High Resolution SIMS in Electroceramic Materials in Energy Storage Devices

Secondary Ion mass spectrometry (SIMS) is a surface analysis technique based on ion beam and mass spectrometry technologies to characterise the surface and sub-surface of materials. SIMS is a unique and indispensable surface analysis technique in solid state materials science with many advantageous capabilities. It is capable of measuring all the elements in the periodic table as well as their isotopes and molecular species, and the technique has extremely high sensitivity with trace element detection limits in ppm/ppb range, in certain cases. Under optimum conditions, it is possible to achieve sub-micron or even tens of nanometres lateral resolution and 1-2 nm surface specificity.

For electroceramics with applications in renewable energy, most of the materials used are complex oxides. Examples include (La,Sr)(Co,Fe)O_3-δ (LSCF), yttria-stabilised zirconia (YSZ), Li(Ni,Mn,Co)O₂ (NMC), and Lithium lanthanum zirconium oxide (LLZO). For further improvement and development of these materials in energy device application a thorough understanding of their microstructure is essential. SIMS, therefore, potentially has the capability to resolve features and within these systems on the nanoscale. However, these complex oxides are not always strait forward to analyse, and in many cases the features of interest may be buried far from the near surface and the samples themselves must be handled within a glove box. With these issues in mind, the Hi5 SIMS instrument was developed at Imperial College, London. The instrument possesses ion beams able to perform high rates of material removal (Xe⁺) to reveal buried structures and features, coupled with a highly focussed O₂⁺ plasma ion beam for subsequent SIMS analysis on a sub-micron scale. In particular, the instrument has been successfully applied to characterise the SEI (solid electrolyte interphase) regions of a polycrystalline Li(Ni_0.8Co_0.1Mn_0.1)O₂ (NMC811) cathode material, isolating individual particles. This work presents a new exciting characterisation methodology at high spatial resolution using the Hi5 SIMS.