TY - JOUR
T1 - Effect of Concentration on the Electrochemistry and Speciation of the Magnesium Aluminum Chloride Complex Electrolyte Solution
AU - See, Kimberly A.
AU - Liu, Yao Min
AU - Ha, Yeyoung
AU - Barile, Christopher J.
AU - Gewirth, Andrew A.
N1 - Funding Information:
This work was partially supported by the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. K.A.S. acknowledges postdoctoral funding from the St. Elmo Brady Future Faculty Postdoctoral Fellowship. Y.-M.L. acknowledges access to the Orbitrap-MS in the Mass Spectrometry Laboratory at UIUC. C.J.B. acknowledges funding from the National Science Foundation Graduate Research Fellowship (No. NSF DGE-11444245) and a Springborn Fellowship. The authors thank Dr. Taras Pogorelov and Mike Hallock for assistance with Gaussian calculations.
Publisher Copyright:
© 2017 American Chemical Society.
PY - 2017/10/18
Y1 - 2017/10/18
N2 - Magnesium batteries offer an opportunity to use naturally abundant Mg and achieve large volumetric capacities reaching over four times that of conventional Li-based intercalation anodes. High volumetric capacity is enabled by the use of a Mg metal anode in which charge is stored via electrodeposition and stripping processes, however, electrolytes that support efficient Mg electrodeposition and stripping are few and are often prepared from highly reactive compounds. One interesting electrolyte solution that supports Mg deposition and stripping without the use of highly reactive reagents is the magnesium aluminum chloride complex (MACC) electrolyte. The MACC exhibits high Coulombic efficiencies and low deposition overpotentials following an electrolytic conditioning protocol that stabilizes species necessary for such behavior. Here, we discuss the effect of the MgCl2 and AlCl3 concentrations on the deposition overpotential, current density, and the conditioning process. Higher concentrations of MACC exhibit enhanced Mg electrodeposition current density and much faster conditioning. An increase in the salt concentrations causes a shift in the complex equilibria involving both cations. The conditioning process is strongly dependent on the concentration suggesting that the electrolyte is activated through a change in speciation of electrolyte complexes and is not simply due to the annihilation of electrolyte impurities. Additionally, the presence of the [Mg2(μ-Cl)3·6THF]+ in the electrolyte solution is again confirmed through careful analysis of experimental Raman spectra coupled with simulation and direct observation of the complex in sonic spray ionization mass spectrometry. Importantly, we suggest that the ∼210 cm-1 mode commonly observed in the Raman spectra of many Mg electrolytes is indicative of the C3v symmetric [Mg2(μ-Cl)3·6THF]+. The 210 cm-1 mode is present in many electrolytes containing MgCl2, so its assignment is of broad interest to the Mg electrolyte community.
AB - Magnesium batteries offer an opportunity to use naturally abundant Mg and achieve large volumetric capacities reaching over four times that of conventional Li-based intercalation anodes. High volumetric capacity is enabled by the use of a Mg metal anode in which charge is stored via electrodeposition and stripping processes, however, electrolytes that support efficient Mg electrodeposition and stripping are few and are often prepared from highly reactive compounds. One interesting electrolyte solution that supports Mg deposition and stripping without the use of highly reactive reagents is the magnesium aluminum chloride complex (MACC) electrolyte. The MACC exhibits high Coulombic efficiencies and low deposition overpotentials following an electrolytic conditioning protocol that stabilizes species necessary for such behavior. Here, we discuss the effect of the MgCl2 and AlCl3 concentrations on the deposition overpotential, current density, and the conditioning process. Higher concentrations of MACC exhibit enhanced Mg electrodeposition current density and much faster conditioning. An increase in the salt concentrations causes a shift in the complex equilibria involving both cations. The conditioning process is strongly dependent on the concentration suggesting that the electrolyte is activated through a change in speciation of electrolyte complexes and is not simply due to the annihilation of electrolyte impurities. Additionally, the presence of the [Mg2(μ-Cl)3·6THF]+ in the electrolyte solution is again confirmed through careful analysis of experimental Raman spectra coupled with simulation and direct observation of the complex in sonic spray ionization mass spectrometry. Importantly, we suggest that the ∼210 cm-1 mode commonly observed in the Raman spectra of many Mg electrolytes is indicative of the C3v symmetric [Mg2(μ-Cl)3·6THF]+. The 210 cm-1 mode is present in many electrolytes containing MgCl2, so its assignment is of broad interest to the Mg electrolyte community.
KW - Mg dimer
KW - electrolyte conditioning
KW - magnesium aluminum chloride complex
KW - magnesium battery electrolyte
KW - magnesium deposition
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U2 - 10.1021/acsami.7b08088
DO - 10.1021/acsami.7b08088
M3 - Article
C2 - 28933814
AN - SCOPUS:85031702507
SN - 1944-8244
VL - 9
SP - 35729
EP - 35739
JO - ACS applied materials & interfaces
JF - ACS applied materials & interfaces
IS - 41
ER -