Nanostructured Pseudocapacitors Based on Atomic Layer Deposition of V₂O₅onto Conductive Nanocrystal‐based Mesoporous ITO Scaffolds

Abstract

6717wileyonlinelibrary.com ability to attain high energy densities while maintaining high power densities. [ 1 ] Pseudocapacitors store charge through fast and reversible faradaic processes that involve surface or near-surface redox reactions. These charge storage mechanisms are different than those in traditional batteries because they are not limited by the diffusion of ions into the bulk material. Therefore, pseudocapacitors can offer several benefi ts when compared to batteries including fast charge/discharging within seconds, good charge/discharge cycling stability, and the ability to deliver >10× more power. [ 2 ] An ideal pseudocapacitor electrode architecture should comprise a redox-active material (e.g., a metal oxide) that has a nanodimensional structure to accommodate shorter ion diffusion lengths. In addition, the material should have a high surface area in order to maximize electrolyte accessible redox-active sites, and, have an open interconnected porosity to facilitate solvent diffusion to all of these redox-active sites. Finally, electrical conductivity should be integrated and wired into the redox-active component in order to simultaneously achieve both higher energy and power densities in one structure.The improvements to electrochemical energy storage resulting from building electrical conductivity into electrode materials are well established in the literature. Carbon-based materials such as carbon nanotubes (CNT) and graphene have been shown to act as good conductive platforms for the construction of composite electrodes. For example, CNTbased composites of manganese oxide (MnO 2 ), [ 3 ] titanium oxide (TiO 2 ), [ 4 ] tin oxide (SnO 2 ), [ 4 ] lithium manganese oxide (LiMn 2 O 4 ), [ 5 ] and V 2 O 5 [ 6-10 ] have been reported. Graphenebased composites of LiMn 2 O 4 , [ 5 ] iron oxide (Fe 3 O 4 ), [ 11 ] SnO 2 , [ 12 ] Ni(OH) 2 , [ 13 ] and MnO 2 [ 14 ] have also been produced as well as other carbon scaffolds with interesting architectures. [ 15,16 ] In addition to carbon-based conductors, metals have also been integrated into composite electrodes with unique architectures including an interpenetrated nickel inverse opal, [ 17 ] nanoporous gold, [ 18 ] nickel porous foams, [ 19,20 ] copper pillar arrays, [ 21 ] and stainless steel meshes. [ 22 ] In the examples above, the conductive component provided a network for good electrical transport Solution processing of colloidal nanocrystals into porous architectures using block co-polymer templating offers a simple yet robust route to construct materials with open porosity and high surface area. These features, when realized in materials that show effi cient redox activity and good conductivity, should be ideal for electrochemical energy storage because they allow for effi cient electrolyte diffusion and ample surface and near-surface redox reactions. Here, a route to synthesize nanoporous pseudocapacitors is presented using preformed ITO nanocrystals to make a conductive scaffold, coated with a conformal layer of vanadia deposited using atomic ...

Electrochemical kinetics of nanostructure LiFePO 4 /graphitic carbon electrodes

“…Differently from MnO 2 [4,5], TiO 2 [6] or Nb 2 O 5 [16], this pseudocapacitive behavior is extrinsic in origin, since it is related to the presence of Fe 3+ defects in the structure [15,21,22]. To get further insights on the electrochemical reaction kinetics in the two different potential ranges (peaks A and B), we divided the total current into two contributions such as proposed by Dunn's group [15,16,26,27]. One part of the current comes from semi-infinite diffusion processes and changes with v 1/2 and the other is related to capacitive (surface) processes and varies linearly with v. Therefore, the current response (I) at a fixed potential (V) can be described as the combination of these two separate mechanisms (Eq.…”

Atomic layer deposition of vanadium oxide thin films from tetrakis(dimethylamino)vanadium precursor

“…5 V 2 O 5 also has a fairly wide scope of applications. Examples include cathode materials for lithium-ion batteries 6 and sodiumion batteries, 7 active materials for supercapacitors, 8,9 charge-injection-layer materials for field-effect transistors, 10 and catalysts for organic synthesis.…”

“…Over the years, various preparation approaches have been developed for VO x thin films, such as sol-gel, 12 spray pyrolysis, 13 electrodeposition, 14 evaporation, 15 magnetron sputtering, 16 pulsed laser deposition, 17 chemical vapor deposition, 18 and atomic layer deposition (ALD). 6,8,[19][20][21][22][23][24][25][26][27][28][29][30][31][32] Among these approaches, ALD is of particular interest for preparing thin films. ALD employs alternate saturated self-limiting surface chemistry reactions, and allows one to deposit thin films in a well-controlled layer-by-layer fashion.…”

“…33 The properties of ALD films, such as composition, crystal structure, and morphology, are highly consistent, reproducible, and uniform over large area, and meanwhile the thickness of deposited films can be precisely controlled at an atomic level by digitally adjusting the total ALD cycles. Moreover, ALD also allows for conformal thin-film coating on high aspect-ratio 3D structures, which is essential for realizing the above-mentioned high-performance batteries/supercapacitors applications 6,8,9 as well as various other applications. [34][35][36] ALD of VO x has been reported using several types of vanadium precursors.…”

“…[34][35][36] ALD of VO x has been reported using several types of vanadium precursors. Vanadyl triisopropoxide was a commonly used vanadium precursor, 6,8,[19][20][21][22][23] and was applied for both thermal (with water 6,[19][20][21] or ozone 8,22 ) and plasma-enhanced 23 ALD processes. A similar precursor, vanadium n-propoxide, could also be used along with acetic acid to produce ALD V 2 4 ] was described with water or ozone for depositing VO x thin films.…”