Solid-state batteries are widely considered the most promising candidate to begin displacing conventional lithium ion batteries for electric vehicles and consumer electronics in the next decade, but several challenges remain. High energy density and long cycle must still be demonstrated in large automotive-relevant cells. Low cost and scalable production also need to be proven. Solid Power is working to meet these challenges by combining a sulfide-based solid electrolyte, a nickel-rich NMC cathode, and a lithium metal anode in cells that surpass conventional lithium ion in energy density and safety.

Solid Power and its collaborators have developed a suite of solid electrolytes, cathode materials, Nb-free surface treatments and production processes that deliver excellent energy density and cycle life in laboratory-scale cells. The attached figure shows early cycling performance for a recent 2 cm² laboratory type lithium metal cell at 70°C and C/10 rate with a 4.3V charge voltage. This cell delivers 193 mAh/g based on surface-treated LiNi_0.6Mn_0.2Co_0.2O₂ (NMC622) mass and retains 191 mAh/g after 80 cycles at 100% depth-of-discharge. The excellent cycling stability of this composite cathode comes from improved electrochemical stability at the cathode-electrolyte interfaces as well as the ability to accommodate the volume changes of the NMC during cycling.

Now focus is on scaling of both cell capacity and production throughput. Cells are currently produced up to 250 mAh, and larger cells up to 20 Ah in capacity with improved performance are planned for the next year as Solid Power’s pilot scale production line is completed in early 2019. This production line is built on low-cost processes and equipment that mirror lithium ion production and will be capable of producing up to 1 MWh per month when fully operational. Remaining challenges for Solid Power include demonstrating long life with lithium metal anodes in full-scale cells and working toward low-temperature operation.