“<scp>Win‐Win</scp>” Scenario of High Energy Density and Long Cycling Life in a Novel Na<sub>3.</sub><scp><sub>9</sub>MnCr<sub>0</sub></scp><sub>.</sub><scp><sub>9</sub>Zr<sub>0</sub></scp><sub>.1</sub>(<scp>PO<sub>4</sub></scp>)<sub>3</sub> Cathode
Yao Wang, Yukun Liu, Yukun Liu, Pingge He, Junteng Jin, Xudong Zhao, Qiuyu Shen, Jie Li, Xuanhui Qu, Yongchang Liu, Yongchang Liu, Lifang Jiao
Abstract
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 Na 4 MnCr(PO 4 ) 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 Mn 3+ . Herein, the selective substitution of Cr by Zr in Na 4 MnCr(PO 4 ) 3 was explored to enhance the structural stability, due to the pinning effect of Zr ions and the ≈2.9‐electron reactions, as‐prepared Na 3.9 MnCr 0.9 Zr 0.1 (PO 4 ) 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 Cr 3+ /Cr 4+ , Mn 3+ /Mn 4+ , and Mn 2+ /Mn 3+ 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 Na 3.9 MnCr 0.9 Zr 0.1 (PO 4 ) 3 /C electrode. This work offers new opportunities for designing high‐energy and high‐stability NASICON cathodes by ion doping.