Effect of 3D Metal on Electrochemical Properties of Sodium Intercalation Cathode P2-NaxMe1/3Mn2/3O2 (M = Co, Ni, or Fe)

Abstract

This research aims to evaluate the influence of different 3D metals (Fe, Co, and Ni) substituted to Mn on the electrochemical performance of P2-NaxMe1/3Mn2/3O2 material, which was synthesized by the coprecipitation process followed by calcination at high temperature. X-ray diffraction (XRD) results revealed that the synthesized Mn-rich materials possessed a P2-type structure with a negligible amount of oxide impurities. The materials possessed their typical cyclic voltammogram and charge-discharge profiles; indeed, a high reversible redox reaction was obtained by NaxCo1/3Mn2/3O2 sample. Both NaxCo1/3Mn2/3O2 and NaxFe1/3Mn2/3O2 provided a high specific capacity of above 140 mAh·g−1; however, the former showed better cycling performance with 83% capacity retention after 50 cycles at C/10 and high rate capability. Meanwhile, the Ni-sub NaxNi1/3Mn2/3O2 exhibited excellent cycling stability but a low specific capacity of 110 mAh·g−1 and inferior rate capability. The diffusion coefficient of Na+ ions into the structure tended to decrease with a depth of discharge; those values were in the range of 10−10–10−9 cm2·s−1 and 10−11–10−10 cm2·s−1 in the solid solution region and biphasic region, respectively.

High Performance of Porous, Hierarchically Structured P2‐Na0.6Al0.11 − xNi0.22 − yFex + yMn0.66O2 Cathode Materials

“…In P2‐type oxides, the process of Ni 3 + / Ni 4 + oxidation/reduction takes place at around 3.5 to 3.7 V (against Na|Na + ) [ 23,30 ] and Fe 3 + /Fe 4 + oxidation/reduction occurs at approx. 4.0 to 4.1 V. [ 31 ] It is necessary to understand if and to what extend Fe is electrochemically active in these iron containing cathode materials in the different voltage regimes. Mößbauer spectroscopy was performed on the pristine materials after sintering at T S = 950 °C, and after charging to 4.6 V. For the materials recovered after charging, thick cathode sheets were used (coated with 800 µm gap size, ca.…”

“…The different behavior of c at high voltage might be due to the oxidation of Fe 3 + to Fe 4 + , which takes place at higher voltages than Ni 3 + /Ni 4 + in P2 layered oxides. [ 31,39 ] For NAFMO a moderate change of lattice parameter a together with the smallest change in c can be observed, which is related to the absence of a phase transition. If the charge‐process was not complete for NAFMO, then this might be a reason for the absence.…”