Promising aqueous dispersions of carbon black for semisolid flow battery application

Abstract

In this systematic study, we attempt to thoroughly understand the aggregation mechanism of conductive carbon black in aqueous dispersing medium and optimize the formulation of suspension electrodes for aqueous sodium–ion semisolid flow battery applications. For the first time, we present branched micelle solution as an electrolyte that introduces the widest electrochemical stability window of 3.5 V, from –3 to + 0.5 V vs. Ag/AgCl, with relatively low viscosity, rendering it as promising aqueous dispersing medium for suspension electrodes (anolytes). The simultaneous rheo-electrical measurements revealed that the aggregation of conductive ketjenblack (KB) particles was controlled by the electrostatic repulsion forces that doubly originate from the inter-aggregate soft interaction and bulk micelle interactions. This remarkable interaction rendered the dispersions electrically percolated at low carbon content (0.9 wt%) and importantly able to conserve the electrical conductivity under extremely high shear rates. Under the quiescent conditions, the percolated KB dispersion could sustain higher load of active material (up to 30 wt% Na2Ti3O7 as an active material) without severe influence on the rigidity (rheological plateau modulus G0) and electrical conductivity (Σ) of the suspensions. These promising findings propound further investigation for the electrochemical performance of these aqueous sodium–ion suspension electrodes under flow conditions.