Abstract
Evidence is provided here that a class of materials with dielectric constants greater than 105 at low frequency (<10−2 Hz), herein called super dielectric materials (SDM), can be generated readily from common, inexpensive materials. Specifically it is demonstrated that high surface area alumina powders, loaded to the incipient wetness point with a solution of boric acid dissolved in water, have dielectric constants, near 0 Hz, greater than 4 × 108 in all cases, a remarkable increase over the best dielectric constants previously measured for energy storage capabilities, ca. 1 × 104. It is postulated that any porous, electrically insulating material (e.g., high surface area powders of silica, titania, etc.), filled with a liquid containing a high concentration of ionic species will potentially be an SDM. Capacitors created with the first generated SDM dielectrics (alumina with boric acid solution), herein called New Paradigm Super (NPS) capacitors display typical electrostatic capacitive behavior, such as increasing capacitance with decreasing thickness, and can be cycled, but are limited to a maximum effective operating voltage of about 0.8 V. A simple theory is presented: Water containing relatively high concentrations of dissolved ions saturates all, or virtually all, the pores (average diameter 500 Å) of the alumina. In an applied field the positive ionic species migrate to the cathode end, and the negative ions to the anode end of each drop. This creates giant dipoles with high charge, hence leading to high dielectric constant behavior. At about 0.8 V, water begins to break down, creating enough ionic species to “short” the individual water droplets. Potentially NPS capacitor stacks can surpass “supercapacitors” in volumetric energy density.
Highlights
There are several distinct capacitor technologies, and for understanding the import of the present work it is helpful to compare/contrast two types; “supercapacitors”, and traditional electrostatic capacitors [1]
The dielectric constant can be obtained from the time constant and this standard equation: C 0 R
From the plots of one multi-cycle data set (Figure 2) it is clear that in all cases below about 0.8 V at very low frequency the A-super dielectric materials (SDM) have nearly constant time constants, constant capacitance. Using these measured time constants, the resistance value, and the physical parameters of the capacitors the dielectric constants were computed for all three charge and discharge cycles
Summary
There are several distinct capacitor technologies, and for understanding the import of the present work it is helpful to compare/contrast two types; “supercapacitors”, and traditional electrostatic (or “ceramic”) capacitors [1]. Most of the volume of an EDLC is the high surface area electrode in the form of electrically conductive powder, a material for which “dielectric constant” is a meaningless parameter. EDLC/supercapacitor performance is generally reported as “per gram” or per unit volume This explains the recent interest in employing graphene in EDLC/supercapacitors [2,3,4], as graphene is arguably the “ultimate” material for creation of high surface area electrodes. It has a very high electrical conductivity and the measured surface of some graphene forms are near the theoretical limit (~2700 m2/g). Once the best EDLC/supercapacitors incorporate graphene, supercapacitor energy density will be near a theoretical limit, further significant energy density increase is unlikely
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