Coated Co₉S₈/carbon nanotube (Co₉S₈/2CNTs) microspheres were constructed and successfully applied to aqueous ammonium-ion batteries. The introduction of carbon nanotubes in the Co₉S₈ microspheres increased the electronic conductivity, shortened the diffusion distance for NH₄⁺ ions and improved the buffering ability against volume changes in the cycling processes. As a result, Co₉S₈/2CNTs microspheres had a reversible capacity of 112 mA·h/g at 0.1 A/g. In addition, the ammonium ion energy storage mechanism accompanied by the formation of reversible phase transition product CoSO₄·6H₂O and establishment/breaking of intermolecular hydrogen bonds in Co₉S₈/2CNTs was investigated.