A new approach to flow battery design is demonstrated wherein diffusion-limited aggregation of nanoscale conductor particles at ~1 vol% concentration is used to impart mixed electronic-ionic conductivity to redox solutions, forming flow electrodes with embedded current collector networks that self-heal after shear. Lithium polysulfide flow cathodes of this architecture exhibit electrochemical activity that is distributed throughout the volume of flow electrodes rather than being confined to surfaces of stationary current collectors. The nanoscale network architecture enables cycling of polysulfide solutions deep into precipitation regimes that historically have shown poor capacity utilization and reversibility, and may thereby enable new flow battery designs of higher energy density and lower system cost. Lithium polysulfide half-flow cells operating in both continuous and intermittent flow mode are demonstrated for the first time.

We introduce an modular fixture designed for stress-controlled rheometers to perform simultaneous rheological and electrical measurements on strongly conductive complex fluids under shear. By means of a nontoxic liquid metal at room temperature, the electrical connection to the rotating shaft is completed with minimal additional mechanical friction, allowing for simultaneous stress measurements at values as low as 1 Pa. Motivated by applications such as flow batteries, we use the capabilities of this design to perform an extensive set of rheoelectric experiments on gels formulated from attractive carbon-black particles, at concentrations ranging from 4 to 15 wt %. First, experiments on gels at rest prepared with different shear histories show a robust power-law scaling between the elastic modulus G 0 0 and the conductivity σ 0 of the gels-i.e., G 0 0 ∼ σ α 0 , with α ¼ 1.65 AE 0.04, regardless of the gel concentration. Second, we report conductivity measurements performed simultaneously with creep experiments. Changes in conductivity in the early stage of the experiments, also known as the Andrade-creep regime, reveal for the first time that plastic events take place in the bulk, while the shear rate _ γ decreases as a weak power law of time. The subsequent evolution of the conductivity and the shear rate allows us to propose a local yielding scenario that is in agreement with previous velocimetry measurements. Finally, to establish a set of benchmark data, we determine the constitutive rheological and electrical behavior of carbon-black gels. Corrections first introduced for mechanical measurements regarding shear inhomogeneity and wall slip are carefully extended to electrical measurements to accurately distinguish between bulk and surface contributions to the conductivity. As an illustrative example, we examine the constitutive rheoelectric properties of five different grades of carbon-black gels and we demonstrate the relevance of this rheoelectric apparatus as a versatile characterization tool for strongly conductive complex fluids and their applications.

The rapidly increasing deployment of wind and solar energy has resulted in an urgent need for a smarter, more efficient and reliable electronic grid for load balancing. [1,2] Currently, only a small fraction of the total electric production is tied to grid storage, with the vast majority 2 being pumped hydro installations. [3] While the latter technology is mature, cost effective, and efficient, it is geographically limited. [3] Alternate modes of energy storage that can be deployed in a distributed manner include batteries, compressed air, thermochemical energy, and flywheels. [3] Flow batteries are particularly attractive due to their decoupled energy and power, providing design flexibility especially at large scales. [4][5][6] Many flow battery chemistries, however, suffer from limited complex solubility and low nominal voltage, resulting in low energy densities. [7] To overcome this, Duduta et al. developed the semi-solid flow cell (SSFC), [8] in which traditional liquid catholytes and anolytes are replaced by attractive colloidal suspensions composed of Li-ion compounds. They also replaced traditional stationary current collectors with conductive carbon nanoparticle networks within the flowing suspensions. These suspensions, which take advantage of Li-ion battery's high energy density with flow battery's design flexibility, have been investigated both experimentally [8][9][10][11][12] and computationally. [10,13,14] Similar concepts have recently emerged for electrochemical flow capacitors [15] and polysulfide flow batteries. [16] To fully optimize SSFCs, the flowing electrodes must have high active material content coupled with an adequate conductive filler network to overcome the resistive nature of most electrochemically active Li-ion compounds. However, as their solids loading increases, dramatic changes in their rheological properties ensue, which inhibit flow. The key to maximizing active material content while retaining satisfactory flowability and conductivity is to simultaneously tailor the respective interactions between all particles present within these electrode suspensions.[17] 3Here, we report the design and characterization of biphasic SSFC electrode suspensions with high energy density, fast charge transport, and low-dissipation flow. To create these biphasic mixtures [18,19] we specifically tailor the interactions between the active particles, i.e., LiFePO 4 (LFP), to be repulsive, the interactions between the conductive particles, Ketjenblack EC-600JD (KB), to be attractive, and the cross-interactions between LFP-KB to also be repulsive. 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 ...

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Aqueous foams present an anomalous macroscopic viscoelastic response at high frequency, previously shown to arise from collective relaxations in the disordered bubble packing. We demonstrate experimentally how these mesoscopic dynamics are in turn tuned by physico-chemical processes on the scale of the gas-liquid interfaces. Two specific local dissipation processes are identified, and we show how the rigidity of the interfaces selects the dominant one, depending on the choice of the surfactant.