Chemical Decomposition of the TFSI Anion Under Aqueous Basic Conditions



Understanding the interfacial reactivity of aqueous electrolytes is crucial for their use in future batteries. We investigate the reactivity of the bis(trifluoromethane)sulfonimide (TFSI) anion when exposed to a strong alkaline medium, by means of ab initio molecular dynamics and enhanced sampling techniques. In particular, we study the nucleophilic attack by the hydroxide anion, which was proposed as a mechanism for the formation of the solid electrolyte interphase at the negative electrode with water-in-salt electrolytes. While in the gas phase we recover a stable gaseous product, namely fluoroform, we observe the formation of trifluoromethanol in strong basic conditions, which then rapidly deprotonates to form CF3O-. This anion was suggested recently as a key compound leading to the formation of a solid electrolyte interphase on an Si-C anode. Such an approach could be leveraged to discover convenient additives leading to the formation of a stable interphase.


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Supplementary material

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Supporting Information
Technical details about the molecular dynamics simulations.
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Gas phase reaction
Reaction mechanism in gas phase from the products state (fluoroform and the N(SO$_2$CF$_3$)SO$_3$ anion) to the reactants state (TFSI and OH$^-$)
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Liquid phase reaction
Reaction mechanism under basic aqueous conditions from the reactants state (TFSI and OH$^-$) to the unexpected products state (trifluoromethanol and the N(SO$_2$CF$_3$)SO$_2$ anion)