1) Understanding the mechanism of lithium plating underneath coatings as an approach to circumventing lithium dendrites

Lithium metal has long been considered the anode of choice for next-generation high energy density batteries due to its low standard reduction potential (-3.04 V vs. SHE) and high specific capacity (3860 mAh g-1, ten times that of commercially used graphite) which ultimately provides a high energy density (energy density depends on both the specific capacity and the voltage window of operation- for an anode, we want a material that has a low redox potential, such that when paired with a high voltage cathode, we can have large voltage window of operation). For the commerically used graphite anode, Li-ions are shuttled in and out of the layers of graphite, resulting in no structural changes (a topotactic reaction) to the graphite host other than some slight volume expansion ~10%; however, for a lithium metal anode, the reaction mechanism for charge storage occurs through plating/stripping where Li ions are reduced to Li (neutral) and vice versa in the oxidative process. Therefore, in this kind of system, it is possible to have an “anodeless” battery design with just a current collector in which lithium from the cathode can be removed and plated onto the anode current collector. Seems too good to be true right? Well, turns out it sort of is.
The challenge of using a lithium metal anode stems from safety concerns in addition to long term stability/performance (Low Coulombic Efficiency and Dead Lithium). Both concerns can more or less be pin pointed at the formation of “lithium dendrites,” that is, finger-like and branch like lithium deposits that form and grow upon repeated plating and stripping cycles. Lithium dendrites have been found to puncture through separators and reach the cathode, resulting in a short circuit (large currents, high heat, flammable electrolyte= big safety issue). In order to address the problem, the interface, a critical region where breakdown and decomposition often occurs, must be properly understood and stabilized.
The use of coating layers on the lithium surface have been found to show promise in suppressing dendrite formation to some degree by tuning the morphology of the plated lithium. However, while most lithium coatings result in plating on top of the coating whereby the coating serves as a nucleation substrate, less studied is the case where the lithium can be transported through the layer and deposited underneath. The basic idea is that by confining lithium deposition to take place underneath the coating, we can effectively suppress lithium dendrite formation at the surface. The ability to understand the mechanism of plating underneath is both of fundamental and practical interest in better understanding the critical parameters to drive lithium transport through a layer and the ability to apply design principles to create a layer that can supress lithium dendrite growth.

Here’s a link to a Perspective my collaborator Qizhang and I helped write in Applied Physics Letters about interface engineering of the challenging lithium metal interface and our two cents on where we see the field going.

Here’s a link to my work studying the mechanism of plating lithium underneath lithium-tin based intermetallic coatings as an approach to circumvent lithium dendrites published in Journal of Materials Research

I presented at the Materials Research Society (MRS) Fall 2020 Conference at symposium EN03 (Overcoming the Challenges with Metal Anodes for High-Energy Batteries) and my talk was presented with a “Best Presentation Award.” Here’s a link to my abstract.