Activating the Inert Na1 Sites in Na₂FePO₄F Toward High Performance Sodium Storage

Abstract

Na2FePO4F, an iron‐based fluorophosphate with facile 2D sodium ion channels, is considered as a promising cathode material for sodium‐ion batteries because of low cost, resource abundance, and nontoxicity. However, its application is considerably restricted by the limited intrinsic electronic conductivity and specific capacity. Herein, a doping strategy represented by Cu2+ is proposed to boost the electrochemical performance, attributed to the derivation of a new active Na3 site originated from the inert Na1 site and the band gap reduction due to the d‐orbital hybridization. Consequently, the as‐obtained Na2Fe0.95Cu0.05PO4F/C composite can deliver an excellent rate capacity of 74 mAh g⁻1 at 20 C and a decent specific capacity of 119 mAh g⁻1 at 0.1 C, which is superior to the previously reported Na2FePO4F‐based cathode materials. This study sheds new light on developing high performance fluorophosphates cathode materials via regulating the Na site and electronic structure.

Atomic Manufacturing in Electrode Materials for High-Performance Batteries

“…This can change the electronic structure and surface activity of the original inert sites, thus regulating the reaction activity of the site. The crystal structure of Na 2 FePO 4 F contains two kinds of Na sites in the Na layer, denoted as active Na2 and inert Na1 (Figure a) . When doping Cu atoms, a portion of the original Na1 sites transforms into the newly formed Na3 site, resulting in an average bond length of Na–O/F from 2.50 to 2.52 Å (Figure b).…”

“…(b) Depiction of the Na 3 environment deriving from Na1 in FeCu-0.05. (c) Cycling performance at 10 C. Reproduced with permission from ref . Copyright 2023 Wiley-VCH.…”

“…The crystal structure of Na 2 FePO 4 F contains two kinds of Na sites in the Na layer, denoted as active Na2 and inert Na1 (Figure 3a). 65 When doping Cu atoms, a portion of the original Na1 sites transforms into the newly formed Na3 site, resulting in an average bond length of Na−O/F from 2.50 to 2.52 Å (Figure 3b). This observation suggests that the electrochemical activity of Na + at the Na3 site is higher compared to that at the Na1 site.…”

First-Principles Studies on the Structural and Electronic Properties of α-Na2FePO4F with Strong Antisite Disorder

“…However, the poor intrinsic conductivity and limited active sodium sites of β-Na 2 FePO 4 F make its rate capability and reversible capacity unsatisfactory. Huang et al proposed a doping strategy represented by Cu 2+ to improve the electrochemical performance, and the prepared Na 2 Fe 0.95 Cu 0.05 PO 4 F/C composites showed better electrochemical performance than the previously reported Na 2 FePO 4 F . Jin et al found that the average voltage could be increased, and the band gap and the Na ion diffusion barrier could be reduced by co-doping four metal elements (Ti, Co, Ni, and Sn) .…”

“…23 However, the poor intrinsic conductivity and limited active sodium sites of β-Na 2 FePO 4 F make its rate capability and reversible capacity unsatisfactory. chemical performance than the previously reported Na 2 FePO 4 F. 24 Jin et al found that the average voltage could be increased, and the band gap and the Na ion diffusion barrier could be reduced by co-doping four metal elements (Ti, Co, Ni, and Sn). 25 Kacemi et al found that Mn doping could significantly increase the conductivity and voltage of β-Na 2 FePO 4 F, resulting in a high-energy density SIB cathode.…”