According to a press release, Oak Ridge researchers have developed a new type of scanning probe microscopy called electrochemical strain microscopy that examines the movement of Li-ions through a battery’s cathode material. The research, “Nanoscale mapping of ion diffusion in a lithium-ion battery cathode,” is published in Nature Nanotechnology.
Results were achieved by applying voltage with an ESM probe to the surface of the battery’s layered cathode. By measuring the corresponding electrochemical strain, scientists are able to visualize how lithium ions flowed through the material.
“These are the first measurements, to our knowledge, of lithium ion flow at this spatial resolution,” says research team member Sergei Kalinin.
In an email, Kalinin explains that ESM is scanning probe microscopy-based method. He says it maps “ionic currents in solid-state ionics based on the measurement of dynamic strains induced by coupling between ionic concentration and molar volume.”
Kalinin suggests one way to conceive of the differences that will now exist among microscopy methods is that scanning tunneling microscopy probes electronic currents; atomic force microscopy probes forces; and ESM is scanning probe microscopy that specifically probes ionic currents for time- and voltage spectroscopies.
The research group believes the method will improve measurements by many orders of magnitude because measuring atomically small strains is much easier then atomically small currents. “The simple estimates suggest that we can probe ionic transport and electrochemical processes in volumes 106 – 108 times smaller then conventional electrochemical methods,” says Kalinin, “and hence can be extended to probing ionic transport and electrochemical activity down to the level of single defect.’
The researchers hope to extend Li-ion 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 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 need to be examined and correlated to overall battery functionality.
Although the research focused on Li-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.