Chemical Synthesis of 3D Graphene‐Like Cages for Sodium‐Ion Batteries Applications

Abstract

sodium hosts. Among these, sodium (Na) super ion conductor (NASICON) structured Na 3 V 2 (PO 4 ) 3 (NVP) is a good candidate cathode material due to its excellent structural stability, good thermal stability, and high energy density. [18,32] In addition, the NASICON structure also has an open 3D framework and large interstitial channels for fast Na + ion diffusion. However, similar to other polyanion compounds (i.e., Li 3 V 2 (PO 4 ) 3 and K 3 V 2 (PO 4 ) 3 ), [33,34] NVP suffers from intrinsically inferior electronic conductivity (about 10 −9 S cm −1 ).Two key strategies are applied to improve the conductivity of NVP. First, nanostructured NVP has been demonstrated to improve the sodium ion diffusion kinetics due to the reduced ion diffusion distance. [35][36][37] Zhou et al. reported template-assisted synthesis of nanostructured NVP 3D foams, which exhibit a capacity of 73 mA h g −1 at a rate of 100 C. [35] An et al. prepared NVP/C nanoflakes with high rate capability and excellent cycling stability. [36] Making NVP and carbon composites can also improve the electronic conductivity and electrochemical performances. Saravanan et al. reported the preparation of porous NVP/C with good rate capability and long cycle life (30000 cycles at 40C). [38] Zhu et al. designed NVP embedded in a porous carbon matrix with high rate capability of 44 mA h g −1 at 200C. [39] Klee et al. recently reported an oleic acid-based surfactant-assisted solid reaction method, which produced a uniform carbon coating on NVP nanoparticles and improved properties. [40] In addition, graphite-like carbon coating was applied by chemical vapor deposition or mechanical mixing. [21,22,[41][42][43] Herein, we report a detailed study of the formation of graphene-like cages structures on NVP nanoflake (NVP-NFs) arrays using the solid-state reaction approach in a molten surfactant-paraffin media. [44,45] As illustrated in Figure 1a, The NVP nanoflakes are uniformly capped with a graphene-like carbon layer, which are in situ generated in the calcination process. The graphene-like layers are connected each other to form a 3D conductive carbon network. The unique architecture provides a large contact area between electrode and electrolyte and fast electron diffusion pathway. As a cathode material for SIBs, the NVP-NFs encapsulated in the 3D graphene-like cages manifest close to theoretical capacity, excellent rate capability, and ultralong-life cycling performance. In addition, the NVP can Sodium (Na) super ion conductor structured Na 3 V 2 (PO 4 ) 3 (NVP) is extensively explored as cathode material for sodium-ion batteries (SIBs) due to its large interstitial channels for Na + migration. The synthesis of 3D graphene-like structure coated on NVP nanoflakes arrays via a one-pot, solid-state reaction in molten hydrocarbon is reported. The NVP nanoflakes are uniformly coated by the in situ generated 3D graphene-like layers with the thickness of 3 nm. As a cathode material, graphene covered NVP nanoflakes exhibit excellent electrochemical performances, includ...

Micro/Nanostructured Materials for Sodium Ion Batteries and Capacitors

“…e) Schematic illustration of the fabrication process and the proposed formation mechanism of 3D graphene‐capped NVP‐NFs. f) Galvanostatic discharge profiles from 1 to 200 C. Reproduced with permission . Copyright 2017, Wiley‐VCH.…”

“…The well‐interconnected structure guaranteed a remarkable reversible capacity of 94 mA h g −1 at 100 C. In addition to the self‐assembly of low‐dimensional nanomaterials, the construction of 3D conductive carbon networks is also common. Recently, Cao et al developed NVP nanoflake arrays (NVP‐NFs) coated with 3D graphene‐like carbon cages via a solid‐state reaction in a molten surfactant‐paraffin medium . In the sintering process, the highly polar groups of the surfactant were linked to the Na–V–P complex, and the nonpolar tails were exposed to the paraffin medium, as shown in Figure e.…”

Pseudocapacitive Vanadium‐based Materials toward High‐Rate Sodium‐Ion Storage

“…This phase transformation displays distinct redox couple peaks in the cyclic voltammogram (CV) ( Figure 1d) and plateaus in the galvanostatic (GV) charge-discharge profiles. [21] Typical battery-type sodium-ion intercalation materials include Na 3 V 2 (PO 4 ) 3 [21,22] and NaTi 2 (PO 4 ) 3 . [23] In contrast, pseudocapacitive materials present a highly reversible, nearly linear dependence of oxidation state change with potential.…”

“…Sodium vanadium phosphate, Na 3 V 2 (PO 4 ) 3 (NVP), is a battery‐type intercalation material that undergoes two‐phase transformation reactions accompanied with reversible Na + intercalation and extraction. [ 21 ] The CV curves (Figure 1d) show very distinct redox couple peaks that shift considerably with a gradual increase in sweep rate, indicating an increase in overpotential. Figure 1e shows the linear relationship between the peak current vs. the square root of sweep rate () for NVP, which is indicative of a b ‐value of 0.5.…”

Nonaqueous Sodium‐Ion Full Cells: Status, Strategies, and Prospects

“…The average voltage of a full cell assembled by Liang et al is 2.7 V, which combined with a graphene anode and a graphene‐covered Na 3 V 2 (PO 4 ) 3 cathode. At 0.1 C, an initial discharge capacity of 109.2 mA h g −1 can be achieved with a capacity retention of 77.1% after 200 cycles . By tailoring the particle size of Na 3 V 2 (PO 4 ) 3 , the average voltage of the full cell based on HC anode was significantly increased from 2.8 to 3.3 V .…”