Improving the Electrical Percolating Network of Carbonaceous Slurries by Superconcentrated Electrolytes: An Electrochemical Impedance Spectroscopy Study

Semisolid redox flow batteries simultaneously address the need for high energy density and design flexibility. The electrical percolating network and electrochemical stability of the flowable electrodes are key features that are required to fully exploit the chemistry of the semisolid slurries. Superconcentrated electrolytes are getting much attention for their wide electrochemical stability window that can be exploited to design high-voltage batteries. Here, we report on the effect of the ion concentration of superconcentrated electrolytes on the electronic percolating network of carbonaceous slurries. Slurries based on different concentrations of lithium bis(trifluoromethane)sulfonamide in tetraethylene glycol dimethyl ether (0.5, 3, and 5 mol/kg) at different content of Pureblack carbon (from 2 up to 12 wt %) have been investigated. The study was carried out by coupling electrochemical impedance spectroscopy (EIS), optical fluorescence microscopy, and rheological measurements. A model that describes the complexity and heterogeneity of the semisolid fluids by multiple conductive branches is also proposed. For the first time, to the best of our knowledge, we demonstrate that besides their recognized high electrochemical stability, superconcentrated electrolytes enable more stable and electronically conductive slurry. Indeed, the high ionic strength of the superconcentrated solution shields interparticle interactions and enables better carbon dispersion and connections.