MSMR half-cell OCP fit

Fit MSMR species parameters to negative-electrode half-cell open-circuit potential data with MSMRHalfCell, MSMRHalfCellModel, and DataFit.

This fits one direction. For lithiation/delithiation hysteresis, set direction on MSMRHalfCellModelOptions and give each direction its own objective; only the combined single-plot overlay has no schema equivalent.

from ionworks import Ionworks
import ionworks_schema as iws
import matplotlib.pyplot as plt
import pandas as pd
import pybamm

# Synthetic example half-cell OCP: cumulative Capacity [A.h], falling Voltage [V].
# Swap in your own export, or read a measurement with `client.cell_measurement`.
data = pd.read_csv(iws.example_data("msmr_half_cell_ocp"))

known = iws.direct_entries.DirectEntry(
    parameters={"Ambient temperature [K]": 298.15},
)

# Seed the species from the library material closest to your chemistry.
material = iws.Material.from_library("Graphite - Verbrugge 2017")

# The library holds one value per species; scalarize_dict expands each list
# into the indexed names the model uses, e.g. "... (0) [V]".
initial_values = pybamm.scalarize_dict(
    {k: v for k, v in material.parameter_values.items() if "host site" in k}
)

# Seed capacity and lower excess capacity from the observed window.
Q_data = float(data["Capacity [A.h]"].max() - data["Capacity [A.h]"].min())
initial_values["Negative electrode capacity [A.h]"] = Q_data
initial_values["Negative electrode lower excess capacity [A.h]"] = 0.01 * Q_data

def bounds_function(var, initial_value):
    if "host site occupancy fraction" in var:
        # allow +/- 0.1 of the initial value, staying a fraction
        return (max(0.0, initial_value - 0.1), min(1.0, initial_value + 0.1))
    elif "ideality factor" in var:
        return (1e-2, 100.0)
    elif "standard potential" in var:
        # allow +/- 200 mV of the initial value
        return (initial_value - 0.2, initial_value + 0.2)
    elif "capacity" in var:
        # allow +/- 2% of the initial value
        return (initial_value * 0.98, initial_value * 1.02)
    else:
        raise ValueError(f"No bounds defined for parameter: {var}")

def prior_function(var, initial_value):
    if "standard potential" in var:
        return iws.stats.Normal(mean=initial_value, std=0.01)
    else:
        return None

parameters = {}
for name, value in initial_values.items():
    parameter = iws.Parameter(
        name,
        initial_value=value,
        bounds=bounds_function(name, value),
        prior=prior_function(name, value),
    )
    # Log10 the ideality factor since it may span several orders of magnitude.
    if "ideality factor" in name:
        parameters[name] = iws.transforms.Log10(parameter)
    else:
        parameters[name] = parameter

objectives = {
    "msmr": iws.objectives.MSMRHalfCell(
        data=data,
        options=iws.objectives.MSMRHalfCellOptions(
            model=iws.models.MSMRHalfCellModel(
                electrode="negative", options={"species format": "Xj"}
            )
        ),
    )
}
fit = iws.DataFit(
    objectives=objectives,
    parameters=parameters,
    # No cost: MSMRHalfCell's default weights capacity against the
    # differentials. ScipyLeastSquares is its default too, capped for speed.
    optimizer=iws.optimizers.ScipyLeastSquares(max_nfev=50),
)

client = Ionworks()
submission = client.pipeline.create(iws.Pipeline({"known": known, "msmr": fit}))
client.pipeline.wait_for_completion(submission.id)
result = client.pipeline.result(submission.id)
fit_result = result.element("msmr")
figs = fit_result.plot_fit_results()
plt.show()