Synergistic Dual Pinning Engineering through Regulating TM–O Bond Interactions toward Structurally Robust Fe/Mn-Based Layered Oxide Cathodes for Sodium-Ion Batteries

Fe/Mn-based layered oxides are considered highly competitive cathode materials for sodium-ion batteries due to the sustainability and availability of their raw materials. However, their practical application has been hindered by challenges such as Jahn–Teller (J-T) distortions of Mn3+/Fe4+, Fe migration in deeply desodiated states, and irreversible phase transitions. Herein, we propose a strategy of codoping with Mg/Al to stabilize a bipartite structure, which modulates the ionic covalency of the Fe/Mn–O bond to alter the local electronic environment and achieve dual pinning engineering. This results in the Na0.67Mg0.06Fe0.34Mn0.54Al0.06O2 (NFM-MA06) cathode material exhibiting a capacity retention of 86.2% after 100 cycles at a rate of 0.5 C, and retains 86.6% of its capacity after 300 cycles at 2 C. The enhanced stability, compared to the original cathode (which showed 54.5% and 33.1% capacity retention after 100 cycles at a rate of 0.5 and 150 cycles at 2 C, respectively), is attributed to the successful suppression of Jahn–Teller distortions and Fe migration. In addition, in situ XRD and in situ EIS tests (with corresponding DRT analysis) were performed to examine the structural evolution and enhanced reaction kinetics. This work lays the foundation for the advancement of economically viable Fe/Mn-based materials.