JP2012202951A - Infrared spectral analysis apparatus and utilization thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an infrared spectral analysis apparatus which is available appropriately to infrared spectral measurement of a non-aqueous electrolyte secondary battery containing a fluorine compound in an electrolyte, an analysis method and a prism for analysis.SOLUTION: An infrared spectral analysis apparatus 1 comprises a prism 10 for full reflection including a prism substrate (germanium crystal or the like) 12 and a metal oxide film (alumina film or the like) 14 provided on a bottom face 12a of the substrate, an active electrode 32 disposed on a surface of the metal oxide film 14, a counter electrode 36 and a reference electrode 38. Furthermore, an optical system is provided which makes infrared rays incident to an interface (a bottom face of the prism substrate 12) 12a between the prism substrate 12 and the metal oxide film 14, for collecting reflection rays of the infrared rays reflected on the interface 12a. Moreover, an infrared spectroscope is provided for obtaining spectrum of the reflection rays.

Description

  The present invention relates to an infrared spectroscopic analysis technique based on an attenuated-total-reflection (ATR) method.

  In-situ measurement of the electrode surface provides information that enables the elucidation of the electrode reaction mechanism, the elucidation of side reactions of the electrode reaction, and the optimization of the electrode structure. This technology greatly contributes to the development of As a technique that enables surface structure analysis at the molecular level, such as molecular bonding state, functional group, and orientation state, there is infrared spectroscopy measurement. Infrared spectroscopic measurement is expected as a technique that greatly contributes to elucidation of electrode reaction mechanisms on electrode surfaces, elucidation of side reactions of electrode reactions, and the like. Patent Document 1 is cited as a technical document related to in-situ infrared spectroscopic measurement of the electrode surface. Patent document 2 is a document regarding the technique which utilizes infrared spectroscopy for the measurement of the electrical capacity of a storage battery.

JP 2008-128652 A JP 2004-134409 A

Now, lithium ion secondary batteries and other non-aqueous electrolyte secondary batteries are becoming increasingly important as on-vehicle power supplies or personal computers and portable terminals. In particular, a lithium ion secondary battery that is lightweight and obtains a high energy density is expected to be preferably used as a vehicle-mounted high-output power source (for example, a driving power source for a hybrid vehicle or an electric vehicle). Non-aqueous electrolytes for lithium ion secondary batteries include solvents (carbonate solvents) containing carbonates such as ethylene carbonate, propylene carbonate, and diethyl carbonate as main components, and fluorine compounds (typically as support salts). Specifically, those in which a lithium salt such as LiPF ₆ is dissolved are widely used.

  Such a non-aqueous electrolyte secondary battery can realize a high voltage exceeding the electrolysis voltage of water, but the electrolyte is easily decomposed due to the high voltage. Such decomposition of the electrolytic solution is one factor that hinders high performance (e.g., improved output, extended life) of the secondary battery. Through in-situ infrared spectroscopic measurement, the mechanism of chemical reactions in non-aqueous electrolyte secondary batteries (such as the chemical reaction of the electrolyte on the electrode surface) is elucidated. For example, the decomposition reaction mechanism and electrolysis of the electrolyte accompanying repeated charge and discharge If information on the long-term stability of the liquid can be obtained, it can be useful for improving the performance of the secondary battery.

However, in order to perform in-situ infrared spectroscopic analysis of the electrode surface during charge and discharge, an ATR prism (germanium crystal or the like) is brought into contact with an electrolyte solution (fluorine compound-containing electrolyte solution) containing a fluorine compound such as LiPF _6. When the measurement is performed, the electrolytic solution may cause a chemical reaction to generate hydrogen fluoride (HF) derived from the fluorine compound. HF is a highly corrosive acid and may corrode the prism (window material). When the prism corrodes, for example, as shown in FIG. 7, the accuracy of the infrared spectroscopic measurement is lowered due to the distortion of the baseline, the increase of noise, or the like. The reduction in measurement accuracy due to prism corrosion is not limited to in-situ infrared spectroscopic measurement of the electrode surface of a lithium ion secondary battery, and the acid is generated during a liquid containing a corrosive acid (for example, HF) or during measurement. This is a problem that may occur in common with measurement modes in which the prism is brought into direct contact with the liquid to be obtained (for example, measurement of the corrosion potential of metals).

  Therefore, the present invention relates to an infrared spectroscopic analysis technique based on the ATR method, for infrared spectroscopic measurement (for example, in-situ infrared spectroscopic measurement of an electrode surface) of a non-aqueous electrolyte secondary battery containing a fluorine compound in the electrolytic solution. It is another object of the present invention to provide an infrared spectroscopic analysis apparatus, an infrared spectroscopic analysis method, and an ATR prism suitable for the infrared spectroscopic analysis.

  According to this specification, an infrared spectroscopic analyzer using the ATR method is provided. The infrared spectroscopic analysis apparatus may include an ATR (ATR measurement) prism, a working electrode, a counter electrode that is paired with the working electrode, and a reference electrode that defines a potential of the working electrode. The ATR prism includes a prism base (for example, germanium crystal) and a metal oxide film provided on the bottom surface of the base. The working electrode is disposed on the surface of the metal oxide film. The apparatus also includes an optical system that receives infrared light through the prism at the interface between the base material and the metal oxide film, and reflects the reflected light emitted from the prism after the infrared light is reflected at the interface. . Furthermore, an infrared spectrometer for obtaining a spectrum of the reflected light may be included.

  According to the infrared spectroscopic analyzer having such a configuration, since the metal oxide film is interposed between the prism base material and the working electrode, for example, the potential of the working electrode impregnated with the fluorine compound-containing electrolyte is changed. When an in-situ infrared analysis of the electrode surface is performed, even if the fluorine compound-containing electrolyte is decomposed to generate a corrosive substance such as HF (or HF or the like is added to the electrolyte from the beginning). Even if a corrosive substance is included, direct contact between the corrosive substance and the prism substrate can be prevented. Thereby, since corrosion of the prism base material is prevented, the accuracy of infrared spectroscopic analysis can be improved.

  The infrared spectroscopic analysis device disclosed herein typically brings the working electrode, the counter electrode, and the reference electrode into contact with a fluorine compound-containing electrolyte, and simultaneously proceeds an electrochemical reaction at the working electrode. The surface of the working electrode is configured to be able to perform in-situ infrared spectroscopic measurement by reflecting the infrared ray at the interface between the prism base material and the metal oxide film (while proceeding). According to this configuration, the prism base material is prevented from being corroded by the metal oxide film interposed between the prism base material and the working electrode, so that the in-situ infrared spectroscopic measurement can be performed with higher accuracy. it can.

Preferable examples of the metal oxide film include an alumina (Al ₂ O ₃ ) film and a zirconia (ZrO ₂ ) film. Both the alumina film and the zirconia film have high chemical stability and excellent performance in protecting the prism base material from chemical damage (corrosion, etc.). In addition, since the reduction potential is low, it is also suitable for use under measurement conditions where the potential of the working electrode is low, such as analysis of an electrochemical reaction that can occur on the negative electrode surface of a nonaqueous secondary battery. Furthermore, since none of them is alloyed with lithium (Li), there is no fear of causing alteration due to the formation of a Li alloy, even if it is used under measurement conditions in which the potential of the working electrode can be equal to or lower than that of Li metal. .

The thickness of the metal oxide film is preferably set to a thickness that does not significantly impair the optical characteristics of the prism base material (at least the optical characteristics with respect to infrared rays in the measurement wavenumber region). Normally, evanescent waves generated from infrared rays totally reflected at the interface between the prism base material and the metal oxide film penetrate into the thickness direction of the metal oxide film and reach the working electrode disposed on the metal oxide film. In order to obtain, it is good to set the thickness of the said metal oxide film to 1/4 or less of the infrared wavelength corresponding to the smallest wave number among measurement wave number ranges. For ^example, 400 cm in infrared spectroscopic analysis device that may be used in the measurement wavenumber region of ^-1 ~4000cm -1, approximately 600nm or less the thickness of the metal oxide film appropriate to the (typically about 20nm~600nm in) It is.

As an example of a preferable application of the infrared spectroscopic analyzer disclosed herein, infrared spectroscopic measurement (particularly, in-situ infrared spectroscopic measurement) of a non-aqueous electrolyte secondary battery containing a fluorine compound in the electrolytic solution can be given. It is done. For example, it is suitable for in-situ infrared spectroscopic measurement of a lithium ion secondary battery containing lithium hexafluorophosphate (LiPF ₆ ) in the electrolytic solution.

  In the present specification, the “secondary battery” refers to a general power storage device that can be repeatedly charged and discharged, and is a term including a so-called storage battery such as a lithium secondary battery and a power storage element such as an electric double layer capacitor. The “non-aqueous secondary battery” refers to a battery provided with a non-aqueous electrolyte (typically, an electrolyte containing a supporting salt (supporting electrolyte) in a non-aqueous solvent). The “lithium secondary battery” refers to a secondary battery that uses lithium ions as electrolyte ions and is charged and discharged by the movement of lithium ions between the positive and negative electrodes. A secondary battery generally referred to as a lithium ion secondary battery is a typical example included in the lithium secondary battery in this specification.

  According to this specification, a method for analyzing a non-aqueous electrolyte secondary battery containing a fluorine compound in the electrolyte is also provided. In the method, a test solution containing the fluorine compound (or the electrolytic solution may be used) is prepared by using an ATR prism including a prism base material and a metal oxide film provided on the bottom surface of the base material, and the metal oxide. And contacting a working electrode disposed on the surface of the material film, a counter electrode of the working electrode and a reference electrode, and causing an electrochemical reaction to proceed at the working electrode. In addition, while proceeding with the electrochemical reaction, infrared light is incident on the interface between the base material and the metal oxide film through the prism base material, and the infrared light is reflected at the interface and emitted from the prism. Including daylighting. Then, in-situ infrared spectroscopic measurement is performed on the surface of the working electrode using the reflected light.

  According to such an analysis method, for example, the chemical reaction of the electrolytic solution (for example, reductive decomposition of the electrolytic solution) on the electrode surface of the nonaqueous electrolytic solution secondary battery (for example, lithium ion secondary battery) having the fluorine compound-containing electrolytic solution, etc. Information about the mechanism can be obtained more accurately. Such information can be useful, for example, in the development of higher performance non-aqueous electrolyte secondary batteries.

In the technique disclosed herein, the fluorine compound may be, for example, a lithium salt (that is, a salt of an anion having fluorine as a constituent atom and lithium ion (Li ⁺ ); hereinafter also referred to as a fluorine-containing lithium salt). . Specific examples of the fluorine-containing lithium salt include LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ). ₂ , LiC (CF ₃ SO ₂ ) _{3 and the} like.

  In a preferred aspect of the technology disclosed herein, the working electrode includes a carbon material capable of reversibly inserting and removing lithium ions. Such a carbon material (typically, a carbon material having a graphite structure at least partially) is useful as an electrode active material of a non-aqueous electrolyte secondary battery (for example, a negative electrode active material of a lithium ion secondary battery). It is. If infrared spectroscopic measurement of an event occurring on the surface of the working electrode provided with such a carbon material can be performed with higher accuracy, a higher-performance nonaqueous electrolyte secondary battery can be efficiently developed.

  According to this specification, a prism used for infrared spectroscopic analysis by the ATR method is further provided. The ATR prism includes a prism base material and a metal oxide film provided on the bottom surface of the base material. The ATR prism causes infrared light to enter the interface between the base material and the metal oxide film through the prism, generates an evanescent wave at the interface, and reflects the reflected light emitted from the prism after being reflected at the interface. The measurement sample disposed on the metal oxide film is configured to be capable of infrared spectroscopic measurement.

  Since the ATR prism having such a structure is provided with a metal oxide film on the bottom surface of the prism base material, even if the bottom surface is exposed to a corrosive compound such as HF, the prism base material is highly prevented from corroding. be able to. As a result, the accuracy of infrared spectroscopic analysis using the prism can be improved. The ATR prism is suitable, for example, as a prism used in any of the infrared spectroscopic analysis apparatuses or methods disclosed herein.

It is sectional drawing which shows the principal part of the infrared spectroscopy analyzer which concerns on one Embodiment. It is sectional drawing which expands and shows a part of FIG. It is a schematic diagram which shows schematic structure of the infrared spectroscopy analyzer which concerns on one Embodiment. It is a characteristic view which shows the difference spectrum accompanying the electric potential change at the time of the first charge obtained by the in-situ FT-IR measurement of the electrode surface using the prism for ATR which concerns on Example 1. FIG. It is a characteristic view which shows the difference spectrum accompanying the electric potential change at the time of the first discharge obtained by the in-situ FT-IR measurement of the electrode surface using the prism for ATR which concerns on Example 1. FIG. 6 is a characteristic diagram showing an infrared absorption spectrum obtained by the ATR prism according to Example 2. FIG. It is a characteristic view which illustrates the influence which corrosion of the prism for ATR has on a measurement spectrum.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field. Moreover, in the following drawings, the same code | symbol is attached | subjected to the member and site | part which show | plays the same effect | action, and the overlapping description may be abbreviate | omitted or simplified. The dimensional relationship (length, width, thickness, etc.) in each figure does not reflect the actual dimensional relationship.

  The infrared spectroscopic analysis apparatus disclosed herein typically includes an ATR (ATR measurement) prism, a working electrode, a counter electrode paired with the working electrode, and a reference that defines the potential of the working electrode. A pole, an optical system for collecting infrared light incident on the ATR prism, reflected from the prism and emitted from the prism, and an infrared spectrometer for obtaining a spectrum of the reflected light. The technique disclosed herein is characterized by having a metal oxide film on the bottom surface of the prism base material in the structure of the prism for ATR. The working electrode is disposed on the surface of the metal oxide film. In other words, the working electrode is disposed on the bottom surface of the prism base material via the metal oxide film provided on the bottom surface.

  An example of such an infrared spectroscopic analyzer will be described with reference to FIGS. FIG. 1 is a partial cross-sectional view schematically showing an infrared spectroscopic cell 20 provided in a Fourier Transform Infrared Spectroscopy Infrared Spectroscopy (FT-IR) analyzer 1 according to the present embodiment. FIG. 2 is an enlarged cross-sectional view showing a part thereof. FIG. 3 is a schematic diagram showing a schematic configuration of the FT-IR analyzer 1.

  In FIG. 1, an electrolyte solution 22 containing a fluorine compound is injected into an infrared spectroscopic cell 20 whose bottom surface is composed of the bottom surface 10 a of the ATR prism 10. The outer space of the infrared spectroscopic cell 20 into which the electrolyte solution 22 is injected is partitioned by a case 24 that forms a cylindrical inner peripheral wall surface. The space between the bottom surface 10a of the prism 10 and the bottom surface of the case 24 is sealed by an O-ring 26 to prevent the electrolyte solution 22 from exuding to the outside.

  The working electrode 32 is inserted into the cell 20 so that the surface 32a of the working electrode 32 faces the bottom surface 10a of the prism 10, and is pressed against and contacts the prism 10. A part of the electrolytic solution 22 soaks into the surface 32 a of the working electrode 32. For example, when the surface 32a of the working electrode 32 has a configuration in which the powder material is bound, the soaked electrolytic solution 22 is bound to the surface of the working electrode 32 and the electrolyte 32 filled between the particles of the powder material. In the case where a polymer such as an adhesive is present, it may be an electrolyte solution absorbed by the polymer (swelling the polymer), or the like.

  A counter electrode 36 disposed on the back surface 32 b of the working electrode 32 and a reference electrode 38 that defines the potential of the working electrode 32 are immersed in the electrolytic solution 22. The working electrode 32, the counter electrode 36, and the reference electrode 38 are connected to a potentiostat (external power source) 40 so that the potential of the working electrode 32 can be arbitrarily controlled. In this embodiment, the potentiostat 40 can also be grasped as a charge / discharge unit of the cell 20.

  The counter electrode 36 is not particularly limited in material and shape as long as a current can be passed through the working electrode 32 to be observed, and a common electrode can be used. The reference electrode 38 only needs to exhibit a stable potential that serves as a reference for the potential of the working electrode 32 in the electrolytic solution 22 to be used, and is a standard hydrogen electrode (SHE or NHE), a saturated calomel electrode (SCE), a reversible. In addition to general reference electrodes such as hydrogen electrode (RHE), silver-silver chloride electrode (Ag / AgCl), mercury / mercury sulfide electrode, etc., use lithium metal, silver wire, platinum wire, etc. as pseudo reference electrode Can do.

  The ATR prism 10 includes a prism base 12 and a metal oxide film 14 formed on the bottom surface 12a. The shape (outer shape) of the prism substrate 12 is not particularly limited, and a general material used in infrared spectroscopy can be used. For example, a hemispherical shape, a semi-cylindrical shape (kamaboko shape), a pyramid shape, a trapezoidal shape, a triangular prism shape, and the like can be given. In the case of using an infrared microscope, it is preferable to use a hemispherical prism base material 12 from the viewpoint that the spot diameter of infrared light can be narrowed down to a minute region without defocusing. When an infrared microscope is not used, a triangular prism shape or a trapezoidal shape is preferable. The dimensions of the prism base 12 are not particularly limited, and may be appropriately determined in consideration of the measurement wave number range, the number and size of working electrodes to be provided, and the like. Usually, a prism having a size generally used in an electrochemical infrared spectrometer can be preferably used.

  The material of the prism substrate 12 may be any material that has a small infrared absorption in the measurement region (wave number region) and a large refractive index (typically a material that is larger than the refractive index of a metal oxide film described later). There is no particular limitation. For example, germanium (Ge; refractive index 4), zinc selenide (ZnSe; refractive index 2.4), KRS-5 (thallium bromoiodide) used in conventional general infrared spectroscopic prisms Refractive index 2.73), silicon (Si; refractive index 3.4), zinc sulfide (ZnS; refractive index 2.2), KRS-6 (thallium bromochloride; refractive index 2.17), etc. It can employ | adopt as a constituent material of the prism base material 12 in the technique disclosed.

Among them, germanium has a high refractive index and low infrared absorption in a low wavenumber region such as 1000 cm ⁻¹ or less, and can transmit infrared light up to 600 cm ⁻¹ . Therefore, the sensitivity in the low wavenumber region is high. Show excellent optical properties. On the other hand, germanium has a relatively low chemical stability and is easily corroded by the above-mentioned corrosive substances (HF or the like) or alloyed with Li. Therefore, in an embodiment in which the constituent material of the prism base 12 is germanium (typically an embodiment using germanium crystals (preferably a single crystal) as the prism base), the technique disclosed herein is applied to form a prism base. It is particularly meaningful to prevent the material 12 from being altered (corrosion, alloying, etc.), and this can effectively improve the accuracy of infrared spectroscopic analysis.

The ATR prism 10 in the technology disclosed herein has a metal oxide film 14 on the bottom surface 12 a of the prism base 12. A working electrode 32 is disposed on the metal oxide film 14. The metal oxide film 14 functions to protect the prism base 12 from damage such as corrosion. Therefore, the material constituting the metal oxide film 14 is preferably a material having high chemical stability and excellent corrosion resistance (particularly corrosion resistance against acids such as HF). Further, (usually wavenumber range of approximately ^{400cm -1 ~4000cm} -1 suitable for viewing the change in binding or functional groups of the organic substance) measuring wavenumber range of interest so that the relative infrared, hinder analysis A material that does not exhibit a strong absorption peak is preferable.

  As shown well in FIG. 2, in the prism 10 having such a configuration, the interface between the prism substrate 12 and the metal oxide film 14 (from the prism substrate 12) (from the prism substrate 12) (from the prism substrate 12). When infrared light is incident on the bottom surface 12a) at an incident angle larger than the critical angle, the infrared light is totally reflected at the interface 12a. At this time, an evanescent wave penetrates from the interface 12a through the metal oxide film 14 to the working electrode (measurement sample) 32 disposed thereon, and the metal oxide film 14 and the working electrode 32 are contacted at the time of reflection. It is absorbed by chemical species present near the surface. Therefore, as shown in FIG. 3, the reflected light reflected from the interface 12a between the prism base 12 and the metal oxide film 14 and emitted from the prism 10 is introduced into the infrared spectrometer 58 from the daylighting window 56 and absorbed. By analyzing the above, it becomes possible to detect and identify chemical species present near the surface of the electrode (here, the surface 32a of the working electrode 32).

  Here, the chemical species on the electrode surface include chemical species adsorbed on the electrode surface and those floating near the interface between the working electrode 32 and the electrolytic solution 22 without adsorbing on the electrode surface. Examples include reaction products, reaction intermediates, and reaction by-products in the reaction.

  According to the technique disclosed herein, it is possible to measure a change in chemical species on the electrode surface accompanying a change in potential of the working electrode or a change in current. That is, according to the present invention, in addition to the main reaction that proceeds in the electrode, such as the reaction of the solvent and solute contained in the electrolytic solution, the reaction of the material constituting the electrode, the potential of the electrode, the current value, etc. It can be observed together with the evaluation of electrical conditions. Therefore, according to the present invention, for example, the mechanism of the decomposition of the solvent of the electrolytic solution, which is one of the problems that hinder the long life of the lithium ion battery, can be clarified.

In the technique disclosed herein, the thickness of the metal oxide film 14 can sufficiently penetrate the evanescent wave to the surface opposite to the surface in contact with the prism base 12 (that is, the surface 32a of the working electrode 32). It is appropriate to make it thin. Accordingly, it is possible to analyze the surface of the working electrode 32a with higher accuracy through infrared light that is incident from the inside of the prism base 12 and is reflected by the interface 12a. Specifically, the thickness of the metal oxide film 14 may be set to ¼ or less of the infrared wavelength corresponding to the largest wave number in the measurement wave number region. For ^example, 400 cm in infrared spectroscopic analysis device that may be used in the measurement wavenumber region of ^-1 ~4000cm -1, approximately 600nm or less the thickness of the metal oxide film appropriate to the (typically about 20nm~600nm in) It is.

  The thickness of the metal oxide film 14 can be measured by a scanning electron microscope (SEM), a scanning tunneling microscope (STM), a scanning atomic force microscope (AFM), or the like. Further, the film thickness may be obtained by conversion from mass measurement using a quartz crystal microbalance. Alternatively, a calibration curve may be obtained in advance for the metal oxide film fabrication conditions and the obtained metal oxide, and the thickness of the metal oxide film fabricated under predetermined conditions may be estimated based on the calibration curve.

  As a constituent material of the metal oxide film 14, a material having a refractive index smaller than that of the prism base 12 can be preferably used. As a result, the infrared rays can be appropriately totally reflected at the interface 12a. The greater the difference in refractive index between the prism substrate 12 and the metal oxide film 14, the greater the depth of penetration of the evanescent wave from the interface 12a to the metal oxide film 14 side. This means that the penetration depth of the evanescent wave that penetrates the working electrode 32 through the metal oxide film 14 is increased, and the absorption intensity due to the chemical species on the surface of the working electrode 32 is increased. Therefore, the detection sensitivity of the chemical species can be improved by using the prism base 12 having a refractive index as large as possible. Further, it is possible to observe chemical species existing in a wider range from the surface 32 a to the inside of the working electrode 32. Increasing the penetration depth of the evanescent wave from the interface 12a to the metal oxide film 14 side can also increase the range that can be selected when setting the thickness of the metal oxide film 14 (for example, more It is also preferable from the viewpoint of being able to be thickened.

  The penetration depth of the evanescent wave may vary depending on the incident angle and wavelength of infrared light, the material of the working electrode 32, and the like in addition to the material (refractive index) of the prism base 12. The incident angle of infrared rays is larger than the critical angle, and may be an angle at which total reflection occurs at the interface 12a between the prism base 12 and the metal oxide film 14, and the specific angle is not limited. Usually, it is appropriate to set the incident angle to about 45 ° to 60 °.

In selecting the material of the metal oxide film 14, other matters that should be considered as necessary include that it is easy to form a dense thin film on the prism base 12, and adhesion to the prism base 12. Such as being easy to form a good film, having high electrochemical stability (for example, at least a low reduction potential), and being difficult to form an alloy with Li. A material satisfying at least one of these optional considerations can be preferably employed. Particularly preferred materials include Al ₂ O ₃ and ZrO ₂ . That is, a preferred example of the metal oxide film 14 in the technique disclosed herein is an Al ₂ O ₃ film. Another preferred example is a ZrO ₂ film.

  The metal oxide film 14 is provided so as to cover at least a range (region) in which the working electrode 32 is disposed on the bottom surface 12 a of the prism base 12. That is, at least in the range where the working electrode 32 is disposed, the metal oxide film 14 is interposed between the working electrode 32 and the electrolytic solution 22 impregnated therein and the prism base material 12 to prevent direct contact thereof. Yes. The generation of the corrosive substance (HF or the like) described above mainly occurs near the surface 32a of the working electrode 32. Therefore, the concentration of the corrosive substance tends to be highest near the surface 32a. This is because the necessity of protecting the prism base 12 is particularly high within a range.

  In a preferred embodiment, the metal oxide film 14 is not limited to the range in which the working electrode 32 is disposed, but in the range in which direct contact between the electrolytic solution 22 and the prism base 12 can be prevented (in the example shown in FIG. 1, the bottom surface 10a). And a range inside the O-ring 26, typically a position where the O-ring 26 abuts and a range inside thereof). According to this aspect, the prism base 12 can be more reliably protected from corrosion. As in the example shown in FIG. 1, the metal oxide film 14 may be provided over the entire range of the bottom surface 10a.

The method for forming the metal oxide film 14 is not particularly limited, and for example, known methods such as a vacuum deposition method, a sputtering method, and a sol-gel method can be used alone or in appropriate combination. The metal oxide film 14 may be crystalline or amorphous. In one aspect of the technology disclosed herein, even if the metal oxide film 14 (for example, an Al ₂ O ₃ film) is amorphous, corrosion of the prism base 12 is appropriately prevented and infrared spectroscopic analysis measurement is performed. The effect of improving the accuracy of the is obtained. The amorphous metal oxide film 14 can be used in this way, for example, when the metal oxide film 14 is formed on the bottom surface 12a of the prism base material 12, damage to the prism base material 12 (for example, This is preferable from the viewpoint of reducing damage caused by heat.

  An optical system that injects infrared light into the interface between the electrode surface of the working electrode and the electrolytic solution and collects reflected light that is reflected at the interface and emitted from the window material is an infrared light source (IR light source), Infrared spectrometer (detector) for obtaining the spectrum of reflected light, adjusting the path of the emitted light from the IR light source (for example, the incident angle to the prism), or generating parallel light and convergent light from the emitted light, A lens, a mirror, a slit, and the like for extraction can be included in an appropriate combination. Examples of the spectrometer (detector) for obtaining the spectrum of reflected light include an MCT detector, a TGS detector, an InGaAs detector, a PbSe detector, and the like. In the infrared spectroscopic analysis apparatus 1 according to the embodiment shown in FIG. 3, the infrared rays emitted from the IR light source 52 are reflected by the mirrors 54 a and 54 b, are incident on the prism 10 at a predetermined incident angle, and are reflected from the prism 10. The optical system 50 is configured so that light can be reflected by the mirrors 54 c and 54 d and introduced into the infrared spectroscope 58 from the daylighting window 56.

  The technique disclosed here can be preferably applied to grasping (analysis, observation, analysis, etc.) of events occurring on the electrode surface during charge / discharge of a lithium ion secondary battery containing a fluorine compound in a nonaqueous electrolyte solution, for example. For example, as the working electrode 32, one having the same material and structure as the electrode surface can be used. Further, a working electrode 32 having a simplified material or structure with an emphasis on an arbitrary feature of the electrode surface may be used. As the electrolytic solution 22, one having the same composition as the non-aqueous electrolytic solution can be used. Alternatively, a simplified composition with an emphasis on any characteristic of the non-aqueous electrolyte, a composition that emphasizes the characteristic (for example, a composition with an increased concentration of a fluorine compound, or a simplified composition of a non-aqueous solvent) In addition, an electrolytic solution (test solution) 22 having a composition containing an additive in addition to the fluorine compound may be used.

In the technology disclosed herein, the electrolytic solution (test solution) 22 used for infrared spectroscopy includes at least a fluorine compound. The fluorine compound may be a lithium salt that can be used as a supporting salt for a lithium ion secondary battery. Specific examples include LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiC (CF ₃ Various lithium salts known to be capable of functioning as a supporting salt for lithium ion secondary batteries, such as SO ₂ ) ₃ , can be mentioned. Among them, a preferred fluorine compound is LiPF ₆ which is widely used as a supporting salt for lithium ion secondary batteries. The electrolytic solution 22 may further include a supporting salt other than the fluorine compound (for example, a lithium compound having no fluorine atom, such as LiClO ₄ or LiB [(OCO) ₂ ] ₂ ).

  The electrolytic solution 22 typically has a form in which the fluorine compound is dissolved in a non-aqueous solvent. As such a non-aqueous solvent, various aprotic solvents that are generally known to be usable as solvents for non-aqueous electrolytes can be used. For example, various aprotic solvents such as carbonates, esters, ethers, nitriles, sulfones, and lactones can be used alone or in appropriate combination of two or more. Specific examples include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), 1,2-dimethoxyethane, 1,2-diethoxyethane. , Tetrahydrofuran, 2-methyltetrahydrofuran, dioxane, 1,3-dioxolane, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, acetonitrile, propionitrile, nitromethane, N, N-dimethylformamide, dimethyl sulfoxide, sulfolane, γ-butyrolactone, etc. .

  As a preferred example of the electrolytic solution 22, the non-aqueous solvent contains one or more carbonates, and the total volume of the carbonates accounts for 50% by volume or more of the total volume of the non-aqueous solvent (carbonates). Electrolytes which are system solvents). For example, the electrolytic solution 22 in which the total volume of carbonates accounts for 75% by volume or more (more preferably 85% by volume or more, or substantially 100% by volume) of the total volume of the nonaqueous solvent is preferable. . The concentration of the fluorine compound in the electrolytic solution 22 is not particularly limited, and may be, for example, approximately the same as the electrolytic solution of a general lithium ion secondary battery (for example, approximately 0.8 mol / L to 1.5 mol / L). it can. Alternatively, the concentration of the fluorine compound may be higher than that of a general lithium ion electrolyte (for example, approximately 2 mol / L to 3 mol / L).

  As the working electrode 32, for example, a negative electrode active material capable of reversibly inserting and removing lithium ions can be used assuming a negative electrode of a lithium ion secondary battery. As the negative electrode active material, one type or two or more types of materials conventionally used in lithium ion secondary batteries can be used without any particular limitation. In a preferred embodiment, the negative electrode active material is a powder material. For example, the working electrode 32 may have a surface 32a having a porous structure in which the powder material is bound with a binder. The working electrode 32 having such a structure is suitable for observing the behavior of the electrolytic solution on the electrode surface because the electrolytic solution 22 is easily held on the surface 32a (such as a gap between particles constituting the powder material).

  As a suitable example of the negative electrode active material, a particulate carbon material (carbon particles) including a graphite structure (layered structure) at least in part can be given. Any carbon material of a so-called graphitic material (graphite), non-graphitizable carbon material (hard carbon), easily graphitized carbon material (soft carbon), or a combination of these materials is preferably used. obtain. Among these, graphite particles such as natural graphite can be preferably used. Examples of the binder include carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), and polyvinylidene fluoride (PVDF).

In addition, assuming a positive electrode of a lithium ion secondary battery, a working electrode 32 having a positive electrode active material capable of reversibly inserting and removing lithium ions may be used. As the positive electrode active material, one kind or two or more kinds of substances conventionally used for lithium ion secondary batteries (for example, an oxide having a layered structure or an oxide having a spinel structure) can be used without any particular limitation. Preferable examples include lithium-containing composite oxides such as lithium nickel composite oxides, lithium cobalt composite oxides, and lithium manganese composite oxides. Other suitable examples of the material that can be used as the positive electrode active material include olivine type lithium phosphate and other polyanion materials. The lithium olivine is, for example, an olivine-type lithium phosphate (LiFePO ₄ , LiMnPO _4, etc.) represented by a general formula LiMPO ₄ (M is at least one element of Co, Ni, Mn, and Fe). possible. The positive electrode active material is preferably a powder material, the working electrode 32 having a porous surface 32a in which the powder material is bound with a binder, the preferred example of the binder, etc. Is the same as in the case of the working electrode 32 having a negative electrode active material.

According to the technology disclosed herein, the prism base material 12 is prevented from being corroded by the metal oxide film 14, so that the red color can be accurately obtained even under conditions where the potential of the working electrode is low (or can be lowered during measurement). External spectroscopic analysis can be performed. For example, the potential at which the working electrode potential (vs. Li / Li ⁺ ) can be 1 V or less (typically 0.5 V or less, more preferably 0.3 V or less, and even 0.1 V or less) at least at one time during measurement. Particularly useful in conditions. Because of this feature, the technology disclosed herein can grasp (analyze) events that occur on the negative electrode surface of a non-aqueous electrolyte secondary battery (typically a lithium ion secondary battery) containing a fluorine compound in the electrolyte, for example. , Observation, analysis, etc.) and can be useful for the development of higher performance batteries.

  Several examples relating to the present invention will be described below, but the present invention is not intended to be limited to the specific examples.

<Example 1: Production and evaluation of prism for ATR having Al ₂ O ₃ film>
Using an infrared spectroscopic analyzer having a schematic configuration shown in FIGS. 1 to 3, the working electrode was impregnated with an electrolytic solution containing LiPF ₆ and in-situ FT-IR measurement was performed on the electrode surface.

As the prism substrate 12, a hemispherical Ge crystal (size: diameter 15 mm) was used. The temperature of this prism base material (Ge window material) 12 was adjusted to 300 ° C., and sputtering was performed under the conditions of an output of 150 W and an Ar atmosphere of 5 × 10 ⁻³ Torr using Al ₂ O ₃ as a target. As a result, an Al ₂ O ₃ film (metal oxide film) 14 is produced over the entire area of the bottom surface 10 a of the prism base 12, and the ATR prism (Ge window material with Al ₂ O ₃ film) 10 according to this example is prepared. Obtained. When the thickness of the Al ₂ O ₃ film 14 was measured with a scanning electron microscope (SEM), it was confirmed to be a thin film of 1 μm or less.

The ATR prism 10 was attached to the bottom surface of the case 24 to construct a cylindrical infrared spectroscopic cell 20. The working electrode 32 is formed by mixing graphite particles (average particle size of about 20 μm) as an electrode active material with a binder of 5 to 10% by mass and forming a disk shape having a diameter of 0.5 cm and a thickness of 0.15 mm. A composite electrode was used. PVDF was used as the binder. Li metal was used as the counter electrode 36 and the reference electrode 38. The cell 20 was filled with the electrolytic solution 22 and impregnated in the working electrode 32 and brought into contact with the counter electrode 36 and the reference electrode 38. As the electrolytic solution 22, a nonaqueous electrolytic solution containing LiPF ₆ at a concentration of 1.0 mol / liter in a 1: 1 (volume ratio) mixed solvent of EC and DEC was used. Infrared light was incident on the ATR prism 10, and the ATR spectrum R _i of the working electrode surface 32a was measured by FT-IR.

Next, assuming that the working electrode 32 is used as a negative electrode of a lithium ion secondary battery, the potential of the working electrode 32 (vs. Li / Li ⁺⁾ is observed in order to observe the spectral change of the negative electrode surface during charging and discharging of the battery. ) potential in the initial state _{(R i} measured, i.e. by changing from 1.22V) was measured ATR spectrum. The electrode potential was controlled by a cyclic voltammetry method, and the sweep rate was 10 mV / min. By substituting the spectrum R _{i at the} initial potential and the spectrum R ₁ when the potential of the working electrode decreases from 1.22 V to 0.92 V into the following equation, a difference spectrum (Subtractively Normalized FTIR; SNIFTIR) is obtained. It was.
ΔR / R = (R ₁ −R _i ) / R _i (1)

Similarly, the potential of the spectrum R ₂ , R ₃ , R ₄ and the potential of the working electrode 32 when the potential of the working electrode 32 sequentially decreases from 0.92 V to 0.62 V, 0.32 V, and 0.02 V, and the potential of the working electrode 32 is 0. Spectra R ₅ , R ₆ , R ₇ , and R ₈ were measured from 0.2V (reversal potential) to 0.32V, 0.62V, 0.92V, and 1.22V, respectively. The difference spectrum before and after was obtained.
ΔR / R = (R _{n + 1} −R _n ) / R _n (2)

FIG. 4 shows a difference spectrum at the time of initial charge (when Li ions are inserted into the electrode active material included in the working electrode 32) obtained from the in-situ FI-IR measurement. FIG. 5 shows a difference spectrum during ion desorption. The number shown above each difference spectrum represents the potential of the working electrode (reference potential in parentheses) (vs. Li / Li ⁺ ). In these difference spectra, the upward peak indicates that the chemical species corresponding to the absorption is decreased, and the downward peak indicates that the chemical species corresponding to the absorption is increased. In the lower part of FIG. 4 and FIG. 5, the ATR spectrum indicating the characteristic absorption of the electrolytic solution alone is indicated by a dotted line. Based on this information, the interface behavior was analyzed.

In the charging process shown in FIG. 4, the largest change was observed at 0.02 V (vs. Li / Li ⁺ ), and a behavior suggesting decomposition of the electrolytic solution 22 and desolvation of Li ions was observed. On the other hand, in the discharge process shown in FIG. 5, a large peak was observed in the potential range of 0.02 V to 0.32 V, and a behavior in which Li ions were solvated was observed. In both the charge and discharge processes, no significant change in the baseline suggesting corrosion of the prism base material (Ge window material) 12 was observed, and the Al ₂ O ₃ film 14 on the Ge window material 12 was effectively used as a protective film. Confirmed to work. Furthermore, it was also confirmed that the decrease in spectral intensity due to the formation of the Al ₂ O ₃ film 14 is not particularly problematic in measurement.

A HF solution for a corrosion resistance test containing HF in an amount of 10 to 100 times the normal amount was prepared by simulating an increase in HF in the electrolytic solution due to salt corrosion. Using a test piece (using a test piece made of germanium crystals, which is the same in Examples 2 to 4) to which a film similar to the ATR prism according to this example is attached, the test piece is immersed in the HF solution, Left at room temperature for more than a day. Thereafter, the test piece was taken out and evaluated by SEM observation and X-ray photoelectron spectroscopy. As a result, discoloration and peeling of the Al ₂ O ₃ film, exposure of the base material (germanium), and the like were not recognized.

In order to grasp the crystallinity of the Al ₂ O ₃ film produced in this example, XRD (X-ray diffraction) measurement was performed. In the obtained XRD spectrum, no peak corresponding to the Al ₂ O ₃ crystal was observed, and it was confirmed that the Al ₂ O ₃ film was amorphous. This result supports that the metal oxide film 14 provided on the prism substrate 12 is not limited to a crystalline one, and the amorphous metal oxide film 14 can provide a sufficient protective function. .

<Example 2: Production and evaluation of ATR prism having organic film>
A coating solution containing a polyimide precursor was applied to the bottom surface of the same prism base material (Ge window material) as in Example 1, dried and cured. As a result, an ATR prism (Ge window material with a polyimide resin film) having a polyimide resin film with a thickness of 0.15 μm on the bottom surface of the prism base material was obtained.
A test piece having the same film as that of the ATR prism was immersed in the same corrosion resistance test HF solution used in Example 1 and allowed to stand at room temperature for more than a day. Thereafter, the test piece was taken out and evaluated by SEM observation and X-ray photoelectron spectroscopy. As a result, discoloration, peeling, and exposure of the base material were not recognized.

The ATR prism according to this example was used in place of the ATR prism according to Example 1, and the ATR spectrum R _i on the working electrode surface was measured by FT-IR in the same manner as in Example 1 for other points. Thereafter, in the same manner as in Example 1, the potential of the working electrode was changed between 1.22 V and 0.02 V (vs. Li / Li ⁺ ). Then, when the prism for ATR was removed from the cell and the appearance was visually evaluated, no discoloration or peeling of the polyimide resin film was observed. However, in the ATR prism of the present embodiment, as shown in FIG. 6, appeared the absorption peak derived from polyimide resin (approximately 980～1530Cm ^-1 and 1650～1800Cm ^-1 in this example) Major IR observation range In addition, the phenomenon that the polyimide resin film swells with the electrolytic solution was observed. From these circumstances, it was determined that the ATR prism (Ge window material with polyimide resin film) according to this example is not suitable for in-situ observation and analysis of the decomposition behavior of the electrolytic solution.

<Example 3: Production and evaluation of prism for ATR having DLC film>
A diamond-like carbon (DLC) film was produced on the bottom surface of the same prism base material (Ge window material) as in Example 1 at a deposition temperature of 200 ° C. by the PVD method. By changing the deposition time, three types of ATR prisms (Ge window materials with a DLC film) having DLC film thicknesses of 20 nm, 75 nm, and 150 nm, respectively, were produced.
The test pieces with the same films as those of the ATR prisms were respectively immersed in the same corrosion resistance test HF solution used in Example 1 and allowed to stand at room temperature for one day or more. Thereafter, the test piece was taken out and evaluated by SEM observation and X-ray photoelectron spectroscopy. As a result, none of the DLC film was discolored, peeled off, or exposed from the base material.

Instead of the ATR prism according to Example 1, the three types of ATR prisms according to this example were used, respectively. For other points, the ATR spectrum R _i of the working electrode surface was obtained by FT-IR in the same manner as in Example 1. It was measured. Thereafter, in the same manner as in Example 1, when the potential of the working electrode was changed between 1.22 V and 0.02 V (vs. Li / Li ⁺ ), generation of abnormal current was confirmed on the way. When the prism of ATR was removed from the cell and the surface of the prism was observed with a scanning electron microscope (SEM), the DLC film was peeled off at the center (inside the O-ring), and the Ge window material was corroded in the vicinity. It was.

<Example 4: Examination of Al vapor deposition film>
A test piece formed by depositing an aluminum (Al) deposited film having a thickness of 0.01 to 0.1 μm by a vacuum deposition method is immersed in the same HF solution for corrosion resistance test as that used in Example 1, and at room temperature. Left for more than a day. Then, when the test piece was taken out and evaluated by SEM observation and X-ray photoelectron spectroscopy, most of the Al deposited film was peeled off from the base material.

  As mentioned above, although this invention was demonstrated in detail, the said embodiment and Example are only illustrations and what changed and changed various the specific example mentioned above is included in the invention disclosed here. In the above description, the technique disclosed herein has been focused on the application to the analysis of a non-aqueous electrolyte secondary battery equipped with a fluorine-containing electrolyte. Widely applicable to various measurements (for example, measurement of corrosion potential of metals, etc.) characterized in that the ATR prism is brought into direct contact with a liquid containing an acidic acid (for example, HF) or a liquid that can generate an acid during the measurement. Can be done.

1 FT-IR analyzer (infrared spectrometer)
10 ATR prism 10a bottom surface 12 prism base material 12a bottom surface (interface between prism base material and metal oxide film)
14 Metal oxide film 20 Infrared spectroscopic cell 22 Electrolytic solution (test solution)
24 Case 26 O-ring 32 Working electrode 32a Front surface 32b Rear surface 36 Counter electrode 38 Reference electrode 40 Potentiostat (charge / discharge unit)
50 Optical System 52 IR Light Sources 54a, 54b, 54c, 54d Mirror 56 Lighting Window 58 Infrared Spectrometer

Claims (10)

An infrared spectroscopic analysis apparatus using an attenuated-total-reflection (ATR) method:
A total reflection prism comprising a prism substrate and a metal oxide film provided on the bottom surface of the substrate;
A working electrode disposed on the surface of the metal oxide film;
A counter electrode paired with the working electrode;
A reference electrode defining the potential of the working electrode;
An optical system that injects infrared light into the interface between the base material and the metal oxide film through the prism base material, and reflects the reflected light emitted from the prism after the infrared light is reflected at the interface; and
An infrared spectrometer for obtaining a spectrum of the reflected light;
An infrared spectroscopic analyzer.   The working electrode, the counter electrode, and the reference electrode are brought into contact with an electrolyte solution containing a fluorine compound, and the infrared ray is transmitted at the interface between the prism base material and the metal oxide film while an electrochemical reaction proceeds in the working electrode. The apparatus according to claim 1, wherein the apparatus is configured to be able to perform in-situ infrared spectroscopic measurement of the surface of the working electrode by reflection.   The apparatus according to claim 1, wherein the metal oxide film is an alumina film or a zirconia film.   The apparatus according to claim 1, wherein the metal oxide film has a thickness of 20 nm to 600 nm.   The apparatus according to claim 1, wherein the prism base material is a germanium crystal.   The apparatus as described in any one of Claim 1 to 5 used for the in-situ infrared spectroscopy measurement of the nonaqueous electrolyte secondary battery which contains a fluorine compound in electrolyte solution. A method for analyzing a non-aqueous electrolyte secondary battery that includes a fluorine compound in an electrolyte solution:
A test liquid containing the fluorine compound, a prism base material and a total reflection prism including a metal oxide film provided on the bottom surface of the base material; and a working electrode disposed on the surface of the metal oxide film; Contacting the counter electrode of the working electrode with a reference electrode to allow an electrochemical reaction to proceed at the working electrode; and
While proceeding with the electrochemical reaction, infrared light is incident on the interface between the base material and the metal oxide film through the prism base material, and the reflected light is reflected from the interface and emitted from the prism. To do;
And the surface of the working electrode is subjected to in-situ infrared spectroscopic measurement using the reflected light.   The method according to claim 7, wherein the fluorine compound is a lithium salt.   The method according to claim 7 or 8, wherein the working electrode has a carbon material capable of reversibly inserting and removing lithium ions. A prism used for infrared spectroscopic analysis by a total reflection method,
A prism base material, and a metal oxide film provided on the bottom surface of the base material,
Infrared light is incident on the interface between the base material and the metal oxide film through the prism base material, an evanescent wave is generated at the interface, and the reflected light that is reflected at the interface and emitted from the prism is used. A total reflection prism configured to be capable of infrared spectroscopic measurement of a measurement sample disposed on the metal oxide film.

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