Journal
JOURNAL OF SOLID STATE CHEMISTRY
Volume 156, Issue 2, Pages 286-291Publisher
ACADEMIC PRESS INC
DOI: 10.1006/jssc.2000.8990
Keywords
in situ XAFS analysis; Li secondary battery; Li1-x(Mn, M)(2)O-4 (M = Cr, Co, Ni); Jahn-Teller distortion
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Chemical states and structural changes accompanying the electrochemical Li deintercalation of Li1-x(Mn, M)(2)O-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 (similar to 5 V) in the cathode materials of an Li secondary battery is due to the oxidation of M3+ to M4+ (M = Cr, Co) and M2+ to M4+ (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 Mn3+ to Mn4+. The extended X-ray absorption fine structure (EXAFS) analysis of Li1-x(Mn, Ni)(2)O-4 revealed that Ni2+ is oxidized to Ni4+ via the Ni3+ state with a Jahn-Teller distorted Ni3+-O octahedron. (C) 2001 Academic Press.
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