Solid Polymer Electrolytes from Polyanionic Lithium Salts Based on the LiTFSI Anion Structure

Abstract

Effects of anion size on ionic conductivity were studied for a series of solid polymer electrolytes prepared from lithium polyanionic salts based on a series of lithium bis͓͑perfluoromethyl͒sulfonyl͔imide ͑LiTFSI͒ units connected together by perfluoroalkane linkers to form oligomeric anionic chains of variable length. Solid polymer electrolytes were prepared from the salts using polyethylene oxide as the host and characterized using X-ray diffraction, differential scanning calorimetry, and electrochemical impedance spectroscopy. Ionic conductivities were measured over a temperature range between 120°C and ambient for electrolytes with ethylene oxide ͑EO͒/Li ratios of 30:1 and 10:1. Solid polymer electrolytes prepared from the lithium polyanionic salts exhibited ionic conductivities that were consistently lower ͑by factors of between 2 and 10͒ relative to those of monomeric LiTFSI-based electrolytes over the entire temperature and salt concentration ranges. This finding probably reflects a diminished contribution of anions to the overall conductivity for salts with large, polymeric anions. Trends in ionic conductivity with respect to anion chain length and EO/Li ratio were studied. The existence of an optimal anion chain length that is different for solid polymer electrolytes of differing EO/Li ratio was noted and is rationalized in terms of the cumulative effects of anion mobility, ion-pairing, variations in host chain dynamics in the vicinity of ions as a function of anion structure, and salt-phase segregation on the conductivity.

Solid polymer electrolytes based on poly(lithium carboxylate) salts

“…reported that in the single-ion graft copolymer electrolyte of poly[(oxyethylene) 9 methacrylate-ran-lithium methacrylate]-graft-poly(dimethyl-siloxane), conversion of lithium methacrylate units via addition of BF 3 , Lewis acid, that is, a large increase in the number of mobile cations and an effective delocalization of the carboxylate anion charge through complexation with BF 3 (COOBF 3 − ) enhanced the ionic conductivity by two orders of magnitude [13,14]. In order to obtain the evidence of this effect in the poly(lithium carboxylate)-based polymer electrolytes, we measured the infrared spectra for the Poly (Li-A) This shift to higher frequency can be linked to an enhanced dissociation of lithium cation and carboxylate anion, that is, a shift of the carboxylate anion stretch to higher wave numbers due to ion-dipole interactions between the lithium cation and oxygen in PEO.…”

“…To attain the high lithium ion transference number, polyanionic lithium salts, lithium salts with weakly coordinating anion, and single-ion type polymer electrolytes have been designed [9][10][11][12][13]. And also, recently, it was reported that complexation of carboxylate anion in the single-ion conductor by Lewis acid BF 3 might improve ionic conductivity [14,15]. More recently, we investigated the solid polymer electrolytes composed of PEO and polyanionic lithium salts, poly(lithium sorbate) and poly (lithium muconate), with and without BF 3 ·OEt 2 and found that their ionic conductivities might be enhanced by one to two orders of magnitude with addition of BF 3 ·OEt 2 and also the transference number of lithium ion might be improved [16].…”

Synthesis and characterization of a novel electrolyte based on bis[(perfluoroalkyl)sulfonyl]triimide trianion

“…But many challenges have to be met in its synthetic work. Very recently, DesMarteau prepared a series of similar dilithium salts based on bis[(perfluoroalkyl)sulfonyl] diimides dianions [6]. PEO electrolyte containing these salts exhibited comparable ionic conductivity to PEO-LiTFSI.…”

Mechanism for improvement in mechanical and thermal stability in dispersed phase polymer composites

“…with alkali metal salts/acids (LiClO 4 , NaClO 4, NH 4 ClO 4 , H 3 PO 4 , etc.) offer electrical (ionic) conductivity in the range of 10 −4 to 10 −7 S cm −1 at room temperature [1][2][3][4][5]. Almost all the solid polymer electrolytes (SPEs) are endowed with some inherent drawbacks that impose limitations on their applicability in devices.…”

“…These are: (1) their semi-crystalline nature that hinders mobility of ions thereby lowering their conductivity, (2) poor thermomechanical stability, (3) slow kinetics, and (4) poor interfacial properties, etc. [1][2][3][4][5][6][7][8]. In order to overcome these chronic problems of ion-conducting polymers, various modifications such as co-polymerization, plasticization, ceramic dispersion, etc.…”