Effect of Salt Concentration on Properties of Lithium Ion Battery Electrolytes: A Molecular Dynamics Study

Abstract

Electrolyte solutions of 1 M concentration are typically used in lithium ion batteries (LIB) for optimal performance. However, recently, superconcentrated electrolytes have been proposed to be a promising alternative to 1 M solutions. Despite their improved stability features, application of the concentrated electrolytes is hindered by their poor transport properties. We probe EC-LiPF 6 electrolyte system for a range of concentrations: 0.06 to 4 M using molecular dynamics simulations to study the effect of concentration on transport and structural properties. Molecular structure of the solution changes with concentration from a predominantly solvent separated ion pair (SSIP) configuration at the dilute limit to an aggregate rich configuration at high concentration. Depletion of SSIPs and formation of more aggregates at higher concentrations affect the transport properties. The present work provides insights into the relation between molecular structure and performance of the electrolyte solution and suggests ways to design novel concentrated electrolytes.

Anion Coordination Characteristics of Ion-pair Complexes in Highly Concentrated Aqueous Lithium Bis(trifluoromethane- sulfonyl)amide Electrolytes

“…[7][8][9][10][11] This concept has been widely investigated, not only in the field of LIB chemistry/technology, but also for fundamental science at the molecular level (structure and dynamics in the liquid state), both experimentally and theoretically. [12][13][14][15][16][17] Highly concentrated electrolytes can be successfully applied to both non-aqueous [18][19][20][21][22] and aqueous [23][24][25][26] solution systems to enable reversible, stable, and working LIBs with adequate electrode materials. The bis(trifluoromethanesulfonyl) amide (TFSA) anion is commonly used as the counterion of the Li salt because TFSA is hard to coordinate with Li ions in solutions, leading to much higher salt solubilities.…”

Re‐weighted random series path integral simulations of molecular clusters: Applications to lithium solvated by a mixed Stockmayer cluster

“…The magnitude of the nuclear quantum effects we observe at room temperature is comparable in magnitude to those found for lithium solvated by water clusters, where the ion‐dipole interaction is weaker than in the current system . Therefore, the inclusion of nuclear quantum effects are likely to be important to the community of investigators who employ simulations to provide insights into the relation between molecular structure and performance of the electrolyte solution, at the electrode‐electrolyte interface, and to suggest ways to design novel electrolytes, to name a few important applications involving lithium ions.…”

“…Even though the body of knowledge gathered to date on clusters is vast, we find surprisingly little work dedicated to the study of Stockmayer and ion‐Stockmayer clusters in the literature. The present goals are of fundamental importance for the research and development of lithium ion batteries, as a practical application. Lithium ion batteries are complex bulk systems, and their direct simulations will likely require more realistic models to extend the scope of the present investigation.…”

Enabling High Performance Potassium‐Based Dual‐Graphite Battery Cells by Highly Concentrated Electrolytes

“…Therefore, molecular dynamic (MD) simulations and density functional theory calculations have to be performed to further evaluate the results regarding the exact wavenumber for each solution structure. However, results from Ravikumar et al., who calculated proportions of SSIPs, CIPs and AGGs via MD simulations for a system with lithium hexafluorophosphate (LiPF 6 ) in EC as electrolyte, are remarkably similar to the KFSI in EMC electrolyte system . Therefore, the here conducted mathematical fitting can be seen as a valid method to investigate the solution structure of this electrolyte.…”