At a Glance
We are studying a fundamental question in battery research—whether apparently negative and inevitable physical phenomena in an electrochemical cell, such as corrosion and anisotropic growth, can be exploited for benefit. We use various imaging techniques to examine the deposition and removal of plate metals during cell operation and in conditions that emulate practical usage patterns.
In our first full year working with the Carbon Mitigation Institute we posed a fundamental question in energy storage research: can apparently inevitable physical outcomes in a cell such as corrosion and anisotropic growth be exploited for benefit rather than suppressed and avoided?
In a closed electrochemical cell, the maximum energy density is achieved when the lightest possible electrochemically active components are paired with the largest possible potential window. While this demands use of a heretofore unrealized fluoride compound as an oxidizing agent, it also requires use of metallic lithium as a reducing agent. Metallic lithium has been used successfully as a primary metal anode for half a century, but its use as a secondary anode has been limited by both the chaotic nature of its redeposition during a charging cycle and the possibility of an explosion when there is an uncontrolled short circuit. Its application as a secondary anode is feasible only where performance requires a minimal safety factor.
Building upon our previous studies of the growth of zinc at potentials beyond the onset of reactant starvation, we have spent the last year establishing the laboratory infrastructure required to examine the deposition and removal of plate metals while the cells are operating (Figure 2.3.). This includes optical microscopy, electrochemical acoustic analysis, and transmission X-ray microscopy.
We have imaged lithium and zinc with all of these methods, and we are beginning our second year with stability analysis of plate metal systems deposited and removed in various regimes that emulate practical usage patterns. We now have further evidence that better utilization of the active material is achieved with asperities that are pre-grown at the correct length scales rather than the flat structures dictated by conventional design.
Although flat structures are easiest to imagine being “predictable,” in actuality the complex competition between nucleation and growth during crystal growth quickly turns a flat surface into a rough structure. Instead, by starting with a rough structure that is “sympathetic” to the length scales natural to a given growth rate, more of a metal anode can be used reliably.
Going forward this year, we want to test the limits of how much of this rough scaffold can be utilized before the effect is no long present, and what impurities might be leveraged to act as scaffold.
Park, J.H., D.A. Steingart, S. Kodambaka, and F.M. Ross, 2017. Electrochemical Electron-Beam Lithography: Write, Read and Erase Metallic Nanocrystals on Demand, in revision.
Schneider, N.M., J.H. Park, J.M. Grogan, S. Kodambaka, D.A. Steingart, H.H. Bau, and F.M. Ross, 2017. Nanoscale evolution of interface morphology during electrodeposition, in review.