Design And Performance Research Of Hard Carbon Composite Anode For Lithium Ion Capacitors

As an emerging electrochemical energy storage device,lithium ion capacitors with both high energy and high power have gradually become a major research focus.Lithium-ion capacitors match the anode of a lithium-ion battery with the cathode of a supercapacitor.The capacitive electrode drives an increase in power density,and the battery-type electrode drives an increase in energy density.Therefore,a lithium-ion capacitor based on a reasonable design can simultaneously achieve high energy density,high power density and an excellent cycle of life.At present,the development of lithium-ion capacitors is mainly restricted by the imbalance of electrochemical reaction kinetics between the battery-type anode based on the faraday reaction mechanism and the capacitive cathode based on the nonfaraday mechanism.The imbalance of reaction kinetics leads to the mismatch between the cathode and anode of the lithium ion capacitor during the charge and discharge process,and the anode lags behind the cathode significantly.Therefore,the current research hotspots of lithium ion capacitors are mainly focused on the anode materials,and the cathode and anode reaction kinetics of lithium ion capacitors can be balanced by enhancing the reaction kinetic performance of the anode.Based on its own special structure,hard carbon materials have more active sites and lower ion intercalation barriers,and are highly expected as the anodes of lithium ion capacitors.However,because the hard carbon material has no obvious lithium ion insertion platform,there is a large potential change during the charging and discharging process,which causes the energy storage potential range of the capacitive cathode of the lithium ion capacitor to become smaller,so that the lithium ion capacitor device cannot achieve high energy density.The main content of this paper is summarized as follows:In this thesis,the hard carbon material is compounded with a transition metal compound with a large specific capacity,and nitrogen-doped hard carbon microspheres（NCS-CoSe₂）embedded with CoSe₂ nanoparticles are synthesized by hydrothermal synthesis,pyrolysis,and selenization.The two-dimensional cross-linked three-dimensional carbon material（NC-MoS₂）supported by MoS₂ was synthesized by solvent-free coating and chemical vapor deposition.NCS-CoSe₂//AC and NC-MoS₂//AC have energy densities of 144,82 and 160,94 Whkg^-1 at power densities of 335 and 6700 Wkg^-1,respectively.And these two devices have high cycle stability.The hard carbon is compounded with the transition metal compound based on the conversion mechanism,and the compounded material has a good cycle life while having excellent electrochemical dynamic performance and high specific capacity through a synergistic effect.It can effectively reduce the potential change of the anode during the charging and discharging process of the lithium ion capacitor,to realize the high energy density,high power density and good cycle life.