THE CITY COLLEGE OF NEW YORK
CHEMICAL ENGINEERING DEPARTMENT
Professor Nicolas Alvarez
Monday, December 3, 2018
Seminar will be held in ST-160 (Lecture Hall) at 2:00 PM
Reception will be held in Steinman Hall, Exhibit Room from 3:15 – 4:00 PM
Correlating Electrode Slurry Microstructure to Final Electrode Performance: A Rheological Approach
Particle-polymer composite electrodes are ubiquitous throughout practical electrochemical systems such as: lithium-ion batteries, emerging sodium or multivalent ion batteries, microbial fuel cells, and electrochemical systems for desalination and environmental remediation. All of which are predicted to play a substantial role in growing concerns over the energy and environmental landscape. Regardless of the application, device-level limitations play a major role in determining electrochemical performance, lifetime, and cost. One of the greatest of these limitations is charge transport. Electrodes must have sufficiently fast electron and ion transport to utilize reactants and prevent resistive losses. The rate of transport is determined not only by material properties, but also by the electrode microstructure.
Despite decades of commercial relevance, there is still no universal recipe for manufacturing electrodes with desirable microstructures. Electrode slurries are highly non-Newtonian, and each step of mixing, casting, drying, and calendering is sensitive to a large number of chemical and process parameters. For instance, the exact same slurry ingredients mixed in a different order result in electrodes with vastly different performance and lifetime. Experience shows that any change to formulation requires intensive trial-and-error experimentation to achieve homogeneous electrodes with acceptable performance and lifetime.
Battery electrodes are composed of active and inactive materials. The inactive materials fall into two categories of conductive additive and polymer binder. The electrochemically active material is typically mixed metal oxides. It is well known that the mixing of these materials induce complex interactions that lead to inhomogeneous suspensions. For example, through depletion and electrostatic interactions, nanosized particles form aggregate structures that in some cases lead to colloidal gel-like responses at very low volume fractions. Nanosized carbon black conductive additive can form a colloidal gel at extremely low critical volumes fractions (f = 0.02) independent of the presence of micron sized non-Brownian particles (active material). In this seminar we will discuss key parameters that control slurry microstructure and the importance of the initial slurry microstructure on optimizing electrode performance.
Nicolas J. Alvarez earned a BS in Chemical Engineering from the University of Florida in 2006 and a PhD in Chemical Engineering from Carnegie Mellon University in 2011. After three years of postdoctoral work at the Technical University of Denmark in Lyngby, he joined the Department of Chemical and Biological Engineering at Drexel as an Assistant Professor in 2014. Alvarez’s research interests involve development of unique experimental tools to understand and characterize the behavior of polymers and surfactants in nonlinear flows, at interfaces, and in bulk. These tools are used to understand how certain processing windows lead to advantageous material properties. One such tool, used for the characterization of extensional rheology, has been commercialized by Alvarez and colleagues. Alvarez is developing a consortium of companies interested in the development of analytical tools to better understand the relationship between chemical structure, processing, and material performance. Alvarez teaches an elective course on non-Newtonian fluid mechanics that introduces students to real-world materials encountered in modern day chemical plants.