Lithium-sulfur battery promises 3x energy density, pricing that undercuts combustion.

Might lithium-sulfur batteries push solid-state aside as The Next Big Thing in battery technology? Silicon Valley battery tech company Lyten just came out of stealth mode at September's Motor Bella car show/mobility conference in metro Detroit after several years of federally funded research, and it made a very promising pitch: Triple the energy per weight!

- Frank Markus

Charged ions of lithium metal do the heavy lifting in today's batteries. When your Tesla is tethered to the Supercharger, these ions migrate through the electrolyte, across the separator, and plate out on the anode. Then floor the accelerator, they head in the other direction, forming chemical bonds with the cathode material. In today's EV batteries, these cathode materials (typically nickel/manganese/cobalt-oxide molecules) can only host 0.5 to 0.7 lithium ions each, whereas a single sulfur atom can host two lithium ions. Eurekagravimetric densities jump from between 150 and 260 Wh/kg to 500 or more. Suddenly you'll get triple the range or lighten the battery weight by a third.

The many buzzkills that have so far kept lithium-sulfur chemistry off the road include the extremely low electrical conductivity of sulfur, physical expansion of the cathode as sulfur atoms become Li, S molecules, and the dreaded “polysulfide shuttle” effect. Engineered materials solved the first by attaching sulfur atoms to more conductive carbon structures like nanotubes. The expansion problem is shared with today's solid-state battery technologies and seems surmountable. The third has proven way thornier. See, sometimes when these Red Rover lithium ions head back over to the anode, they bring sulfur atoms with them, depleting the cathode. This causes lithium-sulfur batteries to die after maybe 100 charging cycles.