Effect of Alkali and Alkaline Earth Metal Salts on Suppression of Lithium Dendrites

Lithium dendrites are needle-like structures that form during the electrodeposition of lithium metal. These whiskers complicate the use of lithium metal as an anode in lithium batteries because they can puncture the separator and short circuit the battery. In addition, the large surface area and poor adhesion of the deposit contributes to loss of coulombic efficiency. The effect of alkali and alkaline earth metal ions on the morphology of electrodeposited lithium metal has been studied. Varying concentrations of alkali and alkaline earth metal ions were added to a 1 M lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) trimethylbutylammonium bis(trifluoromethanesulfonyl)imide (N 1114 -TFSI) electrolyte. Lithium metal was electrodeposited from each electrolyte and examined ex-situ by scanning electron microscopy (SEM). Alkali metal ions, with the exception of sodium, had little or no effect on the deposited lithium morphology. However, alkaline earth metal ions at 0.05 M concentration significantly reduced the occurrence of dendrites. When the concentration of the alkaline earth metal ions was increased to 0.1 M, dendrites were completely eliminated and lithium was deposited in a sphere-like morphology. Energy dispersive X-ray spectroscopy (EDX) showed that no alkaline earth metals were found in the sphere-like deposits, suggesting that dendrite mitigation occurred through an adsorption mechanism.