Pumpable electrons to drive gasoline into oblivion?

24M also claims that by using fluids of much higher energy density than aqueous chemistries, it can produce a more cost-competitive flow battery system for gridscale storage.

Cambridge Crude technology
The official name for the Cambridge Crude technology is the semi-solid flow cell (SSFC), because of the high viscosity of the liquid and its similarity, in some respects, to fuel cells. SSFCs aim to combine the high energy density of rechargeable batteries with the scalability of fuel cells and the longevity of flow batteries. Although 24M is holding back many of the details of its process to avoid tipping off competitors before commercialization, the underlying principle of SSFCs is to store the liquid charge-transfer compounds in suspensions of solid storage compounds that are sufficiently dilute to percolate through networks of nanoscale anodes and cathodes.

One disadvantage of SSFCs compared with traditional batteries is that they rely on a complex system of mechanical pumps, sensors and control units that move the Cambridge Crude from the "gas tank" to a secondary containment vessel for spent fuel.

Also, the energy densities of flow batteries in general have been much lower than that of high-performance Li-ion battery packs, and thus far even 24M's most advanced prototypes are no exception. The startup also admits that the electrical conductivity of the spontaneously forming carbon nanoparticle networks needs to be improved a hundredfold to foster widespread adoption.

Cambridge Crude (in bottle) is a liquid electrolyte that flows through a reactor, where a copper electrode (top) and an aluminum electrode (bottom) extract electrons to power an electric motor or any other dc load. Source: MIT

But 24M claims to have seminal technologies in the works that will solve all of Cambridge Crude's shortcomings over the next five years.

The company says the advantages of SSFCs make them worth the risk for 24M's investors. It claims to have solved the longevity problems that nixed General Motors' foiled billion-dollar effort to develop automotive fuel cells (see sidebar, page 24) with a technology that offers twice the energy density of traditional batteries and 10 times the energy density of competing flow battery designs.

For instance, SSFCs separate the power-producing and energy-storage components, allowing each to be scaled separately for specific applications. Also, SSFCs' life cycle will be longer than those of all currently competing technologies, because SSFCs don't rely on solid-phase changes that can fatigue.

Further, their architecture does not require subdivision into cells, whereas conventional batteries must be divided into multiple 1.5-V cells.

SSFCs reportedly retain the good characteristics of traditional batteries, fuel cells and other flow battery designs. Like Li-ion batteries, SSFCs have a quick response time; like fuel cells, they release no harmful emissions into the environment; and like other flow battery designs, they can be scaled in size to suit apps from mobile devices to power generation utilities.

24M plans to work with A123 to bring out advanced commercial SSFC designs for those two markets at opposite ends of the size spectrum, and various others in between.

- R. Colin Johnson
??EE Times

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