Critical Role of Pressure for Chemo-Mechanical-Induced Stability of Sodium Metal Battery Anodes

In this work we demonstrate that cell pressure controlsthe morphologyand stability of electroplated sodium metal deposits on carbon blacknucleation layers in ether-based electrolytes. At pressures below500 kPa we observe the presence of three-dimensional Na nuclei accompaniedby low Coulombic efficiencies (CEs less than 98%). Conversely, atpressures between 500 and 1272 kPa we observe smooth, planar Na deposits,high CEs up to 99.9%, and stable electrochemical cycling. Througha series of tests conducted at elevated current densities and withor without rest stages, our findings elucidate the balance of importantcompeting time scales for creep and morphology evolution under pressureand the rate of charge transfer that determines Na morphology andstability. This highlights how chemo-mechanical effects at pressureranges relevant for battery packaging in coin and pouch cells arekey factors in the design and operation of Na metal batteries.