A series of novel Co–S composites composed of metallic Co and Co9S8 were prepared via a facile hydrothermal method and investigated as negative electrodes for secondary alkaline batteries. Instrumental analyses reveal that the incorporation of Co9S8 nanoflakes leads to better dispersion of Co particles and increases the interspacing between Co particles, greatly increasing the Brunauer–Emmett–Teller (BET) surface area. Thus, the electrochemical performance of the Co electrode is significantly improved. The maximum discharge capacity of the Co–S electrode reaches 420mAhg−1 and remains at 410mAhg−1 after 200 cycles, which is much higher than the capacity of a pure Co electrode. The shift of the redox peaks in the CV curves and the negative movement of the discharge–potential plateau are attributed to the dissolution of sulfur in the composite, which also favors the capacity of Co. The measurements reveal that the reversible faradic reaction between highly dispersed Co and Co(OH)2 is dominant for the Co–S composites.