Li Ion Conducting Polymer Gel Electrolytes Based on Ionic Liquid/PVDF-HFP Blends

Abstract

Ionic liquids thermodynamically compatible with Li metal are very promising for applications to rechargeable lithium batteries. 1-methyl-3-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide (P 13 TFSI) is screened out as a particularly promising ionic liquid in this study. Dimensionally stable, elastic, flexible, nonvolatile polymer gel electrolytes (PGEs) with high electrochemical stabilities, high ionic conductivities and other desirable properties have been synthesized by dissolving Li imide salt (LiTFSI) in P 13 TFSI ionic liquid and then mixing the electrolyte solution with poly(vinylideneco-hexafluoropropylene) (PVDF-HFP) copolymer. Adding small amounts of ethylene carbonate to the polymer gel electrolytes dramatically improves the ionic conductivity, net Li ion transport concentration, and Li ion transport kinetics of these electrolytes. They are thus favorable and offer good prospects in the application to rechargeable Li batteries including open systems like Li/air batteries, as well as more "conventional" rechargeable lithium and lithium ion batteries.As is well known, Li is the most electropositive and lightest metal, and thus has the greatest theoretical specific capacity of 3860 Ah/kg.1 , 2 This has attracted worldwide efforts of researchers and manufacturers to develop advanced battery technologies based on lithium. To date, the rechargeable lithium ion battery has already been one of the best choices in view of specific capacity and cycle stability. 1 However, rechargeable lithium metal batteries with even higher specific capacities are still unavailable in the market, especially lithium/air batteries which possess the highest theoretical specific energy (as high as 13,000 Wh/g, excluding the oxygen from the air). Conventional Li/air batteries based on aqueous electrolytes suffer from fast capacity loss due to corrosion of lithium by water and are also nonrechargeable. Abraham and Jiang first reported a rechargeable lithium/oxygen cell using organic polymer gel electrolytes and demonstrated its advantages such as an all solid state design, rechargeablity and a high capacity. 3 Read studied the effect of electrolyte and air cathode formulation on the electrochemical properties of an Li/O 2 organic electrolyte cell and found that electrolyte composition has the largest effect on discharge capacity and rate capability. 4 Both groups incorporated common organic solvents in the electrolyte, i.e., ethylene carbonate (EC), propylene carbonate (PC), 1,2-dimethoxyethane, diethyl carbonate (DEC), dimethyl carbonate, γ-butyrolactone, tetrahydrofuran, or tetrahydropyran. 3, 4 The highly reactive lithium metal cannot, however, be thermodynamically compatible with common organic solvents. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript considerable additional challenges in improving the properties of the electrolytes being used, such as meeting the requirements of little to no volatility, moisture insensitivity and air stability. Our efforts are concerned with developing s...

Safer Electrolytes for Lithium‐Ion Batteries: State of the Art and Perspectives

“…[270] Similarly,Y ee tal., [271] Navarra et al, [272] and Hofmann et al [273] reported very promising resultsi nt erms of safety and electrochemical performance for PVdF-HFP-based quaternary electrolyte systems; this also revealed good compatibility with graphite anodes and Li(Ni 1/3 Mn 1/3 Co 1/3 )O 2 cathodes. Nevertheless, intrinsic safety issues related to the utilization of volatile and flammable organic solvents might be substantially reduced, but not completely overcome.…”

Effects of Surfactants on the Morphology and Properties of Electrospun Polyetherimide Fibers

“…They also reported that surface tension and viscoelastic properties were the main parameters for bead generation. The net charge density carried by the electrospinning jet, solution viscosity, and surface tension of the polymer solutions are the main factors that influence bead formations [26,27].…”

Ionic Liquid‐Based Membranes as Electrolytes for Advanced Lithium Polymer Batteries

“…Indeed, the good thermal, electrochemical, and interfacial properties of this type of hybrid membranes have been demonstrated in our laboratory [19] and in other laboratories. [20,21] Therefore, it appeared to us of interest to extend the study by considering a new organic solvent mixture (EC-PC-DMC) and evaluating its effect on the performances of PVdF-HFP membranes containing LiTFSI-Py 24 TFSI electrolyte solutions. We expected that the use of the ternary organic solvent mixture would lead to important advances in terms of: a) enhancement of ion dissociation owing to the high dielectric constants of both EC and PC; b) optimization of interfacial behavior owing to the passivating film-forming ability of EC; [22] c) improvement of fast ion transport owing to the low viscosity of DMC and d) widening of the temperature range of high ionic conductivity owing to the synergic effect of the three solvents with the thermally stable ionic liquid component.…”