Author: HeatSync Technical Team
Date: November 2025
Executive Summary
This blog provides an overview of the workflow used to design a complete battery thermal management system—from defining the core problem, to testing and characterizing cells, establishing design constraints, building thermal models, validating prototypes, and defining virtual sensing and control strategies for production-ready EV battery packs.
Statement of the problem
Maintaining the li-ion battery cells at the desire range of temperature is crucial to maintain performance, reliability, durability and saftey of the battery packs. In general, there are three main thermal related damages to li-ion battery cells namely, ageing, lithium metal plating, and thermal abuse.
Not only Maintaining the temperature within the range is required but also the gradient of the temperature within a cell and among the neighbouring cells, module and battery pack are important to ensure safe and durable operation of the battery pack. The main objective of the thermal solution for a battery pack is to maintain the temperate and spatial gradient of the temperature of the battery cells within the acceptable range. Note that the thermal system should be capable of both cooling and heating the cells to maintain them with the range at a wide range of environmental and operational conditions.
Step 1: Test Sequence to Characterize a Battery Cell in Normal Use Conditions
Battery cells play a pivotal role in our modern world, powering a vast array of electronic devices, electric vehicles, and renewable energy storage systems. Ensuring the reliability, safety, and performance of these cells is of paramount importance. To achieve this, a well-structured test sequence is employed to characterize a battery cell in normal use conditions. This article outlines the key steps involved in this crucial process.
- Preconditioning
Preconditioning is the initial step in characterizing a battery cell. Its primary objectives are to (i) remove passivation to which the battery was subjected to, between the manufacturing time and the initial tests and (ii) stabilize capacity.
This is crucial for obtaining consistent and reliable test results, as variations in capacity can affect a battery’s performance in real-world scenarios.
- Relaxation test
The relaxation test aims to determine the time required for the battery cell to achieve thermodynamic stability after the load current is switched off. This is crucial for accurate measurements, as the cell’s properties may change immediately after discharging. A proper relaxation period ensures that the cell has settled into a stable state for reliable testing.
- Capacity test
Battery capacity is a fundamental parameter, defining the electric energy content of a battery in ampere-hours (Ah). To understand the dependency of capacity on temperature and load current, a capacity test is performed. This test provides insights into how the cell’s performance may vary under different operating conditions, helping to optimize its usage.
Open-Circuit Voltage (OCV) is a key parameter in battery characterization. It represents the potential difference between a cell’s electrodes, measured at its terminals in a no-load condition. Measuring OCV is essential for understanding the cell’s voltage behavior when it is not under any external influence. This information is vital for predicting the cell’s behavior in real-world applications.
- Understanding Battery Dynamics
In order to gain a profound understanding of a battery cell’s dynamic behavior under various load conditions and real-world use cases, we rely on Equivalent Circuit Models (ECM). ECMs are widely utilized to forecast a battery’s electrical and thermal performance when subjected to transient load events. To determine the parameters of ECMs, two prevalent testing methods are typically employed: HPPC and EIS.
- Hybrid Pulse Power Characterization (HPPC): HPPC entails subjecting the battery cell to a direct current (DC) pulse, closely monitoring its voltage response.
- Electrochemical Impedance Spectroscopy (EIS): EIS is another essential technique. It involves applying a small sinusoidal current or voltage to the battery while measuring both the amplitude and phase shift of the resulting voltage or current, respectively.
- Verification
The final step in the battery cell characterization process is verification. It involves validating the data collected from the preceding measurements. This step ensures that the test results are accurate and reliable. Any inconsistencies or anomalies can be identified and addressed, allowing for more confident conclusions about the battery cell’s performance.
In conclusion, a systematic test sequence is imperative for characterizing battery cells under normal use conditions. By following these steps, we can ensure that the batteries powering our devices, vehicles, and energy storage systems are reliable, safe, and optimized for their intended applications. This comprehensive characterization process contributes to the development of more efficient and durable battery technology, paving the way for a sustainable energy future.