Investigating Element Composition of High-Entropy Layered Oxides: Insights on Performance Influence for Sodium-Ion Batteries

The application potential of layered oxides for sodium-ion batteries is expanded by the entropy stabilization strategy. However, specific research on the selection of elements and interpretation of the function of high-entropy materials are limited. In this study, we have developed several types of high-entropy materials, NaNi_0.25Fe_0.15Mn_0.3Ti_0.1Sn_0.05Co_0.05Li_0.1O₂ (HEO-TS), NaNi_0.25Fe_0.15Mn_0.3Ti_0.05Sn_0.1Co_0.05Li_0.1O₂ (HEO-ST), NaNi_0.25Fe_0.15Mn_0.3Ti_0.15Co_0.05Li_0.1O₂ (HEO-Ti), and NaNi_0.25Fe_0.15Mn_0.3Sn_0.15Co_0.05Li_0.1O₂ (HEO-Sn). Through the analysis of the physical and electrochemical properties, the introduction of Ti into the transition metal layer enhances air stability and rate performance. It exhibits excellent electrochemical properties under a high voltage. Furthermore, the partial introduction of Sn⁴⁺ increases the voltage difference of redox potential and electrochemical polarization. When the transition metal layer contains a large amount of Sn, the material exhibits poor electrochemical properties and struggles to form high crystallinity cathode materials. This work provides a solution for the element design of high-entropy layered oxides and investigates the relationship between the elements and electrochemical properties.