News Article | March 8, 2016
For these reasons and more, many experts are increasingly interested in making electricity a local affair. This idea, useful for both cost savings and for backup power, moves the main source of electricity away from remote large-scale plants to smaller local ones. This approach is called distributed energy. Distributed energy devices can produce enough electricity to power a home, business, or small community, making them ideal backups for power when energy is cut from the main grid in the case of a power outage. They can be solar panels, small wind turbines, batteries, fuel cells or microturbines that connect directly to the home or local electrical grid, but their purpose is to meet the specific power needs of a local population. "Until maybe about 10 years ago, we never accommodated people's different energy needs—now we can," said George Crabtree, director of Argonne's Joint Center for Energy Storage Research center. "It may be the solar panel on my roof or the battery in my garage, but in the end, these different needs give rise to new technologies that give us a greater amount of choice, and ultimately, control." Large power plants have several major drawbacks. Firstly, they waste a lot of energy—about two-thirds —when converting fuel to electricity. Secondly, many of them sit idle for a good part of the year (on average about half the time) as they may only be needed to meet peak demand—usually the time of day when the majority of people come home in the evening. Thirdly, in shipping the power from the large stations to the consumer, we waste another 5-7% in transmission and distribution losses. On the other hand, distributed systems present smaller, more flexible options. And because they are located close to where the power is needed, less energy is lost in delivery. Distributed energy devices such as solar panels, fuel cells, microturbines, and batteries come in a variety of types and sizes, from as little as 1 kilowatt—enough to power ten 100-watt light bulbs—up to as much as 10,000 kilowatts, which might be enough to power a university campus or a neighborhood or community microgrid. Single homes and small businesses can benefit from rooftop solar panels on sunlit days or portable natural gas generators in the evening. Hospitals and small towns that use considerably more energy can use a mix of microturbines, generators, and industrial-scale batteries. However, tying these devices together in a way that allows them to communicate with electrical grid operators is a challenge. Each new device connected to the grid becomes another device that operators have to account for when balancing an area's energy demand. As information-sharing between devices gets more complex, and as more consumers install distributed systems in their homes and communities, the next challenge becomes how to share data with local utilities so they can accurately respond to real-time energy demand. Distributed energy resources are growing rapidly in some parts of the country. At the end of 2014, the U.S. had close to 650,000 solar-powered homes with a new a solar project installed every 2.5 minutes, and the grid has managed to handle it fine so far. "But if we're talking about moving from coordinating distributed energy for tens of millions of people, we can't even envision that amount of data," said Argonne energy systems analyst Guenter Conzelmann. "We are talking about a very different scale than the one we are used to, and we just don't have the systems in place to handle that right now." National grid operators are quite efficient at balancing energy supply and demand, because they can rely on hundreds of power plants to respond instantly each time a device is turned on or off. This type of balance becomes more challenging on smaller neighborhood scales. "Controlling things on a smaller scale can be more challenging because you have fewer resources," said Jianhui Wang, the head of Argonne's Advanced Power Grid Modeling section. "The solar panels, the wind or gas turbines, the electric cars—all of these things have to communicate with to each other to balance out the demand and supply within that community, just as an electrical grid operator has to balance out a region." Figuring out how distributed energy systems will communicate effectively within a grid the size of a neighborhood is the focus of a new project on Chicago's south side. Argonne and the Illinois Institute of Technology (IIT) are teaming up with electrical utility ComEd to build a microgrid in the Chicago neighborhood of Bronzeville. A microgrid is a small community that can make and use most or all of its own power using a mix of distributed energy generators and energy storage units. Argonne is working with ComEd, IIT, and a number of industry partners to develop advanced control system software to help this microgrid balance relatively few resources within a strictly defined area, while matching the energy demand of its community. Though we'll still rely on remotely-generated power, an increase in the number of distributed systems will decrease this reliance over time, Argonne experts say. "That transition is going to happen, but you need to tie in all of these resources into the grid to be able to manage it," said Argonne mechanical engineer Sreenath Gupta. "Thankfully, innovation is driving costs down, which is definitely going to help increase the adoption of these types of technologies."
News Article | March 31, 2016
Ever worry that your cell phone will fade when you need it most? Or that the same thing will happen when driving your electric car? Lightweight lithium-sulfur batteries could be the answer, holding two times the energy of those on store shelves, but they often fade and won't hold a charge for long. Through the Joint Center for Energy Storage Research (JCESR), scientists at DOE's Pacific Northwest National Laboratory identified one of the reasons behind this problem.
News Article | March 31, 2016
« Navigant Research projects annual capacity of second-life EV batteries for stationary energy storage to reach 11 GWh by 2035 | Main | FTA to award up to $55M in 2016 Low or No Emission Program for transit vehicles » Researchers at Pacific Northwest National Laboratory (PNNL) investigating the stability of the anode/electrolyte interface in Li-Sulfur batteries have found that Li-S batteries using LiTFSI-based electrolytes are more stable than those using LiFSI-based electrolytes. In their study, published in the journal Advanced Functional Materials, they determined that the decreased stability is because the N–S bond in the FSI− anion is fairly weak; the scission of this bond leads to the formation of lithium sulfate (LiSO ) in the presence of polysulfide species. By contrast, in the LiTFSI-based electrolyte, the lithium metal anode tends to react with polysulfide to form lithium sulfide (LiS ), which is more reversible than LiSO formed in the LiFSI-based electrolyte. This fundamental difference in the bond strength of the salt anions in the presence of polysulfide species leads to a large difference in the stability of the anode-electrolyte interface and performance of the Li-S batteries with electrolytes composed of these salts. Therefore, they concluded, anion selection is one of the key parameters in the search for new electrolytes for stable operation of Li-S batteries. Background. Lithium-sulfur batteries—comprising a sulfur cathode and Li metal anode—are widely seen as a very promising next-generation electric energy storage system due to their very high theoretical specific energy (2550 Wh kg−1) and energy density (2862 Wh L−1). The chemistry faces some fundamental barriers—polysulfide dissolution, low sulfur utilization, large volume expansion, and low Coulombic efficiency. The polysulfide shuttle—the migration of lithium polysulfides formed during charge and discharge from cathode to anode—leads to serious self-discharge, poor efficiency and limited cycle life. However, a great deal of progress has been made on the cathode side to accommodate sulfur species, mitigate the dissolution of polysulfides, and block the shuttle effect. This, say the PNNL researchers makes addressing the stability of the Li metal anode an even more urgent challenge in the quest for long-term stability for Li-S batteries. The study. To determine the influence of electrolytes in lithium-sulfur batteries, the team did experiments with both LiTFSI and a similar electrolyte, called LiFSI, which has less carbon and fluoride. After continually measuring the amount of energy that the battery held and released, the team did a post-mortem analysis to study the electrodes. They did this work using instruments at DOE’s EMSL, an Office of Science scientific user facility. They found that salts used in the liquid in the batteries make a big difference. When LiTFSI salt is packed in the liquid, a test battery can hold most of its charge for more than 200 uses. The LiTFSI helps bind up lithium atoms and sulfur on the electrode but quickly releases them. In contrast, a similar liquid ties up the lithium and sulfur but doesn’t release it. The result is an electrode that quickly degrades; the battery fades after a few dozen uses. They discovered that with the LiTFSI, the electrode’s lithium atoms became bound up with sulfur. The result is lithium sulfide (LiS ) forming on the electrode’s surface. With LiFSI, lithium sulfate (LiSO ) formed. By calculating the strength with which the compounds clung to the lithium, they found that the lithium sulfide easily broke apart to release the lithium. However, the lithium sulfate was hard to separate. The oxygen in the lithium sulfate was the culprit. The next step for the researchers is to develop an electrolyte additive that forms a protective layer on the lithium anode’s surface, protecting it from the electrolyte. This work was supported by the Joint Center for Energy Storage Research (JCESR), an Energy Innovation Hub funded by the US Department of Energy, Office of Science, Basic Energy Sciences.
News Article | September 1, 2016
« Ballard MOU with strategic partner Broad-Ocean targets fuel cell modules for buses and commercial vehicles | Main | Ceres Power and Cummins win DOE award to develop SOFC systems for data centers » Researchers at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have directly probed the solid/liquid interface of the electrochemical double layer (EDL) using a novel X-ray toolkit. The X-ray tools and techniques could be extended, the researchers say, to provide new insight about battery performance and corrosion, a wide range of chemical reactions, and even biological and environmental processes that rely on similar chemistry. Originally conceived by Hermann von Helmholtz in the 19th century, the EDL is a key concept in the modern electrochemistry of electrified interfaces. The properties of the interface formed by a charged electrode surface immersed in an electrolyte governs the charge transfer processes through the interface itself, thus influencing the electrochemical responses of the electrode/electrolyte system. These concepts and models together serve as the foundation of modern electrochemistry, the researchers noted in an open-access paper describing the work published in Nature Communications. The researchers used ambient-pressure x-ray photoelectron spectroscopy (AP-XPS) to study the ECL. AP-XPS is a technique available from two of the beamlines at the Advanced Light Source at the Lab. X-ray photoelectron spectroscopy (XPS) is a powerful and versatile surface characterization technique that can provide quantitative information about elemental composition and chemical specificity. However, conventional XPS measurements require ultra-high vacuum (UHV) conditions to avoid electron scattering with gas molecules as well as the surface contaminations. To apply XPS to liquid and gas phases, researchers developed the ambient pressure XPS (AP-XPS) technique enabling the use of a laboratory-based X-ray source in near ambient pressure conditions. In 2015, Berkeley Lab researchers used AP-XPS to explore the electrochemical oxidation of the Pt electrode at an oxygen evolution reaction (OER) potential (Axnanda et al.). A key breakthrough enabling the latest experiment was in tailoring “tender” X-rays (also used in the Axnanda study)—which have an energy range tuned in a middle ground between the typical high-energy (or “hard”) and low-energy (or “soft”) X-rays used in research—to focus on chemistry within the double layer of a sample electrochemical system. In a battery, this electrochemical double layer describes the layer of charged atoms or molecules in the battery’s fluid that are drawn in and cling to the surface of the electrode because of their opposite electrical charge—an essential step in battery operation—and a second and closely related zone of chemical activity that is affected by the chemistry at the electrode’s surface. The complex molecular-scale dance of charge flow and transfer within a battery’s double layer is central to its function. The latest work shows changes in the electric potential in this double layer. This potential is a location-based measure of the effect of an electric field on an object—an increased potential would be found in an electric charge moving toward a lightbulb, and flows to a lower potential after powering on the lightbulb. To be able to directly probe any attribute of the double layer is a significant advancement. Essentially, we now have a direct map, showing how potential within the double layer changes based on adjustments to the electrode charge and electrolyte concentration. Independent of a model, we can directly see this—it’s literally a picture of the system at that time. This will help us with guidance of theoretical models as well as materials design and development of improved electrochemical, environmental, biological, and chemical systems. —Ethan Crumlin, a research scientist at Berkeley Lab’s ALS who led the experiment Zahid Hussain, division deputy for scientific support at the ALS, who participated in the experiment, added, “The problem of understanding solid/liquid interfaces has been known for 50-plus years—everybody has been using simulations and modeling to try to conceive of what’s at work. Solid/liquid interfaces are key for all kinds of research, from batteries to fuel cells to artificial photosynthesis.” The latest work has narrowed the list of candidate models that explain what’s at work in the double layer. In the experiment, researchers from Berkeley Lab and Shanghai studied the active chemistry of a gold electrode and a water-containing electrolyte that also contained a neutrally charged molecule called pyrazine. They used AP-XPS to measure the potential distribution for water and pyrazine molecules across the solid/liquid interface in response to changes in the electrode potential and the electrolyte concentration. The experiment demonstrated a new, direct way to precisely measure a potential drop in the stored electrical energy within the double layer’s electrolyte solution. These measurements also allowed researchers to determine associated charge properties across the interface (known as the “potential of zero charge” or “pzc”). The technique is well-suited to active chemistry, and there are plans to add new capabilities to make this technique more robust for studying finer details during the course of chemical reactions, and to bring in other complementary X-ray study techniques to add new details, Hussain said. An upgrade to the X-ray beamline where the experiment was conducted is now in progress and is expected to conclude early next year. Also, a brand new beamline that will marry this and several other X-ray capabilities for energy-related research, dubbed AMBER (Advanced Materials Beamline for Energy Research) is under construction at the ALS and is scheduled to begin operating in 2018. Researchers from the Joint Center for Artificial Photosynthesis, the Joint Center for Energy Storage Research, the Gwangju Institute of Science and Technology in the Republic of Korea, the Shanghai Institute of Microsystem and Information Technology in China, and the School of Physical Science and Technology in China participated in this research. The work was supported by the US Department of Energy Office Science, the National Natural Science Foundation of China, and the Chinese Academy of Sciences-Shanghai Science Research Center. The Advanced Light Source is a DOE Office of Science User Facility.
News Article | October 6, 2016
« Wolfspeed delivers industry’s first 1000V SiC MOSFET for efficient EV fast chargers | Main | ICAO agrees to market-based measure to address aviation CO2 » Berkeley Lab hosted a battery research workshop last week to explore what role researchers in the University of California (UC) system can play in bridging the gap between science research and technology deployment of new batteries. A new battery technology can take decades to develop, Lab battery scientist Venkat Srinivasan, who is also deputy director of the Department of Energy’s Joint Center for Energy Storage Research (JCESR), said in his introductory presentation. One key problem is a gap in the technology-readiness-level (TRL) spectrum between the basic and applied science end of the spectrum and the technology maturation end of the spectrum, he said. The purpose of this workshop is to see what role UC can play in bridging the gap in applied research, Srinivasan said. The workshop addressed the need for energy storage for both transportation and the grid. The keynote speaker was California Energy Commissioner David Hochschild. Other speakers included Susan Kennedy, former chief of staff of Gov. Arnold Schwarzenegger and now CEO of Advanced Microgrid Solutions, and Mark Verbrugge of GM and the U.S. Advanced Battery Consortium (USABC). In the next few weeks, a set of recommendations and a roadmap for next steps will be distributed. This is the beginning of the conversation. We plan to build on this meeting and organize smaller working groups focused on specific topics such as understanding the broader trends on the grid and the roadmap of where storage technologies need to be in the next five, 10, and 20 years.
News Article | January 13, 2016
Scientists at the US Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab) have developed a novel electrolyte for use in solid-state lithium batteries. This electrolyte overcomes many of the problems that plague other solid electrolytes while also showing signs of being compatible with next-generation cathodes. Berkeley Lab battery scientist Nitash Balsara, working with collaborator Joseph DeSimone at the University of North Carolina at Chapel Hill, came up with a highly conductive hybrid electrolyte that combines the two primary types of solid electrolyte – polymer and glass. Their discovery is detailed in a paper published in Proceedings of the National Academy of Sciences (PNAS), co-authored by Berkeley Lab researchers Irune Villaluenga, Kevin Wujcik, Wei Tong, and Didier Devaux, and Dominica Wong of the University of North Carolina. Villaluenga, a postdoctoral fellow at Berkeley Lab, played a key role in designing and realizing the solid electrolyte; Balsara and DeSimone are the senior authors. "The electrolyte is compliant, which means it can readily deform to maintain contact with the electrode as the battery is cycled, and also has unprecedented room temperature conductivity for a solid electrolyte," said Balsara. The electrolyte carries electrical charge between the battery's cathode and anode and in most commercial batteries is liquid. Researchers are striving to develop a battery with all solid components, as it would likely perform better, last longer and be safer. The two main candidates as solid electrolytes – polymer and glass or ceramic – each come with their own set of issues. Polymer electrolytes don't conduct well at room temperature and need to be heated up. Ceramic electrolytes, on the other hand, do conduct well at room temperature but require a great deal of pressure to maintain contact with the electrodes. "It needs something like one ton over every square centimeter, so you need a big truck sitting on the battery as it cycles," Balsara said. The new material they developed, a glass-polymer hybrid, was made by taking particles of glass and attaching perfluoropolyether chains to their surface, adding salt, and then making a film out of these components. By tuning the polymer-to-glass ratio, the scientists were able to come up with a compliant electrolyte with high conductivity at room temperature and excellent electrochemical stability. Although the conductivity is not as good as that of a liquid electrolyte, being about 10 to 15 times lower, "it's probably good enough for some applications," Balsara said. "We don't necessarily need to match a liquid electrolyte because nearly all of the current in the hybrid electrolyte is carried by the lithium ion. In conventional lithium electrolytes, only 20–30% of the current is carried by the lithium ion. Nevertheless, it is likely that playing around with different glass compounds, particle size, and length and concentration of the polymer chains will result in improved conductivity." The researchers also demonstrated that their hybrid electrolyte should work with two of the most promising next-generation cathode materials being developed: sulfur and high-voltage materials such as lithium nickel manganese cobalt oxide. "People would like to use 5-volt cathodes, but electrolytes that are stable against those 5-volt cathodes are not readily available," Balsara said. "We have demonstrated this electrolyte is stable at 5 volts, though we have not incorporated the hybrid electrolyte in the cathode yet." Further experiments demonstrated that the hybrid electrolyte can be well suited to work with a sulfur cathode, which operates at a relatively low voltage but has the advantages of high capacity and low cost. A major failure mode in lithium-sulfur cells with conventional liquid electrolytes is the dissolution into the electrolyte of intermediate compounds formed as sulfur in the cathode is converted to lithium sulfide. However, the intermediates were found to be insoluble in the glass-polymer electrolyte. "Although much work remains to be done, we believe that our work opens a previously unidentified route for developing hybrid solid electrolytes that will address the current challenges of lithium batteries," the researchers wrote in the PNAS article. Funding for the research at Berkeley Lab was provided by DOE's Office of Science through the Joint Center for Energy Storage Research, a DOE Energy Innovation Hub. Part of the work was done at the Stanford Synchrotron Radiation Lightsource at SLAC National Accelerator Laboratory and at the Advanced Light Source at Berkeley Lab, both DOE Office of Science User Facilities. Balsara was one of the co-founders of battery startup Seeo, founded in 2007 to develop a solid block copolymer electrolyte. Balsara and DeSimone have also co-founded a startup company called Blue Current, which aims to commercialize a perfluoropolyether-based nonflammable electrolyte they developed together. This story is adapted from material from Lawrence Berkeley National Laboratory, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.
News Article | February 21, 2017
Because the sun doesn't always shine, solar utilities need a way to store extra charge for a rainy day. The same goes for wind power facilities, since the wind doesn't always blow. To take full advantage of renewable energy, electrical grids need large batteries that can store the power coming from wind and solar installations until it is needed. Some of the current technologies that are potentially very appealing for the electrical grid are inefficient and short-lived. University of Utah and University of Michigan chemists, participating in the U.S. Department of Energy's Joint Center for Energy Storage Research, predict a better future for a type of battery for grid storage called redox flow batteries. Using a predictive model of molecules and their properties, the team has developed a charge-storing molecule around 1,000 times more stable than current compounds. Their results are reported today in the Journal of the American Chemical Society. "Our first compound had a half-life of about eight-12 hours," says U chemist Matthew Sigman, referring to the time period in which half of the compound would decompose. "The compound that we predicted was stable on the order of months." For a typical residential solar panel customer, electricity must be either used as it's generated, sold back to the electrical grid, or stored in batteries. Deep-cycle lead batteries or lithium ion batteries are already on the market, but each type presents challenges for use on the grid. All batteries contain chemicals that store and release electrical charge. However, redox flow batteries aren't like the batteries in cars or cell phones. Redox flow batteries instead use two tanks to store energy, separated by a central set of inert electrodes. The tanks hold the solutions containing molecules or charged atoms, called anolytes and catholytes, that store and release charge as the solution "flows" past the electrodes, depending on whether electricity is being provided to the battery or extracted from it. "If you want to increase the capacity, you just put more material in the tanks and it flows through the same cell," says University of Michigan chemist Melanie Sanford. "If you want to increase the rate of charge or discharge, you increase the number of cells." Current redox flow batteries use solutions containing vanadium, a costly material that requires extra safety in handling because of its potential toxicity. Formulating the batteries is a chemical balancing act, since molecules that can store more charge tend to be less stable, losing charge and rapidly decomposing. Sanford began collaborating with Sigman and U electrochemist Shelley Minteer through the U.S. Department of Energy's Joint Center for Energy Storage Research (JCESR), an Energy Innovation Hub dedicated to creating next-generation battery technologies. Sanford's lab developed and tested potential electrolyte molecules, and sought to use predictive technology to help design better battery compounds. Minteer contributed expertise in electrochemistry and Sigman employed a computational method, which uses the structural features of a molecule to predict its properties. A similar approach is widely used in drug development to predict the properties of candidate drugs. The team's work found that a candidate compound decomposed when two molecules interacted with each other. "These molecules can't decompose if they can't come together," Sanford says. "You can tune the molecules to prevent them from coming together." Tuning a key parameter of those molecules, a factor describing the height of a molecular component, essentially placed a bumper or deflector shield around the candidate molecule. The most exciting anolyte reported in the paper is based on the organic molecule pyridinium. It contains no metals and is intended to be dissolved in an organic solvent, further enhancing its stability. Other compounds exhibited longer half-lives, but this anolyte provides the best combination of stability and redox potential, which is directly related to how much energy it can store. Sigman, Minteer and Sanford are now working to identify a catholyte to pair with this and future molecules. Other engineering milestones lay ahead in the development of a new redox flow battery technology, but determining a framework for improving battery components is a key first step. "It's a multipart challenge, but you can't do anything if you don't have stable molecules with low redox potentials," Sanford says. "You need to work from there." The team attributes their success thus far to the application of this structure-function relationship toolset, typically used in the pharmaceutical industry, to battery design. "We bring the tools of chemists to a field that was traditionally the purview of engineers," Sanford says. This release and an accompanying GIF can be found here. Funding for the project was provided by the Joint Center for Energy Storage Research, a Department of Energy Innovation Hub supported by DOE's Office of Science. The Joint Center for Energy Storage Research (JCESR), a DOE Energy Innovation Hub, is a major partnership that integrates researchers from many disciplines to overcome critical scientific and technical barriers and create new breakthrough energy storage technology. Led by the U.S. Department of Energy's Argonne National Laboratory, partners include national leaders in science and engineering from academia, the private sector, and national laboratories. Their combined expertise spans the full range of the technology-development pipeline from basic research to prototype development to product engineering to market delivery.
News Article | February 21, 2017
University of Utah and University of Michigan chemists, participating in the U.S. Department of Energy's Joint Center for Energy Storage Research, predict a better future for a type of battery for grid storage called redox flow batteries. Using a predictive model of molecules and their properties, the team has developed a charge-storing molecule around 1,000 times more stable than current compounds. Their results are reported today in the Journal of the American Chemical Society. "Our first compound had a half-life of about eight-12 hours," says U chemist Matthew Sigman, referring to the time period in which half of the compound would decompose. "The compound that we predicted was stable on the order of months." For a typical residential solar panel customer, electricity must be either used as it's generated, sold back to the electrical grid, or stored in batteries. Deep-cycle lead batteries or lithium ion batteries are already on the market, but each type presents challenges for use on the grid. All batteries contain chemicals that store and release electrical charge. However, redox flow batteries aren't like the batteries in cars or cell phones. Redox flow batteries instead use two tanks to store energy, separated by a central set of inert electrodes. The tanks hold the solutions containing molecules or charged atoms, called anolytes and catholytes, that store and release charge as the solution "flows" past the electrodes, depending on whether electricity is being provided to the battery or extracted from it. "If you want to increase the capacity, you just put more material in the tanks and it flows through the same cell," says University of Michigan chemist Melanie Sanford. "If you want to increase the rate of charge or discharge, you increase the number of cells." Current redox flow batteries use solutions containing vanadium, a costly material that requires extra safety in handling because of its potential toxicity. Formulating the batteries is a chemical balancing act, since molecules that can store more charge tend to be less stable, losing charge and rapidly decomposing. Sanford began collaborating with Sigman and U electrochemist Shelley Minteer through the U.S. Department of Energy's Joint Center for Energy Storage Research (JCESR), an Energy Innovation Hub dedicated to creating next-generation battery technologies. Sanford's lab developed and tested potential electrolyte molecules, and sought to use predictive technology to help design better battery compounds. Minteer contributed expertise in electrochemistry and Sigman employed a computational method, which uses the structural features of a molecule to predict its properties. A similar approach is widely used in drug development to predict the properties of candidate drugs. The team's work found that a candidate compound decomposed when two molecules interacted with each other. "These molecules can't decompose if they can't come together," Sanford says. "You can tune the molecules to prevent them from coming together." Tuning a key parameter of those molecules, a factor describing the height of a molecular component, essentially placed a bumper or deflector shield around the candidate molecule. The most exciting anolyte reported in the paper is based on the organic molecule pyridinium. It contains no metals and is intended to be dissolved in an organic solvent, further enhancing its stability. Other compounds exhibited longer half-lives, but this anolyte provides the best combination of stability and redox potential, which is directly related to how much energy it can store. Sigman, Minteer and Sanford are now working to identify a catholyte to pair with this and future molecules. Other engineering milestones lay ahead in the development of a new redox flow battery technology, but determining a framework for improving battery components is a key first step. It's a multipart challenge, but you can't do anything if you don't have stable molecules with low redox potentials," Sanford says. "You need to work from there." The team attributes their success thus far to the application of this structure-function relationship toolset, typically used in the pharmaceutical industry, to battery design. "We bring the tools of chemists to a field that was traditionally the purview of engineers," Sanford says. Explore further: Long-lasting flow battery could run for more than a decade with minimum upkeep More information: Physical Organic Approach to Persistent, Cyclable, Low-Potential Electrolytes for Flow Battery Applications, J. Am. Chem. Soc., Article ASAP, pubs.acs.org/doi/abs/10.1021/jacs.7b00147
News Article | August 22, 2016
A new approach to the design of a liquid battery, using a passive, gravity-fed arrangement similar to an old-fashioned hourglass, could offer great advantages due to the system’s low cost and the simplicity of its design and operation, says a team of MIT researchers who have made a demonstration version of the new battery. Liquid flow batteries — in which the positive and negative electrodes are each in liquid form and separated by a membrane — are not a new concept, and some members of this research team unveiled an earlier concept three years ago. The basic technology can use a variety of chemical formulations, including the same chemical compounds found in today’s lithium-ion batteries. In this case, key components are not solid slabs that remain in place for the life of the battery, but rather tiny particles that can be carried along in a liquid slurry. Increasing storage capacity simply requires bigger tanks to hold the slurry. But all previous versions of liquid batteries have relied on complex systems of tanks, valves, and pumps, adding to the cost and providing multiple opportunities for possible leaks and failures. The new version, which substitutes a simple gravity feed for the pump system, eliminates that complexity. The rate of energy production can be adjusted simply by changing the angle of the device, thus speeding up or slowing down the rate of flow. The concept is described in a paper in the journal Energy and Environmental Science, co-authored by Kyocera Professor of Ceramics Yet-Ming Chiang, Pappalardo Professor of Mechanical Engineering Alexander Slocum, School of Engineering Professor of Teaching Innovation Gareth McKinley, and POSCO Professor of Materials Science and Engineering W. Craig Carter, as well as postdoc Xinwei Chen, graduate student Brandon Hopkins, and four others. Chiang describes the new approach as something like a “concept car” — a design that is not expected to go into production as it is but that demonstrates some new ideas that can ultimately lead to a real product. The original concept for flow batteries dates back to the 1970s, but the early versions used materials that had very low energy-density — that is, they had a low capacity for storing energy in proportion to their weight. A major new step in the development of flow batteries came with the introduction of high-energy-density versions a few years ago, including one developed by members of this MIT team, that used the same chemical compounds as conventional lithium-ion batteries. That version had many advantages but shared with other flow batteries the disadvantage of complexity in its plumbing systems. The new version replaces all that plumbing with a simple, gravity-fed system. In principle, it functions like an old hourglass or egg timer, with particles flowing through a narrow opening from one tank to another. The flow can then be reversed by turning the device over. In this case, the overall shape looks more like a rectangular window frame, with a narrow slot at the place where two sashes would meet in the middle. In the proof-of-concept version the team built, only one of the two sides of the battery is composed of flowing liquid, while the other side — a sheet of lithium — is in solid form. The team decided to try out the concept in a simpler form before making their ultimate goal, a version where both sides (the positive and negative electrodes) are liquid and flow side by side through an opening while separated by a membrane. Solid batteries and liquid batteries each have advantages, depending on their specific applications, Chiang says, but “the concept here shows that you don’t need to be confined by these two extremes. This is an example of hybrid devices that fall somewhere in the middle.” The new design should make possible simpler and more compact battery systems, which could be inexpensive and modular, allowing for gradual expansion of grid-connected storage systems to meet growing demand, Chiang says. Such storage systems will be critical for scaling up the use of intermittent power sources such as wind and solar. While a conventional, all-solid battery requires electrical connectors for each of the cells that make up a large battery system, in the flow battery only the small region at the center — the “neck” of the hourglass — requires these contacts, greatly simplifying the mechanical assembly of the system, Chiang says. The components are simple enough that they could be made through injection molding or even 3-D printing, he says. In addition, the basic concept of the flow battery makes it possible to choose independently the two main characteristics of a desired battery system: its power density (how much energy it can deliver at a given moment) and its energy density (how much total energy can be stored in the system). For the new liquid battery, the power density is determined by the size of the “stack,” the contacts where the battery particles flow through, while the energy density is determined by the size of its storage tanks. “In a conventional battery, the power and energy are highly interdependent,” Chiang says. The trickiest part of the design process, he says, was controlling the characteristics of the liquid slurry to control the flow rates. The thick liquids behave a bit like ketchup in a bottle — it’s hard to get it flowing in the first place, but then once it starts, the flow can be too sudden. Getting the flow just right required a long process of fine-tuning both the liquid mixture and the design of the mechanical structures. The rate of flow can be controlled by adjusting the angle of the device, Chiang says, and the team found that at a very shallow angle, close to horizontal, “the device would operate most efficiently, at a very steady but low flow rate.” The basic concept should work with many different chemical compositions for the different parts of the battery, he says, but “we chose to demonstrate it with one particular chemistry, one that we understood from previous work. We’re not proposing this particular chemistry as the end game.” Venkat Viswanathan, an assistant professor of mechanical engineering at Carnegie Mellon University, who was not involved in this work, says: “The authors have been able to build a bridge between the usually disparate fields of fluid mechanics and electrochemistry,” and in so doing developed a promising new approach to battery storage. “Pumping represents a large part of the cost for flow batteries,” he says, “and this new pumpless design could truly inspire a class of passively driven flow batteries.” The work was supported by the Joint Center for Energy Storage Research, funded by the U.S. Department of Energy. The team also included graduate students Ahmed Helal and Frank Fan, and postdocs Kyle Smith and Zheng Li.
News Article | April 4, 2016
Improving batteries' performance is key to the development and success of many much-hyped technologies, from solar and wind energy to electric cars. They need to hold more energy, last longer, be cheaper and safer. Research into how to achieve that has followed several avenues, from using different materials than the existing lithium-ion batteries to changing the internal structure of batteries using nanoparticles—parts so small they are invisible to the naked eye. Nanotechnology can increase the size and surface of batteries electrodes, the rods inside the batteries that absorb the energy. It does so by effectively making the electrodes sponge-like, so that they can absorb more energy during charging and ultimately increasing the energy storage capacity. Prague-based company HE3DA has developed such a technology by using the nanotechnology to move from the current flat electrodes to make them three dimensional. With prototypes undergoing successful testing, it hopes to have the battery on the market at the end of this year. "In the future, this will be the mainstream," said Jan Prochazka, the president. He said it would be targeted at high-intensity industries like automobiles and the energy sector, rather than mobile phones, because that is where it can make the biggest difference through its use of his bigger electrodes. In combination with an internal cooling system the batteries, which are being tested now, should be safe from overheating or exploding, a major concern with existing technologies. Researchers at the University of Michigan and MIT have likewise focused on nanotechnology to improve the existing lithium-ion technology. Others have sought to use different materials. One of the most promising is lithium oxygen, which theoretically could store five to 10 times the energy of a lithium ion battery, but there have been a number of technical problems that made it inefficient. Batteries based on sodium-ion, aluminium-air and aluminium-graphite are also being explored. There's even research on a battery powered by urine. Tesla Motors has been building a $5 billion "gigafactory" to produce lithium-ion batteries for use in its electric cars and potentially to store electricity for homes. It is not using any new technologies, however, just producing very large battery units and marketing them for new purposes. More efficient batteries are crucial if cars are to increase their driving range, which is currently limited compared with what fossil fuels can provide. In renewable energy, powerful batteries are needed to store the energy created by solar panels or wind farms, which gets dispersed when it is sent for long distances. George Crabtree, a Distinguished Fellow at the Argonne National Laboratory in the United States and director of the Joint Center for Energy Storage Research, called the nanotechnology model "a very interesting battery." "There's no doubt that increasing the size of the electrodes that is making them 3D instead of 2D would be a big step forward. That is actually a very right target for advancing lithium ion batteries," he said. "The energy is stored in the electrode, so if you can make the electrodes bigger, say 10 times bigger, then you can have 10 times the amount of energy stored on one charge." Prochazka's battery company is among a group of Czech nanotechnology companies that are gaining international interest. A production facility of HE3DA will be financed by a Chinese investor with an initial investment of almost 1.5 billion koruna ($62 million) that is forecast to double. Explore further: New cathode material creates possibilities for sodium-ion batteries