Abstract
The lithium ion capacitor (LIC), combining supercapacitors with lithium-ion batteries, has drawn considerable attention as a new class of energy storage system. Typically, LIC was composed of graphite as anode and activated carbon (AC) as cathode, which energy density is limited by the small capacity of AC cathode. To overcome this limitation, the innovative electrode material – nitrogen-doped graphene (NGR) is prepared. Doping heteroatoms such as nitrogen into graphene can improve the conductivity and electrochemical properties of the electrode material. However, NGR has the problem of agglomeration due to the restacking force between the NGR sheets, which limits the specific surface of NGR. In order to further improve the properties of NGR, carbon nanotubes (CNTs) are added into NGR to connect each layer of NGR sheets. Bridging NGRs with CNTs is proposed in this study, namely [NGR-CNT], with lamellar structure by amidation reaction. CNTs attached onto the edges and the surface of NGR not only act as spacers to increase the electrolyte-accessible surface area, but also provide a 3-D electrical conductive paths. The characteristics of the configuration, the surface area, the pore distribution and the electrochemical analysis of NGR and [NGR-CNT] for LICs are investigated. The LIC employing [NGR-CNT] shows high cycling stability that capacitance retention remains 93.5% at scan rate of 200mVs-1 after 1000 cycles. Moreover, LIC exhibits high energy density of 71.1 Whkg-1 at a power density of 1.50 kWkg-1, operated in the voltage of 1.5-4.5V. Consequently, [NGR-CNT] is the promising electrode material for high performance LIC.