Specific Heat Capacity of Lithium Ion Batteries Using a Hot Disk Hot Cell®

Specific Heat Capacity of Lithium Ion Batteries Using a Hot Disk Hot Cell®

Image Credit: https://www.hotdiskinstruments.com

Lithium-ion batteries charge fast, discharge under load, and cycle through repeated temperature changes across their lifetime. These temperature changes affect battery performance and safety. To study and analyze the battery’s thermal behavior, it is important to test their specific heat capacity (Cp). It quantifies how much heat a battery needs to absorb before its temperature rises by one degree. This directly shapes the design of thermal management systems and validates safety under fast-charging conditions.

Conventional calorimetric methods can measure specific heat capacity, but they are often time-consuming and difficult to apply to intact battery cells. For battery R&D, EV development, energy storage research, or thermal testing segments, TPS sensor-based, accurate, non-destructive testing (NDT) for effective Cp measurement provides a powerful tool for battery analysis. This post covers how Hot Disk Hot Cell® sensors enable accurate, non-destructive testing of the specific heat capacity of lithium batteries in real lab environments and on real cells.

Why Specific Heat Capacity is Critical in Lithium Batteries

To know the accurate thermal behavior of batteries, studying only the electrical properties, such as voltage curves, impedance spectra, capacity fade is not enough. Specific heat capacity (Cp) is the amount of heat required to raise the temperature of one kilogram of a material by one degree Celsius (or Kelvin). In a battery, Cp influences how much the cell temperature changes when heat is generated during operation. Here are some pointers.

  • During fast charging: In this case, current flows in, electrochemical reactions accelerate, and heat builds up internally. Measuring Cp helps determine how much the temperature of the cell can rise for a given amount of generated heat and how the cell accommodates this heat increase.A cell with a higher specific heat capacity has more thermal buffer. It takes longer to reach dangerous temperatures. A cell with a lower Cp reaches that upper limit faster.
  • From a thermal runaway standpoint: Runaway onset temperatures, heat generation rates, and propagation dynamics all depend on accurate thermal property data. Without reliable Cp values, thermal runaway models and safety simulations rely more heavily on assumptions.
  • Cooling system: Battery pack designers need Cp data along with other thermal propertiesto correctly size thermal management components.
  • Operational life: Temperature extremes accelerate degradation in terms of lithium plating, SEI growth, and electrolyte decomposition. Batteries that stay within their thermal operating window generally last longer, and this is where Cp data helps.

Challenges in Testing Specific Heat Capacity of Lithium Batteries

Here are some challenges involved in testing specific heat capacity of lithium batteries using conventional methods.

  • Measuring Composite Cp Values: Measurements of the specific heat capacity of lithium ion batteries is more complex than this measurement on a standard homogeneous sample because the internal structure of a lithium-ion cell includes laminated stacks of anodes, cathodes, separators, and electrolyte. Each layer has different thermal properties, and the real-world thermal performance depends on their composite behavior. When attempting to characterize the thermal properties of the full cell, capturing this combined behavior can become complex.
  • Destructive measurement methods: It is challenging for battery engineers to measure intact, commercial-format cells in cylindrical, pouch, or prismatic formats. These cells are sealed, often under internal pressure, and can’t be disassembled without altering their chemistry and therefore, their thermal performance.
  • Conventional calorimetric methods: Differential scanning calorimetry (DSC) may work well on small, homogeneous samples containing a few milligrams of electrode material, carefully extracted and dried. But the conditions that reflect the real thermal behavior of a full cell under operating conditions are quite different. As a result, DSC measurements typically represent the Cp of individual extracted materials rather than the composite Cp of the entire battery cell. Also, various safety parameters, such as ventilation, charge state management, and temperature controls, are required in a lab setting. This adds to the complexity. Variability in sample preparation, heterogeneous material structure, and thermal contact conditions can sometimes lead to differences in Cp measurements when testing battery materials.

Inconsistent thermal contact between sensor and sample is often the culprit; thankfully, this issue can be solved with the right sensor geometry and measurement protocol.

Hot Disk Hot Cell® Sensors: Measurement Principle

The Hot Disk Hot Cell® sensors use the Transient Plane Source (TPS) method, which is described in ISO 22007-2 for thermal conductivity measurements. This approach to thermal property measurement has been refined and validated across decades of materials research. Here’s how they work.

  • A known, controlled heat pulse is applied through a flat sensor element placed in contact with the sample surface. As heat flows into the material, the sensor simultaneously records the temperature response over time. From that transient response, thermal conductivity and thermal diffusivity are determined, and volumetric heat capacity (ρCp) is derived; specific heat capacity (Cp) can then be calculated when the material density is known.
  • While Cp is significant, you get a broader thermal property profile from a single measurement. These are useful for building thermal models, where all three parameters are typically required as inputs.
  • The Hot Cell® Sensor facilitates battery testing due to the cell’s geometry. Standard TPS sensors are flat disks designed to be sandwiched between two identical sample halves. Hot Cell® Sensors are engineered to make reliable, repeatable contact with curved and flat battery surfaces, allowing measurements on intact cells without disassembly or special sample preparation.
  • Total measurement time is typically a few minutes per test. In this method, the sample remains intact and there is no need to handle or expose the internal electrolyte. Also, the same cell can be tested at multiple states of charge, temperatures, or after cycling, enabling longitudinal characterization studies.

Selecting the Right Hot Cell® Sensor for Your Battery Format

Here are some selection criteria:

  • Variation across formats: While many commercial batteries follow common form factors (such as cylindrical, pouch, and prismatic cells), dimensions, surface structures, and packaging details still vary across manufacturers. Cells differ in terms of diameters, surface types, and lengths. The sensor you use needs to match the geometry of the cell you’re testing.
  • Knowing the cell geometry: Selecting the right sensor isn’t complicated once you know your cell geometry. But, knowing it is crucial because a sensor with the wrong contact geometry can create uneven thermal contact and inconsistent contact pressure, which produces inconsistent results.

Hot Cell® Sensors are specifically engineered for battery thermal characterization. Each sensor in the range is designed to ensure proper thermal contact with specific cell formats, which directly affects measurement accuracy and repeatability. The sensor catalog includes options for cylindrical, pouch, and prismatic formats, covering the most common commercial cell sizes used in EV, consumer electronics, and stationary storage applications.

Laboratory Workflow for Testing Specific Heat Capacity of Lithium Batteries Using Hot Cell® Sensors

Thermal property measurement can be complex, and sample preparation alone can take longer than the actual test. With the Hot Disk Hot Cell® the measurement workflow is straightforward. Here’s a typical workflow for testing specific heat capacity of lithium batteries using Hot Cell® Sensors:

  • Step 1: Verify battery condition and state-of-charge

Before any measurement, confirm the cell is within its normal operating state-of-charge range and shows no signs of damage or swelling. Document the SOC as it affects thermal properties and is important for result traceability.

  • Step 2: Select and position the appropriate Hot Cell® Sensor

Match sensor geometry to your cell format. Position the sensor against the cell surface with consistent contact pressure. Most measurements are taken on the outer casing.

  • Step 3: Configure measurement parameters

Set the heat pulse duration and power level appropriate for your cell size and expected thermal properties. The Hot Disk software provides guidance on parameter selection.

  • Step 4: Perform the transient measurement

Run the measurement. The system records the transient temperature response and calculates thermal conductivity and diffusivity, from which specific heat capacity can be determined when material density is known. A typical single measurement takes two to five minutes.

  • Step 5: Analyze, validate, and document results

Review the derived Cp values along with measured conductivity and diffusivity results. Run at least three repeat measurements per cell to confirm repeatability. Document cell chemistry, format, SOC, and lab temperature alongside results for full traceability.

A few best practices when testing specific heat capacity of lithium batteries:

  • Maintain stable lab temperature throughout the test sequence as thermal drift introduces noise.
  • Apply consistent contact pressure between sensor and cell surface for every measurement.
  • Record battery chemistry and SOC as Cp varies with both, and this information is essential for comparing results across studies.
  • Conduct repeat measurements on each cell; typically, three or more replicates give you confidence in your reported values.

Applications for Specific Heat Capacity Testing

Here are some applications where accurate Cp data adds real value.

  • EV battery pack design: When optimizing thermal management systems, engineers use Cp as an input to thermal models to estimate heat storage and temperature rise within the pack. They then use this information to optimize coolant flow rates and validate that the pack stays within safe operating temperatures under worst-case charge and discharge scenarios.
  • Energy storage systems: Cp data supports both system design and regulatory compliance documentation in large-scale installations where heat buildup across a battery bank can become a serious safety concern.
  • Fast-charging research: Cp measurement helps understand how battery cells store heat and respond thermally when different cell chemistries and formats are subjected to high currents.
  • Battery safety validation: This is particularly for cells in aerospace, medical, or grid applications that may require formal thermal property documentation. Cp measurement using a validated, standardized method (ISO 22007-2) provides data that meets audit and certification requirements. Here, Cp helps characterize thermal response and supports models used to assess conditions that may lead to thermal runaway.
  • Manufacturing quality assurance: Thermal properties can be sensitive indicators of cell consistency. Cp can help verify thermal property consistency between batches and identify deviations from expected material behavior.

Barnett Technical Services offers Hot Disk Hot Cell® Sensors

Thermal characterization tells you why it behaves the way it does, and whether it’s safe to push further. Hot Disk Hot Cell® Sensors from Barnett Technical Services provide a practical, accurate, and non-destructive path to evaluating thermal transport properties and determining specific heat capacity (Cp) on intact commercial cells. If you’re building thermal models, validating battery safety, or developing next-generation fast-charging protocols, contact the team at Barnett for the thermal property data you need.

Explore the full range of Hot Disk Hot Cell® Sensors for your battery format:

https://barnett-technical.com/products-category/hot-cell-sensors