Refillable liquid batteries may empower electric vehicles

A novel battery technology stores energy in what researchers are calling "rechargeable fuel"—electrodes in liquid form. The result can be either recharged like a conventional battery or replaced by pumping in new fuel like gasoline. The materials could theoretically allow an electric car to travel 500 miles on a charge, five times farther than most electric vehicles can now, say the researchers developing the technology, who are based at Argonne National Laboratory and the Illinois Institute of Technology. Replacing them at a fueling station would take just a few minutes. In contrast, even the fastest charging stations for conventional batteries take an hour to provide a full charge. Limited driving range and long recharging times are two of the biggest challenges for electric cars. Liquid battery electrodes could allow longer range by increasing the amount of energy battery packs can store, and because fewer non-energy-storing components would be needed, it could also make them cheaper.

Batteries that use liquid electrodes could also be safer than conventional ones, says Ping Liu, a program manager at the Advanced Research Projects Agency for Energy, which is funding the work. Positive and negative electrode materials would be stored in separate tanks, rather than inside the same battery cell as in conventional batteries. This could prevent the short circuits and overheating that can cause lithium-ion batteries to catch fire. Rechargeable fuels are at an early stage, but ARPA-E has deemed them promising, announcing funding for four groups that are developing the technology. In addition to the Illinois project, it is backing projects at GE, the National Renewable Energy Laboratory, and 24M, an MIT spinoff.

The Illinois researchers have so far demonstrated a small "half-cell" battery that uses one fluid electrode and one solid one. For their $3.4 million ARPA-E-funded project, which started last month, they plan to build a prototype that uses liquids for both the positive and negative electrodes. This battery should store one kilowatt-hour of energy, enough for a few miles of driving. In conventional electric-car batteries, as much as 75 percent of the material inside a battery pack consists of components that don't store energy—cell packaging, sensors, electrical connections, cooling systems, and so on. With fluid energy storage, at least in theory, much of that material can be eliminated, decreasing the size and cost of battery packs.