Evaluation method of internal state of battery

Abstract

To sufficiently and accurately estimate and evaluate an internal state, including a state of an electrolyte, of a battery.SOLUTION: An evaluation method of an internal state of a battery according to the present disclosure is a method for estimating and evaluating the internal state of the battery including an electrolyte. The evaluation method includes: preparing an initial battery and a degraded battery; simultaneously irradiating the initial battery and the degraded battery with first X-ray having first peak energy, and acquiring first intensity of the first X-ray transmitted through each of the initial battery and the degraded battery; simultaneously irradiating the initial battery and the degraded battery with second X-ray having second peak energy, and acquiring second intensity of the second X-ray transmitted through each of the initial battery and the degraded battery; and calculating changes in the salt concentration and thickness of the electrolyte in the degraded battery from the initial battery based on the first intensity and the second intensity.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for evaluating the internal state of a battery containing an electrolyte. [Background technology]

[0002] As a method for estimating and evaluating the deterioration of a secondary battery containing an electrolyte, for example, Patent Document 1 proposes a method for evaluating the internal state of a battery based on the rate of change in the X-ray absorption intensity ratio caused by a change in the crystal structure (structural distortion) of the positive electrode active material, using a lithium ion secondary battery that has only been initially charged (hereinafter referred to as an "initial battery") and a similar battery suspected of performance deterioration due to charging and discharging (hereinafter referred to as a "deteriorated battery"). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2013-131338 A Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, it is known that during charging and discharging of a secondary battery, a distribution of salt concentration in the electrolyte occurs between the electrodes and within the electrode surface, which causes an increase in the internal resistance of the secondary battery. This distribution of salt concentration becomes prominent during high-current charging and high-current discharging (high-rate charging and discharging), and it is also known that the internal resistance increases significantly accordingly, and such phenomena are called "high-rate degradation" or "transient degradation". In other words, in secondary batteries, performance degradation due to changes in the electrolyte as well as changes in the properties of the positive electrode active material is observed, so it is difficult to fully estimate and evaluate the internal state of the battery using the above-mentioned conventional methods.

[0005] More specifically, for example, in the case of a lithium-ion secondary battery, when high-rate charging and discharging are performed, the salt concentration may be biased in the thickness direction between the positive and negative electrodes. In addition, due to the expansion of the electrolyte due to heat generation and / or the expansion of the negative electrode due to changes in the charging rate or state of charge (SOC), the electrolyte on the negative electrode side with a low salt concentration is pushed out to the outer edge of the electrode, and as a result, the salt concentration may be biased in the surface direction of the electrode. Furthermore, due to the expansion of the electrolyte and the electrode, the distance between the positive and negative electrodes may be enlarged. When these phenomena occur, the performance deterioration due to the increase in the internal resistance of the battery progresses, so in order to use the battery safely and eliminate the deterioration, it is effective to appropriately control the output and input of the battery (charge and discharge control) and to appropriately implement a constraint design of the battery.

[0006] Therefore, in order to grasp the transient internal state related to the deterioration of the secondary battery, it is desirable to measure the salt concentration distribution of the electrolyte nondestructively. Here, if we pay attention to the fact that the higher the salt concentration of the electrolyte, the more difficult it is for X-rays to be absorbed and to transmit, it is conceivable to apply the above-mentioned conventional X-ray irradiation method to the electrolyte and obtain the salt concentration distribution of the electrolyte from the X-ray absorption intensity or X-ray transmission intensity of the electrolyte.

[0007] However, since the X-ray absorption intensity and X-ray transmission intensity change depending not only on the salt concentration of the electrolyte but also on its thickness (volume), even if the above conventional method is applied to the electrolyte as it is, it is not possible to distinguish between the variation in the salt concentration and the variation in the thickness of the electrolyte. Therefore, it is possible to calculate two variable solutions (unknowns) of the electrolyte, the salt concentration and thickness, by using multiple types of X-rays with different energies and measuring the respective X-ray absorption intensity or X-ray transmission intensity.

[0008] However, since an X-ray source usually generates X-rays having continuous energy by colliding an electron beam with a target and generating the X-rays with continuous energy by the bremsstrahlung, the X-ray output (dose) tends to vary, and the degree of variation of the X-ray output varies depending on the X-ray energy, and tends to change randomly over time. On the other hand, although it is theoretically possible to predict the variation of such X-ray output and suppress the variation by controlling the X-ray emission time, in reality, such control is extremely difficult from the viewpoint of sufficiently increasing the prediction accuracy and the measurement sensitivity. And, if such control is not possible, the variation of the X-ray output becomes excessive, and the measurement accuracy of the salt concentration of the electrolyte may be reduced to an inconvenient level.

[0009] Therefore, the present invention has been made in consideration of the above circumstances, and aims to provide a method for fully and accurately estimating and evaluating the internal state of a battery, including the state of the electrolyte. [Means for solving the problem]

[0010] In order to solve the above problem, a method for evaluating the internal state of a battery according to one example of the present disclosure is a method for evaluating the internal state of a battery containing an electrolyte, and includes preparing an initial battery and a degraded battery, simultaneously irradiating the initial battery and the degraded battery with first X-rays having a first peak energy and obtaining a first intensity of the first X-rays that have passed through each of the initial battery and the degraded battery, simultaneously irradiating the initial battery and the degraded battery with second X-rays having a second peak energy and obtaining a second intensity of the second X-rays that have passed through each of the initial battery and the degraded battery, and calculating a change in salt concentration and thickness of the electrolyte in the degraded battery from the initial battery based on the first intensity and the second intensity.

[0011] In the method for evaluating the internal state of a battery having such a configuration, a first battery and a deteriorated battery are simultaneously irradiated with multiple types of X-rays having different energies, and the intensities of the X-rays transmitted through the first battery and the deteriorated battery are obtained. Then, the distribution of the concentration and amount of the electrolyte in the deteriorated battery is calculated using the measured intensities. Effect of the Invention

[0012] As described above, according to the present disclosure, it is no longer necessary to consider the variation in the output of X-rays irradiated to an initial battery and a deteriorated battery, and the deterioration of measurement accuracy, which was a concern in the past, can be suppressed. This makes it possible to estimate and evaluate the internal state of a battery, including the state of the electrolyte in a deteriorated battery, sufficiently and accurately, and makes it possible to appropriately implement measures and constraint design to improve battery performance. [Brief description of the drawings]

[0013] [Figure 1] 1 is a schematic block diagram showing an example of a hardware configuration of a system for executing a battery state evaluation method according to an embodiment of the present disclosure. [Diagram 2] FIG. 11 is a flow diagram showing an example of a procedure for evaluating the internal state of a battery using a system according to an embodiment of the present disclosure. [Diagram 3] This is a conceptual diagram that shows a state in which X-rays Rx are irradiated from an X-ray source 10 to an initial cell Ca and a deteriorated cell Cb, and the two-dimensional intensity distribution of X-rays Ra, Rb that pass through the initial cell Ca and the deteriorated cell Cb is measured by an X-ray detector 20. [Figure 4] FIG. 4 is a schematic diagram showing an example of an X-ray transmission image 50 of an initial cell Ca and a deteriorated cell Cb captured under the arrangement conditions shown in FIG. [Diagram 5] 13 is a conceptual diagram showing a schematic relationship between the salt concentration distribution of the electrolyte that can occur in a deteriorated cell Cb and the two-dimensional intensity distribution in an X-ray transmission image 50b. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. The same elements are given the same reference numerals and duplicated explanations will be omitted. Furthermore, the shape and dimensional ratios are merely examples and are not limited to those shown in the drawings.

[0015] 1 is a schematic block diagram showing an example of a hardware configuration of a system 100 for performing an evaluation method for an internal state of a battery according to an embodiment of the present disclosure. The system 100 has a configuration in which a control and arithmetic device 30 is connected to an X-ray source 10 for irradiating an initial cell Ca (initial battery) and a deteriorated cell Cb (deteriorated battery) of a lithium-ion secondary battery with X-rays Rx, and an X-ray detector 20 for measuring the intensities of X-rays Ra and Rb transmitted through the initial cell Ca and the deteriorated cell Cb, respectively.

[0016] The X-ray source 10 is not limited as long as it can output X-rays Rx having multiple different types of energy (which may be a monochromatic spectrum or a continuous spectrum), and is particularly preferably capable of outputting X-rays Rx having multiple (at least two) different energy peaks. In this case, the X-rays Rx emitted at one time may be dual X-rays having a continuous spectrum including multiple energy peaks, or multiple X-rays Rx having single energy peaks different from each other may be separately emitted. More specifically, for example, a dual X-ray generator using a K filter method using a K absorption edge described in "Takashi Suzuki, Noboru Sakurai: Dual X-ray Generation Method and Application to Bone Density Measurement, Tokyo Metropolitan Industrial Technology Research Institute Research Report No. 8 (2005), pp. 44-46" can be suitably used as the X-ray source 10.

[0017] The X-ray detector 20 is not particularly limited as long as it can simultaneously detect the two-dimensional intensity distribution of the X-rays Ra and Rb transmitted through objects such as the initial cell Ca and the deteriorated cell Cb, and may be configured to visualize or image the two-dimensional intensity distribution. More specifically, when the X-rays Rx are the dual X-rays described above, a detector configured to measure the two-dimensional intensity distribution of the X-rays Ra and Rb using a NaI(Tl) detector, a signal amplifier, and a multichannel pulse height analyzer in which a pulse height analyzer is connected, as described in the same document, can be suitably used as the X-ray detector 20. In this case, instead of the NaI(Tl) detector, for example, a Ge semiconductor detector can be used. When the X-rays Rx having a single energy peak are used, the X-ray detector 20 may be configured to measure the two-dimensional intensity distribution of the X-rays Ra and Rb using an X-ray film, an FPD (flat panel detector), or the like.

[0018] Furthermore, the control and calculation device 30 is configured to include, for example, a control and calculation unit 31, a communication interface (I / F) unit 32, a memory unit 33, an input unit 34, and an output unit 35, and these components are connected to each other so that they can communicate with each other via a bus line 36.

[0019] More specifically, the control calculation unit 31 includes a CPU, a RAM, a ROM, etc., and controls each component and performs various calculations according to information processing. The communication I / F unit 32 is a communication module for communicating with other components, and the communication method is not particularly limited and is arbitrary. The X-ray source 10 and the X-ray detector 20 are provided so as to be able to communicate with the control calculation unit 31 and the like via the communication I / F unit 32. Furthermore, the storage unit 33 is an auxiliary storage device such as an HDD or SSD, and stores various calculation, control, and calculation programs, various setting parameters, various data (bases), etc. In this way, the various programs stored in the storage unit 33 are executed by the control calculation unit 31, thereby realizing the processing in the evaluation method of the internal state of a battery, which is an example of the present disclosure. On the other hand, the input unit 34 is an interface device (e.g., a mouse, keyboard, touch panel, audio microphone, etc.) for accepting various input operations from the operating user of the system 100, and the output unit 35 is an interface device (display, speaker, printer, etc.) for notifying the operating user of various information by display, audio, printing, etc.

[0020] Next, FIG. 2 is a flow diagram showing an example of a procedure when evaluating the internal state of a battery (deteriorated cell Cb) using the system 100 according to an embodiment of the present disclosure. Also, FIG. 3 is a conceptual diagram showing a state in which an initial cell Ca and a deteriorated cell Cb are irradiated with X-rays Rx from an X-ray source 10, and a two-dimensional intensity distribution of X-rays Ra and Rb transmitted through the initial cell Ca and the deteriorated cell Cb is measured by an X-ray detector 20. Note that each process described below is merely an example, and each process may be changed as much as possible within the scope of the technical concept of the present disclosure. Also, steps in the processes described below can be omitted, replaced, and added as appropriate.

[0021] First, in step S10, the X-ray source 10 and the X-ray detector 20 are prepared, and the initial cell Ca and the deteriorated cell Cb are arranged side by side at a predetermined X-ray irradiation position between them, which are arranged in an appropriate geometric relationship as shown in FIG. 3. Here, the initial cell Ca and the deteriorated cell Cb have the same cell structure and electrode design, and differ only in the state of the internal electrolyte, and in this evaluation method, the initial cell Ca serves as a reference cell for the deteriorated cell Cb. In addition, since the X-rays Rx emitted from the X-ray source 10 generally have an output distribution that attenuates concentrically from the center of the beam, it is desirable to arrange the initial cell Ca and the deteriorated cell Cb so as to be symmetrical with respect to the output distribution of the X-rays Rx. In this way, step S10 corresponds to the process of "preparing an initial battery and a deteriorated battery".

[0022] Next, in step S20, the initial cell Ca and the deteriorated cell Cb are simultaneously irradiated with X-rays Rx (first X-rays) having a predetermined peak energy (first peak energy), and the two-dimensional intensity distribution (first intensity) of the X-rays Ra and Rb that have passed through the initial cell Ca and the deteriorated cell Cb is measured. In addition, the initial cell Ca and the deteriorated cell Cb are simultaneously irradiated with X-rays Rx (second X-rays) having a different predetermined peak energy (second peak energy), and the two-dimensional intensity distribution (second intensity) of the X-rays Ra and Rb that have passed through the initial cell Ca and the deteriorated cell Cb is measured. At this time, it is preferable to perform irradiation and measurement of the X-rays Rx at the same positions without changing the installation positions of the initial cell Ca and the deteriorated cell Cb when irradiating the X-rays Rx having the first peak energy and the X-rays Rx having the second peak energy. As described above, step S20 corresponds to a step of "obtaining a first intensity of a first X-ray" and a step of "obtaining a second intensity of a second X-ray" (that is, step S20 serves as both steps).

[0023] Here, Fig. 4 is a schematic diagram showing an example of an X-ray transmission image 50 of the initial cell Ca and the deteriorated cell Cb captured under the arrangement conditions shown in Fig. 3. On such an X-ray transmission image 50, X-ray transmission images 50a, 50b of the initial cell Ca and the deteriorated cell Cb, each having a positive electrode Ct and a negative electrode An, are projected, and the two-dimensional intensity distribution of the transmitted X-rays Ra, Rb can be visualized.

[0024] 5 is a conceptual diagram showing the relationship between the salt concentration distribution of the electrolyte that may occur in the deteriorated cell Cb and the two-dimensional intensity distribution in the X-ray transmission image 50b. As described above, in the deteriorated cell Cb, there is a possibility that the salt concentration may be biased in the thickness direction and the surface direction between the positive electrode Ct and the negative electrode An. As shown by, for example, the curve L1 in FIG. 5, the salt concentration is relatively high in the center part L1C in the surface direction, while the salt concentration is relatively low in the outer edge part L1P. In response to this, as shown by, for example, the curve L2 in FIG. 5, in the X-ray transmission image 50b, the amount of X-ray absorption is relatively large in the center part L2C in the surface direction (the amount of X-ray transmission is relatively small, so that the brightness of the image becomes dark, or the count value of X-rays is small), while the amount of X-ray absorption is relatively small in the outer edge part L2P (the amount of X-ray transmission is relatively large, so that the brightness of the image becomes bright, or the count value of X-rays is large).

[0025] Next, in step S30, the changes in the salt concentration and thickness of the electrolyte in the deteriorated cell Cb from those in the initial cell Ca are calculated, for example, by the following procedure. That is, first, the intensities (brightness) of the X-rays Ra and Rb transmitted through the initial cell Ca and the deteriorated cell Cb are expressed by the relationship shown in the following formula (1). IB i =IA i ·exp{(-μV·ρV·Δt)+(-μL·ρB·Δt·Δc)} …(1) i: Subscript for distinguishing X-rays Rx having a given peak energy i=1: X-ray Rx having the first peak energy (first X-ray) i=2: X-ray Rx having the second peak energy (second X-ray) IA i : Intensity (brightness) of X-rays Ra transmitted through the initial cell Ca IBi : Intensity (brightness) of X-ray Rb transmitted through deteriorated cell Cb μV: X-ray absorption coefficient of the electrolyte solvent (depends on the energy of X-ray Rx) μL: X-ray absorption coefficient of the solute in the electrolyte (depends on the energy of X-rays Rx) ρV: Density of the electrolyte solvent ρB: Density of the electrolyte solute Δc: Change in the salt concentration of the electrolyte in the deteriorated cell Cb from that in the initial cell Ca Δt: Change in thickness of electrolyte solvent in deteriorated cell Cb from that in initial cell Ca

[0026] Measurement value IA when X-rays Rx having the first peak energy (first X-rays) and X-rays Rx having the second peak energy (second X-rays) are irradiated to the initial cell Ca and the deteriorated cell Cb. i ,IB i Substituting this into equation (1), we obtain the following equations (2) and (3). Note that the measured value IA i ,IB i uses the measured values ​​at the same in-plane position in the initial cell Ca and the aged cell Cb. IB1=IA1·exp{(-μV·ρV·Δt)+(-μL·ρB·Δt·Δc)}…(2) IB2=IA2·exp{(-μV·ρV·Δt)+(-μL·ρB·Δt·Δc)}…(3)

[0027] In this way, two equations are obtained for the two unknowns Δc and Δt, and by solving these simultaneous equations, it is possible to determine the change Δc in the salt concentration of the solute in the electrolyte in the degraded cell Cb from the initial cell Ca, and the change Δt in the thickness of the solvent in the electrolyte in the degraded cell Cb from the initial cell Ca. In this way, step S30 corresponds to the process of "calculating the changes in the salt concentration and thickness of the electrolyte in the degraded battery from the initial battery."

[0028] Then, in step S40, the internal state of the deteriorated cell Cb can be evaluated from the obtained change in salt concentration Δc of the electrolyte and the change in thickness Δt, which can contribute to optimizing the control processing of the output and input of the secondary battery cell.

[0029] According to the method for evaluating the internal state of a battery according to an embodiment of the present disclosure, including each of the steps described above, and the system 100 for executing the method, the initial cell Ca and the deteriorated cell Cb are simultaneously irradiated with X-rays Rx having different peak energies, and the intensities of the X-rays Ra and Rb transmitted through each cell are simultaneously measured, so that the deterioration of the measurement accuracy caused by the variation of the conventional X-ray output can be suppressed. In other words, the intensities of the transmitted X-rays Ra and Rb measured in advance for the initial cell Ca are used in the conventional method, but in this case, the output of the X-rays Rx when measuring the deteriorated cell Cb separately is different, so that a measurement error inevitably occurs in the intensity of the transmitted X-rays Ra and Rb for the deteriorated cell Cb. In contrast, according to an embodiment of the present disclosure, the occurrence of such a measurement error can be suppressed. As a result, the distribution of the concentration and amount of the electrolyte in the deteriorated cell Cb can be accurately grasped, so that it is possible to appropriately take measures to improve the battery performance. In addition, since it is possible to grasp the in-plane distribution of the electrolyte concentration and amount in the deteriorated cell Cb, it is possible to identify the location and extent to which the fluctuations in the electrolyte concentration and amount should be controlled, and to effectively implement a constraint control design to improve battery performance.

[0030] Although the above embodiment has been described in detail as an example of the present disclosure, the above description is merely an example of the present disclosure in every respect, and it goes without saying that various improvements and modifications can be made without departing from the scope of the present disclosure. In addition, the above embodiment may be partially replaced or may be configured in appropriate combination. [Explanation of symbols]

[0031] 10...X-ray source, 20...X-ray detector, 30...control and calculation device, 31...control and calculation section, 32...communication interface (I / F) section, 33...memory section, 34...input section, 35...output section, 36...bus line, 50, 50a, 50b...X-ray transmission image, 100...system, An...negative electrode, Ca...initial cell (initial battery), Cb...degraded cell (degraded battery), Ct...positive electrode, L1, L2...curve, L1C, L2C...center, L1P, L2P...outer edge, Ra, Rb...transmitted X-ray, Rx...X-ray (first X-ray, second X-ray), S10 to S40...step, Δc...change in salt concentration of solute of electrolyte in degraded cell Cb from initial cell Ca, Δt...change in thickness of solvent of electrolyte in degraded cell Cb from initial cell Ca.

Claims

[Claim 1] A method for evaluating an internal state of a battery containing an electrolyte, comprising: Providing an initial battery and a depleted battery; irradiating the initial battery and the degraded battery with first X-rays having a first peak energy at the same time, and acquiring first intensities of the first X-rays transmitted through the initial battery and the degraded battery, respectively; irradiating the initial battery and the degraded battery with second X-rays having a second peak energy at the same time, and acquiring second intensities of the second X-rays transmitted through the initial battery and the degraded battery, respectively; calculating a change in salt concentration and thickness of the electrolyte in the deteriorated battery from that in the initial battery based on the first intensity and the second intensity; A method for evaluating the internal state of a battery, comprising:

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