A research team led by the Department of Energy’s Pacific Northwest National Laboratory (PNNL) demonstrated what they said is a new design for a grid energy storage battery built with low-cost metals sodium and aluminum.
They said the design provides a pathway towards a “safer and more scalable” stationary energy storage system that could help integrating renewable energy into the nation’s grid.
If it proves able to move from the lab to commercial deployment, the technology could enable low-cost, daily shifting of solar energy into the electrical grid over a 10- to 24-hour period.
The novel molten salt battery design has the potential to charge and discharge faster than other conventional high-temperature sodium batteries, operate at a lower temperature, and maintain an “excellent” energy storage capacity, researchers said.
The battery uses two distinct reactions. The team previously reported a neutral molten salt reaction. Their latest work shows that this neutral molten salt can undergo a further reaction into an acidic molten salt, increasing the battery’s capacity. They said that after 345 charge/discharge cycles at high current, the acidic reaction mechanism retained 82.8% of peak charge capacity.
The energy that a battery can deliver in the discharge process is called its “specific energy density,” which is expressed as watt hour per kilogram (Wh/kg). The researchers speculated that it could result in a practical energy density of up to 100 Wh/kg.The new sodium-aluminum battery design allows only sodium (depicted as yellow balls) to move through the solid-state electrolyte to charge the battery. Being constructed of inexpensive Earth-abundant materials such as sodium salts and aluminum wool, a scrap product of aluminum manufacturing, is an advantage. (Credit: Sara Levine | Pacific Northwest National Laboratory)
In comparison, the energy density for lithium-ion batteries used in commercial electronics and electric vehicles is around 170–250 Wh/kg. The researchers said, however, that the new sodium-aluminum battery design has the advantage of being inexpensive and easy to produce in the United States from much more abundant materials.
Scientists worked with U.S.-based Nexceris to assemble and test the battery. Nexceris, through its business Adena Power, supplied a solid-state, sodium-based electrolyte to test the battery’s performance. This battery component allows the sodium ions to travel from the negative (anode) to the positive (cathode) side of the battery as it charges.
One design innovation was to shift the battery from a traditional tubular shape to a flat, scalable shape that can be stacked and expanded as the technology develops from its current coin-sized battery to a larger grid-scale demonstration size.
The flat cell design also is expected to allow cell capacity to grow by using a thicker cathode. Researchers used the design to demonstrate a triple capacity cell with sustained discharge of 28.2-hours under laboratory conditions.
Researchers said the battery is a variation of a sodium-metal halide battery. A similar design using a nickel cathode as part of the system was shown to be effective at commercial scale and is commercially available.