Materials scientists have sussed out the physical phenomenon underlying the promising electrical properties of a class of materials called superionic crystals. A better understanding of such materials could lead to safer and more efficient rechargeable batteries than the current standard-bearer of lithium ion.
Becoming a popular topic of study only within the past five years, superionic crystals are a cross between a liquid and a solid. While some of their molecular components retain a rigid crystalline structure, others become liquid-like above a certain temperature, and are able to flow through the solid scaffold.
In a new study, scientists from Duke University, Oak Ridge National Laboratory (ORNL) and Argonne National Laboratory (ANL) probed one such superionic crystal containing copper, chromium and selenium (CuCrSe2) with neutrons and X-rays to determine how the material’s copper ions achieve their liquid-like properties. The results appear online on Oct. 8 in the journal Nature Physics.
“When CuCrSe2 is heated above 190 degrees Fahrenheit, its copper ions fly around inside the layers of chromium and selenium about as fast as liquid water molecules move,” said Olivier Delaire, associate professor of mechanical engineering and materials science at Duke and senior author on the study. “And yet, it’s still a solid that you could hold in your hand. We wanted to understand the molecular physics behind this phenomenon.”
Novel materials can considerably improve storage capacity and cycling stability of rechargeable batteries. Among these materials are high-entropy oxides (HEO), whose stability results from a disordered distribution of the elements. With HEO, electrochemical properties can be tailored, as was found by scientists of the team of nanotechnology expert Horst Hahn at Karlsruhe Institute of Technology (KIT). The researchers report their findings in the journal Nature Communications.
Sustainable energy supply requires reliable storage systems. Demand for rechargeable electrochemical energy storage devices for both stationary and mobile applications has increased rapidly in the past years and is expected to continue to grow in the future. Among the most important properties of batteries are their storage capacity and their cycling stability, i.e. the number of possible charging and discharging processes without any loss of capacity. Thanks to its high stability, an entirely new class of materials called high-entropy oxides (HEO) is expected to result in major improvements. Moreover, electrochemical properties of HEO can be customized by varying their compositions. For the first time, scientists of KIT’s Institute of Nanotechnology (INT) and Karlsruhe Nano Micro Facility (KNMF), of the Helmholtz Institute Ulm (HIU) established jointly by KIT and Ulm University, and of the Indian Institute of Technology in Madras have now demonstrated the suitability of HEO as conversion materials for reversible lithium storage. Conversion batteries based on electrochemical material conversion allow for an increase of the stored amount of energy, while battery weight is reduced. The scientists used HEO to produce conversion-based electrodes that survived more than 500 charging cycles without any significant degradation of capacity.
Tesla is at the forefront of industrial battery technology research.
Electric cars are accelerating commercially. General Motors has already sold 12,000 models of its Chevrolet Bolt and Daimler announced in September 2017 that it is to invest $1bn to produce electric cars in the US, with Investment bank ING, meanwhile, predicts that European cars will go fully electric by 2035.
‘Batteries are a global industry worth tens of billions of dollars, but over the next 10 to 20 years it will probably grow to many hundreds of billions per year,’ says Gregory Offer, battery researcher at Imperial College London. ‘There is an opportunity now to invest in an industry, so that when it grows exponentially you can capture value and create economic growth.’
The big opportunity for technology disruption lies in extending battery lifetime, says Offer, whose team at Imperial takes market-ready or prototype battery devices into their lab to model the physics and chemistry going on inside, and then figures out how to improve them.
Lithium batteries, the battery technology of choice, are built from layers, each connected to a current connector and theoretically generating equivalent power, which flows out through the terminals. However, improvements in design of packs can lead to better performance and slower degradation.
Lithium batteries need to be adapted for electric vehicle use.Image: Public Domain Pictures
For many electric vehicles, cooling plates are placed on each side of the battery cell, but the middle layers get hotter and fatigue faster. Offer’s group cooled the cell terminals instead, because they are connected to every layer. ‘You want the battery operating warmish, not too hot and not too cold,’ he says.
Rechargeable zinc metal batteries (RZMBs) could be a viable alternative to lithium ion batteries, which are currently used to power many types of electronic devices, as well as electric vehicles. Recent studies suggest that using optimized electrolytes could lead to RZMBs with highly reversible zinc plating/stripping, achieving Coulombic efficiencies (CEs) close to 100%.
Nonetheless, as teams who set out to design optimized electrolytes for RZMBs used different experimental methods, comparing existing electrolytes and identifying the most efficient ones has so far proved challenging. In a recent paper published in Nature Energy, researchers at the U.S. Army Research Laboratory (ARL) review recent progress in the development of these electrolytes, outlining a set of protocols that could be used to evaluate them and compare their performance. The lead author of this work is Lin Ma, a distinguished postdoctoral fellow at ARL.
“Our research focuses on developing transformative materials that will enable next-generation batteries for both consumer and army energy storage applications,” Mashall A. Schroeder and Kang Xu, two of the researchers who carried out the study, told TechXplore via email. “After joining the Department of Energy’s Joint Center for Energy Storage Research (JCESR 2.0) in the fall of 2018, we took a closer look at multivalent-ion (Mg2+, Ca2+, Zn2+, Al3+, etc.) battery systems, which promise to offer unique benefits compared to Li but at the cost of addressing major fundamental challenges.”
