Computational Raman spectroscopy of organometallic reaction products in lithium and sodium-based battery systems

Abstract

A common approach to understanding surface reaction mechanisms in rechargeable lithium-based battery systems involves spectroscopic characterization of the product mixtures and matching of spectroscopic features to spectra of pure candidate reference compounds. This strategy, however, requires separate chemical synthesis and accurate characterization of potential reference compounds. It also assumes that atomic structures are the same in the actual product mixture as in the reference samples. We propose an alternative approach that uses first-principles computations of spectra of the possible reaction products and by-products present in advanced battery systems. We construct a library of computed Raman spectra for possible products, achieving excellent agreement with reference experimental data, targeting solid-electrolyte interphase in Li-ion cells and discharge products of Li-air cells. However, the solid-state crystalline structure of Li(Na) metal-organic compounds is often not known, making the spectra computations difficult. We develop and apply a novel technique of simplifying spectra calculations by using dimer-like representations of the solid state structures. On the basis of a systematic investigation, we demonstrate that molecular dimers of Li(Na)-based organometallic material provide relevant information about the vibrational properties of many possible solid reaction products. Such an approach should serve as a basis to extend existing spectral libraries of molecular structures relevant for understanding the link between atomic structures and measured spectroscopic data of materials in novel battery systems.

Revealing instability and irreversibility in nonaqueous sodium–O2 battery chemistry

“…24 However, the peak at 1147 cm -1 is also close to computed torsion and stretching modes from CH 3 O and C-O groups, consistent with the presence of sodium methoxide or sodium methyl carbonate-type decomposition products. 25 Here we point out that the reactivity of NaO 2 with the electrolyte (DME) observed in this study is markedly different from that reported recently by Kim at al. 26 This previous study reveals Na 2 O 2 .2H 2 O from Raman spectroscopy immediately after discharge in diethylene glycol dimethyl ether (diglyme) containing NaCF 3 SO 3 in contrast to NaO 2 only found in this work.…”

Methylammonium Lead Trihalide Perovskite Solar Cell Semiconductors Are Not Organometallic: A Perspective

“…From the various insights provided, it is concluded that the trihalide perovskite solar cells are indeed not organometallic , nor do they have anything to do with it . These are no more organometallic than Na‐acetate, because these latter are also consisting of organic and inorganic ions, which do not encompass any coordinate/covalent bonding between the metal and the carbon …”

Capturing Nano‐Scale Inhomogeneity of the Electrode Electrolyte Interface in Sodium‐Ion Batteries Through Tip‐Enhanced Raman Spectroscopy

“…Among these, the most intense band (≈1141 cm −1 ) originates from a combination of C─O‐stretching of C─ONa‐groups and the rocking vibration of ─CH 2 ($$\upsilon _{{\mathrm{sy}}}^{C - O} + {r}^{ - C{H}_2}$$). [ 24a,28 ] The other Raman bands are associated with different types of ─CH 3 deformation,─CH 3 rocking, ─CH 2 wagging vibration (≈1173, 1208, 1246, and 1282 cm −1 ) that are present mostly on long chain alkoxide salts. [ 24a ] At the same time, the carboxylate group identifier Raman bands at ≈1547 and 1588 cm −1 are also present.…”