New flow battery from PNNL projected to cost 60 percent less than

A whole new organic, aqueous flow battery power technology promises to drastically lower the cost as well as increase the durability of running safe energy storage systems. The technology, which was established at the Pacific Northwest National Laboratory (PNNL), uses low cost and sustainable synthesized compounds instead of the usual precious metals, and is retrofitted to fit existing batteries.

Flow batteries vary in both form and performance compared to the more common lithium-ion batteries. They store their active chemicals — liquid electrolytes — in just two external tanks. To produce power, these liquids are pumped to a central stack with a couple of electrodes that are separated by the membrane. They exchange ions throughout this membrane, which generates electricity. To save electricity, the process is reversed.

Flow batteries are more secure and more scalable than lithium-ion battery packs, and they can resist greater temperatures or even periods of idleness, which makes them well matched to storing and delivering the power produced by alternative energy such as solar panel systems and wind mills — particularly in residential areas.

The caution is that the standard electrolyte components are vanadium and bromide, which are dangerous, expensive, and toxic commodity metals. Nearly 79 percent of existing flow batteries stick to this standard.

However, the PNNL researchers imagine their new organic electrolytes (methyl viologen as anolyte and 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl as catholyte, plus sodium chloride, which makes it possible for discharging) becoming a new standard. They anticipate a flow battery with all the new design to cost $180 per kilowatt hour, which is certainly cheaper at around 60 percent less than a typical vanadium-based flow battery. This revolutionary water-based liquid electrolyte seemed to be designed as a drop-in replacement for existing systems, so there will be no reason to replace the current infrastructure.

The researchers examined the technology in a small, 600-milliwatt battery. It was steady for 100 cycles with “nearly” 100 percent proficiency at current densities starting from 20 to 100 mA per square centimeter, with optimal performance with a rating of 40-50 MA per square centimeter — at which about 70 percent of the battery’s initial voltage was retained.

The researchers now decide to make a more substantial test version that could provide the peak load of a usual American home (approximately around five kilowatts). They are trying to increase the cycling to ensure the battery can maintain its storage capacity for a longer time without changing the electrolytes.

The latest design will face competition from a different new kid on the block, as well. Harvard scientists just recently developed a similarly sustainable flow battery making use of quinones — naturally occurring chemicals involved in photosynthesis and ferrocyanide, frequently used as a food preservative or fertilizer. The Harvard battery has similar efficiency and an extended cycling lifetime compared to new PNNL design, nonetheless it has a lower energy density.

These new technologies are described in depth in a paper published in the journal Advanced Energy Materials.