Bis(μ-hydroxo)dicopper(II,II) bearing a naphthyridine-based ligand has been synthesized and characterized in the solid state and solution. Cyclic voltammetry at room temperature displays a reversible redox system that corresponds to the monoelectronic oxidation of the complex. Spectroscopic and time-resolved spectroelectrochemical data coupled to theoretical results support the formation of a charge-localized mixed-valent Cu(II,III)2 species.

Solid state batteries are seen as a key for the development of safer and higher energy density batteries, by limiting flammability and enabling the use of the lithium metal anode, respectively. Composite polymer/ceramic electrolytes are a possible solution for their realisation, by benefitting from the combined mechanical properties of the polymer electrolyte and the thermal stability and high conductivity of the ceramic electrolyte. Here, we use different liquid electrolyte chemistries as models for the polymer electrolytes, and evaluate the effect of adding a variety of porous and dense ceramic electrolytes on the conductivity. All results can be modelled with the effective medium theory, allowing predictions to be made on electrolyte combinations.We unambiguously determine that highly conductive porous particles act as insulators in such systems, whereas dense particles act as conducting, thereby advancing our understanding of composite electrolyte conductivity.