Carbon Nanofiber-based Composites As Anode Material For Potassium-ion Hybrid Capacitor

Rechargeable lithium-ion battery（LIBs）has been widely us ed in m obile phones,laptop computers and other electronic devi ces because of their high energy/power density and light weight.Currently,LIBs have been extended to the application fields of electric vehicles and smart grids.However,the lithium resources are not very abundant,causing the cost of lithium-ion batteries to gradually increase,so we need to develop alternatives to LIBs.At the same time,lithium-ion batterie is also limited in the use of large-scale energy storage devices due to their lower power density.Metals K and Li are in the same main group,so they have similar chemical proper ties,and because of the rich res ources of potassium metal,the development of Potassium-based energy storage equipment instead of LIBs has become attract ed the attention of researchers.Compared with traditi onal secondary batteries and capacitors,hybrid capacitors（HEC）are considered the best energy storage devices becaus e they exhibit higher energy density.HEC exhibits the dual working characteristics of ion-batterie and capacitor.It is a new type of energy storage device with great development potent ial and application prospects.At present,many researchers are com mitted to further improving the energy density and power density of the HEC syst em.One effective method is using an asymmetric hybrid supercapacitor system.Increasing the working voltage of the capacitor,thereby increasing the energy density of the asymmetric HEC.Therefore,this thesis’s research is the topic of the asymmetric HEC assembled by activated carbon electrode and battery electrode material.Researching and improving the energy storage of electrode materi als by combining with sel enide and doping,thereby increasing the energy/power density of HEC.The main research achievement s are as follows:（1）Based on the high theoretical capacity of t ransition metal selenide,in Chapter2,we synthesized the composite MoSe ₂/CNF through electrospinning and solid-phase thermal technology.A series of charact erizat ion techniques SEM,TEM,XRD,XPS,etc.are used to charact erize their microscopic morphology.In additi on,they are tested for ele ctrochemical performance.For P IBs,it can obtain an initial discharge capacity of 801 m Ah g^-1,and the current After 100 cycles at a density of 100 m A g^-1,it can reach 316 m A h g^-1,which is much higher than pure carbon nanofiber(187 m Ah g^-1);for P IHC,aft er 100 cycles at 100 m A g^-1,81 m Ah g^-1 is obtained,and the capacity retention rate after 1000 cycles at 1A g^-1 is 81.58%,indicating that the composite MoSe₂/CNF greatly improves the purity carbon fiber capacity.（2）Heteroatom doping is an effective method to improve the conductivity of carbon materi als.Therefore,in Chapter 3,we use thiourea as the initial N source,using electrospinning technology and high temperature carbonizati on technology to prepare high nitrogen content N（19.78 at%）C₃N₄@NCNF.High N content is beneficial to increas e defect sites and improve capacity and rate performance.For P IBs and PIHC,energy density(62 Wh kg^-1),power density(2102 W kg^-1)and long-cycle stability can be obt ained,further indicating that het eroatom doping is effective for improving the electrochemical performance of carbon m aterials.