ECM parameterization

Fit OCV, R0, and RC-pair parameters of an equivalent circuit model from experimental cycling data, in-browser

The ECM Parameterization tool fits an equivalent circuit model (ECM) to experimental battery cycling data directly in the browser. Fit a measurement that you’ve already uploaded to a project, upload your own file, or use one of the built-in example datasets to extract OCV, R0, and RC-pair parameters as functions of state of charge (SOC).

There are two ways to launch the tool:

• Inside a project — open the ECM Fitting page from the project sidebar. You can pick a measurement that’s already attached to one of the project’s cells and the result is saved back to the project.
• Standalone demo — visit studio.ionworks.com/ecm-demo directly. No login is required, and you can experiment with example datasets or upload a one-off file without saving anything.

How it works

The tool fits a circuit consisting of an open-circuit voltage (OCV) source, a series resistance (R0), and one or more RC pairs to time-series voltage and current data. The fitting process extracts parameters as smooth functions of SOC.

The circuit structure looks like this:

  ┌───[ R0 ]───┬───[ R_rc1 ]───┬───[ R_rc2 ]───┐
  │             │               │               │
 OCV         [ C_rc1 ]       [ C_rc2 ]         V_terminal
  │             │               │               │
  └─────────────┴───────────────┴───────────────┘

Each RC pair captures a different timescale of dynamic polarization behavior. More RC pairs produce a more accurate fit but also increase model complexity.

Fitting a measurement in a project

Use this workflow when you want the fit to be associated with a specific project and cell, and to use a measurement you’ve already uploaded.

1. Open ECM Fitting from your project

   Open the project, then click ECM Fitting in the sidebar. The page lists the cells in the project and the measurements attached to each one.

2. Pick a measurement

   Select the cell measurement you want to fit. A preview plot of the voltage and current trace is shown so you can confirm it’s the right data before running the fit.

   Only time_series measurements with voltage, current, and time data can be fit. Properties and file-type measurements aren’t shown in the picker.

3. Configure and run the fit

   Set the number of RC pairs (0–5) and toggle Fit OCV as described in Configure the fit. Click Run fit to start.

4. Save the result to the project

   When the fit completes, review the results and click Save to attach the fitted parameter set to the project’s cell. Saved fits appear in the cell’s measurement history and can be used as a starting point when creating a parameterized model.

Using the tool

The standalone demo at studio.ionworks.com/ecm-demo — and the fit configuration step inside a project — share the same controls.

1. Select your data

   Choose from built-in example datasets or upload your own cycling data file. (Inside a project, you instead pick a measurement attached to one of the project’s cells, as described above.)

   Built-in examples include cells from published literature (Chen 2020, Ecker 2015, Prada 2013, and others) as well as drive-cycle profiles (UDDS, mixed current). Each example shows a recommended number of RC pairs.

   Uploaded files are automatically detected and parsed. The tool supports common cycler formats including CSV, Excel, and formats from BaSyTec, Maccor, and Biologic. Your file must contain time, voltage, and current columns. If an Open-circuit voltage [V] column is present, you can use it directly instead of fitting OCV.

2. Configure the fit

   Set the number of RC pairs (0–5). More RC pairs capture faster dynamics but increase complexity. The recommended value depends on your data — example datasets show a suggested count.

   Toggle Fit OCV on or off. When your data includes a measured OCV column, you can disable OCV fitting to use the provided values directly and only fit R0 and RC parameters.

3. View results

   After fitting, you see:

   • Model vs. data voltage comparison plot and RMSE
   • OCV(SOC) and R0(SOC) parameter curves
   • R_rc(SOC), C_rc(SOC), and τ_rc(SOC) curves for each RC pair

   Full RC-pair parameters require ECM results access to be enabled for your organization. Contact [e-mail] to request access.

Downloading results as CSV

After a fit completes, click the Download CSV button in the results header to export the fitted parameters.

The CSV contains 200 interpolated SOC points with these columns:

Column	Description
SOC	State of charge (0 to 1)
OCV [V]	Open-circuit voltage
R0 [mOhm]	Series resistance in milliohms
R_rc_N [mOhm]	RC pair N resistance
C_rc_N [F]	RC pair N capacitance
tau_N [s]	RC pair N time constant

Columns for each fitted RC pair follow this pattern (e.g. R_rc_1, R_rc_2, …).

RC-pair columns are included only when ECM results access is enabled for your organization. Otherwise the CSV contains SOC, OCV, and R0 only. Contact [e-mail] to request access.

Data requirements

Your cycling data must include:

• Time [s] — time in seconds
• Voltage [V] — terminal voltage
• Current [A] — applied current

Optionally, include Open-circuit voltage [V] to skip OCV fitting and use measured OCV directly.

The tool uses ionworksdata for format detection, so data exported from common cyclers is usually recognized automatically.

Next steps

• Upload measurements to a project so you can fit them in place
• Create a Parameterized Model with your fitted parameters
• Learn about ECM and other model types available in Ionworks Studio
• Explore the data format requirements for uploading cycling data