title: P2 Orthorhombic Na0.7[Mn1-xLix]O2+yas Cathode Materials for Na-Ion Batteries.
abstract: 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-Na0.7[Mn1-xLix]O2+y(x = 0.02, 0.04, 0.07, and 0.25), α-Na0.7MnO2+y, and β-Na0.7MnO2+zare 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-Na0.7[Mn1-xLix]O2+yis 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 on disordered Li distribution in the Mn layer, (ii) reversible capacities on the initial Mn oxidation state, (iii) redox potentials on the Jahn-Teller distortion, (iv) capacity fading on phase transitions during charging and discharging, and (v) electrochemical performance on Li dopant vs Mn vacancy. Finally, we demonstrate that the optimized β-Na0.7[Mn1-xLix]O2+y(x = 0.07) exhibits excellent electrochemical performance including a high reversible capacity of ∼183 mA h g-1and stable cycle performance over 120 cycles.
authors.affiliation: School of Chemical and Biological Engineering, Institute of Chemical Processes, Seoul National University , 1, Gwanak-ro, Gwanak-gu, Seoul 08826, South Korea.
authors.forename: Mi-Sook
authors.initials: MS
authors.lastname: Kwon
authors.affiliation: School of Chemical and Biological Engineering, Institute of Chemical Processes, Seoul National University , 1, Gwanak-ro, Gwanak-gu, Seoul 08826, South Korea.
authors.forename: Shin Gwon
authors.initials: SG
authors.lastname: Lim
authors.affiliation: School of Chemical and Biological Engineering, Institute of Chemical Processes, Seoul National University , 1, Gwanak-ro, Gwanak-gu, Seoul 08826, South Korea.
authors.forename: Yuwon
authors.initials: Y
authors.lastname: Park
authors.affiliation: Battery Research Center, Korea Electrotechnology Research Institute , 12 Bulmosan-ro 10 bean-gil, Changwon 51543, South Korea.
authors.forename: Sang-Min
authors.initials: SM
authors.lastname: Lee
authors.affiliation: Center for Energy Convergence Research, Korea Institute of Science and Technology , Hwarang-ro 14-gil 5, Seongbuk-gu, Seoul 02792, South Korea.
authors.forename: Kyung Yoon
authors.initials: KY
authors.lastname: Chung
authors.affiliation: UNIST Central Research Facilities & School of Natural Science, Ulsan National Institute of Science and Technology , 50 UNIST-gil, Eonyang-eup, Ulju-gun, Ulsan 44919, South Korea.
authors.forename: Tae Joo
authors.initials: TJ
authors.lastname: Shin
authors.affiliation: School of Chemical and Biological Engineering, Institute of Chemical Processes, Seoul National University , 1, Gwanak-ro, Gwanak-gu, Seoul 08826, South Korea.
authors.forename: Kyu Tae
authors.identifier: http://orcid.org/0000-0003-2769-3372
authors.initials: KT
authors.lastname: Lee
keywords: cathode; layered manganese oxide; mechanism; orthorhombic structure; sodium ion battery