Preparation And Potassium Storage Properties Of Hierarchical Porous Carbon-based Anode

Lithium-ion hybrid capacitors（LIHCs）have already been widely concerned and studied by scientists because they can integrate the advantages of ion batteries and supercapacitors.However,with a large number of commercial lithium-ion hybrid capacitors used in energy storage equipment,and the low reserves of lithium metal in the earth’s crust（only 0.0017 wt%of the total amount of the earth’s crust）,the consumption of lithium metal is insufficient,which leads to the rapid rise of its price and makes it unsustainable to be used by human beings.Nowadays,potassium-ion hybrid capacitors（KIHCs）have attracted great interest due to the low redox potential of K/K⁺and the sufficient reserves of potassium.In addition,carbon-based electrode materials are considered as the most promising anode materials for ion hybrid capacitors because of high abundance and high conductivity.Many previous studies have proved that heteroatom doping can effectively change the structure of carbon materials.By increasing defects in the material,more active sites can be obtained.And it can also promote the conductivity of electrons,improve kinematics,and accelerate charge transfer to improve the energy storage performance of the material at the same time.Based on this,we prepared functional carbon-based electrode material with excellent structural design and heteroatom doping.By assembling potassium-ion hybrid capacitors,the potassium storage performance was investigated,and the synergistic effect of structure and doping was also discussed.The main content and innovation are as follows:（1）In Chapter 2,N-doped carbon nanotubes（NCNTs）were synthesized by a one-step method as anode for robust K-ion batteries（KIBs）and potassium-ion hybrid capacitors（KIHCs）.NCNTs with a hierarchical structure and high content of N doping can provide enough space to relieve volume expansion and provide channels to effectively transport electrons and ions.Therefore,NCNTs display high reversible capacity,excellent rate performance and excellent cycle stability(after 3600 cycles,the capacity is 190.2 m A h g^-1 at a high current density of 1000 m A g^-1,the average decay rate of each cycle is 0.00238%).In addition,KIHCs based on NCNTs anode present high energy density(117.1 W h kg^-1 at 50 m A g^-1 current density),high power density(1713.4 W kg^-1 at 1 A g^-1),and long cycle life(2000 cycles at 1 A g^-1)and high retention rate（81.6%after 2000 cycles）.In addition,through the analysis of in-situ Raman spectrum,the excellent electrochemical reversibility of the KIHCs was proved.（2）In Chapter 3,a starch-derived hierarchically porous nitrogen-doped carbon（SHPNC-1000）anode was rationally designed for high-energy and robust KIHCs.The layered structure and abundant nitrogen doped in the SHPNC-1000 anode can expand the space between graphite layers to buffer the volume expansion during the K⁺insertion/extraction process,and provide more el ectrochemically active sites to achieve high specific capacity.Therefore,KIHCs assembled by SHPNC-1000 anode and commercial activated carbon cathode can provide a high energy density of 165 W h kg^-1 at a current density of 50 m A g^-1,and a long cycle life of 10000 cycles at a current density of 1 A g^-1.