Pumpable electrons to drive gasoline into oblivion?

24M's core technology was born of Chiang's seminal research at A123, which in turn was inspired by research he conducted at MIT for the Defense Advanced Research Projects Agency. A123 has an equity stake in 24M, a seat on its board and an emerging role in facilitating the development of its technology.

A123 will also hedge its bets by continuing to develop its advanced Li-ion batteries, which have a head start in the market but could eventually compete with 24M's more adventuresome approach.

"A123's nanophosphate technology excels in hybrids," said 24M president Throop Wilder, whereas

"all-electric vehicles require batteries that are cost-optimized for greater capacity and longer duration. This is 24M's sweet spot. Because our flow batteries separate power from energy, you build the [reactor] stack where energy extraction takes place for a specific horsepower requirement, then add storage tanks of a size to meet the desired range of the vehicle. That is the same model the internal-combustion engine uses, where the gasoline tank size determines the range of the vehicle, and the size of the engine how fast you can get there."

Traditional batteries vs. flow batteries
In a traditional battery, the solid electrolyte that bears the electrons is trapped inside the battery cells and is released by a chemical reaction at the electrodes. Flow batteries, by contrast, maintain the electrons in a liquid electrolyte that is pumped through a reactor to harvest the electrons.

Thus, instead of recharging, a flow battery merely refills its electrolyte "tank."

In addition to transcending the 1.5V limit of traditional battery cells, flow batteries house all the elements that wear out in the solid electrolyte and electrodes of a traditional battery's cells; only the pumps, sensors and reactor are subject to fatigue and require maintenance. Thus, long-term reliability is greatly enhanced.

Also, because it separates the battery capacity (tank size) from the power output (reactor size), the flow battery can be scaled for nearly any application, from micron-sized units for mobile devices to decameter-sized versions for municipal power stations.

DOE-funded projects have already produced flow batteries based on a variety of aqueous chemistries, such as vanadium redox and zinc halogen systems. All of these efforts, however, have energy density limitations that prevent them from meeting electric vehicle requirements, according to 24M. The company claims to have created the first "semi-solid" flow battery design, in which the electrodes store as much as 10 times the energy of aqueous chemistries by using liquid suspensions of the solid active materials used in lithium ion batteries, such as lithium-cobalt-oxide powder, along with nanoscale electroconductive carbons suspended in an alkyl carbonate electrolyte. The nanoscale carbon particles spontaneously form a conductive network in the fluid, providing a direct pathway for electrons to reach the batteries' current-collecting electrodes.

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