Li2Ni0.5Mn1.5O4, spinel type cathode material with high reversible capacity

A new Li-rich Li2Ni0.5Mn1.5O4 spinel cathode material is prepared chemically for the first time. Rietveld refinement confirms a cubic structure with Li2 cations occupying the 8b sites. Such crystal structure offers the cathode a theoretical capacity of 282.6 mAh g−1, which has never been realized in spinel cathodes. XPS suggests mixed cations of Ni2+/Ni3+ and Mn3+/Mn4+ within the Li2Ni0.5Mn1.5O4 compound, which suggests that both Ni and Mn redox pairs are involved during the charge/discharge process, as confirmed subsequently by the CV test with three redox pairs of Ni2+/Ni4+, Mn3+/Mn4+ and Mn2+/Mn3+ near 4.7 V, 4.0 V and 2.8 V respectively. Upon electrochemical test, a high reversible capacity of 260.4 mAh g−1 is obtained, corresponding to a coulombic efficiency of 92.2%. Compared to the other cathode materials in practical application, the spinel Li2Ni0.5Mn1.5O4 cathode material shows advantage on both the specific capacity and the energy density, indicating a high potential for future application. Further studies reveal a fast fading on the capacity retention (207.1 mAh g−1, 80.2% after 50 cycles) and poor rate performance (260.4 mAh g−1 at 0.05C and 28 mAh g−1 at 5C), suggesting that further works are needed before the material can be practically employed.