Reaction Mechanisms of Fluoroethylene Carbonate Degradation, an Additive of Lithium-Ion Batteries, Unraveled by Radiation Chemistry

Marin Puget (1) , Viacheslav Shcherbakov (2) , Sergey Denisov (2) , P. Moreau (3) , Jean-Pierre Dognon (4) , Mehran Mostafavi (2) , Sophie Le Caer (1)

1 LIONS - Laboratoire Interdisciplinaire sur l'Organisation Nanométrique et Supramoléculaire
2 ICP - Institut de Chimie Physique
3 IMN - Institut des Matériaux Jean Rouxel
4 LSDRM - Laboratoire Structure et Dynamique par Résonance Magnétique (LCF)

Numerous additives are used in electrolytes of lithium-ion batteries, especially for the formation of efficient solid electrolyteinterphase at the surface of the electrodes. It is, therefore, necessary to elucidate the degradation processes of these compoundssince it directly affects the lifetime of the battery. These mechanisms can be obtained through radiolysis. In this work, weinvestigated the degradation mechanisms induced by irradiation in fluoroethylene carbonate (FEC), a cyclic carbonate, whichis an additive commonly used in lithium-ion batteries. The first reaction steps were studied by pulse radiolysis. At longtimescales, the radiolytic yields of produced gases (H$_2$, CO, and CO$_2$) were quantified. Pulse radiolysis experimentsevidenced the formation of the FEC$^{●-}$ radical anion, characterized by an absorption band centered ca. 430 nm. The radicalanion is not detected when FEC is solubilized in other solvents: ethanol, diethylcarbonate, etc. This radical is indeed stabilizedin neat FEC, whereas the ring opens to form more stable radical anions when FEC is a solute in other solvents, as confirmedby calculations. A multi-species deconvolution of the spectrum measured in pure FEC revealed a small absorption bandcentered around 560 nm, attributed to the solvated electron, decaying in ca. 100 ps. In neat FEC, excess electrons primarilyundergo attachment compared to solvation. Together with gas chromatography coupled to mass spectrometry measurements,all these observations have allowed us to propose a reaction scheme for both the oxidizing and reducing pathways at stake inirradiated FEC. This work gives clues for the reaction mechanisms undergone by FEC present in electrolytes of lithium-ionbatteries and evidences that the nature of the primary species formed in FEC depends on the amount of FEC in the solution

Domaines: Matériaux

Marin Puget, Viacheslav Shcherbakov, Sergey Denisov, P. Moreau, Jean-Pierre Dognon, et al.. Reaction Mechanisms of Fluoroethylene Carbonate Degradation, an Additive of Lithium-Ion Batteries, Unraveled by Radiation Chemistry. EMIRUM 2021, Jan 2021, Palaiseau, France. ⟨cea-03126694⟩