Advance could lead to improved battery safety, performance and cost
A team of researchers at the University of Maryland Energy Research Center and A. James Clark School of Engineering have announced a transformative development in the race to produce batteries that are at once safe, powerful, and affordable.
The researchers are developing game-changing solid-state battery technology, and have made a key advance by inserting a layer of ultra-thin aluminum oxide between lithium electrodes and a solid non-flammable ceramic electrolyte known as garnet. Prior to this advance, there had been little success in developing high-performance, garnet-based solid-state batteries, because the high impedance, more commonly called resistance, between the garnet electrolyte and electrode materials limited the flow of energy or current, dramatically decreasing the battery’s ability to charge and discharge.
The University of Maryland team has solved the problem of high impedance between the garnet electrolyte and electrode materials with the layer of ultrathin aluminum oxide, which decreases the impedance 300 fold. This virtually eliminates the barrier to electricity flow within the battery, allowing for efficient charging and discharging of the stored energy.
A new paper describing the research was published online December 19 in the peer-reviewed journal Nature Materials.
“This is a revolutionary advancement in the field of solid-state batteries—particularly in light of recent battery fires, from Boeing 787s to hoverboards to Samsung smartphones,” said Liangbing Hu, associate professor of materials science and engineering and one of the corresponding authors of the paper. “Our garnet-based solid-state battery is a triple threat, solving the typical problems that trouble existing lithium-ion batteries: safety, performance, and cost.”
Lithium-ion batteries typically contain a liquid organic electrolyte that can catch fire, as shown by numerous consumer electronic battery fires and even the temporary grounding of the Boeing 787 fleet for a series of battery fires. This fire risk is eliminated by the UMD team’s use of the non-flammable garnet-based solid-state electrolyte.
“The work by [the University of Maryland research team] effectively solves the lithium metal–solid electrolyte interface resistance problem, which has been a major barrier to the development of a robust solid-state battery technology,” said Bruce Dunn, UCLA materials science and engineering professor. Dunn, a leading expert in energy storage materials, was not involved in this research.
In addition, the high stability of these garnet electrolytes enable the team to use metallic lithium anodes, which contain the greatest possible theoretical energy density and are considered the ‘holy grail’ of batteries. Combined with high-capacity sulfur cathodes, this all solid-state battery technology offers a potentially unmatched energy density that far outperforms any lithium-ion battery currently on the market.
“This technology is on the verge of changing the landscape of energy storage. The broad deployment of batteries is critical to increase the flexibility of how and when energy is used, and these solid-state batteries will both increase the safety and decrease size, weight, and cost of batteries,” said Eric Wachsman, professor and director of the University of Maryland Energy Research Center and the other corresponding author of the paper.
“This [finding] is of considerable interest to those working to replace the flammable liquid electrolyte of the lithium-ion rechargeable battery with a solid electrolyte from which a lithium anode can be plated dendrite-free when a cell is being charged,” said acclaimed lithium-ion battery pioneer John B. Goodenough, Virginia H. Cockrell Centennial Chair in Engineering at the University of Texas, who was unaffiliated with the study. Read Goodenough’s full commentary on the Maryland team’s battery advance here.
Researcher at TU Graz demonstrates in Nature Materials that it is possible to combine the high-energy density of batteries with the high-power output of super capacitors in a single system – thanks to liquid energy storage materials.
Batteries and super capacitors are electrochemical energy storage media, but they are as different as night and day. Both are capable of energy storage and targeted energy release – and yet there are major differences between the two. Batteries store very large amounts of energy that is released slowly but constantly. By contrast, super capacitors can only store small amounts of energy, but they release this energy much faster and more powerfully with large short-term peak currents.
Stefan Freunberger at TU Graz together with a group of researchers from Université de Montpellier in Southern France had a sudden flash of insight. Why not exploit the benefits of batteries and super capacitors simultaneously and combine them in some kind of energy hybrid, they asked themselves. In the current issue of renowned scientific journal Nature Materials the group introduces its approach, describing a liquid energy storage material for the first time in a European Research Council (ERC) sponsored study. While the energy density of this material is comparable to that of a battery, its power output equals that of a super capacitor.
Ions with an urge to move
“Batteries release energy so slowly and take so long to charge because their energy storage materials are solid. This make it difficult for the ions to move. But as the ions in a super capacitor move in a liquid, they are much more mobile than in a solid body,” explains Stefan Freunberger from the Institute of Chemistry and Technology of Materials at TU Graz. The novel redox active ionic liquid developed by Freunberger in co-operation with the French colleagues consists of an organic salt that is liquid at a temperature of just below 30 °C – only slightly above room temperature. Similar to a solid storage medium this liquid can store many ions, but allows them to be much more mobile.
The sudden flash of insight of Freunberger and colleagues culminated in a first approach to create an integrated energy supply system that offers a constant energy supply with high-power output. In some cases we are still faced with an either/or decision. Automatic doors, for example in trams or trains, are typical candidates for super capacitors. Energy is only needed for a very short time but when it is, a high-power output is of the essence. In other cases batteries are clearly the first choice. “But our principle of an energy hybrid can offer enormous advantages, for example when applied in electric vehicles. So far, electric vehicles often carry a combination of different battery types or battery systems together with super capacitors. If we had a single system that combines the benefits of both energy storage types, we could save considerable space and resources,” remarks Freunberger.
Learn more: Energy hybrid: Battery meets supercapacitor
Environmentally-friendly battery is long-lasting and high voltage
A team of University of Toronto chemists has created a battery that stores energy in a biologically-derived unit, paving the way for cheaper consumer electronics that are easier on the environment.
The battery is similar to many commercially-available high-energy lithium-ion batteries with one important difference. It uses flavin from vitamin B2 as the cathode: the part that stores the electricity that is released when connected to a device.
“We’ve been looking to nature for a while to find complex molecules for use in a number of consumer electronics applications,” says Dwight Seferos, an associate professor in U of T’s department of chemistry and Canada Research Chair in Polymer Nanotechnology.
“When you take something made by nature that is already complex, you end up spending less time making new material,” says Seferos.
Background battery basics
To understand the discovery, it’s important to know that modern batteries contain three basic parts:
- a positive terminal – the metal part that touches devices to power them – connected to a cathode inside the battery casing
- a negative terminal connected to an anode inside the battery casing
- an electrolyte solution, in which ions can travel between the cathode and anode electrodes
When a battery is connected to a phone, iPod, camera or other device that requires power, electrons flow from the anode – the negatively charged electrode of the device supplying current – out to the device, then into the cathode and ions migrate through the electrolyte solution to balance the charge. When connected to a charger, this process happens in reverse.
The reaction in the anode creates electrons and the reaction in the cathode absorbs them when discharging. The net product is electricity. The battery will continue to produce electricity until one or both of the electrodes run out of the substance necessary for the reactions to occur.
Organic chemistry is kind of like Lego
While bio-derived battery parts have been created previously, this is the first one that uses bio-derived polymers – long-chain molecules – for one of the electrodes, essentially allowing battery energy to be stored in a vitamin-created plastic, instead of costlier, harder to process, and more environmentally-harmful metals such as cobalt.
“Getting the right material evolved over time and definitely took some test reactions,” says paper co-author and doctoral student Tyler Schon. “In a lot of ways, it looked like this could have failed. It definitely took a lot of perseverance.”
Schon, Seferos and colleagues happened upon the material while testing a variety of long-chain polymers – specifically pendant group polymers: the molecules attached to a ‘backbone’ chain of a long molecule.
“Organic chemistry is kind of like Lego,” he says. “You put things together in a certain order, but some things that look like they’ll fit together on paper don’t in reality. We tried a few approaches and the fifth one worked,” says Seferos.
Building a better power pack
The team created the material from vitamin B2 that originates in genetically-modified fungi using a semi-synthetic process to prepare the polymer by linking two flavin units to a long-chain molecule backbone.
This allows for a green battery with high capacity and high voltage – something increasingly important as the ‘Internet of Things’ continues to link us together more and more through our battery-powered portable devices.
“It’s a pretty safe, natural compound,” Seferos adds. “If you wanted to, you could actually eat the source material it comes from.”
B2’s ability to be reduced and oxidized makes its well-suited for a lithium ion battery.
“B2 can accept up to two electrons at a time,” says Seferos. “This makes it easy to take multiple charges and have a high capacity compared to a lot of other available molecules.”
A step to greener electronics
“It’s been a lot of trial-and-error,” says Schon. “Now we’re looking to design new variants that can be recharged again and again.”
While the current prototype is on the scale of a hearing aid battery, the team hopes their breakthrough could lay the groundwork for powerful, thin, flexible, and even transparent metal-free batteries that could support the next wave of consumer electronics.
The team’s paper outlining the discovery appeared in the July issue of Advanced Functional Materials.
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 extreme winter environments.
Chemists from Hiroshima University developed a new synthesis method for organic radical batteries that are re-chargeable and continue to function at below-freezing temperatures. 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.
Most 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 batteries in TV remote controls.
Organic radical re-chargeable 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.