Method for manufacturing secondary battery and use thereof

Abstract

To provide a technique for manufacturing a secondary battery outstanding in a high rate resistant property with a high precision.SOLUTION: A manufacturing method disclosed herein includes: a constructing step S10 for constructing a battery assembly in which an electrode body and an electrolytic solution are accommodated inside a battery case; an increase amount measuring step S20 for performing an inspection charge on the battery assembly for a predetermined period so as to measure an increase amount LΔ of the excess electrolytic solution for the inspection charge; and a first determination step S30 for selecting the battery assembly, whose increase amount LΔ of the excess electrolytic solution is equal to or less than a predetermined upper limit threshold LMAX as a good quality product. This wording "increase amount LΔ of the excess electrolytic solution" represents an amount of the electrolytic solution having flown out to an outside of the electrode body due to an expansion of the electrode for the inspection charge, and thus a high rate resistant property of the battery assembly can be evaluated properly. Therefore, by selecting the battery assembly whose increase amount LΔ of the excess electrolytic solution becomes equal to or less than the upper limit threshold LMAX, as a good quality product, the secondary battery outstanding in the high rate resistant property can be manufactured with a high precision.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The technology disclosed herein relates to a method for manufacturing a secondary battery and a technology using the manufacturing method.

Background Art

[0002] Secondary batteries such as lithium-ion secondary batteries are widely used in various fields. This secondary battery has, for example, a configuration in which an electrolytic solution and an electrode body are housed in a battery case. In the secondary battery having such a configuration, the electrolytic solution penetrates inside the electrode body (between the positive electrode and the negative electrode). Further, in this type of secondary battery, surplus electrolytic solution that does not penetrate inside the electrode body may be generated outside the electrode body (between the electrode body and the battery case). Thereby, when the electrolytic solution inside the electrode body becomes insufficient, the electrolytic solution can be supplied to the inside of the electrode body.

[0003] Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2021-170436) discloses a method for determining whether a secondary battery can be reused based on the liquid volume of surplus electrolytic solution. Specifically, the inspection method described in Patent Document 1 includes a step of irradiating the secondary battery with X-rays or ultrasonic waves and measuring the transmittance thereof, a step of calculating the surplus liquid volume of the electrolytic solution based on the transmittance, and a step of determining whether the secondary battery can be reused according to the surplus liquid volume. It is thereby said that it is possible to determine whether a secondary battery can be reused non-destructively.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Incidentally, in the secondary battery having the above configuration, a degradation phenomenon (high-rate degradation) in which the battery resistance rapidly increases may occur during rapid charging. This high-rate degradation occurs when the electrolytic solution inside the electrode body flows out due to the expansion of the electrode (especially the negative electrode) during rapid charging. Therefore, even if the surplus electrolytic solution is measured for an uncharged secondary battery, it is difficult to determine whether the resistance to high-rate degradation (high-rate tolerance) is excellent. The technology disclosed herein has been made to solve such problems, and an object thereof is to provide a technology for manufacturing a secondary battery excellent in high-rate tolerance with high accuracy.

Means for Solving the Problems

[0006] In order to solve the above problems, a method for manufacturing a secondary battery having the following configuration (hereinafter, also simply referred to as "manufacturing method") is provided by the technology disclosed herein.

[0007] The manufacturing method disclosed herein includes a construction step of constructing a battery assembly in which an electrode body and an electrolytic solution are housed in a battery case, and a test charge is performed on the battery assembly for a predetermined period, and the increase amount L Δ of the surplus electrolytic solution in the test charge is measured. Δ A first determination step of selecting a battery assembly in which the increase amount L MAX of the surplus electrolytic solution is equal to or less than a predetermined upper limit threshold value L

[0008] As described above, in the manufacturing method disclosed herein, the increase amount L Δ of the surplus electrolytic solution in the test charge is measured. This "increase amount L Δ of the surplus electrolytic solution" indicates the amount of the electrolytic solution that has flowed out of the electrode body due to the expansion of the electrode during the test charge. That is, a battery assembly with a small increase amount L Δ of the surplus electrolytic solution can be regarded as a battery in which the outflow of the electrolytic solution (high-rate degradation) during charging is less likely to occur. Therefore, by selecting a battery assembly in which the increase amount L Δ of the surplus electrolytic solution is equal to or less than the upper limit threshold value L MAX as a non-defective product, a secondary battery excellent in high-rate tolerance can be manufactured with high accuracy.

[0009] Also, in a preferred embodiment of the manufacturing method disclosed herein, the increased amount L of the excess electrolytic solution Δ is such that a battery assembly with an increased amount of excess electrolytic solution L equal to or greater than a predetermined lower threshold value L MIN is further included in a second determination step of selecting the battery assembly as a non-defective product. By this means, it is possible to remove a battery assembly in which some abnormality may be occurring in the charge-discharge reaction.

[0010] Also, in a preferred embodiment of the manufacturing method disclosed herein, the increased amount L of the excess electrolytic solution Δ is calculated by the following formula (1), where the liquid amount of the excess electrolytic solution before the start of the inspection charge is defined as the initial liquid amount L0, the liquid amount of the excess electrolytic solution at a predetermined point during the inspection charge is defined as the inspection liquid amount L1, and the total amount of the electrolytic solution present in the battery case is defined as the total liquid amount L T . By this means, it is possible to measure the increased amount L of the excess electrolytic solution that accurately reflects the high-rate tolerance of the battery assembly. Δ L Δ = (L1 - L0) / L T (1)

[0011] Also, in a preferred embodiment of the manufacturing method disclosed herein, the liquid amount of the excess electrolytic solution is measured based on image analysis of an X-ray transmission image of the battery assembly. By this means, it is possible to accurately measure the liquid amount of the excess electrolytic solution.

[0012] Also, in a preferred embodiment of the manufacturing method disclosed herein, in the image analysis of the X-ray transmission image, a measurement line along the side surface of the battery case is set in the region between the electrode body and the battery case, and the liquid amount of the excess electrolytic solution is measured by analyzing the change in luminance on the measurement line. By this means, it is possible to more accurately measure the liquid amount of the excess electrolytic solution.

[0013] Also, in a preferred embodiment of the manufacturing method disclosed herein, the X-ray transmission image is captured with the battery assembly tilted at a predetermined tilt angle θ. By this means, it is possible to more accurately measure the liquid amount of the excess electrolytic solution.

[0014] Also, in a preferred embodiment of the manufacturing method disclosed herein, the battery case is formed of aluminum and resin. Thereby, a clear X-ray transmission image can be easily obtained.

[0015] Also, in a preferred embodiment of the manufacturing method disclosed herein, the upper limit threshold L MAX is set within the range of 0.05% to 10%. Thereby, a secondary battery particularly excellent in high-rate tolerance can be manufactured with high accuracy.

[0016] Also, in a preferred embodiment of the manufacturing method disclosed herein, the inspection liquid volume L1 is measured when the SOC of the battery assembly reaches a predetermined inspection value set within the range of 60% to 90%. Thereby, the increase amount L Δ of the surplus electrolyte that more accurately reflects the high-rate tolerance of the battery assembly can be measured.

[0017] Also, as another aspect of the technology disclosed herein, a battery pack is provided. The battery pack disclosed herein includes at least a plurality of single cells and a connection member that electrically connects each of the plurality of single cells. And, in the battery pack disclosed herein, 90% or more of the plurality of single cells are secondary batteries in which the increase amount L Δ of the surplus electrolyte in the inspection charge for a predetermined period is MAX equal to or less than a predetermined upper limit threshold L.

[0018] According to the technology disclosed herein, a secondary battery excellent in high-rate tolerance can be manufactured with high accuracy. As a result, a battery pack can be realized in which most (90% or more) of the single cells included in the battery pack are secondary batteries excellent in high-rate tolerance. Such a battery pack can exhibit high performance as a whole.

[0019] Also, in a preferred embodiment of the battery pack disclosed herein, all of the plurality of single cells are secondary batteries in which the increase amount L Δ of the surplus electrolyte is MAX equal to or less than the upper limit threshold L. Such a battery pack can perform control capable of exhibiting very high performance as a whole.

[0020] In a preferred embodiment of the battery pack disclosed herein, there are 20 or more single cells. According to the technology disclosed herein, even a battery pack having a large number of 20 or more single cells can be mostly constructed of a secondary battery with excellent high-rate tolerance.

Brief Description of the Drawings

[0021]

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Embodiments for Carrying Out the Invention

[0022] <First Embodiment> Hereinafter, an embodiment of the technology disclosed herein will be described in detail with reference to the drawings. Note that matters other than those specifically mentioned in this specification and matters necessary for the implementation of the technology disclosed herein can be grasped as design matters of those skilled in the art based on the prior art in the relevant field. The technology disclosed herein can be implemented based on the content disclosed in this specification and the common general knowledge in the relevant field. In the following drawings, members and parts having the same function are denoted by the same reference numerals for description. Furthermore, the dimensional relationships (length, width, thickness, etc.) in each figure do not reflect the actual dimensional relationships.

[0023] 1. Method for manufacturing secondary battery First, an embodiment of the method for manufacturing a secondary battery disclosed herein will be described. FIG. 1 is a flowchart for explaining the manufacturing method according to this embodiment. FIG. 2 is a perspective view schematically showing the appearance of the battery assembly. FIG. 3 is a longitudinal sectional view schematically showing the internal structure of the battery assembly shown in FIG. 2. FIG. 4 is a flowchart for explaining an example of the increase amount measurement step. FIG. 5 is a longitudinal sectional view for explaining an example of the procedure for measuring the liquid volume of the excess electrolyte. FIG. 6 is an example of an X-ray transmission image of the battery assembly. FIG. 7 is the measurement line M L in FIG. 6, which is a line profile showing the change in luminance. FIG. 8 is a graph showing the relationship between the increase amount L Δ (%) of the excess electrolyte and the resistance increase rate (%). Note that in the figures described in this specification, the reference symbol X indicates the width direction, the reference symbol Y indicates the depth direction, and the reference symbol Z indicates the height direction. Furthermore, the reference symbols L, R, F, Rr, U, and D indicate the left, right, front, rear, upper, and lower directions, respectively. However, these directions are defined for convenience of explanation and are not intended to limit the usage mode of the secondary battery after manufacturing.

[0024] As shown in FIG. 1, the manufacturing method according to this embodiment includes at least a construction step S10, an increase amount measurement step S20 of the excess electrolyte, and a first determination step S30. The manufacturing method according to this embodiment also includes a non-defective product labeling step S40 and a defective product labeling step S50. Hereinafter, each step will be described.

[0025] (1) Construction process S10 In this process, a battery assembly 1 in which an electrode body 20 and an electrolyte 30 are housed in a battery case 10 is constructed (see FIGS. 2 and 3). Note that the "battery assembly" in this specification refers to a structure in which the components of a secondary battery are assembled so as to be chargeable and dischargeable, and for which the evaluation of high-rate resistance has not been performed. And the "secondary battery" in this specification refers to a battery assembly that has a certain high-rate resistance and has been determined to be ready for shipment. That is, the battery assembly 1 shown in FIGS. 2 and 3 has the same configuration as a secondary battery after shipment, except that the processes S20 to S40 described later have not been performed. Hereinafter, an example of the structure of the battery assembly 1 will be described.

[0026] (1-a) Battery case The battery case 10 is a box-shaped container having an internal space. The electrode body 20 and the electrolyte 30 are housed in the internal space of the battery case 10. As shown in FIGS. 2 and 3, the battery case 10 in the present embodiment is a flat rectangular parallelepiped container. Specifically, the battery case 10 includes a case body 14 which is a box-shaped member having an upper surface opening, and a sealing plate 12 which is a plate-shaped member that closes the upper surface opening of the case body 14. When acquiring an X-ray transmission image in the later-described increase amount measurement process S20, the battery case 10 is preferably formed of aluminum (including an aluminum alloy), resin, or the like. The battery case 10 formed of these materials has a high X-ray transmittance, so that a clear X-ray transmission image can be acquired in the increase amount measurement process S20.

[0027] In addition, the sealing plate 12 is provided with a liquid injection hole 12a for injecting the electrolyte 30 into the battery case 10. Note that this liquid injection hole 12a is sealed with a sealing member 16 after the injection of the electrolyte 30. Further, a pair of electrode terminals 40 are attached to the sealing plate 12. Each electrode terminal 40 is a structure in which a plurality of conductive members are combined, and extends along the height direction Z. And the current collecting member 40a constituting the lower end portion of the electrode terminal 40 is connected to the electrode body 20 inside the battery case 10.

[0028] (1 - b) Electrode body The electrode body 20 is a member in which a positive electrode and a negative electrode face each other via a separator. As an example of the structure of such an electrode body 20, a wound electrode body, a laminated electrode body, etc. can be mentioned. The wound electrode body is formed by winding a long sheet-like positive electrode, negative electrode, and separator. On the other hand, the laminated electrode body is formed by alternately laminating short positive electrodes and negative electrodes so that a separator is interposed between the electrodes. Note that the constituent members of the electrode body 20 (positive electrode, negative electrode, separator, etc.) can use materials that can be used in general secondary batteries without particular limitation, and since they do not limit the technology disclosed herein, detailed description thereof is omitted.

[0029] (1 - c) Electrolyte solution The electrolyte solution 30 is a liquid electrolyte that moves charge carriers between the positive electrode and the negative electrode. Most of the electrolyte solution 30 has penetrated inside the electrode body 20 (between the positive electrode and the negative electrode). Also, in the present embodiment, an excess electrolyte solution 32 that does not penetrate inside the electrode body 20 exists outside the electrode body 20 (between the electrode body 20 and the battery 10 case). Thereby, when the electrolyte solution 30 inside the electrode body 20 is insufficient, the electrolyte solution 30 can be supplied to the inside of the electrode body 20. Note that the electrolyte solution 30 can also be used without particular limitation as long as it can be used in general secondary batteries.

[0030] (2) Increase amount measurement step S20 In the excess electrolyte solution increase amount measurement step S20, the battery assembly 1 is subjected to inspection charging for a predetermined period, and the increase amount L of the excess electrolyte solution in the inspection charging is measured. Δ This "increase amount L of the excess electrolyte solution" indicates the amount of the electrolyte solution 30 that has flowed out to the outside of the electrode body 20 due to the expansion of the electrode during the inspection charging. That is, it can be considered that the battery assembly 1 with a large increase amount L of the excess electrolyte solution is likely to cause high-rate deterioration due to the outflow of the electrolyte solution 30. On the other hand, the battery assembly 1 with a small increase amount L of the excess electrolyte solution can be considered to have excellent high-rate resistance. Δ Δ Δ

[0031] The following is an example of the measurement procedure for the "increase amount L of the excess electrolyte" in the increase amount measurement step S20 Δ in the increase amount measurement step S20. As shown in FIG. 4, the increase amount measurement step S20 in the present embodiment includes measurement S21 of the initial liquid amount L0, start S22 of the inspection charge, measurement S23 of the inspection liquid amount L1, acquisition S24 of the total liquid amount L T , and calculation S25 of the increase amount L Δ .

[0032] (2-a) Measurement S21 of the initial liquid amount L0 In this increase amount measurement step S20, first, measurement S21 of the initial liquid amount L0 is performed. The "initial liquid amount L0" measured here is the liquid amount (ml) of the excess electrolyte before the start of the inspection charge. Note that the battery assembly 1 used for the measurement S21 of the initial liquid amount L0 is preferably the battery assembly 1 after the initial charge and discharge and the aging process are performed. Thereby, since the liquid amount of the excess electrolyte of the battery assembly 1 with less uneven distribution of the electrolyte 30 in the electrode body 20 can be set as the "initial liquid amount L0", the increase amount L of the excess electrolyte described later Δ can be calculated more accurately. Specifically, the measurement S21 of the initial liquid amount L0 is preferably performed on a battery assembly with an SOC of 10% to 20% (for example, about 17%) after the aging process.

[0033] Note that the "liquid amount (ml) of the excess electrolyte" is preferably measured based on the image analysis of the X-ray transmission image of the battery assembly 1. Thereby, the liquid amount of the excess electrolyte 32 can be accurately measured. Hereinafter, the measurement of the liquid amount of the excess electrolyte using the X-ray transmission image will be specifically described.

[0034] First, it is preferable to capture an X-ray transmission image of the battery assembly 1 with the battery assembly 1 tilted at a predetermined tilt angle θ. For example, in the example shown in FIG. 5, the battery assembly 1 held by the restraint member B is placed on a pedestal P having an installation surface tilted at a predetermined tilt angle θ (for example, 45°). As a result, surplus electrolytic solution 32 is collected in the vicinity of the corner 10c1, which is the one arranged downward D in the height direction Z, among the corners 10c1 and 10c2 on the bottom surface 10b side of the battery case 10. In this state, by capturing an X-ray transmission image of the region A including the corner 10c1, accurate measurement can be performed even when the amount of the surplus electrolytic solution 32 is small. Note that the imaging conditions of the X-ray transmission image are preferably adjusted as appropriate to conditions that can accurately recognize the liquid surface 32a of the surplus electrolytic solution 32. As an example, the tube voltage of the X-ray irradiation device is preferably set in the range of 125 kV to 175 kV (for example, 150 kV). Also, the tube current is preferably set in the range of 175 μA to 225 μA (for example, 200 μA).

[0035] Also, as described above, in the present embodiment, an X-ray transmission image is captured with the flat surface 10f (see FIG. 2) of the battery case 10 sandwiched between a pair of restraint members B and a restraint pressure applied thereto. Thereby, the high-rate resistance in a state where the actual usage situation of the secondary battery is appropriately reflected can be evaluated. Note that the restraint pressure at this time is preferably set so that a load of 15 kN to 25 kN (for example, about 20 kN) is applied to the battery assembly 1 with an SOC of 17%. Also, the restraint member B is preferably a member made of a transparent resin. Thereby, an X-ray transmission image that is easy to analyze can be obtained.

[0036] Next, an example of the procedure for analyzing the X-ray transmission image will be described with reference to FIG. 6. In this image analysis, first, a measurement line M extending along the side surface 10s of the battery case 10 is set in the region between the electrode body 20 and the battery case 10 in the captured X-ray transmission image. L is set. Then, using a predetermined image analysis software (such as Image-J), the measurement line M LAnalyze the change in luminance above. For example, in the analysis result shown in FIG. 7, the luminance value rapidly decreases near 100 pixels. This is because the X-ray transmittance in the region where the excess electrolyte 32 exists is low. That is, in FIG. 7, it can be considered that the liquid surface 32a of the excess electrolyte 32 exists at a position near 100 pixels. Next, in FIG. 7, the luminance value further decreases at a position near 400 pixels. This is because it has reached the bottom surface 10b of the battery case 1 with almost no X-ray transmittance. From this, in the analysis result shown in FIG. 7, it can be analyzed that the excess electrolyte 32 exists in the region of 100 to 400 pixels. And in this embodiment, a preliminary test for determining the relational expression between "the existing region (pixels) of the excess electrolyte 32 in the X-ray transmission image" and "the liquid volume (ml) of the actual excess electrolyte" is carried out in advance. Thereby, the liquid volume (ml) of the excess electrolyte can be measured based on the existing region of the excess electrolyte 32 on the X-ray transmission image.

[0037] (2-b) Start of inspection charging S22 Next, in the increase amount measurement step S20, inspection charging for charging the battery assembly 1 under predetermined conditions is started (S22). Note that the conditions for the inspection charging are set so that the outflow of the electrolyte 30 due to the expansion of the electrode body 20 can occur. For example, in the inspection charging, it is preferable to perform so-called rapid charging (high-rate charging). Thereby, since a certain amount or more of the electrolyte 30 flows out during the inspection charging, the increase amount L Δ of the excess electrolyte can be easily calculated. Note that the detailed conditions for the inspection charging are appropriately set according to the dimensions and materials of the battery assembly 1 and the like, and since they are not elements that limit the technology disclosed herein, detailed description thereof is omitted.

[0038] (2-c) Measurement of inspection liquid volume L1 S23 Next, in the increase amount measurement step S20, the measurement S23 of the inspection liquid volume L1 is performed. The "inspection liquid volume L1" measured here is the liquid volume (mL) of the excess electrolyte at a predetermined time point during the inspection charging. For example, the inspection liquid volume L1 is measured when the SOC of the battery assembly 1 reaches an inspection value set within the range of 60% to 90% (for example, about 78%). Thus, since the liquid volume of the excess electrolyte in a state where the inspection charging has sufficiently progressed can be defined as the "inspection liquid volume L1", the high-rate tolerance of the battery assembly 1 can be evaluated more accurately. Also, the inspection liquid volume L1 is measured in the same procedure as the initial liquid volume L0, except that the battery assembly 1 during the inspection charging is the measurement target. That is, the inspection liquid volume L1 can be measured based on the image analysis of the X-ray transmission image of the battery assembly 1. Since the measurement of the inspection liquid volume L1 based on this X-ray transmission image would result in duplicate explanations, the explanation here is omitted.

[0039] (2-d) Total liquid volume L T Acquisition S24 In the increase amount measurement step S20, next, the total amount of the electrolyte 30 present in the battery case 10 (total liquid volume L T ) is acquired (S24). The "total liquid volume L T " here is the total amount of the excess electrolyte 32 present outside the electrode body 20 and the electrolyte 30 that has penetrated inside the electrode body 20. By reflecting the total liquid volume L Δ in the calculation of the increase amount L T of the excess electrolyte described later, the high-rate tolerance of the battery assembly 1 can be evaluated regardless of the amount of electrolyte injected for the electrolyte 30. Note that for the total liquid volume L T of the electrolyte 30, the standard value at the time of battery design may be used, or the measured value measured at the time of construction of the battery assembly 1 (when injecting the electrolyte 30) may be used.

[0040] (2-e) Increase amount L Δ Calculation S25 And in this step, based on each parameter acquired in S21 to S24, the increase amount L Δ of the excess electrolyte is calculated (S25). Specifically, the increase amount L Δ of the excess electrolyte is the initial liquid volume L0, the inspection liquid volume L1, and the total liquid volume L TBased on this, it can be calculated by the following formula (1). The increased amount L of the surplus electrolyte Δ is the amount of electrolyte (L1 - L0) that has flowed out of the electrode body due to the expansion of the electrode during the inspection charge, normalized by the total amount L of the electrolyte 30 T is the value. L Δ =(L1 - L0) / L T (1)

[0041] (3) The first determination step S30 Next, in the manufacturing method according to the present embodiment, the increased amount L of the surplus electrolyte Δ is less than or equal to a predetermined upper limit threshold value L MAX The first determination step S30 is performed to select the battery assembly 1 as a non-defective product. Specifically, in the first determination step S30, the increased amount L of the surplus electrolyte Δ and the upper limit threshold value L MAX are compared. The upper limit threshold value L MAX at this time is appropriately set according to the specifications of the secondary battery to be manufactured. For example, the upper limit threshold value L MAX can be set within the range of 0.05% to 10%.

[0042] And when the increased amount L of the surplus electrolyte Δ exceeds the upper limit threshold value L MAX (in the case of S30: NO), it is understood that a large amount of electrolyte has flowed out of the electrode body 20 during the inspection charge. In this case, the battery assembly 1 to be inspected is determined to be a battery with low high-rate resistance and is subjected to the defective product labeling step S50. In the defective product labeling step S50, it is labeled that the battery assembly 1 to be inspected is a defective product. Then, the battery assembly 1 after defective product labeling is subjected to reinspection, correction processing, disposal, etc.

[0043] On the other hand, when the increased amount L of the surplus electrolyte Δ is less than or equal to the upper limit threshold value L MAXIf the following is true (S30: YES), it is understood that the amount of electrolyte 30 leaking during inspection charging is small. In this case, the battery assembly 1 to be inspected is determined to be a battery with excellent high-rate resistance, and is sent to a good-quality labeling process S40. In the good-quality labeling process S40, the battery assembly 1 to be inspected is labeled as a good-quality product. After being labeled as a good-quality product, the battery assembly 1 is then determined to be a shippable secondary battery, and is shipped after any necessary post-processing (such as construction of a battery pack) is performed.

[0044] (4) Summary As described above, in the method for producing a secondary battery according to the present embodiment, the increase in the amount of excess electrolyte during test charging L Δ Measure the increase in the excess electrolyte L Δ The quality of the battery assembly 1 is judged based on the amount of excess electrolyte increase L Δ indicates the amount of electrolyte 30 that flows out due to the expansion of the electrodes during the test charge. That is, the increase in the amount of excess electrolyte L Δ The battery assembly 1 with less electrolyte leakage is less likely to occur during charging, and can be said to have excellent high-rate resistance. This is also supported by experiments conducted by the present inventor. Specifically, as shown in FIG. 8, the increase in the amount of excess electrolyte during test charging L Δ It has been confirmed that the smaller the amount of increase in resistance during high-rate charging, the lower the increase in the amount of excess electrolyte L Δ Since the quality of the battery assembly 1 is judged based on this, a secondary battery with excellent high-rate resistance can be manufactured with high accuracy.

[0045] 2. Battery pack Next, the manufacturing method according to this embodiment can contribute to improving the performance of the battery pack 100 having the configuration shown in Fig. 9. This will be specifically described below.

[0046] As shown in FIG. 9, the assembled battery 100 according to the present embodiment includes a plurality of single batteries 110. Each single battery 110 is arranged such that the flat surfaces 10f (see FIG. 2) of the battery cases 10 face each other. Further, a spacer 120 is disposed between two adjacent single batteries 110. Then, the plurality of single batteries 110 are sandwiched between a pair of restraint plates 130. The pair of restraint plates 130 are connected by a crosslinking member 140 extending along the arrangement direction (the depth direction Y in FIG. 9). Thereby, each single battery 110 is restrained with a predetermined restraint pressure. Further, the assembled battery 100 shown in FIG. 9 includes a connection member 150 that electrically connects each of the plurality of single batteries 110. The connection member 150 connects the electrode terminals 40 of adjacent single batteries 110. Thereby, the assembled battery 100 having a plurality of single batteries 110 can be used as one battery unit.

[0047] And in the assembled battery 100 according to the present embodiment, in 90% or more of the plurality of single batteries 110, the increase amount L of the excess electrolyte Δ is the secondary battery that is equal to or less than the upper limit threshold value L MAX is used. In other words, most of the single batteries 110 in the present embodiment are secondary batteries determined to be non-defective in the first determination step S30. Thereby, since an assembled battery 100 in which most of the single batteries having excellent high-rate resistance can be constructed, high-rate deterioration hardly occurs even during rapid charge and discharge. For this reason, the assembled battery 100 according to the present embodiment can exhibit high performance as an entire battery unit.

[0048] Note that if the above-described manufacturing method is used, all (100%) of the plurality of single batteries 110 have excellent high-rate resistance (the increase amount L of the excess electrolyte Δ is the upper limit threshold value L MAXIt is also possible to realize a battery pack 100 that becomes a secondary battery as follows. Such a battery pack 100 enables charge and discharge control that exhibits particularly high performance. Specifically, in a general battery pack, in order to prevent high-rate deterioration as a battery unit, charge and discharge control is performed based on the single cell with the lowest high-rate tolerance. Therefore, if a single cell with low high-rate tolerance is mixed in a plurality of single cells, even if the other single cells have high high-rate tolerance, control with restricted rapid charge and discharge is implemented. On the contrary, by using the manufacturing method according to this embodiment, since the battery pack 100 can be constructed only with the single cells 110 having excellent high-rate tolerance, it is possible to realize charge and discharge control that repeats rapid charge and discharge, which has been difficult to implement conventionally.

[0049] In addition, the technology disclosed herein can be particularly preferably applied to a battery pack 100 in which the number of single cells 110 is 20 or more (more preferably 40 or more, still more preferably 60 or more, and particularly preferably 80 or more). According to the technology disclosed herein, even for a battery pack 100 including a very large number of single cells 110, it is possible to easily realize a battery pack in which single cells with excellent high-rate tolerance occupy the majority.

[0050] <Other Embodiments> The above describes one embodiment of the manufacturing method disclosed herein. Note that the manufacturing method disclosed herein is not limited to the above-described embodiment, and various matters can be changed as appropriate. Hereinafter, an example of matters that can be changed from the above-described embodiment will be described.

[0051] 1. Addition of the Second Determination Step In the manufacturing method according to the above-described embodiment, the first determination step S30 is performed to compare and determine the increase amount L of the surplus electrolyte during inspection charging Δ with the upper limit threshold value L MAX However, the manufacturing method disclosed herein may include a determination step other than the first determination step S30. For example, in the manufacturing method shown in FIG. 10, the increase amount L of the surplus electrolyte Δ is the upper limit threshold value L MAXFor the battery assembly 1 in which the increase in the excess electrolyte L Δ and the lower threshold L MIN Here, the increase in the excess electrolyte L Δ is the lower threshold L MIN If the result is less than the threshold (S60: NO), it is determined that some kind of defect may have occurred. Specifically, even in a battery with excellent high-rate resistance, the electrodes may expand slightly during the test charging, and the excess electrolyte may increase by a certain amount or more. Δ On the other hand, if almost no electrolyte leakage is observed during the test charging, the increase in the amount of excess electrolyte L Δ There is a possibility that some defect occurred in the measurement (defect in the inspection charge, defect in the analysis of the X-ray image, etc.). Δ The lower threshold L MIN By setting up a comparison with the increase in the excess electrolyte L Δ It is possible to ensure that the measurement of the upper limit threshold L has been properly performed. This can further improve the reliability of the secondary battery manufactured by the manufacturing method disclosed herein. MAX Similarly, the lower threshold L MIN The lower threshold value L is set appropriately according to the specifications of the secondary battery to be manufactured and is limited to a specific value. MIN can be set within the range of 0% to 0.03%.

[0052] 2. Timing of measuring the amount of test fluid In the above embodiment, the increase amount L of the excess electrolyte based on the initial liquid amount L0 and the test liquid amount L1 is Δ Calculate only one, and calculate the increase in the excess electrolyte L Δ However, the excess electrolyte increase L Δ The timing and number of times of measuring the test liquid amount are not limited to the technology disclosed herein. For example, the test liquid amount is measured every time the SOC increases by a certain amount (for example, about 5%) during the test charging, and a plurality of test liquid amounts L1 to L Nmay be obtained. And with these plural inspection liquid amounts L1 to L N used, the increased amounts L Δ1 to L ΔN of the excess electrolytic solution can be calculated plurally. And by comparing these increased amounts L Δ1 to L ΔN with a plurality of upper limit thresholds L MAX1 to L MAXN respectively, the high-rate tolerance over time according to the change in SOC can be evaluated.

[0053] 3. Measuring means for the increased amount L Δ of the excess electrolytic solution In the above-described embodiment, the liquid amounts (initial liquid amount L0, inspection liquid amount L1) of the excess electrolytic solution are measured based on the image analysis of the X-ray transmission image, and the increased amount L Δ of the excess electrolytic solution is calculated based on the measurement result. However, the means for measuring the liquid amount of the excess electrolytic solution is not limited to the image analysis of the X-ray transmission image. The technology disclosed herein can use, without particular limitation, conventionally known means used for grasping the liquid amount of the excess electrolytic solution in the battery case. For example, the liquid amount of the excess electrolytic solution can also be measured using the voltage value at full charge, the change amount of the voltage during charge and discharge, etc. The means using the voltage value at full charge is disclosed in Japanese Unexamined Patent Application Publication No. 2022-44621. Also, the means using the change amount of the voltage during charge and discharge is disclosed in Japanese Unexamined Patent Application Publication No. 2021-182474. Further, as described in Patent Document 1, the liquid amount of the excess electrolytic solution can also be measured based on the image analysis of the ultrasonic image of the battery assembly. The image analysis of the ultrasonic image at this time can adopt a method using the luminance analysis of the image, similar to the image analysis of the X-ray transmission image described above. The manufacturing method disclosed herein includes a technology for measuring the increased amount L Δ of the excess electrolytic solution during inspection charging using the above-described measurement technology, and performing the first determination step based on the increased amount L Δ of the excess electrolytic solution. However, since the liquid amount of the excess electrolytic solution based on the voltage value is a so-called estimated value, it may be different from the actual liquid amount of the excess electrolytic solution. Therefore, considering the precision of the measurement result, it is preferable to use means (such as image analysis of X-ray transmission images and ultrasonic images) that can directly measure the liquid amount of the excess electrolytic solution.

[0054] The embodiments of the technology disclosed herein have been described above. However, the above description is merely illustrative and does not limit the scope of the claims. The technology described in the claims includes various modifications and changes to the specific examples illustrated in the above description.

[0055] That is, the technology disclosed herein encompasses the technologies described in the following [Item 1] to [Item 10].

[0056] [Item 1] A construction step of constructing a battery assembly in which an electrode body and an electrolytic solution are housed in a battery case, performing an inspection charge on the battery assembly for a predetermined period, and measuring an increase amount L Δ of the surplus electrolytic solution in the inspection charge; an increase amount measurement step, wherein the increase amount L Δ of the surplus electrolytic solution is below a predetermined upper limit threshold value L MAX ; and a first determination step of selecting the battery assembly as a non-defective product, A method for manufacturing a secondary battery, including the above steps.

[0057] [Item 2] The manufacturing method according to Item 1, further including a second determination step of selecting, as a non-defective product, a battery assembly in which the increase amount L Δ of the surplus electrolytic solution is equal to or greater than a predetermined lower limit threshold value L MIN .

[0058] [Item 3] The increase amount L Δ of the surplus electrolytic solution is calculated by the following formula (1), where the liquid amount of the surplus electrolytic solution before the start of the inspection charge is defined as an initial liquid amount L0, the liquid amount of the surplus electrolytic solution at a predetermined time point during the inspection charge is defined as an inspection liquid amount L1, and the total amount of the electrolytic solution present in the battery case is defined as a total liquid amount L T : The manufacturing method according to Item 1 or 2. L Δ =(L1 - L0) / L T (1)

[0059] [Item 4] The manufacturing method according to item 3, wherein the amount of the surplus electrolytic solution is measured based on image analysis of an X-ray transmission image of the battery assembly.

[0060] [Item 5] In the image analysis of the X-ray transmission image, a measurement line along the side surface of the battery case is set in the region between the electrode body and the battery case, and the amount of the surplus electrolytic solution is measured by analyzing the change in luminance on the measurement line. The manufacturing method according to item 4.

[0061] [Item 6] The X-ray transmission image is captured in a state where the battery assembly is tilted at a predetermined tilt angle θ. The manufacturing method according to item 4 or 5.

[0062] [Item 7] The battery case is formed of aluminum or resin. The manufacturing method according to any one of items 4 to 6.

[0063] [Item 8] The upper limit threshold value L MAX is set within a range of 0.05% to 10%. The manufacturing method according to any one of items 3 to 7.

[0064] [Item 9] The inspected liquid amount L1 is measured when the SOC of the battery assembly reaches a predetermined inspection value set within a range of 60% to 90%. The manufacturing method according to any one of items 3 to 8.

[0065] [Item 10] A plurality of single cells, a connection member for electrically connecting each of the plurality of single cells, and at least, wherein more than 90% of the plurality of single cells have an increase amount L of surplus electrolytic solution Δ in the inspection charge for a predetermined period that is MAX less than or equal to a predetermined upper limit threshold value L. A battery pack which is a secondary battery.

[0066] [Item 11] All of the plurality of single cells have an increase amount L of the excess electrolyte Δ is the upper limit threshold value L MAX The assembled battery according to item 10, which is a secondary battery with the following conditions

[0067] [Item 12] The assembled battery according to item 10 or 11, which includes 20 or more single cells

Description of reference numerals

[0068] 1 Battery assembly 10 Battery case 12 Sealing plate 12a Liquid injection hole 14 Case body 16 Sealing member 20 Electrode body 30 Electrolyte 32 Excess electrolyte 40 Electrode terminal

Claims

1. A construction step of constructing a battery assembly in which an electrode body and an electrolytic solution are housed in a battery case, Performing inspection charging on the battery pack assembly for a predetermined period, and measuring an increase amount L of surplus electrolyte in the inspection charging Δ An increase amount measurement step of measuring The increased amount L of the surplus electrolyte Δ is equal to or less than a predetermined upper limit threshold value L ＭＡＸ and a first determination step of selecting a battery assembly that meets the above conditions as a non-defective product including, The increased amount measurement step includes: A step of measuring an initial liquid amount L0 which is the liquid amount of the surplus electrolytic solution before the start of the inspection charging; A step of starting the inspection charging for the battery assembly; A step of measuring an inspection liquid amount L1 which is the liquid amount of the surplus electrolytic solution during the inspection charging; A step of obtaining a total liquid amount LT which is the total amount of the surplus electrolytic solution existing outside the electrode body and the electrolytic solution permeating into the electrode body; A step of measuring an increase amount LΔ of the surplus electrolytic solution by the following formula (1) based on the initial liquid amount L0, the inspection liquid amount L1, and the total liquid amount LT and is provided with, The liquid amount of the surplus electrolytic solution is measured by setting a measurement line along the side surface of the battery case in a region between the electrode body and the battery case in an X-ray transmission image taken in a state where the battery assembly is tilted at a predetermined inclination angle θ and analyzing a change in luminance on the measurement line. A method for manufacturing a secondary battery. LΔ = (L1 - L0) / LT (1)

2. The increased amount L of the surplus electrolyte Δ is equal to or greater than a predetermined lower threshold value L ＭＩＮ The manufacturing method according to claim 1, further comprising a second determination step of selecting a battery assembly that meets the above condition as a non-defective product.

3. The manufacturing method according to claim 1, wherein the battery case is formed of aluminum or resin.

4. The upper limit threshold value L ＭＡＸ is set within the range of 0.05% to 10%, and the manufacturing method according to claim 1.

5. The inspection liquid volume L １ is the manufacturing method according to claim 1, which is measured when the SOC of the battery assembly reaches a predetermined inspection value set within the range of 60% to 90%.

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