P2 Orthorhombic Na0.7[Mn1–xLix]O2+y as Cathode Materials for Na-Ion Batteries

P2-type manganese-based oxide materials have received attention as promising cathode materials for sodium ion batteries because of their low cost and high capacity, but their reaction and failure mechanisms are not yet fully understood. In this study, the reaction and failure mechanisms of β-Na 0.7 [Mn 1– x Li x ]O 2+ y ( x = 0.02, 0.04, 0.07, and 0.25), α-Na 0.7 MnO 2+ y, and β-Na 0.7 MnO 2+ z are compared to clarify the dominant factors influencing their electrochemical performances. Using a quenching process with various amounts of a Li dopant, the Mn oxidation state in β-Na 0.7 [Mn 1– x Li x ]O 2+ y is carefully controlled without the inclusion of impurities. Through various in situ and ex situ analyses including X-ray diffraction, X-ray absorption near-edge structure spectroscopy, and inductively coupled plasma mass spectrometry, we clarify the dependence of (i) reaction mechanisms …