(301e) Design, Synthesis, and Characterization of Mixed Ionic/Electronic Conducting Surface Layers Adsorbed on Metal Oxide Particles

Inexpensive grid-scale storage remains a major hurdle slowing the wide-scale adoption of renewable energy by public power utilities. Flow batteries have been proposed as one viable solution. Whereas, the capacity of a traditional battery is limited by its packaging, flow batteries pump redox active fluids from external storage tanks through a flow cell where electrical energy is extracted or stored via reversible redox reactions. In this way, the capacity of the battery becomes scalable independent of the specific redox chemistry and battery geometry. Semi-Solid flow batteries (SSFBs) use “flowable electrodes” for both the anode and cathode materials that consist of a mixture of lithium containing metal oxide particles and carbon black particles. Carbon black is added to these dispersions to improve the utilization of lithium as the particles flow by the electrodes. Unfortunately, the presence of this percolated carbon black network leads to significant increases in viscosity, both at low and high shear rates. In this work, we outline the synthesis of a composite polyelectrolyte/conjugated polymer adsorbed surface layer on cationic silica particles. This layer is formed through the adsorption of poly(styrene sulfonate) onto oppositely charged metal oxide particles and subsequent polymerization of the surface polyelectrolyte with 3,4-ethylenedioxithiophene (EDOT) monomer. The PEDOT:PSS layer is characterized as a function of EDOT:SO₄^-2 loading using a combination of light scattering, neutron scattering and dielectric spectroscopy to understand the connection between the surface layer’s composition, nanostructure and electrical properties. These properties are then connected to the rheological performance of suspensions in propylene carbonate and the mechanical and electrical properties identified.