The use of lithium (Li) metal as an anode material has emerged as one highly attractive option for achieving high specific energy due to lithium having the highest capacity (3876 mAh g-1) of all potential anode materials. However, the reliable use of these exceptionally high capacity anodes in a commercial cell has not been achieved due to safety and reliability concerns resulting from thermal runaway and short-circuit issues due to dendritic growth on the metal anode from lithium plating during charge-discharge cycles. Solid-state electrolytes (SSE) have been identified as one option to address this cell failure mode, but SSE technologies must be developed that combine high conductivity and mechanical properties conducive to smooth Li plating with feasible manufacturing processes. Also, the Li anode must be combined with an ultra-high capacity cathode in order to reach NASA's aggressive cell-level energy goals. To address this need, Solid Power proposes to utilize a Li-metal-compatible solid-state battery design to far exceed the specific energies achieved by state-of-the-art (SOTA) Li-ion batteries in a format that also provides for intrinsic safety and abuse tolerance. Phase I will demonstrate the feasibility of surpassing 600 Wh/kg and 1000 Wh/L at the cell level which will give a 3-5X improvement over the best battery technologies planned for NASA missions today.