docs: add initial dataset card

README.md

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+---
+license: cc-by-4.0
+language:
+  - en
+size_categories:
+  - 100M<n<1B
+task_categories:
+  - time-series-forecasting
+  - tabular-regression
+tags:
+  - battery
+  - state-of-charge
+  - state-of-health
+  - lithium-ion
+  - LFP
+  - lithium-iron-phosphate
+  - fast-charging
+  - cycling
+  - kalman-filter
+  - benchmark
+  - bsebench
+  - tier-2-canonical
+  - parquet
+  - bpx-1.1
+pretty_name: "Severson 2019 LFP Fastcharge — BSEBench Canonical (Tier 2)"
+---
+
+# severson-2019
+
+**Tier 2 BSEBench-canonical** Parquet harmonization of the Severson et al.
+2019 LFP fastcharge cycling dataset. Hosted under the [BSEBench](https://bsebench.org)
+organization for filter benchmark reproducibility.
+
+## Status
+
+🚧 **Harmonization pending** — placeholder dataset card. Awaiting :
+
+1. Tier 1 raw mirror upload at [`bsebench-org/severson-2019-raw`](https://huggingface.co/datasets/bsebench-org/severson-2019-raw)
+2. Publication of `bsebench-specs` v0.2.0 with the canonical
+   `TimeSeriesSchema` Pydantic model
+3. Implementation + testing of the Severson harmonization adapter at
+   [`bsebench-datasets/src/bsebench_datasets/adapters/severson_2019.py`](https://github.com/bsebench-org/bsebench-datasets/blob/main/src/bsebench_datasets/adapters/severson_2019.py)
+
+## What this will be
+
+The Severson 2019 dataset converted to the **BSEBench canonical Parquet schema** :
+
+| Column | Type | Description |
+|---|---|---|
+| `cell_id` | string | identifier within the dataset |
+| `time_s` | float64 | seconds since experiment start (`t=0` at first sample) |
+| `voltage_V` | float64 | terminal voltage, always positive |
+| `current_A` | float64 | BPX-1.1 sign convention : charge=positive, discharge=negative |
+| `temperature_C` | float64 | cell surface temperature |
+| `cycle_number` | int32 | cycle counter, 1-indexed |
+| `step_id` | string | within-cycle step identifier |
+| `capacity_Ah` | float64? | running cumulative capacity |
+
+Partitioned by `cell_id` for parallel reading. Total expected size ≈ 50 GB
+uncompressed, ≈ 8 GB after Zstandard compression.
+
+## Why "canonical" tier
+
+This is the version **users should consume** for filter benchmarking. It :
+
+- Maps Severson's original column names to BSEBench's standardized schema
+- Harmonizes sign conventions to BPX-1.1
+- Strips metadata not needed for state-estimation
+- Loads in 1 line via `bsebench-datasets`
+
+For provenance / audit, see the [Tier 1 raw mirror](https://huggingface.co/datasets/bsebench-org/severson-2019-raw).
+
+## Anchor standards
+
+- Sign convention : [BPX 1.1](https://bpxstandard.com/) (discharge = negative)
+- Time-series schema : [LF Energy BDF](https://lfenergy.org/lf-energy-battery-data-alliance-announces-the-battery-data-format-bdf/)
+  (Dec 2025) where applicable
+
+## License
+
+[CC-BY-4.0](https://creativecommons.org/licenses/by/4.0/) — same as the
+original Severson 2019 publication.
+
+## How to use (target API)
+
+```python
+# Once shipped (M2.1)
+from bsebench_datasets import load_bsebench
+
+ds = load_bsebench("severson-2019", revision="v1.0")
+print(ds.chemistry)  # "LFP"
+print(ds.first_cell_data().head())  # canonical Parquet columns
+```
+
+## Citation
+
+```bibtex
+@article{severson2019,
+  author  = {Severson, K. A. and Attia, P. M. and Jin, N. and Perkins, N.
+             and Jiang, B. and Yang, Z. and Chen, M. H. and Aykol, M.
+             and Herring, P. K. and Fraggedakis, D. and Bazant, M. Z.
+             and Harris, S. J. and Chueh, W. C. and Braatz, R. D.},
+  title   = {Data-driven prediction of battery cycle life before
+             capacity degradation},
+  journal = {Nature Energy},
+  volume  = {4},
+  pages   = {383--391},
+  year    = {2019},
+  doi     = {10.1038/s41560-019-0356-8},
+}
+
+@misc{bsebench2026,
+  author = {Akir, Oussama and BSEBench Contributors},
+  title  = {{BSEBench}: an open-source benchmark for battery state-estimation filters},
+  year   = {2026},
+  url    = {https://bsebench.org},
+}
+```
+
+## Provenance
+
+Derived from [`bsebench-org/severson-2019-raw`](https://huggingface.co/datasets/bsebench-org/severson-2019-raw)
+via [`bsebench-datasets/src/bsebench_datasets/adapters/severson_2019.py`](https://github.com/bsebench-org/bsebench-datasets/blob/main/src/bsebench_datasets/adapters/severson_2019.py).
+The harmonization script's commit SHA is recorded in the manifest YAML at
+[`bsebench-datasets/manifests/severson_2019_lfp.yaml`](https://github.com/bsebench-org/bsebench-datasets/tree/main/manifests).