Milling of electrodes for cross sectional imaging was performed using a Hitachi IM4000plus Broad Beam Ion Miller. Wavelength-dispersive X-ray fluorescence (WD-XRF) spectroscopy was conducted at the University of Warwick X-Ray Diffraction Research Technology Platform (RTP) using a Rigaku Primus IV system, equipped with a 4 kW Rh tube. Elemental compositions were calculated in a semi-quantitative manner via the Fundamental Parameters (FP) method using intensity libraries derived from standards analysed by the instrument manufacturer.