Study reveals new factor that could limit the life of hybrid and electric car batteries

December 12, 2012

COLUMBUS, Ohio - A new study of the batteries commonly used in hybrid and electric-only cars has revealed an unexpected factor that could limit the performance of batteries currently on the road.

Researchers led by Ohio State University engineers examined used car batteries and discovered that over time lithium accumulates beyond the battery electrodes - in the "current collector," a sheet of copper which facilitates electron transfer between the electrodes and the car's electrical system.

This knowledge could aid in improving design and performance of batteries, explained Bharat Bhushan, Ohio Eminent Scholar and Howard D. Winbigler Professor of Mechanical Engineering.

"Our study shows that the copper current collector plays a role in the performance of the battery," he said.

The study, which appears in a recent issue of the journal Scripta Materialia, reflects an ongoing collaboration between Bhushan and Suresh Babu, professor of materials science and engineering and director of the National Science Foundation Center for Integrative Materials Joining for Energy Applications, headquartered at the university. The team is trying to determine the factors that limit battery life.

Lithium-ion batteries are the rechargeable batteries used in most hybrid-electric cars and all-electric cars as well. Inside, lithium ions shuttle back and forth between the anode and cathode of the battery - to the anode when the battery is charging, and back to the cathode when the battery is discharging.

Previously, the researchers determined that, during aging of the battery, cyclable lithium permanently builds up on the surface of the anode, and the battery loses charge capacity.

This latest study revealed that lithium migrates through the anode to build up on the copper current collector as well.

"We didn't set out to find lithium in the current collector, so you could say we accidentally discovered it, and how it got there is a bit of a mystery. As far as we know, nobody has ever expected active lithium to migrate inside the current collector," Bhushan said.

Shrikant Nagpure, now postdoctoral researcher at Ohio State, carried out this research as a part of his doctoral degree. He examined batteries that were aged in collaboration with the university's Center for Automotive Research, where colleagues Yann Guezennec and Giorgio Rizzoni have studied battery aging for several years, in collaboration with the automotive industry.

Key to the discovery of lithium in the current collector was collaboration between the Ohio State team and Gregory Downing, a research chemist at the National Institute of Standards and Technology and an expert on a technique called neutron depth profiling (NDP), a tool for impurity analysis in materials.

Previously, the researchers used NDP to study the cathodes and anodes of six off-the-shelf lithium-ion car batteries - one new battery and five batteries which they aged themselves in the laboratory - and found that lithium builds up on the anode surface over time.

To understand more about how these batteries degrade, Bhushan and his colleagues have been studying the batteries further, at various scales ranging from the millimeter (millionths of a meter) down to the nanometer (billionths of a meter) with different techniques.

In the NDP technique, researchers pass neutrons through a material and capture the charged particles that emerge from the fission reaction between neutrons and lithium in the electrodes. Since different chemical elements emit a certain signature set of particles with specific energies, NDP can reveal the presence of impurities in a material.

In this latest study, NDP detected the presence of lithium in the copper current collector from one of the aged batteries. The detection was measured as a ratio of the number of copper atoms in the collector to the number of lithium atoms that had collected there. The test yielded a ratio of up to 0.08 percent, or approximately one lithium atom per 1250 copper atoms in the collector.

That's a small number, but high enough that it could conceivably affect the electrical performance of the current collector - and, in turn, the performance of a battery, Bhushan said. He hopes that battery makers will further investigate this phenomenon and use the information to design new materials that might prevent lithium from escaping the electrode material.

Next, he and his colleagues will study the impedance, or internal electrical resistance, of lithium-ion batteries on the nanoscale.
-end-
Funding for this study came from the Institute for Materials Research at Ohio State.

Contact: Bharat Bhushan, (614) 292-0651; Bhushan.2@osu.edu
Written by Pam Frost Gorder, (614) 292-9475; Gorder.1@osu.edu

Ohio State University

Related Batteries Articles from Brightsurf:

New research says Sodium-ion batteries are a valid alternative to Lithium-ion batteries
A team of scientists including WMG at the University of Warwick combined their knowledge and expertise to assess the current status of the Na-ion technology from materials to cell development, offering a realistic comparison of the key performance indicators for NBs and LIBs.

Fast calculation dials in better batteries
A simpler and more efficient way to predict the performance of batteries will lead to better batteries, according to Rice University engineers.

Building the batteries of cells
A new study, led by Dr. Ruchika Anand and Prof.

Researchers create a roadmap to better multivalent batteries
Lithium-ion batteries power everything from mobile phones to laptop computers and electric vehicles, but demand is growing for less expensive and more readily available alternatives.

New NiMH batteries perform better when made from recycled old NiMH batteries
A new method for recycling old batteries can provide better performing and cheaper rechargeable hydride batteries (NiMH) as shown in a new study by researchers at Stockholm University.

Seeing 'under the hood' in batteries
A high-sensitivity X-ray technique at Berkeley Lab is attracting a growing group of scientists because it provides a deep, precise dive into battery chemistry.

Better, safer batteries
For the first time, researchers who explore the physical and chemical properties of electrical energy storage have found a new way to improve lithium-ion batteries.

New catalyst provides boost to next-generation EV batteries
A recent study, affiliated with South Korea's Ulsan National Institute of Science and Technology (UNIST) has introduced a new composite catalyst that could efficiently enhance the charg-discharge performances when applied to metal-air batteries (MABs).

New lithium batteries from used cell phones
Research from the University of Cordoba (Spain) and San Luis University (Argentina) was able to reuse graphite from cell phones to manufacture environmentally friendly batteries.

Safe potassium-ion batteries
Australian scientists have developed a nonflammable electrolyte for potassium and potassium-ion batteries, for applications in next-generation energy-storage systems beyond lithium technology.

Read More: Batteries News and Batteries Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.