Limited lifetime is a key concern for most Li-ion battery types. Simolka et al. report for the first time the use of electrochemical strain microscopy (ESM) for the study of aging in Lithium Iron Phosphate (LFP) cathodes. ESM measurements were performed on cross sectioned fresh and aged cathodes using a Bruker Dimension Icon AFM in a glove box. Electrochemical activity and available Lithium-ion content are found to be lower in the aged samples. PeakForce QNM data shows the presence of a second, softer phase in aged but not fresh cathodes, suggesting that the capacity reduction with aging might be due to build-up of an inactive, softer cathode phase, possibly due to iron dissolution.