Simulation of lithium-ion batteries based on pulsed current characterization
Bibliographic record
Abstract
Simulation of lithium-ion and other cells is important for basic understanding, design of cells, application in devices including automotive, and as part of system simulations for control and safety purposes. This thesis proposes a new cell equivalent circuit model, called the distributed state of charge model, which consists of a series resistance, and a non-linear RC transmission line. The circuit model components are dependent on the SOC, with the circuit being unique in considering the local (depth dependent) charge state. A pulsed discharge and charge technique is put forth for extracting the model parameters, and their dependence on cell state of charge. The extraction method is applied to commercial lithium-ion cells. It is shown that the extracted parameters are largely independent of magnitude of the pulsed currents. This distinguishes the model from other widely used equivalent circuits in which parameter extraction is generally performed as a function of current. Therefore, this approach is promising for reducing time required for this extraction phase. Validation experiments are performed using both static discharge and a variable-current profile. Two versions of the model are developed based on the governing diffusion mechanism – planar or spherical. Simulations using the planar model matched experimental results well for large current pulses (up to 2.0 C discharge) with slow average discharge (0.20 C discharge) – root-mean-square error typically within 0.84%, and maximum error within 3.7%. On the other hand, the spherical model performs well for higher continuous discharge current (up to 0.50 C discharge), but for lower current pulses (up to 0.67 C discharge) – root-mean-square error typically within 0.95%, and maximum error within 3.3%. This tradeoff may be attributed to the distribution of capacitances in the corresponding electrode models. Parameters of the proposed equivalent-circuit are also extracted for a lithium-alloying tin electrode. Tin is an electrode of interest due to its high specific and volumetric capacity. The response is much different from those obtained from the commercial lithium ion cells, including apparent drops in effective diffusion coefficient by three orders of magnitude over narrow regions of SOC. These characteristics are explained qualitatively using the phase transformation effect.
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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 | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".