performance.Moreover,the electrode material has a good ability of slow charge and fast discharge.The time ratio of charge to discharge is about 60:1.The superior electrochemical properties of H-Fe S@C may provide a new method for designing new materials with high rate and long-term stability.(2)In Chapter 3,A sodium based dual carbon battery with high rate performance was constructed using soft carbon as anode electrode and hard carbon as cathode electrode.From the battery structure,the dual carbon battery avoids the use of metal,which can effectively reduce the production cost of the battery.In the electrochemical performance test of half cell,soft carbon showed excellent rate performance(98 mA h g-1 reversible capacity at current density of 2000 mA g-1);N-doping hard carbon has excellent anion(PF6-)storage capacity,which laid the foundation for the preparation of dual carbon battery.NDCBs possess a wide voltage range(0.01-4.7 V),high energy density of 245.7 Wh kg-1 at a power density of 1626 W kg-1,long cycle life(1000cycles),and outstanding rate performance.Furthermore,the excellent ability of fast charge and slow release and the advantage of normal work at low temperature provide new way for the research of low-temperature battery.(3)In Chapter 4,in order to improve the reversible capacity and rate performance of,Fe S2 nanoparticles with nitrogen-doped multi-wall carbon nanotubes(NCNT@Fe S2)was prepared through simple heat-treating.NCNT acts as a conductive carbon matrix to maintain good electrical for Fe S2,greatly increasing electron conduction rate and achieving good rate performance.Because the electronegativity of nitrogen is lower than that of carbon,N-doping can effectively improve the wettability of the composite,improving the reaction rate for high rate performance.Finally,the hollow structure of carbon nanotubes and the addition of amorphous carbon provide sufficient space for electrode materials to cover with the volume expansion of Fe S2 in the electrochemical reaction process and improve the cycle stability of the reaction.As the anode electrode of potassium ion battery,NCNT@Fe S2 deliveries high reversible capacity of 190 mA h g-1,when the current density is 5000 mA g-1.And,a high reversible capacity of 288 mA h g-1 can still be maintained after 150 cycles(current density of 500 mA g-1).(4)In Chapter 5,in order to improve the rate performance of potassium ion battery and reduce the cost,a new hierarchical structure-N-doped hollow carbon fibers with N-doped carbon cluster(NHCF@NCC)-is prepared for a new-type anode electrode.The electrode materials based on porous N-doped hollow carbon fibers as the backbone,which will effectively shorten the diffusion length of potassium ion and increase the interface between electrode materials and electrolyte.For another,irregular N-doped carbon cluster attached on hollow carbon fibers can provide more reaction sites.Specially,NHCF@NCC,due to the ultrahigh aspect ratio,could be a freestanding electrode material with a 3D interconnected conductive network.On this basic,NHCF@NCC shows excellent performance when as the freestanding anode materials of KIBs,exhibiting a high reversible capacity of 310 mA h g-1 when the current density is100 mA g-1,long cycle stability of 1000 cycles with a negligible degradation.At the same time,a superior rate performance of 153 mA h g-1 can still be maintained at current density of 2000 mA g-1. |
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