High-Entropy Mn/Fe-Based Layered Cathode with Suppressed P2–P′2 Transition and Low-Strain for Fast and Stable Sodium Ion Storage

Mn/Fe-based layered oxides are deemed to be a highly suitable cathode for sodium-ion batteries (SIBs) due to their high capacity and abundant Mn/Fe resources, but they still suffer from a complicated phase transition and large volume variation. To conquer these problems, high-entropy Mn/Fe-based layered oxide P2-Na_0.67Mn_0.5Fe_0.334Cu_0.045Mg_0.014Ti_0.014Al_0.014Zr_0.014Sn_0.014O₂ (Mn-Fe-HEO) is rationally designed and fabricated. When used as a cathode for SIB, high-entropy Mn-Fe-HEO exhibits much higher reversible capacity and better rate capability than low-entropy Na_0.67Mn_0.5Fe_0.334Cu_0.164O₂ (Mn-Fe-LEO) within a wide voltage range of 1.5-4.3 V. Ex situ X-ray diffraction combined with diffusion kinetics tests and microstructural characterizations demonstrate that high-entropy enhanced structural stability effectively prevents the Jahn-Teller distortion of Mn³⁺, stabilizes the Na⁺ diffusion channels, and enables the smooth transfer of more working Na⁺. These lead to a stable and fast redox electrochemistry in high-entropy Mn-Fe-HEO. This work deepens the understanding of the relationship between high-entropy structure and performance and provides important guidance for the rational design of future high-entropy layered cathodes.