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 0.67 Mn 0.5 Fe 0.334 Cu 0.045 Mg 0.014 Ti 0.014 Al 0.014 Zr 0.014 Sn 0.014 O 2 (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 0.67 Mn 0.5 Fe 0.334 Cu 0.164 O 2 (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 Mn 3+ , 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.