| Lithium-ion Capacitor(LIC)is a new type of asymmetric electrochemical capacitor.The LIC is composed of double-layer capacitor electrode material and lithium-ion battery electrode material intersected with lithium salt as electrolyte.Compared with supercapacitors,LIC improved its power density;and compared with lithium-ion batteries,LIC achieved an increase in energy density.LIC is widely used in new energy supporting facilities,electronic equipment,transportation and other fields.In recent years,with the prosperity of mobile electronic devices and the development of flexible wearable electronic devices,flexible energy storage devices have become a research hotspot.In this paper,graphene and carbon nanotubes were used as flexible framework materials,and activated carbon and lithium titanate were introduced to prepare electrode materials for flexible lithium ion capacitors through facile ultrasonication and vacuum filtration method.The preparation of the flexible electrode material of the lithium ion capacitor is realized.The electrode material prepared in this research is binder-free,conductive agent free and current collector free,thereby,which is favorable to improve the energy density.Moreover,the self-supporting electrode material presents the characteristics of flexibility and bendability,which has guiding significance for the development of flexible energy storage devices in the future.The specific contents include the following aspects.1).Using graphene and carbon nanotubes as skeleton materials,flexible composite materials were prepared by facile ultrasonication and vacuum filtration method.Graphene is a two-dimensional lamellar structure,and carbon nanotube is a one-dimensional tubular structure.Under the action of ultrasonic mixing,the carbon nanotube enters the graphene sheet layers,and block the agglomeration of graphene sheets and carbon nanotubes by van der Waals force.Furthermore,through vacuum filtration,a flexible composite material with macroscopic self-supporting properties is prepared.2)Activated carbon/carbon nanotube/graphene(AC/CNT/rGO)flexible composites were prepared by introducing activated carbon into graphene and carbon nanotube frameworks.As a cathode material for lithium ion capacitors,the energy storage mechanism is electrostatic adsorption.Making full use of the large specific surface area properties of activated carbon,carbon nanotubes,and graphene.By assembling a symmetrical double-layer capacitor,the test results show that the optimal ratio of the comprehensive performance is 50:5:45 for AC/CNT/rGO.The corresponding energy density and power density can achieve 30Wh kg-1 and 1800 W kg-1,respectively.3)Lithium titanate with nanorod-like morphology was prepared by a two-step hydrothermal method.Then,it is combined with graphene-carbon nanotube skeleton materials to prepare the flexible composite material of lithium titanate nanorod/carbon nanotube/graphene(LTO-NR/CNT/RGO).Finally,using the lithium foil as the counter electrode,LTO-NR/CNT/rGO was assembled into a half-cell to test its electrochemical properties.The experimental results show that the good electrical conductivity of graphene and carbon nanotubes improves the rate performance of lithium titanate.By studying the ratio of lithium titanate to graphene in the composite.it is concluded that the best ratio of LTO-NR:CNT:RGO is 70:5:25.At 2C(1C=175 mA g-1)current density,the specific capacity was 203 mAh g-1,after 1000 cycles,the specific capacity was maintained at 191 mAh g-1 corresponding to the capacity retention rate was 94.1%.The specific capacity at a current density of 20 C was 147 mAh g-1.4)Asymmetric full capacitors are fabricated by assembling cathode(AC/CNT/RGO=50/5/45)and anode(LTO-NR/CNT/RGO=75/5/25)materials,which have been prepared.According to the experimental results,the cathode and anode electrode quality is 2.38,similar to the theoretical value 2.57.And the specific capacity of this asymmetric LIC is 71 F g-1,and the capacity have 41 F g-1 after 1000 cycles at a current density of 0.35 A g-1. |
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