ReaxFF: Teflon coating reduces Li-S battery electrolyte decomposition

Lithium released from the anode is a highly exothermic process in lithium-sulfur batteries, and as such can lead to reactions with the electrolyte. In a recent ReaxFF study, the lithium discharge from a single-walled carbon nanotube (SWCNT) composite electrode was studied, and indeed the hot lithium ions lead to many dissociation events, resulting in unwanted build up of ethylene. Coating the Li/SWCNT anode with a layer of porous Teflon, acting as a unreactive thermal buffer, leaves the electrolyte mainly intact and reduces the amount of ethylene formation by 90%.

These ReaxFF simulations give precious atomic-level insight in the fundamental processes at the electrode-electrolyte interface, which are necessary for further designing safer and longer-lived Li-S batteries.

ReaxFF simulation of anodic Li discharge

ReaxFF simulation results for Li-S battery cell with TEGDME electrolyte, with bare Li/SWCNT anode (top) and Teflon-coated Li/SWCNT anode (bottom). Left: snapshots at 10ps during the atomic discharge, right: local temperature profile at 1ps, just after discharge (blue 60 K, red >1000 K).

Links: ADF/ReaxFF overview, ReaxFF Tutorial: Battery Discharge Voltages, ReaxFF Tutorial: Li-Ion diffusion coefficients, ReaxFF-GUI tutorials, Advanced 2-day ReaxFF workshop, ReaxFF reparametrization tutorial.

Look at the web presentation to learn how to parametrize ReaxFF force fields with the MMC-SA optimizer.

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M. M. Islam, V. S. Bryantsev, and A. C. T. van Duin, ReaxFF Reactive Force Field Simulations on the Influence of Teflon on Electrolyte Decomposition during Li/SWCNT Anode Discharge in Lithium-Sulfur Batteries, J. Electrochem. Soc. 161, E3009-E3014 (2014).

Key concepts