Marie-Liesse Doublet

To meet the challenges of our society in terms of energy, the autonomy and lifespan of Li-ion batteries must be considerably improved. This implies increasing the energy density of electrode materials and controlling the electrochemical reactions at the electrode/electrolyte interfaces. The energy density depends on the electrochemical potential and the specific capacity of the electrode materials. These quantities are not intrinsic properties of a given material but response properties to a change in lithium composition. For this reason, high-throughput and/or combinatorial theoretical approaches such as those developed in this field over the 20 past years have not yet made it possible to design new efficient materials for Li-ion batteries. In contrast, more conceptual approaches, based on the concepts of chemical bonding and electronic structure have proven their effectiveness in identifying the chemical, structural and electronic descriptors at the origin of the electrochemical properties of a material, therefore enabling more rational design of electrode materials. This research has contributed to the discovery of a new class of positive electrodes presenting record energy densities thanks to a dual cationic and anionic redox activity lithium-rich transition metal oxides. [1,2]

As a counterpart, the improvement of the positive electrode potential has led to questions about the stability of electrolyte in the vicinity of the electrode/electrolyte interfaces. In particular, parasitic reactions occurring at these interfaces lead to the formation of passivate layers, the so-called Solid Electrolyte Interphase (SEI) which can be detrimental to the battery operation. This problem is at the heart of a new European Flagship Initiative (BATT2030+) which requires the development of new theoretical methods capable of modeling electrode/electrolyte interfaces at the quantum level to understand and predict the mechanisms of battery degradation. In this context, a Grand Canonical DFT approach was developed to take into account the potential dependence of the electrochemical reactions at play and to identify the electrolyte decomposition products during electrochemical cycling. [3] This method can be transferred to any type of interface and makes it possible to design new stable electrolytes for post-Li technologies. [4,5] This presentation will propose an overview of the different theoretical approaches used today in the field of electrochemical energy storage to guide experimentalists in their quest for more efficient devices, and will aim at identifying the methodological challenges that remain to be overcome.

[1] M. Sathiya, et al. Reversible anionic redox chemistry in high-capacity layered-oxide electrodes Nature Materials (2013) 12, 827-835.
[2] M. Ben Yahia, et al. Unified Picture of Anionic Redox in Li/Na-Ion Batteries Nature Materials (2019) 18, 496-502.
[3] A. Kopac-Lautar, et al. Electrolyte Reactivity in the Double Layer in Mg Batteries: An interface potential-dependent DFT Study JACS (2020) 142 (11), 5146-5153.
[4] L. H. B. Nguyen, et al. Investigation of Alkali and Alkaline Earth Solvation Structures in Tetraglyme Solvent Phys. Chem. Chem. Phys. (2021) 23, 26120–26129.
[5] L. H. B. Nguyen, et al. Investigating the abnormal conductivity behaviour of divalent cations in low dielectric constant tetraglyme-based electrolytes Phys. Chem. Chem. Phys. (2022) 2022, 24, 21601-2161123.