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.

A polymer/ionic liquid thermoplastic solid electrolyte based on poly(ethylene oxide) (PEO), modified sepiolite (TPGS-S), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and 1-Butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI) ionic liquid is prepared using solvent free extrusion method. Its physical-chemical, electrical, and electrochemical properties are comprehensively studied. The investigated solid electrolyte demonstrates high ionic conductivity together with excellent compatibility with lithium metal electrode. Finally, truly Li-LiFePO4 solid state coin cell with the developed thermoplastic solid electrolyte demonstrates promising electrochemical performance during cycling under 0.2 C/0.5 C protocol at 60 °C.

The development of novel solid electrolytes, which can be processed using solvent-free methods, is one of the keys for successful industrialization of solid state batteries and their further implementation in electrical vehicles. Here, we study thermoplastic solid state electrolytes based on polyethylene oxide (PEO), 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and two inorganic fillers with different morphology and nature (modified sepiolite (TPGS-S) and garnet-type Li7La3Zr1.75Nb0.25O12 (LLZNO) prepared by solvent free extrusion method. Several thermoplastic polymer electrolytes (TPEs) are prepared and comprehensively studied. Composite thermoplastic electrolyte TPE-S10G10 containing 10 wt% of TPGS-S and 10 wt% of LLZNO fillers shows the best electrochemical performance in Li-LiFePO4 solid state batteries operating under 0.2C/0.5D cycling conditions at 60 °C. Solid state cell with TPE-S10G10 electrolyte retains 80% of initial discharge capacity after 540 cycles. Thus, a synergetic effect of using two different fillers, which can be exploited during the development of TPEs, is clearly demonstrated.

Composite materials of conjugated polymers/cellulose were fabricated by incorporating different polythiophene-derivative polymers: Poly(3,4-ethylenedioxythiophene) (PEDOT) and an alkylated derivative of poly(3,4-propylenedioxythiophene) (PProDOT). These conjugated polythiophenes were deposited by casting or spray coating methodologies onto three different cellulose substrates: Conventional filters papers as cellulose acetate, cellulose grade 40 Whatman® and cellulose membranes prepared from cellulose microfibers. The preparation of composite materials was carried out by two methodologies: (i) by employing in-situ polymerization of 3,4-ethylenedioxithiophene (EDOT) or (ii) by depositing solutions of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) or lab-synthetized PProDOT. Composite materials were studied in terms of electrical conductivity and surface morphology assessed by impedance spectroscopy, surface conductivity, SEM, and 3D optical profilometry. In-situ composite materials prepared by spray coating using iron trifluoromethane sulfonate as oxidizing agent can be handled and folded as the original cellulose membranes displaying a surface conductivity around 1 S∙cm−1. This versatile procedure to prepare conductive composite materials has the potential to be implemented in flexible electrodes for energy storage applications.

A solvent-free method that allows thermoplastic solid electrolytes based on poly(ethylene oxide) PEO to be obtained under controlled atmosphere conditions is presented. This method comprises two steps, the first one being the melt compounding of PEO with a filler, able to physically crosslink the polymer and its pelletizing, and the second the pellets’ swelling with an electroactive liquid phase. This method is an adaptation of the step described in previous publications of the preparation of thermoplastic electrolytes by a single melt compounding. In comparison to the single step extrusion methodology, this new method permits employing electroactive species that are very sensitive to atmospheric conditions. The two-step method can also be designed to produce controlled phase-segregated morphologies in the electrolyte, namely polymer-poor and polymer-rich phases, with the aim of increasing ionic conductivity over that of homogeneous electrolytes. An evaluation of the characteristics of the electrolytes prepared by single and two-step procedures is done by comparing membranes prepared by both methods using PEO as a polymeric scaffold and a solution of the room-temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide (EMI TFSI) and the bis(trifluoromethanesulfonyl) imide lithium salt (Li TFSI) as liquid phase. The electrolytes prepared by both methods have been characterized by Fourier transform infrared spectroscopy and optic microscopy profilometry, differential scanning calorimetry, self-creep experiments, and dielectric spectroscopy. In this way, the phase separation, rheology, and ionic conductivity are studied and compared. It is striking how the electrolytes prepared with this new method maintain their solid-like behavior even at 90 °C. Compared to the single step method, the two-step method produces electrolytes with a phase-separated morphology, which results in higher ionic conductivity.