Around the world, energy producers are looking to clean and renewable energy generated from natural sources, such as solar and wind. These fluctuating sources can only be incorporated into electrical grids if housed in energy storage systems, allowing them to charge and discharge at the best times. Redox flow batteries, especially all-vanadium-based flow batteries, that provide electrical energy converted from chemical energy are well suited to energy storage. They can tolerate fluctuating power supplies, repetitive charge/discharge cycles at maximum rates, and overcharging and overdischarging. However, the disadvantages of low energy density and poor stability limit their applications.

Delivering higher energy density and more stable cell performance 

Researchers at Pacific Northwest National Laboratory have developed a high-performance cell stack, as well as an improved electrolyte composition delivering much higher energy density and more stable cell performance across a wide operating temperature window.

The high-performance cell stack comprises the following components to minimize high shunt currents and large pressure drops that plague other stack designs:

• A redox flow battery stack support frame holding a number of individual cells connected in series or parallel, each cell comprising an anode and a cathode separated by an ion exchange membrane
• A monolithic bipolar plate of polyvinyl chloride (PVC) integrated within the support frame and made up of many interlocking flow channels on at least one surface.

Both the anode and the cathode comprise species of vanadium. The electrolytes are novel, in that they contain additives of ammonium phosphate dibasic and magnesium chloride, which act to stabilize and improve the all-sulfate solution.

The new electrolytes increase energy capacity by as much as 70 percent and are more stable and soluble at temperatures ranging from -5 to 50 degrees Celsius compared to conventional vanadium-sulfate electrolytes. More importantly, they are much safer and more environmentally friendly. 

Applicability: Supports large-scale renewable and grid energy storage

This significant improvement over current technology can support large-scale renewable and grid energy storage applications, such as those used for electric utilities.