(632f) Developing Adhesive Coatings to Protect the Lithium Metal Anode

Current lithium-ion batteries have reached their practical energy density limits. Therefore, much work has focused on developing “beyond Li-ion chemistries” such as lithium-sulfur and lithium-air with higher energy densities. However, the high energy density promise of these “beyond” chemistries depend on using lithium metal as the anode. Compared to graphite in todays’ Li-ion battery, lithium metal provides a gravimetric capacity an order of magnitude greater. However, the use of lithium metal is plagued by its high reactivity, an unstable solid electrolyte interface (SEI), and the formation of dendrites that can short the cell and lead to fire hazards. To address these challenges, researchers have focused on protecting the lithium metal surface with lithium fluoride (LiF), lithium composite alloys, or with a deposited polymer layer. However, these protection layers are typically poorly ionically conductive, do not adhere strongly to the lithium metal surface, and can easily detach, leading to much higher lithium deposition/stripping overpotentials with cycling.

In this work, we show a novel method to modify the lithium metal surface to create adhesive coatings that are ionically conductive and can generate a more stable and robust SEI. Once lithium metal is coated, the overpotentials associated with lithium deposition and stripping are significantly reduced in a multitude of different electrolyte systems. We study the influence of the coating functionalities and correlate with observed electrochemical performance. Furthermore, we study the composition and morphology of the lithium interface, and the changes observed with cycling. Coupling the treated lithium anode with a typical LiFePO₄ cathode, we show full-cell cycling performance.

The methods we show are versatile, and knowledge gained from this work can be applied to other non-lithium metal-based systems such as sodium and magnesium, where controlling and modifying the SEI is vital.