Design And Synthesis Of Heteroatom-Doped Carbon And Its Composites For Lithium-Ion Capacitors

As one of the most promising energy storage systems,lithium-ion capacitors（LICs）integrate the advantages of lithium-ion batteries（LIBs）and supercapacitors（SCs）,and are expected to meet the current demands of large-scale electricity grids and electric vehicles.However,the imbalance of reaction kinetics between the capacitive cathode and the battery-type anode hinders the practical application of LICs.To solve the above issues,in this dissertation,heteroatom-doped novel carbon composites were rational designed and fabricated,and used them as the electrodes of LICs,their electrochemical performance and kinetics mechanism were also further explored.The detailed research content is as follows:（1）Ntrogen doped porous carbon nanosheets（NMCK）were prepared by self-templating method,which uses sodium citrate as precursor,urea as nitrogen source and potassium hydroxide as the activated reagent.The NMCK possesses abundant micropores and mesoporous,large specific surface area and multifarious heteroatom functional groups,which can increase the diffusion rate of Li⁺.As cathode material for LICs,NMCK electrodes display high reversible specific capacity of 60 m Ah g^-1 at 2 A g^-1 after 3000 cycles,which is a promising cathode for LICs.（2）Nitrogen and phosphorous co-doped carbon hollow spheres with polypyrrole composites（NPHCS@PPy）were designed using silica nanospheres template.The Heteroatomic doping improves the pseudocapacitance and the existence of polypyrrole is beneficial to the improvement of the electronic conductivity.The NPHCS@PPy anode display excellent rate capability and long-term stability in a half-cell.When assembled with NMCK cathode,the NMCK//NPHCS@PPy-LICs can achieve high energy densities of 145 and 59 Wh kg^-1 at power densities of 225 and 22500 W kg^-1（92%capacity retention after 7500 cycles）.（3）The bimetallic oxide nanosheets（Ni Co O₂）were synthesized by hydrothermal method.Then they coated with dopamine carbon to form Ni Co O₂@C compound material.Due to the synergistic effect of nickel cobalt oxide and carbon,the assembled NMCK//Ni Co O₂@C-LICs display high energy densities of 128 and 61 Wh kg^-1 at power densities of 450 and 11250 W kg^-1,respectively.Additionally,the LICs exhibit excellent cyclic performance with the capacity retention of 94%after 9000 cycles at the current density of 1 A g^-1.