Boosting the reactivity of Ni2+/Ni3+ redox couple via fluorine doping of high performance Na0.6Mn0.95Ni0.05O2-xFx cathode

Though P2-type Na-Mn-Ni-O cathodes with low cost and environmental benign have been extensively investigated, it is still challenging to fulfill practical application with limited cycle stability and low operating potential. However, the research of the reactive Ni2+/Ni3+ redox pair that enable both high working potential and high reversible capacity was almost ignored. And traditional cationic doping mainly focusses on crystal modulation and structure stabilization. In this study, an anion doping strategy (F-doping) was carried out to further boost the activity of Ni2+. The multi-function including structural parameter modulation and robust Ni-F bond significantly promote the activation of Ni2+/Ni3+ and advance the respective working potential. Related reaction kinetics and structural evolution were also investigated to elucidate the F-doping mechanism. The Na-0.Mn-6(0).95Ni0.05O1.95F0.(05) with appropriate F content could deliver a high capacity of 80.76 mA h g(-1) at 2C with 75.0% retained after 960 cycles. The excellent rate capability and full cell performance also demonstrate the high potential. This study may provide a new sight for the development of P2-type layered Na-Mn-Ni-O cathode, which could be extended to other oxides cathode. (C) 2019 Elsevier Ltd. All rights reserved.