How Cool is This Liquid Battery?

Many of the prospects for a cleaner and prosperous future — autonomous vehicles, economical renewable energy, more efficient electronics — are made more likely and/or more affordable with improvements in energy storage. Tesla’s advances in the technology, form factor, and scale of production of lithium ion batteries are well known (and in fact I think of Tesla as a battery company, not a car company). Lots of researchers are working on other battery technologies, with different metals or new combinations like graphene batteries on organic substrates.

The size and weight of batteries have been constraints on electric vehicles since the 1980s, when the energy efficiency of the internal combustion engine made that the dominant automobile propulsion technology. As internal combustion engines hit the diminishing returns that are common in mature technologies, at the margin battery innovations make electric vehicles more attractive. Another factor that has limited electric vehicles is the chicken-and-egg problem of charging stations — charging stations aren’t profitable until a lot of people own EVs, which won’t happen until they have access to charging stations, and so on, and so on.

One area of battery innovation that could be useful in a variety of applications is the liquid flow battery. In 2016 researchers in Shanghai developed a flow battery without metals that has a long 50,000-cycle charging life, with grid storage as an application target. More recently, Purdue scientist John Cushman has developed a flow battery targeted at vehicles:

Cushman’s method uses water, ethanol (the same type of alcohol you’d find in alcoholic beverages), salt and dissolved metals. It would allow electric car owners to recharge their cars quickly and easily, using existing gas stations converted into battery recharging stations. … Typically, flow batteries use membranes to separate the two liquids. But Cushman’s battery uses water and ethanol, and salt to force the water and ethanol to separate into two layers, with no membrane needed. This gives the battery an advantage over traditional flow batteries, Cushman says, since membranes are often the weak link.

Testing flow batteries in applications outside of the lab is an important next step, to see how they perform in vehicles of varying weights. This ethanol-salt flow battery has appealing environmental and national security features — no metals and no rare earth minerals — and is also inexpensive to produce relative to other batteries that do have metals and other costly inputs.

One thing we learn from the economic history of technology is that incremental innovations and marginal gains can have big impacts on human welfare (as measured by utility and profits), so this kind of innovation path may turn out to be a factor in turning gas stations into battery recharging stations. Another thing we learn from economic history is that mature technologies and new technologies coexist, sometimes for decades (six decades in the case of the steam engine and the water wheel, as described in this post of mine from December 2002). For that reason I would expect gas stations to start offering charging services, whether fast charging plugs for lithium ion or liquid recharging for flow batteries, or both), while still selling gasoline. Technology transitions are almost never discrete, and I think this is an exciting incremental step.

One thought on “How Cool is This Liquid Battery?

  1. Lynne: Please do not fall for battery hype. And it is all hype. Tesla is a veritable hype machine. Their batteries are not high tech wonders. The existing battery packs consist of 6,000 to 8,000 “18650” Li Ion cells. which are cylinders 18.6 mm in diameter and 65.2 mm long. These cells produce between 1500 and 3600 mA at 3.7 V.

    The packs must be composed of thousands of cells because they have to be in long strings to get a useful voltage (Battery current is DC and cannot be stepped up by transformers, and battery voltage is fixed by the batteries chemistry.) and there have to be a lot of strings to get the Amperage needed to drive an automobile.

    These batteries are purely commodity items that are manufactured cheaply in Asia. They are common in laptops and flashlights. There is no reason to believe that there are any real cost reductions to look forward to.

    Tesla’s new “gigafactory” will make a new form factor battery cell they call 2170 because it will be 21 x 70 mm, and have a 30% greater volume than the 18650. My guess as to why they are changing from a standard to a non-standard size cell is to lock their customers into using factory batteries for replacement when the battery packs have to be replaced. An automobile can easily last three or four times as long as a battery pack.

    Moving on to flow batteries. It is true that they can be refueled by pouring new reactant into storage tanks. But that advantage comes with a big disadvantage. Fossil fuel powered internal combustion engines only have to carry one reactant. The other is air which is free and ubiquitous. Further, they have the same issues with voltage and Amperage that solid state batteries have. A flow battery is not much different than a fuel cell. And fuel cells using hydrogen and air have already proved to be intractably expensive.

    Another point to remember is that batteries are a mature technology. The first battery was built by Volta in Italy 217 years ago. Batteries are based on inorganic chemistry which is a mature science with no surprises in store. The reason why charging is a slow process is that it is subject to immutable physical laws. Watts = Amps x Volts is not just a good idea it is the law.

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