A1572 Journal of The Electrochemical Society, 161 (10) A1572-A1579 (2014) 0013-4651/2014/161(10)/A1572/8/$31.00 © The Electrochemical Society Ultra High-Precision Studies of Degradation Mechanisms in Aged
Bibliographic record
Abstract
Twenty LiCoO2/Graphite cells with ages between 0 and 12 years having different cycling histories but identical chemistry and construction were obtained from Medtronic Inc. These cells presented a unique opportunity to learn about aging mechanisms in Li-ion cells. The cells were studied using the ultra-high precision chargers (UHPC) at Dalhousie University, electrochemical impedance spectroscopy (EIS) and differential voltage versus capacity (dV/dQ vs Q) measurements. Even after 12 years of operation at 37◦C, the cells still retained 80 % of their initial capacity and their coulombic efficiency was 0.99985 when measured at C/20 and 40◦C. The capacity loss of the aged cells could be explained by loss of lithium inventory through growth of the solid electrolyte interphase (SEI) at the negative electrode which led to impedance increase. There is no evidence of any active material loss due to electrical disconnect in these cells suggesting the cells have excellent electrodes. A low upper cutoff voltage (4.075 V) is crucial to the long lifetime of these cells due to electrolyte oxidation reactions at the positive electrode, revealed by the UHPC experiments. Comparing similar cells that were cycled to either 4.075 or 4.175 V showed that those cycled to higher voltages under the same conditions failed significantly sooner. These results suggest that electrolyte additives that reduce electrolyte oxidation at the positive electrode, will prolong the cycle and calendar life of these Li-ion cells.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.024 | 0.006 |
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".