Newswise – Researchers from Argonne and partner institutions highlight the important implications of “aggregates” for future battery performance.
Keeping track of the most recent scientific literature is an essential part of a scientist’s job, as it could yield insights that will turn into tomorrow’s breakthroughs.
In 2018, Lei Cheng, a battery a chemist at the US Department of Energy’s (DOE) Argonne National Laboratory, was doing just that when she came across a few studies of battery electrolytes that described the presence of structures called nanoscale aggregates. These are clusters of tens to hundreds of charged particles called ions whose total diameter is greater than one nanometer. Until then, most research on battery electrolytes had focused on much smaller structures.
“An important goal of future research is to find out when aggregates are beneficial and when they are not. When they have adverse effects, you would want to remove them from the electrolyte. — Larry Curtiss, Argonne Senior Chemist and Distinguished Fellow
Electrolytes are chemical solutions that play an essential role in the functioning of a battery. They contain positively charged ions that move back and forth between the positive and negative sides of a battery.
Cheng is a technical lead at the Joint Center for Energy Storage Research (JCESR), an energy innovation center launched by the DOE and led by Argonne. JCESR brings together more than 150 researchers from 20 institutions – including national laboratories, universities and industry – to design and manufacture materials enabling the next generation Battery. Such Battery can help usher in major energy transitions in vehicles, the grid, and even electric flight.
Cheng and several other JCESR researchers agreed that the aggregates deserved closer examination. After all, the team was well aware that the structure of electrolytes can have a significant impact on their properties and ultimately play an important role in the performance of Battery. For example, working to develop better lithium-ion Batteryresearchers have found that adding small amounts of certain salt molecules to electrolytes can make them more stable.
“Aggregates weren’t a big deal back then,” Cheng said. “Scientists didn’t talk much about their impact on the properties of electrolytes. That’s why we decided to start research projects to investigate further.
Fast forward from 2018 to 2021: JCESR researchers have accumulated a large enough body of research to conclude that aggregates are an important emerging topic with potentially important implications for next-generation performance Battery. To alert the battery science community, they published an aggregate research survey and analysis in Energy Letters of the American Chemical Society. The Perspective article incorporates the results of 60 studies conducted by JCESR researchers and other scientists.
Impacts on electrolyte properties
The Perspective article explores how aggregates can have unique effects on electrolyte properties, including stability and ion transport.
Stability can impact many critical aspects of battery performance. These include life (the number of charge and discharge cycles), safety, energy density, and charge and discharge rates. For example, an unstable electrolyte tends to break down. This can shorten the life of a battery and lead to security issues.
Ion transport refers to the rate at which ions move through an electrolyte. This property can affect the charge and discharge rate of a battery. Rapid ion transport can enable faster charging of electric vehicles as well as faster grid-scale discharging Battery. Another potential benefit could be improved performance of electrolytes made of very large molecules called polymers. These electrolytes are safer than liquid electrolytes.
Aggregates can have beneficial or negative effects on battery performance. For example, they could slow down or speed up the transport of ions.
“An important focus of future research is to find out when aggregates are beneficial and when they are not,” said Larry Curtiss, a veteran Argonne chemist and one of the paper’s authors. Perspective. “When they have adverse effects, you would want to remove them from the electrolyte.”
An example of a known beneficial impact of aggregates occurs in lithium-oxygen Battery. These new generations Battery work by transporting oxygen through an electrolyte to the cathode. There it reacts with lithium to form lithium peroxide. Compared to lithium ion Battery, lithium-oxygen devices have a much higher energy density and could potentially be used to electrify long-haul trucking and aviation. Simulations and calculations by Curtiss and other researchers suggest that the aggregates can enhance oxygen transport as well as reactions at the cathode-electrolyte interface. However, it is not understood why these effects occur.
“This is an area for future study,” Curtiss said.
How are aggregates formed?
The formation of aggregates is not yet fully understood. The researchers believe it depends on the strength of various interactions between ions and solvent molecules in an electrolyte. Solvents are materials capable of dissolving other materials.
“If the ions react weakly with the solvent molecules, you can get much smaller structures like ion pairs,” Curtiss said. “If the ion-ion interactions are very strong, you can get aggregates.”
“There is no complete, uniform theory of how aggregates form,” Cheng said. “We still need to know what parameters you can adjust to manipulate their formation and structure.”
Many knowledge gaps and research needs
Most global research to date has focused on lithium-ion Battery. However, the electrolytes used in lithium-ion Battery – such as ethylene carbonate and propylene carbonate – are not compatible with electrode materials found in many Battery in development. Such Battery include lithium-oxygen and lithium-sulfur Battery. As researchers develop alternative electrolytes for these advanced technologies Batterythey will have to study the effects of aggregates.
Additionally, most of the existing research on aggregates has looked at their effects only on electrolytes. “There have been very few studies on their impact on the electrode-electrolyte interface, which is critical to battery performance,” Curtiss said. ion transfer across the interface. And we don’t know if they could cause electrons to leak out of the cathode and destroy the electrolyte.
“A big knowledge gap is how aggregates organize at interfaces and how that affects charge transfer,” Cheng said.
Cheng added that there is a need to develop new experimental characterization tools capable of targeting these interfaces. These can include spectroscopic tools, which use light to characterize the composition and structure of materials. Improved X-ray techniques, such as those being developed at the Argonne Advanced Photon Source, can help detect the presence of aggregates and characterize their composition and evolution over time.
An active area of research involves improving computational and simulation methods to accurately describe the complex interactions between aggregates, ions and molecules. machine learning can potentially be used to learn from the large amounts of data collected about these interactions.
Cheng, Curtiss and other JCESR researchers plan to pursue several lines of global research. One ongoing area is varying ions and other parameters to better understand how aggregates form. The Argonne researchers also plan to continue their research with the University of Illinois at Urbana-Champaign on the effects of aggregates at electrode interfaces.
Interestingly, the formation of aggregates is not unique to battery electrolytes. Aggregates can play a role in the production processes of materials used in other industries such as pharmaceuticals. Knowledge from global research on battery electrolytes could benefit these other processes.
Co-authors of the Perspective paper are Zhou Yu, Argonne National Laboratory; Nitash Balsara, University of California, Berkeley/Lawrence Berkeley National Laboratory; Oleg Borodin, US Army Research Laboratory; Andrew Gewirth, University of Illinois at Urbana-Champaign; Nathan Hahn, Sandia National Laboratories; Edward Maginn, University of Notre Dame; Kristin Persson, Lawrence Berkeley National Laboratory/University of California, Berkeley; Venkat Srinivasan, Argonne Collaborative Center for Energy Storage Science; Michael Toney, University of Colorado, Boulder; Kang Xu, US Army Research Laboratory; and Kevin Zavadil, Sandia National Laboratories.
The Joint Energy Storage Research Center (JCESR)a DOE Energy Innovation Center, is a major partnership which integrates researchers from many disciplines to overcome critical scientific and technical hurdles and create breakthrough new energy storage technology. Led by the U.S. Department of Energy’s Argonne National Laboratory, partners include national science and engineering leaders from academia, industry and national laboratories. Their combined expertise spans the full spectrum of the technology development pipeline, from basic research, to prototype development, to product engineering and market release.
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