Effect of hydrochloric acid activation on properties of graphite carbonitride(g-C₃N₄) structure and g-C₃N₄/S cathode composites for lithium-sulfur batteries

Graphite carbonitride (g-C₃N₄) was prepared from melamine and hydrothermally treated with hydrochloric acid to obtain acid-activated g-C₃N₄. The effects of hydrochloric acid activation on the structure and morphology of g-C₃N₄ and the electrochemical performance of g-C₃N₄/S cathode composites were investigated experimentally. The experimental results show that g-C₃N₄ layer spacing does not change significantly after hydrochloric acid activation. With the increase of hydrochloric acid concentration, the specific surface area of the g-C₃N₄ sample first increases and then decreases. When the concentration of hydrochloric acid is 2.5wt%, the maximum specific surface area is 86.1 m²·g^-1, which is 5-6 times higher than untreated g-C₃N₄ of 13 m²·g^-1. The specific capacity and cycle performance of hydrochloric acid activated g-C₃N₄/S cathode composites also increase first and then decrease. When the concentration of hydrochloric acid is 2.5wt%, the specific capacity and cycle performance of the hydrochloric acid activated g-C₃N₄/S cathode composite sample are the best, and the specific capacity is 1 538 mAh·g^-1. After 50 cycles, its capacity holding rate is 77.8%. The electrochemical performance and specific surface area of hydrochloric acid activated g-C₃N₄/S cathode composites show a strong correlation.