“Win‐Win” Scenario of High Energy Density and Long Cycling Life in a Novel Na3.9MnCr0.9Zr0.1(PO4)3 Cathode

The development of high‐energy and long‐lifespan NASICON‐type cathode materials for sodium‐ion batteries has always been a research hotspot but a daunting challenge. Although Na4MnCr(PO4)3 has emerged as one of the most promising high‐energy‐density cathode materials owing to its three‐electron reactions, it still suffers from serious structural distortion upon repetitive charge/discharge processes caused by the Jahn‐Teller active Mn3+. Herein, the selective substitution of Cr by Zr in Na4MnCr(PO4)3 was explored to enhance the structural stability, due to the pinning effect of Zr ions and the ≈2.9‐electron reactions, as‐prepared Na3.9MnCr0.9Zr0.1(PO4)3/C delivers a high capacity retention of 85.94% over 500 cycles at 5 C and an ultrahigh capacity of 156.4 mAh g−1 at 0.1 C, enabling the stable energy output as high as 555.2 Wh kg−1. Moreover, during the whole charge/discharge process, a small volume change of only 6.7% was verified by in situ X‐ray diffraction, and the reversible reactions of Cr3+/Cr4+, Mn3+/Mn4+, and Mn2+/Mn3+ redox couples were identified via ex situ X‐ray photoelectron spectroscopy analyses. Galvanostatic intermittent titration technique tests and density functional theory calculations further demonstrated the fast reaction kinetics of the Na3.9MnCr0.9Zr0.1(PO4)3/C electrode. This work offers new opportunities for designing high‐energy and high‐stability NASICON cathodes by ion doping. High energy density and long cycling life are simultaneously realized in a novel NASICON‐type Na3.9MnCr0.9Zr0.1(PO4)3/C cathode. The introduced Zr ions can firmly support the NASICON framework against structural distortion and enlarge the unit cell volume to facilitate the reversible Na+ extraction/insertion.