As industries and consumers seek improved battery power sources, a new microscopy technique developed by Oak Ridge National Laboratory (ORNL) researchers is providing a novel perspective on how lithium-ion batteries function.
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.
"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.
The team 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 was able to visualize 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.
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. The researchers hope to extend the batteries' performance by lending engineers a finely tuned knowledge of battery components and dynamics.
The team's ESM imaging can display features such as individual grains, grain clusters, and defects within the cathode material. The high-resolution mapping showed, for example, that the lithium ion flow can concentrate along grain boundaries, which could lead to cracking and battery failure. These types of nanoscale phenomena need to 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.