May 15, 2013

Shelving Energy Storage Project

This week I decided to shelve the energy storage project we've been working on. (I might come back to it at some point in the future, but for now it's on hold.) Ideally, I should have been blogging about progress all along, but most of the work we were doing was confidential, with the potential for patent applications at the end of this year.
Here is a brief summary of the progress we made. It's not meant to be a complete detailed description (that may follow when there's time/energy), but just an overview of the project.

In May 2012 I undertook a project to find a way to meet or exceed the energy density of gasoline with a rechargeable electric storage device. (Briefly, energy density is the measure of how many energy can be stored in an object with a certain weight, such a car battery or a tank of gas.)
Starting from a clean slate, I was open to using any technology that would achieve that goal. I researched a wide array of technologies and partnered with experts in the field to build prototypes and experiment in the lab.

Over the course of about a year we were able to complete four major iterations:

1. Ultra Capacitor

The idea here was to use novel geometries and materials to achieve much higher capacitance than had previously been reported. However, after many months of modeling, simulation, and research, it became clear that the theoretical limit of ultracapacitor energy density was actually not much higher than the current levels achieved in the lab, and nowhere near as dense as batteries. The net result was covered in a previous blog post: a paper detailing the practical limits of energy density in ultracapacitors.
FatCap-TestRig01.jpg FatCap-nacre05_01.jpg

2. High Temperature Solid Oxide Fuel Cell (Lithium-Air)

This was a novel approach to lithium-air electrochemistry that used a LiCl+KCl eutectic mixture as the anolyte, and lithium metal as the fuel. We submitted preliminary patent application (PPA) for this idea to the US patent office. Since we're no longer pursuing this idea, I've decided to make the PPAs publicly available:

High-Temp01.jpg High-Temp02.jpg

3. High Temperature Cell with Cuprous Oxide cathode

The idea here was to continue using the high temperature LiCl+KCl eutectic mixture as the electrolyte, but eliminate the fragile and expensive SOFC catholyte disks. We were also able to drop the projected operating temperature range from 850C to 450C. A layer of high surface area copper was placed in contact with the electrolyte and continuously oxidized by exposure to air.

Low Temperature Cell with Deep Eutectic Solvent

The idea here was to replace the corrosive high-temperature LiCl+KCl eutectic with a new electrolyte based on deep eutectic solvents (DES).
Low-Temp-Cu2O-01.jpg Low-Temp-Cu2O-02.jpg Low-Temp-Cu2O-03.jpg

The executive summary is that none of these techniques achieved the energy density we were hoping to attain. In future blog posts I may add more details here. Feel free to direct questions to me.

Posted by todd at May 15, 2013 09:51 AM