September 29
@
4:00 PM
–
5:00 PM
Jeffrey Lopez
Assistant Professor
Department of Chemical and Biological Engineering
Northwestern University
Interfacial Reaction Mechanisms Toward Precision Engineering of Interphase Chemistry in Next-Generation Batteries
While lithium based battery technologies are becoming increasingly widespread in our energy landscape, both in electric vehicles and grid scale storage, there is a continued need to increase energy density, reduce costs, and improve the sustainability of their manufacturing. At the heart of every battery is an ionically conductive but electronically insulating electrolyte that dictates the safety, charge rate, and cycling lifetime of the device. Furthermore, for every new battery technology, a new electrolyte must be identified and optimized so that it is compatible with the desired electrode components. Electrolyte decomposition is engineered to produce stabilizing interphases that kinetically passivate electrode surfaces, but the mechanisms to form these interphases and their ideal microstructure and composition are not well understood. In this presentation, I will discuss recent progress in our group toward improving the precision with which interphases can be designed to enable high energy density and low cost storage.
First, I will detail our group’s efforts to better understand electrolyte reaction mechanisms that initiate and propagate organic SEI matrix growth. I will discuss the development of spin trapping to stabilize radical intermediates in electrolyte reduction pathways to clarify reaction mechanisms. Through this approach, we have confirmed a ring opening mechanism for fluoroethylene carbonate (FEC) reduction and the reduction of 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropylether (TTE) into vinyl monomers that protect inorganic interphase components. Second, the kinetic competition between electrolyte components influences the composition of the organic phase of the SEI. We have used operando FTIR to identify how lithium hexafluorophosphate (LiPF6) modulates the competition between FEC and lithium bis(fluorosulfonyl)imide (LiFSI) during interphase formation, and we have used quantitative measurements of selectivity to anion decomposition to develop a framework for estimating the solvent vs anion selectivity in interphase formation. Finally, I will discuss efforts to understand and control the morphology of the composite electrodes within which these interphase formation reactions take place. We have used Contrast Variation Small Angle Neutron Scattering (CV-SANS) for quantitative analysis of nanoscale interfaces in the composite electrode and surface modification to control the electrode-binder interfaces and improve dry battery electrode manufacturing. Increased cohesion between the active material and the PTFE dry binder enables more uniform distribution of the carbon and binder throughout the electrode and the use of only 0.1 wt% binder to fabricate dry electrodes. Together, these results build toward a more detailed understanding of critically important interphase chemistry. With a comprehensive view of reaction mechanisms, kinetics, and electrode structure, new opportunities will arise for precise design and control of the interphase in next generation batteries.