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From Theory to Microgrid: New Ideas from the Sustainable Power and Energy Center Research Summit

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Members of the Sustainable Power and Energy Center (SPEC) tour the new Battery Fabrication Laboratory, which was launched at the SPEC Research Summit

San Diego, Calif., July 31, 2017 -- Software that can design new materials for energy storage. X-ray visualization techniques to “see” inside batteries and solar cells. Green processes for making batteries. These were some of the projects presented at the Sustainable Power and Energy Center (SPEC) Research Summit at the University of California San Diego on July 18.

The one-day event featured talks by faculty and industry members on developing next generation green energy materials, batteries and solar cells to meet society’s energy storage needs. “The vision of SPEC is to take the lead in enabling a sustainable energy future,” said Shirley Meng, director of the Sustainable Power and Energy Center and a nanoengineering professor at UC San Diego. “We’re taking an interdisciplinary approach to explore how we can solve the grand challenge of deep decarbonization.”

“Collaboration is vital to the success of SPEC,” said Ping Liu, a nanoengineering professor at UC San Diego. “Everybody plays a role in formulating innovative ideas, defining and solving problems and taking our projects to the next level.”

One of these collaborations is the Battery500 consortium, a multi-institutional battery research effort led by Pacific Northwest National Laboratory and involving UC San Diego, along with nine other universities, national labs and companies in the U.S. The Battery500 consortium’s goal is to develop a lithium battery with a specific energy of 500 watt-hours per kilogram — almost triple the specific energy of today’s batteries — while keeping the battery small, lightweight and inexpensive. Liu and Meng are leading SPEC researchers as part of this grand effort.

The Center recently opened its Battery Fabrication Laboratory, which was built in partnership between UC San Diego and MTI Corporation. The lab provides space and state-of-the-art equipment for researchers to design and test new battery devices. “I’m excited to be a part of this big step to move the Center forward,” said Andy Huang, Marketing Manager at MTI Corporation who was involved with setting up the new lab.

Fundamental Energy Research at the Nanoscale

SPEC researchers presented a broad range of approaches to solving key technical challenges in energy generation, storage and management. “Our motto is from atom to system, or ‘from theory to microgrid,’ in which we combine both basic and applied research and work our way up to final integration,” Meng said.

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Nanoengineering professor and SPEC director Shirley Meng

Understanding what’s happening inside batteries at the level of single atoms and molecules is a hallmark of Meng’s research. She spoke about her group’s work using cryo microscopes to observe how lithium metal behaves as the battery cycles. Researchers essentially watch lithium metal change and grow “one electron at a time” to better understand how dendrites form. Meng’s group has also used 3D X-ray imaging techniques to visualize how nano-sized defects move inside cathode materials as the battery is charged to higher voltages. This work, which was published in Science, provides nanoscale insights that could enable battery developers to design cathodes that work well at high voltages.

Nanoengineering professor David Fenning also studies nanoscale defects, but in solar cells — particularly in silicon solar cells and a class called hybrid perovskite solar cells. Fenning’s group uses synchrotron-based X-ray methods to create high resolution elemental maps of defect migration in solar cell materials. The goal is to better understand how defects limit the efficiency of today’s solar cells. “

“By studying defects and their chemistry, we can look to improve the stability of solar cell devices,” Fenning said.

Fenning recently received an award from the U.S. Department of Energy SunShot Initiative to develop a tool to detect moisture present in photovoltaic modules and model how water degrades performance at the atomic level and up. “No one yet has a good way to measure moisture in commercial solar panels,” Fenning said. By developing fundamental knowledge of how moisture degrades PV modules, researchers will be able to propose and analyze new module designs engineered to last years longer, which will help lower the overall cost of solar power, he added.

Improving Battery Components

Designs for next-generation energy storage systems will also require next-generation components. For batteries, this involves upgrading the electrodes and electrolytes. Nanoengineering professor Ping Liu is working toward this goal by constructing new 3D electrode architectures. His group is developing techniques to create straight channels in thick electrodes. Thick electrodes can store more energy, but they don’t provide much boost in power. That’s because ions typically have to zig-zag their way through an electrode, so the resistance to ion transport increases as the electrode gets thicker. With straight channels, thick electrodes could overcome this hurdle and potentially enhance both the energy density and power of batteries.

Another bottleneck to improving battery performance is the electrolyte. A trend in battery research has been to move away from conventional liquid electrolytes and explore solid state electrolytes, but a group of SPEC researchers has taken a radical approach and explored electrolytes made from liquefied gas solvents. The idea came from Cyrus Rustomji, a former postdoctoral researcher in Meng’s group and the founder of South 8 Technologies. 

Rustomji and his colleagues in Meng’s group published the work in June in Science. The team demonstrated that their new liquefied gas electrolytes can enable lithium batteries to run at temperatures as low as minus 60 degrees Celsius — today’s lithium-ion batteries stop working at minus 20 degrees Celsius. The electrolytes also enable electrochemical capacitors to run as low as minus 80 degrees Celsius — their current low temperature limit is minus 40 degrees Celsius. Ultra-low temperature batteries and capacitors can be used to power craft in the extreme cold, such as high atmosphere WiFi drones and weather balloons, satellites and other aerospace applications. The new electrolytes also offer a unique safety advantage: they can prevent thermal runaway in batteries by shutting off conductivity at high temperatures. Rustomji is continuing to improve the liquefied gas electrolytes under South 8 Technologies. A goal is to extend their low temperature operation down to minus 100 degrees Celsius to power spacecraft sent to explore the outer planets such as Jupiter and Saturn.

But designing a better battery isn’t just about developing better electrodes and electrolytes, as nanoengineering professor Shyue Ping Ong noted during his talk. “We need to take a holistic approach and find optimal combinations of cathode, electrolyte and anode in which the interfaces match properly,” he said. Ong’s lab works not just on designing new battery materials, but also on finding the various material combinations that work well together, as well as those that do not.

All of this work is done computationally. Ong’s group builds software infrastructure that can generate large amounts of materials data, which enable researchers to discover and propose new candidates for energy storage materials that haven’t yet been explored. These data can also be used to predict which materials (and their combinations) work best for specific applications. Ong makes these data publicly available in the hopes that they will become valuable resources for the materials research community. One example is an open-source database developed by Ong’s group called Crystalium, which is the world’s largest database of elemental crystal surfaces and shapes. Researchers could use this database to design new materials for applications such as fuel cells, catalytic converters, computer microchips and solid-state batteries.

Sustainable Power and Energy

Sustainability was another key topic at the SPEC Research Summit. Nanoengineering professor Zheng Chen, who joined UC San Diego and SPEC in 2016, spoke about developing techniques to mine lithium from the ocean for making batteries. “As the price for lithium metal rises, we need to look for a sustainable lithium source. We have a big lithium reservoir right next door: the Pacific Ocean,” he said. He envisions combining lithium mining with water desalination for increased viability and sustainability.

Chen also spoke about designing a closed-loop lithium-ion battery manufacturing process. His team is developing a way to recycle and regenerate spent cathode materials so that they can be reused to make new batteries. The process essentially involves taking out the used cathode particles from a battery and removing the impurities. Chen showed that he was able to restore the cathode’s cycling capacity and stability back to a fresh state.

Along similar lines, Hieu Duong, Senior Research Manager at Maxwell Technologies, Inc., presented an environmentally friendly process to manufacture electrodes. This so-called dry electrode processing technology, which is what Maxwell is known for, uses no solvent. This provides significant energy savings versus traditional wet coated electrode manufacturing processes, in which 60 to 70 percent of the energy is used to remove solvent and dry the electrode, Duong noted. Going solvent-free also cuts down on waste and infrastructure. “Our manufacturing footprint is small because we eliminate all the equipment needed to deal with solvent,” Duong said. The resulting electrodes are compatible with state of the art lithium battery chemistries and exhibit high performance, with a resistance that is up to 30 percent lower than traditional wet coated electrodes.

Energy efficiency in information technologies was addressed in electrical engineering professor Eric Fullerton’s talk. His group is developing ultra-low power information storage, memory and processing components. Fullerton’s approach is inspired by the human brain, which he described as a computer developed in an energy starved environment. “The human brain is designed to do an enormous amount of calculations at an incredibly low amount of power,” he said. The brain uses low energy ion transport processes to both store and process information. According to Fullerton, materials being developed for ion-based energy storage might also be used for low-energy information technologies.

Graduate Student Talks

Research by graduate students was also on display at the summit. During the Graduate Student Fire Pitch competition, 12 students each gave 90-second research presentations and were evaluated by a panel of judges. First prize was awarded to Meng Wang, a materials science and engineering graduate student in structural engineering professor Yu Qiao’s lab. His project is about developing a micro-structured current collector to mitigate thermal runaway in lithium-ion batteries. The second prize went to Mohammed A. Alkhadra, a chemical engineering graduate in nanoengineering professor Darren Lipomi’s lab. Alkhadra presented his work on stretchable, ultra-flexible and wearable organic electronics for sustainable energy production. Wang and Alkhadra received their prizes in the form of $250 and $150 Amazon gift cards, respectively.

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