The performance of a lithium ion-cell where the cathode is a layered-layered lithium rich cathode material xLiMO2 (1-x)Li2MNO3, M being a transition metal selected from the group consisting of Co, Ni, or Mn, is improved by coating the surface of the cathode with a sulfonyl-containing compound, such as poly(l,4-phenylene ether-ether-sulfone), inhibits the reactivity of the electrolyte with the oxidized electrode surface while allowing lithium ion conduction.