From the Passivation Layer on Aluminum to Lithium Anode in Batteries

Many low-density metals are also reactive. This article draws inspiration from the passivation oxide layer formed on aluminum to the design of electrochemically stable surface layers on lithium metal electrodes in batteries. First, reactive molecular dynamics simulations are used to compare the oxide layer formation on lithium and aluminum metal surfaces. While a uniform dense aluminum oxide layer forms on aluminum, vertical cracks in the lithium oxide layer lead to a deformed lithium oxide layer. These observations are consistent with the empirical Pilling-Bedworth Ratio (PBR) that uses the molar volume ratio of oxide to metal to determine whether a metal is likely to passivate in dry air by creating a protective oxide layer. A passivation layer needs to form on the lithium metal surface in the presence of electrolytes. The PBR concept is thus extended to the multiple compounds found in the spontaneously formed solid electrolyte interphase (SEI). It is suggested that a mixture of LiF/Li2CO3 or LiF/Li2O or replacing Li2O with Li2S can effectively create a PBR that is in the 1 to 1.3 range for better passivation. While these analyses are consistent with some experimental evidence, a seeding layer concept is proposed to further prevent dendrite growth and simplify the battery manufacturing process. The role of metallic nanoparticles in the metal-carbon nanocomposite seeding layer to control lithium nucleation and growth is investigated by an atomically informed phase field model (AI-PFM). The model predicts the formation of a Li-rich phase with Ag nanoparticles but non-uniform lithium metal nucleation on Au nanoparticles, showing the AI-PFM model to be a desired design tool to evaluate which metallic nanoparticles can be used to control the Li deposition morphology. These results collectively emphasize the need for highly coupled electrochemical-mechanical modeling to solve the challenges of designing a multifunctional passivation layer for metal electrodes in batteries.