"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 & AP;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.