Ion-beam milling induced systematic error in correlative microscopy of Li-ion battery materials

Correlative microscopy enables spatially resolved characterization of Li-ion battery materials by combining various microscopic and spectroscopic techniques. However, for these measurements to be meaningful, the microscopically measured properties must accurately represent the original sample. Here, we show that room temperature ion-beam milling, a common sample preparation method, can induce surface lithium depletion in transition metal oxide cathodes, leading to altered surface properties and systematically biased results in surface sensitive techniques. Conductive atomic force microscopy measurements on ion-beam polished LiNixMnγCozO2 cathodes revealed artificially low electrical conductivity due to Li depletion, raising concerns about data interpretation. Alternative sample preparation methods, such as cryogenic ion milling and gas cluster ion sputtering, offer potential solutions, though experimental validation remains limited. Our findings underscore the need for careful sample preparation to ensure accurate nanoscale characterization of battery materials.