A Strategy to Mitigate Jahn Teller Effect of Mn‐Rich NASICON Framework for Sodium‐Ion Batteries

Abstract Mn‐based sodium superionic conductors have driven attention to the low‐cost advanced cathode materials for sodium‐ion batteries (SIBs). However, low‐rate capability and unsatisfactory cyclic performance due to the Jahn teller effect of Mn 3+ redox couple which occurs from the change in Mn‐O bond length at the octahedral site of crystal structure during charge–discharge, eventually limiting their application. Herein, a disordered and sodium deficient NASICON Na 4‐x Mn(FeVCrTi) 0.25 (PO 4 ) 3 (termed as Na 4‐x Mn(HE)) is synthesized to mitigate this Jahn teller effect to achieve high rate and ultrastable cathode material. Interestingly, the as‐prepared Na 3.5 Mn(HE) shows five reversible electron reactions (i.e., Ti 3+ /Ti 4+ , Fe 2+ /Fe 3+ , V 3+ /V 4+ , Mn 2+ /Mn 3+ , and Mn 3+ /Mn 4+ ) and demonstrates 141 mA h g −1 at 0.2 C with 80% capacity retention at 1 C after 500 cycles which is far superior to its counterparts binary Mn‐based materials. The excellent cyclic performance is due to the remediation of the Jahn teller effect in sodium‐deficient entropy‐stabilized material. The structural reversibility, enhanced kinetics, and electronic properties are further studied in detail by in situ X‐ray diffraction (XRD), ex situ X‐ray photoelectron spectroscopy (XPS), and first principal calculations. Na 3.5 Mn(HE)//HC full cell delivered 89.7 mAh g −1 capacity at 0.2 C. This work sheds light on designing Mn‐based cathodes with superior electrochemical performance for wide energy storage applications.