The cathode electrolyte interphase is believed to be important in affecting capacity fade in commercial Li-ion chemistries. However, little is known about its chemical evolution as a function of voltage and cycle number and how these factors influence capacity fade. This work reports on a novel model geometry utilized to study cathode surface chemistry using in-situ XPS and AES. The surface chemistry measured in-situ in UHV matches ex-situ measurements surprisingly well. A variety of cathode materials such as LMO, LNO, LCO, LFP, and NMC are characterized in detail. The evolution of their surface chemistry is found to be quite distinct and provides insights into degradation mechanisms in the different systems.