In situ transmission X-ray absorption fine structure analysis of the charge-discharge process in LiMn2O4, a rechargeable lithium battery material

The in situ XAFS technique has been applied for the first time to reveal variations in the local structures of Mn atoms during the charge-discharge process of LiMn2O4, Li(Mn1.93Li0.07)O-4, and Li(Mn1.85Li0.15)O-4 cathode materials of lithium-ion secondary batteries, It has been demonstrated that the valence state of manganese is in a linear correlation with the peak energy of the Mn K-edge XANES spectrum. EXAFS analysis disclosed the coexistence of Mn3+ and Mn4+ in LiMn2O4, with two distinct Mn-O bond distances of 1.98 and 1.88 Angstrom for the Mn3+-O-6 and Mn4+-O-6 octahedra, respectively. Li deintercalation leads to the oxidation of Mn3+ to Mn4+ and finally to MnO2, in which the Mn atom exhibits a uniform octahedral oxygen coordination, with a Mn-O distance of approximately. 1.9 Angstrom. The large variation in the local structure around the Mn atom during the charge-discharge process may be responsible for the cyclic instability of the battery material. (C) 1997 Academic Press.