Identification of electrochemical reaction products in lithium–oxygen cells with <sup>7</sup>Li nutation spectroscopy
Bibliographic record
Abstract
In the Li–O2 battery system, it is has been shown to be challenging to differentiate the discharge products or determine the electrolyte stability with direct 7Li NMR. Defined 7Li quadrupole lineshapes are not observed for cycled cathodes. Here, 7Li nutation NMR is demonstrated to be an effective method for the identification of Li2O2 in cycled cathodes. The 7Li quadrupole interaction of Li2O2 (35 kHz) and Li2CO3 (120 kHz) are of similar magnitude to typically radiofrequency fields (ranging from 40 to 60 kHz). The 7Li nutation frequency will therefore be influenced by both interactions. The discharge products of the cycled cathodes were determined by comparing the 7Li nutation frequencies of the cycled cathodes to the 7Li nutation frequency of the pristine materials when the applied radiofrequency field was 30 kHz. Li2CO3 was determined to be the main discharge product in the propylene carbonate/dimethyl carbonate and trimethyl phosphate electrolyte systems, since the 7Li nutation frequencies of the cathodes corresponded to the 7Li nutation frequency of pristine Li2CO3. The 7Li nutation frequency of the tetraethylene glycol dimethyl ether cathode was between the 7Li nutation frequencies of both pristine Li2O2 and pristine Li2CO3, indicating that both Li2O2 and Li2CO3 were discharge products influencing the observed nutation frequency. From 7Li nutation NMR the novel trimethyl phosphate electrolyte was determined to be an unsuitable Li–O2 electrolyte, as the fast 7Li nutation frequency indicated that Li2O2 was not a primary discharge species. With 17O NMR, Li2CO3 was confirmed to be a main discharge product formed with the trimethyl phosphate electrolyte.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
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".