By Owais AliReviewed by Lexie CornerJun 19 2024The widespread adoption of Li-ion batteries, especially in the automotive industry, can be attributed to their high energy density, long cycle life, and decreasing cost. However, potential risks such as thermal runaway and spontaneous ignition remain a concern. This has driven the need for new, cost-effective diagnostic techniques to monitor battery performance and durability.
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Among the various diagnostic methods, ultrasonic techniques have emerged as a promising non-destructive testing (NDT) approach for lithium-ion battery diagnostics. These techniques enable real-time monitoring of the battery's internal state, defect detection, and overall health assessment without causing damage or disruption, facilitating timely interventions and optimized management strategies.1,2
Principles of Ultrasonic Diagnostics
Ultrasonic diagnostics uses ultrasonic transducers to generate, propagate, and detect ultrasonic waves, typically in the 0.1 to 15 MHz range. These waves are transmitted into the material under inspection.
As the waves encounter boundaries between different materials, defects, or variations in density or porosity, a portion of the energy is reflected (pulse-echo) or received by a secondary transducer (through transmission). These ultrasonic waves carry valuable information about the material's internal characteristics, which can be analyzed to gain insights into its condition.3
Interaction of Ultrasonic Waves with Battery Materials
Factors such as material properties, density, and porosity influence the interaction of ultrasonic waves with battery materials. In lithium-ion batteries, wave propagation can be described using theories like Biot's theory for fluid-saturated porous media or the slurry model for electrode coatings.
A key parameter analyzed is the time-of-flight (ToF), representing the time it takes for an ultrasonic wave to travel through the material and return as an echo. By measuring the ToF and correlating it with known material properties, researchers can detect defects, density changes, or variations in the battery's internal structure.
Additionally, the amplitude and frequency of reflected or transmitted waves provide information about the material's characteristics, with changes indicating alterations in the battery components' mechanical properties linked to electrochemical processes during charging and discharging cycles.4
Applications in Lithium-Ion Batteries
Ultrasonic techniques have numerous applications in lithium-ion battery diagnostics, offering unique capabilities and insights that complement and extend traditional diagnostic methods.
Detecting Internal Defects and Degradation
One of the primary applications of ultrasonic techniques in battery diagnostics is the detection of internal defects and signs of degradation.
Ultrasonic tomography, a specialized ultrasonic technique, has proven valuable for studying metal defect detection in lithium-ion batteries. This method involves emitting ultrasonic waves into the battery samples and analyzing the reflected or transmitted waves.
These signals help create tomographic images of the internal battery structure, allowing researchers to visualize and analyze defects without damaging the battery. This capability is particularly valuable for quality control and identifying potential safety hazards that could lead to thermal runaway or other catastrophic failures.5
Monitoring State of Charge (SoC) and State of Health (SoH)
Ultrasonic analysis for SoC monitoring involves tracking changes in ultrasonic waveforms corresponding to the battery's charging and discharging states. This method relies on measuring the ToF of ultrasonic waves, which varies with the battery's mechanical properties during cycling.
Changes in signal amplitude during the charge/discharge cycle indicate structural changes, enabling SoC determination and over-discharge detection without complex algorithms or additional hardware. This approach can also monitor the battery's SoH, providing insights into its overall condition, enabling early detection of cell damage, aiding in battery refurbishment, identifying faulty cells, and estimating the remaining useful life.
Monitoring Solid-Electrolyte Interphase (SEI) Formation
The formation and evolution of the SEI layer play are crucial for lithium-ion battery performance and longevity. Ultrasonic techniques can be employed to monitor this process by analyzing changes in the acoustic properties of the electrode during cycling.
As the SEI layer evolves, its mechanical properties change, altering the propagation of ultrasonic waves. By correlating these changes with electrochemical measurements, researchers can gain valuable insights into the SEI formation process and its impact on battery performance.7
Diagnosing Electrodes
Spatially resolved ultrasound acoustic measurements provide a powerful diagnostic tool for analyzing the condition of lithium-ion battery electrodes. By performing ultrasonic measurements at multiple locations across the battery's surface and over the full operating voltage range, signal intensity and ToF changes can be correlated with the lithiation/delithiation processes and the associated density and structural changes occurring within the individual anode and cathode layers.
This method also provides information about electrode expansion behavior. It can identify regions where expansion is inhibited due to factors like current collector geometry, offering an economical and high-resolution diagnostic capability to monitor internal structural evolution in operando.2
Advantages and Limitations
Ultrasonic techniques offer several advantages for lithium-ion battery diagnostics, including non-destructive and non-invasive monitoring, early degradation detection, real-time monitoring, and high spatial resolution. These capabilities enable continuous battery health assessment, proactive maintenance, and targeted diagnostics, enhancing battery lifespan and performance.
However, challenges such as complex signal interpretation, susceptibility to external interference, limited penetration depth, and potential equipment requirements may arise.
Despite these challenges, the benefits of early degradation detection and improved performance often outweigh the drawbacks, especially in critical applications prioritizing battery safety and longevity.8
Future Outlook
Ultrasonic techniques for lithium-ion battery diagnostics have significant potential to enhance battery systems' safety, efficiency, and reliability. Advancements in transducer technology, signal processing, and machine learning are expected to improve their accuracy and reliability further.
Developing portable and cost-effective ultrasonic diagnostic systems could also lead to widespread use in applications such as electric vehicles and stationary energy storage, enabling real-time monitoring and predictive maintenance.
While challenges remain, ongoing research aims to enhance ultrasonic diagnostics, contributing to developing more efficient and safer lithium-ion batteries.8
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References and Further Reading
- Webster, M., Frankforter, E., Juarez, P. (2023, April). Evaluation of ultrasonic battery inspection techniques. In Non-destructive Characterization and Monitoring of Advanced Materials, Aerospace, Civil Infrastructure, and Transportation XVII. doi.org/10.1117/12.2656667
- Robinson, JB., Maier, M., Alster, G., Compton, T., Brett, DJ., Shearing, PR. (2019). Spatially resolved ultrasound diagnostics of Li-ion battery electrodes. Physical Chemistry Chemical Physics. doi.org/10.1039/C8CP07098A
- Chacón, XCA., Laureti, S., Ricci, M., Cappuccino, G. (2023). A Review of Non-Destructive Techniques for Lithium-Ion Battery Performance Analysis. World Electric Vehicle Journal. doi.org/10.3390/wevj14110305
- Gold, L., Herzog, T., Schubert, F., Heuer, H., Giffin, G. A. (2023). Ultrasound Propagation in Lithium‐Ion Battery Cell Materials: Basis for Developing Monitoring and Imaging Methods. Energy Technology. doi.org/10.1002/ente.202200861
- Yi, M., Jiang, F., Lu, L., Hou, S., Ren, J., Han, X., Huang, L. (2021). Ultrasonic tomography study of metal defect detection in lithium-ion battery. Frontiers in Energy Research. doi.org/10.3389/fenrg.2021.806929
- Davies, G., Knehr, KW., Van Tassell, B., Hodson, T., Biswas, S., Hsieh, AG., Steingart, DA. (2017). State of charge and state of health estimation using electrochemical acoustic time of flight analysis. Journal of The Electrochemical Society. doi.org/10.1149/2.1411712jes
- Bommier, C., Chang, W., Li, J., Biswas, S., Davies, G., Nanda, J., & Steingart, D. (2020). Operando acoustic monitoring of SEI formation and long-term cycling in NMC/SiGr composite pouch cells. Journal of The Electrochemical Society. doi.org/10.1149/1945-7111/ab68d6
- Wang, Q., Song, D., Lin, X., Wu, H., & Shen, H. (2024). Application of machine learning in ultrasonic diagnostics for prismatic lithium-ion battery degradation evaluation. Frontiers in Energy Research. doi.org/10.3389/fenrg.2024.1379408
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