It seems like new ideas for batteries are a dime a dozen these days, but one scheme at MIT has gotten a $7 million vote of confidence from the newly established federal agency ARPA-E (Advanced Research Projects Agency, Energy).
The technology is being patented and could lead to very large-scale commercialization, so MIT researcher Donald Sadoway will not discuss the details of the materials being used. But according to MIT's news service, both Sadoway and ARPA-E say the battery is based on low-cost, domestically available liquid metals that have the potential to shatter the cost barrier to large-scale energy storage as part of the nation's energy grid. In announcing its funding of Sadoway’s work, ARPA-E said the battery technology “could revolutionize the way electricity is used and produced on the grid, enabling round-the-clock power from America's wind and solar power, increasing the stability of the grid, and making blackouts a thing of the past."
A large, utility-owned system “doesn’t have to be crash-worthy; it doesn’t have to be ‘idiot-proof’ because it won’t be in the hands of the consumer'” says Sadoway. To keep costs down, the new liquid batteries that Sadoway and his team are designing use low-cost, abundant materials. The basic principle is to place three layers of liquid inside a container: Two different metal alloys, and one layer of a salt. The three materials are chosen so they have different densities that let them separate naturally into three distinct layers, with the salt in the middle separating the two metal layers —like novelty drinks with different layers.
The energy is stored in the liquid metals that want to react with one another but can do so only by transferring ions across the electrolyte, which results in the flow of electric current out of the battery. When the battery is being charged, some ions migrate through the insulating salt layer to collect at one of the terminals. Then, when the power is being drained from the battery, those ions migrate back through the salt and collect at the opposite terminal.
The whole device is kept at a high temperature, around 700 degrees Celsius, so that the layers remain molten. Sadoway says that in the full-scale version, the electrical current being pumped into, or out of, the battery will be sufficient to maintain that temperature without any outside heat source.
More info is at MIT's site: