Battery pack inspection method

Abstract

To provide a method for inspecting a battery pack, having a good inspection efficiency.SOLUTION: The present disclosure provides a method for inspecting a battery pack including: a laminate comprising a plurality of flat battery cells laminated therein; and a binding band compressing the laminate in a lamination direction and binding the laminate. The method for inspecting the battery pack includes: a binding load acquisition step of applying a compressive force along the lamination direction on the laminate with the binding band attached to acquire, as a binding load on the laminate by the binding band, the compressive force when a change in the shape of the biding band satisfies a specified condition; and a first determination step of determining that the battery pack is abnormal if the acquired binding load is larger than a first threshold.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a method for inspecting a battery pack. [Background technology]

[0002] There is known a battery pack in which multiple battery cells are restrained by a restraining member. For example, Patent Document 1 discloses an inspection method for measuring the value of the compressive load of the battery pack and judging whether the battery pack is in a reusable state based on the measured value. Patent Document 2 discloses a method for judging whether the restraining load of a battery module in which multiple battery cells are restrained by a restraining member exceeds a restraining load limit. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-131076 A [Patent Document 2] JP 2017-147021 A Summary of the Invention [Problem to be solved by the invention]

[0004] As shown in Patent Document 1, a method is known for determining whether a battery pack is normal or not based on the restraining load of the battery pack. However, the method described in Patent Document 1 requires that the restraining members (restraining bands) be removed from the battery cells when measuring the restraining load. Therefore, if no abnormality is found during the inspection, the battery cells must be restrained again, and there is a demand for improving the efficiency of the inspection.

[0005] The present disclosure has been made in consideration of the above-mentioned circumstances, and has as its main object to provide a method for inspecting a battery pack with good inspection efficiency. [Means for solving the problem]

[0006] In order to solve the above problems, the present disclosure provides a method for inspecting an assembled battery including a stack of multiple flat-shaped battery cells and a restraint band that compresses and restrains the stack in the stacking direction, the method including a restraint load acquisition step of applying a compressive force along the stacking direction to the stack to which the restraint band is attached, and acquiring the compressive force when a change in shape of the restraint band satisfies a specified condition as a restraint load of the stack by the restraint band, and a first judgment step of judging the assembled battery to be abnormal if the acquired restraint load is greater than a first threshold value.

[0007] According to the present disclosure, inspection of the assembled battery is performed with the restraint bands attached, and therefore inspection efficiency is good. Effect of the Invention

[0008] The present disclosure has an effect of providing a method for inspecting a battery pack with good inspection efficiency. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic plan view illustrating an example of a battery pack according to the present disclosure. [Diagram 2] 4 is a flowchart illustrating an example of a method for inspecting a battery pack according to the present disclosure. [Diagram 3] 4 is a flowchart illustrating an example of a method for inspecting a battery pack according to the present disclosure. [Figure 4] 4 is a graph illustrating the relationship between compressive force (load) and strain of a restraining band in the present disclosure. [Diagram 5] 1 is a schematic cross-sectional view showing an example of a battery cell according to the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The battery pack inspection method according to the present disclosure will be described in detail below.

[0011] Fig. 1 is a schematic plan view showing an example of a battery pack according to the present disclosure. The battery pack 10 shown in Fig. 1 includes a stack 2 in which a plurality of flat battery cells 1 are stacked, and a restraining band 3 that compresses and restrains the stack 2 in a stacking direction D. The battery pack 10 shown in Fig. 1 also includes a sensor 4 that measures the distortion of the restraining band 3.

[0012] FIG. 2 is a flow chart for explaining an example of a method for inspecting a battery pack according to the present disclosure. In the method for inspecting a battery pack according to the present disclosure, first, a compressive force along the stacking direction is applied to the stack to which the restraining bands are attached. The applied compressive force is gradually increased, and the compressive force at the time when the change in the shape of the restraining bands satisfies a prescribed condition (for example, when the distortion of the restraining bands reaches an inflection point) is acquired as the restraining load of the stack by the restraining bands (restraining load acquisition step, S1). Next, if the acquired restraining load value is greater than a first threshold value, the battery pack is judged to be abnormal, and if the acquired restraining load value is equal to or less than the first threshold value, the battery pack is judged to be normal (first judgment step, S2). The battery pack judged to be normal can be collected as a reusable battery. If the battery pack is judged to be normal in S2, the process may proceed to S3 to S7 as shown in FIG. 3 described later.

[0013] According to the present disclosure, the battery pack is inspected with the restraining bands attached, improving inspection efficiency. In the above-mentioned Patent Document 1, in a battery pack restrained by restraining bands, it is determined whether the battery pack can be reused based on the value of the compressive load. In Patent Document 1, the value of the compressive gravity (restraining load) is measured by measuring the reaction force of the compressive load. In such a method, it is necessary to cut the restraining bands, and a battery pack that is determined to be normal in the inspection needs to be restrained again with the restraining bands.

[0014] In contrast, in the present disclosure, since the restraint load is measured based on the change in shape of the restraint bands, there is no need to remove the restraint bands from the stack. Therefore, if the inspection reveals that the battery pack is normal, there is no need to reattach the restraint bands to the stack. As a result, the battery pack can be inspected efficiently. Furthermore, by performing steps S3 to S7 described below, the battery pack can be inspected more accurately, and the reliability of the reusable battery pack can be improved.

[0015] 1. Restraint load acquisition process The constraint load acquisition process in the present disclosure is a process of applying a compressive force along the stacking direction to a laminate to which a constraint band is attached, and acquiring the compressive force when the change in shape of the constraint band satisfies specified conditions as the constraint load of the laminate caused by the constraint band.

[0016] An example of the specified condition is the strain inflection point of the restraining band. Figure 4 is a graph showing the relationship between the compression force (load) and the strain of the restraining band. As shown in Figure 4, when a compressive force along the lamination direction is gradually applied to a laminate with a restraining band attached, an inflection point occurs because the rate of decrease in strain before the restraining band returns to its original length differs from the rate of decrease in strain after the restraining band returns to its original length. The compression amount corresponding to this inflection point can be obtained as the restraining load of the laminate by the restraining band. The strain of the restraining band can be measured, for example, by a strain gauge.

[0017] Another example of a specified condition is the inflection point of the displacement of the restraining band. When a compressive force along the lamination direction is gradually applied to a laminate with a restraining band attached, an inflection point occurs because the displacement (shrinkage) before the restraining band returns to its original length differs from the displacement (shrinkage) after the restraining band returns to its original length. The amount of compression corresponding to this inflection point can be obtained as the restraining load of the laminate by the restraining band. The displacement of the restraining band can be measured, for example, by image inspection.

[0018] 2.First judgment step The first determination step in the present disclosure is a step of determining that the battery pack is abnormal when the measured binding load is greater than a first threshold value, and determining that the battery pack is normal when the measured binding load is equal to or less than the first threshold value.

[0019] The first threshold value can be set, for example, by conducting a preliminary test as follows. For multiple battery packs that have been used for a certain period of time, the restraint load is obtained in the same manner as in the above-mentioned restraint load acquisition process. After that, the restraint bands are removed from the battery packs, and the presence or absence of expanding battery cells is confirmed. Then, the first threshold value (upper limit of the restraint load) is set based on the restraint load of the battery packs in which no expansion of the battery cells was confirmed. The first threshold value can be set appropriately depending on conditions such as the configuration of the battery cells and the number of layers.

[0020] 3. Battery cell state measuring step, second determination step, and third determination step 3, in the battery pack inspection method according to the present disclosure, if the battery pack is determined to be normal in the first determination step, a battery cell state measurement step (S3) and a second determination step (S4) may be further performed. By performing the battery cell state measurement step and the second determination step, an abnormal battery cell in the battery pack can be detected.

[0021] The battery cell state measuring step is a step of measuring the state of each battery cell in the stack. The state of the battery cell is evaluated, for example, by at least one of the capacity and the IV resistance.

[0022] The second determination step is a step of determining that the battery pack is normal if the state of each battery cell in the stack satisfies the condition of the second threshold, and determining that the battery pack is abnormal if the state of each battery cell does not satisfy the condition of the second threshold. For example, when the state of the battery cell is evaluated by capacity, the battery cell is determined to be normal if the capacity is equal to or greater than the second threshold. When the state of the battery cell is evaluated by IV resistance, the battery cell is determined to be normal if the IV resistance is equal to or less than the second threshold. For example, when the battery pack has at least one abnormal battery cell, the battery pack is determined to be abnormal.

[0023] In the battery pack inspection method disclosed herein, when the battery pack is determined to be normal in the second determination step, a third determination step (S5) is further performed, so that abnormal battery cells can be detected with high accuracy. The third determination step is a step of determining the adjacent battery cells as normal when the capacity difference between the adjacent battery cells is equal to or less than a third threshold, and determining one of the adjacent battery cells as abnormal when the capacity difference is greater than the third threshold. Here, when the capacity difference between the battery cell A and the adjacent battery cell B on one side of the battery cell A is greater than the third threshold, one of the battery cells A and the battery cell B is determined to be an abnormal battery cell. In this situation, when the capacity difference between the battery cell A and the adjacent battery cell C on the other side of the battery cell A is greater than the third threshold, the battery cell A is determined to be an abnormal battery cell. On the other hand, when the capacity difference between the battery cell A and the battery cell C is equal to or less than the third threshold, the battery cell B is determined to be an abnormal battery cell. In this manner, the abnormal battery cell is identified.

[0024] 4. Thickness measurement process and fourth judgment process 3, in the battery pack inspection method according to the present disclosure, if it is determined in the third determination step that an abnormal battery cell is present in the battery pack, a thickness measurement step (S6) and a fourth determination step (S7) may be further performed. By performing the thickness measurement step and the fourth determination step, abnormal battery cells can be detected with high accuracy.

[0025] The thickness measurement step is a step of measuring the thickness in the stacking direction of the abnormal battery cell identified in the third determination step under low temperature and low SOC conditions. There is a correlation between a battery cell with deteriorated capacity and its internal pressure. In addition, under low temperature and low SOC conditions, the thickness of a battery cell with normal capacity (normal internal pressure) is small, but the thickness of a battery cell with deteriorated capacity and high internal pressure is not small. Therefore, by measuring the thickness under low temperature and low SOC conditions, it is possible to accurately determine whether a battery cell is abnormal. In addition, under low temperature and low SOC conditions, the thickness of the battery cell can be measured when the restraining load of the restraining band is at its lowest, that is, when the effect of the restraining load is at its smallest.

[0026] The temperature under the low temperature condition is, for example, −10° C. or lower and −40° C. or higher. The SOC under the low SOC condition is, for example, 30% or lower and 10% or higher. The thickness of the battery cell can be measured, for example, by an image inspection device.

[0027] The fourth determination step is a step of determining that the battery cell is abnormal if the thickness of the battery cell measured in the thickness measurement step is greater than a fourth threshold value. The fourth threshold value can be set by measuring the thicknesses of a plurality of normal battery cells in advance and taking into account the variation in the thicknesses (for example, the average value + 3σ).

[0028] 5. Battery pack As shown in Fig. 1, the battery pack according to the present disclosure includes a stack 2 in which a plurality of battery cells 1 are stacked, and a restraining band 3. Fig. 5 is a schematic cross-sectional view showing an example of a battery cell according to the present disclosure. The battery cell 1 shown in Fig. 5 includes a positive electrode active material layer 11, a negative electrode active material layer 12, an electrolyte layer 13 formed between the positive electrode active material layer 11 and the negative electrode active material layer 12, a positive electrode current collector 14 that collects current from the positive electrode active material layer, a negative electrode current collector 15 that collects current from the negative electrode active material layer 12, and a battery case 16 that houses the above members.

[0029] The positive electrode current collector, the positive electrode active material layer, the electrolyte layer, the negative electrode active material layer, the negative electrode current collector, and the battery case can be members used in conventional batteries. The electrolyte contained in the electrolyte layer may be a solid electrolyte or a liquid electrolyte. Examples of the solid electrolyte include inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and halide solid electrolytes.

[0030] The battery cell is preferably an all-solid-state battery in which the electrolyte is an inorganic solid electrolyte. The battery cell is usually a secondary battery capable of charging and discharging. The battery cell is preferably a lithium-ion battery. The number of stacked battery cells in the present disclosure can be set appropriately. The restraining band is not particularly limited, and a restraining band used in a conventional battery can be used.

[0031] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present disclosure and exhibits similar effects is included in the technical scope of the present disclosure. [Explanation of symbols]

[0032] 1 ... Battery cell 2 ...Laminate 3. Restraint band 4. Sensor 10...Battery pack 11...Cathode active material layer 12...electrolyte layer 13...Negative electrode active material layer 14...Positive electrode current collector 15...Negative electrode current collector 16 ... Battery case

Claims

[Claim 1] 1. A method for inspecting a battery pack including a stack in which a plurality of flat battery cells are stacked, and a restraint band that compresses and restrains the stack in a stacking direction, comprising: a constraint load acquisition step of applying a compressive force along the stacking direction to the laminate to which the constraint band is attached, and acquiring the compressive force at an inflection point in a compression force-strain curve of the constraint band as a constraint load of the laminate by the constraint band; a first determination step of determining that the battery pack is abnormal when the acquired binding load is greater than a first threshold value; the first threshold value is a value set by a preliminary test, the preliminary test is a test in which the restraint load is obtained for the battery pack in a manner similar to that of the restraint load acquisition process, the restraint bands are then removed from the battery pack, and the first threshold value is set based on the restraint load for the battery pack in which expansion of the battery cells is not confirmed.

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