A phosphite-based layered framework as a novel positive electrode material for Na-ion batteries

Abstract

A phosphite-based layered polyanionic material, Na2[(VOHPO3)2(C2O4)]·2H2O, exhibits a superior rate performance (∼80 mA h g−1 at 10C rate) and a long-term cycling stability for 1000 cycles at 2C rate in Na cells.

Regulated Synthesis of α-NaVOPO4 with an Enhanced Conductive Network as a High-Performance Cathode for Aqueous Na-Ion Batteries

“…So far, considerable efforts have been expended on the families of cathode materials, including polyanionic compounds, − layered oxides, − and Prussian blue analogues. − In particular, V-based phosphates show favorable appeal with robust 3D structure, demonstrating high redox protentional and superior cycling performance, such as Na 3 V 2 (PO 4 ) 3 , , Na 3 (VOPO 4 ) 2 F, − Na 3 (VPO 4 ) 2 F 3 , , NaVPO 4 F, NaVOPO 4 , − and so forth. ,, Among them, the compound NaVOPO 4 crystallizes in three distinct crystallographic phases (α, β, and α I ), which exhibits distinguishable electrochemical behavior due to the differences in the spatial disposition of PO 4 tetrahedra and VO 6 octahedral units. , With respect to electronic structure, the density of states of the α-phase is similar to that of β and α I phases, showing semiconductor properties with wide band gap. , Also, they share the same theoretical capacity of 145 mA h g –1 with the whole de/intercalation of Na + ions. Turning to Na-ion diffusion features, α-phase NaVOPO 4 is proved to diffuse preferably in the 2D channels of a and c directions; α I -NaVOPO 4 with the layered structure shows favorable ion conductivity with 3D Na + moving pathways, whereas β-NaVOPO 4 exhibits insufficient performance derived from the 1D channels for Na + migration along the b axis. , In terms of material synthesis, the β and α I polymorphs were usually synthesized from the lithium counterparts through delithiation and intercalation with mediocre thermodynamical stability, and only α phase can be obtained via simple steps. ,, Combined with the aspects of performance and preparation, α-NaVOPO 4 can be regarded as a more accessible candidate for NIBs.…”

“…19−21 In particular, V-based phosphates show favorable appeal with robust 3D structure, demonstrating high redox protentional and superior cycling performance, such as Na 3 V 2 (PO 4 ) 3 , 22,23 Na 3 (VOPO 4 ) 2 F, 24−26 Na 3 (VPO 4 ) 2 F 3 , 27,28 NaVPO 4 F, 29 NaVOPO 4 , 30−32 and so forth. 12,33,34 Among them, the compound NaVOPO 4 crystallizes in three distinct crystallographic phases (α, β, and α I ), which exhibits distinguishable electrochemical behavior due to the differences in the spatial disposition of PO 4 tetrahedra and VO 6 octahedral units. 35,36 With respect to electronic structure, the density of states of the α-phase is similar to that of β and α I phases, showing semiconductor properties with wide band gap.…”

Transition Metal Oxalate-Based Materials: An Emerging Material Family for Alkali-Ion Battery Cathodes

“…Also, through the room-temperature solution-based method, Hameed et al synthesized the novel material Na 2 [(VOHPO 3 ) 2 (C 2 O 4 )]·2H 2 O . To improve the crystallinity of the material, it was reheated solvothermally in isopropyl alcohol at 150 °C for 2 h. When used as a cathode in SIBs, the material can exhibit a flat high-voltage platform at around 3.7 V, a discharge capacity of 101 mA h g –1 , and good cycling stability, especially for the ball-mill-treated samples (bm-NVPox) with enhanced kinetics (Figure a,b).…”

“…(c) Contour maps of in situ XRD during the first cycle and (d) charge/discharge profile during the in situ XRD measurement. Reproduced from ref . Copyright 2021 Royal Society of Chemistry.…”

TiO2 bunchy hierarchical structure with effective enhancement in sodium storage behaviors

“…For the anode material, it is divided into three types according to its charge and discharge mechanism. Alloying/dealloying materials, such as Sn, 6,7 Sb, [8][9][10] and P, [11][12][13] generally have serious volume changes in the process of sodiumization and de-sodiumization, which can easily lead to follow-up pulverization, endangering battery safety. The initial Coulombic efficiency of the conversion reaction electrode will be very low, and there will be a higher potential hysteresis.…”