| The vastly growing clean and renewable energy have urgent needs for energy storage devices.Lithium ion batteries（LIB）have been widely used in commercial applications because of its high energy density but limited in high-power fields due to its relatively low power density.On the contrary,supercapacitors（SC）possess the properties of high power characteristics and long cycle life but due to the low energy density,which could only be applied in specific high-power fields or conjunction with other energy storage devices.Lithium ion capacitor（LIC）composed of an electric double layer capacitor（EDLC）type cathode and a LIB type anode,which can provide a higher power density than LIB and a higher energy density than EDLC.This article aimed to improve the energy density and power density of LIC,and took three different systems of lithium ion capacitors as the research object,namely,LHC/AC lithium ion capacitors,LPO@LHC/AC lithium ion capacitors,HC/（AC+NCM 523）lithium ion capacitors,through optimization research on pre-insertion of lithium and coating modification on the hard carbon anode of lithium ion capacitors,the lithium ion capacitor can simultaneously exhibit with high energy density,high power density and stable cycle life has been developed.Taking the hard carbon（HC）anodes of lithium ion capacitors as the research object,the pre-lithiation hard carbon material was prepared by the methods of single discharge lithium insertion and cyclic charging and discharging lithium insertion.Characterize the morphology and structure of the pre-lithiated HC electrodes by scanning electron microscope（SEM）,and X-ray photoelectron spectroscopy（XPS）was used to analyze the material composition on the surface of the electrodes.Activated carbon and lithium-intercalated hard carbon electrodes are used as the positive and negative active materials to assemble LHC/AC lithium ion capacitors.After1000 cycles of LIC at 1 C,the capacity becomes 76.7%of the original;which is greater than that when lithium is inserted in a single discharge 67%,when the power density is 1256.52Wkg-1,the energy density can reach 32.46 Wh kg-1.Taking the hard carbon（HC）anode materials of lithium ion capacitors as the research object,the HC is coated and modified with lithium metaphosphate（LPO）by solid-phase method,physical characterization and electrochemical performance testing of the coated materials were carried out through XRD,TEM,XPS and other testing methods.The half-cell composed of 3%LPO@HC has a reversible capacity of 515.3mAhg-1 at 0.1 C,which is much higher than the251.7mAhg-1 of the original hard carbon before coating.Perform cyclic prelithiation of 3%LPO@HC,use the prelithified electrode as the negative electrode and AC as the positive electrode to assemble the LIC.After the LIC is cycled 1000 times at 1C,the capacitance retention rate is 80.9%,which is much higher than the 76.7%before coating,when the power density is 3.8kWkg-1,the energy density can reach 17.8Whkg-1.Taking the active carbon（AC）cathode material of lithium ion capacitors as the research object,a composite material（LAC）of LiNi0.5Co0.2Mn0.3O2（NCM 523）and AC was prepared by a physical compound method.Indirectly insert lithium into the HC negative electrode by methodes of internal parallel connection.The composite material was characterized by SEM,XRD,CV and EIS.The charge and discharge results showed that the specific capacity of LAC increased with the increase of NCM 523,but the cycle and rate performance was inhibited.When the mass fraction of NCM 523 is 20%,the specific capacity of LAC is 43.8mAhg-1.After50 cycles（0.1C）,the capacity becomes 42.9mAhg-1,and the capacity retention rate is 97.95%.Regard LAC as the positive electrode and HC as the negative electrode assembly HC/（AC+NCM523）lithium ion capacitor,when the mass fraction of NCM 523 is 20%,the capacity retention rate of LIC after 800 cycles of charging and discharging is 46.93%.When the power density is8.67Wkg-1,the energy density is 38.20Whkg-1. |
