TEM Characterisation of Electrode–Electrolyte Interfaces in Solid-State Fuel Cells and Batteries

Solid heterointerfaces are a common source of weakness in solid oxide cells (SOCs) and solid-state batteries (SSBs). Although pristine interfaces may be produced during synthesis, the quality of these interfaces may degrade during operation due to chemical and electrochemical instabilities or high operating temperatures (for SOCs). As these interfacial changes are often limited in scale (nm to µm), bulk characterisation techniques often cannot track and trace these changes. In light of this, transmission electron microscopy (TEM), plays a unique role in interface characterisation. This chapter explores solid hetero-interfacial characterisation in both SOCs and SSBs using advanced TEM techniques. This includes high resolution scanning TEM (HR-STEM), electron energy loss spectroscopy (EELS) and in-operando TEM. Furthermore, new and emerging techniques including cryo-TEM, 4D-scanning TEM (4D-STEM) and developing in-operando TEM methods are also discussed.