Anyone who owns an electronic device knows that lithium ion batteries could work better and last longer. Now, scientists examining battery materials on the nano-scale reveal how nickel forms a physical barrier that impedes the shuttling of lithium ions in the electrode, reducing how fast the materials charge and discharge. Published last week in Nano Letters, the research also suggests a way to improve the materials.
The researchers, led by the Department of Energy's Pacific Northwest National Laboratory's Chongmin Wang, created high-resolution 3D images of electrode materials made from lithium-nickel-manganese oxide layered nanoparticles, mapping the individual elements. These maps showed that nickel formed clumps at certain spots in the nanoparticles. A higher magnification view showed the nickel blocking the channels through which lithium ions normally travel when batteries are charged and discharged.
"We were surprised to see the nickel selectively segregate like it did. When the moving lithium ions hit the segregated nickel rich layer, they essentially encounter a barrier that appears to slow them down," said Wang, a materials scientist based at EMSL, the Environmental Molecular Sciences Laboratory, a DOE user facility on PNNL's campus. "The block forms in the manufacturing process, and we'd like to find a way to prevent it."
Lithium ions are positively charged atoms that move between negative and positive electrodes when a battery is being charged or is in use. They essentially catch or release the negatively charged electrons, whose movement through a device such as a laptop forms the electric current.
In lithium-manganese oxide electrodes, the manganese and oxygen atoms form rows like a field of cornstalks. In the channels between the stalks, lithium ions zip towards the electrodes on either end, the direction depending on whether the battery is being used or being charged.
Researchers have known for a long time that adding nickel improves how much energy the electrode can hold, battery qualities known as capacity and voltage. But scientists haven't understood why the capacity falls after repeated usage -- a situation consumers experience when a dying battery holds its charge for less and less time.
To find out, Wang, materials scientist Meng Gu and their collaborators used electron microscopy at EMSL and the National Center for Electron Microscopy at Lawrence Berkeley National Laboratory to view how the different atoms are arranged in the electrode materials produced by Argonne National Laboratory researchers. The electrodes were based on nanoparticles made with lithium, nickel, and manganese oxides.
First, the team took high-resolution images that clearly showed rows of atoms separated by channels filled with lithium ions. On the surface, they saw the accumulation of nickel at the ends of the rows, essentially blocking lithium from moving in and out.
To find out how the surface layer is distributed on and within the whole nanoparticle, the team used a technique called three-dimensional composition mapping. Using a nanoparticle about 200 nanometers in size, they took 50 images of the individual elements as they tilted the nanoparticle at various angles. The team reconstructed a three-dimensional map from the individual elemental maps, revealing spots of nickel on a background of lithium-manganese oxide.
The three-dimensional distribution of manganese, oxygen and lithium atoms along the surface and within the particle was relatively even. The nickel, however, parked itself in small areas on the surface. Internally, the nickel clumped on the edges of smaller regions called grains.
To explore why nickel aggregates on certain surfaces, the team calculated how easily nickel and lithium traveled through the channels. Nickel moved more easily up and down the channels than lithium. While nickel normally resides within the manganese oxide cornrows, sometimes it slips out into the channels. And when it does, this analysis showed that it flows much easier through the channels to the end of the field, where it accumulates and forms a block.
The researchers used a variety of methods to make the nanoparticles. Wang said that the longer the nanoparticles stayed at high temperature during fabrication, the more nickel segregated and the poorer the particles performed in charging and discharging tests. They plan on doing more closely controlled experiments to determine if a particular manufacturing method produces a better electrode.
This work was supported by PNNL's Chemical Imaging Initiative.
Reference: Meng Gu, Ilias Belharouak, Arda Genc, Zhiguo Wang, Dapeng Wang, Khalil Amine, Fei Gao, Guangwen Zhou, Suntharampillai Thevuthasan, Donald R. Baer, Ji-Guang Zhang, Nigel D. Browning, Jun Liu, and Chongmin Wang. Conflicting Roles of Ni in Controlling Cathode Performance in Li-ion Batteries, NanoLetters Sept. 17, 2012, doi: dx.doi.org/10.1021/nl302249v. (http://pubs.acs.org/doi/abs/10.1021/nl302249v)
EMSL, the Environmental Molecular Sciences Laboratory, is a national scientific user facility sponsored by the Department of Energy's Office of Science. Located at Pacific Northwest National Laboratory in Richland, Wash., EMSL offers an open, collaborative environment for scientific discovery to researchers around the world. Its integrated computational and experimental resources enable researchers to realize important scientific insights and create new technologies. Follow EMSL on Facebook, LinkedIn and Twitter.
Interdisciplinary teams at Pacific Northwest National Laboratory address many of America's most pressing issues in energy, the environment and national security through advances in basic and applied science. PNNL employs 4,700 staff, has an annual budget of nearly $1.1 billion, and has been managed for the U.S. Department of Energy by Ohio-based Battelle since the laboratory's inception in 1965. For more, visit the PNNL's News Center, or follow PNNL on Facebook, LinkedIn and Twitter.
Mary Beckman | EurekAlert!
Silicon as a new storage material for the batteries of the future
24.04.2018 | Christian-Albrechts-Universität zu Kiel
Improved stability of plastic light-emitting diodes
19.04.2018 | Max-Planck-Institut für Polymerforschung
At the Hannover Messe 2018, the Bundesanstalt für Materialforschung und-prüfung (BAM) will show how, in the future, astronauts could produce their own tools or spare parts in zero gravity using 3D printing. This will reduce, weight and transport costs for space missions. Visitors can experience the innovative additive manufacturing process live at the fair.
Powder-based additive manufacturing in zero gravity is the name of the project in which a component is produced by applying metallic powder layers and then...
Physicists at the Laboratory for Attosecond Physics, which is jointly run by Ludwig-Maximilians-Universität and the Max Planck Institute of Quantum Optics, have developed a high-power laser system that generates ultrashort pulses of light covering a large share of the mid-infrared spectrum. The researchers envisage a wide range of applications for the technology – in the early diagnosis of cancer, for instance.
Molecules are the building blocks of life. Like all other organisms, we are made of them. They control our biorhythm, and they can also reflect our state of...
University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.
Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.
Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.
Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...
Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.
The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...
13.04.2018 | Event News
12.04.2018 | Event News
09.04.2018 | Event News
24.04.2018 | Information Technology
24.04.2018 | Earth Sciences
24.04.2018 | Life Sciences