The fundamental understanding of the electrode/electrolyte interfacial processes in lithium–sodium ion batteries (LIBs) and of their dynamics upon cycling is of prime importance for the development of new-generation electrode materials. Operando analyses using the utmost sensitive techniques are required to produce an accurate depiction of the underlying processes at the origin of the battery performance decay. Although enhanced Raman spectroscopy through the use of signal nanoamplifiers shows the required sensitivity, its implementation in operando conditions and particularly on functional materials in contact with organic electrolytes remains challenging. This work using extensive optimization of shell-isolated nanoparticle-enhanced Raman spectroscopy conditions for operando diagnosis of LIB materials, including the design of near-infrared active amplifiers and the control of the photon dose, demonstrates the possibility to track the dynamics of composition of the electrode/electrolyte interface upon cycling of LIB coin-cells and uncovers the origin of the irreversible capacity of tin electrodes proposed as an alternative to graphite anodes.

Performances of lithium-ion batteries (LIBs) are closely related to the control of solid-electrolyte interface (SEI) stability. To decrease the capacity losses linked to the build-up of this interface or potentially reverse such losses, electrolyte formulations have been continuously optimized over years to evaluate how they affect SEI. However, direct molecular characterization of the diverse interphases remains extremely challenging. Herein, we report the molecular imaging of SEI components formed on graphite electrodes by laser desorption ionization (LDI) coupled to ultrahigh-resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS). By exploiting the surface analysis offered by LDI combined with the molecular formula attributions provided by the FT-ICR MS, it is possible to unambiguously identify/exclude suspected molecules in the SEI such as lithium ethylene dicarbonate and lithium ethylene mono carbonate. Moreover, thousands of unknown species were observed, which could be exploited for further understanding of the surface composition. We believe this methodology to be a critical advance for the design of high-performance LiBs.

New positive electrode materials operating at higher voltage (such as LiNi0.5Mn1.5O4 - LNMO), hold great promise for the next generation of high energy lithium-ion batteries (LIB), but show a rapid degradation of their performance upon cycling, which limits their immediate development. One major problem associated to the high operational voltage of such electrode materials, is the pronounced oxidation of standard electrolytes used in LIBs and the concomitant dissolution of the LNMO material and the possible impact on the negative electrode (cross-talking). Through the development of a set of operando diagnostic techniques, this work aims at establishing during the charge/discharge cycles the correlation between the structural changes in LNMO, the interfacial processes (electrolyte oxidation, formation of Cathode Electrolyte Interphase: CEI, LNMO transition metal dissolution) and the cross-talk process depending on the electrodes/separator assembly.We will introduce in this presentation our recent developments on operando SHINERS1 (Shell-Isolated Nanoparticles-Enhanced Raman Spectroscopy) to track the dynamic of the interfacial processes2 at LNMO electrodes3. We will also present how temporally and spatially resolved confocal fluorescence and X-Ray spectroscopy measurements implemented operando on the edge of the electrode assembly can be used to quantify the LNMO dissolution upon cycling. The electrolyte composition and the role of electrolyte additives to stabilize the high-voltage cathode / electrolyte interface will be discussed. Li, J.F., Huang, Y.F., Ding, Y., Yang, Z.L., Li, S.B., Zhou, X.S., Fan, F.R., Zhang, W., Zhou, Z.Y., Wu, D.Y., et al. (2010). Shell-isolated nanoparticle-enhanced Raman spectroscopy. Nature 464, 392–395.Gajan, A., Lecourt, C., Torres Bautista, B.E., Fillaud, L., Demeaux, J., and Lucas, I.T. (2021). Solid Electrolyte Interphase Instability in Operating Lithium-Ion Batteries Unraveled by Enhanced-Raman Spectroscopy. ACS Energy Lett., 1757–1763.Dumaz, P., Rossignol, C., Mantoux, A., Sergent, N., and Bouchet, R. (2020). Kinetics analysis of the electro-catalyzed degradation of high potential LiNi0,5Mn1,5O4 active materials. Journal of Power Sources 469, 228337. Figure 1

The fundamental understanding of the electrode/electrolyte interfacial processes in Lithium/Sodium-ion Batteries (LIBs) and of their dynamics upon cycling is of prime importance for the development of new generation electrode materials. Operando analyses using the utmost sensitive techniques are required to produce an accurate depiction of the underlying processes at the origin of the battery performance decay. Although Raman spectroscopy is already largely used to characterize operating battery materials, it is totally blind to extract the composition of extremely thin layers such as SEI, as the Raman scattering process is in most scenario very inefficient. This can be solved using plasmonic amplifiers (Au@SiO2 core shell nanoparticles) deposited on the electrodes, the so-called SHINERS (Shell-Isolated Nanoparticles-Enhanced Raman Spectroscopy). Introduced by Tian’s group in 2010 [1], the SHINERS technique has yet been scarcely used for the characterization of energy materials. [2] [3] If enhanced Raman Spectroscopy through the use of signal nano-amplifiers (SHINs) shows the required sensitivity, its implementation in operando conditions and particularly on functional materials in contact with organic electrolytes remains challenging. This work through extensive optimization of SHINERS conditions for operando diagnosis of LIB materials, including the design of near-infrared active amplifiers and the control of the photon dose, demonstrates the possibility to track the dynamics of composition of the electrode/electrolyte interface upon cycling of LIB button-cells[4].This study while addressing three major gaps in analytical studies of interfacial processes in LIB electrolyte using enhanced Raman spectroscopy (ex situ and operando), i.e. the usual misconception of in situ cells or/and the inaccurate interpretation of SEI/CEI chemical signatures based on infrared spectra or computed Raman spectra (DFT), provides important insights in the degradation mechanism of organic carbonate electrolytes[5-6] and the origin of the interfacial instability specific to tin.[1] J. F. Li et al., “Shell-isolated nanoparticle-enhanced Raman spectroscopy”, Nature, 464 (2010) 392[2] L. Cabo-Fernandez, D. Bresser, F. Braga, S. Passerini, et L. J. Hardwick, “In-Situ Electrochemical SHINERS Investigation of SEI Composition on Carbon-Coated Zn 0.9 Fe 0.1 O Anode for Lithium-Ion Batteries “, Batteries & Supercaps, 2 (2019) 168[3] C.-Y. Li et al., “Surface Changes of LiNix Mny Co1– x – yO2 in Li-Ion Batteries Using in Situ Surface-Enhanced Raman Spectroscopy “, J. Phys. Chem. C, 124 (2020) 4024[4] Gajan, A. et al .; Lecourt, C.; Bautista, B. E. T.; Fillaud, L.; Demeaux, J.; Lucas, I. T. “Solid Electrolyte Interphase Instability in Operating Lithium-Ion Batteries Unraveled by Enhanced-Raman Spectroscopy”. ACS Energy Letters 2021, 7.[5] L. Wang et al., « Identifying the components of the solid–electrolyte interphase in Li-ion batteries », Nat. Chem., 11 (2019) 789[6] S. A. Freunberger, « Interphase identity crisis », Nat. Chem., 11 (2019) 7...