Pacific Northwest National Laboratory (PNNL) is announcing a new zinc-polyiodide redox flow battery that uses an electrolyte that has more than two times the energy density of the next-best flow battery and may exceed lithium-ion.
The zinc-polyiodide redox energy density approaches that of one of a type of lithium-ion battery that’s used to power portable electronic devices and some small electric vehicles.
Imre Gyuk, energy storage program manager at the Department of Energy’s Office of Electricity Delivery and Energy Reliability said, “With improved energy density and inherent fire safety, flow batteries could provide long-duration energy storage for the tight confines of urban settings, where space is at a premium. This would enhance the resiliency and flexibility of the local electrical grid.”
The high energy density, which reduces its size and cost makes it well suited to store energy in densely populated cities, ideal for large cities where space is at a premium, store renewable energy and support the power grid.
Wei Wang, a materials scientist at DOE’s Pacific Northwest National Laboratory and the study’s corresponding author added, “Another, unexpected bonus of this electrolyte’s high energy density is it could potentially expand the use of flow batteries into mobile applications such as powering trains and cars.”
The press release background points out both flow and lithium-ion batteries were invented in the 1970s, but only the lithium-ion variety took off at that time. Lithium-ion batteries could carry much more energy in a smaller space than flow batteries, making them more versatile. As a result, lithium-ion batteries have been used to power portable electronics for many years. And utilities have begun using them to store the increasing amounts of renewable energy generated at wind farms and solar power facilities.
But the high-energy lithium-ion batteries’ packaging can make them prone to overheating and catching fire. Flow batteries, on the other hand, store their active chemicals separately until power is needed, greatly reducing safety concerns. This feature has prompted researchers and developers to take a serious second look at flow batteries.
Like other flow batteries, the zinc-polyiodide battery produces power by pumping liquid from external tanks into the battery’s stack, a central area where the liquids are mixed. The external tanks in PNNL’s new battery hold aqueous electrolytes, watery solutions with dissolved chemicals that store energy.
When the battery is fully discharged, both tanks hold the same electrolyte solution: a mixture of the positively charged zinc ions, Zn2+, and negatively charged iodide ion, I-. But when the battery is charged, one of the tanks also holds another negative ion, polyiodide, I3-. When power is needed, the two liquids are pumped into the central stack. Inside the stack, zinc ions pass through a selective membrane and change into metallic zinc on the stack’s negative side. This process converts energy that’s chemically stored in the electrolyte into electricity that can power buildings and support the power grid’s operations.
To test the feasibility of their new battery concept, Wei and his PNNL colleagues created a small battery on a lab countertop. They mixed the electrolyte solution, separating a black zinc-polyiodide liquid and a clear zinc-iodide liquid in two glass vials as miniature tanks. Hoses were connected between the vials, a pump and a small stack.
They put the 12-watt-hour capacity battery – comparable to about two iPhone batteries – through a series of tests, including determining how different concentrations of zinc and iodide in the electrolyte affected energy storage. Electrical capacity is measured in watt-hours; electric cars use about 350 watt-hours to drive one mile in the city.
The demonstration battery put out far more energy for its size than today’s most commonly used flow batteries: the zinc-bromide battery and the vanadium battery. PNNL’s zinc-polyiodide battery also had an energy output that was about 70 percent that of a common lithium-ion battery called a lithium iron phosphate battery, which is used in portable electronics and in some small electric vehicles.
Lab tests revealed the demonstration battery discharged 167 watt-hours per liter of electrolyte. In comparison, zinc-bromide flow batteries generate about 70 watt-hours per liter, vanadium flow batteries can create between 15 and 25 watt-hours per liter, and standard lithium iron phosphate batteries could put out about 233 watt-hours per liter. Theoretically, the team calculated their new battery could discharge even more – up to 322 watt-hours per liter – if more chemicals were dissolved in the electrolyte.
PNNL’s zinc-polyiodide battery is also safer because its electrolyte isn’t acidic like most other flow batteries. It’s nearly impossible for the water-based electrolyte to catch fire and it doesn’t require expensive materials that are needed to withstand the corrosive nature of other flow batteries.
Another advantage of PNNL’s new flow battery is that it can operate in extreme climates. The electrolyte allows it to work well in temperatures as cold as -4º Fahrenheit and as warm as +122º. Many batteries have much smaller operating windows and can require heating and cooling systems, which cut into a battery’s net power production.
One problem the team encountered was a build-up of metallic zinc that grew from the central stack’s negative electrode and went through the membrane, making the battery less efficient. Researchers reduced the buildup, called zinc dendrite, by adding alcohol to the electrolyte solution.
Managing zinc dendrite formation will be a key in enabling PNNL’s zinc-polyiodide battery to be used in the real world.
Wei and his colleagues will continue to experiment with different alcohols and other additives and use advanced instruments to characterize how the battery’s materials respond to those additives. The team will also build a larger, 100-watt-hour model of the battery for additional testing.
No information has been given on costs, but one might think if the price is right one might want one in the basement for charging when power is cheap and using power during peak rates.
322 watt-hours per liter with a solved zinc dendrite matter makes the market opportunities a lot bigger than the team is thinking today.
Rongjia Tao proposed in 2006 a more efficient way of improving flow rates by applying an electric field to the oil. The idea is to electrically align particles within the crude oil, which reduces viscosity and turbulence.
The traditional custom is heating pipeline oil over several miles in order to reduce the oil’s thickness (which is also known as viscosity), but this requires a large amount of energy and counter-productively increases turbulence within the flow.
To test the theory Tao collaborated with energy company Save The World Air, Inc. to develop an Applied Oil Technology (AOT) device that links to oil pipelines and produces an electric field along the direction of the oil flow. Recent trials on oil pipelines in Wyoming and China verified that crude oil particles form short chains in an electric field. These chains reduce viscosity in the direction of flow to a minimum. At the same time the viscosity perpendicular to the flow increases, which helps suppress turbulence in the overall flow.
This past summer Tao and his colleagues also successfully tested the AOT device on a section of the Keystone pipeline near Wichita, Kansas.
The study paper was published in the January 2015 edition of Physical Review E and Tao will present the additional Keystone pipeline test results at the American Physical Society March Meeting 2015 in San Antonio (March 2-6).
Tao said, “People were amazed at the energy savings when we first tested this device. They didn’t initially understand the physics. A second test with an independent company was arranged and found the same thing.”
Tests on a section of the Keystone pipeline found that the same flow rate could be achieved with a 75 percent reduction of pump power from 2.8 megawatts to 0.7 megawatts, thanks to the AOT device. The device itself uses 720 watts.
Those are astonishing numbers.
Once aligned, the oil retained its low viscosity and turbulence for more than 11 hours before returning to its original viscosity. But the process is repeatable and Tao and his colleagues envision AOT stations spaced along a pipeline, significantly reducing the energy necessary to transport oil.
The inventiveness and innovation that finds its way to energy supplies is sometimes astonishing. Much of the crude oil worldwide is fairly thick stuff and moving it to where it needs to be is another expense that if saved can save consumers money.
In spite of the presidential administration’s avoidance of responsibility on major pipeline progress, research marches on. One was to wonder where else this technology might apply.
Tao has also shown that the same technique applied with a magnetic field can reduce blood viscosity by 20 to 30 percent. That study paper was published in 2011 in Physical Review E. With clinical trials, Tao says this could represent a future treatment for heart disease.
Lots of liquids get pumped. This might turn out to be quite a big but unseen thing.
The materials chitin and chitosan found in crustacean shells are abundant and significantly cheaper to produce than the expensive metals such as ruthenium, which is similar to platinum, that are currently used in making nanostructured solar-cells.
For now the efficiency of solar cells made with these biomass-derived materials is low but if it can be improved they could be placed in everything from wearable chargers for tablets, phones and smartwatches, to semi-transparent films over window.
Researchers, from QMUL’s School of Engineering and Materials Science, used a process known as hydrothermal carbonization to create the carbon quantum dots from the widely and cheaply available chemicals found in crustacean shells. They then coat standard zinc oxide nanorods with the carbon quantum dots to make the solar cells.
The performance of the devices was dependent on the functional groups found on the carbon quantum dots. The highest efficiency was obtained using a layer-by-layer coating of two different types of carbon quantum dots.
Dr Joe Briscoe, one of the researchers on the project, said: “This could be a great new way to make these versatile, quick and easy to produce solar cells from readily available, sustainable materials. Once we’ve improved their efficiency they could be used anywhere that solar cells are used now, particularly to charge the kinds of devices people carry with them every day.”
Professor Magdalena Titirici, Professor of Sustainable Materials Technology at QMUL, said: “New techniques mean that we can produce exciting new materials from organic by-products that are already easily available. Sustainable materials can be both high-tech and low-cost.”
“We’ve also used biomass, in that case algae, to make the kinds of supercapacitors that can be used to store power in consumer electronics, in defibrillators and for energy recovery in vehicles,” she added.
It is definitely a research effort that brings on a smile. Who would have imagined that chitin and chitosan, problematic chemistries found on ocean going ship’s hulls worldwide, would have a redeeming quality. On the other hand it really its a good idea as these chemistries are very adaptive, tough and strong.
Its not likely though that perovskite is going to be obsolete anytime soon.
February 25, 2015 | Leave a Comment
Researchers at the University of California, Riverside’s Bourns College of Engineering have developed a new silicon based paper-like material for lithium-ion batteries. The development has the potential to boost by several times the specific energy, or amount of energy that can be delivered per unit weight of the battery.
The new paper-like material is composed of sponge-like silicon nanofibers more than 100 times thinner than a human hair. The sponge-like material could be used in batteries for electric vehicles and personal electronics.
The development results have been published in the paper, “Towards Scalable Binderless Electrodes: Carbon Coated Silicon Nanofiber Paper via Mg Reduction of Electrospun SiO2 Nanofibers,” in the journal Nature Scientific Reports.
The nanofibers were produced using a technique known as electrospinning, where 20,000 to 40,000 volts are applied between a rotating drum and a nozzle, which emits a solution composed mainly of tetraethyl orthosilicate, a chemical compound frequently used in the semiconductor industry. The nanofibers are then exposed to magnesium vapor to produce the sponge-like silicon fiber structure.
Conventionally produced lithium-ion battery anodes are made using copper foil coated with a mixture of graphite, a conductive additive, and a polymer binder. But, because the performance of graphite has been nearly tapped out, researchers are experimenting with other materials, such as silicon, which has a specific capacity, or electrical charge per unit weight of the battery, at nearly 10 times higher than graphite.
The problem with silicon as a battery component is that is suffers from significant volume expansion, which can quickly degrade the battery. The silicon nanofiber structure created in the lab circumvents this issue and allows the battery to be cycled hundreds of times without significant degradation.
Graduate student Zach Favors offered, “Eliminating the need for metal current collectors and inactive polymer binders while switching to an energy dense material such as silicon will significantly boost the range capabilities of electric vehicles.”
The technology also solves a problem that has plagued free-standing, or binderless, electrodes for years: scalability. Free-standing materials grown using chemical vapor deposition, such as carbon nanotubes or silicon nanowires, can only be produced in very small quantities (micrograms). However, Favors was able to produce several grams of silicon nanofibers at a time even at the lab scale.
The UC Riverside Office of Technology Commercialization has already filed for patents on the inventions reported in the research paper. The research is being supported by Temiz Energy Technologies.
The researchers’ plan future work involving implementing the silicon nanofibers into a pouch cell format lithium-ion battery, which is a larger scale battery format that can be used in EVs and portable electronics.
The full team includes Mihri Ozkan, a professor of electrical and computer engineering, Cengiz S. Ozkan, a professor of mechanical engineering, and six of their graduate students: Favors, Hamed Hosseini Bay, Zafer Mutlu, Kazi Ahmed, Robert Ionescu and Rachel Ye.
The press release has lit up some bloggers that are making big claims. The team is offering a capacity of 802 mAh g−1 after 659 cycles with a Coulombic efficiency of 99.9%, which outperforms the conventionally used slurry-prepared graphite anodes by over two times on an active material basis.
Bloggers astonishment and back of the envelope multipliers aside, 802 mAh g−1 after 659 cycles is very impressive, indeed.
The Finns are focused on the challenge that comes with the increased use of renewable energy – how to store electric energy. Platinum has traditionally been used as the electrocatalyst in electrolysers that store electric energy as chemical compounds. But platinum is a rare and expensive metal.
Senior scientist Tanja Kallio said, “We developed an electrocatalyst that is made of iron and carbon. Now the same efficiency that was achieved with platinum can be obtained with a less expensive material. Nearly 40 percent of the material costs of energy storage with an electrolyser come from the electrocatalyst.”
The manufacturing process has been developed in cooperation with a research group led by Professor Esko Kauppinen from Aalto University School of Science. The carbon nanotube the group developed conducts electricity extremely well and serves as the support, while the now added only single carbon layer covered iron functions as the catalyst. The manufacturing process has a single stage.
Iron nanoparticles are carbon-encapsulated into a single-shell that are decorated on single-walled carbon nanotubes. The constructed catalysts is introduced as a novel highly active and durable non-noble-metal catalyst for an efficient hydrogen evolution reaction.
The new catalyst exhibits catalytic properties superior to previously studied nonprecious materials and its comparable to those of platinum.
The construction is synthesized by a novel fast and low-cost aerosol chemical vapor deposition method in a one-step process. The single-shell carbon-encapsulated iron nanoparticle layer does not prevent desired access of the reactants to the vicinity of the iron nanoparticles but it does protect the active metallic core from oxidation.
Kallio noted, “The method has been altered to make the electro catalyst very active. By active, we refer to the small amount of energy needed to store electric energy as hydrogen. This reduces the losses caused by chemical storage and the process is economically viable.”
Platinum cost is a major roadblock to several technologies mostly involving catalyzing hydrogen. The Finns look to have come up with a very low cost solution if the building of the catalyst can scale up to industrial production. It looks like the iron side can scale, but there is still some progress needed for producing the carbon nanotubes.
One of these days a platinum replacement is going to break out into the market and really change the potential of fuel cells and hydrogen production.