Structural and Thermodynamic Understandings in Mn‐Based Sodium Layered Oxides during Anionic Redox. Issue 16 (2nd July 2020)

• Record Type: Journal Article
• Authors: Kang, Seok Mun; Kim, Duho; Lee, Kug‐Seung; Kim, Min‐Seob; Jin, Aihua; Park, Jae‐Hyuk; Ahn, Chi‐Yeong; Jeon, Tae‐Yeol; Jung, Young Hwa; Yu, Seung‐Ho; Mun, Junyoung; Sung, Yung‐Eun
• Is Part Of: Advanced science. Volume 7:Issue 16(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-07-02
• Subjects: anionic redox -- cathodes -- sodium ion batteries -- two‐phase reactions; Science -- Periodicals; 505
• DOI: 10.1002/advs.202001263
• Languages: English
• ISSNs: 2198-3844

Abstract

Abstract: A breakthrough utilizing an anionic redox reaction (O 2− /O n− ) for charge compensation has led to the development of high‐energy cathode materials in sodium‐ion batteries. However, its reaction results in a large voltage hysteresis due to the structural degradation arising from an oxygen loss. Herein, an interesting P2‐type Mn‐based compound exhibits a distinct two‐phase behavior preserving a high‐potential anionic redox (≈4.2 V vs Na + /Na) even during the subsequent cycling. Through a systematic series of experimental characterizations and theoretical calculations, the anionic redox reaction originating from O 2p‐electron and the reversible unmixing of Na‐rich and Na‐poor phases are confirmed in detail. In light of the combined study, a critical role of the anion‐redox‐induced two‐phase reaction in the positive‐negative point of view is demonstrated, suggesting a rational design principle considering the phase separation and lattice mismatch. Furthermore, these results provide an exciting approach for utilizing the high‐voltage feature in Mn‐based layered cathode materials that are charge‐compensated by an anionic redox reaction. Abstract : P2‐type Na0.60 Li0.20 Mn0.80 O2 undergoes a reversible two‐phase reaction at high voltage (≈4.2V vs Na + /Na), in which oxygen ion contributes the charge compensation. The detailed reaction mechanism is thoroughly investigated through experimental and theoretical analyses including in situ XRD and XAS observations. The combined study provides a rational material design for the reversible two‐phase reaction.