Researchers in Singapore have created a new kind of redox flow battery with an energy density around ten times higher than conventional redox flow batteries. Never heard of a redox flow battery? These rechargeable batteries have more in common with fuel cells than conventional batteries. They use two circulating liquids separated by a membrane as an electrolyte. Each liquid has its own tank, and you can recharge it by pumping in fresh electrolyte. The redox in the name is short for reduction-oxidation and refers to the process that stores energy in the two liquids. You can learn more about flow batteries in the video from Harvard below.
The energy capacity of a redox flow battery depends on the volume of the liquid tanks. This property makes them attractive for storing lots of energy (for example, the output of a solar or wind generator). What makes traditional cells unattractive is that they have low specific energy — making them too heavy for something like electric vehicles — and low specific power, which makes them expensive for storing energy from stationary sources like wind turbines. The new cells, using a lithium-based solution on the cathode and a titanium-based solution on the anode, allows for cells that store about 500 watt-hours per liter of solution.
We’ve talked about homebrew molten salt batteries and lithium-air batteries, too. Building a redox flow battery doesn’t seem that difficult if you can master the membrane. Typical materials include glass-ceramics and Nafion polymer. The new battery uses a composite membrane made from Nafion and PVDF.