context: By comparing the C 1s, Li 1s, and O 1s XPS spectra and the corresponding area proportions, we found corroborative results. Firstly, a great amount of residual carbonate on the pristine LiNiO2 surface illustrates the continued challenge in avoiding carbonate formation during calcination and quick transferal. There was a clear increase in inorganic carbonates (C 1s, Li 1s, and O 1s XPS spectra) concurrent with the decrease of lattice Li and O proportions after exposure to ambient environment, which was amplified under continuous human exhalation (lattice Li and O are almost negligible on the surface) (Fig. 1). This is indicative of the continuous formation of inorganic carbonates, which strongly attenuates the photoelectron signals from underneath LiNiO2 layers. Our observation is consistent with previous studies suggesting that dense concentration of water and CO2 on the oxide cathode surface facilitates chemical reactions to yield increased amounts of surface inorganic carbonates. Previous studies have shown the surface chemical bonding and structure of NMC materials are readily transformed by certain environments, including CO2, H2O, O2, and other reactive gases in a glove box. These gases react with layered oxides by extracting lithium from the lattice, further generating LiOH and/or Li2CO3 as well as oxygen vacancies. Lithium residuals on NMC and NCA materials also have been confirmed by infrared spectroscopy, Raman spectroscopy, and TEM. It is a consensus that surface instability is one of the common challenges for many battery materials. Other materials, such as sodium-containing layered cathode materials and Li-rich materials, also encounter surface-air instability, which leads to Na/Li residual formation and elevated pH on the particle surfaces. For sodium-containing layered cathode materials, water intercalation or Na+/H+ exchange also takes place, which can disrupt the layered structure. These changes would trigger slurry alkalization, degassing problem, and electrolyte decomposition. Based on our results and previous findings, we recommend that the details about sample handling should be specified in the journal publications, especially those involving delicate surface chemical analysis.
answer: oxide 