In lithium-ion batteries, several electrical and physical parameters are responsible for the degradation of the electrode materials. Here the application of Kelvin probe microscopy (KPM) is demonstrated to measure the charge sustaining capability of the LiFePO4 cathode under aged and unaged conditions. The aged sample shows lower surface potential than the unaged sample, which can be attributed to changes in physical and chemical properties including particle size, phase of the surface layer and nanocrystalline deposits.