As a complement to last week’s discussion about SOC, this week we’re exploring State-of-Health (SOH), its significance, how it’s measured, & its implications for battery applications, with a focus on lithium-ion batteries.
Contact: Betsy Barry
State of Health (SOH) serves as a barometer for assessing the overall health of a battery. Unlike physical quantities such as voltage or current, SOH cannot be directly measured by external sensors; rather, SOH must be estimated according to external features to get insight into a battery’s ability to perform as expected.
Accordingly, there are several factors that influence a battery’s SOH:
- Charge and Discharge Cycles: Every time a battery is charged and discharged, it undergoes stress. Over time, this stress contributes to the degradation of the battery’s overall health.
- Power Fade: Power fade refers to the reduction in a battery’s ability to deliver its rated power. It occurs due to changes in the internal chemistry of the battery over the course of its normal lifecycle, which affect its performance over time.
- Storage and Operation Conditions: The environment in which batteries are stored and operated is important, and these can significantly impact the SOH. High temperatures, for instance, can accelerate degradation.
Measuring SOH: Capacity and Internal Resistance
SOH is determined by comparing the remaining capacity of the battery (C(t)) to its initial capacity (CIni). SOH is determined by a percentage so that a battery with 100% SOH has its full original capacity, while a lower percentage indicates capacity degradation.
Importance of SOH for Second-Life Applications
Lithium-ion batteries have found a second life in various applications after their primary use in electric vehicles or consumer electronics. In these cases, knowing the remaining useful life of a battery is crucial, as it becomes a determining factor in second-life usage. A high SOH (100%) suggests a fresh battery ready for optimal performance. As time passes, degradation leads to a lower SOH, indicating reduced capacity and performance. So, while a lithium-ion battery pack may have degraded past the SOH threshold needed to reliably operate an EV, it may be suitable for use in an application like an electric mower or forklift, for example. Thus, SOH estimation is an important tool in extending the overall life of a battery, which is also an important aspect of sustainability.
As battery technology continues to evolve, ensuring the reliability & longevity of these power sources becomes increasingly important. One key metric that engineers & researchers use to gauge a battery’s performance & overall health is the State of Health (SOH).
SOH Assessment and Predictive Maintenance
Monitoring SOH is essential not only for understanding a battery’s lifecycle but also for predicting maintenance needs and managing warranty issues. By tracking SOH, manufacturers and operators can foresee potential performance issues and schedule maintenance before critical failures occur. This approach reduces downtime, extends the lifetime of batteries, and increases overall satisfaction with the product.
Advances in SOH Assessment Methods
Researchers and engineers have developed various algorithms to estimate SOH, informed by experimental data and the latest advancements in battery technology. These algorithms incorporate variables such as charge and discharge profiles, temperature variations, and internal resistance measurements. By applying these methods, it’s possible to accurately determine a battery’s SOH and make informed decisions about its usage.
SOH serves as a critical parameter for evaluating the overall health and performance of batteries, especially lithium-ion batteries commonly used in modern electronics and electric vehicles. By understanding SOH, manufacturers, researchers, and operators can make informed decisions about battery maintenance, repurposing, and replacement. As battery technology continues to advance, accurate SOH assessment will remain a fundamental tool in ensuring the reliability and longevity of energy storage systems, reducing costs, and contributing to a sustainable future.