Science-Watching: Why Do Batteries Sometimes Catch Fire and Explode?

[from Berkeley Lab News, by Theresa Duque]

Key Takeaways
  • Scientists have gained new insight into why thermal runaway, while rare, could cause a resting battery to overheat and catch fire.
  • In order to better understand how a resting battery might undergo thermal runaway after fast charging, scientists are using a technique called “operando X-ray microtomography” to measure changes in the state of charge at the particle level inside a lithium-ion battery after it’s been charged.
  • Their work shows for the first time that it is possible to directly measure current inside a resting battery even when the external current measurement is zero.
  • Much more work is needed before the findings can be used to develop improved safety protocols.

How likely would an electric vehicle battery self-combust and explode? The chances of that happening are actually pretty slim: Some analysts say that gasoline vehicles are nearly 30 times more likely to catch fire than electric vehicles. But recent news of EVs catching fire while parked have left many consumers – and researchers – scratching their heads over how these rare events could possibly happen.

Researchers have long known that high electric currents can lead to “thermal runaway” – a chain reaction that can cause a battery to overheat, catch fire, and explode. But without a reliable method to measure currents inside a resting battery, it has not been clear why some batteries go into thermal runaway, even when an EV is parked.

Now, by using an imaging technique called “operando X-ray microtomography,” scientists at Lawrence Berkeley National Laboratory (Berkeley Lab) and UC Berkeley have shown that the presence of large local currents inside batteries at rest after fast charging could be one of the causes behind thermal runaway. Their findings were reported in the journal ACS Nano.

“We are the first to capture real-time 3D images that measure changes in the state of charge at the particle level inside a lithium-ion battery after it’s been charged,” said Nitash P. Balsara, the senior author on the study. Balsara is a faculty senior scientist in Berkeley Lab’s Materials Sciences Division and a UC Berkeley professor of chemical and biomolecular engineering.

“What’s exciting about this work is that Nitash Balsara’s group isn’t just looking at images – They’re using the images to determine how batteries work and change in a time-dependent way. This study is a culmination of many years of work,” said co-author Dilworth Y. Parkinson, staff scientist and deputy for photon science operations at Berkeley Lab’s Advanced Light Source (ALS).

The team is also the first to measure ionic currents at the particle level inside the battery electrode.

3D microtomography experiments at the Advanced Light Source enabled researchers to pinpoint which particles generated current densities as high as 25 milliamps per centimeter squared inside a resting battery after fast charging. In comparison, the current density required to charge the test battery in 10 minutes was 18 milliamps per centimeter squared. (Credit: Nitash Balsara and Alec S. Ho/Berkeley Lab. Courtesy of ACS Nano)
Measuring a battery’s internal currents

In a lithium-ion battery, the anode component of the electrode is mostly made of graphite. When a healthy battery is charged slowly, lithium ions weave themselves between the layers of graphite sheets in the electrode. In contrast, when the battery is charged rapidly, the lithium ions have a tendency to deposit on the surface of the graphite particles in the form of lithium metal.

“What happens after fast charging when the battery is at rest is a little mysterious,” Balsara said. But the method used for the new study revealed important clues.

Experiments led by first author Alec S. Ho at the ALS show that when graphite is “fully lithiated” or fully charged, it expands a tiny bit, about a 10% change in volume – and that current in the battery at the particle level could be determined by tracking the local lithiation in the electrode. (Ho recently completed his Ph.D. in the Balsara group at UC Berkeley.)

A conventional voltmeter would tell you that when a battery is turned off, and disconnected from both the charging station and the electric motor, the overall current in the battery is zero.

But in the new study, the research team found that after charging the battery in 10 minutes, the local currents in a battery at rest (or currents inside the battery at the particle level) were surprisingly large. Parkinson’s 3D microtomography instrument at the ALS enabled the researchers to pinpoint which particles inside the battery were the “outliers” generating alarming current densities as high as 25 milliamps per centimeter squared. In comparison, the current density required to charge the battery in 10 minutes was 18 milliamps per centimeter squared.

The researchers also learned that the measured internal currents decreased substantially in about 20 minutes. Much more work is needed before their approach can be used to develop improved safety protocols.

Researchers from Argonne National Laboratory also contributed to the work.

The Advanced Light Source is a DOE Office of Science user facility at Berkeley Lab.

The work was supported by the Department of Energy’s Office of Science and Office of Energy Efficiency and Renewable Energy. Additional funding was provided by the National Science Foundation.

New Ultrathin Capacitor Could Enable Energy-Efficient Microchips

Scientists turn century-old material into a thin film for next-gen memory and logic devices

[from Berkeley Lab, by Rachel Berkowitz]

Electron microscope images show the precise atom-by-atom structure of a barium titanate (BaTiO3) thin film sandwiched between layers of strontium ruthenate (SrRuO3) metal to make a tiny capacitor. (Credit: Lane Martin/Berkeley Lab)

The silicon-based computer chips that power our modern devices require vast amounts of energy to operate. Despite ever-improving computing efficiency, information technology is projected to consume around 25% of all primary energy produced by 2030. Researchers in the microelectronics and materials sciences communities are seeking ways to sustainably manage the global need for computing power.

The holy grail for reducing this digital demand is to develop microelectronics that operate at much lower voltages, which would require less energy and is a primary goal of efforts to move beyond today’s state-of-the-art CMOS (complementary metaloxide semiconductor) devices.

Non-silicon materials with enticing properties for memory and logic devices exist; but their common bulk form still requires large voltages to manipulate, making them incompatible with modern electronics. Designing thin-film alternatives that not only perform well at low operating voltages but can also be packed into microelectronic devices remains a challenge.

Now, a team of researchers at Lawrence Berkeley National Laboratory (Berkeley Lab) and UC Berkeley have identified one energy-efficient route—by synthesizing a thin-layer version of a well-known material whose properties are exactly what’s needed for next-generation devices.

First discovered more than 80 years ago, barium titanate (BaTiO3) found use in various capacitors for electronic circuits, ultrasonic generators, transducers, and even sonar.

Crystals of the material respond quickly to a small electric field, flip-flopping the orientation of the charged atoms that make up the material in a reversible but permanent manner even if the applied field is removed. This provides a way to switch between the proverbial “0” and “1” states in logic and memory storage devices—but still requires voltages larger than 1,000 millivolts (mV) for doing so.

Seeking to harness these properties for use in microchips, the Berkeley Lab-led team developed a pathway for creating films of BaTiO3 just 25 nanometers thin—less than a thousandth of a human hair’s width—whose orientation of charged atoms, or polarization, switches as quickly and efficiently as in the bulk version.

“We’ve known about BaTiO3 for the better part of a century and we’ve known how to make thin films of this material for over 40 years. But until now, nobody could make a film that could get close to the structure or performance that could be achieved in bulk,” said Lane Martin, a faculty scientist in the Materials Sciences Division (MSD) at Berkeley Lab and professor of materials science and engineering at UC Berkeley who led the work.

Historically, synthesis attempts have resulted in films that contain higher concentrations of “defects”—points where the structure differs from an idealized version of the material—as compared to bulk versions. Such a high concentration of defects negatively impacts the performance of thin films. Martin and colleagues developed an approach to growing the films that limits those defects. The findings were published in the journal Nature Materials.

To understand what it takes to produce the best, low-defect BaTiO3 thin films, the researchers turned to a process called pulsed-laser deposition. Firing a powerful beam of an ultraviolet laser light onto a ceramic target of BaTiO3 causes the material to transform into a plasma, which then transmits atoms from the target onto a surface to grow the film. “It’s a versatile tool where we can tweak a lot of knobs in the film’s growth and see which are most important for controlling the properties,” said Martin.

Martin and his colleagues showed that their method could achieve precise control over the deposited film’s structure, chemistry, thickness, and interfaces with metal electrodes. By chopping each deposited sample in half and looking at its structure atom by atom using tools at the National Center for Electron Microscopy at Berkeley Lab’s Molecular Foundry, the researchers revealed a version that precisely mimicked an extremely thin slice of the bulk.

“It’s fun to think that we can take these classic materials that we thought we knew everything about, and flip them on their head with new approaches to making and characterizing them,” said Martin.

Finally, by placing a film of BaTiO3 in between two metal layers, Martin and his team created tiny capacitors—the electronic components that rapidly store and release energy in a circuit. Applying voltages of 100 mV or less and measuring the current that emerges showed that the film’s polarization switched within two billionths of a second and could potentially be faster—competitive with what it takes for today’s computers to access memory or perform calculations.

The work follows the bigger goal of creating materials with small switching voltages, and examining how interfaces with the metal components necessary for devices impact such materials. “This is a good early victory in our pursuit of low-power electronics that go beyond what is possible with silicon-based electronics today,” said Martin.

“Unlike our new devices, the capacitors used in chips today don’t hold their data unless you keep applying a voltage,” said Martin. And current technologies generally work at 500 to 600 mV, while a thin film version could work at 50 to 100 mV or less. Together, these measurements demonstrate a successful optimization of voltage and polarization robustness—which tend to be a trade-off, especially in thin materials.

Next, the team plans to shrink the material down even thinner to make it compatible with real devices in computers and study how it behaves at those tiny dimensions. At the same time, they will work with collaborators at companies such as Intel Corp. to test the feasibility in first-generation electronic devices. “If you could make each logic operation in a computer a million times more efficient, think how much energy you save. That’s why we’re doing this,” said Martin.

This research was supported by the U.S. Department of Energy (DOE) Office of Science. The Molecular Foundry is a DOE Office of Science user facility at Berkeley Lab.

Education and the Historical Swirl: Part II

We concluded Part I on this topic with the following comments which we wish students to incorporate into their educations, irrespective of the major, field or concentration:

The gold standard itself, dominated from London led to intricate problems: Golden Fetters: The Gold Standard and the Great Depression, 1919-1939 (published in 1992) by Barry Eichengreen, the leading historian of monetary systems, shows the downstream pitfalls of the gold standard.

In other words, the de facto emergence of Britain/London as the world commercial and policy center and the relation of this emergence to empire and international tensions and rivalries, means it is very problematical for any country to steer a course other than staying in tandem with British moods and ideologies, such as free trade. Any country by itself would find it difficult to have a more independent policy. (Friedrich List of Germany, who died in 1846, wrestles with these difficulties somewhat.) The attempts to find “autonomy and autarky” in the interwar years (Germany, Japan, Italy) led to worse nightmares. The world seems like a “no exit” arena of ideologies and rivalries.

The “crazy dynamics” and the semi-anarchy of the system, which continues to this day and is even worse, means that policy-making is always seen through a “dark windshield.”

History in the globalizing capitalist centuries, the nineteenth and the twentieth, is a kind of turbulent swirl and not a rational “walk.”

Here’s a bizarre but necessary comment on this sense of turbulent and surprising swirl propelling history forwards and backwards and sidewards at the same time:

The historian, Barry Eichengreen (mentioned above), is a distinguished analyst of world monetary systems at U.C. Berkeley and perhaps the leading expert today on the evolution of such systems.

From movies such as Shoah and Last of the Unjust by the great filmmaker Claude Lanzmann, we know that Barry Eichengreen’s mother was Lucille Eichengreen, a Jew born in Hamburg, Germany (1925) and deported to the Łódź Ghetto in Poland during World War II. She survived through many miraculous accidents and contingencies, then wrote about her experiences.

We get a deeper insight into “the way of the world” by seeing that the Holocaust itself has as a backdrop the anarcho-craziness of the world. The Fascists and Nazis were jumping from the “frying pan into the fire” by imagining that world conquest and world-murdering could “stop the world.” They and their favored populations could “get off” and step into a racial dreamworld. They were taking today’s concept of “gated community” and applying it to the “racial community” (Volksgemeinschaft, in German).

This led to the phenomenon depicted in Goya’s famous aquatint: The Sleep of Reason Produces Monsters.

The perceived madness of the world and the madness of leaders that this perception leads to have never been analyzed together.

The fact that the behavior of world leaders could be “crazy like a fox” (half-insane, half-opportunistic, or Machiavellian “clever”) is a complicating factor or twist from Mussolini until today.

Essay 116: Reports of Rising Police-Society Conflict in China

Interview with Suzanne Scoggins (November 25, 2019)

China is facing a rising tide of conflict between the nation’s police officers and the public. While protest events receive considerable media attention, lower-profile conflicts between police officers and residents also make their way onto the internet, shaping perceptions of the police. The ubiquity of live events streamed on the internet helps illuminate the nature of statesociety conflict in China and the challenges faced by local law enforcement.

Simone McGuinness spoke with Suzanne Scoggins, a fellow with the National Asia Research Program (NARP), about the reports of rising policesociety conflict in China. Dr. Scoggins discusses how the Chinese Communist Party has responded to the upsurge, what channels Chinese citizens are utilizing to express their concerns, and what the implications are for the rest of the world.

What is the current state of police-society relations in China?

Reports of police violence have been on the rise, although this does not necessarily mean that violence is increasing. It does, however, mean that the media is more willing to report violence and that more incidents of violence are appearing on social media.

What we can now study is the nature of that violence—some are big events such as riots or attacks against the police, but there are also smaller events. For example, we see reports of passengers on trains who get into arguments with transit police. They may fight because one of the passengers is not in the right seat or is carrying something prohibited. Rather than complying with the officer, the passenger ends up getting into some sort of violent altercation. This kind of violence is typically being captured by cellphone cameras, and sometimes it makes the news.

The nature of the conflict matters. If somebody is on a train and sitting in a seat that they did not pay for, then it is usually obvious to the people reading about or watching the incident that the civilian is at fault. But if it is chengguan (城管, “city administration”) telling an elderly woman to stop selling her food on the street and the chengguan becomes violent, then public perceptions may be very different. It is that second type of violence that can be threatening to the state. The public’s response to the type of conflict can vary considerably.

What are the implications for China as a whole?

Regarding what this means for China, it’s not good for the regime to sustain this kind of conflict between street-level officers or state agents and the public. It lowers people’s trust in the agents of the government, and people may assume that the police cannot enforce public security. There are many state agents who might be involved in a conflict, such as the chengguan, the xiejing (auxiliary officer), or the official police. The type of agent almost doesn’t matter because the uniforms often look similar.

When information goes up online of state agents behaving poorly, it makes the state a little more vulnerable. Even people who were not at the event might see it on social media or in the news and think, “Oh, this is happening in my community, or in my province, or across the nation.” This violates public expectations about how the police or other state agents should act. People should be able to trust the police and go to them when they have problems.

How has the Chinese government responded to the increase in reporting violence?

There is a twofold approach. The first is through censorship. When negative videos go up online or when the media reports an incident, the government will go in and take it down. We see this over time. Even while collecting my research, some of the videos that were initially available online are no longer accessible simply because they have been censored. The government is removing many different types of content, not only violence. Censors are also interested in removing any sort of misinformation that might spread on social media.

If step one is to take the video or report down, step two is to counteract any negative opinion by using police propaganda. This is also referred to as “public relations,” and the goal is to present a better image of the police. Recently, the Ministry of Public Security put a lot of money and resources into their social media presence. Many police stations have a social media account on WeChat or Weibo (微博, “microblogging”) and aim to present a more positive, friendly image of the police. The ministry also teamed up with CCTV to produce television content. This has been going on for some time, but recently shows have become more sophisticated.

There is one program, for example, called Police Training Camp. It is a reality show where police officers are challenged with various tasks, and the production is very glossy. The ministry also produces other sorts of specials featuring police who are out in the field helping people. It shows the police officers working really long shifts, interacting positively with the public, and really making a difference in people’s lives. In this way, the government is counteracting negative opinions about police violence or misconduct.

In general, I will say that it is difficult for people in any society to get justice with police officers because of the way legal systems are structured and the power police hold in local government politics. In China, one of the things people are doing beyond reaching out to local governments or pursuing mediation is calling an official hotline.

This is a direct channel to the Ministry of Public Security, and all these calls are reviewed. There is not a whole lot that citizens can do about specific corruption claims. But if somebody has a particular goal, then the hotline is slightly more effective because it allows citizens to alert the ministry. However, many people do not know about the hotline, so the ministry is trying to increase awareness and also help staff the call center so that it can more effectively field calls.

As for how much relief people feel when they use these channels, this depends on what their goal is. If the goal is to get somebody fired, then the hotline may not work. But if someone is looking to air their grievances, then it may be helpful.

What are the implications of increased police-society conflict in China for the rest of the world? What can the United States or other countries do to improve the situation?

These are really sticky issues that are difficult to solve. When discussing policesociety conflict, it is important to step back and think about who the police are—the enforcement agents of the state. So by their very nature, there will be conflict between police and society, and that is true in every country. In China, it really depends on where and what type of police climate we are talking about.

Xinjiang, for instance, has a very different police climate than other regions in China. There is a different type of policing and police presence. Chinese leaders certainly do not want any international intervention in Xinjiang. They see this as an internal issue. While some governments in Europe and the United States might want to intervene, that is going to be a nonstarter for China.

As for police problems more generally, I would say that if China is able to reduce some of the policesociety conflict in other areas of the country, then this is good for the international community because it leads to a more stable government. We also know that there is a fair amount of international cooperation between police groups. China has police liaisons that travel and learn about practices and technology in different countries. The police in these groups attend conferences and take delegates abroad.

There are also police delegations from other nations that go to China to learn about and exchange best practices. But that work will not necessarily address the underlying issues that we see in a lot of the stations scattered throughout China outside the big cities like Beijing (北京) or Shanghai (上海). Those are the areas with insufficient training or manpower. Those issues must be addressed internally by the Ministry of Public Security.

How is the Chinese government improving its policing capabilities?

Recently, the ministry has tried to overcome manpower and other ground-level policing problems by using surveillance cameras and artificial intelligence. Networks of cameras are appearing all over the country, and police are using body cameras for recording interactions with the public. This type of surveillance is not just in large cities but also in smaller ones. Of course, it is not enough to just put the cameras up—you also need to train officers to use that technology properly. This process takes time, but it is one way that the ministry hopes to overcome on-the-ground problems such as the low number of police per capita.

How might the Hong Kong protests influence or change policing tactics in China?

The situation in Hong Kong is unlikely to change policing tactics in China, which are generally more aggressive in controlling protests than most of what we have seen thus far in Hong Kong. It is more likely that things will go in the other direction, with mainland tactics being used in Hong Kong, especially if we continue to observe increased pressure to bring the protestors in check.

Suzanne Scoggins is an Assistant Professor of Political Science at Clark University. She is also a 2019 National Asia Research Program (NARP) Fellow. Dr. Scoggins holds a Ph.D. in Political Science from the University of California, Berkeley, and her book manuscript Policing in the Shadow of Protest is forthcoming from Cornell University Press. Her research has appeared in Comparative Politics, The China Quarterly, Asian Survey, PS: Political Science and Politics, and the China Law and Society Review.

This interview was conducted by Simone McGuinness, the Public Affairs Intern at NBR.