Soft x-ray absorption spectroscopic studies of Li[Ni_xCo _1-2xMn_x]O₂ for Li rechargeable batteries

Mn and Ni L_II, _III-edge XAS results, in the FY mode, indicate that charge compensation in the bulk during charge mainly by the oxidation of Ni²⁺ to Ni⁴⁺ ions. PEY results at the Ni L_{II, III}-edges indicate that Ni ions on the surface of the electrode remain unchanged in the Ni²⁺ oxidation state during charge. A comparison of the nickel-based compounds (LiNiO₂ and Li _1-xNi_0.5Mn_0.5O₂) in the PEY and FY modes indicates that the surface of the nickel-based compounds has a different electronic structure from the bulk. Changes in the features on the low energy side of pre-edge peak at the O K-edge, at higher states of charge, indicate that the holes compensating lithium ion deintercalation are located in O 2p states as well as Ni 3d states.