Method of analyzing lithium-ion secondary battery

Abstract

To enable in-situ measurement of a passive film formed on a surface of an electrode of a lithium-ion secondary battery.SOLUTION: A method of analyzing a lithium-ion secondary battery is provided, the method comprising inserting a Raman spectroscopic probe 2 into a space between a positive electrode W1 and a negative electrode W2 of a lithium-ion secondary battery, irradiating a surface of the positive electrode W1 or the negative electrode W2 with excitation light L1 to detect Raman scattered light L2, and using the detected Raman scattered light L2 to analyze a passive film Wx formed on the surface of the positive electrode W1 or the negative electrode W2.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method for analyzing a lithium ion secondary battery. [Background technology]

[0002] A solid electrolyte interphase (SEI) film is formed on the surface of the negative electrode of a lithium-ion secondary battery. This SEI film is known to affect the charge / discharge performance of lithium-ion secondary batteries, and analysis of the SEI film is believed to be useful in evaluating the performance of lithium-ion secondary batteries.

[0003] Incidentally, a conventional method for analyzing lithium ion secondary batteries, as disclosed in Patent Document 1, involves dismantling an electricity storage element, removing the used negative electrode, and measuring it using microscopic Raman spectroscopy. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 7042589 Summary of the Invention [Problem to be solved by the invention]

[0005] However, while the above analytical method may be capable of analyzing the SEI film formed on the negative electrode after dismantling the energy storage element and removing it from use, it is not capable of analyzing the SEI film formed on the surface of the negative electrode in situ.

[0006] Therefore, the present invention has been made in consideration of the above-mentioned problems, and its main objective is to analyze in situ the passive film formed on the surface of an electrode of a lithium ion secondary battery. [Means for solving the problem]

[0007] That is, the method for analyzing a lithium ion secondary battery according to the present invention is characterized in that a Raman spectroscopy probe having an excitation fiber that irradiates excitation light and a detection fiber that detects Raman scattered light is inserted between the positive electrode and the negative electrode of a lithium ion secondary battery, the excitation light is irradiated onto a surface of the positive electrode or the negative electrode to detect Raman scattered light, and the detected Raman scattered light is used to analyze a passive film formed on the surface of the positive electrode or the negative electrode.

[0008] In such a battery spectroscopic analysis method, a Raman spectroscopic probe is inserted between the positive electrode and the negative electrode of a lithium-ion secondary battery, and excitation light is irradiated onto the surface of the positive electrode or the negative electrode to detect Raman scattered light, so that the detected Raman scattered light can be used to analyze the passive film formed on the surface of the positive electrode or the negative electrode in situ.

[0009] It is known that a passive film is formed on the surface of a positive electrode or a negative electrode when a lithium-ion secondary battery is charged or discharged. In order to analyze the formation process of this passive film, it is desirable to detect Raman scattered light by the Raman spectroscopy probe when the lithium-ion secondary battery is charged or discharged.

[0010] In order not to inhibit the charge / discharge reaction in the analysis target area during charging or discharging of the lithium ion secondary battery, it is desirable to insert the probe so as not to obstruct the space between the analysis target area on one surface of the positive electrode or the negative electrode and the other surface of the positive electrode or the negative electrode facing the analysis target area. With this configuration, the process of formation of a passivation film during charging or discharging of a lithium ion secondary battery can be analyzed with high accuracy.

[0011] In order to irradiate the surface of the positive electrode or negative electrode with excitation light and make it easier to detect Raman scattered light emitted from the surface of the positive electrode or negative electrode, it is desirable to insert the Raman spectroscopy probe between the positive electrode and the negative electrode so that the tip of the Raman spectroscopy probe contacts the surface of the positive electrode or negative electrode.

[0012] In order to analyze the process of formation of the passive film at each portion between the electrodes, it is desirable to analyze the passive film at multiple locations on the surface of the positive electrode or the negative electrode using the Raman spectroscopic probe.

[0013] In order to analyze the formation process of the passive film at each portion between the electrodes, it is desirable to analyze the passive film while moving the Raman spectroscopic probe in the planar direction between the positive and negative electrodes.

[0014] Since the passive film contains many P=O bonds or POC bonds, in order to analyze the passive film accurately by Raman spectroscopy, it is desirable to analyze the passive film using the peaks due to P=O bonds or POC bonds in the Raman spectrum obtained from the detected Raman scattered light.

[0015] Specifically, the method for analyzing the lithium ion secondary battery preferably involves analyzing a solid electrolyte interphase (SEI) film formed on the surface of the negative electrode.

[0016] In a method for analyzing a lithium-ion secondary battery, it is preferable to position the tip of the Raman spectroscopy probe so that an end face of the tip of the excitation fiber, which is an emission surface from which the excitation light is emitted, faces the surface side of the positive electrode or the negative electrode, and to irradiate the surface of the positive electrode or the negative electrode with the excitation light to detect Raman scattered light.

[0017] With this configuration, the surface area of ​​the positive or negative electrode included in the analysis region of the Raman spectroscopic probe can be increased, which increases the intensity of the excitation light irradiated onto the surface of the positive or negative electrode, thereby increasing the amount of Raman scattered light that can be detected, and improving the accuracy of analysis of the non-conductive film formed on the surface of the positive or negative electrode.

[0018] In order to stably maintain a high intensity state of excitation light irradiated onto the surface of the positive electrode or negative electrode, it is preferable to position the tip of the Raman spectroscopy probe so that the end face of the tip of the excitation fiber faces the surface of the positive electrode or negative electrode when the excitation fiber and the detection fiber are in contact with the surface of the positive electrode or negative electrode.

[0019] Another aspect for stably maintaining a high intensity state of the excitation light irradiated onto the surface of the positive electrode or negative electrode is that the Raman spectroscopy probe further has a support member that supports the excitation fiber against the surface of the positive electrode or negative electrode, and the tip of the Raman spectroscopy probe is positioned so that an end face of the tip of the excitation fiber faces the surface side of the positive electrode or negative electrode when the detection fiber and the support member are in contact with the surface of the positive electrode or negative electrode.

[0020] When the excitation fiber and the detection fiber are inserted between the positive and negative electrodes of the lithium ion secondary battery, there is a risk that the excitation fiber or the detection fiber may be broken. Therefore, at least one of the excitation fiber and the detection fiber may be molded with a resin to prevent the excitation fiber or the detection fiber from being broken. Effect of the Invention

[0021] According to the present invention described above, the passive film formed on the surface of the electrode of a lithium ion secondary battery can be analyzed in situ. [Brief description of the drawings]

[0022] [Figure 1] 1 is an overall schematic diagram of an analysis system for a lithium ion secondary battery according to an embodiment of the present invention. [Diagram 2] 3A and 3B are a side view and a view seen from the tip side, showing a specific configuration of the tip of the Raman spectroscopic probe according to the embodiment. [Diagram 3]4 is an enlarged view showing a schematic diagram of the positional relationship between a negative electrode and a tip of the Raman spectroscopic probe during analysis in the embodiment. FIG. [Figure 4] 4 is an enlarged view showing a schematic diagram of the positional relationship between a negative electrode and a tip of the Raman spectroscopic probe during analysis in the embodiment. FIG. [Diagram 5] FIG. 13 is an enlarged view showing a schematic positional relationship between a negative electrode and a tip of a Raman spectroscopic probe during analysis in a modified embodiment. [Figure 6] 4 is an enlarged view showing a schematic diagram of the positional relationship between a negative electrode and a tip of the Raman spectroscopic probe during analysis in the embodiment. FIG. [Figure 7] FIG. 2 is an enlarged cross-sectional view showing a schematic positional relationship between a negative electrode and a tip of a Raman spectroscopic probe during analysis in the embodiment. [Figure 8] FIG. 2 is an enlarged cross-sectional view showing a schematic positional relationship between a negative electrode and a tip of a Raman spectroscopic probe during analysis in the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] <One embodiment of the present invention> Hereinafter, an embodiment of an analysis system and an analysis method for a lithium ion secondary battery according to the present invention will be described with reference to the drawings. In addition, in any of the drawings shown below, for the purpose of easy understanding, some parts are omitted or exaggerated in schematic form as appropriate. The same components are denoted by the same reference numerals and the description thereof is omitted as appropriate.

[0024] <Configuration of an analysis system for lithium-ion secondary batteries> 1, an analysis system 100 for a lithium ion secondary battery W according to this embodiment analyzes a passivation film Wx formed on the surface of a flat positive electrode W1 or a flat negative electrode W2 of a lithium ion secondary battery W. In the following, an example of analyzing a solid electrolyte interphase (SEI) film Wx formed on the surface of a negative electrode W2 of a lithium ion secondary battery W will be described. Note that a separator W3 is provided between the positive electrode W1 and the negative electrode W2, and the space between the positive electrode W1 and the negative electrode W2 is filled with an electrolyte (not shown).

[0025] Specifically, as shown in FIG. 1, the analysis system 100 includes a Raman spectroscopy probe 2 that is inserted between a positive electrode W1 and a negative electrode W2, irradiates the surface of the negative electrode W2 with excitation light L1, and detects Raman scattered light L2 from the surface, an excitation light source 3 that causes excitation light L1 to be incident on the Raman spectroscopy probe 2, a spectrometer 4 that disperses the Raman scattered light detected by the Raman spectroscopy probe 2, and a signal processing unit 5 that generates a Raman spectrum based on the light intensity signal dispersed by the spectrometer 4.

[0026] As shown in FIGS. 1 and 2, the Raman spectroscopic probe 2 has an excitation fiber 21 that irradiates excitation light L1 and a detection fiber 22 that detects Raman scattered light L2.

[0027] The excitation fiber 21 is an optical fiber having a core portion 211 and a clad portion 212. The diameter of the excitation fiber 21 may be, for example, 30 μm to 50 μm, as long as it can be inserted between the positive electrode W1 and the negative electrode W2 (specifically, between the separator W3 and the negative electrode W2). The excitation light L1 is incident from the excitation light source 3 to the base end, which is one end of the excitation fiber 21. The end face 21a of the tip, which is the other end of the excitation fiber 21, is inclined with respect to the fiber axis C1. The end face 21a of the tip is a flat surface and is inclined, for example, 45 degrees with respect to the fiber axis C1. The end face 21a is provided with a mirror coat 213 made of, for example, a metal film. With these configurations, the excitation light L1 emitted from the excitation fiber 21 is irradiated in a direction intersecting the fiber axis C1 (to the side of the excitation fiber 21).

[0028] The detection fiber 22 is an optical fiber having a core portion 221 and a clad portion 222, similar to the excitation fiber 21. The diameter of the detection fiber 22 may be, for example, 30 μm to 50 μm, so long as it can be inserted between the positive electrode W1 and the negative electrode W2 (specifically, between the separator W3 and the negative electrode W2). An end surface 22a of the tip portion, which is one end of the detection fiber 22, is a flat surface and is perpendicular to the fiber axis C2.

[0029] The detection fiber 22 is disposed on the side irradiated with the excitation light L1 reflected by the end face 21a of the excitation fiber 21. The detection fiber 22 is disposed so as to detect the Raman scattered light L2 generated by the excitation light L1 irradiated to the excitation fiber 21. Specifically, the end face 22a of the detection fiber 22 is disposed so as to be located at the rear end of or behind the end face 21a of the excitation fiber 21 in the direction of the fiber axes C1, C2. The Raman scattered light L2 detected by the detection fiber 22 is output to the spectrometer 4 from the other end, that is, the rear end, of the detection fiber 22.

[0030] In the above-mentioned Raman spectroscopic probe 2, the area where the irradiation area R1 of the excitation light L1 irradiated from the end face 21a of the excitation fiber 21 and the light receiving area R2 of the end face 22a of the detection fiber 22 overlap becomes the analysis area R3 of the Raman spectroscopic probe 2.

[0031] The excitation light source 3 irradiates excitation light L1 that excites the surface of the negative electrode W2 and the SEI coating Wx formed on the surface. The excitation light source 3 is, for example, a laser light source, and irradiates light with a wavelength of, for example, 532 nm as the excitation light L1. An incident optical system 6 such as a condenser lens may be provided between the excitation light source 3 and the base end of the excitation fiber 21.

[0032] The spectrometer 4 separates the Raman scattered light output from the detection fiber 22. This spectrometer separates the Raman scattered light into wavelengths and outputs the resulting spectral signals (light intensity signals) to a signal processing unit. A detection optical system 7 such as a condenser lens may be provided between the spectrometer 4 and the eaves end of the detection fiber 22.

[0033] The signal processing unit 5 generates a Raman spectrum based on the spectroscopic signal (light intensity signal) obtained by the spectrometer 4. The signal processing unit 5 can extract peaks due to, for example, CC bonds (e.g., D band and / or G band), P=O bonds, or POC bonds from the generated Raman spectrum. Furthermore, the signal processing results such as the Raman spectrum generated by the signal processing unit 5 can be output to an output unit 8 such as a display.

[0034] <Analysis method for lithium-ion secondary battery W> Next, a method for analyzing the lithium ion secondary battery W using the above-mentioned analysis device will be described.

[0035] 3 and 4, in this analysis method, a Raman spectroscopic probe 2 is inserted between the positive electrode W1 and the negative electrode W2 of a lithium ion secondary battery W (specifically, between the separator W3 and the negative electrode W2), excitation light L1 is irradiated onto the surface of the negative electrode W2 to detect Raman scattered light L2, and the detected Raman scattered light L2 is used to analyze the SEI coating Wx formed on the surface of the negative electrode W2. Here, the SEI coating Wx is analyzed using peaks due to CC bonds, P=O bonds, or POC bonds in the Raman spectrum obtained from the detected Raman scattered light L2.

[0036] When inserting the Raman spectroscopic probe 2 between the positive electrode W1 and the negative electrode W2, for example, the lithium ion secondary battery W is arranged so that the stacking direction of the positive electrode W1 and the negative electrode W2 is vertical. Then, the Raman spectroscopic probe 2 is inserted between the positive electrode W1 and the negative electrode W2 so that the surface of the negative electrode W2 is included in the analysis region R3 of the Raman spectroscopic probe 2. Specifically, the Raman spectroscopic probe 2 is inserted between the positive electrode W1 and the negative electrode W2 so that the tip portion 2A of the Raman spectroscopic probe 2 contacts the surface of the negative electrode W2. In this embodiment, the fiber axes C1 and C2 of the tip portion 2A of the Raman spectroscopic probe 2 are brought into contact with the surface of the negative electrode W2 so as to be parallel or approximately parallel to the surface of the negative electrode W2.

[0037] When the Raman spectroscopic probe 2 is inserted into the positive electrode W1 and the negative electrode W2, excitation light L1 is irradiated, and Raman scattered light L2 is detected, the area to be analyzed W on the surface of the negative electrode W2 is target and the analysis area W target The tip 2A of the Raman spectroscopic probe 2 is positioned so as not to block the area between the negative electrode W2 and the opposing positive electrode W1. Specifically, during charging and discharging, the area to be analyzed W target and the analysis area W targetThe tip 2A of the Raman spectroscopy probe 2 is positioned so as not to impede the movement of lithium ions moving between the negative electrode W1 facing the negative electrode W2. In detail, the tip 2A of the Raman spectroscopy probe 2 is positioned so that the arrangement direction of the excitation fiber 21 and the detection fiber 22 of the Raman spectroscopy probe 2 is along the surface of the negative electrode W2. More specifically, the tip 2A of the Raman spectroscopy probe 2 is positioned so that the end face 21a of the excitation fiber 21 of the Raman spectroscopy probe 2 does not face the surface of the negative electrode W2, but the end face 21a is perpendicular to the surface of the negative electrode W2.

[0038] Furthermore, in this analysis method, the Raman scattered light L2 is detected by the Raman spectroscopic probe 2 during charging or discharging of the lithium ion secondary battery W. This makes it possible to generate a Raman spectrum during charging or discharging. As a result, it is possible to analyze the formation process of the SEI film Wx during charging or discharging.

[0039] Furthermore, in this analysis method, the SEI coating Wx at multiple locations on the surface of the negative electrode W2 can also be analyzed using the Raman spectroscopic probe 2. In this case, it is considered that the SEI coating Wx at multiple locations on the surface of the negative electrode W2 is analyzed using multiple Raman spectroscopic probes 2. It is also considered that the SEI coating Wx at multiple locations on the surface of the negative electrode W2 is analyzed by moving the Raman spectroscopic probe 2 in the planar direction between the positive electrode W1 and the negative electrode W2.

[0040] <Effects of this embodiment> According to the method for analyzing the lithium ion secondary battery W of the present embodiment configured as described above, the Raman spectroscopic probe 2 is inserted between the positive electrode W1 and the negative electrode W2 of the lithium ion secondary battery W, and the excitation light L1 is irradiated onto the surface of the negative electrode W2 to detect the Raman scattered light L2. Therefore, the detected Raman scattered light L2 can be used to analyze the SEI film Wx formed on the surface of the negative electrode W2 in situ.

[0041] <Other embodiments> For example, in the analysis method of the above embodiment, a Raman spectrum may be obtained before charging the lithium ion secondary battery W, and the D band and / or G band in the Raman spectrum may be analyzed to analyze the state of the crystallites of the negative electrode active material, such as locations with many or few breaks in the crystallites. The analysis result of the crystallite state may be combined with the analysis result of the SEI film Wx of the above embodiment to analyze the lithium ion secondary battery W.

[0042] In the above embodiment, the thickness and composition (inorganic material, organic material, polymer, or the like) of the SEI coating Wx can also be analyzed based on the amount of change in the peak due to C-C bonds (D band and / or G band), P=O bonds, P-O-C bonds, or the like in the Raman spectrum during charging or discharging.

[0043] 5, the tip 2A of the Raman spectroscopic probe 2 may be disposed so as to be inclined with respect to the surface of the negative electrode W2. Specifically, the fiber axes C1 and C2 at the tip 2A of the Raman spectroscopic probe 2 may be in contact with the surface of the negative electrode W2 so as to be inclined with respect to the surface of the negative electrode W2. With this configuration, the surface area of ​​the negative electrode W2 included in the analysis area R3 of the Raman spectroscopic probe 2 (analysis target area W target As a result, the intensity of the excitation light L1 irradiated onto the surface of the negative electrode W2 can be increased, and the amount of the detectable Raman scattered light L2 can be increased, thereby improving the analytical accuracy of the SEI coating Wx formed on the surface of the negative electrode W2.

[0044] In addition, as shown in Fig. 6, the excitation fiber 21 and the detection fiber 22 may be arranged at a tilt with respect to the surface of the negative electrode W2 at the tip 2A of the Raman spectroscopic probe 2. Specifically, the detection fiber 22 may be arranged at the tip 2A in such a way that it contacts the surface of the negative electrode W2 and the excitation fiber 21 is arranged at a tilt away from the surface of the negative electrode W2. In other words, the tip 2A of the Raman spectroscopic probe 2 is arranged so that the end face 21a of the excitation fiber 21 of the Raman spectroscopic probe 2 faces the surface side of the negative electrode W2 and the end face 21a is tilted toward the surface of the negative electrode W2. With this configuration, the surface region of the negative electrode W2 included in the analysis region R3 of the Raman spectroscopic probe 2 (analysis target region W target As a result, the intensity of the excitation light L1 irradiated onto the surface of the negative electrode W2 can be increased, and the amount of the detectable Raman scattered light L2 can be increased, thereby improving the analytical accuracy of the SEI coating Wx formed on the surface of the negative electrode W2.

[0045] In addition, as shown in Fig. 7(a) and Fig. 7(b), the tip 2A of the Raman spectroscopic probe 2 may be arranged so that the end face 21a of the excitation fiber 21 faces the surface side of the negative electrode W2 in a state where the excitation fiber 21 and the detection optical fiber 22 are in contact with the surface of the negative electrode W2 in the tip 2A. Specifically, in the tip 2A, the end face 21a of the excitation fiber 21 faces the surface side of the negative electrode W2 in a state where the arrangement direction of the excitation fiber 21 and the detection fiber 22 is along the surface of the negative electrode W2. In this case, the end face 21a of the excitation fiber 21 is inclined at a predetermined angle with respect to the surface of the negative electrode W2 so that the overlapping area between the irradiation area R1 of the excitation light L1 and the light receiving area R2 of the end face 22a of the detection fiber 22 on the negative electrode W2 side becomes large.

[0046] Here, the angle at which the end face 21a of the excitation fiber 21 is inclined relative to the surface of the negative electrode W2 is preferably such that the overlapping area between the irradiation area R1 of the excitation light L1 and the light receiving area R2 of the end face 22a of the detection fiber 22 is maximized on the negative electrode W2 side. Then, as the end face 21a of the excitation fiber 21 is gradually inclined toward the surface of the negative electrode W2, the overlapping area between the irradiation area R1 of the excitation light L1 and the light receiving area R2 of the end face 22a of the detection fiber 22 on the negative electrode W2 side becomes maximum and constant. On the other hand, if the end face 21a of the excitation fiber 21 is inclined too much toward the surface of the negative electrode W2, the overlapping area between the irradiation area R1 and the light receiving area R2 on the electrolyte side becomes small, making it difficult to analyze substances generated on the electrolyte side. Therefore, it is desirable that the angle at which the end face 21a of the excitation fiber 21 is inclined relative to the surface of the negative electrode W2 is an angle at which the overlapping area between the irradiation area R1 of the excitation light L1 and the light receiving area R2 of the end face 22a of the detection fiber 22 is maximized on the negative electrode W2 side.

[0047] With this configuration, when the tip 2A of the Raman spectroscopic probe 2 is arranged so that the end face 21a of the excitation fiber 2 faces the surface, both the excitation fiber 21 and the detection fiber 22 are in contact with the surface of the negative electrode W2. As a result, the state in which the end face 21a of the excitation fiber 2 faces the surface side of the negative electrode W2 can be stably maintained. Therefore, the state in which the intensity of the excitation light L1 irradiated to the surface of the negative electrode W2 is high can be stably maintained.

[0048] Furthermore, as shown in FIG. 8(a) and FIG. 8(b), the Raman spectroscopic probe 2 may further include a support member 23 that supports the excitation fiber 21 against the surface of the negative electrode W2. In this case, the tip 2A of the Raman spectroscopic probe 2 may be arranged so that the end face 21a of the excitation fiber 21 faces the surface side of the negative electrode W2 in a state where the detection optical fiber 22 and the support member 23 are in contact with the surface of the negative electrode W2 at the tip 2A. Specifically, in a state where the detection fiber 22 is in contact with the surface of the negative electrode W2 at the tip 2A and the excitation fiber 21 is inclined away from the surface of the negative electrode W2, the support member 23 is interposed between the excitation fiber 21 and the negative electrode W2. Here, the support member 23 is in contact with the excitation fiber 21 and the detection fiber 22, and the arrangement direction of the detection fiber 22 and the support member 23 is along the surface of the negative electrode W2. In this state, the end face 21a of the excitation fiber 21 faces the surface side of the negative electrode W2. In this case, the end face 21a of the excitation fiber 21 is inclined at a predetermined angle with respect to the surface of the negative electrode W2 so that the overlapping area between the irradiation area R1 of the excitation light L1 and the light receiving area R2 of the end face 22a of the detection fiber 22 on the negative electrode W2 side is large.

[0049] 8(a) and (b), if the end face 21a of the excitation fiber 21 is too inclined with respect to the surface of the negative electrode W2, there is a risk of inhibiting the charge / discharge reaction in the analysis region R3 during charging or discharging of the lithium ion secondary battery. Therefore, it is preferable that the angle at which the end face 21a of the excitation fiber 21 is inclined with respect to the surface of the negative electrode W2 is an angle at which the overlapping region R1 of the excitation light L1 and the light receiving region R2 of the end face 22a of the detection fiber 22 becomes larger on the negative electrode W2 side, and that the angle is not an angle at which the charge / discharge reaction in the analysis region R3 during charging or discharging of the lithium ion secondary battery is inhibited.

[0050] The support member 23 may be a dummy fiber that is a fiber simulating the excitation fiber 21 or the detection fiber 22, or may be a support stand that supports the excitation fiber 21 on the surface of the negative electrode W2. The support member 23 only needs to support at least the excitation fiber 21, and the support member 23 does not need to be in contact with the detection fiber 22.

[0051] 7, when the tip 2A of the Raman spectroscopic probe 2 is arranged so that the end face 21a of the excitation fiber 2 faces the surface, both the detection fiber 22 and the support member 23 are in contact with the surface of the negative electrode W2. As a result, the state in which the end face 21a of the excitation fiber 2 faces the surface side of the negative electrode W2 can be stably maintained. Therefore, the state in which the intensity of the excitation light L1 irradiated to the surface of the negative electrode W2 is high can be stably maintained.

[0052] Furthermore, when the excitation fiber 21 and the detection fiber 22 are inserted between the positive electrode W1 and the negative electrode W2 of the lithium ion secondary battery, there is a risk that the excitation fiber 21 or the detection fiber 22 may be broken and damaged. Therefore, at least one of the excitation fiber 21 and the detection fiber 22 may be molded with a resin to prevent the excitation fiber 21 or the detection fiber 22 from being broken and damaged.

[0053] Examples of the location where the resin molding is applied include the outer peripheral surface of the excitation fiber 21 or the outer peripheral surface of the detection fiber 22. More specifically, the location where the resin molding is applied is the location where the excitation fiber 21 and the detection fiber 22 are bundled, that is, the location of the Raman spectroscopic probe 2 that is inserted between the positive electrode W1 and the negative electrode W2 of the lithium ion secondary battery. In the embodiment of FIG. 8, the resin molding may also be applied to the support member 23.

[0054] In the above embodiment, the SEI film Wx formed on the surface of the negative electrode W2 is analyzed, but the passive film formed on the surface of the positive electrode W1 may be analyzed. In this case, the Raman spectroscopic probe 2 is inserted so that the surface of the positive electrode W1 is included in the analysis region of the Raman spectroscopic probe 2.

[0055] In the above-described analysis method, the lithium ion secondary battery W is arranged so that the stacking direction of the positive electrode W1 and the negative electrode W2 is vertical. However, the arrangement of the lithium ion secondary battery W is not limited to this, and may be, for example, arranged so that the stacking direction is horizontal.

[0056] Furthermore, the configuration of the Raman spectroscopic probe 2 is not limited to the above embodiment, and may be anything that can be inserted between the electrodes and can detect Raman scattered light by irradiating the surface of the positive or negative electrode with excitation light.

[0057] The lithium ion secondary battery W in the above embodiment uses an electrolytic solution as an electrolyte between the positive electrode W1 and the negative electrode W2, but may be an all-solid-state lithium ion secondary battery using a solid as the electrolyte.

[0058] In addition, various modifications and combinations of the embodiments may be made as long as they do not go against the spirit of the present invention. [Explanation of symbols]

[0059] 100...Analyzer 2. Raman Spectroscopy Probes 21 Excitation fiber 22 Detection Fiber 3. Excitation Light Source 4...Spectrometer 5 Signal Processing Section

Claims

1. A Raman spectroscopic probe having an excitation fiber for irradiating excitation light and a detection fiber for detecting Raman scattered light is inserted between the positive electrode and the negative electrode of the lithium ion secondary battery; irradiating a surface of the positive electrode or the negative electrode with the excitation light and detecting Raman scattered light; A method for analyzing a lithium ion secondary battery, comprising: analyzing a passive film formed on a surface of the positive electrode or the negative electrode using the detected Raman scattered light.

2. The method for analyzing a lithium ion secondary battery according to claim 1 , wherein Raman scattered light is detected by the Raman spectroscopic probe during charging or discharging of the lithium ion secondary battery.

3. 3. The method for analyzing a lithium ion secondary battery according to claim 1, wherein the probe is inserted so as not to obstruct a space between an analysis target area on a surface of one of the positive electrode or the negative electrode and the other of the positive electrode or the negative electrode facing the analysis target area.

4. 4. The method for analyzing a lithium ion secondary battery according to claim 1, wherein the Raman spectroscopic probe is inserted between the positive electrode and the negative electrode so that a tip of the Raman spectroscopic probe contacts a surface of the positive electrode or the negative electrode.

5. The method for analyzing a lithium ion secondary battery according to claim 1 , further comprising the step of analyzing a passive film at a plurality of locations on a surface of the positive electrode or the negative electrode using the Raman spectroscopic probe.

6. The method for analyzing a lithium ion secondary battery according to claim 1 , wherein the passive film is analyzed while the Raman spectroscopic probe is moved in a planar direction between the positive electrode and the negative electrode.

7. The method for analyzing a lithium ion secondary battery according to any one of claims 1 to 6, wherein the passive film is analyzed using a peak due to a P=O bond or a P-O-C bond in a Raman spectrum obtained from the detected Raman scattered light.

8. The method for analyzing a lithium ion secondary battery according to claim 1 , further comprising analyzing a solid electrolyte interphase (SEI) film formed on a surface of the negative electrode.

9. The tip of the Raman spectroscopic probe is arranged so that an end face of the tip of the excitation fiber, which is an emission surface from which the excitation light is emitted, faces a surface side of the positive electrode or the negative electrode; The method for analyzing a lithium ion secondary battery according to claim 1 , further comprising irradiating a surface of the positive electrode or the negative electrode with the excitation light and detecting Raman scattered light.

10. 10. The method for analyzing a lithium ion secondary battery according to claim 9, wherein a tip of the Raman spectroscopy probe is disposed such that an end face of a tip of the excitation fiber faces a surface side of the positive electrode or the negative electrode in a state where the excitation fiber and the detection fiber are in contact with a surface of the positive electrode or the negative electrode.

11. The Raman spectroscopy probe further includes a support member that supports the excitation fiber against a surface of the positive electrode or the negative electrode, 10. The method for analyzing a lithium ion secondary battery according to claim 9, wherein a tip of the Raman spectroscopy probe is disposed such that an end face of a tip of the excitation fiber faces a surface side of the positive electrode or the negative electrode in a state where the detection fiber and the support member are in contact with a surface of the positive electrode or the negative electrode.

12. The method for analyzing a lithium ion secondary battery according to claim 1 , further comprising the step of: providing a resin molding to at least one of the excitation fiber and the detection fiber.

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