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Sujet de stage / Master 2 Internship

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Screening of electrolytes for lithium-ion batteries by radiolysis

Contact: LE-CAER Sophie, , sophie.le-caer@cea.fr, +33 1 69 08 15 58
Summary:
The aging of lithium-ion batteries is an important societal problem. We have shown that radiolysis enables simulating aging of electrolytes very quickly (within a few hours). We propose to use radiolysis to screen various electrolytes and to study in details the behavior of the most promising ones.
Possibility of continuation in PhD: Oui
Deadline for application:13/04/2018

Full description:
The depletion of fossil fuels and environment related issues due to the extensive use of fossil fuels create an ever pressing thrust to find out alternate storage mechanisms, wherein lithium-ion battery (LIB) could be considered as a reasonable and greener portable energy storage device, driven by factors such as light weight, high operating voltage, and high theoretical capacity than other secondary batteries. LIBs generally consist of a carbonaceous anode and a transition-metal-oxide cathode. Commercial electrolytes are usually composed of a conducting salt, such as lithium hexafluorophosphate (LiPF6), dissolved in a mixture of linear (low dielectric constant and low viscosity) and cyclical (high dielectric constant and high viscosity) carbonates. It is well known that the capacity of these batteries is usually limited up to portable electronics market and is not quite adequate yet for electrical vehicles and large-scale smart grids due to the limitations posed by electrodes and safety issues related to electrolytes. Indeed, ageing phenomena significantly reduce the cycle life of LIBs and lead to the production of hazardous compounds as recently evidenced by the thermal runaway of a Samsung mobile phone. Over the last years, many efforts have been devoted to improving the stability of electrolytes. Consequently, the study of ageing and degradation mechanisms in LIBs is an urgent need.
A fast screening method, enabling a thorough and global analysis of the system behavior, will enable the identification of the optimal system in terms of lifetime and safety. We have recently demonstrated that radiolysis (i.e. the chemical reactivity induced by the interaction between matter and ionizing radiation) provides an elegant solution to these issues, as it is a powerful tool for the quick identification (minutes to days as it strongly accelerates aging processes) of the species produced by the degradation of a LIB electrolyte after several weeks to months of cycling. , , Indeed, the highly reactive species created in the irradiated solution are the same as the ones obtained during the charging of a LIB using similar solvents. So, the radiolysis approach is a very suitable method to focus on the aging phenomena of different electrolytes and, then, on their reactivity to find a suitable electrolyte for LIBs.
During this internship, we propose to screen different electrolytes to identify the most robust one towards radiolysis, knowing that the electrolyte resistant towards ionizing radiation will be resistant towards electrolysis. For this purpose, gas chromatography and mass spectrometry techniques will be used. The reactivity of the most promising systems will be investigated thoroughly using pulse radiolysis techniques that give access to kinetic and time-resolved spectral data. Lastly, additives are usually used in electrolytes, as they are known to polymerize. The different steps of polymerization reactions will be also studied by means of pulse radiolysis.
Technics/methods used during the internship:
gas phase chromatography mass spectrometry pulse radiolysis

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