(637g) Solid Electrolyte Interphase Evolution and Passivation on Lithium Metal Anode

Higher density and longer lasting batteries are required by the demands of modern technology including applications such as long-range electric vehicles, distribute energy storage for green energy and commercial personal electronics. In the search for next generation batteries, lithium-based technologies such as lithium-sulfur are promising due to their higher theoretical energy densities along with cheaper materials of construction. One of the current issues keeping lithium-sulfur batteries from practical use is problems related to the use of a lithium metal anode. The high reactivity of lithium metal creates a challenging engineering problem due to the formation and evolution of the solid electrolyte interphase (SEI) layer from the degradation of the electrolyte. In order to create a stable SEI with desirable properties, we must understand more about the SEI from a fundamental perspective.

Here, we investigate the passivation properties of different SEI components with different electrolytes with ab-initio level simulations. We have created systems larger than those that have been studied before on the order of ~5 nm that contain lithium metal, and SEI component and an electrolyte layer. We compared the passivation behavior of LiF, Li₂CO₃ , Li₂O and LiOH with electrolytes consisting of pure DME, DME with 1M LiTFSI, DME with 1M LiFSI and DME with Li₂S₈ . Ab-initio molecular dynamics is used to observe the progression of the systems over time which provides fundamental information about the extent, time, and speciation of the reductions between the different SEI components. The reactions can be followed at a precise level. The structure of the SEI/Li and SEI/electrolyte interface and other important structural properties are also investigated as further reactions occur.

We found, that Li₂O passivated the least in all of the different electrolytes explored. LiF , Li₂CO₃, and LiOH provided a more significant passivation effect but the exact trend differed based on the particular electrolyte in question. In every case, the presence of SEI components provided passivation compared to the bare lithium metal. This information provides guidance to the greater scientific community about how the SEI should be engineered to address the stability of a lithium metal anode.