Study of electrode/electrolyte interfaces in lithium-ion technology by surface-enhanced Raman spectroscopy in situ
Résumé
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.
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