In order to ensure the energy transition, efficient and affordable energy storage systems must be developed quickly. New generation Lithium-ion batteries, including new electrode materials with high lithium storage capacity or high voltage, have high promise, but an inevitable degradation of their cycling performance limits their development. A major problem is related to the reactions of the electrolyte on the electrodes upon charging. In addition to damaging the electrode materials, these reactions lead to the formation of solid interfacial layers (Solid Interphase Electrolyte or "SEI" on the anode and Cathode Electrolyte Interphase or "CEI" on the cathode). The loss of battery capacity is closely linked to the formation of these layers. The objective of the present work is to control their formation dynamics and compositions by tuning the electrolyte and the electrode composition. To get a better understanding of the underlying degradation mechanism during battery operation, operando diagnostic techniques have to be developed. One possible approach is to implement in situ Raman spectroscopy on operating battery electrode in LIB electrolyte. However, because the Raman scattering is very inefficient at such interfaces (extremely thin interphase), their chemical signature must be amplified (“enhanced”) to be measurable. This is achieved by using plasmonic amplifiers, i.e., gold nanoparticles coated with nonconductive silica (SiO2), deposited on the surface of the electrodes, the so-called SHINERS (Shell-Isolated Nanoparticles-Enhanced Raman Spectroscopy). A first part of the study was dedicated to the synthesis nanoparticles with controlled properties (sizes, shapes etc.) to achieve the highest amplification factors at specific Raman excitation wavelength. Then, as many parameters may alter the enhancement of the Raman signal (dielectric properties of the surrounding medium, i.e. of the electrolyte, electrochemical potential of the battery interface, optical coupling between nanoamplifiers…) and the detection of the signal (signal screening by Raman & fluorescence signal of the electrolyte…) under operando conditions, a step-by-step approach was carried out to optimize diagnostic capabilities of SHINERS on Lithium-ion systems. References: Li, Jian-Feng, Yue-Jiao Zhang, Song-Yuan Ding, Rajapandiyan Panneerselvam, and Zhong-Qun Tian. Core–Shell Nanoparticle-Enhanced Raman Spectroscopy, Chemical Reviews 117 (7): 5002‑69. (2017). Hy, S., Felix, Chen, Y. H., Liu, J. Y., Rick, J., Hwang, B. J., In situ surface enhanced Raman spectroscopic studies of solid electrolyte interphase formation in lithium ion battery electrodes, Journal of Power Sources, 256, 324-328, (2014) Liu, Mingzhao, Philippe Guyot-Sionnest, Mechanism of Silver(I)-Assisted Growth of Gold Nanorods and Bipyramids. The Journal of Physical Chemistry B 109 (47): 22192‑200. (2005) Sánchez-Iglesias, Ana, Naomi Winckelmans, Thomas Altantzis, Sara Bals, Marek Grzelczak, Luis M. Liz-Marzán. High-Yield Seeded Growth of Monodisperse Pentatwinned Gold Nanoparticles through Thermally Induced Seed Twinning. Journal of the American Chemical Society 139 (2017) Galloway, Thomas A., Laura Cabo-Fernandez, Iain M. Aldous, Filipe Braga, and Laurence J. Hardwick. Shell Isolated Nanoparticles for Enhanced Raman Spectroscopy Studies in Lithium–Oxygen Cells, Faraday Discussions 205: 469‑90 (2017)