Comparison of structure and electrochemical properties for 5 V LiNi0.5Mn1.5O4 and LiNi0.4Cr0.2Mn1.4O4 cathode materials

Spinel LiNi0.5Mn1.5O4 and LiMn1.4Cr0.2Ni0.4O4 cathode materials have been successfully synthesized by the sol–gel method using citric acid as a chelating agent. The structure and electrochemical performance of these as-prepared powders have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and the galvanostatic charge–discharge test in detail. XRD results show that there is a small LiyNi1-yO impurity peak placed close to the (4 0 0) line of the spinel LiNi0.5Mn1.5O4, and LiMn1.4Cr0.2Ni0.4O4 has high phase purity, and the powders are well crystallized. SEM indicates that LiMn1.4Cr0.2Ni0.4O4 has a slightly smaller particle size and a more regular morphological structure with narrow size distribution than those of LiNi0.5Mn1.5O4. Galvanostatic charge–discharge testing indicates that the initial discharge capacities of LiMn1.4Cr0.2Ni0.4O4 and LiNi0.5Mn1.5O4 cycled at 0.15 C are 129.6 and 130.2 mAh g−1, respectively, and the capacity losses compared to the initial value, after 50 cycles, are 2.09% and 5.68%, respectively. LiMn1.4Cr0.2Ni0.4O4 cathode has a higher electrode coulombic efficiency than that of the LiNi0.5Mn1.5O4 cathode, implying that Ni and Cr dual substitution is beneficial to the reversible intercalation and de-intercalation of Li+.