Listening to ultrasonic signals reveals the mechanical behavior of next-generation batteries

Simón Montoya-Bedoya – simonmontoyabedoya@gmail.com
Bluesky: @simontoyabe.bsky.social
Instagram: @simontoyabe
Walker Department of Mechanical Engineering, The University of Texas at Austin, Austin, Texas, 78712-1591, United States

Prof. Michael R. Haberman (Walker Department of Mechanical Engineering, The University of Texas at Austin)

Other contributors to the research:
Donal P. Finegan (National Laboratory of the Rockies, Golden, CO, US)
Hadi Khani (Texas Materials Institute, The University of Texas at Austin)
Ofodike Ezekoye (Walker Mechanical Engineering Department, The University of Texas at Austin)

Popular version of 2aPAb4 – Non-destructive ultrasonic monitoring of next-generation lithium-ion batteries
Presented at the 189th ASA Meeting
Read the abstract at https://eppro02.ativ.me/appinfo.php?page=Session&project=ASAASJ25&id=3977608&server=eppro02.ativ.me

–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–

Have you noticed how heavily our current society depends on batteries? Batteries are used everywhere, from powering your phone to electrifying mobility, and energy storage to mitigate the intermittent nature of renewable energy sources like wind and sun. This increased demand for lithium-ion batteries (LIBs) has led to the exploration of new technologies with improved attributes such as safer operation or improved lifetime. For example, silicon solid-state batteries (Si-SSB) are promising because silicon as an anode material offers a higher specific capacity (~3500 mAh/g) than graphite (~300 mAh/g) used in conventional LIBs. They are also potentially safer to operate due to the use of a solid electrolyte rather than the flammable liquid electrolyte used in conventional LIBs.

However, Si-SSBs come with their own challenges associated with the avoidance of a liquid electrolyte, primarily the requirement to maintain reliable interfacial contact between all the solid layers for lithium-ion movement. Si-SSBs are therefore more brittle and more prone to contact loss and fracture.

Another challenge in studying the intricate mechanical changes that arise from the electrochemical processes in the battery is that we are “blind” to them, in other words, we cannot see inside batteries while they are operating. That’s why, just as a doctor uses ultrasound to monitor a beating heart, we can use ultrasonic waves to monitor batteries without opening them, as represented by the cartoon in Fig. 1. The key to understanding what changes within the batteries is having information about how the movement of lithium ions alters its mechanical properties. When lithium ions migrate during charging and discharging, they cause swelling, internal stresses, and sometimes fracture within the battery structure. These mechanical changes can significantly affect the propagation of ultrasonic waves through the material. This is specifically true for the silicon anode, where silicon forms alloys with the lithium ions, rather than the lithium ions becoming embedded in the molecular structure as occurs in conventional batteries. These electrochemical changes lead to large volumetric and mechanical changes. Thus, SSBs are a compelling technology to explore using ultrasound using ultrasonic signals observables, such as shifts in the time of flight (TOF) of the wave through the battery, or changes in how sound is absorbed or scattered. These “acoustic fingerprints” can potentially help us gain more insights into degradation in these next-generation (“next-gen”) batteries and therefore improve the technology for more widespread use in commercial products.

Figure 1. Analogy of the usage of ultrasonic waves for battery diagnostics, similar to how a doctor would use ultrasonics to monitor heart health. [Image generated with AI using Google NanoBanana Pro]

We aim to extend the use of ultrasonic testing methods for next-gen batteries and investigate opportunities and challenges associated with evaluating this new technology. In this work, we investigated both contact-based and immersion ultrasonic testing to monitor changes in the mechanical properties of Si-SSBs under cycle-induced aging.

In general, our experiments showed an overall stiffness reduction with aging as indicated by the increase in ultrasonic wave TOF (see Fig 2a). Further, we observed an overall reduction of transmitted energy with increased cycling. These two findings may be associated with the accumulation of damage at layer interfaces associated with the creation of solid-gas interfaces and/or debonding between layers. Finally, ultrasonic imaging using immersion testing provided information regarding the distribution and evolution of damage in space as these next-gen batteries are aged (see Fig 2b).

By refining these techniques to evaluate next-gen battery technologies, we will develop more sensitive methods to determine when something is wrong before it’s too late. In a world increasingly dependent on safe and reliable energy storage, the ability to “listen” to batteries might be precisely what we need to power the clean energy revolution.

Figure 2. Evolution of cell stiffness during aging. a) Stiffness of the SSB, normalized to its initial value, plotted against discharge capacity for both charged (blue) and discharged (red) states. With representative ultrasonic images from transmitted signals at two states of the SSB: b.1) pristine before cycling, and b.2) after 40 cycles of aging. We observed a significant reduction in transmission in the middle region of the SSB. Warmer colors indicate higher transmission, and dashed outlines mark the active cell region.