Transition metal compounds with a general formula A_xM_aX_b (A=Li, Na, M= transition metal, X= O, S, SO₄^2-, PO₄^3-) constitute a group of potential electrode materials for a new generation of alkaline batteries. This application is related to the fact that these compounds can reversibly intercalate high amounts of alkaline ions (1 or more moles per mole of M_aX_b) already at room temperature, without significant changes in their crystallographic structure. Nowadays, further development of rechargeable batteries is focused on the discovery of new, high-performance and low-cost electrode materials. Recently, Na-ion batteries have attracted much attention due to their many advantages, such as: high abundance of sodium in the Earth’s crust, its low cost and suitable redox potential (only 0.3 V above that of lithium).

The author of this work basing on her own investigations of numerous group of cathode materials  has demonstrated that the electronic structure of the electrode materials plays an important role in the electrochemical  intercalation process [1,2]. The paper reveals correlation between crystal and electronic structure, chemical disorder, transport and electrochemical properties of layered NaxNi_1/5Co_1/5Fe_1/5Mn_1/5Ti_1/5O₂ high entropy oxides, polyanions Na₂Fe₂(SO₄)₃ and Prussian Blue Analogues cathode materials. 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 detailed analysis presented in this work provides a strong proof that the high-entropy Na_xMn_0.2Fe_0.2Co_0.2Ni_0.2Ti_0.2O₂ oxide with reduced content of cobalt and nickel, Na₂Fe₂(SO₄)₃ and Prussian Blue Analogues might be applicable in sodium batteries technology, especially in terms of large-scale energy storage units.