Co₉S₈-carbon composite as anode materials with improved Na-storage performance

The synthesis and electrochemical performance of a composite of Co₉S₈ nanoparticles and amorphous carbon is studied as an anode material for sodium-ion batteries. The Co₉S₈-carbon composite powder was fabricated through a one-pot spray pyrolysis process using thiourea and polyvinylpyrrolidone as sulfur and carbon sources, respectively. The Co₉S₈ nanoparticles are entirely covered by an amorphous carbon layer. The initial discharge and charge capacities of the Co₉S₈-carbon composite powder were 689 and 475 mA h g^-1, respectively, at a current density of 0.5 A g^-1. The Co₉S₈-carbon composite powders exhibited a stable cyclability with a reversible capacity of 404 mA h g^-1 for the 50th cycle and a superior rate capability compared with bare Co_1-xS powder. The improvement of Na-storage performance could be attributed to the small size and entanglement of the Co₉S₈ nanoparticles within the carbon matrix.