A high-performance lithium-ion capacitor with carbonized NiCo2O4 anode and vertically-aligned carbon nanoflakes cathode

Lithium ion capacitors (LICs) are energy storage devices integrating the complementary features of both supercapacitors and lithium ion batteries to simultaneously reach high energy and power densities. One of the major challenges in LIC technology is the kinetic imbalance between the faradaic insertion anode and capacitive cathode. Therefore, the design of electrode materials is crucial to enhance the rate performance of anode and the capacitance of the cathode in LIC devices. In this work, novel LICs were demonstrated with nanostructured cathode and anode. A vertically-aligned carbon nanoflakes (VACNFs) cathode provided high electrochemically active surface area and excellent conductivity, while a metal organic framework (MOF) derived carbonized nickel cobalt oxide (cNiCo2O4) anode ensured fast conversion reactions and remarkable cyclability. Electrochemical characterization of individual electrode confirmed that both electrodes exhibited good electron and ion transport capability. The LICs were fabricated with optimized electrode active materials loading to deliver high energy densities at desired charge/discharge rates. The devices exhibited energy density up to 136.9 W h/kg (at 200 W/kg). At higher power density of 40 kW/kg, under which a full charge-discharge can be finished within 4 s, the LICs could still deliver an energy density of 26.44 W h/kg. The devices also showed a good cycle stability (≈90% capacitance retention after 9000 cycles, under current density of 4 A/g) within the voltage range of 1–4.2 V.