Mar
29
Ultracapacitors Get Really Disruptive Technology
March 29, 2013 | 2 Comments
Ionova Technologies, Inc. reports that its zinc-ion-based ZIP-Cap asymmetric ultracapacitor is expected to provide a huge improvement in ultracapacitor design. Tracking into the two notorious problems of cost and density Ionova has announced a 25-fold improvement in build costs and a 5-fold improvement in energy density. These are major improvements, especially for consumers building power dense products.
The ZIP-Cap is said to offer energy density up to 35Wh/L. They would be manufactured without the ultra-pure materials or expensive “dry-room” facilities that are necessary to build today’s commercial ultracapacitors. Today’s ultracapacitors exist only in rarified markets. Ionova looks to change that.
Ionova’s asymmetric ultracapacitor isn’t symmetric, meaning the anode and cathode are completely different instead of the same. The ZIP-Cap achieves greater energy density compared to 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 Compared to EDLC graphic describing the ZIP-Cap architecture and how it differs from that of the EDLC. Click image for the largest view.
The ZIP-Cap technology 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.
Typically asymmetric ultracapacitors designs are based on non-aqueous electrolytes provide improvements in energy density but they do so at the expense of power density while providing no improvement in cost, safety or in environmental impact.
Thus, Ionova researched aqueous (water-based) asymmetric ultracapacitors that 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.
The research is partner based. Ionova used a Department of Energy Phase II Small Business Technology Transfer from 2010 to partner with Dr. Jim P. Zheng of Florida State University.
The team went to work to further develop an asymmetric ultracapacitor with water-based electrolytes based on a 3-dimensional nanofilm oxide cathode (3DN) investigated during the preceding Phase I program. The Phase I program set out to 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. Click image for the largest view.
Fraser Seymour, Ionova founder and CEO explains that during the course of work on the first 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.
They discovered ionic hydrogen evolves on the surface of the asymmetric ultracapacitor (AUC) throughout the interior of the macro-scale electrode and nanoscale AUC particle interior which, when the electrode potential is increased during cell discharge, the hydrogen is oxidized that in turn causes a “pseudo-capacitive” effect, Seymour explained. 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 a charge accumulates, causing capacitance fade over accumulating cycles.
Mr. Seymour points to the issue for product builders saying, “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.”
With this in mind Ionova investigated some new anode materials. However, the characteristics of the metal/ion pseudo-capacitor architecture or MIP-Cap, proved too desirable and the MIP-Cap was chosen for further development.
Seymour describes the design and astonishing result, “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 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.”
How about this: 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 minus 50 °C.
Seymour said that Ionova sees the ZIP-Cap as useful in 12-volt start-stop hybrid vehicles (in versions above 35Wh/L) and high-power 400-volt electric vehicle applications, in power distribution for automotive, aerospace and computing applications, and in a number of roles in renewable systems and grid applications.
Ionova is actively pursuing opportunities for the ZIP-Cap and will be presenting at the upcoming National Innovation Summit in May.
Seymour and his Ionova may just be the solution for much more electric vehicle and electric bicycle sales.
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Seymour and his Ionova may just be the solution for much more electric vehicle and electric bicycle sales.
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