Imagine a future where renewable energy storage is not just efficient but also sustainable, scalable, and ethical. This vision is what drives Charley Thomas, a fifth-year PhD student working on cutting-edge battery technology. From solid electrolytes to sodium-ion batteries, Thomas is tackling some of the most pressing challenges in energy storage.

In her current research with the Ban Surface Science and Engineering Research Group, Thomas works on two distinct projects: stress-testing solid electrolytes and developing cathodes for sodium-ion batteries. While both are pivotal in advancing battery science, each presents its own unique challenges and rewards.

Solid electrolytes are a promising alternative to traditional liquid-based systems in lithium-ion batteries. However, testing them is notoriously complex. “Stress-testing solid electrolytes sucks,” Thomas said. “There’s no perfect method for evaluating their performance.”

One commonly used test involves symmetrical cells, where the same electrode is placed on both sides of the solid electrolyte. Critical current density testing—ramping up the current until a short circuit occurs—is used to evaluate the material's performance. But this method has its flaws. “Critical current density isn’t a true material property. It’s influenced heavily by the experimental setup,” Thomas explained.

Despite these challenges, Thomas is dedicated to refining her methods, even when it involves tedious and high-stakes procedures like dipping electrolyte pellets into molten lithium at 180 C. “It’s frustrating when the pellets shatter during the process, but each failure teaches us something valuable,” she said.

Thomas’ second project, focused on sodium-ion batteries, offers a hands-on approach to cathode development. Sodium-ion technology has the potential to address ethical and material scarcity concerns associated with lithium-based systems, as sodium is far more abundant and affordable.

“What excites me about this project is that I get to start from the ground up,” Thomas shared. Using common salts—sometimes even dietary supplements—she synthesizes particles, cleans and dries them, and assembles them into electrodes for testing.

This process has deepened Thomas’ understanding of battery fundamentals. “Unlike solid electrolyte testing, which uses symmetrical cells, working with cathodes involves real chemical potential differences and redox reactions. It’s helping me truly grasp how batteries work,” she said.

Thomas’ ultimate goal is to contribute to sustainable energy storage systems that could revolutionize how we power our world. While initially drawn to academia for its teaching opportunities, she is now exploring postdoctoral research as the next step.

“Work-life balance is important to me, so I’m reevaluating my long-term plans,” she said. “But no matter where I end up, I want to be part of the shift towards renewable, ethical energy storage.”

As she continues refining solid electrolytes and advancing sodium-ion technology, Thomas’ work embodies the intersection of innovation, sustainability, and first-principles science. “When a project finally works—when a battery has great capacity or lasts a long time—it’s the best feeling,” she said.

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A team of engineers and material scientists in the Paul M. Rady Department of Mechanical Engineering at ����������ý�Ļ���Ʒ has developed a new technology to turn thermal radiation into electricity in a way that literally teases the basic law of thermal physics.

The breakthrough was discovered by the , led by Assistant Professor Longji Cui. Their work, in collaboration with researchers from the National Renewable Energy Laboratory (NREL) and the University of Wisconsin-Madison, was recently . 

The group says their research has the potential to revolutionize manufacturing industries by increasing power generation without the need for high temperature heat sources or expensive materials. They can store clean energy, lower carbon emissions and harvest heat from geothermal, nuclear and solar radiation plants across the globe.

In other words, Cui and his team have solved an age-old puzzle: how to do more with less.

“Heat is a renewable energy source that is often overlooked,” Cui said. “Two-thirds of all energy that we use is turned into heat. Think of energy storage and electricity generation that doesn’t involve fossil fuels. We can recover some of this wasted thermal energy and use it to make clean electricity.”

Breaking the physical limit in vacuum

High-temperature industrial processes and renewable energy harvesting techniques often utilize a thermal energy conversion method called thermophotovoltaics (TPV). This method harnesses thermal energy from high temperature heat sources to generate electricity. 

But existing TPV devices have one constraint: Planck’s thermal radiation law. 

PhD student Mohammad Habibi showcasing one of the group's TPV cells used for power generation. Habibi was the leader of both the theory and experimentation of this groundbreaking research.

“Planck’s law, one of most fundamental laws in thermal physics, puts a limit on the available thermal energy that can be harnessed from a high temperature source at any given temperature,” said Cui, also a faculty member affiliated with the Materials Science and Engineering Program and the Center for Experiments on Quantum Materials. “Researchers have tried to work closer or overcome this limit using many ideas, but current methods are overly complicated to manufacture the device, costly and unscalable.”

That’s where Cui’s group comes in. By designing a unique and compact TPV device that can fit in a human hand, the team was able to overcome the vacuum limit defined by Planck’s law and double the yielded power density previously achieved by conventional TPV designs. 

“When we were exploring this technology, we had theoretically predicted a high level of enhancement. But we weren’t sure what it would look like in a real world experiment,” said Mohammad Habibi, a PhD student in Cui’s lab and leader of both the theory and experiment of this research. “After performing the experiment and processing the data, we saw the enhancement ourselves and knew it was something great.”

The zero-vacuum gap solution using glass

The research emerged, in part, from the group’s desire to challenge the limits. But in order to succeed, they had to modify existing TPV designs and take a different approach.

“There are two major performance metrics when it comes to TPV devices: efficiency and power density,” said Cui. “Most people have focused on efficiency. However, our goal was to increase power.”

The zero-vacuum gap TPV device, designed by the Cui Research Group.

To do so, the team implemented what’s called a “zero-vacuum gap” solution into the design of their TPV device. Unlike other TPV models that feature a vacuum or gas-filled gap between the thermal source and the solar cell, their design features an insulated, high index and infrared-transparent spacer made out of just glass. 

This creates a high power density channel that allows thermal heat waves to travel through the device without losing strength, drastically improving power generation. The material is also very cheap, one of the device’s central calling cards.

“Previously, when people wanted to enhance the power density, they would have to increase temperature. Let’s say an increase from 1,500 C to 2,000 C. Sometimes even higher, which eventually becomes not tolerable and unsafe for the whole energy system,” Cui explained. “Now we can work in lower temperatures that are compatible with most industrial processes, all while still generating similar electrical power than before. Our device operates at 1,000 C and yields power equivalent to 1,400 C in existing gap-integrated TPV devices.”

The group also says their glass design is just the tip of the iceberg. Other materials could help the device produce even more power.

“This is the first demonstration of this new TPV concept,” explained Habibi. “But if we used another cheap material with the same properties, like amorphous silicon, there is a potential for an even higher, nearly 20 times more increase in power density. That’s what we are looking to explore next.”

The broader commercial impact

Assistant Professor Longji Cui (middle) and the Cui Research Group. 

Cui says their novel TPV devices would make its largest impact by enabling portable power generators and decarbonizing heavy emissions industries. Once optimized, they have the power to transform high-temperature industrial processes, such as the production of glass, steel and cement with cheaper and cleaner electricity.

“Our device uses commercial technology that already exists. It can scale up naturally to be implemented in these industries,” said Cui. “We can recover wasted heat and can provide the energy storage they need with this device at a low working temperature.

“We have a patent pending based on this technology and it is very exciting to push this renewable innovation forward within the field of power generation and heat recovery.” 

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Research doesn’t always go as planned, and sometimes results can appear to be abnormal. Some professors, like Xiaoyun Ding, see this as an opportunity to achieve the next big discovery. 

Ding, an associate professor in the Paul M. Rady Department of Mechanical Engineering, leads the Biomedical Microfluidics Laboratory (BMMLab) at ����������ý�Ļ���Ʒ. His team stumbled across an interesting anomaly during a cell sensing project that used different forms of acoustic waves to measure cell mechanics.

Associate Professor Xiaoyun Ding (right) and his lab group during summer 2024.

When using a surface acoustic wave to rearrange DNA particles, Yu Gao, a research associate in Ding’s group, managed to assemble the particles in a diamond shape. This type of shape assembly has never been observed before in a microfluidic environment using acoustic waves. 

But what did it mean?

“Normally, acoustic wave patterns resemble a kind of circular-shaped aggregation of particles,” said Ding, also a faculty member in biomedical engineering. “After seeing this pattern, though, we had a feeling it could be a completely new wave mode that is contributing to this phenomenon.

“So we reached out to our collaborators Thomas Voglhuber-Brunnmaier and Bernhard Jakoby in Austria. They helped us model our experiment. Sure enough, their results matched our initial observation.”

According to Ding, the newly discovered wave mode has a few unique traits compared to the traditional acoustic wave modes used in acoustic tweezer research. First, it contains a horizontal polarization, allowing the wave to move sideways along the interface rather than oscillating across a vertical plane. 

The wave mode can also apply electric force to a particle or cell, instead of standard acoustic force. He says being able to configure the various wave modes and switch between them on demand can lead to even more major breakthroughs when studying cell mechanics or cell manipulation.

“I always tell my students: in both research and life, you will see something you don’t expect,” Ding said. “It’s not called failure. The result that you do not expect could be an opportunity.”

“Cells with different properties, like cancer cells, respond differently to electric force,” Ding said. “Manipulating the electric field will allow us to separate these cells with more sensitivity and accuracy. We’ll be able to detect more of their properties and study their mechanics more efficiently.

“Before this discovery, there was no intrinsic control over generating acoustic force or electric force. Now, we can selectively generate these different wave modes and apply different forces simply by changing the frequency.”

The research conducted by Ding and his colleagues, titled “,” has been published by Physical Review Letters. Professor Massimo Ruzzene is also a co-author of the paper.

Their work serves as another example of interdisciplinary collaboration, a common theme in the College of Engineering and Applied Science.

“Our group is actively working with people in the medical and biology fields. They tell us their problems, and we try to develop technology that can solve those problems,” said Ding. “We take on their issues, and we try to make their lives easier.”

But Ding says the BMMLab atmosphere isn’t only focusing on biomedical problem-solving. There are other lessons to be learned that go far beyond the laboratory. 

“I always tell my students: in both research and life, you will see something you don’t expect,” Ding said. “It’s not called failure. The result that you do not expect could be an opportunity.”

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Watch Jacob Segil, CEO of Afference and research professor in the Paul M. Rady Department of Mechanical Engineering, showcase a new piece of haptic technology in an episode of Freethink's Hard Reset docuseries that will "redraw the borders of reality."

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