CuCo2 S4 -rGO Microflowers: First-Principle Calculation and Application in Energy Storage.

This paper demonstrates the ability of a CuCo2 S4 -reduced graphene oxide (rGO) composite to perform robust electrochemical performances applying to supercapacitors (SCs) and lithium ion batteries (LIBs). The first-principle calculation based on density functional theory is conducted to study the electronic property of CuCo2 O4 and CuCo2 S4 and provide a theoretical basis for this work. Then, the 3D spinel-structured CuCo2 O4 and CuCo2 S4 microflowers are synthesized and compared as electrodes for both SCs and LIBs. The CuCo2 S4 microflowers can provide a larger specific surface area, which enlarges the contact area between the electrode material and the electrolyte and contributes to high-efficiency electrochemical reactions. The reduced graphene oxides are coated on the CuCo2 S4 microflowers, therefore effectively increasing the conductivity, and further absorbing the stress produced in the reaction process. As an electrode of a symmetric supercapacitor, the optimized CuCo2 S4 -rGO composite exhibits an energy density of 16.07 Wh kg-1 and a maximum power density of 3600 W kg-1 . Moreover, the CuCo2 S4 -rGO composite can also be used as an anode for lithium ion batteries, exhibiting a reversible capacity of 1050 mAh g-1 after 140 cycles at the current density of 200 mA g-1 . The galvanostatic intermittence titration techniques also reveal superior Li-ion diffusion behavior of the CuCo2 S4 -rGO composite during redox reactions.