Surface roughness creates false signals in nanoscale battery analysis, study shows

KAIST researchers discovered that a signal long believed to show ion movement inside batteries is often just an optical illusion caused by rough surfaces. Typically, experts use atomic probes like Electrochemical Strain Microscopy (ESM) to map how ions flow inside battery materials. However, bumps and microscopic unevenness alter the probe’s touch, creating false signals that look like moving ions. The revelation, led by Professor Seungbum Hong alongside Professors Jong Min Yuk and Nam-Soon Choi, calls into question years of foundational data. The new study suggests that ESM has often misidentified simple surface roughness as active ion movement. Researchers eliminated these false signals by using a cooling cross-section polisher (CCP), establishing a reliable baseline for analyzing next-generation battery materials. “This research clearly demonstrates how variations in surface height affect the results of nanoscale battery-material analysis,” said Professor Hong. “We expect our findings to enable more accurate tracking of ion movement within batteries and contribute to understanding the operating mechanisms of next-generation battery materials and designing improved materials.” Schematic illustrating the trace–retrace discrepancy observed in DART-ESM measurements. Credit: KAIST Grain boundary misconception To understand how top battery minds were fooled, you have to look at how ESM operates. ESM tracks how ions move by running an ultra-fine, needle-like probe across a material’s surface. As ions migrate, they subtly expand or contract the material underneath. The microscope reads these nanoscale expansions, translating physical strain into a visual map of ion flow. And, as it turns out, it is easily tricked. When the scanning tip encounters a rough surface, the mechanical contact between the probe and the sample changes. That shift produces a electrical fluctuation nearly identical to real ion transport To prove that surface height variations create false readings, the KAIST team etched tiny trenches into a piece of single-crystal silicon. Silicon cannot conduct ions; hence, any signal detected by the microscope showed that surface topography generated the measurement artifacts instead of actual ion movement. As a result, the instrument lit up like a Christmas tree. The height variations alone generated strong ESM signals, proving that false data could appear out of thin air. When testing real graphite anodes and sodium solid electrolytes, the team observed the same ghost signals, particularly at the crystal seams known as grain boundaries. Once the surfaces were smoothed, these strong readings vanished, revealing that regions long believed to be fast lanes for ion transport were actually just microscopic valleys on the material’s surface. Shaving down the error Instead of building costly new equipment, the team solved the issue by flattening the material’s surface using a Cooling Cross-section Polisher. This device uses a beam of inert argon ions to smooth microscopic bumps without disturbing the sample’s underlying chemistry, eliminating the false signals. Once polished, the phantom signals evaporated. What remained was pure, unambiguous data on true ion transport. This revealed that regions long considered fast-ion highways were actually measurement illusions created by surface height variations. Developing high-performance batteries requires accurately mapping how ions travel through materials. As the world scrambles to commercialize safer solid-state batteries and cheaper sodium-ion alternatives, knowing exactly how ions move is everything. Flawed nanoscale data leads to flawed material design. Furthermore, as machine-learning models are increasingly deployed to predict battery lifespans, feeding them artifact-ridden data guarantees bad results. The study was published in the journal Small Methods. Get the latest in engineering, tech, space & science - delivered daily to your inbox.Mrigakshi is a science journalist who enjoys writing about space exploration, biology, and technological innovations. Her work has been featured in well-known publications including Nature India, Supercluster, The Weather Channel and Astronomy magazine. If you have pitches in mind, please do not hesitate to email her.