Abstract:

 Mesoporous graphene/carbon black (G/SC) composite conductive additive has been applied for lithium ion capacitor anode. G/SC conductive additive has been comparatively studied with carbon black (SC), graphene nanosheets/carbon nanotube/carbon black conductive slurry (GNC/SC), and carbon nanotube/carbon black (CNC). The morphologies and structures of G, SC, GNC, CNC and hard carbon have been characterized by scanning electron microscopy and X-ray diffraction, respectively. The electrochemical impedance spectra of hard carbon anode shows that the G/SC conductive additive can decrease the charge transfer resistance and the solid electrolyte interphase resistance. Compared with other conductive additives, the hard carbon anode with G/SC has the highest specific capacity (155 mA·h·g1), best rate capability (60 mA·h·g1 at the current density of 2 A·g1). The cyclic voltammetry analysis indicates that the faradaic diffusion of lithium ion in the electrode bulk transforms into rapid diffusion on the anode surface as the scan rate increases, G/SC conductive additive and hard carbon have formed “point-to-plane” conducting network, which promotes the electron transfer in hard carbon anode and the lithium ion diffusion on anode surface.. Lithium ion capacitors have been fabricated with hard carbon anode and activated carbon cathode, which shows excellent electrochemical performances. The energy density of lithium ion capacitor with G/SC is 81.1 W·h·kg1, and the power density is 22.3 kW·kg1, the capacity retention ratio is 98.7% after 2000 cycles at a C-rate of 20 C.

Key words: mesoporous graphene, conductive additives, hard carbon, carbon nanotubes, lithium ion diffusion, lithium ion capacitor