Structural Evolution and Redox Processes Involved in the Electrochemical Cycling of P2–Na<sub>0.67</sub>[Mn<sub>0.66</sub>Fe<sub>0.20</sub>Cu<sub>0.14</sub>]O<sub>2</sub>
Bibliographic record
Abstract
We report the synthesis and structural evolution of P2–Na 0.67 [Mn 0.66 Fe 0.20 Cu 0.14 ]O 2 during charge and discharge as a positive electrode for Na-ion batteries. Operando X-ray diffraction analysis revealed the existence of two phase transitions in the voltage window between 1.5–4.3 V. Ex situ pair distribution function analysis was used to characterize the local structure of the high-voltage phase which is disordered along the c -axis and is derived by the migration of a fraction of iron ions into the interlayer space. Operando X-ray absorption spectroscopy was employed to monitor the local structural evolution of the transition metals and shows the existence of Mn 3+/4+ redox below ∼3.4 V, followed by the redox activity of Cu and Fe ions at higher voltages. However, no change was observed in the K-edge X-ray absorption near-edge spectrum of any of the transition metals at voltages above 4.1 V, where the growth of the high-voltage phase is initiated. The combination of these results implies the reversible contribution of oxide ion redox to the capacity, which is coincident with metal migration. The above processes result in voltage fading over cycling, similar to that exhibited by Li 2 MnO 3 -based positive electrode materials in Li-ion batteries.
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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 | 0.002 | 0.001 |
| Meta-epidemiology (narrow) | 0.002 | 0.002 |
| Meta-epidemiology (broad) | 0.002 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.002 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| 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".