Investigation of Fumed Silica/Aqueous NaCl Superdielectric Material

Abstract

A constant current charge/discharge protocol which showed fumed silica filled to the point of incipient wetness with aqueous NaCl solution to have dielectric constants >108 over the full range of dielectric thicknesses of 0.38–3.9 mm and discharge times of 0.25–>100 s was studied, making this material another example of a superdielectric. The dielectric constant was impacted by both frequency and thickness. For time to discharge greater than 10 s the dielectric constant for all thicknesses needed to be fairly constant, always >109, although trending higher with increasing thickness. At shorter discharge times the dielectric constant consistently decreased, with decreasing time to discharge. Hence, it is reasonable to suggest that for time to discharge >10 s the dielectric constant at all thicknesses will be greater than 109. This in turn implies an energy density for a 5 micron thick dielectric layer in the order of 350 J/cm3 for discharge times greater than 10 s.

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.…”

“…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.…”

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

“…For example, several alumina powders mixed and filled with salt (NaCl) water were found to have dielectric constants as much as seven orders of magnitude higher than that of the best dielectric, barium titanate. 1,2,4 More recently, a second type of SDM, tube SDM (T-SDM), was built and tested. 3 These were transition metal oxide nanotube arrays, created by anodization of a metal foil substrate, and filled with aqueous salt solutions.…”

“…[1][2][3][4] These dielectric materials are made up of porous, electrically insulating solids in which the pores are filled with liquids containing ionic species (e.g., water with dissolved salt). The SDM hypothesis is that any porous dielectric material filled with a liquid phase containing ions in solution will have very high dielectric values, at least at low frequency, by virtue of the separation of ions/dipole formation in the liquid phase induced by an applied field.…”