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.