Valence‐Optimized Vanadium Oxide Supercapacitor Electrodes Exhibit Ultrahigh Capacitance and Super‐Long Cyclic Durability of 100 000 Cycles

Advanced Energy Materials

et al. 2017

121

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...

Section: Figure 2asupporting

confidence: 70%

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

Cao

Pan

Advanced Energy Materials

et al. 2017

121

“…The shapes of the CV curves are roughly rectangular mirror images characteristic, which indicates ideal capacitive behaviour and good high-rate capability [16,17]. cycling at a current density of 7 Ag -1 .The specific capacitance of the MwAF electrode continuously increases in the initial cycles, which is due to the electrochemical active process of electrodes [18,19]. During the first 5000 cycles, its specific capacitance increases from 191.1 F g -1 to 312 F g -1 , showing an 170 % retention.…”

Section: Resultsmentioning

confidence: 79%

Welded-Ag-nanowires/FTO conducting film with high transmittance and its application in transparent supercapacitors

Qiao

Yang

IOP Conf. Ser.: Mater. Sci. Eng.

et al. 2017

Enhancement of the electrical properties of silver nanowire transparent conductive electrodes by atomic layer deposition coating zinc oxide Anh-Tuan Pham, Xuan-Quang Nguyen, Duc-Huy Tran et al. Abstract. Silver nanowires (AgNW)with a small diameter weresynthesized by a facile and novel polyol reduction method. Ag nanowires ink was then spun on the surface of F-doped SnO 2 (FTO) to form the AgNW/FTO conducting film. Welding treatment of the AgNW/FTO conducting film not only increased the optical transmittance from 71.9 % to 79.3 % at 550 nm and decreased the sheet resistance from 11.4 ohm sq -1 to 9.8 ohm sq -1 , but also improved the adhesivity of AgNW network on FTO substrate. Furthermore, MnO 2 nanosheets were directly deposited on welded-AgNW/FTO (wAF) substrate to prepare a transparent MnO 2 /weledAgNW/FTO (MwAF) composite electrode. The MwAF electrode displayed excellent electrochemical performance, including high specific capacitance (375 F g -1 at 5 mV s -1 ) and superior cycle stability (173.3 % of the initial capacitance after 20000 GCD cycles).

“…Many mixed valence VO x have been discovered for pseudocapacitors, such as V 2 O 3 / rGO/VO 2 , [199] V 2 O 3 /VO 2 @C, [200] hydrated VO x (2 < x < 2.5), [201] hydrated V 6 O 13 /V 2 O 5 , [202] VO x (1.5 < x < 2.5), [203] and Ti-doped VO x (2 < x < 2.5). [204] However, it was difficult to tell what the influence of different oxidation states is.…”

Section: Vanadium Oxide Nanocomposites In Pseudocapacitorsmentioning

confidence: 99%

Recent Advances in Nanostructured Vanadium Oxides and Composites for Energy Conversion

Advanced Energy Materials

Tang

et al. 2017

227

127

Vanadium oxides are known for their multioxidation states and diverse crystalline structures. Owing to their excellent interactions with molecules or ions, outstanding catalytic activities, and/or strong electron–electron correlations, nanostructured vanadium oxides have been extensively studied for energy conversion in the recent years. Here is a review of the recent advances in the development of nanostructured vanadium oxides and their applications. The synthesis strategies and structural properties of various vanadium oxide nanostructures, including vanadium dioxide (VO2), vanadium pentoxide (V2O5), and others, are summarized. The applications of vanadium oxides in energy conversion are discussed, focusing on three important types of energy sources: chemical energy (LIBs, pseudocapacitors and fuel cells), solar energy (photovoltaics and photocatalytic hydrogen evolutions), and heat (thermoelectric generation). Finally, conclusion with our remarks on the prospects of nanostructured vanadium oxides in energy conversion are provided.