Electronegativity and entropy design of layered oxides for sodium-ion batteries

Abstract

Exploring sodium-ion layered oxides with broad compositional diversity is an important approach for the development of high-performance positive electrodes. Structural chemistry determined by composition plays a decisive role in performance improvement, but the relationship between composition and structure becomes more elusive in complex multi-component systems. Here we propose an electronegativity entropy weight concept to understand entropy-dominated phases formation. Electronegativity and configurational entropy are used to quantify key interactions in layered materials. Guided by this understanding, we design a sodium-deficient layered oxide with an O3 stacking sequence. This material demonstrates good structural and thermal stability, along with air stability (negligible performance degradation after air exposure), cycling stability (93.02% capacity retention after 200 cycles), and rate capability (retaining 69.1% capacity retention from 86.5 mA g⁻¹ to 1.73 A g⁻¹). Even in potassium-ion batteries with larger inserted ions, the material still exhibits cycling stability. This strategy provides valuable compositional guidance for the rational design of high-performance layered oxide materials.