Synthesis and Electrochemical Characterization of P2- and O3-Phase Na2/3Fe1/2Mn1/2O2 Layered Oxide
Layered oxides, NaMO2 (M = Cr, Mn, Fe, Co, Ni, and mixture of 2-3 transition metal) show one of the largest capacities among the Na-ion cathode candidates due to their structural simplicity. Particularly, Na(FeMn)O2 is of great interest because Fe and Mn are abundant and environmentally benign. Recently, one of the largest capacities was reached with P2-phase Na2/3Fe1/2Mn1/2O2. O3-phase of the same composition, however, could not be prepared because each phase depends on the Na concentration.
Here, we report synthesis and direct comparison of electrochemistry between P2- and O3-phase Na2/3Fe1/2Mn1/2O2. The pure phases of P2 and O3 are confirmed by XRDs as shown in figure 1 and we have obtained a similar electrochemical performance in terms of capacity and cyclability for both phases. Our focus is to rationalize electrochemical behavior based on the structural types and Na surrounding environment while keeping the composition of oxide layer the same.
Figure 1. XRD pattern matching of a) P2-Na2/3Fe1/2Mn1/2O2 and b) O3-Na2/3Fe1/2Mn1/2O2.
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