Lithium-ion Battery State of Health Using Impedance

Abstract

Introduction The growth in production of lithium-ion batteries (LiB) has been driven by the increasing adoption of electrical vehicles. As these batteries reach the end of their first life in EVs (typically at 80% state-of-health (SOH)), they hold substantial potential for second-life applications, such as energy storage systems for renewable energy, enhancing sustainability and reducing environmental impact. However, the lack of accurate and cost-effective characterization techniques hampers their reuse. Electrochemical Impedance Spectroscopy (EIS) has emerged as a powerful technique for SOH measurement due to its non-destructive nature and speed. However, several measurement and metrology challenges must be addressed to fully leverage EIS for SOH assessment. Measurement and Metrology Challenges One primary challenge in using EIS for SOH measurement is the complexity of interpreting impedance spectra, influenced by factors like temperature, state of charge, and relaxation time to open-circuit voltage before measurement. Additionally, standardized testing protocols and calibration procedures are essential for consistency and comparability of EIS measurements across different laboratories and LiB types. Another significant challenge is developing methods to test LiB modules. The heterogeneity in aging among cells within a module can lead to discrepancies in impedance measurements, necessitating techniques to isolate and analyze individual cell contributions. Impact Addressing these challenges will profoundly impact the battery industry. A standardized and consistent SOH measurement method will allow for comparability across different battery manufacturers. Improved SOH measurement techniques will enhance predictive maintenance, reduce the risk of unexpected failures, and extend battery life. This will lower the total cost of ownership for battery-powered systems, especially second-life batteries, and contribute to the sustainability of EVs and renewable energy storage solutions. Recent Progress and Future Work Recent advancements in impedance measurements have focused on establishing traceable measurements in the mΩ and sub-mΩ range, at arbitrary phase angles, and across a wide range of frequencies. Calibration procedures have also been developed for impedance meters, leading to more accurate and reliable measurements. More work is needed in using EIS for SOH measurement of LiB modules, as this will reduce the laborious task of dismantling modules into cells for reuse and repurposing. Looking ahead, the future evolution of EIS for SOH measurement will likely involve developing real-time, in-situ monitoring systems. These systems will enable continuous SOH assessment during battery operation, providing immediate feedback and potentially allow for safety monitoring. There is also a need for comprehensive databases of EIS measurements across different battery chemistries and aging conditions to support the development of more generalized and robust SOH models. Advancements in sensor technology and data acquisition systems are also needed to enable high-precision EIS measurements in real-world operating environments. In conclusion, while EIS presents significant opportunities for improving battery SOH measurement, addressing the associated metrology challenges is crucial for realizing its full potential. Continued research and innovation in this field will drive the development of more accurate, reliable, and standardized SOH assessment techniques, ultimately supporting the advancement of battery technologies and their applications.