Formation of artificial solid electrolyte interphase by radiolysis

International audience; Among energy storage devices, Lithium ion batteries (LlBs) are efficient power sources used for many applications inc1uding mobile microelectronics. However, ageing phenomena are not yet fully understood. These 8henomena are a crucial issue to pro vide safe and stable batteries!. LIBs are usually compbsed of a negative electrode where the active material is graphite, a positive electrode usualli a lithium metal oxide and an organic liquid electrolyte. Ortiz et al. have shown that radiolysis is a powerful tool to simulate the degradation of the latter one in short time: minutes/hours instead of weeks/months by electrolysis (Fig. 1). Moreover, radiolysis allows performing experiments at the picosecond time scale thus giving access to reaction mechanisms. During the first cycles of the battery, the reduced surface of the negative electrode reacts with the electrolyte producing a solid interphase (solid electrolyte interphase, SEI) which is responsible for the capacity loss of the battery. In this work, we investigated the SEI formation by radiolysis at the surface of various carbonaceous materials inc1uding crystalline graphite (lithiated or not) and carbon nanoparticles (amorphous as weIl as organized) prepared by laser pyrolysis. Materials were dispersed in a mixture of carbonate solvents containing LiPF. Composition and morphology of SEI were invesigated by XPS and TEM while the composition of gas and liquid phases was studied by gas chromatography and high resolution mass spectrometry, respectively. We show that an artificial SEI can be produced by radiolysis. We observe always the same degradation mechanisms of the electrolyte but interestingly the SEI composition depends on the carbonaceous material. The artificial SEI formed at the surface of graphite is composed of Li carbonate, oxalate and oligomers of poly(ethylene oxide) while the SEI formed at the surface of carbon nanoparticles contains Li salts as Li$_2$CO$_3$. Radiolysis allows producing materials with modified surface that will be tested as new materials for negative electrode.