Battery Data Format for Time-Series Data (.bdf)

Why introduce an industry standard format for battery data?

It is well known that organizing, cleaning, and preparing battery data for analytics takes significant time and effort, creating a high barrier to leveraging advances in battery modeling for battery development cycles.

A 2024 Forrester study surveyed 165 decision-makers in the automotive industry responsible for EV battery testing, validation, and development in the US and Europe. Among the respondents, 57% cited deciphering complex relationships in vast, multiparameter datasets as a significant barrier to battery validation, and 61% estimated months to years of time savings from AI-powered cell characterization testing that leverages standardized data sets.

Goal of launching the BDF

The Battery Data Format (BDF) provides a standard structure for data generated in battery labs, offered to the community by the Battery Data Alliance, a Linux Foundation Energy project. It is our hope that adoption of the BDF will empower the battery science community to leverage advances in open-source battery models.

Developed with input from leading scientists and engineers, the BDF addresses two main challenges:

• Data Consistency: With a common format, labs and cycler brands can eliminate the inconsistencies in data structure that arise with each software update.
• Model Compatibility: A unified format means battery model developers can easily adapt their models to accept BDF data, making it possible for scientists to experiment with multiple models without custom coding each time.

Initial Scope of the BDF

• The initial scope is intended to facilitate use and comparison of cycler time-series data.
• The BDF provides a fixed table schema for time-series battery data, which is supplemented with a machine-readable application ontology for integration with the Semantic Web.
• The BDF application ontology is defined as an extension of the BattINFO domain ontology, which provides interoperability within the broader field of battery data.
• An immediate next step will be launching a parallel format for storing metadata for the BDF.
• Future development will focus on formats for other types of lab data such as impedance data.

Defining the BDF for Cycler Time-Series Data

1. Each file contains time-series data for one and only one cell.

   • Multiple files can be provided for the same cell.

2. Required quantities

Preferred Label	Machine-readable name	Description	IRI
Test Time / ms	test_time_millisecond	Elapsed time since the start of the test, recorded in millisecond.	https://w3id.org/battery-data-alliance/ontology/battery-data-format#test_time_millisecond
Current / A	current_ampere	Instantaneous current applied to or from the test object, in ampere.	https://w3id.org/battery-data-alliance/ontology/battery-data-format#current_ampere
Voltage / V	voltage_volt	Instantaneous voltage measured across the test object, in volt.	https://w3id.org/battery-data-alliance/ontology/battery-data-format#voltage_volt

Recommended quantities

Preferred Label	Machine-readable name	Description	IRI
Unix Time / ms	unix_time_millisecond	Timestamp of the measurement in Unix time (millisecond since Jan 1, 1970 UTC). Used to align data.	https://w3id.org/battery-data-alliance/ontology/battery-data-format#unix_time_millisecond
Cycle Count / 1	cycle_count	Sequential index of the current cycle in the test program, increasing monotonically throughout the dataset.	https://w3id.org/battery-data-alliance/ontology/battery-data-format#cycle_count
Step Count / 1	step_count	Sequential index of the current step in the test program, increasing monotonically throughout the dataset.	https://w3id.org/battery-data-alliance/ontology/battery-data-format#step_count
Temperature / °C	temperature_celsius	Measured temperature of the test object (e.g., surface or internal), in degree Celsius.	https://w3id.org/battery-data-alliance/ontology/battery-data-format#temperature_celsius

Optional quantities

Preferred Label	Machine-readable name	Description	IRI
Step Index / 1	step_index	Index identifying the type of step being executed, as defined in the test program. May repeat across the dataset.	https://w3id.org/battery-data-alliance/ontology/battery-data-format#step_index
Charging Capacity / Ah	charging_capacity_ampere_hour	Accumulated capacity during a charging phase, in ampere hour.	https://w3id.org/battery-data-alliance/ontology/battery-data-format#charging_capacity_ampere_hour
Discharging Capacity / Ah	discharging_capacity_ampere_hour	Accumulated capacity during a discharging phase, in ampere hour.	https://w3id.org/battery-data-alliance/ontology/battery-data-format#discharging_capacity_ampere_hour
Charging Energy / Wh	charging_energy_watt_hour	Accumulated energy during a charging phase, in watt hour.	https://w3id.org/battery-data-alliance/ontology/battery-data-format#charging_energy_watt_hour
Discharging Energy / Wh	discharging_energy_watt_hour	Accumulated energy during a discharging phase, in watt hour.	https://w3id.org/battery-data-alliance/ontology/battery-data-format#discharging_energy_watt_hour
Internal Resistance / Ohm	internal_resistance_ohm	Internal resistance of the test object, measured in ohm.	https://w3id.org/battery-data-alliance/ontology/battery-data-format#internal_resistance_ohm
Ambient Temperature / °C	ambient_temperature_celsius	Temperature of the surrounding environment, in degree Celsius.	https://w3id.org/battery-data-alliance/ontology/battery-data-format#ambient_temperature_celsius
Ambient Pressure / Pa	ambient_pressure_pascal	Atmospheric pressure in the test environment, in pascal.	https://w3id.org/battery-data-alliance/ontology/battery-data-format#ambient_pressure_pascal
Applied Pressure / Pa	applied_pressure_pascal	Mechanical pressure applied directly to the test object, in pascal.	https://w3id.org/battery-data-alliance/ontology/battery-data-format#applied_pressure_pascal

5. Data structure:

   • The first row contains a header row with the preferred label of the quantity in the corresponding column.
   • The units of the quantities are fixed.
   • All rows must match the initial header in column count, ensuring consistent formatting.

6. File naming conventions:

   • Recommended format:

     InstitutionCode__CellName__YYYYMMDD_XXX.csv
     

     Example:

     UCam__A0001__20241031_001.csv
     

   • Additional metadata (e.g., cell model, serial number, unique identifier) should be stored within a parallel metadata file.

7. File extension:

   • Files using text-based serialization can be saved with the .bdf extension.
   • If another extension is necessary, it can be supplemented with a .bdf prefix (e.g. example.bdf.parquet)
   • Stream compressors like gzip can be used to save space, resulting in .bdf.gz files.
   • It is assumed that .bdf files adhere to the BDF conventions, and future validator functions may be created to enforce this.

Summary

The Battery Data Format (.bdf) is a step toward unifying and accelerating battery research and development. By adopting this open-source standard, we can foster collaboration, enhance model interoperability, and unlock the full potential of data-driven battery innovation.