JP2021077582A - Inspection method for secondary battery - Google Patents

Abstract

To determine propriety of a secondary battery with respect to a charge/discharge cycle on the basis of an estimated rate of impregnation of an electrolyte in an electrode body which is obtained by utilizing ultrasonic waves.SOLUTION: An inspection method for a secondary battery includes an attenuation factor measurement step S01, an impregnation rate estimation step S02 and a determination step S03. In the attenuation factor measurement step S01, ultrasonic waves are transmitted to a battery container and ultrasonic waves transmitted through the battery container are received, thereby obtaining distribution of attenuation factors of ultrasonic waves. In the impregnation rate estimation step S02, an impregnation rate Ri of an electrolyte in an electrode body is estimated on the basis of the distribution obtained in the attenuation factor measurement step S01. In the determination step S03, propriety of the secondary battery with respect to a resistance increase rate is determined on the basis of a previously calculated correlation between a resistance increase rate of the secondary battery after a charge/discharge cycle and the impregnation rate Ri estimated in the impregnation rate estimation step, and a predetermined propriety reference relating to the resistance increase rate.SELECTED DRAWING: Figure 3

Description

The present invention relates to a method for inspecting a secondary battery.

For example, Japanese Patent Application Laid-Open No. 2010-181290 discloses a immersion inspection device that irradiates a battery cell with ultrasonic waves and determines the degree of immersion of the electrolytic solution in the electrode body based on the transmission intensity of the ultrasonic waves. .. According to the above publication, ultrasonic waves have a property of being easily transmitted through the battery case when the electrode body is sufficiently immersed in the electrolytic solution, and difficult to be transmitted when the electrode body is sufficiently immersed in the electrolytic solution. .. This immersion inspection device determines that the immersion of the electrolytic solution is completed when the intensity of the transmitted ultrasonic waves is equal to or higher than the threshold value found in advance, and the immersion of the electrolytic solution is completed when the intensity is equal to or lower than the threshold value. It is configured to determine that there is no such thing.

Japanese Unexamined Patent Publication No. 2010-181290

Here, we propose a method for determining the suitability for the charge / discharge cycle of the secondary battery based on the estimated impregnation rate of the electrolytic solution in the electrode body obtained by using ultrasonic waves.

The secondary battery inspection method proposed here includes a preparation step for preparing the secondary battery, a attenuation rate measurement step, an impregnation rate estimation step, and a determination step. The secondary battery includes an electrode body in which a positive electrode active material layer and a negative electrode active material layer are stacked with a separator interposed therebetween, an electrolytic solution, and a battery container in which the electrode body and the electrolytic solution are housed.
In the attenuation rate measuring step, ultrasonic waves are transmitted to at least the region where the electrode body is arranged in the battery container, and the ultrasonic waves transmitted through the battery container are received to obtain the distribution of the attenuation rate of the ultrasonic waves.
In the impregnation rate estimation step, the impregnation rate of the electrolytic solution into the electrode body is estimated based on the distribution obtained in the attenuation rate measurement step.
In the determination step, the previously obtained correlation between the resistance increase rate of the secondary battery after the charge / discharge cycle performed under predetermined conditions and the impregnation rate estimated in the impregnation rate estimation step, and the resistance increase rate The compatibility of the secondary battery with respect to the resistance increase rate is determined based on the predetermined conformance criteria for.

According to the above secondary battery inspection method, the charge / discharge cycle is performed by using the correlation between the impregnation rate and the resistance increase rate of the secondary battery after the charge / discharge cycle from the impregnation rate estimated in the impregnation rate estimation step. It is possible to identify a secondary battery that is not expected to meet the conformity criteria. Thereby, the suitability of the secondary battery for the charge / discharge cycle can be determined.

FIG. 1 is a schematic side view of a lithium ion secondary battery and an impregnation rate measuring device. FIG. 2 is a schematic diagram showing a method of estimating the impregnation rate of the electrolytic solution from the attenuation rate of ultrasonic waves. FIG. 3 is a flowchart of a process for determining suitability for high-rate deterioration evaluation of a lithium ion secondary battery. FIG. 4 is a graph showing the relationship between the result of the high rate deterioration evaluation and the impregnation rate of the electrolytic solution.

Hereinafter, an embodiment of the secondary battery inspection method proposed here will be described. The embodiments described herein are, of course, not intended to specifically limit the present invention. The present invention is not limited to the embodiments described herein, unless otherwise specified. In the figure, the upper, lower, front, and rear are represented by U, D, F, and Rr, respectively. The left and right directions are orthogonal to the vertical direction and the front-back direction. However, the upper, lower, front, rear, left, and right directions are merely for convenience of explanation, and do not limit the installation mode of the secondary battery or the inspection device.

FIG. 1 is a schematic side view of the secondary battery 10 and the impregnation rate measuring device 50. The type of the secondary battery 10 is not particularly limited, but here, it is a lithium ion secondary battery. A part of the lithium ion secondary battery 10 of FIG. 1 is shown as a cross-sectional view. As shown in FIG. 1, the lithium ion secondary battery 10 includes a battery container 20, an electrode body 30, a positive electrode side take-out portion 40, a negative electrode side take-out portion (not shown), and an electrolytic solution 45.

The battery container 20 contains the electrode body 30 and the electrolytic solution 45. The battery container 20 includes a case main body 21 and a lid 22 joined to the case main body 21. The case body 21 houses the electrode body 30 and the electrolytic solution 45. The case body 21 is a substantially rectangular parallelepiped flat square container. The case body 21 is open on one side between a pair of side surfaces forming opposite wide surfaces. The case body 21 is made of, for example, aluminum or an aluminum alloy. The lithium ion secondary battery 10 is a square battery here. However, the secondary battery 10 is not limited to the square battery. The secondary battery 10 may be, for example, a laminated battery in which the electrode body and the electrolytic solution are housed in a laminate. In that case, the laminate corresponds to the battery container. The lid 22 is attached so as to close the opening of the case body 21. The lid 22 is welded to the peripheral edge of the opening of the case body 21. The lid 22 is also made of, for example, aluminum or an aluminum alloy. In FIG. 1, the wide surface of the lithium ion secondary battery 10 faces in the front-rear direction, and extends in the up-down direction and the left-right direction (paper surface depth direction).

The electrode body 30 includes a positive electrode sheet 31, a negative electrode sheet 32, a first separator sheet 33, and a second separator sheet 34. In the electrode body 30, the positive electrode active material layer 31a formed on the positive electrode sheet 31 and the negative electrode active material layer 32a formed on the negative electrode sheet 32 form a separator (specifically, the first separator sheet 33 and the second separator sheet 34). It is sandwiched and stacked. The positive electrode sheet 31, the negative electrode sheet 32, the first separator sheet 33, and the second separator sheet 34 are long strip-shaped members, respectively. The first separator sheet 33, the positive electrode sheet 31, the second separator sheet 34, and the negative electrode sheet 32 are stacked in this order and wound in the case body 21. The electrode body 30 is housed in the case body 21 in a state of being covered with, for example, an insulating film (not shown).

A positive electrode active material layer 31a containing a positive electrode active material is formed on the positive electrode sheet 31. The positive electrode sheet 31 is a member in which a positive electrode active material layer 31a containing a positive electrode active material is formed on both surfaces of a metal foil (for example, an aluminum foil) having a predetermined width and thickness. In the lithium ion secondary battery 10, the positive electrode active material is a material that can release lithium ions during charging and absorb lithium ions during discharging, such as a lithium transition metal composite material.

A negative electrode active material layer 32a containing a negative electrode active material is formed on the negative electrode sheet 32. The negative electrode sheet 32 is a member in which a negative electrode active material layer 32a containing a negative electrode active material is formed on both surfaces of a metal foil (for example, copper foil) having a predetermined width and thickness. The negative electrode active material is a material that can occlude lithium ions during charging and release the lithium ions occluded during charging during discharging.

For the first separator sheet 33 and the second separator sheet 34, for example, a porous resin sheet having a required heat resistance and through which an electrolyte can pass is used. Various separator sheets 33 and 34 have been proposed and are not particularly limited.

The electrolytic solution 45 is housed in the case body 21. The electrolytic solution 45 is sealed in the case body 21 by the lid 22. For the electrolytic solution 45, for example, an organic solvent in which a lithium salt is dissolved is used. _{The electrolytic solution 45 contains, for example, LiPF 6} at a concentration of about 1 mol / L in a mixed solvent (for example, a volume ratio of 3: 4: 3) of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). A non-aqueous electrolyte solution or the like contained therein. However, various proposals have been made for the electrolytic solution 45, and the present invention is not particularly limited.

The positive electrode sheet 31 wound inside the case main body 21 is taken out of the case main body 21 by the positive electrode side take-out portion 40. The conductive portion of the positive electrode side take-out portion 40 is formed of, for example, aluminum or an aluminum alloy. The positive electrode side take-out portion 40 extends to the outside of the case body 21 through a through hole formed in the lid body 22. The negative electrode sheet 32 is connected to a negative electrode side take-out portion (not shown) provided at an end portion of the electrode body 30 opposite to the side of the positive electrode side take-out portion 40. The negative electrode sheet 32 is taken out of the case main body 21 by the negative electrode side take-out portion. The negative electrode side take-out portion has the same structure as the positive electrode side take-out portion 40. The conductive portion on the negative electrode side is formed of, for example, copper or a copper alloy.

As shown in FIG. 1, the impregnation rate measuring device 50 includes an ultrasonic transmitter 60, an ultrasonic receiver 70, a scanning device (not shown), and a control device 80.

The ultrasonic transmitter 60 includes a crystal oscillator and the like to generate ultrasonic waves. The ultrasonic waves generated by the ultrasonic transmitter 60 are irradiated toward the wide surface of the battery container 20. The ultrasonic receiver 70 is provided on the opposite side of the ultrasonic transmitter 60 with the lithium ion secondary battery 10 interposed therebetween. The ultrasonic transmitter 60 and the ultrasonic receiver 70 face each other with the lithium ion secondary battery 10 interposed therebetween. The ultrasonic receiver 70 is configured to measure the intensity of the irradiated ultrasonic waves. The ultrasonic receiver 70 receives ultrasonic waves transmitted from the ultrasonic transmitter 60 and transmitted through the battery container 20.

A scanning device (not shown) is configured to move the lithium ion secondary battery 10 in the vertical and horizontal directions. However, the scanning device may move the set of the ultrasonic transmitter 60 and the ultrasonic receiver 70 in the vertical direction and the horizontal direction. By moving the lithium ion secondary battery 10 in the vertical direction and the horizontal direction by the scanning device, ultrasonic waves are transmitted to the entire region of the battery container 20 in which the electrode body 30 is arranged without any gap. Preferably, the lithium ion secondary battery 10 is scanned so that the regions irradiated with ultrasonic waves move while partially overlapping.

The control device 80 is connected to the ultrasonic transmitter 60, the ultrasonic receiver 70, and the scanning device. The control device 80 is typically a computer, and includes a storage device (memory or the like) and an arithmetic unit (CPU or the like). Each function of the impregnation rate measuring device 50 can be appropriately embodied by the cooperation between the physical components and the control of the control device 80 based on the calculation result performed according to the predetermined program. The control device 80 includes an impregnation determination unit 81, an image creation unit 82, and an impregnation rate calculation unit 83.

The impregnation determination unit 81 determines whether the attenuation rate of the ultrasonic waves transmitted through the lithium ion secondary battery 10 exceeds a predetermined threshold value or is within the above threshold value. As described above, the ultrasonic wave has a characteristic that it easily permeates the inside of the battery container 20 when the electrode body 30 is sufficiently impregnated with the electrolytic solution 45, and is difficult to permeate when the electrode body 30 is sufficiently impregnated. Are known. In the region where the electrode body 30 of the battery container 20 is arranged, the portion where the ultrasonic attenuation rate exceeds the threshold value is determined to be the portion not impregnated with the electrolytic solution 45. In the region where the electrode body 30 of the battery container 20 is arranged, the portion where the ultrasonic attenuation rate is within the threshold value is determined to be the portion impregnated with the electrolytic solution 45. The threshold value is determined in advance based on, for example, the result of actually measuring the attenuation rate of the ultrasonic waves transmitted through the lithium ion secondary battery 10. Here, the impregnated state of the electrolytic solution 45 is binarized with one threshold value as a boundary, but may be multi-valued with a plurality of threshold values as boundaries.

The threshold value does not have to represent the attenuation rate of the boundary between the portion actually impregnated with the electrolytic solution 45 and the portion not impregnated with the electrolytic solution 45. As will be described in detail later, between the estimated impregnation rate of the electrolytic solution 45 calculated from the data binarized by the above threshold value and the resistance increase rate of the lithium ion secondary battery 10 after the high rate deterioration evaluation is performed. Has a correlation, and in the present embodiment, the suitability of the resistance increase rate of the lithium ion secondary battery 10 is determined based on the correlation. Therefore, it suffices to estimate the impregnation rate for the same type of secondary battery under the same measurement conditions and the same threshold value, and the suitability of the lithium ion secondary battery 10 regarding the resistance increase rate is determined by the electrolytic solution. It does not necessarily depend on the actual state of impregnation of 45.

The image creating unit 82 creates an image showing the distribution of the impregnated state of the electrode body 30 based on the determination of the impregnation determination unit 81. In the present embodiment, the image creation unit 82 creates an image in which the portion impregnated with the electrolytic solution 45 is painted in the first color and the portion not impregnated with the electrolytic solution 45 is painted in the second color.

The impregnation rate calculation unit 83 calculates the impregnation rate of the electrolytic solution 45 into the electrode body 30 by analyzing the image created by the image creation unit 82. FIG. 2 is a schematic view showing a method of estimating the impregnation rate of the electrolytic solution 45 from the attenuation rate of ultrasonic waves. The figure on the left side of FIG. 2 is an image I0 created by the image creation unit 82. In one process by the impregnation rate calculation unit 83, the portion of the image I0 having the second color (representing the unimpregnated portion) is cut out, and the image I1 is created. In the next processing by the impregnation rate calculation unit 83, the area S1 of the image I1 is obtained. In another process by the impregnation rate calculation unit 83, the entire image I0 is cut out and the image I2 is created. In the next processing by the impregnation rate calculation unit 83, the area S2 of the image I2 is obtained. In the next processing by the impregnation rate calculation unit 83, the estimated impregnation rate Ri = (S2-S1) / S2 is obtained. The estimated impregnation rate Ri is the ratio of the portion where the ultrasonic attenuation rate is equal to or less than the threshold value (in other words, the portion where the impregnation is considered to be completed) with respect to the region where the electrode body 30 is arranged.

Hereinafter, a process of determining suitability for high-rate deterioration evaluation of the lithium ion secondary battery 10 by using the estimated impregnation rate Ri of the electrolytic solution 45 will be described. FIG. 3 is a flowchart of a process for determining suitability for high-rate deterioration evaluation of the lithium ion secondary battery 10. As shown in FIG. 3, in the present embodiment, in step S00, a preparatory step for preparing the lithium ion secondary battery 10 is performed. In step S00, the lithium ion secondary battery 10 is set in the impregnation rate measuring device 50.

In the following step S01, ultrasonic waves are transmitted to at least the region where the electrode body 30 is arranged in the battery container 20, and the ultrasonic waves transmitted through the battery container 20 are received to obtain the distribution of the attenuation rate of the ultrasonic waves. Attenuation rate measurement step is performed. In this embodiment, the distribution is obtained by creating a color-coded image based on whether the ultrasonic attenuation factor exceeds a predetermined threshold (see FIG. 2). As a result, the ratio of the portion where the ultrasonic attenuation rate is equal to or less than the predetermined threshold value can be obtained with respect to the region where the electrode body 30 is arranged. The region where the electrode body 30 is arranged corresponds to the image I2 in FIG. In FIG. 2, the portion where the ultrasonic attenuation factor is equal to or less than the predetermined threshold value corresponds to the portion obtained by removing the image I1 from the image I2. In this embodiment, the lithium ion secondary battery 10 is scanned in the vertical direction and the horizontal direction in order to transmit ultrasonic waves to at least the region of the battery container 20 in which the electrode body 30 is arranged.

In step S02, an impregnation rate estimation step of estimating the impregnation rate of the electrolytic solution 45 into the electrode body 30 is performed based on the distribution obtained in the attenuation rate measurement step of step S01. Here, the ratio obtained in the attenuation rate measurement step of step S01 (the ratio of the portion where the attenuation rate of ultrasonic waves is equal to or less than a predetermined threshold value with respect to the region where the electrode body 30 is arranged) is directly applied to the electrode body 30. It becomes the estimated impregnation rate Ri of the electrolytic solution 45 of. However, for example, when the attenuation rate measurement data is multi-valued in the attenuation rate measurement step, the estimated impregnation rate Ri may be obtained through processing such as weighting of the multi-valued data. ..

In step S03, a determination step of determining the suitability of the lithium ion secondary battery 10 with respect to the resistance increase rate after the charge / discharge cycle performed under predetermined conditions is performed. This determination is made in advance regarding the correlation obtained in advance between the resistance increase rate of the lithium ion secondary battery 10 after the charge / discharge cycle and the estimated impregnation rate Ri estimated in the impregnation rate estimation step, and the resistance increase rate. Judgment is made based on the established conformity criteria. Here, the charge / discharge cycle is a high-rate charge / discharge cycle performed in a so-called high-rate deterioration evaluation. However, the charge / discharge cycle is not limited to the high rate charge / discharge cycle.

FIG. 4 is a graph showing the relationship between the result of the high rate deterioration evaluation and the impregnation rate of the electrolytic solution 45. FIG. 4 relates to one standard lithium ion secondary battery 10 and is an example. The horizontal axis of FIG. 4 is the number N of charge / discharge cycles (hereinafter referred to as precycles) performed to increase the impregnation rate. In the precycle, the impregnation rate of the electrolytic solution 45 into the electrode body 30 increases due to the movement of the electrolytic solution 45. FIG. 4 is a graph showing the relationship between the number of precycles and the impregnation rate of the electrolytic solution 45. With respect to the graph G1, the vertical axis of FIG. 4 is the estimated impregnation rate Ri of the electrolytic solution 45. The vertical axis of FIG. 4 is an estimated impregnation rate Ri estimated by the same method as described above, based on the measurement of the attenuation factor of the ultrasonic wave by the same method as described above. As shown in FIG. 4, the estimated impregnation rate Ri increases as the number of precycles increases.

Graph G2 of FIG. 4 is a graph showing the relationship between the number of precycles and the resistance increase rate of the lithium ion secondary battery 10 after evaluation of high rate deterioration. With respect to the graph G2, the vertical axis of FIG. 4 is the resistance increase rate of the lithium ion secondary battery 10 after the high rate deterioration evaluation. Here, the resistance increase rate of the lithium ion secondary battery 10 after the high rate deterioration evaluation is an increase rate based on the resistance value of the lithium ion secondary battery 10 before the high rate deterioration evaluation. In the high-rate deterioration evaluation, the lithium ion secondary battery 10 is subjected to, for example, 1000 cycles or more of charge / discharge cycles. The number of precycles is less than the number of charges and discharges in the high-rate deterioration test, for example, 100 times or less.

As shown in FIG. 4, the resistance increase rate of the lithium ion secondary battery 10 after the high rate deterioration evaluation becomes a constant value when the number of precycles becomes N1 or more. This indicates that the lithium ion secondary battery 10 that has been precycled for the number of times N1 or more has the resistance value converged by the time the charging / discharging of the predetermined number of cycles is completed in the high rate deterioration evaluation.

In FIG. 4, the estimated impregnation rate Ri when the number of precycles is N1 is R1. This indicates that in the lithium ion secondary battery 10 having an estimated impregnation rate Ri of R1 or more, the resistance value converges by the time the charging / discharging of the predetermined number of cycles is completed in the high rate deterioration evaluation. Therefore, from FIG. 4, a correlation can be obtained between the estimated impregnation rate Ri and the resistance increase rate that "the resistance value of the lithium ion secondary battery 10 having an estimated impregnation rate Ri of R1 or more converges in the high rate deterioration evaluation". This correlation has been obtained in advance by experiments and the like. A predetermined conformity criterion for the resistance increase rate of the lithium ion secondary battery 10 is "the resistance value converges in the high rate deterioration evaluation". Therefore, from FIG. 4, it can be seen that there is a high possibility that "the lithium ion secondary battery 10 having an estimated impregnation rate Ri of R1 or more conforms to the high rate deterioration evaluation". In the present embodiment, the lithium ion secondary battery 10 having an estimated impregnation rate Ri of R1 or more is treated as a conforming product conforming to the high rate deterioration evaluation.

As shown in FIG. 3, in the determination step of step S03, it is determined whether or not the estimated impregnation rate Ri of the lithium ion secondary battery 10 is R1 or more. When the estimated impregnation rate Ri is R1 or more (when the result of step S03 is Yes), the lithium ion secondary battery 10 is treated as conforming to the high rate deterioration evaluation. When the estimated impregnation rate Ri is less than R1 (when the result of step S03 is No), the evaluation of whether or not the lithium ion secondary battery 10 conforms to the high rate deterioration evaluation is suspended. In that case, the process proceeds to step S04.

In steps S01 to S03 of forming a loop based on the results of steps S04, S05, and S04, the lithium ion secondary battery 10 is precycled, and the number of precycles N is counted. Further, the estimated impregnation rate Ri is obtained every time a predetermined number of precycles (for example, once, but may be a plurality of times) are performed. The maximum number Nmax is set for the number N of precycles. In step S04, it is determined whether or not the number N of precycles is less than the maximum number Nmax of precycles. When the number of precycles N is less than the maximum number Nmax of precycles (when the result of step S04 is Yes), the lithium ion secondary battery 10 is precycled in step S05. The precycle conditions may be the same as or different from the high rate deterioration evaluation conditions.

After step S05, step S01 is repeated again. That is, the lithium ion secondary battery 10 is irradiated with ultrasonic waves to obtain the distribution of the attenuation rate of the ultrasonic waves. Further, in the second step S02, the estimated impregnation rate Ri after the precycle is obtained. In the second step S03 that follows, the determination step of determining the suitability of the lithium ion secondary battery 10 for the high-rate deterioration evaluation is performed again. Specifically, it is determined whether or not the estimated impregnation rate Ri after the precycle has reached the threshold value R1. The lithium ion secondary battery 10 that has passed the second step S03 is treated as a conforming product that conforms to the high rate deterioration evaluation. The determination of suitability for the high-rate deterioration evaluation of the lithium ion secondary battery 10 that failed in the second step S03 is suspended again, and the process proceeds to step S04. Hereinafter, the same loop is repeated until the result of step S03 becomes Yes (passes) or the result of step S04 becomes No.

When the result of step S04 is No (when the number of precycles N reaches the maximum number Nmax), the lithium ion secondary battery 10 is treated as a nonconforming product that does not conform to the high rate deterioration evaluation. In one preferred example, the maximum number of precycles Nmax may be set equal to the number of precycles N1 at which the estimated impregnation rate Ri of the standard lithium ion secondary battery 10 reaches R1. This is because the lithium ion secondary battery 10 in which the estimated impregnation rate Ri of the standard lithium ion secondary battery 10 does not reach R1 even after the precycle of the number of precycles N1 at which the estimated impregnation rate Ri reaches R1 is further increased. This is because the estimated impregnation rate Ri is unlikely to reach R1 even after pre-cycle, and is unlikely to meet the high-rate deterioration evaluation.

Alternatively, the maximum number of precycles Nmax may be set slightly larger than the number of precycles N1 in FIG. 4 in consideration of the variation of the lithium ion secondary battery 10. Alternatively, the maximum number of precycles Nmax may be set smaller than the number of precycles N1 in FIG. 4 in the sense that the inspection standard is set more strictly. In addition, for example, when the ratio of the lithium ion secondary battery 10 passing in the first step S03 is high and it is more efficient to take the rejected product out of the process than to perform the precycle, step S04, S05 and subsequent loops need not be performed.

As described above, in the method for inspecting the secondary battery according to the present embodiment, ultrasonic waves are transmitted to at least the region where the electrode body 30 is arranged in the battery container 20, and the ultrasonic waves transmitted through the battery container 20 are received. The impregnation rate for obtaining the estimated impregnation rate Ri of the electrolytic solution 45 in the electrode body 30 based on the attenuation rate measurement step S01 for obtaining the distribution of the attenuation rate of ultrasonic waves and the distribution obtained in the attenuation rate measurement step S01. Lithium ion regarding the resistance increase rate based on the correlation between the estimation step S02 and the resistance increase rate and the estimated impregnation rate Ri of the lithium ion secondary battery 10 after the charge / discharge cycle, and the conformity criteria for the resistance increase rate. The determination step S03 for determining the suitability of the secondary battery 10 is included. According to such an inspection method, from the estimated impregnation rate Ri obtained in the impregnation rate estimation step S02, the correlation between the estimated impregnation rate Ri and the resistance increase rate of the lithium ion secondary battery 10 after the charge / discharge cycle is used. It is possible to identify the lithium ion secondary battery 10 that is not expected to meet the conformity criteria in the charge / discharge cycle.

It takes, for example, several days to perform a general high-rate deterioration evaluation. On the other hand, according to the findings of the inventor of the present application, it takes only a few minutes to obtain the estimated impregnation rate Ri of the electrolytic solution 45 in the electrode body 30. Therefore, by determining the suitability of the charge / discharge cycle of the lithium ion secondary battery 10 by the above method, the time required for the evaluation of the lithium ion secondary battery 10 can be significantly shortened.

Further, the secondary battery inspection method according to the present embodiment further includes a precycle step S05 in which the lithium ion secondary battery 10 determined not to satisfy the conformity criteria is charged and discharged under predetermined conditions. Includes. After the precycle step S05, the attenuation rate measurement step S01, the impregnation rate estimation step S02, and the determination step S03 are repeated. By such a method, among the lithium ion secondary batteries 10 that have not been once determined to meet the conformity criteria, those that have met the conformity criteria by precycle can be selected. As a result, non-conforming products due to non-compliance with the standards can be reduced.

In the above, various methods for inspecting the secondary battery proposed here have been described. Unless otherwise specified, the embodiments of the secondary battery inspection method mentioned here do not limit the present invention.

10 Lithium ion secondary battery 20 Battery container 21 Case body 22 Lid body 30 Electrode body 31 Positive electrode sheet 31a Positive electrode active material layer 32 Negative electrode sheet 32a Negative negative active material layer 33 First separator sheet 34 Second separator sheet 40 Positive electrode side take-out part 45 Electrodeole 50 Impregnation rate measuring device 60 Ultrasonic transmitter 70 Ultrasonic receiver 80 Control device 81 Impregnation judgment unit 82 Image creation unit 83 Impregnation rate calculation unit

Claims (1)

Prepare a secondary battery including an electrode body in which a positive electrode active material layer and a negative electrode active material layer are stacked with a separator interposed therebetween, an electrolytic solution, and a battery container containing the electrode body and the electrolytic solution. Preparation process and
Attenuation rate measuring step of transmitting ultrasonic waves to at least the region where the electrode body is arranged in the battery container and receiving the ultrasonic waves transmitted through the battery container to obtain the distribution of the attenuation rate of the ultrasonic waves. ,
An impregnation rate estimation step for estimating the impregnation rate of the electrolytic solution into the electrode body based on the distribution obtained in the attenuation rate measurement step, and an impregnation rate estimation step.
A predetermined correlation between the resistance increase rate of the secondary battery after the charge / discharge cycle performed under predetermined conditions and the impregnation rate estimated in the impregnation rate estimation step, and the resistance increase rate in advance. A determination step for determining the compatibility of the secondary battery with respect to the resistance increase rate based on the defined conformance criteria, and
Secondary battery inspection methods, including.

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