of 3
Supplemental Materials for:
Conditioning-Free
Mg Electrolyte by Minor Addition of Mg(HMDS)
2
Seong Shik Kim, Sarah C. Bevilacqua, and Kimberly A. See
Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena,
California 91125, United States
E-mail: ksee@caltech.edu
Table S1:
Water content of various solutions measured by Karl Fischer Titration.
MACC +
solution
THF MACC 2 mM Mg(HMDS)
2
water content (ppm)
22
71
46
Increased water content in MACC is attributed to water present in the salts. In MACC + 2 mM
Mg(HMDS)
2
, although more salt is added to the solution, water content decreases, confirming the
water-scavenging effect of Mg(HMDS)
2
.
S1
Figure S1:
Typical Coulombic efficiency profile of MACC + 10 mM Mg(HMDS)
2
. CE decreases
due to the formation of a black film. The black film is easily removed from the Pt wire by simple ag-
itation. The electrolyte reaches >90% CE upon when the black film is removed from the electrolyte
(red circle).
S2
Figure S2:
Cyclic voltammograms of cycles 1, 25, and 50 of (a) MACC + 5 mM Mg(HMDS)
2
, (b)
MACC + 5 mM Mg(HMDS)
2
+ 5 mM and (c) 10 mM H
2
O, and (d) MACC + 5 mM Mg(HMDS)
2
aged for 4 days. MACC + 5 mM Mg(HMDS)
2
with and without H
2
O exhibit similar electrochemical
behavior, including Mg deposition/stripping and no cathodic current in the fourth quadrant from
cycle 1. MACC + 5 mM Mg(HMDS)
2
+ 5 mM H
2
O exhibits >99% Coulombic efficiency at cycle 50
while MACC + 5 mM Mg(HMDS)
2
+ 10 mM H
2
O exhibits 84% at cycle 50, likely due to the high
concentration of H
2
O in the solution. The electrolyte does not exhibit cathodic current in the fourth
quadrant with 10 mM of H
2
O addition. In comparison, MACC + 5 mM Mg(HMDS)
2
aged for 4 days
exhibits cathodic current in the fourth quadrant, the region attributed to Al deposition, in cycle 1.
The cathodic current in aged MACC + 5 mM Mg(HMDS)
2
that disappears in subsequent cycles
may be due to the depletion of free Cl
during aging.
S3