Abstract
A series of thermoplastic polymer electrolytes have been prepared employing poly(ethylene oxide) (PEO) as a polymer matrix, bis(trifluoromethane sulfonimide) (LiTFSI), and different room-temperature ionic liquids (RTIL) with bis(fluorosulfonyl)imide (FSI) or TFSI anions. This formulation makes them safe and non-flammable. The electrolytes have been processed in the absence of solvents by melt compounding at 120 °C, using sepiolite modified with d-α-tocoferol-polyethyleneglycol 1000 succinate (TPGS-S) as a physical cross-linker of PEO. Several concentrations of RTILs, lithium salt, and TPGS-S have been tested in order to obtain the highest ionic conductivity (σ) without losing electrolytes’ mechanical stability. The materials’ rheology and ionic conductivity have been extensively characterized. The excellent crosslinking ability of TPGS-S makes the electrolytes behave as thermoplastic materials, even those with the highest liquid concentration. The electrolytes with the highest concentrations of FSI anion present a σ over 10−3 S·cm−1 at 25 °C and close to 10−2 S·cm−1 at 70 °C, and notably behave as solids at temperatures up to 90 °C despite over 65 wt % of their formulation being liquid. The electrolytes thus obtained are safe solid thermoplastics prepared by industrially scalable procedures and are suitable for energy storage devices, proving the adequacy of polymer-based materials as solid electrolytes for batteries or supercapacitors.
Highlights
Energy storage is one of the main items on the current scientific and technological agenda.Polymers have gained prominence as both as electrode and electrolyte materials
The electrolytes obtained are safe solid thermoplastics prepared by industrially scalable procedures and are suitable for energy storage devices, proving the adequacy of polymer-based materials as solid electrolytes for batteries or supercapacitors
Numerous studies can be found in the scientific literature [1,2]
Summary
Energy storage is one of the main items on the current scientific and technological agenda. Polymers have gained prominence as both as electrode and electrolyte materials. The possibility they offer to produce solid electrolytes with adequate mechanical and transport properties is unique. Employing Solid Polymer Electrolytes (SPE) in electrochemical batteries offers many advantages in comparison to liquid ones, and a main drawback, which is the low ionic conductivity inherent to their solid state. On the different ways to prepare SPEs with the highest possible ionic conductivity (σ) and sufficient mechanical stability. These strategies are mostly based on making the electrolyte behave as a liquid at the microscopic scale, so as to increase ionic mobility. Employing working temperatures where the electrolyte becomes a viscous liquid [3] or introducing large ratios of a liquid component [4,5]
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