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PreprintCC BY-NC-NDChemRxiv

Structural evolution of the P2-Na2/3Ni1/3Mn2/3O2 sodium-ion battery cathode material resolved by 3D electron diffraction

  • Hasindhi H. Lokuge1,2,3
  • Kusalvin Dabare1,2,3
  • Jason J. Zhou1,2,3
  • Moinak Dutta1,2,3
  • Mark Del Campo4
  • Claire E. Casaday5,6
  • Molleigh B. Preefer5,6
  • Joshua D. Bocarsly1,2,3
6 affiliations
  1. 1Department of Chemistry
  2. 2University of Houston
  3. 3Texas Center for Superconductivity, University of Houston
  4. 4Rigaku Americas
  5. 5Stanford Synchrotron Radiation Lightsource
  6. 6SLAC National Accelerator Laboratory
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Abstract

P2-Na2/3Ni1/3Mn2/3O2 is a promising cathode for sodium-ion batteries, yet its electrochemical behavior is governed by a complex sequence of structural transformations whose microscopic origins remain poorly understood. In particular, Na+/vacancy ordering is expected to play a central role in the phase evolution but is challenging to resolve using powder diffraction alone. Here, we combine continuous-rotation 3D electron diffraction (3D-ED) with operando and ex situ synchrotron X-ray diffraction (SXRD) to establish a comprehensive structural picture of NaxNi1/3Mn2/3O2 across the full electrochemical window (1.0 V – 4.5 V). 3D-ED resolves Na+/vacancy ordering in sub-micrometer crystallites, revealing ordered P2 structures at Nax = 2/3, 1/2, and 1/3. In each case, Na+/vacancy ordering lowers the symmetry of the parent P2 framework and produces arrangements that minimize electrostatic repulsion while satisfying Pauling’s second rule. Transient phases at Nax = 3/5 and 2/5 are also observed during charging, while two highly sodiated P2 phases are accessed by discharging to low voltages. At high states of charge, extensive Na+ removal drives the P2→O2 transition and produces pronounced stacking disorder, demonstrating that the layer glide is not fully coherent. Bond-valence analysis further tracks transition-metal charge compensation during Na+ extraction. Together, these results establish Na+/vacancy ordering as a key structural variable governing phase stability, charge compensation, and structural transformations in P2-Na2/3Ni1/3Mn2/3O2, while highlighting 3D-ED as a powerful approach for resolving complex ordering phenomena in battery materials.

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Cite

BibTeXRIS
BibTeX
@misc{lokuge2026structural,
  title = {{Structural evolution of the P2-Na2/3Ni1/3Mn2/3O2 sodium-ion battery cathode material resolved by 3D electron diffraction}},
  author = {Hasindhi H. Lokuge and Kusalvin Dabare and Jason J. Zhou and Moinak Dutta and Mark Del Campo and Claire E. Casaday and Molleigh B. Preefer and Joshua D. Bocarsly},
  howpublished = {ChemRxiv},
  year = {2026},
  month = oct,
  doi = {10.26434/chemrxiv.15010983/v1},
  url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010983/v1},
  note = {CC BY-NC-ND},
}
RIS
TY  - UNPB
TI  - Structural evolution of the P2-Na2/3Ni1/3Mn2/3O2 sodium-ion battery cathode material resolved by 3D electron diffraction
AU  - Hasindhi H. Lokuge
AU  - Kusalvin Dabare
AU  - Jason J. Zhou
AU  - Moinak Dutta
AU  - Mark Del Campo
AU  - Claire E. Casaday
AU  - Molleigh B. Preefer
AU  - Joshua D. Bocarsly
PY  - 2026
DA  - 2026/10/23
PB  - ChemRxiv
DO  - 10.26434/chemrxiv.15010983/v1
UR  - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010983/v1
AB  - P2-Na2/3Ni1/3Mn2/3O2 is a promising cathode for sodium-ion batteries, yet its electrochemical behavior is governed by a complex sequence of structural transformations whose microscopic origins remain poorly understood. In particular, Na+/vacancy ordering is expected to play a central role in the phase evolution but is challenging to resolve using powder diffraction alone. Here, we combine continuous-rotation 3D electron diffraction (3D-ED) with operando and ex situ synchrotron X-ray diffraction (SXRD) to establish a comprehensive structural picture of NaxNi1/3Mn2/3O2 across the full electrochemical window (1.0 V – 4.5 V). 3D-ED resolves Na+/vacancy ordering in sub-micrometer crystallites, revealing ordered P2 structures at Nax = 2/3, 1/2, and 1/3. In each case, Na+/vacancy ordering lowers the symmetry of the parent P2 framework and produces arrangements that minimize electrostatic repulsion while satisfying Pauling’s second rule. Transient phases at Nax = 3/5 and 2/5 are also observed during charging, while two highly sodiated P2 phases are accessed by discharging to low voltages. At high states of charge, extensive Na+ removal drives the P2→O2 transition and produces pronounced stacking disorder, demonstrating that the layer glide is not fully coherent. Bond-valence analysis further tracks transition-metal charge compensation during Na+ extraction. Together, these results establish Na+/vacancy ordering as a key structural variable governing phase stability, charge compensation, and structural transformations in P2-Na2/3Ni1/3Mn2/3O2, while highlighting 3D-ED as a powerful approach for resolving complex ordering phenomena in battery materials.
ER  -