Surface studies of high voltage lithium rich composition: Li1.2Mn0.525Ni0.175Co0.1O2

► High voltage cycling (4.9 V) of lithium rich Li1.2Mn0.525Ni0.175Co0.1O2 cathode. ► Surface film formation because of the oxidation of electrolyte. ► Studies of surface film using EIS, XPS and micro-Raman spectroscopy. ► Increase in cell impedance due to formation of polycarbonates, LiF, LixPFy etc. ► Formation of thick surface film is the dominant reason for decrease in capacity.