Résumé
Electrochemical reactions are mainly governed by the interface properties and changing electrode potential. Understanding the nature of electrochemical electrode/electrolyte interfaces is thus a crucial step in the optimization of systems for energy conversion and storage. However, a generally accepted method to consider varying electrode potentials in first-principles calculations does not exist, and modelling interfaces remains one of the biggest challenges for the density functional theory (DFT) community.
Implicit solvent model implemented in some DFT codes [1, 2] together with the inclusion of explicit solvent molecules was used on lithium system and the obtained results were in agreement with experimental values [3]. We use the same methodological approach to study Mg
2+
solvated in monoglyme (DME) and in ethylene carbonate (EC). Using molecular DFT (Gaussian) we first determine the explicit first solvation shell of Mg
2+
in DME and EC. The solvated Mg
2+
complex is then placed in front of Mg electrode in the plane wave DFT calculations (VASP). Potential dependent grand canonical energies, equilibrium (redox) potentials and differential capacitance are obtained for both systems and are in excellent agreement with experimental results. We further develop the method to probe stability regions of the solvents at the interface. We find that the stability of the solvent molecules is drastically modified in the presence of Mg
2+
. Furthermore, the
presented methodological approach can be used to study decomposition pathways. The obtained results give valuable insights into why some solvents are not appropriate for Mg battery systems, and how electrolyte performance can be improved.
[1] K. Mathew et al., The Journal of chemical physics
140
, 084106 (2014).
[2] K. Letchworth-Weaver et al., Physical Review B
86
, 075140 (2012).
[3] N. Lespes et al., Journal of chemical theory and computation
11
, 33753382 (2015).
[4] C. D. Taylor et al., Physical Review B
73
, 165402 (2006).