In this study, we focus on understanding properties of the Solid Electrolyte Interphase (SEI), which plays an important role in the performance of Li-ion batteries. SEI has a complex structure including domains and blends of different organic (such as LEC, LMC, Li₂EDC_, etc.) and inorganic compounds (such as LiF, Li₂O, etc.) which are byproducts of single and double electron reduction processes of electrolyte solvent and ions. Because of this complexity, the detailed structure and characteristics of SEI are still not well understood.

Dilithium carbonate, Li₂CO₃, is known to be one of the important and stable compounds in the SEI structure. While there were some studies considering crystal phase of Li₂CO₃, the properties of amorphous glassy phase that can form at the domain boundaries within SEI or under fast rates of electrolyte reduction has not been investigated. In addition to SEI, amorphous blends of Li₂CO₃ with other oxides have been considered as potential materials for solid electrolytes. To the best of our knowledge, we present the first study considering the amorphous phase from theoretical point of view.

Using atomistic MD simulations and a polarizable force field, we investigated properties of amorphous Li₂CO₃ phase and predict structural, dynamical, and mechanical properties of Li₂CO₃ as a function of temperature as well as the content of Mn²⁺ in the SEI. The latter investigates the influence of SEI “contamination” by divalent cations dissolved from high-voltage cathods or intentional introduction of sacrificial divalent cation salts to promote formation of denser and stronger SEI.

According to our study, Mn_0.2Li_1.6CO₃ forms the glassy state below 600 K, which is a 150 K increase compared to Li₂CO₃ system. Besides, Mn_0.2Li_1.6CO₃ shows 15% higher density. From mechanical property calculations, shear modulus value for Li₂CO₃ is around 8 GPa, while it increases significantly with the addition of Mn²⁺.