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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.

Unformatted postprint, Mixed conductors having both high ionic and electronic conductivity are needed in membrane electrode assemblies (MEA) 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 2 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 whilst an organic ionic plastic crystal [C2mpyr][FSI] is present as both binder and ionic conductor. Surprisingly, both the electronic and ionic conductivity of the composite are enhanced relative to the pure components by a factor of ×9 for electronic and ×180 for ionic. 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. ie. electronic, ionic and redox activity for future energy devices.