MIT’s new approach to the design of a liquid battery uses a passive, gravity-fed arrangement similar to an old-fashioned hourglass. The concept could offer great advantages due to the system’s low cost and the simplicity of its design and operation. The MIT team of researchers has 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 the new flow concept, 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.
Until creative genius kicked in.
The MIT team’s 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, with two graduate students Ahmed Helal and Frank Fan, and postdocs Kyle Smith and Zheng Li..
Chiang described 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 said, 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 said. 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 said.
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 energy density (how much energy it can deliver at a given moment) and its power density (how much total power 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 said.
The trickiest part of the design process, he said, 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 said, 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.”
This is a grand example of innovation and creativity. Congratulations are in order with an applause. Great work here. Its easy to see that others will likely seize on this and innovate more. The potential is huge. In a little while someone will think to move the pivot axis 90º, so as to tilt more than flip, to reduce floor space. There are sure to be lots of ideas on how to increase practicality across environments, demands and resources. Your humble writer thinks MIT might have just lit off the flow battery industry.
Sweden’s KTH The Royal Institute of Technology researchers are using thermoelectric generation to save vehicles hundreds of liters of fuel and reduce their carbon emissions by as much as 1,000 tons per year.
Working with automotive manufacturer Scania, the researchers from Sweden’s KTH Royal Institute of Technology have been testing semi trucks equipped with a system that converts exhaust heat into power – through a process called thermoelectric generation (TEG). The voltage produced by the system can help power the truck and reduce the strain on the engine, explains researcher Arash Risseh.
The TEG system operates on the principle of the thermoelectric effect, by which differences in temperature heat is converted into voltage – a phenomenon discovered in 1821 by German physicist Thomas Johann Seebeck, and often referred to as the “Seebeck effect.”
Researcher Arash Risseh explained, “Most fuel energy is not used to drive a truck forward. Some 30 percent of this unused energy is lost as heat from the exhaust pipes.”
A truck that generates 440kW would see about 132kW of energy disappear in the form of heat coming out of the exhaust pipes, he said. “That’s enough to power a typical passenger vehicle.”
Capturing this excess energy takes a load off the truck’s generator, and in turn, the engine, Risseh said. That means better fuel efficiency and lower emissions.
The Seebeck effect requires a temperature differential – cool on one end of the circuit and hot on the other, which means a truck must rely on a coolant in order to stimulate the voltage. Cooling the circuit is easier with natural alternatives, such as seawater for a ship’s engines. Ships also make good candidates for TEG because their buoyancy offsets the constraints of weight and volume that road vehicles face, Risseh said.
TEG is also regarded as a potential energy saver in data centers that are located in cold climates. Near the Arctic circle in northern Sweden, a data center that uses 1 Terawatt hour per year could potentially recover 1 Gigawatt per year – a savings of some €100,000, he said.
Whatever Risseh is up to working with Scania, the partnership points up some serious commercial attention. Over in Europe, where fuel taxes are from an American point of view outrageously high, there is more economic room for the capital costs of energy recovery. But a foothold into a market for capturing the energy going out the exhaust pipe would be a step into going to scale, a move that would start the drive to lower costs.
Congratulations to the Swedish team. TEG has gotten a wee bit off the ground.
Chemists from Hiroshima University have developed organic radical batteries that are re-chargeable and continue to function at below-freezing temperatures. The Hiroshima team uses a new synthesis method to make an organic battery. The team has a step into one of the hardest problems of batteries – how to function well when cooled down.
Transporting power sources in the coldest places may be easier with a new re-chargeable, non-metallic battery from Japan. This “eco battery” could provide portable sources of power in environments like refrigerated factories or winter environments.
The specific model prototyped by the Hiroshima University team has greater voltage than previously reported styles from other research groups around the world. The method used to create this battery is an improvement on a report from the same Hiroshima University laboratory earlier in 2016.
Many of today’s electrical devices use a lithium-ion battery. Lithium-ion batteries are safer than standard lithium metal batteries, but both styles rely on metal, a finite resource that is in decreasing supply. The same problem of decreasing supply exists for copper and cobalt batteries, like the traditional AA size batteries in TV remote controls.
Organic radical rechargeable batteries have the potential to be cheaper, safer, and longer-lasting than current metal-based batteries, earning them the “eco battery” title. This style of battery can re-charge faster than meal-based batteries, the difference of one minute instead of one hour, because they carry energy chemically rather than physically.
Professor Yohsuke Yamamoto, Ph.D. said, “The chemicals in the battery make it heavy and the synthesis process makes it expensive, so it won’t replace other styles of batteries in the foreseeable future. But our battery could supplement traditional batteries in conditions where traditional Lithium-ion batteries can’t work reliably, particularly in cold locations.”
The team expects that eventually, organic radical batteries could potentially be made in flexible, transparent forms for use in wearable electronics.
The new organic radical synthesis method from the team of researchers at Hiroshima University is modeled on a process first reported in 1985 by an American research group. Yamamoto was a member of that lab in the late 1980s and improved the process in recent years as part of work on unstable organic compounds.
“The original method we used took such a long time and relied on harmful chemicals. Now, over 20 years later, we can synthesize the compound much more quickly and safely. Fundamental research on unstable compounds creates a more detailed understanding of how chemicals bond. Applications like this new battery are the results of research that was never originally about any specific end product,” Yamamoto said.
Yamamoto and collaborators are currently adapting the synthesis process further to make the battery lighter weight and ensure it retains its energy output after numerous re-charge cycles.
This team’s news is very encouraging. For all the excitement of battery powered things, particularly automobiles, little thought is given to the huge drop in battery performance as temperatures go down. While a lot of human population lives in temperate zones with little cold or freezing weather, a large and highly developed segment lives where the seasons change and cold is a common thing for up to or more than half of the year.
Batteries that hold and make their energy readily available well below say 0º F (-18º C) would change the market immensely. The hype of electric storage for transport might fool most all of the press, but it isn’t fooling real buyers looking to spend big money or go into debt. Plug in electric vehicles have to run 365 days a year.
A great battery at room temperature that’s half dead at freezing hasn’t much value for a large part of the market.
Australian engineers at the University of New South Wales (UNSW) have edged closer to the theoretical limits of sunlight to electricity conversion by photovoltaic solar cells with a device that sets a new world efficiency record.
The new solar cell configuration developed by the engineers has pushed sunlight to electricity conversion efficiency up to 34.5% – establishing a new world record for unfocused sunlight and nudging closer to the theoretical limits for such a device.
The record was set by Dr. Mark Keevers and Professor Martin Green, Senior Research Fellow and Director, respectively, of UNSW’s Australian Centre for Advanced Photovoltaics, using a 28-cm2 four-junction mini-module – embedded in a prism – that extracts the maximum energy from sunlight. It does this by splitting the incoming rays into four bands, using a hybrid four-junction receiver to extract even more electricity from each beam of sunlight.
The new UNSW result, confirmed by the US National Renewable Energy Laboratory, is almost 44% better than the previous record – made by Alta Devices of the USA, which reached 24% efficiency, but over a larger surface area of 800 cm2.
Keevers said, “This encouraging result shows that there are still advances to come in photovoltaics research to make solar cells even more efficient. Extracting more energy from every beam of sunlight is critical to reducing the cost of electricity generated by solar cells as it lowers the investment needed, and delivering payback faster.”
The result was obtained by the same UNSW team that set a world record in 2014, achieving an electricity conversion rate of over 40% by using mirrors to concentrate the light – a technique known as CPV (concentrator photovoltaics) – and then similarly splitting out various wavelengths. The new result, however, was achieved using normal sunlight with no concentrators.
Green, a pioneer who has led the field for much of his 40 years at UNSW, said, “What’s remarkable is that this level of efficiency had not been expected for many years. A recent study by Germany’s Agora Energiewende think tank set an aggressive target of 35% efficiency by 2050 for a module that uses unconcentrated sunlight, such as the standard ones on family homes.”
“So things are moving faster in solar cell efficiency than many experts expected, and that’s good news for solar energy,” he added. “But we must maintain the pace of photovoltaic research in Australia to ensure that we not only build on such tremendous results, but continue to bring benefits back to Australia.”
Australia’s research in photovoltaics has already generated flow-on benefits of more than $8 billion to the country, Green said. Gains in efficiency alone, made possible by UNSW’s PERC cells, are forecast to save $750 million in domestic electricity generation in the next decade. PERC cells were invented at UNSW and are now becoming the commercial standard globally.
The record-setting UNSW mini-module combines a silicon cell on one face of a glass prism, with a triple-junction solar cell on the other.
The triple-junction cell targets discrete bands of the incoming sunlight, using a combination of three layers: indium-gallium-phosphide; indium-gallium-arsenide; and germanium. As sunlight passes through each layer, energy is extracted by each junction at its most efficient wavelength, while the unused part of the light passes through to the next layer, and so on.
Some of the infrared band of incoming sunlight, unused by the triple-junction cell, is filtered out and bounced onto the silicon cell, thereby extracting just about all of the energy from each beam of sunlight hitting the mini-module.
The 34.5% result with the 28-cm2 mini-module is already a world record, but scaling it up to a larger 800 cm2 – thereby leaping beyond Alta Devices’ 24% – is well within reach. “There’ll be some marginal loss from interconnection in the scale-up, but we are so far ahead that it’s entirely feasible,” Keevers said. The theoretical limit for such a four-junction device is thought to be 53%, which puts the UNSW result two-thirds of the way there.
Multi-junction solar cells of this type are unlikely to find their way onto the rooftops of homes and offices soon, as they require more effort to manufacture and therefore cost more than standard crystalline silicon cells with a single junction. But the UNSW team is working on new techniques to reduce the manufacturing complexity, and create cheaper multi-junction cells.
But the spectrum-splitting approach is perfect for solar towers, like those being developed by Australia’s RayGen Resources, which use mirrors to concentrate sunlight which is then converted directly into electricity.
The research is supported by $1.4 million grant funding from the Australian Renewable Energy Agency (ARENA), whose CEO Ivor Frischknecht said the achievement demonstrated the importance of supporting early stage renewable energy technologies.
“Australia already punches above its weight in solar R&D and is recognized as a world leader in solar innovation,” Frischknecht said. “These early stage foundations are increasingly making it possible for Australia to return solar dividends here at home and in export markets – and there’s no reason to believe the same results can’t be achieved with this record-breaking technology.”
He noted that the UNSW team is working with another ARENA-supported company, RayGen, to explore how the advanced receiver could be rolled out at concentrated solar PV power plants.
“With the right support, Australia’s world leading R&D is well placed to translate into efficiency wins for households through the ongoing roll out of rooftop solar and utility-scale solar projects such as those being advanced by ARENA through its current $100 million large-scale solar round, he added. “Over the longer term, these innovative technologies are also likely to take up less space on our rooftops and in our fields.”
Other research partners working with UNSW include Trina Solar, a PV module manufacturer and the U.S. National Renewable Energy Laboratory.
The Aussies deserve a lot of credit for their solar achievements. Its also a top of the line press release. A little chest pounding is appropriate. Rah, rah Australia!
Lawrence Berkeley National Laboratory (LBNL) researchers have engineered a strain of bacteria that enables a ‘one-pot’ method for producing advanced biofuels from a slurry of pre-treated plant material. LBNL’s achievement is a critical step in making biofuels a viable competitor to fossil fuels by streamlining the production process.
The achievement is a critical step in making biofuels a viable competitor to fossil fuels because it helps streamline the production process. The study has been published in the journal Green Chemistry.
The Escherichia coli (E. coli) is able to tolerate the liquid salt used to break apart plant biomass into sugary polymers. Because the salt solvent, known as ionic liquids, interferes with later stages in biofuels production, it needs to be removed before proceeding, a process that takes time, equipment, capital, and adds expense. Developing ionic-liquid-tolerant bacteria eliminates the need to wash away the residual ionic liquid.
Study principal investigator Aindrila Mukhopadhyay, vice president of the Fuels Synthesis Division at the Joint BioEnergy Institute (JBEI), a DOE Bioenergy Research Center at Berkeley Lab explains, “Being able to put everything together at one point, walk away, come back, and then get your fuel, is a necessary step in moving forward with a biofuel economy. The E. coli we’ve developed gets us closer to that goal. It is like a chassis that we build other things onto, like the chassis of a car. It can be used to integrate multiple recent technologies to convert a renewable carbon source like switchgrass to an advanced jet fuel.”
The basic steps of biofuel production start with deconstructing, or taking apart, the cellulose, hemicellulose and lignin that are bound together in the complex plant structure. Enzymes are then added to release the sugars from that gooey mixture of cellulose and hemicellulose, a step called saccharification. Bacteria can then take that sugar and churn out the desired biofuel. The multiple steps are all done in separate pots.
Researchers at JBEI pioneered the use of ionic liquids, salts that are liquid at room temperature, to tackle the deconstruction of plant material because of the efficiency with which the solvent works. But what makes ionic liquids great for deconstruction also makes it harmful for the downstream enzymes and bacteria used in biofuel production.
Previous studies have found ways to address these challenges. In 2012, JBEI researchers, including Blake Simmons, a co-author on this new study, had discovered a suite of saccharification enzymes that were tolerant to ionic liquids.
Marijke Frederix, this recent study’s first author and a postdoctoral researcher in Mukhopadhyay’s lab, established that an amino acid mutation in the gene rcdA, which helps regulate various genes, leads to an E. coli strain that is highly tolerant to ionic liquids, providing an important piece to the puzzle. They used this strain as the foundation to build on earlier work – including the ionic-liquid-tolerant enzymes – and take the steps further to the one-pot biofuel finishing line.
Then they proceeded to test the E. coli strain using ionic-liquid pretreated switchgrass provided by the DOE’s Advanced Biofuels and Bioproducts Process Demonstration Unit (ABPDU), a biofuels facility at Berkeley Lab launched in 2011 to accelerate the commercialization of biofuels.
Frederix tells the story, “Armed with the rcdA variant, we were able to engineer a strain of E. coli that could not only tolerate ionic liquid, but that could also produce ionic-liquid-tolerant enzymes that chew up the cellulose, make sugars, eat it and make biofuels. E. coli remains the workhorse microbial host in synthetic biology, and in our study, using the ionic-liquid-tolerant E. coli strain, we can combine many earlier discoveries to create an advanced biofuel in a single pot.”
While ethanol may be one of the more common products to emerge from this process, researchers have looked to more advanced biofuels that can pack more energy punch. In this case, they used production pathways also developed at JBEI previously, and produced d-limonene, a precursor to jet fuel.
Mukhopadhyay points out what’s coming with, “Ultimately, we at JBEI hope to develop processes that are robust and simple where one can directly convert any renewable plant material to a final fuel in a single pot. This study puts us one step closer to this moonshot.”
Mukhopadhyay has a pretty good metaphor there. The biofuels industry is still non competitive with fossil fuels and will always be subject to the ups and downs or markets both for petroleum products and biofuel raw materials. Every step on their “moonshot” closes the gap. Lots of steps to go.