Four Phosphonium‐based Ionic Liquids. Synthesis, Characterization and Electrochemical Performance as Electrolytes for Silicon Anodes

Abstract

Herein, we describe the synthesis, characterization and electrochemical performance of four phosphonium‐based ionic liquids (ILs) as electrolytes, Physicochemical properties such as viscosity, density, ionic conductivity, and thermal stability of ILs and conventional organic solvent ethylene carbonate (EC)/diethyl carbonate (DEC) were experimentally determined at different temperatures. All ILs showed thermal stability greater than 300 °C, surpassing the stability of the conventional organic solvent, whose flash points were 145 and 23 °C for EC and DEC, respectively. Nevertheless, at room temperature, all ILs are much more viscous than EC/DEC. The composite Si ‐[P2224][FSI] (triethyl‐n‐butylphosphonium bis(fluoromethylsulfonyl)imide) and Si‐EC/DEC anodes exhibit initial specific capacities at 0.15 A/g of 2409 and 2631 mAh/g, respectively. This demonstrates that despite the inferior transport properties of ILs, short alkyl‐substituted phosphonium ILs like [P2224][FSI] are potentially competitive for the new generation of electrolytes for LIBs. NMR, DSC, TGA, and galvanostatic discharged/charged were used as characterization techniques.

Temperature and Pressure Dependence of the Transport Properties of the Ionic Liquid Triethyloctylphosphonium Bis(trifluoromethanesulfonyl)amide, [P222,8][Tf2N]

“…Figure shows the deviation plot for the fit to eq and indicates good agreement with the results obtained with the Stabinger viscometer-densimeter. There is a fair agreement with the literature values, − although those measurements had lower reported precisions than that of this work.…”

“…The Stokes− Einstein−Sutherland analysis of the self-diffusion and viscosity results is consistent with the Walden plot for the conductivity. The conductivity data of Phillipi et al 31 are consistent with those of this study, whereas those of Sańchez-Ramı ́rez et al 32 deviate considerably.…”

“…1−8 Literature calorimetric results range from (186 to 192 K). 32,36,37 The Litovitz equation also well reproduced the results with 100•u r (η) = 0.8.…”

“…The relative standard uncertainty of fit is 100· u r ( η ) = 0.6. A glass-transition temperature of 183 K is predicted from the temperature dependence using Angell′s relationship, as employed in our previous studies. − Literature calorimetric results range from (186 to 192 K). ,, …”

“…The dashed lines represent the expanded uncertainty ( k = 2) for the fit, 100· U r = 1.6. Symbols: ●, this work, falling-body viscometer and ■, this work, Stabinger rotating cylinder rheometer, both with expanded relative uncertainty ( k = 2), 100· U r = 2; ○, Fillion et al, cone and plate viscometer, 100· U r = 6; □, Sánchez-Ramı́rez et al, Stabinger rotating cylinder rheometer, 100· U r = 2 (estimated); ◊, Philippi et al, Stabinger rotating cylinder rheometer, 100· U r = 2 (estimated); and △, Shirota et al, reciprocating electromagnetic piston viscometer, 100· U r = 1 (manufacturer).…”