Mixed ionic-electronic conductors, such as poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) are postulated to be the next generation materials in energy storage and electronic devices. Although many studies have aimed to enhance the electronic conductivity and mechanical properties of these materials, there has been little focus on ionic conductivity. In this work, blends based on PEDOT stabilized by the polyelectrolyte poly(diallyldimethylammonium) (PolyDADMA X) are reported, where the X anion is either chloride (Cl), bis(fluorosulfonyl)imide (FSI), bis(trifluoromethylsulfonyl)imide (TFSI), triflate (CF₃SO₃) or tosylate (Tos). Electronic conductivity values of 0.6 S cm⁻¹ were achieved in films of PEDOT:PolyDADMA FSI (without any post-treatment), with an ionic conductivity of 5 × 10⁻⁶ S cm⁻¹ at 70 °C. Organic ionic plastic crystals (OIPCs) based on the cation N-ethyl-N-methylpyrrolidinium (C₂mpyr⁺) with similar anions were added to synergistically enhance both electronic and ionic conductivities. PEDOT:PolyDADMA X / [C₂mpyr][X] composites (80/20 wt%) resulted in higher ionic conductivity values (e.g., 2 × 10⁻⁵ S cm⁻¹ at 70 °C for PEDOT:PolyDADMA FSI/[C₂mpyr][FSI]) and improved electrochemical performance versus the neat PEDOT:PolyDADMA X with no OIPC. Herein, new materials are presented and discussed including new PEDOT:PolyDADMA and organic ionic plastic crystal blends highlighting their promising properties for energy storage applications.

Mixed conductors having both high ionic and electronic conductivities are needed in membrane electrode assemblies (MEAs) present in electrochemical devices from fuel cells to supercapacitors and all battery chemistries. Typically, carbon black, binders, and redox-active materials are combined to make an electrode assembly, into which a liquid electrolyte can impregnate. Solid-state devices require the ionic conduction built into the MEA. In this case, a material which can provide both electronic and ionic conduction as well as a redox functionality is described based on PEDOT–Cl as both the electronic conductor and the redox active component, while an organic ionic plastic crystal [C₂mpyr][FSI] is present as both the binder and ionic conductor. Surprisingly, both the electronic and ionic conductivities of the composite are enhanced relative to the pure components by a factor of ×9 for electronic and ×180 for ionic conductivities. The mixed conducting composites are demonstrated to retain their redox activity in aqueous electrolytes, and in the optimum case, 103 F g^–1 and 296 mF cm^–2 capacitance values are obtained for low- and high-mass loading electrodes. These materials demonstrate an innovative approach to prepare electrode assemblies where all three functionalities are incorporated into the materials, that is, electronic, ionic, and redox activity for future energy devices.

Solid polymer electrolytes that combine both a high lithium-ion transference number and mechanical properties at high temperatures are searched for improving the performance of batteries. Here, we show a salt-free all-polymer nanocomposite solid electrolyte for lithium metal batteries that improves the mechanical properties and shows a high lithium-ion transference number. For this purpose, lithium sulfonamide-functionalized poly(methyl methacrylate) nanoparticles (LiNPs) of very small size (20-30 nm) were mixed with poly(ethylene oxide) (PEO). The morphology of all-polymer nanocomposites was first investigated by transmission electron microscopy (TEM), showing a good distribution of nanoparticles (NPs) even at high contents (50 LiNP wt %). The crystallinity of PEO was investigated in detail and decreased with the increasing concentration of LiNPs. The highest ionic conductivity value for the PEO 50 wt % LiNP nanocomposite at 80 °C is 1.1 × 10^-5 S cm^-1, showing a lithium-ion transference number of 0.68. Using dynamic mechanic thermal analysis (DMTA), it was shown that LiNPs strengthen PEO, and a modulus of ≈10⁸ Pa was obtained at 80 °C for the polymer nanocomposite. The nanocomposite solid electrolyte was stable with respect to lithium in a Li||Li symmetrical cell for 1000 h. In addition, in a full solid-state battery using LiFePO₄ as the cathode and lithium metal as the anode, a specific capacity of 150 mAhg^-1 with a current density of 0.05 mA cm^-2 was achieved.