Li-sulfur is also a low-cost system due to the low cost of sulfur, also offers high energy density, Anandan said. Its key challenge is the accumulation of polysulfides, leading to curtailed cycle life.

Solid-state use solid electrodes and a solid electrolyte material. The solid electrolytes are stable and remove the flammability concerns associated with liquid electrolytes. However, SSBs suffer from low current density, and low cycle life. Scalability, in terms of manufacturing for mass automotive adoption, is also an unknown.

All of the advanced battery systems use Li metal anodes to provide high energy density, Anandan noted.

Solid state is the one lead system that we know right now could offer higher volumetric energy density and safety than all the other systems out there. None of the technologies are ready right now.

—Venkat Anandan

Solid-state batteries have been around for decades; one of the most successful types is the thin film SSB, with an electrode stack of ~ 50 microns. However, energy density is low as is its current density.

One of the solid-state designs that might be applicable for EVs is the bulk-type solid-state battery. The electrode thickness is more than 50 microns. With an electrode thickness of more than 50 microns, we can get an energy density that could be useful for vehicle applications. The bulk-type solid state battery could meet automotive design targets.

—Venkat Anandan

The solid electrolyte should have ionic conductivity of more than 10^-4, he said, should be stable with the active materials, have good mechanical properties, and be readily manufacturable.

Ford found that lithium lanthium zirconia oxide (LLZO) electrolytes could meet most of those criteria. One of Ford’s university partners demonstrated that LLZO can be sintered into thin sheets of around 150-200 microns in thickness and conductivity of 10^-4. Although this is not yet meeting Ford’s targets, Anandan believes it can be achieved.

In November 2016, Ford was awarded a patent on a solid-state battery design (US 20160329594 A1) with Anandan and his colleague Andrew Drews as the inventors. This was followed in January 2017 with a patent (US20170012319 A1) for a flexible composite solid state battery, with Anandan and Drews again the inventors.