Redox and structural stability for sodium-ion batteries through bond structure engineering

Abstract

With the advancement of sodium-ion batteries, layered manganese-based sodium-ion batteries have garnered significant attention due to their high safety and cost-effectiveness, positioning them as strong contenders for grid-scale energy storage solutions. However, the slow kinetics of sodium ions and the complex phase transitions during charge/discharge cycling hinder the application by decreasing rate capability and cycling performance. In this study, bond structure engineering is employed to regulate the elemental composition of TMO₂ slabs by analyzing the bond strength differences within TMO₂ slabs. The aim is to enhance the structural stability and suppress the phase transition by increasing the layer spacing of the Na layer and the shrinkage of the TM layer, thereby improving the Na⁺ ion transport kinetics and mitigating the effects of Na⁺/vacancy ordering and Jahn–Teller distortion. Consequently, the designed high-entropy O3–NaNi_0.2Fe_0.2Mn_0.3Mg_0.1Cu_0.1Sn_0.1O₂ (HE) exhibits improved rate capability and cycling performance. It shows 83.8% capacity retention after 200 cycles at a 3C current density and can stably cycle for 500 cycles at 5C with 75.3% capacity retention. This work provides a new approach for the design of high-entropy manganese-based sodium-layered oxides for energy storage systems.