Non-aqueous carbon black suspensions for lithium-based redox flow batteries: rheology and simultaneous rheo-electrical behavior

Abstract

We report on the rheological and electrical properties of non-aqueous carbon black (CB) suspensions at equilibrium and under steady shear flow. The smaller the primary particle size of carbon black is, the higher the magnitude of rheological parameters and the conductivity are. The electrical percolation threshold ranges seem to coincide with the strong gel rather than the weak gel rheological threshold ones. The simultaneous measurements of electrical properties under shear flow reveal the well-known breaking-and-reforming mechanism that characterises such complex fluids. The small shear rate breaks up the network into smaller agglomerates, which in turn transform into anisometric eroded ones at very high shear rates, recovering the network conductivity. The type of carbon black, its concentration range and the flow rate range are now precisely identified for optimizing the performance of a redox flow battery. A preliminary electrochemical study for a composite anolyte (CB/Li4Ti5O12) at different charge-discharge rates and thicknesses is shown.

Biphasic Electrode Suspensions for Li‐Ion Semi‐solid Flow Cells with High Energy Density, Fast Charge Transport, and Low‐Dissipation Flow

“…These two particle populations are suspended and mixed sequentially in propylene carbonate (PC) with 1M of lithium bis(trifluoromethane)sulfonamide (LiTFSI). It is well known that colloidal particles will rapidly aggregate when suspended in polar solvents under high ionic strength conditions due to van der Waals interactions.[20] Hence, we first introduce a non-ionic dispersant, polyvinylpyrrolidone (PVP), with appropriate amount to selectively stabilize the LFP particles fully, but not the KB particles.[ [21][22][23] PVP has been shown to sterically stabilize colloidal particles in both aqueous [22][23][24] and non-aqueous [25] media leading to well dispersed suspensions. PVP is especially useful for SSFC electrodes, as it confers stability even in systems with high (1 M) salt concentrations that undergo electrochemical charging and discharging.…”

“…[25] We investigated the effects of biphasic suspension composition on the microstructure, flow behavior, and electrochemical performance of these SSFC electrodes. We show that well-dispersed (repulsive) LFP particles, surrounded by a percolating (attractive) KB network, enable quick and efficient charge transport that reduces overpotential during cell cycling.…”

“…[ [21][22][23] PVP has been shown to sterically stabilize colloidal particles in both aqueous [22][23][24] and non-aqueous [25] media leading to well dispersed suspensions. PVP is especially useful for SSFC electrodes, as it confers stability even in systems with high (1 M) salt concentrations that undergo electrochemical charging and discharging.…”

“…We note that in the absence of attractive KB particles, the shear elastic modulus is indeed quite small (1. since the carbon black (KB) network gives rise to both the desired electronic conductivity (which facilitates charge transfer) and a yield stress (which increases pumping pressure). [25,31] To identify the suitable SSFC suspension composition, we developed an electrode-scale model that incorporates efficiency and flowability criteria. For all suspensions, the modeled cell is subjected to a current density i of 10 mA cm -2 with a current-collector length L cc of 20 mm.…”

Thermoreversible gelation in poly(ethylene oxide)/carbon black hybrid melts

“…Nevertheless, it is clear that percolated CB networks are prone to mechanical deformations and even small shear forces can destroy the 3-D connectivity in CB/ polypropylene carbonate suspensions causing a steep drop in viscosity and conductivity (20). In CB/varnish dispersions, the viscosity increases with heating due to the formation of CB clusters that remain intact during subsequent cooling, but do not sustain shearing (21).…”