Operando XPS: A Novel Approach for Probing the Lithium/Electrolyte Interphase Dynamic Evolution

The coupling protocols combining photoemission spectroscopy and other characterization methods such as electrochemical, electrical, optical, thermal, or magnetic paved the way to considerable progress in the field of materials science. Access to complementary data on the same object is relevant, but in the vast majority of cases, it is carried out sequentially and separately. This raises the complex question of the equivalence of the analyzed surfaces subjected to these different characterizations. In the frame of lithium ion battery technology (LIB), several techniques have been developed to follow in operando condition the reactivity of electro-active materials toward liquid or solid electrolytes. Besides the knowledge of the redox processes obtained using operando protocols, especially at the interfaces, some limitations associated with material sensitivity and/or the characterization techniques are still a breakdown to widen our understanding of the origin of the LIB performance degradation processes. Herein, we propose a new design of an operando cell adapted to perform X-ray photoemission spectroscopy (XPS) at the interface between electrode and electrolyte under electrochemical solicitations. To illustrate its performance, the crucial issues associated with the lithium metal interface have been scrutinized using Li/Li symmetrical cells and two types of ionic liquids, 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (C₁C₆ImTFSI) and 1-hexyl-3-methylimidazolium bis(fluorosulfonyl)imide (C₁C₆ImFSI) laden with LiTFSI salt. Our original setup allowed us to follow-up the lithium surface reactivity toward these ionic liquid based electrolytes in open circuit voltage condition and under polarization. Beside the gain of time and the matter saving, we highlighted and optimized the blocking issues to perform accurate OXPS measurement for probing the evolution of the chemical structure and the surface potential change at the interface lithium/electrolyte in dynamic mode.

New Interpretation of X-ray Photoelectron Spectroscopy of Imidazolium Ionic Liquid Electrolytes Based on Ionic Transport Analyses

We reported a new perspective on the correlation between the electronic structure of an ionic liquid (IL)-based electrolyte probed by X-ray photoelectron spectroscopy and the transport properties analyzed by impedance spectroscopy. We highlighted the core level chemical shifts of 1-hexyl-3-methylimidazolium (bis(trifluoromethanesulfonyl)imide) (C₁C₆ImTFSI), 1-hexyl-3-methylimidazolium bis(fluorosulfonyl)imide (C₁C₆ImFSI), and 1-hexyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide (C₁C₁C₆ImTFSI) laden with LiTFSI salt and vinylene carbonate (VC) or fluoroethylene carbonate (FEC) with regard to the transport properties of cations and anions. We pointed out based on detailed binding energy shift analyses a clear effect of the anion on the local organization of Li⁺ ions. The significant peak shift in the case of C₁C₆ImTFSI laden with LiTFSI corroborates the formation of [Li(TFSI)₂]^- complexes. On the contrary, the lower amplitude of the binding energy shift of C₁C₆ImFSI for both anion- and cation-related peaks indicates that the electronic distribution around the cation and the anion is not affected when the LiTFSI salt is added, which plays a strong role in the ion dynamics (lower viscosity) of the electrolyte. The X-ray photoelectron spectroscopy (XPS) result supports the preponderant role of imidazolium ionic liquid based on FSI anion to form an electrolyte less prone to form ionic complexes. The methylation of the imidazolium cation contributes to the reduction of the interaction between the C₁C₁C₆Im cation and TFSI anion, while additives VC and FEC contribute to the change of the alkyl configuration in C₁C₆Im cation, leading to the modification of the macroscopic properties of the ILs.

Electrochemical Impedance Spectroscopy and X-ray Photoelectron Spectroscopy Study of Lithium Metal Surface Aging in Imidazolium-Based Ionic Liquid Electrolytes Performed at Open-Circuit Voltage

Lithium reactivity toward an electrolytic media and dendrite growth phenomenon constitutes the main drawback for its use as an anode material for the lithium battery technology. Ionic liquids (ILs) were pointed out as promising electrolyte solvent candidates to prevent thermal runaway in a lithium battery system. However, the reactivity of lithium toward such a kind of an electrolyte is still under debate. In this study, the interaction between lithium metal and imidazolium-based ILs, 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (C₁C₆ImTFSI) and 1-hexyl-3-methylimidazolium bis(fluorosulfonyl)imide (C₁C₆ImFSI), has been investigated based on the nondestructive methodology coupling electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS) in coin cells aged several days at open-circuit voltage. The main components detected by XPS in the bulk separator and at the surface of the lithium metal are the byproducts of cation and anion degradation. Similarities and differences were noticed depending on the anion nature of bis(trifluoromethylsulfonyl)imide versus bis(fluorosulfonyl)imide. The role of lithium salt addition (LiTFSI) was also pointed, giving rise to the stability improvement of the electrolytic solution toward the lithium anode. A direct correlation between the resistance of the bulk electrolyte and of the interface electrolyte/lithium and chemical composition changes were established based on a detailed EIS and XPS combined study.

Ru-core/Cu-shell bimetallic nanoparticles with controlled size formed in one-pot synthesis

Suspensions of bimetallic nanoparticles (NPs) of Ru and Cu have been synthesized by simultaneous decomposition of two organometallic compounds in an ionic liquid. These suspensions have been characterized by Anomalous Small-Angle X-ray Scattering (ASAXS) at energies slightly below the Ru K-edge. It is found that the NPs adopt a Ru-core, a Cu-shell structure, with a constant Ru core diameter of 1.9 nm for all Ru : Cu compositions, while the Cu shell thickness increases with Cu content up to 0.9 nm. The formation of RuCuNPs thus proceeds through rapid decomposition of the Ru precursor into RuNPs of constant size followed by the reaction of the Cu precursor and agglomeration as a Cu shell. Thus, the different decomposition kinetics of precursors make possible the elaboration of core-shell NPs composed of two metals without chemical affinity.

Targeting adequate thermal stability and fire safety in selecting ionic liquid-based electrolytes for energy storage

The energy storage market relating to lithium based systems regularly grows in size and expands in terms of a portfolio of energy and power demanding applications. Thus safety focused research must more than ever accompany related technological breakthroughs regarding performance of cells, resulting in intensive research on the chemistry and materials science to design more reliable batteries. Formulating electrolyte solutions with nonvolatile and hardly flammable ionic liquids instead of actual carbonate mixtures could be safer. However, few definitions of thermal stability of electrolytes based on ionic liquids have been reported in the case of abuse conditions (fire, shortcut, overcharge or overdischarge). This work investigates thermal stability up to combustion of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C1C4Im][NTf2]) and 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide ([PYR14][NTf2]) ionic liquids, and their corresponding electrolytes containing lithium bis(trifluoromethanesulfonyl)imide LiNTf2. Their possible routes of degradation during thermal abuse testings were investigated by thermodynamic studies under several experimental conditions. Their behaviours under fire were also tested, including the analysis of emitted compounds.

Personalized network-based treatments in oncology

Network medicine aims at unraveling cell signaling networks to propose personalized treatments for patients suffering from complex diseases. In this short review, we show the relevance of network medicine to cancer treatment by outlining the potential convergence points of the most recent technological and scientific developments in both drug design and signaling network analysis.