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If you’re a wireless headphone user, you’re probably familiar with the frustration that comes with one earphone’s battery running out well before the other gets flat.
But what is it that makes these batteries degrade so unevenly?
Scientists have been studying battery degradation and lifespan issues for as long as batteries have existed. However, conventional battery failure analysis usually takes place in controlled laboratory settings that might not be reflective of real-world electronics use.
To bridge that gap — and hopefully answer the question of why his left earbud always outlives his right one — Yijin Liu, PhD, an assistant professor at the University of Texas at Austin, is investigating how batteries degrade when they are housed inside electronics.
With the collaboration of a network of researchers from around the world, Liu led a recent study investigating the degradation of batteries inside wireless earbuds. Published in Advanced Materials, the study found that other components housed inside the earbud, such as the Bluetooth antenna or a microphone, can generate a temperature gradient during normal use that may damage battery health.
To learn more about in-device battery analysis, Technology Networks spoke with Liu about this research and how its findings could apply to other types of electronics that we encounter in our daily lives.
Alexander Beadle (AB):
Science Writer & Editor
Technology Networks
Alexander Beadle is a science writer and editor for Technology Networks. He holds a masters degree in Materials Chemistry from the University of St Andrews, Scotland.
What prompted you to start investigating how batteries behave when they are inside a device?
Associate Professor
University of Texas at Austin
Dr. Yijin Liu received his bachelor of science (2004) and PhD (2009) degrees from the Physics Department at the University of Science and Technology of China. He joined Stanford University as a postdoctoral scholar in 2009 and became an associate staff scientist at the SLAC National Accelerator Laboratory in 2012, a staff scientist in 2015 and a lead scientist in 2020. In August 2023, Liu joined the Walker Department of Mechanical Engineering at UT Austin as an associate professor. In his previous role as a national lab scientist, Liu led technical developments and scientific applications for the transmission X-ray microscopy program at SLAC/Stanford.
With over 15 years of experience in this field, Liu has developed and applied X-ray characterization methods for a broad range of research fields. In more recent years, Liu’s research focused on studying energy storage materials using high-throughput experimental methods as well as machine learning-assisted statistical analysis. Specific areas of focus include battery manufacturing, safety, degradation and failure analysis.
Batteries exhibit complex behavior across multiple scales. While academic research has advanced battery technology from the material to the cell level, real-world applications require integration into larger systems.
This system-level packaging creates a microenvironment that directly affects cell performance, exposing a crucial gap between fundamental research and practical deployment. Meanwhile, industry research and development operates at a rapid pace and often lacks the bandwidth to deeply investigate underlying mechanisms across various length scales. Addressing this gap is essential and it is the motivation behind this work.
Science Writer & Editor
Technology Networks
Alexander Beadle is a science writer and editor for Technology Networks. He holds a masters degree in Materials Chemistry from the University of St Andrews, Scotland.
What kind of external factors might affect a battery?
Associate Professor
University of Texas at Austin
Dr. Yijin Liu received his bachelor of science (2004) and PhD (2009) degrees from the Physics Department at the University of Science and Technology of China. He joined Stanford University as a postdoctoral scholar in 2009 and became an associate staff scientist at the SLAC National Accelerator Laboratory in 2012, a staff scientist in 2015 and a lead scientist in 2020. In August 2023, Liu joined the Walker Department of Mechanical Engineering at UT Austin as an associate professor. In his previous role as a national lab scientist, Liu led technical developments and scientific applications for the transmission X-ray microscopy program at SLAC/Stanford.
With over 15 years of experience in this field, Liu has developed and applied X-ray characterization methods for a broad range of research fields. In more recent years, Liu’s research focused on studying energy storage materials using high-throughput experimental methods as well as machine learning-assisted statistical analysis. Specific areas of focus include battery manufacturing, safety, degradation and failure analysis.
In our investigation of this earbud, we found that the battery's degradation pattern is affected by surrounding device components, such as the printed circuit and microphone. These components generate heat, leading to a temperature gradient that accelerates battery degradation.
Science Writer & Editor
Technology Networks
Alexander Beadle is a science writer and editor for Technology Networks. He holds a masters degree in Materials Chemistry from the University of St Andrews, Scotland.
Why is in-device battery analysis an important avenue of investigation?
Associate Professor
University of Texas at Austin
Dr. Yijin Liu received his bachelor of science (2004) and PhD (2009) degrees from the Physics Department at the University of Science and Technology of China. He joined Stanford University as a postdoctoral scholar in 2009 and became an associate staff scientist at the SLAC National Accelerator Laboratory in 2012, a staff scientist in 2015 and a lead scientist in 2020. In August 2023, Liu joined the Walker Department of Mechanical Engineering at UT Austin as an associate professor. In his previous role as a national lab scientist, Liu led technical developments and scientific applications for the transmission X-ray microscopy program at SLAC/Stanford.
With over 15 years of experience in this field, Liu has developed and applied X-ray characterization methods for a broad range of research fields. In more recent years, Liu’s research focused on studying energy storage materials using high-throughput experimental methods as well as machine learning-assisted statistical analysis. Specific areas of focus include battery manufacturing, safety, degradation and failure analysis.
As mentioned earlier, device and system packaging create a microenvironment that directly influences battery behavior. The performance patterns observed in a stand-alone cell differ from those seen in a fully integrated device, indicating that some laboratory-based testing and analysis may be overly simplified and not fully representative of real-world conditions.
Battery degradation is a highly complex process, driven by the interplay of micromorphology, crystal structure, oxidation state and other factors. To capture these intricacies, we employed multimodal characterization techniques to analyze the battery material. Our findings reveal a tightly interconnected chemomechanical interplay, significantly influenced by local temperature gradients.
Science Writer & Editor
Technology Networks
Alexander Beadle is a science writer and editor for Technology Networks. He holds a masters degree in Materials Chemistry from the University of St Andrews, Scotland.
What kind of techniques did you employ to “see” inside the earbuds and study their batteries?
Associate Professor
University of Texas at Austin
Dr. Yijin Liu received his bachelor of science (2004) and PhD (2009) degrees from the Physics Department at the University of Science and Technology of China. He joined Stanford University as a postdoctoral scholar in 2009 and became an associate staff scientist at the SLAC National Accelerator Laboratory in 2012, a staff scientist in 2015 and a lead scientist in 2020. In August 2023, Liu joined the Walker Department of Mechanical Engineering at UT Austin as an associate professor. In his previous role as a national lab scientist, Liu led technical developments and scientific applications for the transmission X-ray microscopy program at SLAC/Stanford.
With over 15 years of experience in this field, Liu has developed and applied X-ray characterization methods for a broad range of research fields. In more recent years, Liu’s research focused on studying energy storage materials using high-throughput experimental methods as well as machine learning-assisted statistical analysis. Specific areas of focus include battery manufacturing, safety, degradation and failure analysis.
As one can see from the author list, this was quite a heroic effort involving more than 20 researchers from 7 different institutions. We utilized experimental capabilities at the University of Texas at Austin (Texas, USA), SLAC National Lab (California, USA), Brookhaven National Lab (New York, USA), Argonne National Lab (Illinois, USA) and the European Synchrotron Radiation Facility (France).
The transmission X-ray microscopy beamline at the Stanford Synchrotron Radiation Lightsource revealed chemical heterogeneity within individual particles, each just a few micrometers in size. The hard X-ray nanoprobe beamline at Brookhaven National Laboratory enabled nanoscale probing of local phase transitions, a key indicator of material degradation.
At Argonne National Laboratory, the hard X-ray spectroscopy beamline provided insights into atomic bonding and its evolution over the battery’s lifespan. Meanwhile, the European Synchrotron Radiation Facility allowed us to analyze thousands of particles, offering valuable statistical insights into the broader material behavior.
Science Writer & Editor
Technology Networks
Alexander Beadle is a science writer and editor for Technology Networks. He holds a masters degree in Materials Chemistry from the University of St Andrews, Scotland.
While your study focused on batteries in headphones, are there any lessons here that are relatable to electronics more broadly?
Associate Professor
University of Texas at Austin
Dr. Yijin Liu received his bachelor of science (2004) and PhD (2009) degrees from the Physics Department at the University of Science and Technology of China. He joined Stanford University as a postdoctoral scholar in 2009 and became an associate staff scientist at the SLAC National Accelerator Laboratory in 2012, a staff scientist in 2015 and a lead scientist in 2020. In August 2023, Liu joined the Walker Department of Mechanical Engineering at UT Austin as an associate professor. In his previous role as a national lab scientist, Liu led technical developments and scientific applications for the transmission X-ray microscopy program at SLAC/Stanford.
With over 15 years of experience in this field, Liu has developed and applied X-ray characterization methods for a broad range of research fields. In more recent years, Liu’s research focused on studying energy storage materials using high-throughput experimental methods as well as machine learning-assisted statistical analysis. Specific areas of focus include battery manufacturing, safety, degradation and failure analysis.
These findings are especially relevant – and perhaps even more critical – when considering larger systems like electric vehicle (EV) battery packs, where design flexibility introduces additional complexities. If a temperature gradient is unavoidable, one potential approach is to implement a cooling system with a controlled gradient to mitigate its effects.
Furthermore, this study originated from the observation of capacity decay, but it is equally important to assess the implications from a safety perspective. A key question arises: does a degraded cell have a higher risk of thermal runaway? This remains a crucial research topic, particularly in the context of second-life battery applications, such as repurposing retired EV packs for household energy storage. Ensuring safety in such scenarios requires careful evaluation. Our ongoing research continues to explore these critical challenges.
