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. 2025 Mar 3;26(5):e202400832.
doi: 10.1002/cphc.202400832. Epub 2025 Jan 28.

Electrochemical and Thermal Evolution of P2 Na2/3MnO2

B D K K Thilakarathna  1 , Uttam Mittal  1 , Jian Peng  1 , Daniel Brocklebank  1 , Helen E A Brand  2 , Neeraj Sharma  1
Affiliations

Electrochemical and Thermal Evolution of P2 Na2/3MnO2

B D K K Thilakarathna et al. Chemphyschem. .

Abstract

P2 Na2/3MnO2 can be used as a cathode material in sodium-ion batteries. Here, the electrochemical-temperature-dependent evolution of P2 Na2/3MnO2 is investigated using X-ray powder diffraction. P2 Na2/3MnO2 powder under a N2 atmosphere shows evidence of the formation of a monoclinic C2/m phase, from about 450 °C. The P2 Na2/3MnO2 electrode sealed in a capillary undergoes a sequence of phase transitions from the as-prepared hexagonal P63/mmc to a secondary hexagonal P63/mmc phase followed by a transition to Mn3O4 and subsequently MnO. NaF also appears parallel to the formation of the secondary hexagonal phase. These transitions suggest a local reducing environment as the Mn oxidation state evolves from 3+/4+ to 2+. The samples at various states of charge show similar thermal evolution with the exception of the discharged (Na-inserted) state which features a slightly more complex evolution. Understanding the structure and thermal evolution at various states of charge and under various conditions provides insight into the stability of these potential cathode materials.

Keywords: Cathode; Sodium-ion batteries; Structural evolution; Synchrotron X-ray powder diffraction.

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Conflict of interest statement

There are no conflicts of interest to declare.

Figures

Figure 1
Figure 1
(a) Contour plot of the diffraction data (λ=1.5418 Å), (b) Rietveld‐refined fit at 450°C and (c) zoom of the stacking axes (002) in P63 /mmc and (100) in C2/m. The * refers to the Mn3O4 phase.
Figure 2
Figure 2
Lattice parameters of the hexagonal P63/mmc phase, volume and weight fractions of both hexagonal and monoclinic phases as a function of temperature.
Figure 3
Figure 3
(a) Thermal evolution of NaxMnO2 at various states of charge. Weight fractions are derived from Rietveld analysis using a variety of structural models. (b) The contour plots show the evolution of a selected 2θ range (λ =0.68729(1) Å).
Figure 4
Figure 4
Lattice parameters and volume evolution of the two hexagonal P63/mmc phases found between 30–500 °C.
Figure 5
Figure 5
Lattice parameters and volume evolution of the orthorhombic Cmcm phase(s), labelled FD_1 and FD_2 found between 30–400 °C in sample FD.
Figure 6
Figure 6
The (a) volume evolution of the Mn3O4 and MnO phases and (b‐c) the volume and lattice parameter evolution of Mn3O4.
See this image and copyright information in PMC

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