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

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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 Li₂MnO₃ 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 Cr³⁺ and Cr⁶⁺ Manganese remains as Mn⁴⁺ throughout charge and discharge.