Improved Cycling Performance of Li‐Excess Cation‐Disordered Cathode Materials upon Fluorine Substitution. Issue 2 (16th November 2018)

• Record Type: Journal Article
• Authors: Lun, Zhengyan; Ouyang, Bin; Kitchaev, Daniil A.; Clément, Raphaële J.; Papp, Joseph K.; Balasubramanian, Mahalingam; Tian, Yaosen; Lei, Teng; Shi, Tan; McCloskey, Bryan D.; Lee, Jinhyuk; Ceder, Gerbrand
• Is Part Of: Advanced energy materials. Volume 9:Issue 2(2019)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2018-11-16
• Subjects: cyclability -- DFT -- fluorination -- Jahn–Teller distortion -- Li‐excess cation‐disordered cathodes; Energy harvesting -- Materials -- Periodicals; Energy conversion -- Materials -- Periodicals; Energy storage -- Materials -- Periodicals; Photovoltaics -- Periodicals; Fuel cells -- Periodicals; Thermoelectric materials -- Periodicals; 621.31
• DOI: 10.1002/aenm.201802959
• Languages: English
• ISSNs: 1614-6832

Abstract

Abstract: The recent discovery of Li‐excess cation‐disordered rock salt cathodes has greatly enlarged the design space of Li‐ion cathode materials. Evidence of facile lattice fluorine substitution for oxygen has further provided an important strategy to enhance the cycling performance of this class of materials. Here, a group of Mn 3+ –Nb 5+ ‐based cation‐disordered oxyfluorides, Li1.2 Mn 3+ 0.6+0.5 x Nb 5+ 0.2−0.5 x O2− x F x ( x = 0, 0.05, 0.1, 0.15, 0.2) is investigated and it is found that fluorination improves capacity retention in a very significant way. Combining spectroscopic methods and ab initio calculations, it is demonstrated that the increased transition‐metal redox (Mn 3+ /Mn 4+ ) capacity that can be accommodated upon fluorination reduces reliance on oxygen redox and leads to less oxygen loss, as evidenced by differential electrochemical mass spectroscopy measurements. Furthermore, it is found that fluorine substitution also decreases the Mn 3+ ‐induced Jahn–Teller distortion, leading to an orbital rearrangement that further increases the contribution of Mn‐redox capacity to the overall capacity. Abstract : A class of Li‐excess cation‐disordered Mn 3+ –Nb 5+ ‐based oxyfluorides are designed and electrochemically tested. Fluorination is found to improve the cycling performance, especially the retention in a very significant way, by reducing the Mn 3+ ‐induced Jahn–Teller distortion. This structural optimization raises some Mn 3+ energy levels so that more of them can be oxidized before irreversible oxygen oxidation sets in.