JP2021021579A - Lithium deposition inspection device - Google Patents

Abstract

To provide a lithium deposition inspection device which can easily and properly inspect whether or not lithium is deposited on a surface of an electrode mixture layer.SOLUTION: A lithium deposition inspection device 1 comprises: an irradiation unit 10 which emits white light WL toward a surface 159b of an electrode mixture layer 159 of an electrode 156; a light reception unit 20 which acquires image data in the RGB format by receiving reflection light RL obtained by emitting the white light WL and reflecting the light on the electrode 156; a calculation unit 30 which calculates the hue angle and the brightness for each pixel constituting the image data acquired by the light reception unit 20; and a determination unit 40 which determines whether or not lithium is deposited on the surface 159b of the electrode mixture layer 159 on the basis of the hue angle and brightness calculated by the calculation unit 30.SELECTED DRAWING: Figure 4

Description

The present invention relates to a lithium precipitation inspection device.

Patent Document 1 discloses a method for detecting lithium precipitation in a lithium ion secondary battery. Specifically, in Patent Document 1, while charging a lithium ion secondary battery, the battery voltage according to SOC is measured to obtain an SOC-V graph, and a change in battery voltage (dV) according to SOC is obtained from the graph. Obtain a SOC-dV / dQ graph that is / dQ). Then, the point on the SOC-dV / dQ graph where the increase in slope slows down is determined to be the point where lithium precipitation occurs. Furthermore, the charging current is gradually changed by a protocol provided to set the point where the increase rate of the battery voltage of the lithium ion secondary battery slows down as the lithium precipitation generation point and the charging limit, and to change the charging rate stepwise. Charge the lithium-ion secondary battery while adjusting to. By charging the lithium ion secondary battery in this way, the occurrence of lithium precipitation is suppressed.

Special Table 2018-528573

By the way, in recent years, the electrodes (negative electrodes) of the lithium ion secondary batteries used (particularly, lithium ion secondary batteries charged and discharged in a low temperature environment and lithium ion secondary batteries charged and discharged with a large current) have been used. There is a demand for an apparatus capable of easily and appropriately inspecting whether or not lithium is deposited on the surface of the electrode mixture layer (negative electrode mixture layer).
Specifically, for example, in order to grasp the charging conditions (charging / discharging conditions) in which lithium is deposited on the surface of the negative electrode mixture layer, a charging test (charging / discharging) in which the lithium ion secondary battery is charged (charged / discharged) under predetermined conditions (charge / discharge conditions). A charge / discharge test) may be performed, and then the negative electrode taken out by disassembling the lithium ion secondary battery may be inspected for whether or not lithium is deposited on the surface of the negative electrode mixture layer. In such a case, an apparatus capable of easily and appropriately inspecting whether or not lithium is deposited on the surface of the negative electrode mixture layer is required.

The present invention has been made in view of the present situation, and provides a lithium precipitation inspection apparatus capable of easily and appropriately inspecting whether or not lithium is precipitated on the surface of the electrode mixture layer. The purpose is.

One aspect of the present invention is a lithium precipitation inspection apparatus that inspects whether or not lithium is deposited on the surface of the electrode mixture layer among the electrodes having the electrode mixture layer on the surface of the current collecting member. An irradiation unit that irradiates the irradiation light toward the surface of the electrode mixture layer of the electrode and the reflected light reflected by the electrode by irradiating the irradiation light are received to obtain image data in RGB format. Based on the light receiving unit to be acquired, the calculation unit that calculates the hue angle and the brightness of each pixel constituting the image data acquired by the light receiving unit, and the hue angle and the brightness calculated by the calculation unit. It is a lithium precipitation inspection apparatus including a determination unit for determining whether or not lithium is deposited on the surface of the electrode mixture layer.

The above-mentioned lithium precipitation inspection device includes an irradiation unit, a light receiving unit, a calculation unit, and a determination unit. Of these, the irradiation unit is a device that irradiates the surface of the electrode mixture layer with irradiation light (specifically, irradiation light including each element of RGB). Further, the light receiving unit is a device that receives the reflected light reflected by the electrode by irradiating the irradiation light and acquires image data in RGB format (hereinafter, also referred to as RGB image data). The reflected light reflected by the electrode also includes scattered light scattered by the electrode (for example, Rayleigh scattered light by lithium deposited on the surface of the electrode mixture layer). Further, the calculation unit is a device that calculates the hue angle and the brightness of each pixel constituting the image data acquired by the light receiving unit.

Further, the determination unit is a device that determines whether or not lithium is deposited on the surface of the electrode mixture layer based on the hue angle and brightness of each pixel calculated by the calculation unit. Specifically, in the determination unit, lithium is deposited on the surface of the electrode mixture layer with the hue angle and the brightness value calculated by the calculation unit in the pixels constituting the image data. It is determined whether or not a pixel (referred to as a Li pixel), which is a value obtained in the case of the above, exists, and when it is determined that the Li pixel exists, the electrode mixture layer is said to have the above. It is determined that lithium is deposited on the surface.

According to such a lithium precipitation inspection device, whether or not lithium (Li) is deposited on the surface of the electrode mixture layer based on the hue angle and brightness of each pixel calculated by the calculation unit in the determination unit. Can be determined. Therefore, by using the above-mentioned lithium precipitation inspection apparatus, it is possible to easily and appropriately inspect whether or not lithium is precipitated on the surface of the electrode mixture layer.

In the above-mentioned lithium precipitation inspection apparatus, the determination unit determines whether or not lithium is deposited on the surface of the electrode mixture layer, for example, as follows. Specifically, the hue angle and the brightness of each part of the electrode (pixels of each part in the RGB image data acquired in the light receiving part) are grasped in advance by using the above-mentioned lithium precipitation inspection apparatus. As each part of the electrode, the part of the electrode mixture that constitutes the electrode mixture layer that is not subjected to friction (hereinafter, also referred to as the non-rubbed part of the electrode mixture) and the electrode mixture that has gloss due to friction. Examples thereof include a portion (hereinafter, also referred to as a rubbing portion of the electrode mixture), lithium precipitated on the surface of the electrode mixture layer (hereinafter, also referred to as precipitated lithium), and a current collecting member.

For example, an electrode (for example, a negative electrode of a lithium ion secondary battery) including a current collecting member made of copper foil and an electrode mixture having graphite powder as an active material (for example, made of graphite powder and binder). In this case, when white light is used as the irradiation light, the hue angles of the unrubbed part of the electrode mixture, the rubbed part of the electrode mixture, and the precipitated lithium (pixels corresponding to each part in the RGB image data) are , All of which are values in the range of 180 ° to 300 °. On the other hand, the hue angle of the current collector member (pixels of the current collector member in the RGB image data) is a value within the range of 0 ° to 60 ° or 300 ° to 360 °.

As described above, the hue angles of the electrode mixture non-rubbed portion, the electrode mixture rubbing portion, and the precipitated lithium are within the same range (specifically, 180 ° to 300 °). Therefore, it is not possible to distinguish between the negative electrode mixture, the rubbing portion of the negative electrode mixture, and the precipitated lithium only by the hue angle, and it is not possible to determine the presence or absence of the precipitated lithium.

However, the brightness of the unrubbed portion of the electrode mixture and the rubbed portion of the electrode mixture (these pixels in the RGB image data) and the precipitated lithium (the pixels thereof in the RGB image data) may be significantly different. Specifically, the precipitated lithium has a very large brightness value as compared with the non-rubbed portion of the electrode mixture and the rubbed portion of the electrode mixture. Specifically, the magnitude relationship of these lightnesses may be (brightness of precipitated lithium)> (brightness of the unrubbed portion of the electrode mixture)> (brightness of the rubbed portion of the electrode mixture).

Therefore, in this case, a value between the brightness value of the precipitated lithium and the brightness value of the unrubbed portion of the electrode mixture is set as a threshold value, and the hue angle is within the range of 180 ° to 300 °. When there is a part (Li pixel) having a brightness exceeding this threshold among the parts (pixels) that have become values, it is said that lithium is precipitated on the surface of the electrode mixture layer (precipitated lithium is present). Can be determined.

Therefore, in this case, the determination unit is a pixel (Li pixel) in which the hue angle calculated by the calculation unit is a value within the range of 180 ° to 300 ° and the brightness is a value exceeding a preset threshold value. ) Exists or not. When there are pixels (Li pixels) that satisfy such conditions, it can be determined that lithium is deposited on the surface of the electrode mixture layer (precipitated lithium is present). On the contrary, when there is no pixel satisfying such a condition, it can be determined that lithium is not deposited on the surface of the electrode mixture layer (precipitated lithium is not present).

As described above, the determination unit is obtained when the values of the hue angle and the brightness calculated by the calculation unit are deposited on the surface of the electrode mixture layer in the pixels constituting the RGB image data. It is determined whether or not the Li pixel, which is a value, is present, and when it is determined that the Li pixel is present, it is determined that lithium is deposited on the surface of the electrode mixture layer. On the contrary, when it is determined that the Li pixel does not exist, it is determined that lithium is not deposited on the surface of the electrode mixture layer (precipitated lithium does not exist).

It is a partial cross-sectional view of a lithium ion secondary battery. It is a perspective view of the electrode body of the lithium ion secondary battery. It is sectional drawing of the negative electrode of the lithium ion secondary battery. It is the schematic of the lithium precipitation inspection apparatus which concerns on embodiment. It is a figure which shows the intensity of RGB in each part of a negative electrode.

First, the negative electrode 156 to be inspected in the present embodiment and the lithium ion secondary battery 100 including the negative electrode 156 will be described. As shown in FIG. 1, the lithium ion secondary battery 100 is a square sealed lithium ion secondary battery including a rectangular parallelepiped battery case 110, a positive electrode external terminal 121, and a negative electrode external terminal 131. The lithium ion secondary battery 100 is a large-capacity lithium ion secondary battery, and is used as a driving power source for, for example, a hybrid vehicle, a plug-in hybrid vehicle, or an electric vehicle.

The battery case 110 is a hard case having a metal square accommodating portion 111 forming a rectangular parallelepiped accommodating space and a metal lid portion 112. An electrode body 150 or the like is housed inside the battery case 110 (square housing part 111). The electrode body 150 is a flat-wound electrode body in which a band-shaped positive electrode 155 and a band-shaped negative electrode 156 are wound in a flat shape so that a separator 157 is interposed between the positive electrode 155 and the negative electrode 156 (FIG. 2).

The positive electrode 155 has a positive electrode current collecting foil 151 (current collecting member) made of aluminum foil, and a positive electrode mixture layer coated on the surface of the positive electrode current collecting foil 151. The positive electrode mixture layer contains a positive electrode active material, a conductive material made of acetylene black, and a binder. Of the positive electrode 155, a portion where the positive electrode mixture layer is not coated (that is, a portion composed of only the positive electrode current collector foil 151) is referred to as a positive electrode mixture layer uncoated portion 155b. The positive electrode mixture layer uncoated portion 155b is located at the end (right end in FIG. 1) of the width direction DB (left-right direction in FIG. 1) of the positive electrode current collector foil 151 (positive electrode 155), and the positive electrode current collector foil 151 Along one long side of (positive electrode 155), the positive electrode current collecting foil 151 (positive electrode 155) extends in a strip shape in the longitudinal direction.

Further, the negative electrode 156 to be inspected in the present embodiment includes a negative electrode current collecting foil 158 (current collecting member) made of copper foil and a negative electrode mixture layer 159 coated on the surface 158b of the negative electrode current collecting foil 158. (See FIG. 3). The negative electrode mixture layer 159 contains a negative electrode active material (specifically, graphite powder) and a binder. Of the negative electrode 156, a portion where the negative electrode mixture layer 159 is not coated (that is, a portion composed of only the negative electrode current collector foil 158) is referred to as a negative electrode mixture layer uncoated portion 156b. The negative electrode mixture layer uncoated portion 156b extends in a strip shape in the longitudinal direction of the negative electrode current collector foil 158 (negative electrode 156) along one long side of the negative electrode current collector foil 158 (negative electrode 156).

Further, an aluminum positive electrode current collecting terminal 122 is bonded to the positive electrode mixture layer uncoated portion 155b. As a result, the positive electrode mixture layer uncoated portion 155b (positive electrode 155) is electrically connected to the positive electrode external terminal 121 through the positive electrode current collecting terminal 122 (see FIG. 1). Further, a copper negative electrode current collecting terminal 132 is bonded to the negative electrode mixture layer uncoated portion 156b. As a result, the negative electrode mixture layer uncoated portion 156b (negative electrode 156) is electrically connected to the negative electrode external terminal 131 through the negative electrode current collecting terminal 132. The positive electrode external terminal 121 and the positive electrode current collecting terminal 122 are integrally formed to form the positive electrode terminal member 120. Further, the negative electrode external terminal 131 and the negative electrode current collecting terminal 132 are integrally formed to form the negative electrode terminal member 130.

The separator 157 is a separator made of a resin film having electrical insulation. The separator 157 is interposed between the positive electrode 155 and the negative electrode 156 to separate them. The separator 157 is impregnated with a non-aqueous electrolytic solution 140 having lithium ions.

By the way, in the lithium ion secondary battery 100, when charging (charging / discharging) or high-rate charging (charging / discharging) is performed in a low temperature environment (for example, in a temperature environment of 0 ° C. or lower), the negative electrode mixture layer 159 Lithium (Li) may be deposited on the surface 159b of the surface. Most of the lithium deposited on the surface 159b of the negative electrode mixture layer 159 cannot contribute to the charge / discharge reaction of the battery, so that there is a problem that the battery capacity is reduced when such charging (charging / discharging) is repeated. ..

Conventionally, when the lithium ion secondary battery 100 is used as a power source for driving a hybrid vehicle, a plug-in hybrid vehicle, or an electric vehicle, it is charged (charged) in a low temperature environment in consideration of the usage environment and the usage period. Since discharge) may be repeated or high-rate charging (charging / discharging) may be repeated, lithium may be deposited on the surface 159b of the negative electrode mixture layer 159.

Therefore, when the lithium ion secondary battery 100 is used as a driving power source for a hybrid vehicle, a plug-in hybrid vehicle, or an electric vehicle, lithium is prevented from depositing on the surface 159b of the negative electrode mixture layer 159. It is required to control the charging (charging / discharging) rate, temperature, and the like of the ion secondary battery 100. Therefore, the charging condition (charging / discharging condition) in which lithium is deposited on the surface 159b of the negative electrode mixture layer 159 is accurately grasped, and the lithium ion secondary battery 100 is prevented from satisfying such charging condition (charging / discharging condition). It is required to control the charging (charging / discharging) rate and temperature.

Further, it is preferable that the charging condition (charging / discharging condition) in which lithium is deposited on the surface 159b of the negative electrode mixture layer 159 can be grasped in the shortest possible time. That is, it is preferable that the test for grasping the charging condition (charging / discharging condition) in which lithium is deposited on the surface 159b of the negative electrode mixture layer 159 can be completed in the shortest possible time. However, as the test period is shortened, the amount of precipitated lithium decreases, which makes it difficult to detect precipitated lithium.

Therefore, even when the amount of lithium precipitated on the surface 159b of the negative electrode mixture layer 159 is very small, a lithium precipitation inspection device capable of appropriately (accurately) detecting this small amount of precipitated lithium, and a lithium precipitation inspection A method is required. Further, a lithium precipitation inspection device and a lithium precipitation inspection method capable of easily and appropriately inspecting whether or not lithium is deposited on the surface 159b of the negative electrode mixture layer 159 over the entire negative electrode 156 are provided. Desired. The lithium precipitation inspection device 1 and the lithium precipitation inspection method of the present embodiment can meet such a demand.

Therefore, the lithium precipitation inspection apparatus 1 of the present embodiment will be described. The lithium precipitation inspection device 1 includes an irradiation unit 10, a light receiving unit 20, a calculation unit 30, and a determination unit 40. Of these, the irradiation unit 10 is a device that irradiates white light WL (irradiation light) toward the surface 159b of the negative electrode mixture layer 159 (electrode mixture layer) of the negative electrode 156 (electrode) to be inspected. Further, the light receiving unit 20 is a device that receives the reflected light RL reflected by the negative electrode 156 by irradiating the white light WL and acquires image data in RGB format (also referred to as RGB image data). The light receiving unit 20 is composed of, for example, a known 2D camera. The reflected light RL reflected by the negative electrode 156 also includes scattered light scattered by the negative electrode 156 (for example, Rayleigh scattered light by lithium deposited on the surface 159b of the negative electrode mixture layer 159).

In the present embodiment, the irradiation unit 10 has an angle α formed by the angle formed by the white light WL (irradiation light) emitted from the irradiation unit 10 and the surface of the negative electrode 156 (the surface 159b of the negative electrode mixture layer 159). Set the orientation of. By doing so, the light reflected on the mirror surface of the negative electrode 156 is prevented from being taken into the light receiving unit 20 (see FIG. 1). That is, the direction of the irradiation unit 10 (the irradiation direction of the white light WL) with respect to the surface of the negative electrode 156 (the surface 159b of the negative electrode mixture layer 159) is the direction (direction) in which the light reflected on the mirror surface of the negative electrode 156 is not captured by the light receiving unit 20. )I have to.

Further, the orientation of the light receiving portion 20 (the orientation of the lens of the light receiving portion 20) is perpendicular to the surface of the negative electrode 156 (the surface 159b of the negative electrode mixture layer 159) (see FIG. 1). As a result, when lithium (Li) is precipitated on the surface 159b of the negative electrode mixture layer 159, the scattered light Rayleigh scattered by the precipitated lithium (hereinafter, also simply referred to as precipitated lithium) is transmitted to the light receiving unit 20. I am trying to be taken in.

Further, the calculation unit 30 is a device that calculates the hue angle and the brightness of each pixel constituting the RGB image data acquired by the light receiving unit 20. Specifically, the calculation unit 30 includes image processing software that converts the RGB information of each pixel of the RGB image data acquired by the light receiving unit 20 into a hue angle and brightness. Using this image processing software, the calculation unit 30 calculates the hue angle and brightness of each pixel from the RGB information of each pixel of the RGB image data.

Further, the determination unit 40 is a device that determines whether or not lithium is deposited on the surface 159b of the negative electrode mixture layer 159 based on the hue angle and brightness of each pixel calculated by the calculation unit 30. Specifically, in the determination unit 40, lithium is deposited on the surface 159b of the negative electrode mixture layer 159 with the hue angle and lightness values calculated by the calculation unit 30 in the pixels constituting the RGB image data. It is determined whether or not a pixel (this pixel is referred to as a Li pixel), which is a value obtained in the case of Lithium, exists, and when it is determined that a Li pixel exists, lithium is deposited on the surface 159b of the negative electrode mixture layer 159. Judge that it is. On the contrary, when it is determined that the Li pixel does not exist, it is determined that lithium is not deposited on the surface 159b of the negative electrode mixture layer 159 (precipitated lithium does not exist).
The calculation unit 30 and the determination unit 40 are composed of, for example, a microcomputer or the like.

More specifically, a lightness threshold Th for determining whether or not lithium is deposited on the surface 159b of the negative electrode mixture layer 159 is input in advance to the determination unit 40. Then, the determination unit 40 has a pixel (Li pixel) in which the hue angle calculated by the calculation unit 30 is in the range of 180 ° to 300 ° and the brightness is larger than the threshold value Th. Judge whether or not. When it is determined that a pixel (Li pixel) satisfying such a condition exists, it is determined that lithium is deposited on the surface 159b of the negative electrode mixture layer 159 (precipitated lithium is present). On the contrary, when it is determined that there is no pixel (Li pixel) satisfying such a condition, it is determined that lithium is not deposited on the surface 159b of the negative electrode mixture layer 159 (precipitated lithium does not exist).

The lightness threshold Th is determined as follows, for example. Specifically, first, as a sample, a negative electrode 156 in which lithium is deposited on the surface 159b of the negative electrode mixture layer 159 is prepared. In addition, such a negative electrode 156 can be acquired as follows, for example. Specifically, first, the lithium ion secondary battery 100 is repeatedly charged and discharged at a high rate. As a result, in the lithium ion secondary battery 100, lithium is deposited on the surface 159b of the negative electrode mixture layer 159. Next, the lithium ion secondary battery 100 is disassembled to take out the electrode body 150, and further, the electrode body 150 is disassembled to take out the negative electrode body 156. In this way, the negative electrode 156 in which lithium is deposited on the surface 159b of the negative electrode mixture layer 159 is prepared as a sample.

Next, the RGB image data of the negative electrode 156, which is a sample, is acquired by using the lithium precipitation inspection device 1. Specifically, as shown in FIG. 1, the negative electrode 156 as a sample is placed on a mounting table (not shown) with the surface 159b of the negative electrode mixture layer 159 facing upward, and in this state, the irradiation unit. By 10, the white light WL is irradiated toward the surface 159b of the negative electrode mixture layer 159. Then, the light receiving unit 20 receives the reflected light RL reflected by the negative electrode 156 and acquires RGB image data of the negative electrode 156. Next, based on the RGB image data, the calculation unit 30 calculates the hue angle and the brightness of each part of the negative electrode 156 as a sample (pixels of each part in the RGB image data acquired by the light receiving unit 20). Grasp the calculated hue angle and brightness.

As each part of the negative electrode 156, a part of the negative electrode mixture constituting the negative electrode mixture layer 159 that is not subjected to friction (hereinafter, also referred to as a non-rubbed part of the negative electrode mixture) and a negative electrode mixture that is glossy due to friction. Examples thereof include a portion having a negative electrode (hereinafter, also referred to as a rubbing portion of the negative electrode mixture), lithium (precipitated lithium) deposited on the surface 159b of the negative electrode mixture layer 159, and a negative electrode current collecting foil 158 (collecting member). ..

Further, the disassembly work of the lithium ion secondary battery 100 and the electrode body 150 and the inspection using the lithium precipitation inspection device 1 are preferably performed in a dry environment (for example, an environment having a dew point of −40 ° C.). Further, the inspection using the lithium precipitation inspection apparatus 1 (the work of acquiring the RGB image data of the negative electrode 156) is preferably performed in a dark room.

Here, in the RGB image data of the negative electrode 156 as a sample, the RGB information of the negative electrode mixture unrubbed portion, the negative electrode mixture rubbed portion, the precipitated lithium, and the negative electrode current collecting foil 158 is shown in FIG. In FIG. 5, the intensity of each element of RGB (the intensity of light received by the light receiving unit 20) is represented by 256 gradations of 8 bits. Further, in FIG. 5, the intensities of each RGB element (R, G, and B) of the precipitated lithium are plotted by black circles, and these are connected by a solid line. Further, the intensities of each RGB element (R, G, and B) of the negative electrode current collector foil 158 are plotted by a black-painted rhombus, and these are connected by a broken line. Further, the intensities of each RGB element (R, G, and B) of the unrubbed portion of the negative electrode mixture are plotted by a black-painted square, and these are connected by a chain line. Further, the intensities of each RGB element (R, G, and B) of the negative electrode mixture rubbing portion are plotted by black-painted triangles, and these are connected by a two-dot chain line.

As shown in FIG. 5, in the negative electrode mixture rubbing portion, the negative electrode mixture rubbing portion, and the precipitated lithium, the magnitude relationship of RGB satisfies the relationship of B> R and B> G. Therefore, in the negative electrode 156, the negative electrode mixture unrubbed portion (electrode mixed material unrubbed portion), the negative electrode mixed material rubbed portion (electrode mixed material rubbed portion), and the hue angle of the precipitated lithium (at each portion in the RGB image data). The hue angle of the corresponding pixel) is a value in the range of 180 ° to 300 °. On the other hand, in the negative electrode current collector foil 158, the magnitude relationship of RGB satisfies the relationship of R> G and R> B. Therefore, the hue angle of the negative electrode current collector foil 158 (pixels of the negative electrode current collector foil 158 in the RGB image data) is a value within the range of 0 ° to 60 ° or 300 ° to 360 °.

As described above, the hue angles of the unrubbed portion of the negative electrode mixture, the rubbed portion of the negative electrode mixture, and the precipitated lithium are within the same range (specifically, 180 ° to 300 °). Therefore, it is not possible to distinguish the unrubbed portion of the negative electrode mixture, the rubbed portion of the negative electrode mixture, and the precipitated lithium only by the hue angle, and it is not possible to determine the presence or absence of the precipitated lithium.

However, the brightness of the unrubbed portion of the negative electrode mixture and the rubbed portion of the negative electrode mixture (these pixels in the RGB image data) and the precipitated lithium (the pixels thereof in the RGB image data) are significantly different. Specifically, the precipitated lithium has a much larger brightness value than the unrubbed portion of the negative electrode mixture and the rubbed portion of the negative electrode mixture (see FIG. 5). Specifically, the magnitude relationship of these brightnesses is (brightness of precipitated lithium)> (brightness of the unrubbed portion of the negative electrode mixture)> (brightness of the rubbed portion of the negative electrode mixture).

Therefore, in the present embodiment, the value between the value of the brightness of the precipitated lithium and the value of the brightness of the unrubbed portion of the negative electrode mixture is set as the threshold value Th. As a result, if there is a portion (pixel) whose hue angle is in the range of 180 ° to 300 ° and has a brightness exceeding the threshold Th (Li pixel), the negative electrode mixture layer 159 It can be determined that lithium is deposited on the surface 159b of the surface (precipitated lithium is present).

Next, the lithium precipitation inspection method of the present embodiment will be described.
First, a lithium ion secondary battery 100 that has been cycle-charged and discharged is prepared. The cycle charge / discharge cycle is set to various cycles in order to grasp the charging condition (charging / discharging condition) in which lithium is deposited on the surface 159b of the negative electrode mixture layer 159. In addition, the environmental temperature for cycle charging / discharging is also set to various temperatures.

Next, the lithium ion secondary battery 100 is disassembled to take out the electrode body 150, and further, the electrode body 150 is disassembled to take out the negative electrode body 156. Then, the negative electrode 156 is washed with an organic solvent. By this cleaning, the electrolytic solution salt and foreign matter adhering to the negative electrode 156 are removed. In the present embodiment, the disassembly work of the lithium ion secondary battery 100 and the electrode body 150 and the cleaning work of the negative electrode 156 are performed in a dry environment (for example, an environment where the dew point is −40 ° C.).

Next, using the lithium precipitation inspection device 1, the negative electrode 156 is inspected for whether or not lithium is deposited on the surface 159b of the negative electrode mixture layer 159. In the present embodiment, the lithium precipitation inspection using the lithium precipitation inspection apparatus 1 is performed in a dark room in a dry atmosphere (for example, an atmosphere having a dew point of −40 ° C.).

Specifically, as shown in FIG. 4, the negative electrode 156 is placed on a mounting table (not shown) with the surface 159b of the negative electrode mixture layer 159 facing upward. In this state, the irradiation unit 10 irradiates the surface 159b of the negative electrode mixture layer 159 with white light WL (irradiation light) from diagonally above the surface 159b of the negative electrode mixture layer 159. The orientation of the irradiation unit 10 is set so that the angle formed by the white light WL emitted from the irradiation unit 10 and the surface of the negative electrode 156 (the surface 159b of the negative electrode mixture layer 159) is an angle α (FIG. 4). As a result, the light reflected on the mirror surface of the negative electrode 156 is prevented from being taken into the light receiving unit 20.

Then, the light receiving unit 20 receives the reflected light RL reflected by the negative electrode 156 and acquires RGB image data of the negative electrode 156. The orientation of the light receiving portion 20 (the orientation of the lens of the light receiving portion 20) is perpendicular to the surface of the negative electrode 156 (the surface 159b of the negative electrode mixture layer 159) (see FIG. 4). As a result, when lithium (Li) is deposited on the surface 159b of the negative electrode mixture layer 159, the scattered light Rayleigh scattered by the precipitated lithium is taken into the light receiving unit 20 as reflected light.

Next, the calculation unit 30 calculates the hue angle and the brightness of each pixel constituting the RGB image data acquired by the light receiving unit 20. Specifically, the calculation unit 30 inputs RGB information of each pixel constituting the RGB image data from the light receiving unit 20, and calculates the hue angle and brightness of each pixel from the input RGB information of each pixel.

Next, the determination unit 40 determines whether or not lithium is deposited on the surface 159b of the negative electrode mixture layer 159 based on the hue angle and brightness of each pixel calculated by the calculation unit 30. Specifically, in the determination unit 40, lithium is deposited on the surface 159b of the negative electrode mixture layer 159 with the hue angle and brightness values calculated by the calculation unit 30 in the pixels constituting the RGB image data. It is determined whether or not a pixel (Li pixel), which is a value obtained when the value is present, is present, and when it is determined that the Li pixel is present, it is determined that lithium is deposited on the surface 159b of the negative electrode mixture layer 159. To do. On the contrary, when it is determined that the Li pixel does not exist, it is determined that lithium is not deposited on the surface 159b of the negative electrode mixture layer 159 (precipitated lithium does not exist).

More specifically, in the determination unit 40, the hue angle calculated by the calculation unit 30 is a value within the range of 180 ° to 300 ° in the pixels constituting the RGB image data, and the brightness is a threshold value. It is determined whether or not there is a pixel (Li pixel) having a value larger than Th. When it is determined that a pixel (Li pixel) satisfying such a condition exists, the determination unit 40 determines that lithium is deposited on the surface 159b of the negative electrode mixture layer 159 (precipitated lithium is present). On the contrary, when it is determined that there is no pixel (Li pixel) satisfying such a condition, the determination unit 40 does not deposit lithium on the surface 159b of the negative electrode mixture layer 159 (precipitated lithium does not exist). Is determined.

In the present embodiment, in this way, the irradiation light (white light WL) is irradiated toward the surface 159b of the negative electrode mixture layer 159 over the entire negative electrode 156 (the surface 158b side of the negative electrode current collecting foil 158). The RGB image data of the negative electrode 156 is acquired, and it is inspected whether or not lithium is deposited on the surface 159b of the negative electrode mixture layer 159 based on the hue angle and the brightness of each pixel calculated from the RGB image data.

As described above, according to the lithium precipitation inspection device 1 of the present embodiment and the lithium precipitation inspection method of the present embodiment, the surface 159b of the negative electrode mixture layer 159 (electrode mixture layer) covers the entire negative electrode 156. It is possible to easily and appropriately inspect whether or not lithium is precipitated in the water. Moreover, according to the lithium precipitation inspection device 1 of the present embodiment and the lithium precipitation inspection method of the present embodiment, the amount of lithium precipitated on the surface 159b of the negative electrode mixture layer 159 (electrode mixture layer) is very small. Even in this case, this trace amount of precipitated lithium can be detected appropriately (with high accuracy).

In the above, the present invention has been described according to the embodiment, but it goes without saying that the present invention is not limited to the above-described embodiment and can be appropriately modified and applied without departing from the gist thereof.

For example, in the embodiment, a lithium precipitation inspection device 1 for inspecting whether or not lithium is deposited on the surface 159b of the negative electrode mixture layer 159 of the lithium ion secondary battery 100 has been exemplified. However, the lithium precipitation inspection device of the present invention is not limited to such a lithium precipitation inspection device, and any electrode may be used as long as it is an electrode in which lithium may be deposited on the surface of the electrode mixture layer. On the other hand, it can be applied to inspect whether or not lithium is deposited on the surface of the electrode mixture layer.

Further, in the embodiment, as the negative electrode to be inspected, a single-sided coating negative electrode 156 having the negative electrode mixture layer 159 only on the surface 158b of the negative electrode current collector foil 158 (current collector member) is exemplified. However, the negative electrode to be inspected in the present invention may be a double-sided coated negative electrode having a negative electrode mixture layer 159 on both the front surface 158b and the back surface of the negative electrode current collecting foil 158 (current collecting member). In this case, not only the negative electrode mixture layer 159 coated on the front surface 158b of the negative electrode current collector foil 158 (current collector member) but also the back surface of the negative electrode current collector foil 158 (current collector member) is coated. Even in the negative electrode mixture layer 159, lithium may be deposited on the surface thereof. Therefore, in the case of a negative electrode coated on both sides, it is advisable to inspect whether or not lithium is deposited on the negative electrode mixture layer 159 on both sides by using the lithium precipitation inspection device 1.
Further, in the embodiment, white light WL is used as the irradiation light emitted from the irradiation unit 10. However, the irradiation light in the present invention is not limited to white light. The irradiation light emitted from the irradiation unit may be light that includes each element of RGB (R, G, and B).

1 Lithium precipitation inspection device 10 Irradiation unit 20 Light receiving unit 30 Calculation unit 40 Judgment unit 100 Lithium ion secondary battery 110 Battery case 150 Electrode body 155 Positive electrode 156 Negative electrode 157 Separator 158 Negative electrode current collecting foil (collecting member)
158b Surface 159 Negative electrode mixture layer (electrode mixture layer)
159b Surface WL White light (irradiation light)
RL reflected light

Claims (1)

A lithium precipitation inspection device that inspects whether or not lithium is deposited on the surface of the electrode mixture layer among electrodes having an electrode mixture layer on the surface of the current collector member.
An irradiation unit that irradiates irradiation light toward the surface of the electrode mixture layer of the electrode,
A light receiving unit that receives the reflected light reflected by the electrode by irradiating the irradiation light and acquires image data in RGB format.
An arithmetic unit that calculates the hue angle and brightness for each pixel that constitutes the image data acquired by the light receiving unit, and
A lithium precipitation inspection apparatus including a determination unit for determining whether or not lithium is deposited on the surface of the electrode mixture layer based on the hue angle and the brightness calculated by the calculation unit.

Images