Pyrrolidinium FSI and TFSI-Based Polymerized Ionic Liquids as Electrolytes for High-Temperature Lithium-Ion Batteries

Abstract

Promising electrochemical and dynamical properties, as well as high thermal stability, have been the driving forces behind application of ionic liquids (ILs) and polymerized ionic liquids (PILs) as electrolytes for high-temperature lithium-ion batteries (HT-LIBs). Here, several ternary lithium-salt/IL/PIL electrolytes (PIL el ) have been investigated for synergies of having both FSI and TFSI anions present, primarily in terms of physico-chemical properties, for unique application in HT-LIBs operating at 80 • C. All of the electrolytes tested have low T g and are thermally stable ≥100 • C, and with TFSI as the exclusive anion the electrolytes (set A) have higher thermal stabilities ≥125 • C. Ionic conductivities are in the range of 1 mS/cm at 100 • C and slightly higher for set A PIL el , which, however, have lower oxidation stabilities than set B PIL el with both FSI and TFSI anions present: 3.4-3.7 V vs. 4.2 V. The evolution of the interfacial resistance increases for all PIL el during the first 40 h, but are much lower for set B PIL el and generally decrease with increasing Li-salt content. The higher interfacial resistances only influence the cycling performance at high C-rates (1 C), where set B PIL el with high Li-salt content performs better, while the discharge capacities at the 0.1 C rate are comparable. Long-term cycling at 0.5 C, however, shows stable discharge capacities for 100 cycles, with the exception of the set B PIL el with high Li-salt content. Altogether, the presence of both FSI and TFSI anions in the PIL el results in lower ionic conductivities and decreased thermal stabilities, but also higher oxidation stabilities and reduced interfacial resistances and, in total, result in an improved rate capability, but compromised long-term capacity retention. Overall, these electrolytes open for novel designs of HT-LIBs.

Application of Ionic Liquids for Batteries and Supercapacitors

“…Pyrrolidinum-based RTILs have also been widely applied in SCs and Li-ion batteries as a solid-state electrolyte [50]. Substitution of the pyrrolidine cation improves the ionic conductivity of ILs-based electrolytes.…”

“…Lazzari, M. et al reported that the capacitance of AC electrodes and Pyr 14 TFSI/(EMIM)(TFSI) electrolyte-based SCs were greatly influenced by the polarization of the cation parts of the ionic liquids on the surface of AC electrodes [55,56]. However, a lot of research work is going on all over the world on pyrrolidinum-based ILs for Li-ion and SC applications, but low-temperature conductivity and poor cycle life hinder its market application due to larger non-polar or surfactant ILs [50,57]. Quezada, D. et al designed a safer Li-ion battery using zinc stannate as the anodic material and 1 M-LiNTF 2 solution in 1-methyl-1-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide ((MPPyr)(TFSI)) or 1-butyl-1-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide ((BMPyr)(TFSI)) as ILs electrolytes.…”

Pyrrolidinium Containing Ionic Liquid Electrolytes for Li-Based Batteries

“…Despite the higher electrochemical performances in liquid form, the use of C 4 mpyrFSI electrolytes with polymer matrices is not commonly studied. Kerner et al [190] synthesized PIL-based electrolytes, where one set contained C 4 mpyrTFSI, and another set contained C 4 mpyrFSI. Both electrolytes tested with LFP yielded electrode discharge capacities above 140 mAh g −1 at 80 • C when 0.5 C rate was utilized.…”

Influence of Cationic Poly(ionic liquid) Architecture on the Ion Dynamics in Polymer Gel Electrolytes

“…The PDADMA TFSA showing highest conductivity was further utilized for the synthesis of ion gels containing N -butyl- N -methylpyrrolidinium TFSA (Pyr 14 TFSA) and LiTFSA in various compositions . Recently, PDADMA based gels with high lithium concentrations were investigated, as well as gels containing two different anions, FSA and TFSA …”