Ionova Technologies says ZIP-Cap ultracapacitors can offer 5x increase in energy density and 25x reduction in build cost (updated with graphic)
|Sketch describing the ZIP-Cap architecture and how it differs from that of the EDLC. Source: Ionova. Click to enlarge.|
Ionova Technologies, Inc. reports that its zinc-ion-based ZIP-Cap asymmetric ultracapacitor is expected to provide a 25-fold reduction in build cost and a 5-fold increase in energy density (up to 35Wh/L) without the ultra-pure materials or expensive “dry-room” facilities that are necessary to build today’s ultracapacitors.
Asymmetric ultracapacitors achieve greater energy density versus today’s Electric Double Layer Capacitors (EDLCs) by combining one activated carbon EDLC ion-adsorption electrode with one ion-insertion (battery-like) electrode. ZIP-Cap is based on Ionova’s metal/ion pseudo-capacitor (MIP-Cap) architecture and 3-D Nanofilm technology developed under research programs with the US Department of Energy, NASA and the Naval Research Lab.
Asymmetric ultracapacitors based on non-aqueous electrolytes provide improvements in energy density but they typically do so at the expense of power density while providing no improvement in cost, safety or in environmental impact.
Alternatively, aqueous (water-based) asymmetric ultracapacitors can provide improvements not only in cost, safety and in some cases, environmental impact, but can also provide greater energy and power densities than the non-aqueous approach.
Under a FY 2010 Phase II Small Business Technology Transfer (STTR) from the DOE, Ionova partnered with Dr. Jim P. Zheng of Florida State University to further develop an asymmetric ultracapacitor with water-based electrolytes based on a 3-dimensional nanofilm oxide cathode (3DN) (investigated during a preceding Phase I program) that would preserve the cycle life and temperature performance of an EDLC while providing the following characteristics at the multi-cell module level:
|Ionova Phase II STTR project objectives|
|Energy density (Wh/L)||20||3.75||>500%|
|Specific energy (Wh/kg)||10||3||>300%|
|Power density (W/L)||2500||812||>300%|
|Specific power (W/kg)||1500||650||~250%|
|Selling price ($/Wh)||2.2-3.5||2.17||10x better than EDLC|
During the course of work on the DOE-funded program, Ionova found a problem with the double-layer charge storage mechanism in the activated carbon anode that resulted in capacitance fade over cycling, said Fraser Seymour, Ionova founder and CEO.
They found that ionic hydrogen is evolved on the surface of the AC throughout the interior of the macro-scale electrode and nanoscale AC particle interior which, when the electrode potential is increased during cell discharge, is oxidized which causes a “pseudo-capacitive” effect, Seymour said. While this does increase capacitance, it demands the anode be brought back to open circuit potential of the carbon (0 volts for the cell) or charge accumulates, causing capacitance fade over cycling.
This can be a big problem for users of an ultracapacitor since DC-DC converters necessary to most ultracap applications require cell voltage be maintained above 1/2 full cell voltage. While emerging new converters permit deeper discharge, this is actually a problem with commercial EDLCs as well so systems designers should look carefully at the testing protocols used by ultracapacitor manufacturers if they expect the advertised cycle life.—Fraser Seymour
As a result, Ionova investigated some new anode materials, but ultimately decided to pursue the metal/ion pseudo-capacitor architecture (MIP-Cap).
The MIP-Cap can use any cathode material including our 3-D Nanofilm, other functionalized nanocarbons we have developed, or other materials altogether like carbon nanotubes, graphene etc. The novelty of the MIP-Cap is in pairing capacitive behavior with the an M/M+ anode; there is no physical anode per se. Rather, the anode is ionic species as part of a multifunctional electrolyte. Upon charge, these ions are reduced to metal on the anode current collector, and dissolved back into the electrolyte upon oxidation during discharge. Massive electrochemical capacity results.
While the MIP-Cap architecture is independent of chemistry, we have chosen the aqueous zinc chemistry to form the ZIP-Cap. By doing so, we enable ultracapacitors with up to 35Wh/L (5x EDLC) and 25x lower build cost vs. EDLCs—addressing the two most prominent ultracapacitor weaknesses. And this chemistry and architecture allow low-cost, ultra large scale manufacturing facilities used for electrolytic capacitors as well as lead/acid and alkaline batteries to be leveraged.—Fraser Seymour
ZIP-Cap has demonstrated 50,000 charge cycles with a coulombic efficiency above 98% and without degradation of capacitance or resistance. In some configurations, ZIP-Cap could offer a power density of up to 5 kW/kg, Seymour said. ZIP-Cap is expected to provide 1 million charge cycles and withstand temperatures to –50 °C. Ionova is actively pursuing opportunities for the ZIP-Cap and present at the upcoming National Innovation Summit in May.
Seymour said that Ionova sees the ZIP-Cap as enabling to traction uses in 12V start-stop hybrid (in versions above 35Wh/L) and high-power 400V HEV applications, in power distribution for automotive, aerospace and computing applications, and in a number of roles in renewable/grid applications.