Molecular Dynamics Simulations of Polymer–Ionic Liquid (1-Ethyl-3-methylimidazolium Tetracyanoborate) Ternary Electrolyte for Sodium and Potassium Ion Batteries

Abstract

We have performed molecular dynamics (MD) simulations of 1-ethyl-3-methylimidazolium tetracyanoborate ([EMIM]+[B­(CN)4]−) ionic liquid to investigate the impact of addition of Na+/K+[B­(CN)4]− salts and poly­(ethylene oxide) (PEO6) on transport properties. These ternary mixtures are promising electrolyte materials for Na+-ion and K+-ion batteries as alternatives to the traditional Li+-ion ones. In addition, local structure was assessed through radial distribution functions. Our main findings are the following: (1) when compared to systems with larger amounts of Na+ and K+, it was observed that lower concentrations enhance the overall ionic conductivity and decrease viscosity; (2) Na+ and K+ cations prefer to be coordinated to the polymer chains rather than the [B­(CN)4]− anions; (3) transport properties are improved when PEO6 oligomers are included in the electrolyte medium but these improvements continue only up to an optimum amount of PEO6. Beyond this amount, further addition of PEO6 did not have any additional impact on transport properties.

Electrolytes and Interphases in Potassium Ion Batteries

“…Benefiting from the merits of high ionic conductivity, extremely low vapor pressure, wide voltage window and superior electrochemical stability, ionic liquids are a burgeoning class of safe electrolytes. [ 113 ] Ionic liquid electrolytes are less investigated in PIBs, mainly comprising of KFSI‐ and KTFSI‐based electrolytes. Yamamoto et al.…”

“…In order to screen potential ionic liquid electrolytes for PIBs in terms of ionic conductivity, solvation structures and electrochemical voltage window, computer‐aiding screening methods have been used, including molecular dynamics (MD) simulation, density functional theory (DFT) calculation, machine learning, and big data analysis. [ 113,121–124 ] For example, MD simulations were conducted to investigate the ionic transport property of an polymer ionic liquid ternary electrolyte, [EMIM] + [B(CN) 4 ] − ionic liquid|K + [B(CN) 4 ] − salt|poly(ethylene oxide) (PEO) 6 , which was improved with optimized concentration of K + [B(CN) 4 ] − and PEO 6. [ 113 ] These results highlight the potential possibility of ionic liquid electrolytes for high performance PIBs.…”

“…[ 113,121–124 ] For example, MD simulations were conducted to investigate the ionic transport property of an polymer ionic liquid ternary electrolyte, [EMIM] + [B(CN) 4 ] − ionic liquid|K + [B(CN) 4 ] − salt|poly(ethylene oxide) (PEO) 6 , which was improved with optimized concentration of K + [B(CN) 4 ] − and PEO 6. [ 113 ] These results highlight the potential possibility of ionic liquid electrolytes for high performance PIBs. However, it should be pointed out that ionic liquids are usually expensive, which may hinder their widespread commercial use in battery applications.…”

Water–Salt Oligomers Enable Supersoluble Electrolytes for High‐Performance Aqueous Batteries

“…This method has been reported in the literature. [ 48–50 ] The corresponding valley used for calculating coordination numbers are provided in Table S11, Supporting Information.…”

Advancements and Challenges in Potassium Ion Batteries: A Comprehensive Review

“…This study revealed that this ionic liquid mixture is a promising electrolyte for both SIB and KIB technologies. [204] All the aforementioned ionic electrolytes demonstrated promising electrochemical properties when they are employed in KIBs along with suitable electrodes. Hence, the ionic liquid is a promising category of electrolyte for KIB application; however, intense research is necessary to bring this nacent technology to practical application.…”