Can Radiolysis Help Understanding the Decomposition Products of the Electrolytes Used in Lithium-Ion Batteries?

Lithium-ion batteries appear to be one of the most important advances in energy storage. Unfortunately, their performance declines gradually with their use and/or time. Nevertheless, their degradation products affect both the battery performance and its safety. Therefore it is of paramount importance to understand the reaction mechanisms involved in the ageing processes. Among those, redox processes are likely to play a critical role and radiolysis is an interesting approach in order to simulate the ageing phenomena.

One of the aims of our group is then to investigate the effect of ionizing radiation on the different solvents containing or not lithium salts used in batteries. We generate, thus, the decomposition products that are actually comparable to those formed by electrolysis. Moreover, the use of the “radiolysis approach” entails particularly two important benefits: the time needed to degrade the solvent is much shorter than in classical charge/discharge cycles and it offers the possibility to explore different time scales processes (from picoseconds to days).

Our work was first focused on linear alkyl carbonates diethyl and dimethyl carbonate (DEC and DMC) with/without LiPF₆. At short-time scale, picosecond pulse radiolysis has been used in order to explore the primary radiation effects. These experiments reveal, for instance, an unambiguous reaction between the electron and the PF₆^- anion. 

Then, the long-time decomposition products were analyzed both in the gas and liquid phase. To this end, a wide variety of analytical techniques has been used. Gas phase has been analyzed and quantified using Gas Chromatography-Electron Impact-Mass spectrometry (GC-EI-MS) whereas a combination of Electrospray-High Resolution Mass Spectrometry (ESI-HRMS) with both Ion Mobility Spectroscopy (IMS) and Infrared Multi-Photon Dissociation (IRMPD) spectroscopy has been used to characterize the decomposition products in the liquid phase.

In conclusion, we show that the “radiolysis approach” used herein can provide an unprecedented, quantitative and fast overview of the electrolyte decomposition phenomenon.