Unveiling the Impact of Impurity Phases on the Electrochemical Performance of Cobalt-Free Analogs of (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)O as anode for Lithium-ion Batteries

Micrometer-size particles of the pure single-phase rock salt multi-metals oxide, (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)O, have demonstrated long-term cycling stability and excellent rate performance as an anode for lithium-ion batteries. Such a feat has only been achieved with the nanostructuring of binary transition metal oxides. This success has led to the preparation of several pure single-phase spinel multi-metal oxides with significantly higher capacities. A common belief regarding these complex oxides is that the pure single-phase is a prerequisite for their outstanding electrochemical performance. Deviation from a pure single-phase is thought to harm their electrochemical performance. Here, we prepare and characterize the cobalt-free analogs of (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)O using a traditional solid-state synthesis method by replacing cobalt with iron and manganese to give (Mg0.2Fe0.2Ni0.2Cu0.2Zn0.2)O and (Mg0.2Mn0.2Ni0.2Cu0.2Zn0.2)O respectively. These analogs were prepared in an air and an argon atmosphere to yield several compositions with different mixtures of crystalline secondary phases. The electrochemical performance of the pure single-phase (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)O is used as a benchmark to compare the performance of the cobalt-free multi-phase analogs. The results indicate that although these cobalt-free analogs are not pure single-phase materials, their electrochemical performance is similar to that observed with (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)O, suggesting that a pure single-phase might not be a prerequisite for an excellent electrochemical performance for these complex multi-metal oxides.