Thermal and Transport Properties of Na[N(SO₂F)₂]–[N-Methyl-N-propylpyrrolidinium][N(SO₂F)₂] Ionic Liquids for Na Secondary Batteries

Abstract

Understanding ion transport in electrolytes is crucial for fabricating high-performance batteries. Although several ionic liquids have been explored for use as electrolytes in Na secondary batteries, little is known about the transport properties of Na + ions. In this study, the thermal and transport properties of Na[FSA]-[C 3 C 1 pyrr][FSA] (FSA − : bis(fluorosulfonyl)amide and C 3 C 1 pyrr + : N-methyl-Npropylpyrrolidinium) ionic liquids were investigated in order to determine their suitability for use as electrolytes in Na secondary batteries. In the x(Na[FSA]) range of 0.0-0.5 (x(Na[FSA]) = molar fraction of Na[FSA]), a wide liquid-phase temperature range was observed at close to room temperature. The viscosity and ionic conductivity of this system, which obey the Vogel-Tamman-Fulcher equation, increases and decreases, respectively, with an increase in x(Na[FSA]). Further, its viscosity and molar ionic conductivity satisfy the fractional Walden rule. The apparent transport number of Na + in the investigated ionic liquids, as determined by the potential step method at 353 K, increases monotonously with an increase in x(Na[FSA]), going from 0.08 for x(Na[FSA]) = 0.1 to 0.59 for x(Na[FSA]) = 0.7. The Na + ion conductivity, determined by multiplying the ionic conductivity with the apparent transport number, is an indicator of Na + ion transport in Na secondary batteries and is high when x(Na[FSA]) is in the 0.2-0.4 range.

CuP2/C Composite Negative Electrodes for Sodium Secondary Batteries Operating at Room‐to‐Intermediate Temperatures Utilizing Ionic Liquid Electrolyte

“…Organic electrolytes have been applied as electrolytes for Na secondary batteries owing to its high electrochemical stability . Ionic liquids (ILs) composed of only cations and anions have low flammability, low volatility, and high thermal stability, which allow for improved safety characteristics of energy storage devices, and have been investigated as possible electrolytes for Na secondary batteries . Several groups have shown better performance with ILs compared to organic electrolytes in terms of cycle performance and rate capability.…”

Structural and Electrochemical Properties of Hard Carbon Negative Electrodes for Sodium Secondary Batteries Using the Na[FSA]–[C₃C₁pyrr][FSA] Ionic Liquid Electrolyte

“…[1][2][3][4][5][6][7][8][9][10][11] Sodium is abundant in the crust and seawater, showing a relatively low standard redox potential (¹2.71 V vs. SHE). Thus, batteries with low cost and high energy density can be constructed.…”

“…Moreover, ionic liquids are inherently safe due to their negligible volatility and non-flammability, with some of them showing reasonably high ionic conductivities and wide electrochemical windows. 5,6 We have already reported that Na[TFSA]-Cs[TFSA] (TFSA = bis(trifluoromethylsulfonyl)amide) and Na[FSA]-K[FSA] (FSA = bis(fluorosulfonyl)amide) ionic liquids are promising electrolytes for sodium secondary batteries operating at an intermediate temperature range (>353 K). [1][2][3][4] However, these salts are solid at room temperature, while electrolytes with lower melting points are more desirable for the construction of batteries for a wide range of practical applications.…”

“…Recently, we developed a new electrolyte, Na [FSA]-[C 3 C 1 pyrr][FSA] (C 3 C 1 pyrr = N-methyl-N-propylpyrrolidinium), that is a liquid in a wide temperature range, including room temperature. 5,6 For example, several positive electrode materials like We have also investigated the charge-discharge behavior of hard carbon (HC) negative electrodes in this ionic liquid at 363 K. 10,11 HC is mainly composed of two structural domains, i.e., randomly-arranged graphene domains and their interstitial sites (pores), and its charge-discharge behavior as a negative electrode material for sodium secondary batteries has been well investigated in organic solvent electrolytes. [12][13][14][15][16][17][18][19][20] However, there have been few studies on the correlation of HC structure and its electrochemical behavior in ionic liquid electrolytes.…”

Poly(vinyl chloride) Ionic Liquid Polymer Electrolyte Based on Bis(fluorosulfonyl)Amide for Sodium Secondary Batteries

“…6,7 The physical and electrochemical properties of ILs in Na secondary batteries have been studied in recent works. [8][9][10][11][12] In real application, polymerization of the IL is one important technique to retain the advantages of ILs and avoid leakage. As a type of gel polymer electrolytes (GPE), the resulting "ionic liquid polymer electrolytes (ILPEs)" consists of ILs, the host polymer, and another component for electrochemical reactions (e.g alkali metal salt).…”