Solvation and Dynamics of Sodium and Potassium in Ethylene Carbonate from ab Initio Molecular Dynamics Simulations

Abstract

The development of sodium and potassium batteries offers a promising way to meet the scaling and cost challenges of energy storage. However, compared to Li+, several intrinsic properties of Na+ and K+, including their solvation and dynamics in typical organic electrolytes utilized in battery applications, are less well-understood. Here, we report a systematic investigation of Na+ and K+ in ethylene carbonate (EC) using first-principles molecular dynamics simulations. Our simulations reveal significant differences in the solvation structure and dynamical properties of Na+ and K+ compared to Li+. We find that, in contrast to Li+ which exhibits a well-defined first solvation shell, the larger Na+ and K+ ions show more disordered and flexible solvation structures. These differences in solvation were found to significantly influence the ion dynamics, leading to larger diffusion coefficients of Na+ and K+ compared to Li+. Our simulations also reveal a clear and interesting analog in the behavior of the ions in EC and aqueous environments, particularly in the specific ion effects on the solvent dynamics. This work provides fundamental understanding of the intrinsic properties of Na+ and K+ in organic electrolytes, which may ultimately influence the intercalation mechanism at the electrode–electrolyte interface and therefore battery performance, lifetime, and safety.

Ab initio simulations of liquid electrolytes for energy conversion and storage

“…Thick solid and transparent lines denote bonds to carbonyl and ether EC oxygen atoms, respectively. Reproduced from Pham et al, [148] copyright 2017 American Chemical Society FIGURE 10 Mean square displacement computed for all EC molecules in the electrolyte with Li + (black), Na + (red), and K + (blue) ions. The MSD computed for EC molecules only in the first solvation shell of Li + is presented by the dashed line.…”

High‐Performance K–CO2 Batteries Based on Metal‐Free Carbon Electrocatalysts

“…The higher Gibbs free energy for the formation of K 2 CO 3 (Δ f G o (K 2 CO 3 )=−1069.12 kJ mol −1 ) as compared to Na 2 CO 3 (Δ f G o (Na 2 CO 3 )=−1047.67 kJ mol −1 ) could lead to a higher discharge potential of 2.48 V for K–CO 2 batteries than the corresponding value of 2.35 V for Na–CO 2 batteries. Furthermore, K + has the smallest Stokes radius (3.6 Å), as compared to Li + (4.8 Å) and Na + (4.6 Å), in propylene carbonate (PC) solvents, and hence the highest ion mobility and ion conductivity among them . Clearly, therefore, K possesses multiple advantages for the development of metal–CO 2 batteries.…”

“…Furthermore, K + has the smallest Stokes radius (3.6 ), as compared to Li + (4.8 ) and Na + (4.6 ), in propylene carbonate (PC) solvents, and hence the highest ion mobility and ion conductivity among them. [12] Clearly, therefore, K possesses multiple advantages for the development of metal-CO 2 batteries. Unlike Li-CO 2 [4a, 7b] and Na-CO 2 [4b, 10] , which have been reported widely, however, the construction of a K-CO 2 battery has not been realized to date, although the battery reactions (discharge: 4 K + 3 CO 2 + 4 e À !2 K 2 CO 3 + C; charge: 2 K 2 CO 3 + C!4 K + 3 CO 2 + 4 e À ) have recently been demonstrated with a model system.…”

Effect of Cation Size on Solvation and Association with Superoxide Anion in Aprotic Solvents

“…So far, various atomistic modeling techniques have been employed to clarify the solvation of cations in various organic solvents and water at the molecular level . In particular, it was found with the help of the first‐principles molecular dynamics method that the solvation shell of K + and Na + ions in ethylene carbonate (EC) is less stable than the Li + ion shell . In another work, the solvation shell of the Li + ion in DMSO:ACN mixtures was investigated by molecular dynamics (MD) simulation .…”

“…[16][17][18][19][20] In particular, it was found with the help of the first-principles molecular dynamics method that the solvation shell of K + and Na + ions in ethylene carbonate (EC) is less stable than the Li + ion shell. [21] In another work, the solvation shell of the Li + ion in DMSO:ACN mixtures was investigated by molecular dynamics (MD) simulation. [22] The Li + cation is mainly solvated by DMSO molecules at different concentration ratios of DMSO and ACN that is in qualitative agreement with the experiment.…”