Toward solid-state Li metal -air batteries; an SOFC perspective of solid 3D architectures, heterogeneous interfaces, and oxygen exchange kinetics.

The full electrification of transportation will require batteries with both 3-5× higher energy densities and a lower cost than what is available in the market today. Energy densities of >1000 W h kg -1 will enable electrification of air transport and are among the very few technologies capable of achieving this energy density. Li metal -O 2 or Li metal -air are theoretically able to achieve this energy density and are also capable of reducing the cost of batteries by replacing expensive supply chain constrained cathode materials with "free" air. However, the utilization of liquid electrolytes in the Li metal -O 2 /Li metal -air battery has presented many obstacles to the optimum performance of this battery including oxidation of the liquid electrolyte and the Li metal anode. In this paper a path towards the development of a Li metal -air battery using a cubic garnet Li 7 La 3 Zr 2 O 12 (LLZ) solid-state ceramic electrolyte in a 3D architecture is described including initial cycling results of a Li metal -O 2 battery using a recently developed mixed ionic and electronic (MIEC) LLZ in that 3D architecture. This 3D architecture with porous MIEC structures for the O 2 /air cathode is essentially the same as a solid oxide fuel cell (SOFC) indicating the importance of leveraging SOFC technology in the development of solid-state Li metal -O 2 /air batteries.