The author of this work basing on her own investigations of AxMO2 cathode materials (A=Li, Na; M=Ni, Co, Mn, Fe, Ti, Cu ) has demonstrated that the electronic structure of these materials plays an important role in the electrochemical intercalation process [1]. The paper reveals correlation between crystal and electronic structure, chemical disorder, transport and electrochemical properties of layered LixCoO2 , NaxCoO2-y , LixNi1-y-zCoyCuzMn0.1O2 and NaxNi1/5Co1/5Fe1/5Mn1/5Ti1/5O2 high entropy cathode materials and explains of apparently different character of the discharge/charge curve in those systems. The complex studies, including experimental as well as theoretical parts (electronic structure calculations performed using the Korringa-Kohn-Rostoker method with the coherent potential approximation KKR-CPA to account for chemical disorder), showed a strong correlation between structural, transport and electrochemical properties of these materials.

The battery on the base on the developed high entropy oxides NaNi1/5Co1/5Fe1/5Mn1/5Ti1/5O2 cathode materials are characterized by high potential, high capacity and high rate capability guaranteeing high energy and power densities. The quickly appearing of O3-P3 phase transformation in this oxide leads to metallic conductivity and better kinetics of Na|Na+|NaxMn-0.2Fe0.2Co0.2Ni0.2Ti0.2O2 cell. By using the structural analysis methods (operando XRD, XAS and Mossbauer spectroscopy) we described the mechanism that governs the sodium deintercalation/intercalation processes in NaxMn0.2Fe0.2Co0.2Ni0.2Ti0.2O2 cathode with indicating the valence state of transition metals. Our investigation indicated that only titanium is electrochemically inactive during the cell operation, while Mn, Fe, Co, Ni undergo reduction and oxidation processes [2]

 The detailed analysis presented in this work provides a strong proof that the high-entropy NaxMn0.2Fe0.2Co0.2Ni0.2Ti0.2O2 oxide with reduced content of cobalt and nickel, might be applicable in sodium batteries technology, especially in terms of large-scale energy storage units.

Acknowledgements
This work was funded by the National Science Centre Poland (NCN) under the “OPUS 17 programme on the basis of the decision number 2019/33/B/ST8/00196.

References
[1] J.Molenda, A.Milewska, W. Zajac, M.Rybski, J. Tobola, Phys. Chem. Phys. Chem. 19, (2017)25697.
[2] K. Walczak, A. Plewa , C. Ghica, W. Zając, A. Trenczek-Zając, J. Toboła, J. Molenda, Energy Storage Materials, 47(2022)500.