Fig. 5: Boxplots of ToF-SIMS surface analysis.

Comparison of the normalized intensities of a S2−/S3−/S4− and b PO3−/SO3−/NiS− fragments at the surface of cathodes with different SOCs. The intensities of S2−/S3−/S4− signals were normalized with the total ion intensity, and the intensities of PO3−/SO3−/NiS− fragments were normalized in relation to the NiO2− signal. The lines in boxes depict the median, lower and upper box limits indicate 25th and 75th percentiles, respectively. Whiskers extend to ±1.5 × IQR, and points are outliers.