%0 Electronic Article
%A Li, Yongchun
%A Mazzio, Katherine
%A Yaqoob, Najma
%A Sun, Yanan
%A Freytag, Annica
%A Wong, Deniz
%A Schulz, Christian
%A Baran, Volodymyr
%A San Jose Mendez, Alba
%A Schuck, Götz
%A Zając, Marcin
%A Kaghazchi, Payam
%A Adelhelm, Philipp
%T Competing mechanisms determine oxygen redox in doped Ni-Mn based layered oxides for Na-ion batteries
%M PUBDB-2023-07449
%D 2023
%X Cation doping is an effective strategy for improving the cyclability of layered oxide cathode materials through suppression of phase transitions in the high voltage region (> 4.0V). In this study we choose Mg and Sc as representative dopants in P2- Na<sub>0.67</sub>Ni<sub>0.33</sub>Mn<sub>0.67</sub>O<sub>2</sub>. While both dopants have a positive effect on the cycling stability, they are found to influence the properties in the high voltage regime in different ways. Through a combination of RIXS, XRD, XAS, PDF analysis, and DFT, we show that it is more than just suppression of the P2 to O<sub>2</sub> phase transition that is critical for promoting the favorable properties, and that the interplay between Ni and O activity are also critical aspects that dictate the performance. With Mg doping, we could enhance the Ni activity while simultaneously suppressing the O activity. This is surprising because it is in contrast to what has been reported in other Mn-based layered oxides where Mg is known to trigger oxygen redox. We address this contradiction by proposing a competing mechanism between Ni and Mg that impacts differences in O activity in Na<sub>0.67</sub>Mg<sub>x</sub>Ni<sub>0.33−x</sub>Mn<sub>0.67</sub>O<sub>2</sub> (x<0<0.33). These findings provide a new direction in understanding the effects of cation doping on the electrochemical behavior of layered oxides.
%F PUB:(DE-HGF)25
%9 Preprint
%R 10.26434/chemrxiv-2023-jfnmr
%U https://bib-pubdb1.desy.de/record/599477