Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Tracking Heat-Driven Decay in Leading Electric Vehicle Batteries

31.10.2014

Rechargeable electric vehicles are one of the greatest tools against rising pollution and carbon emissions, and their widespread adoption hinges on battery performance.

Scientists specializing in nanotechnology continue to hunt for the perfect molecular recipe for a battery that drives down price, increases durability, and offers more miles on every charge.


Brookhaven National Laboratory

Diagram showing the NCA structural transformation from discrete layers in the pristine sample to disordered spinel and rock-salt configurations as the charge increases—largely a result of oxygen being released from the material.

One particular family of lithium-ion batteries composed of nickel, cobalt, and aluminum (NCA) offers high enough energy density—a measure of the stored electricity in the battery—that it works well in large-scale and long-range vehicles, including electric cars and commercial aircraft. There is, however, a significant catch: These batteries degrade with each cycle of charge and discharge.

As the battery cycles, lithium ions shuttle back and forth between cathode and anode and leave behind detectable tracks of nanoscale damage. Crucially, the high heat of vehicle environments can intensify these telltale degradation tracks and even cause complete battery failure.

"The relationship between structural changes and the catastrophic thermal runaway impacts both safety and performance," said physicist Xiao-Qing Yang of the U.S. Department of Energy’s Brookhaven National Laboratory. "The in-depth understanding of that relationship will help us develop new materials and advance this NCA material to prevent that dangerous degradation."

To get a holistic portrait of the NCA battery's electrochemical reactions, researchers in Brookhaven Lab's Chemistry Department and Center for Functional Nanomaterials (CFN) completed a series of three studies, each delving deeper into the molecular changes. The work spanned x-ray-based exploration of average material morphologies to surprising atomic-scale asymmetries revealed by electron microscopy.

“After each cycle of charge/discharge—or even incremental steps in either direction—we saw the atomic structure transition from uniform crystalline layers into a disordered rock-salt configuration,” said Brookhaven Lab scientist Eric Stach, who leads CFN’s electron microscopy group. “During this transformation, oxygen leaves the destabilized battery compound. This excess oxygen, leached at faster and faster rates over time, actually contributes to the risk of failure and acts as fuel for a potential fire.”

These new and fundamental insights may help engineers develop superior battery chemistries or nanoscale architectures that block this degradation.

Study 1: X-ray snapshots of heat-driven decomposition

The first study, published in Chemistry of Materials, explored the NCA battery using combined x-ray diffraction and spectroscopy techniques where beams of high-frequency photons bombard and bounce off a material to reveal elemental structure and composition. These x-ray studies were conducted at Brookhaven’s National Synchrotron Light Source (NSLS).

“We were able to test the battery cycling in situ, meaning we could watch the effects of increasing heat in real time,” said Brookhaven Lab chemist and study coauthor Seong Min Bak. “We pushed the fully charged NCA coin-cell battery out of thermal equilibrium by heating it all the way to 500 degrees Celsius.”

As the temperature rose, x-rays struck the sample and revealed the widespread transition from one crystal structure to another. The team also measured the amount of oxygen and carbon dioxide released by the NCA sample—a key indicator of potential flammability.

“The oxygen release peaked between 300 and 400 degrees Celsius during our trials, which is above the operating temperature for most vehicles,” Bak said. “But that temperature threshold dropped for a highly charged battery, suggesting that operating at full energy capacity accelerates structural degradation and vulnerability.”

While they further confirmed the results with x-ray absorption spectroscopy and electron microscopy after the heating trials, the team needed to map the changes at higher resolutions.

Study 2: Charge-induced transformations

The next study, also published in Chemistry of Materials, used transmission electron microscopy (TEM) to pinpoint the effect of an initial charge on the battery’s surface structure. The highly focused electron beams available at CFN revealed individual atom positions as an applied current pushed pristine batteries to an overcharged state.

“The surface changes matched the rock-salt evolution found in the x-ray study,” said study coauthor Sooyeon Hwang of the Korea Institute of Science and Technology (KIST). “Even with just one charge on the NCA battery we saw changes in the crystalline structure, and it grew much worse as the charge level increased.”

To capture the atoms’ electronic structures, the scientists used electron energy loss spectroscopy (EELS). In this technique, measurements of the energy lost by a well-defined electron beam reveal local charge densities and elemental configurations.

“We found a decrease in nickel and an increase in the electron density of oxygen,” Hwang said. “This causes a charge imbalance that forces oxygen to break away and leave holes in the NCA surface, permanently damaging the battery’s capacity and performance.”

While this combined crystallographic and electronic data confirmed and clarified the earlier work, temperature effects still needed to be explored with atomic precision.

Study 3: Thermal decay and real-time electron microscopy

The final study, published in Applied Materials and Interfaces, used in situ electron microscopy to track the heat-driven decomposition of NCA materials at different states of charge. The atomic-scale structural investigation under variable temperatures and charge levels offered the most comprehensive portrait yet.

The collaboration found that even though pristine and uncharged NCA samples remained stable up to 400 degrees Celsius, charging introduced the usual decomposition and vulnerabilities. The full story, however, was much more nuanced.

“We saw the same overall degradation patterns, but the real-time TEM revealed an unexpected twist within individual particles,” Stach said. “When fully charged, some particles released oxygen and began to shift toward disorder down at temperatures below 100 degrees Celsius—definitely plausible for a lithium-ion battery’s normal operation.”

Added Hwang, “Those unstable, degraded particles may trigger the chain reaction of so-called thermal runaway at lower temperatures than expected, and that free oxygen would feed the fire springing from an overheated battery.”

The future of batteries

The corroborating data in the three studies points to flaws in the chemistry and architecture of NCA batteries—including the surprising atomic asymmetries—and suggests new ways to enhance durability, including the use of nanoscale coatings that reinforce stable structures.

“We plan to push these investigative techniques even further to track the battery’s structure in real-time as it charges and discharges under real operating conditions—we call this in operando,” Stach said. “Brookhaven’s National Synchrotron Light Source II will be a game-changer for this kind of experimentation, and I’m eager to take advantage of that facility’s ultra-bright x-rays to track internal and surface evolutions in these materials.”

The studies were funded as part of a Korean Government “Global Research Laboratory,” which exists to support and take advantage of leading experimental capabilities abroad. This program specifically supported collaborators Seong Min Bak and Sooyeon Hwang and their research at NSLS and CFN, both DOE Office of Science User Facilities.

Brookhaven National Laboratory is supported by the Office of Science of the U.S. Department of Energy (DOE). Xiao-Qing Yang’ research is supported by the Office of Energy Efficiency and Renewable Energy’s Office of Vehicle Technologies of the DOE under Contract No. DE-AC02-98CH10886.

The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov

One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. Brookhaven is operated and managed for DOE's Office of Science by Brookhaven Science Associates, a limited-liability company founded by the Research Foundation for the State University of New York on behalf of Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit applied science and technology organization.

Contact Information
Justin Eure
Public Affairs Representative
jeure@bnl.gov

Justin Eure | newswise

More articles from Power and Electrical Engineering:

nachricht Multicrystalline Silicon Solar Cell with 21.9 % Efficiency: Fraunhofer ISE Again Holds World Record
20.02.2017 | Fraunhofer-Institut für Solare Energiesysteme ISE

nachricht Six-legged robots faster than nature-inspired gait
17.02.2017 | Ecole Polytechnique Fédérale de Lausanne

All articles from Power and Electrical Engineering >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

Impacts of mass coral die-off on Indian Ocean reefs revealed

21.02.2017 | Earth Sciences

Novel breast tomosynthesis technique reduces screening recall rate

21.02.2017 | Medical Engineering

Use your Voice – and Smart Homes will “LISTEN”

21.02.2017 | Trade Fair News

VideoLinks
B2B-VideoLinks
More VideoLinks >>>