Useful data for SIMS analysis of battery materials: Sputter yield volumes for NMC622 cathode and relative sensitivity factors for Co+ in silicon and graphite anodes

Secondary ion mass spectrometry (SIMS) is increasingly used to study the surface and interfacial chemistry of battery materials owing to its ppm sensitivity and nanometer depth resolution. To support the community and help improve measurement quality, we measured the sputter yield volumes (SYVs) of a typical LiNi0.6Mn0.2Co0.2O2 (NMC622) cathode composed of compressed particles of active material on a foil current collector support. A time-of-flight (ToF)-SIMS instrument with an in situ atomic force microscope allowed accurate depth measurements giving an SYV for 2 keV Cs+ of 0.040 ± 0.005 nm3/ion and a SYV for 2 keV O2+ of 0.026 ± 0.003 nm3/ion. No evidence of SYV heterogeneity was found. We find that a previously reported sputter rate value in the literature is an order of magnitude lower, highlighting the need for better data. We also determined the Relative Sensitivity Factors (RSFs) for 2 keV O2+ sputtering with a 45° angle of incidence for a 50 keV Co+ implant with a fluence of 1 × 1015 ions/cm2 into silicon and graphite (carbon) as model anode materials. The RSF for silicon (Co+/Si+) is 1.5 ± 0.1 × 1022 atoms/cm3, and the RSF for graphite (carbon) (Co+/C+) is 2.8 ± 0.8 × 1020 atoms/cm3. For graphite, a correction was applied to the C+ signal in the region of the Co+ implant owing to enhanced C+ intensities caused by fragmentation of the carbon lattice.