DOI: 10.5061/dryad.v15dv421w
title: Data from: An infrared, Raman, and X-ray database of battery interphase components

description: Further improvements to lithium-ion and emerging battery technologies can
 be enabled by an improved understanding of the chemistry and working
 mechanisms of interphases that form at electrochemically active battery
 interfaces. However, it is difficult to collect and interpret spectra of
 interphases for several reasons, including the presence of a variety of
 compounds. To address this challenge, we herein present a vibrational
 spectroscopy and X-ray diffraction data library of ten compounds that have
 been identified as interphase constituents in lithium-ion or emerging
 battery chemistries. The data library includes attenuated total
 reflectance Fourier transform infrared spectroscopy, Raman spectroscopy,
 and X-ray diffraction data, collected in inert atmospheres provided by
 custom sample chambers. The data library presented in this work (and
 online repository) simplifies access to reference data that is otherwise
 either diffusely spread throughout the literature or non-existent, and
 provides energy storage researchers streamlined access to vital
 interphase-relevant data that can accelerate battery research efforts.
description: <strong>Data Collection</strong>
 Prior to any characterization, all pristine compounds were stored
 in an argon glovebox with base oxygen and water concentrations of ~0.1 ppm
 and ~0.5 ppm, respectively. The sources and purities of the studied
 chemicals are provided in Table 1 of the associated paper.
 <strong>ATR-FTIR Spectroscopy</strong>
 ATR-FTIR spectra were collected from 370 to 4000
 cm<sup>-1</sup> at a spectral resolution of 2
 cm<sup>-1</sup> using a Shimadzu IRTracer-100 instrument with
 an IRIS single reflection diamond accessory. Herein, we generally report
 data in the mid-IR range, with a low-energy cutoff of about 500
 cm­<sup>-1</sup>. This approach was taken because the mid-IR
 range is accessible to experimentalists and because we use some data below
 500 cm­<sup>-1</sup> to aid in the generation of a baseline
 for subtraction (see Data Processing for further details). We encourage
 those particularly interested in data around and below ca. 450
 cm­<sup>-1</sup> to consult the raw data available in the
 online data library. The ATR-FTIR instrument was housed
 in a nitrogen-filled glovebox with an oxygen concentration below 20 ppm.
 We note that to the best of our knowledge, none of the compounds in this
 study react with nitrogen at room temperature, the main offenders are
 oxygen and water, whose concentrations were analogous to levels in an Ar
 glovebox.  Compounds were transferred into the ATR-FTIR enclosure in
 sealed vials and then immediately placed on a clean diamond crystal for
 the ATR-FTIR measurement. This transfer approach was effective at
 minimizing unwanted reactions as described in detail in the Technical
 Validation section below. Most data presented here is an average of 512
 individual spectra (CH<sub>3</sub>COOLi,
 Li<sub>2</sub>CO<sub>3</sub>,
 <sup>7</sup>LiF, <sup>6</sup>LiF,
 Li<sub>2</sub>O, PEO) which was used to maximize the signal to
 noise ratio, while only 50 spectra were accumulated for some of the more
 reactive compounds (LiH, LiPF<sub>6</sub>,
 MnF<sub>2</sub>, NiF<sub>2</sub>) to minimize
 acquisition time and thereby reduce the likelihood of undesired reactions
 with trace amounts of oxygen or water.
 <strong>Raman Spectroscopy</strong>
 Raman spectra were collected using a 2 cm-square and 5 mm thick
 custom-made polyether ketone (PEEK) sample chamber with an optical window
 (2.5 cm-square and 1 mm thick glass microscope slide). The chamber, which
 kept samples in an inert argon environment during measurement, is
 illustrated in Fig. 1a. Prior to cell assembly, PEEK pieces and glass
 slides were sonicated with acetone and then isopropyl alcohol and baked at
 40<sup>o</sup>C for at least 4 hours before being transferred
 into an argon glovebox for assembly. After each sample chamber was
 assembled, it was isolated in a heat-sealed bag before being transferred
 to a Renishaw Qontor microscope where Raman spectroscopy was conducted. A
 488 nm excitation laser was used at a power ranging from 1 to 10 mW to
 collect data over 25 acquisitions from 100 to 3200
 cm<sup>-1</sup>. An additional measurement of the lithium
 oxide sample was performed on the same instrument using a 633 nm laser
 (see Table 6). Unwanted contributions to the Raman spectra from the glass
 optical window were avoided by focusing the laser on the surface of the
 sample inside the chamber. <strong>X-Ray
 Diffraction</strong> The<strong>
 </strong>sample chambers used for XRD measurements were similarly
 assembled in an argon glovebox. Small quantities of each compound were
 placed on clean 2.5 cm-square and 1 mm thick glass microscope slides
 (cleaned and dried using the method described above) and covered with
 several sealing overlayers of polyimide tape (Kapton, Ted Pella, silicone
 adhesive, 70 µm thick) before being heat-sealed in individual plastic
 bags. The sample chambers were then transferred to a Bruker Phaser D2
 instrument (wavelength, λ = 1.54 Å) where X-ray diffraction patterns were
 collected over a 2θ range of 10 to 90 degrees using an acquisition time of
 0.2 seconds per step and a step size of 0.02 degrees per step. All samples
 remained in their sealed bags until right before the measurement was
 started. Kapton tape is not perfectly air-tight but was a sufficient
 barrier to enable the acquisition of data, which was completed within the
 first 15 minutes after the sample chambers were brought into ambient air.
 The XRD patterns were collected through the tape, rather than through the
 glass slide, to prevent significant XRD contributions from the glass. The
 relatively smooth XRD background from the amorphous tape was removed via
 processing as described in the Data Processing subsection. The Technical
 Validation section provides evidence that this approach successfully
 minimized unwanted reactions. <strong>Data
 Processing</strong> The collected raw data was
 processed to isolate features of the spectra and diffraction patterns that
 can be used to identify the presence of these compounds in complex data
 collected from interphases. Unwanted instrumental and background
 contributions were also removed through this processing. All FTIR
 measurements of inorganic compounds – and some organic ones – contained
 strong and broad absorption features below 600 cm<sup>-1</sup>
 which increased in  intensity as the wavenumber decreased. These features
 were so broad that the decreasing intensity side of the feature (e.g. see
 Palik and Hunter’s data on LiF in the <em>Handbook of Optical
 Constants of Solids</em>) was not observed above the instrument’s
 low-energy detection limit of 370 cm<sup>-1</sup>. Because
 most researchers have detectors with similar limits (or even higher in
 energy), the FTIR data was processed to focus on the mid-IR regions (above
 ca. 500 cm<sup>-1</sup>) that are most commonly accessible
 experimentally . As a result, low-wavenumber features (below our reporting
 window) were fit as part of the baseline when defining baseline profiles
 to be subtracted from the raw data across the entire measured range, even
 though they are technically not part of the background. Raw, unsubtracted
 data spanning the entire measured range is available in the data library.
 Panels 2a and 2b provide a representative baseline fitting of the raw data
 (which resulted in the removal of the downward-sloping part of the
 spectral feature that is observed below 600 cm<sup>-1</sup>)
 and the resulting subtracted data, respectively. Spikes in the Raman
 spectra attributable to cosmic ray excitation were removed immediately
 after collection and are not included in the raw data. Raw Raman spectra
 were processed through the subtraction of Gaussian and/or polynomial fits
 to eliminate background contributions that could have been caused by
 several phenomena including fluorescence, glass effects, and surface
 roughness. Because our instrument generated raw Raman data with unevenly
 spaced wavenumber values, we performed an interpolation was required to
 use a fast Fourier transform filter for data smoothing. Gaussian fits to
 determine peak positions from the data before and after interpolation
 confirmed that this transformation did not affect the location or shape of
 spectral features. Gaussian fits were used to subtract
 the amorphous background that the Kapton overlayer generated in XRD
 measurements. This background between 10 and 30 degrees appeared in all
 measurements through Kapton tape (but not in control measurements of bare
 metal foils) and was at lower 2θ than the first diffraction peak of most
 compounds, allowing subtraction of a consistent background in the few
 patterns (like that of lithium acetate) where the first diffraction peak
 was found below 30 degrees. This approach was deemed suitable because the
 there were no consistent and unidentifiable peaks in the processed XRD
 patterns which would have indicated a residual contribution from the
 Kapton overlayer.  A fast Fourier filter was applied to reduce high
 frequency noise (with care taken to avoid distorting spectral features)
 and small vertical offsets were used in some cases to align the high-2θ
 baseline near zero. All data was normalized to take on values from 0 to 1.
 To facilitate comparison with data collected on other instruments,
 d-spacing values (calculated using Braggs Law with λ = 1.54 Å) are
 included in the online repository in addition to a 2θ x-axis.
description: The data files are in a .xlsx format which can be opened using
 Excel (including the free Excel Viewer) and Google Sheets among other
 applications. These files can then be exported as a .csv or in other
 format as desired for use in other software (including data processing and
 plotting programs).
description: # An infrared, Raman, and X-ray database of battery interphase components
 Overview: This data contains **ATR-FTIR**, **Raman spectroscopy,** and
 **X-ray diffraction reference data** for 10 common components of
 electrode-electrolyte interphases in rechargeable lithium-based batteries.
 These chemicals are: lithium acetate [CH3COOLi] lithium carbonate [Li2CO3]
 lithium fluoride [LiF with 6Li and 7Li isotopes] lithium hydride [LiH]
 lithium hexafluorophosphate [LiPF6] lithium oxide [Li2O] manganese(II)
 fluoride [MnF2] nickel(II) fluoride [NiF2] polyethylene oxide
 [H(OCH2CH2)nOH] This dataset contains raw data as well as the processed
 data presented in the figures of the associated publication. The fit used
 in the background subtraction is also provided. For some ATR-FTIR data,
 this removes a genuine spectral feature in the low wavenumber region - see
 "Data Processing" for more details. All subtracted data has also
 been normalized and FTIR and XRD data has had a fast Fourier transform
 applied. Many datasets have been truncated to facilitate background
 removal in the area of interest. An offset has been applied to some
 datasets to ensure that all values are non-negative. The additional
 "Background adjustment" column in the NiF2 Raman provides an
 additional fit that was used to remove a background feature after the data
 interpolation was applied. Data structure: One Excel workbook file is
 provided for each characterization technique (ATR-FTIR, Raman, and XRD).
 Each sheet contains data for one compound, whose identity is indicated by
 the chemical formula and written name. The following column headers are
 used: "Raw": raw data collected by the instrument before any
 processing (with the exception of removal of cosmic rays in Raman data)
 "Background": background subtracted from the raw data during
 processing. This is sometimes the vertical sum of several rounds of
 polynomial or Gaussian fits "Final": the final processed data
 (including filters and normalization) The ATR-FTIR and XRD data files also
 contain an additional sheet with all final data on a single x-axis.
 ATR-FTIR data of Li2O has a different x-axis than other compounds so is
 not plotted with them in the "All Final" sheet. All tabs in the
 XRD data file include d-spacing in addition to 2θ values. The d-spacing is
 intended as an alternative x-axis and is calculated from 2θ using
 Bragg's law and the wavelength of the XRD instrument (λ = 1.54 Å).
 Raw Raman data has uneven x-axis spacing so had to be interpolated in
 order to apply a fast Fourier transform filter. **Note that there are
 therefore different wavenumber axes for the raw and final Raman data.**
 The axes for the final data are provided in each sheet and are visually
 offset from the raw data by an empty column. Access information: This data
 is not publicly available elsewhere. Code/Software: No code was used in
 the preparation of this data. The data files are in the .xlsx format which
 can be opened using Excel (including the free Excel Viewer) and Google
 Sheets among other applications. These files can then be exported in a
 .csv or other format as desired for use in other software (including data
 processing and plotting programs). **Substantive Modifications:**
 ***Version 2:*** The raw Raman data for MnF2 and NiF2 was updated to
 remove cosmic rays near 2400 and 2600 cm^-1 for MnF2 and near 950 cm^-1
 for NiF2. The ATR-FTIR and XRD files were not altered. The README file was
 also modified to include additional information about the processing done
 on the ATR-FTIR data. ***Version 7:*** d-spacing values were added to the
 XRD data.