Li⁺ Transport and Mechanical Properties of Model Solid Electrolyte Interphases (SEI): Insight from Atomistic Molecular Dynamics Simulations

Abstract

A fundamental understanding of solid electrolyte interphase (SEI) properties is critical for enabling further improvement of lithium batteries and stabilizing the anode–electrolyte interface. Mechanical and transport properties of two model SEI components were investigated using molecular dynamics (MD) simulations and a hybrid MD-Monte Carlo (MC) scheme. A many-body polarizable force field (APPLE&P) was employed in all simulations. Elastic moduli and conductivity of model SEIs comprised of dilithium ethylene dicarbonate (Li2EDC) were compared with those comprised of dilithium butylene dicarbonate (Li2BDC) over a wide temperature range. Both ordered and disordered materials were examined with the ordered materials showing higher conductivity in the conducting plane compared to conductivity of the disordered analogues. Li2BDC was found to exhibit softening and onset of anion mobility at lower temperatures compared to Li2EDC. At 120 °C and below, both SEI model compounds showed single ion conductor behavior. Ordered Li2EDC and Li2BDC phases had highly anisotropic mechanical properties, with the shear modulus of Li2BDC being systematically smaller than that for Li2EDC.

Structural, Mechanical, and Dynamical Properties of Amorphous Li2CO3 from Molecular Dynamics Simulations

“…In comparison to regular flexible-cell MD simulation in the NPT ensemble, this MD-MC approach provides a more effective sampling of distributions of simulation cell dimensions, as has been confirmed in our earlier studies of other SEI systems. [4,24]…”

“…Lithium ion (Li-ion) batteries have been widely used in many technologies, from hybrid and electrical vehicles, to laptops and cellphones [2]. These various applications of Li-ion batteries necessitate improvements in their safety, durability, and efficiency, which in turn depend on designing stable and efficient electrodes [3], requiring understanding of electrode-electrolyte interfaces to enable better engineering of these interfaces [4,5].…”

“…Yet, the SEI also creates additional resistance for Li-ion transport to/from anode during cycling. Typically, the SEIs formed on graphite, Si, and Li metal anodes in contact with carbonate-based electrolytes are thought to consist of inner and outer layers, in which the inner layer principally includes crystalline domains of the fully reduced compounds such as Li 2 CO 3 , Li 2 O, and LiF, [4,7,8] while the outer layer is comprised of much softer and more porous phases of dilithium alkyldicarbonates. Li 2 CO 3 is one of the electrochemically stable and lowest energy products of carbonate based electrolytes' reductive decomposition and has been reported to be in SEI films formed on both cathode and anode surfaces [9][10][11].…”

Review on modeling of the anode solid electrolyte interphase (SEI) for lithium-ion batteries

“…188 According to the recent simulations with the APPLE&P force field, Li 2 BDC is less stiff than Li 2 EDC. 177 In addition to the bulk modulus, the work of adhesion is equally important for the SEI. Adhesion of Li 2 CO 3 on bare and lithiated graphite has been modeled using DFT and only the (001) surface of Li 2 CO 3 tightly bonds with graphite with a work of adhesion of 1.86 J m −2 .…”

Developing High‐Performance Lithium Metal Anode in Liquid Electrolytes: Challenges and Progress

“…According to the solid‐state stress and inelastic deformation models discussed above, the interface stability of SEI/lithium metal and ability of preventing LMI are largely affected by the mechanical properties of SEI, which depend on the electrolyte components (solvents, lithium salts, and additives), and therefore, it is reasonable to improve the SEI properties by optimizing the liquid electrolyte. Based on the dual‐layer model of SEI films, although the mechanical strength is codetermined by the outer organic layer and inner organic layer, the shear modulus of the inorganic SEI is usually an order of magnitude higher than that of organic SEI, thus it is reasonable to assume that the mechanical properties are mainly influenced by the inorganic species of low oxidation states. Among those SEI components, LiF is believed to be an excellent passivation compound due to the reasons we mentioned in Section , and therefore high‐DFC electrolytes, which largely encourage the formation of LiF‐rich SEI, are usually good candidates.…”