Thin Lithium Metal Anodes for Solid State Batteries: The Case for Scalable Evaporation

Solid state lithium-metal batteries show substantial promise for overcoming theoretical limitations of state-of-the-art Li-ion batteries to enable gravimetric and volumetric energy densities upwards of 500 Wh kg−1 and1000WhL−1, respectively. Whilezerolithiumexcessconfigurationsareparticularlyattractivefrom both an energy density and a manufacturing standpoint, inhomogeneous lithium plating on charge results in active lithium loss and a subsequent coulombic efficiency penalty accrued from Li anode irreversibility, which severely limits cycle life. Excess lithium in the form of a lithium foil is therefore currently needed to extend cycle life to practical values. On the other hand, excess lithium negatively impacts energy density and thus limiting its thickness is essential to derive any practical benefit from adoption of a lithium metal-based battery architecture. Currently, costs associated with the production of these foils at such thicknesses and scale are a major impediment to adoption by industry. Here we discuss the viability of various technologies in the realisation of thin lithium films that can be scaled up to surface areas required for gigafactory production. We identify thermal evaporation as a potentially cost-effective route to address these challenges and provide a technoeconomic assessment of the projected costs associated with the fabrication of thin, dense lithium metal foils using this process. Finally we estimate solid state pack costs made using thermally evaporated Li foils.