Synthesis, Structure, and Na-Ion Migration in Na<sub>4</sub>NiP<sub>2</sub>O<sub>7</sub>F<sub>2</sub>: A Prospective High Voltage Positive Electrode Material for the Na-Ion Battery
Bibliographic record
Abstract
In the recent hunt for novel Na-ion cathode hosts, a variety of sodium analogues of classic Li-ion structures have been thoroughly explored. However, Na-ion analogues generally possess modified structures and dissimilar Na-ion energetics compared to their Li-ion analogues due to the large size of Na + (102 pm) vs Li + (76 pm), often resulting in sluggish Na + kinetics. Materials development targeted toward new and different specific host structures possessing optimum properties for Na-ion migration is crucial. Here, we report the first sodium metal fluoropyrophosphate Na-ion host with a three-dimensional framework—Na 4 NiP 2 O 7 F 2 —which is predicted to have a high voltage (∼5 V) based on its Ni 2+/3+/4+ redox couple and composition. Structure solution from single crystal diffraction data combined with atomistic simulation computation suggests the presence of low activation energy Na-ion migration pathways (<0.6 eV) in all three dimensions. The particularly low barrier of 0.36 eV calculated for migration along the [010] direction is in full accord with temperature dependent ionic conductivity measurements that yield an experimental value of 0.32 eV. Spacious Na-ion pathways endow the material with good ionic conductivity as determined by ac impedance spectroscopy, and facile exchange of three Na + ions for Li + is observed at slightly elevated temperatures. Furthermore, the polycrystalline material exhibits excellent thermal stability under ambient atmosphere up to 600 °C, crucial for the safe operation of a Na-ion battery.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.002 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; both teacher heads agree on what is shown here.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".