Efficient Supercapacitors Based on Co ₉ S ₈ /Graphene Composites for Electric Vehicles 2018-01-0440

Nowadays, SC is recognized as a key element of hybrid energy storage system in modern energy supply chain for electric vehicles (EVs). Co₉S₈ as a promising electrode material attracts much attention for supercapacitor owing to its superior electrochemical capacity. However, its poor stability and electronic conductivity, which result in inferior cycling performance and rate capability, have seriously limited the practical application of Co₉O₈ in supercapacitors.

In this article, Co₉S₈ nanoparticles were embedded in reduced graphene oxide (rGO) via a simple anneal approach as high efficient and stable electrodes for SCs. The Co₉S₈/rGO composites were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The Co₉S₈ nanoparticles were inserted tightly between the rGO layers due to strong intermolecular forces, preventing the cluster in reduction process of rGO from graphene oxide (GO). The rGO provides the conductive network for Co₉S₈ and shortens the ion diffusion paths, improving rate performance and enhancing the stability of the electrode material. The as-prepared Co₉S₈/rGO takes full advantages of high capacitance performance of Co₉S₈ nanoparticles and excellent conductivity and electrochemical stability of rGO. Thus, Co₉S₈/rGO composites exhibit high specific capacity of 708.3 F g⁻¹ with the active material mass of 2 mg at current density of 1A g⁻¹. In addition, the asymmetric hybrid SC (Co₉S₈/rGO//rGO) delivered an excellent energy density of 41.1 Wh kg⁻¹ and a high power density of 750.3 W kg⁻¹. The Co₉S₈/rGO composites introduced here represent a high efficiency ideal electrode that can be easily applied in automotive field with excellent performance.