Effects of abundant Co doping on the structure and electrochemical characteristics of LiMn1.5Ni0.5−xCoxO4

The structure and electrochemical properties of LiMn1.5Ni0.5−xCoxO4 (0.0 ⩽ x ⩽ 0.5) cathodes for lithium ion batteries were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV) and galvanostatic charge–discharge tests. Cathode materials with different Co contents which were synthesized by a spray-drying method showed a single-phase spinel structure without any impurity. The XRD data reveal that the lattice parameter decreases and the structure stability is improved on increasing the amount of Co substitution. Cyclic voltammetric studies indicated three voltage regions of electrochemical activity, the three pairs of peaks related to the redox couples Mn3+/Mn4+, Ni2+/Ni4+ and Co3+/Co4+. The amount of Co doping induced a variation in the CV peak intensity and charge/discharge plateau length. Galvanostatic tests showed that with an increase in the value of x in the composition, the cycling stability was improved significantly at high temperature. For the LiMn1.5Ni1.4Co0.1O4, the initial capacity still had a high value of over 123 mAh g−1, and after 20 cycles, it retained over 115 mAh g−1 at 55 °C. When the value of x is 0.4 or 0.5, after cycling, the capacity nearly did not nearly fade between 3.20 and 4.95 V at 55 °C.