The effects of Co substitution on the structure and electrochemical performances of spinel Ni(Mn2-xCox) O-4 (x = 0, 0.5, and 1.0) have been investigated. With the increase of Co content the lattice parameters decrease owing to the smaller ion radius of Co than Mn. The reversible capacity and cyclability of Ni (Mn2-xCox)O-4 first increase and then decrease with the increase of Co content and NiMn1.5Co0.5O4 shows the best electrochemical performance in compared to the other two samples. Neutron diffraction and Rielveld refinement are further applied to analyze the site occupancies of the elements of Mn, Co, O and Ni. A certain amount of Co ions substitution are favorable to enhance the electrochemical performance, but excessive Co ions in 8a and 16d sites reduce the stability of host structure which leads to the poor electrochemical performance. (C) 2016 Elsevier Ltd. All rights reserved.