A Multielectron-Reaction and Low-Strain Na<sub>3.5</sub>Fe<sub>0.5</sub>VCr<sub>0.5</sub>(PO<sub>4</sub>)<sub>3</sub> Cathode for Na-Ion Batteries
Han Li, Yao Wang, Xudong Zhao, Junteng Jin, Qiuyu Shen, Jie Li, Yukun Liu, Yukun Liu, Xuanhui Qu, Lifang Jiao, Yongchang Liu, Yongchang Liu
Abstract
Natrium superionic conductor (NASICON)-type phosphates have attracted widespread attention as cathodes for sodium-ion batteries (SIBs) due to their 3D open frameworks facilitating Na + diffusion, but they are characterized by mediocre energy density or rapid capacity decay. Herein, we delicately design a multielectron-reaction and low-strain Na 3.5 Fe 0.5 VCr 0.5 (PO 4 ) 3 /C cathode material featuring a high working voltage (∼3.43 V), high reversible capacity (148.5 mAh g –1 ), and high cycling stability (95.1% capacity retention over 2000 cycles). The deviation in the reaction potential of each redox couple (Fe 2+ /Fe 3+, V 3+ /V 4+ /V 5+, and Cr 3+ /Cr 4+ ) efficaciously alleviates the lattice strain accumulation, ensuring a small cell volume variation of 3.87% during the highly reversible charge–discharge processes, as confirmed by systematic in situ / ex situ analyses. Moreover, the fast reaction kinetics and the unexpected reversible Na1-ion (6b site) release/uptake are elucidated via multiple electrochemical characterizations and theoretical computations. This rational design strategy of incorporating versatile redox couples with different roles will broaden the horizons of high-performance NASICON-type cathodes.