Electron energy loss spectroscopy of thin film electrodes and membranes in all-solid-state batteries

Electron energy loss spectroscopy (EELS) is based on inelastic scattering of electrons in the TEM. The technique allows evaluating the chemical composition, the oxidation states and therefore, also the bonding characteristics of layered samples with a spatial resolution in the nanometer range. For the experiments, model batteries comprising of layers of LiCoO2, Li-Borate glasses and V2O5 are deposited onto ITO-coated glass substrates. Single layer thickness ranges from 50 to 400 nm. Electron transparent cross section samples are prepared by conventional ion milling and FIB technique. Measuring the observed chemical shift in the absorption edges of the energy loss spectra and comparing these to appropriate reference materials, different charge states of the electrodes can be distinguished and the amount of Li intercalated in the structure is quantified. The talk demonstrates how these data are used to optimize the conditions of sputter deposition and to achieve suitable functional properties of the thin films. Reversible Li-intercalation in the model thin film battery with active layers of 200 nm thickness and 50 nm thick membranes is demonstrated by cyclic voltametry.