In Situ XAFS Analysis of Li(Mn, M)

Chemical states and structural changes accompanying the electrochemical Li deintercalation of Li{sub 1-x}(Mn, M){sub 2}O{sub 4} (M=Cr, Co, Ni) were studied by the in situ X-ray absorption fine structure (XAFS) technique. The X-ray absorption near-edge structures (XANES) of Mn and M as a function of x showed that the high voltage ({approximately}5 V) in the cathode materials of an Li secondary battery is due to the oxidation of M{sup 3+} to M{sup 4+} (M=Cr, Co) and M{sup 2+} to M{sup 4+} (in the case of M=Ni), while the origin of the low voltage (3.9-4.3 V) can be ascribed to the oxidation of Mn{sup 3+} to Mn{sup 4+}. The extended X-ray absorption fine structure (EXAFS) analysis of Li{sub 1-x}(Mn,Ni){sub 2}O{sub 4} revealed that Ni{sup 2+} is oxidized to Ni{sup 4+} via the Ni{sup 3+} state with a Jahn-Teller distorted Ni{sup 3+}-O octahedron.