Experimental correlation of anionic mass transport and lithium dendrite growth in solid-state polymer-based lithium metal batteries

Various metal deposition models have been proposed for alkali metal batteries, but the experimental accessibility of designated driving forces and characteristics of specific morphologies is still limited. A combined method portfolio comprising operando 1D 19 F MRI, in situ 7 Li NMR, and dynamic electrochemical impedance spectroscopy (EIS) experiments is presented. Experimental evidence of the relation of capacity-degrading dendritic Li metal growth and anionic mass-transport quantities beyond Sand's time in polymer-based Li metal batteries is demonstrated. Comparison of anionic mass transport and morphological changes in Li metal in Li||Li and NMC 622 ||Li cells revealed that elevated anion drift velocities within electrolytes are correlated with pronounced dendrite growth. Higher cell voltages are associated with increased anion drift velocities and hence dendrite growth, as reflected by a 2.5-fold increase in velocities in NMC 622 ||Li compared to Li||Li cells. This highlights the potential of the introduced method portfolio for experimental evaluation of polymer electrolytes and artificial coatings suitable for alkali metal batteries.