S-Co(OH)2 composite is prepared via a facile co-precipitation method and investigated as negative electrode of Ni/Co battery. The addition of amorphous S improves the electrochemical properties of Co(OH)2 electrode. The discharge capacity of S-Co(OH)2 electrode can reach 413.2mAhg−1 and still keep about 340mAhg−1 after 300 cycles, which is much higher than that of S-free Co(OH)2 electrode. Amorphous S in S-Co(OH)2 electrode shows two functions during the charge–discharge process. One is that the addition of amorphous S with high specific surface area improves the dispersion of Co(OH)2 platelets. The other is that the dissolution of amorphous S in electrode brings the new interspaces among the Co(OH)2 platelets, these two factors largely increase the interspaces among Co(OH)2 platelets. More interspaces are correlated to larger contact area with alkaline solution, which is in favor of the surface electrochemical redox. Thus, the capacity utilization of Co(OH)2 is enhanced.