Achieving the Stable Structure and Superior Performance of Na₃V₂(PO₄)₂O₂F Cathodes via Na-Site Regulation

Abstract

Na 3 V 2 (PO 4 ) 2 O 2 F (NVPOF) is considered as a promising cathode material for sodium-ion batteries due to its high structural stability and high average operating voltage (3.8 V). However, its low electronic conductivity and slow sodium-ion diffusion kinetics hinder its practical application. Here, an approach of Na-site regulation is proposed to adjust the intrinsic Na + diffusion efficiency and electronic conductivity, thus improving the electrochemical performance of NVPOF. Guided by density functional theory calculations, we demonstrate that Na-site regulation can be subtly realized by accurate Li substitution on the Na2 site in NVPOF. The as-prepared Na 2.75 Li 0.25 V 2 (PO 4 ) 2 O 2 F (NLVPOF) shows an increase of 1.53 and 1.55 times in rate capability and capacity retention (500 cycles) than NVPOF, respectively. Such a simple and effective Na-site regulation provides a new avenue in constructing advanced Li/Na-ion cathode materials.

Ostwald Ripening Tailoring Hierarchically Porous Na3V2(PO4)2O2F Hollow Nanospheres for Superior High‐Rate and Ultrastable Sodium Ion Storage

“…[15][16][17][18][19] Moreover, better rate capability and lower electrode polarization in Na 3 V 2 (PO 4 ) 2 (O 2−2x F 1+2x ) series can be anticipated by reducing the F content to weaken the inductive effects and thus to facilitate the Na + migration in the lattice. [20][21][22] Therefore, Na 3 V 2 (PO 4 ) 2 O 2 F (abbreviated as NVPF) is highly desirable as cathode material for SIBs from the practical application of SIBs' point of view and investigations on the synthesis and performance of NVPF is strongly necessary. [23][24][25][26] Though encouraging attempts have been made to make its electrochemical performance up-to-date, such as conductive matrix coating, [27][28][29][30] nanostructure engineering, [31] as well as morphology optimization, [32] its poor rate capability due to its intrinsically low electronic conductivity still cannot satisfy the demands for practical applications.…”

3D Printing Flexible Sodium‐Ion Microbatteries with Ultrahigh Areal Capacity and Robust Rate Capability

“…[ 33 ] The high‐crystallinity NVPF demonstrated a uniformly cuboid shape with a length of 1–2 µm and width of 300 nm (Figure 1g,i and Figures S2a and S3a, Supporting Information), along with the uniform distribution of Na, V, P, O, and F (Figure S4, Supporting Information), and two distinct fringes with crystal spacing of 0.541 and 0.457 nm (Figure 1h), assigned to (101) and (110) planes, respectively. [ 34 ] Likewise, NTP nanoparticles were used as anode, also displaying the NASICON structure with 3D open pathways for ion transfer (Figure 1j). NTP with abundant mesopores was uniformly coated with an ≈2 nm thick carbon layer (Figure 1k–m, and Figures S2b, S3b, and S5, Supporting Information), which was conducive to the rapid conversion of ions and electrons.…”

Unfolding the structural features of NASICON materials for sodium‐ion full cells

“…The intrinsic electronic conductivity of NVOPF improved with ionic doping, carbon coating, and porous nanostructuring (Figure 13D). 55,[91][92][93][94][95][193][194][195] Ru-doped porous hollow spheres of Na 3 (VOPO 4 ) 2 F were synthesized using a solvothermal method. It delivered 116.8 mAh g −1 initial discharge capacity at 0.5 C, with an excellent rate capability of 84.1 mAh g −1 at 20 C. 91 Ru-doped NVOPF shows long-term cyclic stability by retaining 90.2% capacity after 1000 cycles and 65% retention after 7500 cycles at 20 C. The superior electrochemical performance is due to the RuO 2 conductive coating achieved by doping of Ru, and the hierarchical porous structure will also promote the good charge storage performance.…”

“…The intrinsic electronic conductivity of NVOPF improved with ionic doping, carbon coating, and porous nanostructuring (Figure 13D). 55,91–95,193–195 Ru‐doped porous hollow spheres of Na 3 (VOPO 4 ) 2 F were synthesized using a solvothermal method. It delivered 116.8 mAh g −1 initial discharge capacity at 0.5 C, with an excellent rate capability of 84.1 mAh g −1 at 20 C 91 .…”