Novel 3D Co9S8@graphene nanocomposites prepared by deep eutectic solvents for lithium-ion storage

Transition metal sulfides(TMSs) are an ideal alternative for use in lithium-ion batteries(LIBs) owing to their high theoretical capacity and environmental advantages. However, bulk expansion problems of TMSs and the classical method of electrode synthesis limit their large-scale development. In this study, 3D hydrangea-shaped Co ₉S ₈ @graphene nanocomposites were successfully prepared by one-step in-situ pyrolytic sulfidation. The resulting Co ₉S ₈ @graphene composites were tested as anodes of LIBs and showed excellent electrochemical properties with a high discharge specific capacity of 1530.3mAh·g ⁻¹ at a current density of 0.1 A·g ⁻¹, superior multiplicative properties reaching 415.7mAh·g ⁻¹ at a current density of 5 A·g ⁻¹, and rapid recovery to 726.4mAh·g ⁻¹ when the current density returned to its initial value. The electrodes also displayed superior capacity retention and cycling stability at high current densities with a stable discharge capacity of 550mAh·g ⁻¹ after 1000 cycles at a current density of 1 A·g ⁻¹ . These features were attributed to the 3D hydrangea-like graphene structure, which greatly increased the specific surface area of the material, facilitating contact with the electrolyte during electrochemical reactions. The nanoparticles also provided more space, thereby improving the volume expansion of the material during the electrochemical processes. In sum, these findings offer a new synthetic route to future preparation of metal sulphide@graphene composites.