How we store energy will be critical to the future of the electric car. While lithium-ion batteries are likely to remain the standard for at least the next decade, academic researchers and startup companies are racing to discover, design, and manufacture alternatives that will move beyond the limits of today’s chemistries. The following three technologies show the greatest potential
In brief: Here, energy is stored in tanks as two liquid electrolytes rather than in the positive and negative electrodes. The electrolytes generate electricity as they’re pumped through the battery cells. Recharging can occur either onboard by reversing the process or by replacing the electrolyte at a fuel station.
What might stop it: Many experts believe that achieving adequate range with a flow battery will require storage tanks too large to be practical in a vehicle.
Where it stands: NanoFlowcell, a company based in Liechtenstein, claims that it has a working flow-cell prototype vehicle that drove for 14 hours at city speeds with two 42-gallon tanks of electrolytes, although skepticism runs high in the scientific community. A startup founded by MIT researchers, 24M recently pivoted from reduction-oxidation flow batteries to what it calls semisolid lithium-ion batteries, specifically due to the packaging constraints of the large storage tanks.’
In brief: A solid ceramic electrolyte replaces the liquid electrolyte in today’s lithium-ion cells, leading to a battery that is nonflammable, doesn’t degrade over time, and doubles the amount of energy that can be stored in a given volume. That last part is possible because the solid electrolyte enables the use of pure metallic lithium in the negative electrode. The performance of solid-state batteries also improves with heat, eliminating the need for liquid cooling.
What might stop it: The ceramic electrolyte is up to five times heavier than the liquid alternative, and the thin, brittle sheets will need protection from jarring road impacts. Perform¬ance also suffers in low temperatures.
Where it stands: Dyson, the vacuum manufacturer that also has a grant from the British government to build an electric car, purchased solid-state-battery startup Sakti3 in 2015. However, Sakti3 uses a thin-film production method that likely won’t scale for automotive applications. Researchers at the Sakamoto Group are working to produce the ceramic material in bulk with batches of powder.
In brief: Part battery, part fuel cell, a metal-air cell uses the oxygen from air pumped through the battery to drive the electricity-¬generating chemical reaction. This is much lighter than storing the oxidant as a solid material in the battery, resulting in batteries with up to 10 times the energy density of a lithium-ion one. ¬Lithium-air batteries grab a lot of headlines, but there’s even more potential in zinc-air cells due to zinc’s abundance and low cost.
What might stop it: Rechargeable metal-air batteries are a fairly recent development and have a limited number of charge-discharge cycles before their storage capacity significantly degrades.
Where it stands: Arizona-¬based Fluidic Energy has installed rechargeable zinc-air batteries in developing countries to act as buffers for unreliable electric grids. Tesla holds a patent for a vehicle that uses a metal-air battery as a range extender after the lithium-ion pack is depleted, thus limiting the number of charge cycles the secondary battery faces.