A Multielectron-Reaction and Low-Strain Na3.5Fe0.5VCr0.5(PO4)(3) Cathode for Na-Ion Batteries

Natriumsuperionic conductor (NASICON)-type phosphates have attractedwidespread attention as cathodes for sodium-ion batteries (SIBs) dueto their 3D open frameworks facilitating Na+ diffusion,but they are characterized by mediocre energy density or rapid capacitydecay. Herein, we delicately design a multielectron-reaction and low-strainNa(3.5)Fe(0.5)V-Cr-0.5(PO4)(3)/C cathode material featuring a high working voltage(& SIM;3.43 V), high reversible capacity (148.5 mAh g(-1)), and high cycling stability (95.1% capacity retention over 2000cycles). The deviation in the reaction potential of each redox couple(Fe2+/Fe3+, V3+/V4+/V5+, and Cr3+/Cr4+) efficaciously alleviatesthe lattice strain accumulation, ensuring a small cell volume variationof 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 unexpectedreversible Na1-ion (6b site) release/uptake are elucidated via multipleelectrochemical characterizations and theoretical computations. Thisrational design strategy of incorporating versatile redox coupleswith different roles will broaden the horizons of high-performanceNASICON-type cathodes.

Automated summary

Natriumsuperionic conductor (NASICON)-type phosphates with 3D open frameworks have attracted attention as cathodes for sodium-ion batteries. However, they suffer from mediocre energy density and rapid capacity decay. In this study, a multielectron reaction and low-strain Na(3.5)Fe(0.5)V-Cr-0.5(PO4)(3)/C cathode material was designed, which exhibited high working voltage, high reversible capacity, and high cycling stability.