Testing the Tube Super-Dielectric Material Hypothesis: Increased Energy Density Using NaCl

Abstract

The focus of the present work is the evaluation of the low-frequency dielectric performance of titanium dioxide nanotube arrays, created by anodization, filled with aqueous NaCl solutions. At low frequency (ca. <10 À2 Hz), capacitors made up of this so-called tube super-dielectric material were found to have extreme dielectric constants, greater than 1 billion. The same capacitors also registered unprecedented energy densities, nearly 400 J/cm 3 , better than that observed (<250 J/cm 3 ) for the same type of anodized titania filled with an aqueous solution of NaNO 3 , and about an order of magnitude better than commercial supercapacitors. Sufficient data were collected to propose a correlation relating dielectric thickness and salt concentration to overall energy density.

Performance of Aqueous Ion Solution/Tube-Super Dielectric Material-Based Capacitors as a Function of Discharge Time

“…In fact, in this and earlier studies, it was found that the capacitance is a function of voltage, leading to 'irregular wave forms' [8][9][10][11][12][13]. As discussed in earlier work, this indicates that the capacitance is voltage dependent, specifically decreasing as voltage increases.…”

“…0.05 mm thick, were anodized, as described elsewhere [8,9,[21][22][23], in an ethylene glycol solution containing small quantities of ammonium fluoride (0.25% w/w) and water (2.75% w/w), using a titanium cathode (2 cm distant from the anode) at a constant DC voltage of 40 V for 46 min. This process created a layer of cylindrical hollow titania tubes on the parent titanium, average length measured to be 7.7+/−0.4 μm [24], but for purposes of conservative computation of energy density and all other parameters, assumed to be 8 μm in length.…”

“…In this study, the intent was to focus only on the impact of the liquid phase composition, thus all the matrix material, that is the anodized titania, was produced using a single protocol and produced nearly identical anodized layers. Typical tubes formed from this process are very regular in structure and densely packed together [8,9,23,24]. They are all oriented with the long axis perpendicular to the surface of the parent foil.…”

“…The theory suggests that capacitors with graphene electrodes could have an ultimate energy density of ~800 J/cm 3 , a value far less than the current generation commercial lithium ion battery (~2200 J/cm Recently, a new type of 'supercapacitor' was invented, NP supercapacitors (NPS) with energy density rivaling the best prototype EDLC, but based on an entirely different paradigm [8][9][10][11][12][13][14]. Unlike EDLC that gain energy density through the use of high surface area electrodes with low dielectric value, NPS use low surface area electrodes and dielectrics with remarkably high dielectric constants, specifically super dielectric materials (SDM), that is materials with dielectric values greater than 10…”

“…SDM are composed of an 'active phase', such as salt dissolved in a liquid, and an 'inactive' mechanical phase such as anodized titania, T-SDM [8,9], high surface area porous refractory oxides, Powder-SDM [10][11][12], or even simple fabrics, Fabric-SDM [13], that hold the active phase in place. The theoretical basis of SDM [8,9] is that in an electric field the ions in solution travel to create dipoles, which are far longer (ca. 1 μm) than those found in solid dielectrics (ca.…”