JP7425812B2 - Evaluation method for energy storage devices - Google Patents

Description

The present invention relates to a method for evaluating the distance between foils in a flat laminated portion of an electrode body of an electricity storage device in which electrode plates are stacked flatly.

There are cases where it is desired to non-destructively analyze or inspect the internal structure of a power storage device such as a lithium ion secondary battery. In such cases, X-ray CT analysis using a computed tomography apparatus (X-ray CT apparatus) using X-rays is used. For example, in Patent Document 1, a line profile of a secondary battery is obtained by X-ray CT analysis, and the foil positions of a plurality of positive electrode plates and negative electrode plates of the secondary battery can be identified. An example is shown.

In addition, Patent Document 2 describes a method for evaluating the deterioration state of a positive electrode composite layer, a negative electrode composite material layer, and a secondary battery from the X-ray absorption amount of each part obtained by X-ray CT analysis. A method for evaluating the stacking state of secondary batteries using tomographic photographs is presented.

International Publication No. 2020/031431 Japanese Patent Application Publication No. 2001-203003

On the other hand, there are cases where it is desired to measure and evaluate the distance between stacked electrode plates in a flat stacked portion of an electrode body of an electricity storage device. For example, there may be areas where an air layer remains between the positive electrode layer and the negative electrode layer due to insufficient penetration of the electrolyte, or a gas layer where gas generated by decomposition of the electrolyte is not discharged outside the electrode body and accumulates. Some existing parts may occur. In addition, in such areas, the air layer or gas layer becomes an obstacle, making it difficult for an appropriate reaction to occur between the electrolyte and the positive or negative electrode layer, so that the metal ions of the charge carrier gradually become metallized and precipitate ( For example, in Li-ion secondary batteries, there may be a metal layer in which metallic Li is precipitated. In addition, in areas where such air layers, gas layers, and precipitated metal layers exist, the distance between the positive electrode plate and the negative electrode plate (positive electrode layer and negative electrode layer) is slightly larger than in areas where these do not exist. It is assumed that

Therefore, by measuring and evaluating the distance between the positive electrode plate and the negative electrode plate, the distance between the positive electrode plates with the negative electrode plate in between, or the distance between the negative electrode plates with the positive electrode plate in between, it is possible to eliminate the gas layer as described above. It is thought that it is possible to detect the existing portion and to judge whether the lamination state of each electrode plate in the flat laminated portion is good or bad.

The present invention has been made in view of the current situation, and provides an evaluation method for an electricity storage device that measures and evaluates the interval between stacked electrode plates in a flat laminated portion of an electrode body of an electricity storage device. It is something to do.

One aspect of the present invention for solving the above problems is (1) performing an X-ray CT analysis on a flat laminated portion in which electrode plates are flatly stacked among the electrode bodies of a power storage device, and an inter-foil distance obtaining step of obtaining an inter-foil distance of 10 or more between electrode foils included in adjacent electrode plates of different polarities or adjacent same-polarity electrode plates with different polarities interposed therebetween, for the evaluation part including a plurality of the electrode plates; , an average deviation calculating step of calculating the average value and standard deviation of the obtained inter-foil distance; a reference distance obtaining step of obtaining an evaluation reference distance obtained by adding three times the standard deviation to the average value; This is a method for evaluating an electricity storage device, comprising: an evaluation step of evaluating whether or not there is a distance between foils that exceeds the standard, which is larger than the evaluation standard distance, in the distance between the foils.

Generally, in a flat laminated part where electrode plates are flatly stacked in the electrode body of a power storage device, the distance between the electrode foils included in adjacent electrode plates of different polarities or of the same polarity adjacent to each other via a different pole is large. It is thought that the distribution of the values is a bell-shaped distribution that approximates a normal distribution function (Gaussian function) centered around the average value.

By the way, as mentioned above, in a power storage device, during the manufacturing stage or during use, some of the positive electrodes of the electrode body of the power storage device are removed between the many positive electrode plates and negative electrode plates that are stacked on top of each other. There may be an abnormality in which an air layer, gas layer, or deposited metal layer exists between the plate and the negative electrode plate. In particular, in the evaluation part of the flat stacked part of the electricity storage device where the electrode plates are stacked flat, if there is an abnormality where an air layer, gas layer, or precipitated metal layer exists between some of the positive and negative electrode plates. includes the distance between the electrode foils (positive electrode foil and negative electrode foil) included in adjacent electrode plates of different polarity at the location where the abnormality occurs, or the distance between electrode plates of the same polarity adjacent to each other via different electrodes. If the distance between the electrode foils (positive electrode foils, negative electrode foils) is larger than the area where no abnormality has occurred (surrounding areas, etc.) or before the formation of a gas layer or precipitated metal layer (for example, the initial state). Conceivable. In addition, the distance between the foils between the remaining majority of electrode plates where no abnormality has occurred has a bell-shaped distribution that approximates a normal distribution function centered on the average value, as in the case where no abnormality has occurred on all of the electrode plates. It is considered to be.

Therefore, in the above-mentioned evaluation method for an electricity storage device, data of 10 or more inter-foil distances DP is acquired for the evaluation part of the electricity storage device using X-ray CT analysis, and the average value M and standard deviation σ of the inter-foil distances DP are obtained. is calculated, and the evaluation reference distance DPB (=M+3σ) is obtained. Then, in the evaluation step, it is evaluated whether there is a reference-exceeding inter-foil distance DPS having a larger inter-foil distance DP than the evaluation reference distance DPB. That is, in the evaluation step, the presence or absence of the inter-foil distance DPS exceeding the standard, which has a value larger than the evaluation standard distance DPB, which almost never occurs under normal conditions without any abnormality, is evaluated.

In this way, it is possible to evaluate the spacing between the stacked electrode plates in the flat stacked portion of the electrode body of the power storage device.

Here, in the normal distribution function of mean value M and standard deviation σ, the probability that the random variable will have a value larger than M+3σ is 0.135%. In other words, if the obtained inter-foil distance DP is distributed according to a normal distribution function, there exists a standard-exceeding inter-foil distance DPS greater than the evaluation reference distance DPB (=M+3σ) among the obtained inter-foil distances. The probability is 0.135%. In other words, a value of the inter-foil distance DP with an occurrence probability of only 0.135% has been detected. In this way, if data of the inter-foil distance DP actually exists in the range of values larger than the evaluation reference distance DPB (=M + 3σ), which is unlikely to occur in reality considering the probability, the evaluation part It can be inferred that there is a high possibility that some kind of abnormality that increases the inter-foil distance DP is occurring in the portion where the large inter-foil distance DP occurs. Thus, using X-ray CT analysis, it is possible to appropriately evaluate the possibility of abnormalities occurring in the air layer, gas layer, deposited metal layer, etc. at the evaluation site of the electricity storage device.

Examples of power storage devices that perform X-ray CT analysis include secondary batteries such as lithium ion secondary batteries, and capacitors such as lithium ion capacitors. The electrode body included in the electricity storage device may be any electrode body having a flat laminated portion in which electrode plates are flatly stacked, and both a laminated type electrode body and a flat wound type electrode body are acceptable. The "electrode plates" to be inspected include, for example, not only positive electrode plates and negative electrode plates, but also bipolar electrode plates.

Examples of "electrode foils included in adjacent electrode plates of different polarities" include the positive electrode foil of the positive electrode plate and the negative electrode foil of the negative electrode plate. Another example is electrode foils of two bipolar electrode plates in which a positive electrode layer and a negative electrode layer are arranged to face each other. On the other hand, "electrode foils included in electrode plates of the same polarity that are adjacent to each other through different electrodes" includes positive electrode foils that are included in positive electrode plates that are adjacent to each other with a negative electrode plate in between, and negative electrode plates that are adjacent to each other with a positive electrode plate in between. Examples include negative electrode foils.

As the method for obtaining the distance between foils, any method that can obtain the distance between foils from the X-ray CT analysis results for the flat stacked portion of the electricity storage device can be adopted. For example, as described in Patent Document 1, a line profile of the X-ray absorption amount is obtained from the analysis results, and each negative electrode foil is directly One method is to specify the foil position of the negative electrode foils and calculate the distance between the negative electrode foils. On the other hand, if a steep peak indicating the position of the electrode foil does not appear in the line profile obtained from the analysis results, but gentle peaks do occur, each gentle peak that appears in the line profile is approximated by curve fitting. It is also possible to assume a curve showing a change, specify the foil position based on the peak position, and calculate the distance between the foils from each specified foil position.

(2) Furthermore, in the method for evaluating an electricity storage device according to (1) above, the evaluation step includes determining the evaluation reference distance in a frequency distribution indicating the frequency of the distance between the foils obtained for each predetermined distance class. A class evaluation step of evaluating whether or not the inter-foil distance exceeding the reference exists based on whether the distance class is such that the inter-foil distance is greater than , and the frequency of the inter-foil distance is 1 or more. It is good to use this as an evaluation method for a certain electricity storage device.

In the above-mentioned evaluation method, a frequency distribution of the obtained inter-foil distance DP is obtained, and as the above-mentioned evaluation step, in this frequency distribution, the inter-foil distance DP is larger than the evaluation reference distance DPB, and the inter-foil distance DP is Since the class evaluation step is performed to evaluate whether or not there is a distance between foils exceeding the standard based on whether or not the frequency has a distance class of 1 or more, the evaluation can be easily performed.

Note that the class width and distance class range to be set when obtaining the frequency distribution of inter-foil distances may be set in consideration of the number of samples of inter-foil distances to be obtained, accuracy, range of inter-foil distances to be obtained, etc. . For example, a width of 1 μm can be adopted as the class width.

(3) The method for evaluating an electricity storage device according to (1) or (2) above, wherein the electricity storage device is evaluated to have a distance between foils that exceeds the standard in the evaluation part in the evaluation step, and It is preferable that the method for evaluating an electricity storage device further includes a deterioration evaluation step of evaluating the degree of deterioration.

This evaluation method includes a deterioration evaluation step, so it is determined that a precipitated metal layer will occur in the evaluation parts of the power storage device, where the distance between the foils exceeds the standard and the distance between the foils exceeds the standard, based on the degree of deterioration of the power storage device. It is possible to appropriately evaluate whether the deterioration of the power storage device due to the above has already occurred to some extent, or whether the deterioration has not progressed yet although an air layer or a gas layer has been formed.

1 is a flowchart showing each step of a battery evaluation method according to an embodiment. FIG. 6 is an explanatory diagram illustrating how, in an analysis step, an X-ray CT analysis device is used to perform an X-ray CT analysis of a battery to obtain the amount of X-ray absorption at each position according to the embodiment. FIG. 2 is an explanatory diagram showing a layer structure of an electrode body in a region to be inspected of a battery according to an embodiment. This is an example of a cross-sectional image of a test area of a battery created from the amount of X-ray absorption at each position obtained by performing X-ray CT analysis. This is an example of a graph showing the on-trajectory X-ray absorption amount at each locus position of a specific virtual locus in the battery, the foil position of each electrode, and the distance between the foils, according to the embodiment. FIG. 6 is an explanatory diagram showing a graph showing the amount of on-trajectory X-ray absorption at each position on the trajectory in the fitting region, an approximate curve, and an estimated foil position according to the embodiment. It is a graph of the frequency distribution of the distance between foils obtained for the first evaluation site, and a normal distribution function having the same average value and standard deviation, according to the embodiment. It is a graph of the frequency distribution of the distance between foils obtained for the second evaluation site, and a normal distribution function having the same average value and standard deviation as this according to the embodiment.

Embodiments of the present technology will be described below with reference to the drawings. FIG. 1 shows a flowchart of each step of a method for evaluating a lithium ion secondary battery 10 (hereinafter also simply referred to as a battery) according to the present embodiment. As shown in FIG. 2, the X-ray CT analyzer XCT used to identify the foil position of the battery 10 and calculate the interpolar distance includes an X-ray source SX that emits X-rays in a conical shape from an X-ray focus SXO, and an X-ray source SX. The apparatus includes an X-ray detector DX that detects X-rays emitted from the X-ray detector DX, and a rotary table RB on which an object to be inspected (in this example, a battery 10) is placed and rotated around a rotation axis AX. Furthermore, in addition to controlling these, the X-ray absorption amount AB (r, θ, z), a cross-sectional image showing the distribution of the X-ray absorption amount AB in an arbitrary virtual cross section, a graph (absorption amount profile) showing the change in the X-ray absorption amount AB along an arbitrary specific virtual trajectory HT, etc. It has a processing computer CMP, and a monitor MN that displays each obtained data, cross-sectional image, absorption profile, etc.

In this embodiment, first, in an analysis step S1, an X-ray CT analysis of the battery 10, which is an object to be inspected, is performed using an X-ray CT analyzer XCT. X-ray absorption amount AB at each position P (r, θ, z) in the cylindrical inspection areas 10S1, 10S2 (where (r, θ, z) indicates coordinates in the cylindrical coordinate system) Obtain (r, θ, z).

In the present embodiment, X-rays are applied to two locations: an area to be inspected 10S1 located approximately at the center of the battery 10, and an area to be inspected 10S2 located 50 mm away from this area to be inspected 10S2 in the direction along the rotation axis AX in FIG. An example of CT analysis is shown below. In the X-ray CT analysis of the region to be inspected 10S2, the height of the rotary table RB is lowered by 50 mm, and analysis step S1 etc. are performed in the same manner as the region to be inspected 10S1.

In the laminated electrode body 20 of the battery 10, within a flat laminated portion 20H in which positive electrode plates 21 and negative electrode plates 25 are alternately and flatly laminated with separators 29 interposed in the lamination direction SH, and in the inspection area 10S1. (See FIG. 3) is subjected to X-ray CT analysis. In this case, for example, an example of a cross-sectional image of the electrode body 20 of the battery 10 shown in FIG. 4 may be obtained. The same applies to the cross-sectional image example for the region to be inspected 10S2.

As shown in FIG. 3, the positive electrode plate 21 used in the battery 10 consists of a positive electrode foil 22 made of aluminum and positive electrode layers 23a and 23b of the same thickness formed on both sides of the positive electrode foil 22, respectively. The positive electrode layers 23a and 23b contain a large amount of positive electrode active material containing a transition metal element such as LiNi _1/3 Co _1/3 Mn _1/3 O ₂ and have a higher X-ray absorption coefficient than the positive electrode foil 22. has. On the other hand, the negative electrode plate 25 consists of a negative electrode foil 26 made of copper and negative electrode layers 27a and 27b of the same thickness formed on both sides of the negative electrode foil 26, respectively. The negative electrode layers 27a and 27b contain a large amount of negative electrode active material made of a carbon-based material such as graphite, and have relatively low X-ray absorption compared to the negative electrode foil 26, the positive electrode foil 22, and the positive electrode layers 23a and 23b. has a coefficient. Separator 29 made of resin such as polyethylene also has a low X-ray absorption coefficient.

Therefore, in FIG. 4, among the positions P (r, θ, z) on the cross section, the portion where the positive electrode plate 21 having the positive electrode layers 23a and 23b with a large amount of X-ray absorption exists is shown relatively white. , the region where the negative electrode plate 25 and the separator 29 having the negative electrode layers 27a and 27b with a small amount of X-ray absorption are present is shown relatively black. Note that the positive electrode foil 22, the negative electrode foil 26, and the separator 29 are thinner (approximately 1/10 or less thick) than the positive electrode layers 23a, 23b and the negative electrode layers 27a, 27b. Therefore, it is difficult to clearly identify the positive electrode foil 22 and the negative electrode foil 26 and to specify their positions from the cross-sectional image of FIG. 4 . In addition, as in the line profile (absorption amount profile) shown in FIGS. 7 and 8 of Patent Document 1, there are cases where the position of the negative electrode foil can be clearly identified and the distance between these foils, etc. can be easily calculated. . However, depending on the size (physique) of the battery subjected to X-ray CT analysis and the energy of the irradiated X-rays, different from the case of Patent Document 1, cross-sectional images may be There may be cases where the position of the negative electrode foil cannot be immediately identified from the absorption amount profile, and the distance between the foils cannot be calculated.

Therefore, in the inter-foil distance acquisition step S2 of the present embodiment, the position of each positive electrode foil 22 in the evaluation region 20HH1 or 20HH2 is specified and the inter-foil distance DP between the positive electrode foils 22 is calculated as follows. .

First, in the absorption amount acquisition step S21, the processing computer CMP selects a specific virtual locus HT shown by a straight dot-dash line extending in the left-right direction in FIGS. Assuming a specific virtual trajectory HT that vertically passes through the positive electrode plate 21 and the plurality of negative electrode plates 25, the X-ray absorption amount on the trajectory is the X-ray absorption amount AB (r, θ, z) at each trajectory position d. Obtain AB(d). The position on the trajectory d is a distance measured along the specific virtual trajectory HT from the origin, which is an arbitrary position on the specific virtual trajectory HT. In FIG. 3, the position d on the trajectory of the point where this specific virtual trajectory HT intersects with the positive electrode foil 22 is defined as the foil position dpf of the positive electrode foil 22, and the position d on the trajectory of the point where the specific virtual trajectory HT intersects with the negative electrode foil 26 is defined as the foil position dpf of the positive electrode foil 22. , and the foil position dnf of the negative electrode foil 26, respectively. That is, the positions of a large number of positive electrode foils 22 and negative electrode foils 26 existing in a linear (straight bar-shaped) evaluation region 20HH1 or 20HH2 through which a specific virtual locus HT passes in the inspection area 10S1 or 10S2 are defined as foil positions dpf and dnf. do.

FIG. 5 shows an example of a graph (absorption amount profile) showing changes in the magnitude of the on-trajectory X-ray absorption amount AB (d) at each trajectory position d (distance d from the origin) on the specific virtual trajectory HT. . In the graph of FIG. 5, in addition to a plurality of peaks where the value of the X-ray absorption amount AB exceeds 100 on the trajectory, which corresponds to the positive electrode layers 23a and 23b of each positive electrode plate 21 with a large amount of X-ray absorption, A valley corresponding to each negative electrode plate 25 with a small amount of linear absorption is observed. However, a small peak is observed in each valley due to the presence of the negative electrode foil made of copper, which is thin but has a large X-ray absorption coefficient. However, as can be easily understood by comparing with FIGS. 7, 8, etc. of Patent Document 1, just looking at the graph of FIG. It turns out that it is difficult to accurately specify (see FIG. 3).

Therefore, in this embodiment, first, in the positive electrode foil position specifying step S22, the foil position dpf (for example, dpf1 to dpf9) of each positive electrode foil 22 is specified as follows. First, in area setting step S221, a range of fitting areas AF (AF1 to AF9 in FIG. 5) including a single positive electrode foil 22 inside the specific virtual locus HT is determined. Specifically, in the graph of FIG. 5, the range where the magnitude of the on-trajectory X-ray absorption amount AB(d) exceeds 100 is set as the fitting region AF (AF1 to AF9).

Next, the fitting step S222 and the positive electrode foil position estimation step S223 are repeated in the repetition determination step S224, and the foil position dpf (for example, dpf1) of the single positive electrode foil 22 is determined for each fitting area AF (for example, AF1 to AF9). ~dpf8).

In the fitting step S222, for example, as shown in FIG. An approximate curve FC6 (indicated by a thick dashed line in FIG. 6) that produces a single peak FCP6 within the range is determined. Note that in this embodiment, a Gaussian function (normal distribution function) is used for the approximate curve FC6. Since the positive electrode plate 21 has positive electrode layers 23a and 23b of the same thickness on both sides of the positive electrode foil 22, a specific virtual trajectory is formed around the trajectory position d (foil position dpf) corresponding to the single peak FCP6. This is because it is appropriate to fit a symmetrical (left-right symmetrical) approximation curve FC6 with respect to HT (distance d, horizontal axis). Thereby, the foil position dpf (dpf1, etc.) of the positive electrode foil 22 can be specified with high accuracy. Note that, for example, a Lorentz function, a quadratic function, a cos function, etc. may be used as the approximate curve FC that is symmetrical with respect to the specific virtual trajectory HT (distance d).

Subsequently, in the positive electrode foil position estimation step S223, for example, in the fitting region AF6, the position d on the trajectory corresponding to the single peak FCP6 in the determined approximate curve FC6 is estimated as the foil position dpf6 of the single positive electrode foil 22. do.

Then, in the repetition determination step S224, it is determined whether or not it is necessary to repeat steps S222 and S223, and for each set fitting area AF (for example, AF1 to AF8), an approximate curve FC is determined in the fitting step S222, and the positive electrode foil position is The fitting step S222 and the positive foil position estimation step S223 are repeated until the foil position dpf of the positive electrode foil 22 can be estimated in the estimation step S223.

Thereby, for each fitting area AF (for example, AF1 to AF8), the foil position dpf (dpf1 to dpf8) of the positive electrode foil 22 included in each fitting area AF can be estimated (see FIG. 5). In this way, the foil position dpf (for example, dpf1 to dpf8) of each positive electrode foil 22 among the plurality of positive electrode foils 22 and negative electrode foils 26 is specified by the positive electrode foil position specifying step S22 including the area setting step S221 to the repeat determination step S224. be able to.

Further, in the inter-foil distance calculation step S23, the distance between the adjacent positive electrode foils 22 with the negative electrode foil 26 interposed therebetween is determined using the foil position dpf (for example, dpf1 to dpf8) of the positive electrode foil 22 specified in the positive electrode foil position specifying step S22. A distance DP (for example, DP1 to DP7) is calculated.

In this way, the inter-foil distance acquisition step S2, which includes the absorption amount acquisition step S21 to the inter-foil distance calculation step S23, allows the accumulation of electricity to result in unclear changes in the X-ray absorption amount on the trajectory when only using X-ray CT analysis (see FIG. 4). Even in devices, the foil position dpf1 etc. of each electrode foil (the positive electrode foil 22 in this embodiment) can be appropriately specified, and the foil position dpf1 etc. of each electrode foil (in this embodiment, the positive electrode foil 22) can be appropriately specified. In this case, the inter-foil distance DP (DP1, etc.) between the negative electrode plates 25 (between adjacent positive electrode foils 22 with the negative electrode foil 26 interposed therebetween) can be appropriately calculated.

In addition, in the battery 10 of this embodiment, in the evaluation part 20HH1 included in the inspection area 10S1 near the center (see FIG. 2), there are 10 or more parts, specifically, a total of 89 parts (total frequency 89). A distance DP between the foils was obtained. Further, in the evaluation site 20HH2 included in the inspected area 10S2 that is 50 mm away from the inspected area 10S1, a total of 92 inter-foil distances DP (total frequency 92) were obtained (see Table 1 described below).

Next, in the average deviation calculation step S3, the average value M and standard deviation σ of the inter-foil distances DP are calculated based on the large number of inter-foil distances DP (for example, DP1 to DP7) acquired in the inter-foil distance acquisition step S2.

Further, in the reference distance acquisition step S4, an evaluation reference distance DPB (=M+3σ) is obtained by adding three times the standard deviation σ to the average value M of the calculated inter-foil distance DP.

Table 1 shows a frequency distribution table of the inter-foil distance DP obtained for each of the evaluation parts 20HH1 and 20HH2 of the battery 10 in the inter-foil distance acquisition step S2, and the average of the inter-foil distance DP calculated from this frequency distribution table. The values of the value M, standard deviation σ, and evaluation reference distance DPB (=M+3σ) are shown.
In addition, in the frequency distribution table shown in Table 1, the range of distance between foils DP = 360 to 383 μm is divided into 24 distance classes SS with equal class width SW = 1.0 μm, and the foils included in each distance class SS are The frequency n of the distance DP is shown. Furthermore, in Table 1, assuming a normal distribution function having the same mean value and standard deviation as the calculated mean value M and standard deviation σ, the value of the normal distribution function corresponding to each foil position dpf (normal distribution The theoretical frequency (assumed) is also shown.

Further, FIG. 7 shows a line graph of the frequency distribution of the inter-foil distance DP obtained for the evaluation site 20HH1, indicated by a solid line, and having the same mean value and standard deviation as the mean value M and standard deviation σ of this frequency distribution, indicated by a broken line. A graph of a normal distribution function is shown. Similarly, FIG. 8 shows a line graph of the frequency distribution of the inter-foil distance DP obtained for the evaluation site 20HH2 shown by the solid line, and the same mean value M and standard deviation σ of this frequency distribution shown by the broken line. 1 shows a graph of a normal distribution function with . In FIGS. 7 and 8, the value indicated by the dashed-dotted vertical line indicates the value of the evaluation reference distance DPB (=M+3σ).

As shown in Table 1 and FIG. 7, the frequency distribution of the inter-foil distance DP obtained for the evaluation site 20HH1 has two peaks with a slightly smaller frequency n near the average value M (370.6 μm). It shows a mountain-shaped distribution. However, the graph of the normal distribution function shown by the broken line shows changes that generally fit the graph of the frequency distribution of the inter-foil distance DP shown by the solid line. In addition, in the graph of the normal distribution function in FIG. 7, the value of the normal distribution function obtained when the distance between the foils DP is equal to the evaluation reference distance DPB = M + 3σ (= 376.7 μm), whose position is indicated by the dot-dashed vertical line, is Very small. Therefore, it is understood that if the size of the distance between foils DP follows a normal distribution function, the possibility (probability) that the distance between foils DP will be larger than the evaluation reference distance DPB (=M + 3σ = 376.7 μm) is extremely low. I can do it.

However, as shown by the thick arrow in FIG. 7, it can be seen that in the acquired evaluation site 20HH1 (total frequency 89), there is data with a value of inter-foil distance DP=379 μmn that exceeds the evaluation reference distance DPB. In the case of this inter-foil distance DP = 379 μm, it is difficult to think that this occurred by chance due to variations in the value of the inter-foil distance DP, and the evaluation region 20HH1 includes a region where the inter-foil distance DP is abnormally large. This is thought to suggest that there is.

On the other hand, as shown in Table 1 and FIG. 8, the frequency distribution of the distance between the foils DP obtained for the evaluation site 20HH2 shows a single peak-shaped distribution with a peak at the frequency n near the average value M (369.5 μm). The graph of the normal distribution function shown by the broken line shows a change that closely fits the graph of the frequency distribution of the inter-foil distance DP shown by the solid line. Also, in the graph of the normal distribution function in FIG. 8, the value of the normal distribution function obtained when the distance between the foils DP is the evaluation reference distance DPB = M + 3σ (= 373.6 μm), whose position is indicated by the dot-dashed vertical line, is It can be understood that the possibility that the inter-foil distance DP becomes a value larger than the evaluation reference distance DPB (=M+3σ=373.6 μm) is extremely small.

Unlike FIG. 7, FIG. 8 and Table 1 show that there is no case where the obtained evaluation site 20HH2 (total frequency 92) has an inter-foil distance DP that exceeds the evaluation reference distance DPB. . This means that, unlike the evaluation site 20HH1 in FIG. 7, in the evaluation site 20HH2, although there is variation in the value of the inter-foil distance DP that approximates a normal distribution, the site where the inter-foil distance DP is abnormally large is not included. This is thought to suggest that it is not.

Therefore, in the class evaluation step S5, it is evaluated whether or not there is data of a reference-exceeding inter-foil distance DPS that is larger than the evaluation reference distance DPB in the inter-foil distance DP acquired in the inter-foil distance acquisition step S2. Specifically, in the class evaluation step S5, in the frequency distribution indicating the frequency n of the inter-foil distance DP obtained for each predetermined distance class SS, the inter-foil distance DP is larger than the evaluation reference distance DPB, and Based on whether the frequency n of the inter-foil distance DP has a distance class SS of 1 or more, it is evaluated whether the inter-foil distance DPS exceeding the standard exists.

When this class evaluation step S5 is applied, in the evaluation part 20HH1 (see Table 1 and FIG. 7), the distance where the inter-foil distance DP = 379 μm, which is larger than the evaluation reference distance DPB (=376.7 μm), is the class value (representative value). It can be seen that the frequency n of class SS is 1 (n=1), and it is evaluated as having the corresponding distance class SS (379 μm). Therefore, in the class evaluation step S5, the evaluation is Yes, and the process proceeds to step S6.

On the other hand, in the evaluation part 20HH2 (see FIG. 8), the frequency n of the distance class SS with a class value larger than the evaluation reference distance DPB (=373.6 μm) is never greater than 1, and there is no corresponding distance class SS. It can be seen that it is evaluated as Note that the battery 10 evaluated as No in the class evaluation step S5 is determined to be a normal battery based on the evaluation result at the evaluation site 20HH2.

In this way, it is possible to appropriately evaluate the interval between the stacked positive electrode plates 21 (positive electrode foils 22) in the flat laminated portion 20H of the electrode body 20 of the battery 10. In particular, in the above-mentioned evaluation method, a frequency distribution of the obtained inter-foil distance DP is obtained, and in the class evaluation step S5, in this frequency distribution, the inter-foil distance DP is larger than the evaluation reference distance DPB, and the inter-foil distance is Since it is evaluated whether or not the inter-foil distance DPS exceeding the standard exists based on whether the frequency n of DP has a distance class SS of 1 or more, the evaluation can be easily performed.

In the subsequent deterioration evaluation step S6, the degree of deterioration is evaluated for the battery 10 that was evaluated in the class evaluation step S5 to have an inter-foil distance DPS exceeding the standard at the evaluation site (for example, 20HH1). Specifically, for example, the magnitude of the IV resistance value of the battery 10 is measured using a known method, and it is determined whether the IV resistance value of the battery 10 is larger than a predetermined reference IV resistance value. If it is larger than the value (Yes), it is determined that the battery 10 has deteriorated.

The cause is thought to be related to the presence of an air layer or the generation of a gas layer. In a portion where an air layer or a gas layer exists between the positive electrode layer and the negative electrode layer, sufficient electrolyte solution does not exist between the positive electrode layer and the negative electrode layer, making it difficult for an appropriate battery reaction to occur. For this reason, it is assumed that due to the use of the battery 10, a precipitated metal layer such as Li metal was generated in the area where the air layer or gas layer existed, and the battery reaction became more difficult to occur, resulting in deterioration (increase in IV resistance value). can. However, depending on the usage conditions of the battery 10, even if an air layer or a gas layer exists between the positive electrode plate 21 and the negative electrode plate 25, a precipitated metal layer does not occur or is difficult to generate, and the battery 10 This is because deterioration (increase in IV resistance) may not be significant in some cases.

Furthermore, since this evaluation method includes a deterioration evaluation step S6, based on the degree of deterioration of the power storage device, Li metal is It is possible to appropriately evaluate whether the electricity storage device has already deteriorated to some extent due to the formation of a precipitated metal layer, or whether the deterioration has not progressed yet although an air layer or a gas layer has formed.

Although the present invention has been described above based on the embodiments, it goes without saying that the present invention is not limited to the embodiments and can be modified and applied as appropriate without departing from the gist thereof. For example, in the embodiment, in determining the foil position dpf1 of the positive electrode foil 22, in the positive electrode foil position specifying step S22, an approximate curve FC that changes by fitting to changes in the X-ray absorption amount AB(d) on the trajectory is determined. Thus, the foil position dpf1 and the like of the positive electrode foil 22 were specified.
However, as in Patent Document 1, even when the foil position dpf1 of the positive electrode foil 22 is specified without going through fitting using the approximate curve FC, the distribution of the obtained inter-foil distance DP is similarly used. , it is possible to evaluate the presence or absence of a region where the inter-foil distance DP is abnormally large.

Further, in the embodiment, a large number of distances DP between the positive electrode foils 22 were obtained, and the presence or absence of an abnormally large value was evaluated for the distance DP between the positive electrode foils 22. In the example shown in the graph of FIG. 4, the magnitude of the X-ray absorption amount AB(d) on the trajectory obtained near the portion corresponding to each negative electrode foil 26 is small, and the approximate curve is similar to the foil position dpf1 of the positive electrode foil 22. This is because it was difficult to appropriately specify the foil position dnf1, etc. of each negative electrode foil 26 using .

However, the magnitude of the on-trajectory X-ray absorption amount AB(d) obtained near the portion corresponding to each negative electrode foil 26 allows the foil position dnf of each negative electrode foil 26 to be appropriately specified using an approximate curve. If the distance is considerably large, an approximate curve may be used to specify the foil position dpf1 of the positive electrode foil 22, etc. In this case, in the step of calculating the distance between the foils, the foil position dpf1 etc. of the positive electrode foil 22 and the foil position dnf1 etc. of the negative electrode foil 26 that have been specified are used to calculate the distance between the adjacent positive electrode foils 22 and negative electrode foils 26 of different polarities. It is also possible to calculate and evaluate the distance between negative electrode foils 26 and the distance between the negative electrode foils 26 .

In addition, in the embodiment, as shown in FIG. 3, a region to be inspected 10S1 in which the positive electrode plate 21, the negative electrode plate 25, and the separator 29 of the stacked electrode body 20 of the battery 10 are all made into a flat plate and stacked. , 10S2, an example in which X-ray CT analysis was performed, the foil position dpf1, etc. of each positive electrode foil 22 was specified, the inter-foil distance DP1, etc. between the positive electrode foils 22 was calculated, and the inter-foil distance DP was evaluated. Indicated. However, the same method as in this embodiment can also be applied to a flat laminated portion of a flat wound electrode body in which a positive electrode plate, a negative electrode plate, and a separator are stacked in a flat plate shape.

10 Battery (electricity storage device)
20 Electrode body SH Lamination direction 20H Flat laminated parts 20HH1, 20HH2 Evaluation part 21 Positive electrode plate (electrode plate)
22 Positive electrode foil (electrode foil)
25 Negative electrode plate (electrode plate)
26 Negative electrode foil (electrode foil)
dpf, dpf1, dpf2,..., dpf6,..., dpf8 (Positive electrode foil) foil position dnf, dnf1, dnf2,..., dnf7 (Negative electrode foil) Foil position DP, DP1, DP2,..., DP7 (Positive electrode foil) ) Inter-foil distance M Average value (of inter-foil distance) σ Standard deviation (of inter-foil distance) DPB Evaluation standard distance DPS Exceeding standard inter-foil distance SS Distance class n Frequency S1 Analysis step S2 Inter-foil distance acquisition step S21 Absorption amount acquisition Step S22 Positive electrode foil position specifying step (foil position specifying step)
S23 Foil distance calculation step S3 Average deviation calculation step S4 Reference distance acquisition step S5 Class evaluation step (evaluation step)
S6 Deterioration evaluation step

Claims (3)

X-ray CT analysis is performed on a flat laminated part where electrode plates are stacked flatly in the electrode body of the electricity storage device. or an inter-foil distance obtaining step of obtaining an inter-foil distance of 10 or more between electrode foils included in electrode plates of the same polarity adjacent to each other via different polarities;
an average deviation calculation step of calculating the average value and standard deviation of the obtained inter-foil distances;
a reference distance obtaining step of obtaining an evaluation reference distance obtained by adding three times the standard deviation to the average value;
An evaluation method for an electricity storage device, comprising: an evaluation step of evaluating whether or not a reference-exceeding inter-foil distance larger than the evaluation reference distance exists in the obtained inter-foil distances. A method for evaluating an electricity storage device according to claim 1, comprising:
The evaluation step includes:
In a frequency distribution indicating the frequency of the distance between the foils obtained for each predetermined distance class, the distance class has the distance between the foils that is larger than the evaluation reference distance, and the frequency of the distance between the foils is 1 or more. An evaluation method for an electricity storage device, which is a class evaluation step of evaluating whether or not the distance between the foils exceeding the reference exists based on whether or not the distance between the foils exceeds the reference value. A method for evaluating an electricity storage device according to claim 1 or 2, comprising:
The method for evaluating an electricity storage device further comprises a deterioration evaluation step of evaluating the degree of deterioration of the electricity storage device for which it has been evaluated in the evaluation step that the distance between foils exceeding the reference exists in the evaluation portion.

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