Flat batteries could improve performance and lower cost of energy storage

In the continuing search for ever more efficient and cheaper batteries, researchers at the Department of Energy’s (DoE) Pacific Northwest National Laboratory (PNNL) have managed to increase the performance of sodium-nickel chloride batteries in an interesting way – flattening them. No, not running them down until they’re out of juice, but rather replacing their typical cylindrical shape with a flat disc design. The redesign allows the battery to deliver 30 percent more power at lower temperatures, making them a viable alternative to lithium-ion batteries.

The batteries are made from abundant materials such as alumina, sodium chloride and nickel, making them cheaper to produce than lithium-ion batteries, while the 30 percent boost in performance reported by the PNNL researchers means they could still offer the performance necessary to compete with lithium-ion batteries in consumer devices. Additionally, sodium-beta batteries aren’t prone to the thermal runaway condition that has seen various lithium-ion batteries catching fire.

Sodium-beta alumina batteries have been around since the 1960s but their traditional tubular, cylindrical shape doesn’t allow for the efficient discharge of stored electrochemical energy. Raising the temperature lowers the battery’s internal resistance but this lowers the cost effectiveness of the battery and shortens its lifespan. These issues resulted in them being surpassed by the better performing lithium-ion batteries that power the bulk of our mobile electronic devices today.

But the PNNL researchers were keen to take advantage of the cheaper materials used in sodium-beta batteries and thought a redesign might overcome the technical and cost issues. They found that a planar design allows for a thinner cathode and a larger surface area for a given cell volume. Because the ions can flow in a larger area and shorter pathway, they experience lower resistance. Additionally, the new design incorporates a layer of solid electrolytes, which also lowers resistance.

It is the resulting reduction in resistance that allows the battery to be operated at lower temperatures while maintaining a power output 30 percent more than a similar-sized battery with a cylindrical design.

Another benefit of the battery redesign is that the battery’s flat components can be easily stacked to produce a much more compact battery. The researchers say this makes the planar batteries an attractive option for large-scale energy storage, such as in electricity substations where they could be used to balance the generation and delivery of wind and solar power on the grid.

"Our goal is to get a safer, more affordable battery into the market for energy storage. This development in battery technology gets us one step closer," said PNNL Scientist Xiaochuan Lu, co-author of the paper detailing the planar battery that appears in the October 8 issue of ECS Transactions.