Local Structure and First Cycle Redox Mechanism of Layered Li 1.2 Cr 0.4 Mn 0.4 O 2 Cathode Material

Electrochemical, X-ray diffraction, and K and L edge X-ray absorption data are reported for the layered cathode material Li1.2Mn0.4Cr0.4O2 . The structural data show that this material can be understood as a solid solution of the layered phases Li 2MnO3 and LiCrO2 , comprising tretravalent Mn and trivalent Cr, with approximately 0.2 lithium incorporated in the transition metal layers. According to the analysis of the K edge extended X-ray absorption fine structure, lithium ions in the transition metal layers are clustered around Mn ions. L edge X-ray absorption near edge spectra show that in the first charge-discharge cycle chromium is the electrochemically active species, cycling between Cr 31 and Cr 61 . Manganese remains as Mn 41 throughout charge and discharge.