Exploring Batteries at the Nanoscale
OAK RIDGE, Tenn., Sept. 24, 2010 — As industries and consumers increasingly seek improved battery power sources, cutting-edge microscopy performed at the Department of Energy’s Oak Ridge National Laboratory (ORNL) is providing an unprecedented perspective on how lithium-ion batteries function.
A new electrochemical strain microscopy (ESM) technique developed at Oak Ridge National Laboratory can map lithium-ion flow through a battery’s cathode material. This 1 μm × 1 μm composite image demonstrates how regions on a cathode surface display varying electrochemical behaviors when probed with ESM.
A research team led by ORNL’s Nina Balke, Stephen Jesse and Sergei Kalinin has developed a new type of scanning probe microscopy called electrochemical strain microscopy (ESM) to examine the movement of lithium ions through a battery’s cathode material. The group reported its efforts in a paper titled “Nanoscale mapping of ion diffusion in a lithium-ion battery cathode” in the online edition of Nature Nanotechnology.
“We can provide a detailed picture of ionic motion in nanometer volumes, which exceeds state-of-the-art electrochemical techniques by six to seven orders of magnitude,” Kalinin said. Researchers achieved the results by applying voltage with an ESM probe to the surface of the battery’s layered cathode. By measuring the corresponding electrochemical strain, or volume change, the team visualized how lithium ions flowed through the material. Conventional electrochemical techniques, which analyze electric current instead of strain, do not work on a nanoscale level because the electrochemical currents are too small to measure, Kalinin said.
“These are the first measurements, to our knowledge, of lithium ion flow at this spatial resolution,” he added.
Lithium-ion batteries, which power electronic devices from cell phones to electric cars, are valued for their low weight, high energy density and recharging ability. Researchers hope to extend the batteries’ performance by lending engineers a finely tuned knowledge of battery components and dynamics.
“We want to understand – from a nanoscale perspective – what makes one battery work and one battery fail. This can be done by examining its functionality at the level of a single grain or an extended defect,” Balke said.
ESM imaging can display features such as individual grains, grain clusters and defects within the cathode material. The high-resolution mapping it provides showed, for example, that the lithium-ion flow can concentrate along grain boundaries, which could lead to cracking and battery failure. Researchers say these types of nanoscale phenomena must be examined and correlated to overall battery functionality.
“Very small changes at the nanometer level could have a huge impact at the device level,” Balke said. “Understanding the batteries at this length scale could help make suggestions for materials engineering.”
Although the research focused on lithium-ion batteries, the team expects that its technique could be used to measure other electrochemical solid-state systems, including other battery types, fuel cells and similar electronic devices that use nanoscale ionic motion for information storage.
“We see this method as an example of the kinds of higher dimensional scanning probe techniques that we are developing at CNMS that enable us to see the inner workings of complex materials at the nanoscale,” Jesse said. “Such capabilities are particularly relevant to the increasingly important area of energy research.”
Balke, Jesse and Kalinin are scientists at ORNL’s Center for Nanophase Materials Science. The research team includes Nancy Dudney, Yoongu Kim and Leslie Adamczyk from ORNL’s Materials Sciences and Technology Division. The key theoretical results in the work were obtained by Anna Morozovska and Eugene Eliseev at the National Academy of Science of Ukraine and Tony Chung and Edwin Garcia at Purdue University.
This research was supported as part of the Fluid Interface Reactions, Structures and Transport Center, an Energy Frontier Research Center funded by the Department of Energy, Office of Science. Part of the work was supported by the Center for Nanophase Materials Sciences (CNMS) at ORNL, one of the five DOE Nanoscale Science Research Centers supported by the DOE Office of Science.
For more information, visit: www.nano.energy.gov
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