Electric Cars Plug in Flow Batteries

Lithium-ion batteries will dominate the automotive scene, but flow batteries are playing an interesting wild card.

Our lithium–ion battery forecast shows the technology will not only dominate in electric vehicles but eventually in conventional car batteries as well given impending carbon dioxide laws. Over the next 15 years, sales of lead acid batteries will peak.

Among contenders we track in a report on advanced and post-lithium-ion batteries, lithium-sulphur is the lead candidate, but it has considerable challenges to overcome such as its volumetric energy density. The batteries are light, but too big.

One wild card is the flow battery. Most people rightly see these as very large units suitable for storage at electric utilities. One or two organizations are thinking about putting them in cars because they are headed for $100 per kWh and their size and weight might just fit the bill in due course. Toyota’s advanced research people told us recently that they would not dismiss the possibility.

For example, Nanoflowcell has been exhibiting a sports car (above) it says will use their flow batteries.  Pure electric cars using the 48V batteries are said to have a range of 1,000 miles.

Design trends in powertrains suggest pure electric cars are generally headed up towards 800V for light weight and performance. Fpr pure electric vehicles 48V is typically only seen in very weak duty cycles such as golf cars and postal delivery vehicles.

Flow battery technology is immature. Pumping liquids from reservoirs does not sound compact or reliable in a car but who knows? Watch this space.

Redox flow batteries typically have a very low energy density, roughly one order of magnitude lower than the best Li-ion. Nanoflowcell aims to introduce redox flow technology in a car is by making use of a non-rechargeable chemistry.

These batteries last much longer than Li-ion or other chemistries, but their contents have to be replaced when they reach their end of life.

A redox flow battery essentially uses two electrolyte tanks containing liquids that react with each other. Once their energy is consumed, these liquids are replaced and the spent fluids hopefully can be recycled. If the combined cost of the electrolytes, the refuelling infrastructure and of the recycling process is competitive, Nanoflowcell can be expected to deliver a pure electric car that can be charged within minutes.

Redox flow electrolytes can be extremely cheap (0.1$/kg for the aqueous ones), which means that they would be a serious competitor of gasoline even in the U.S. Additionally, redox flow batteries are known for their longevity, with many companies already offering 20 years warranty for their stationary batteries.

The end game is to make rechargeable flow batteries that would eliminate the recycling step from the equation, but until then Nanoflowcell’s product proposition offers a viable bridge to pure EVs. Among the disadvantages, it is worth mentioning that flow batteries are not capable of delivering much power, therefore small supercapacitors and/or Li-ion batteries might still be required for acceleration and regenerative braking.

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