Development of Spectroelectrochemical Cells for in situ Neutron Reflectometry

In Situ Neutron Reflectometry Study of Solid Electrolyte Interface (SEI) Formation on Tungsten Thin-Film Electrodes

Tungsten, a non-Li-intercalating material, was used as a platform to study solid-electrolyte interface/interphase (SEI) formation in lithium hexafluorphosphate in mixed diethyl carbonate (DEC)/ethylene carbonate electrolyte solutions using in situ neutron reflectometry (NR). A NR measurement determines the neutron scattering length density (SLD)-depth profile, from which a composition-depth profile can be inferred. Isotopic labeling/contrast variation measurements were conducted using a series of three electrolyte solutions: one with both solvents deuterated, one with neither deuterated, and another with only DEC deuterated. A two-layer SEI formed upon polarization to +0.25 V vs Li/Li⁺. Insensitivity of the inner SEI layer to solvent deuteration suggested limited incorporation of hydrogen atoms from the solvent molecules. Its low SLD indicates that Li₂O could be a major constituent. The outer SEI layer SLD scaled with that of the solution, indicating that it either had solution-filled porosity, incorporated hydrogen atoms from the solvent, or both. Returning the electrode to +2.65 V removed lithium from both surface layers, though the effect was more pronounced for the inner layer. Potential cycling had the effect of increasing the solution-derived species content in the inner SEI and decreased the contrast between the inner and outer layers, possibly indicating intermixing of the layers.

Review of Recent Development of In Situ/Operando Characterization Techniques for Lithium Battery Research

The increasing demands of energy storage require the significant improvement of current Li-ion battery electrode materials and the development of advanced electrode materials. Thus, it is necessary to gain an in-depth understanding of the reaction processes, degradation mechanism, and thermal decomposition mechanisms under realistic operation conditions. This understanding can be obtained by in situ/operando characterization techniques, which provide information on the structure evolution, redox mechanism, solid-electrolyte interphase (SEI) formation, side reactions, and Li-ion transport properties under operating conditions. Here, the recent developments in the in situ/operando techniques employed for the investigation of the structural stability, dynamic properties, chemical environment changes, and morphological evolution are described and summarized. The experimental approaches reviewed here include X-ray, electron, neutron, optical, and scanning probes. The experimental methods and operating principles, especially the in situ cell designs, are described in detail. Representative studies of the in situ/operando techniques are summarized, and finally the major current challenges and future opportunities are discussed. Several important battery challenges are likely to benefit from these in situ/operando techniques, including the inhomogeneous reactions of high-energy-density cathodes, the development of safe and reversible Li metal plating, and the development of stable SEI.

Functional materials analysis using in situ and in operando X-ray and neutron scattering

In situ and in operando studies are commonplace and necessary in functional materials research. This review highlights recent developments in the analysis of functional materials using state-of-the-art in situ and in operando X-ray and neutron scattering and analysis. Examples are given covering a number of important materials areas, alongside a description of the types of information that can be obtained and the experimental setups used to acquire them.