One-step solvothermal synthesis of high-capacity Fe3O4/reduced graphene oxide composite for use in Li-ion capacitor

To obtain high-performance lithium-ion capacitors (LICs), superior Fe 3 O 4 /reduced graphene oxide (rGO) composite has been synthesized by a facile one-step solvothermal method. The morphologies and structures of materials were characterized by powder X-ray diffraction, Raman spectroscopy , X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy and N 2 adsorption–desorption isotherm. Electrochemical performances of materials were evaluated by cyclic voltammetry , galvanostatic charge/discharge and electrochemical impedance spectroscopy in half cell. Compared with the agglomerated pure Fe 3 O 4 , the high-crystallinity Fe 3 O 4 particles uniformly distributes onto the rGO sheets and the Fe 3 O 4 particles possess smaller size of 150–250 nm in Fe 3 O 4 /rGO composite. Therefore, the introduction of rGO can not only increase the specific surface area but also enhance the electrical conductivity of electrode material, leading to the improvement of electrochemical performances. The Fe 3 O 4 /rGO composite can reach high specific capacity of 1065 mAh g −1  at 0.1 A g −1 , and exhibits good rate capability and cyclic stability. Using the as-prepared Fe 3 O 4 /rGO composite as negative electrode and activated carbon (AC) as positive electrode, a Fe 3 O 4 /rGO//AC LIC was fabricated. The assembled Fe 3 O 4 /rGO//AC LIC presents outstanding energy density of 98.8 Wh kg −1 and power density of 3.4 kW kg −1 . Moreover, 78.9% of capacity can be retained after 1000 charge/discharge cycles.