Researchers at the Korea Advanced Institute of Science and Technology announced on September 7 that nanoscale battery analysis signals previously attributed to ion transport can actually be caused by surface height variations. The team proposed using an argon ion beam polishing method to eliminate these measurement artifacts.
A signal that appears to show ions moving inside a battery may be an illusion caused by an uneven surface. A multi-departmental research team at the Korea Advanced Institute of Science and Technology has identified the origin of measurement artifacts in nanoscale battery analysis that can be mistaken for actual ion transport, offering a solution to improve the reliability of advanced energy storage research.
During repeated charging and discharging, lithium or sodium ions travel back and forth within a battery. How fast and smoothly those ions move determines the performance and lifespan of the cell, making it crucial for researchers to pinpoint exactly where ions migrate freely and where their movement is blocked.
Uncovering Topographic Crosstalk in Electrochemical Strain Microscopy
Scientists frequently track these nanoscale volumetric changes using Electrochemical Strain Microscopy, an Atomic Force Microscopy-based technique that scans battery material surfaces with an extremely fine probe. However, the KAIST team demonstrated that uneven surface topography introduces significant measurement errors known as topographic crosstalk.
As the microscope tip moves over a rough surface, variations in height alter the degree of tip-sample contact and local contact stiffness. Delays in the instrument’s feedback loop during Dual AC Resonance Tracking convert these mechanical contact variations into electrical signals that mimic true electrochemical ion transport.
To investigate the origin of these false readings, the researchers created fine trenches on the surface of an ionically inactive single-crystal silicon sample. This experimental environment ensured no ions were moving while the surface remained uneven. The results quantitatively proved that height variations alone generate artificial signals identical to those observed in active battery components.
The team observed the same topographic interference when testing actual battery materials, including a graphite anode and the sodium solid electrolyte. This confirmed that the issue is not limited to a particular substance but is a widespread phenomenon affecting nanoscale analyses across diverse battery materials.
Disappearing Grain Boundary Signals and the Argon Polishing Solution
The research was conducted jointly by teams led by Professor Seungbum Hong and Professor Jong Min Yuk from the Department of Materials Science and Engineering, along with Professor Nam-Soon Choi from the Department of Chemical and Biomolecular Engineering.
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The team focused particularly on grain boundaries—the interfaces where the small crystals making up a battery material meet. Before surfaces were smoothed, strong Electrochemical Strain Microscopy signals appeared at these grain boundaries, leading researchers to interpret them as fast ion pathways.
“This study analyzed battery materials at the nanoscale and clearly revealed how surface height variations affect measurement results, We expect it will help more accurately identify ion motion inside batteries and contribute to understanding and designing the operating principles of next-generation battery materials.”
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Professor Hong Seungbum, KAIST
As a practical remedy, the researchers proposed making battery material surfaces as flat as possible using a cooling cross-section polisher (CCP). This system employs an argon ion beam to precisely trim sample cross sections. Because argon is chemically inert under most conditions, it processes the surface without significantly altering the chemical or structural properties of the sample.
Once treated, surface roughness dropped sharply, and the enhanced signals previously recorded at grain boundaries disappeared. This confirmed that the initial readings were purely topographic artifacts rather than genuine ionic movement.
Implications for Next-Generation Batteries and Artificial Intelligence Modeling
The findings carry significant weight for the development of next-generation energy storage, including all-solid-state and sodium-ion batteries. By establishing a reliable method to differentiate true ion transport from surface noise, the research provides a foundational baseline for designing materials that facilitate smoother ion movement to speed up charging and extend battery lifespan.
The findings were published in the international materials science journal Small Methods.
