Effect of Mg Cation Diffusion Coefficient on Mg Dendrite Formation

Dendrite formation is an important issue for the metal anode-based battery system. The traditional perception that Mg metal anode does not grow dendrite during operation has been challenged recently. Herein, we investigate the Mg electrodeposition behavior in a 0.3 M all-phenyl-complex (APC) electrolyte and confirm that Mg dendrites are readily formed at high current densities. A semiquantitative model indicates that the Mg-ion concentration on the electrode surface, limited by the intrinsic diffusion coefficient of the Mg cation group, decreases with increasing current density, resulting in an extra concentration polarization. However, Mg deposition at the tip of a protrusion on the electrode surface is hardly affected by the concentration polarization, and thus dendrite growth is more prone to occur at the tips. We find that the addition of LiCl in conventional APC electrolytes can suppress the Mg dendrite formation, mainly as a result of the enhanced Mg cation diffusion coefficient due to the influence of the LiCl additive, rather than the less pronounced electrostatic shield effect provided by Li cations.