(62h) Effects of Fluoroethylene Carbonate and Dissolved Manganese on the ANODE SEI Layer Using Reaxff-Based Molecular Dynamics

Lithium manganese oxide cathode and graphite anode based batteries are sought after for high power applications like electric vehicles and energy storage applications, due to their high capacity, low cost, and low toxicity. There are however well-documented problems with capacity fade and cycle life of this battery chemistry, caused by the dissolution of divalent manganese from the cathode surface and deposition of dissolved manganese onto the anode. Most commercial cells use electrolyte additives to develop a stable solid-electrolyte interface layer (SEI) on the surface of the anode to increase cycle life. The speciation and reaction mechanisms of these electrolyte additives are nonetheless not well understood.

In this study, reactive force field-based molecular dynamics (ReaxFF MD) was applied to investigate the decomposition of fluoroethylene carbonate (FEC), a commonly used electrolyte additive, on the surface of a graphite anode. The ReaxFF MD simulations indictate that, contrary to widely-held belief, lithium carbonate, not lithium fluoride, is the product of FEC decomposition. The fate and effect of dissolved manganese ions on the anode SEI layer was also studied. Here, the ReaxFF MD simulations reveal that manganese at the anode-electrolyte interface facilitates the polymerization of ethylene carbonate, forming polymer chains that extend from the anode surface into the electrolyte.