Method for evaluating an electricity storage device, jig set, and method for manufacturing an electricity storage device

Abstract

To improve the reproducibility of a single-layer short circuit in an evaluation method for a power storage device.SOLUTION: A method for evaluating a power storage device includes (a) to (d) in this order: (a) pacing a metal piece 20 on an outer surface of an electrode body 10; (b) pressing the metal piece 20 into the electrode body 10; (c) detecting a short circuit on the basis of a change in a potential difference between an electrode in the electrode body and the metal piece 20; and (d) stopping the pressing of the metal piece 20. (b) includes using a pressing jig 31 and a guide tool 32. The guide tool 32 is provided with a through hole 32a. The pressing jig 31 is inserted into the through hole 32a. The metal piece 20 has a ring shape. The metal piece 20 is arranged in the through hole. The pressing jig 31 presses the metal piece 20 out of the through hole 32a, thereby the metal piece 20 is pressed into the electrode body 10. The pressing jig 31 is conductive. The hardness of the pressing jig 31 is equal to or greater than the hardness of the metal piece 20.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a method for evaluating an electricity storage device, a jig set, and a method for manufacturing an electricity storage device. [Background technology]

[0002] Japanese Patent Application Laid-Open Publication No. 2020-191181 (Patent Document 1) discloses a method for evaluating an electricity storage device. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-191181 Summary of the Invention [Problem to be solved by the invention]

[0004] There is a need to simulate a micro-short circuit caused by the inclusion of foreign matter. Conventionally, a micro-short circuit has been simulated using the "forced internal short circuit test" described in IEC 62660-3. An energy storage device includes an electrode assembly. In the forced internal short circuit test, a charged electrode assembly is partially disassembled to place a metal piece (simulated foreign matter) inside the electrode assembly. The metal piece has an L-shaped outer shape. This work is extremely difficult and can only be performed by skilled workers. A test method that does not require skilled workers is desired.

[0005] Patent Document 1 proposes simulating a micro-short circuit by pushing a metal piece into the electrode body from the outside. This method has the following advantages: It does not require disassembly of the electrode body. Because the metal piece is ring-shaped, the position of the metal piece is stable, and the success rate of pushing is high. The use of a pushing jig and a guide jig reduces the difficulty of the work. However, it was found that there is room for improvement in the following two points.

[0006] First, a short circuit is detected by a voltage drop in the power storage device. The greater the capacity of the power storage device, the smaller the voltage drop due to a short circuit. Therefore, the greater the capacity of the power storage device, the more difficult it is to detect a short circuit. When a voltage drop is detected, there is a possibility that a metal piece has penetrated two or more layers of separator. In reality, a micro-short circuit caused by foreign matter contamination is a "single-layer short circuit." A single-layer short circuit occurs when a foreign object penetrates one layer of separator. Simulation of a single-layer short circuit is required. When a metal piece penetrates two or more layers of separator, it deviates from a single-layer short circuit.

[0007] Second, the pressing tool is made of resin. The pressing tool can be softer than the metal piece. Therefore, the pressing load is less likely to be transmitted to the metal piece and tends to be dissipated into the pressing tool. Because the metal piece is not pressed smoothly into the electrode body, there is a possibility that the metal piece will be pressed in forcefully when it breaks through the outermost layer of the electrode body. As a result, there is a possibility that the metal piece will penetrate two or more layers of separator.

[0008] The present disclosure aims to improve the reproducibility of single layer shorts. [Means for solving the problem]

[0009] The technical configuration and effects of the present disclosure will be described below. However, the mechanism of action in this specification includes speculation. The mechanism of action does not limit the technical scope of the present disclosure.

[0010] 1. In the method for evaluating an electricity storage device, an electricity storage device including an electrode assembly is evaluated. The method for evaluating the electricity storage device includes the following steps (a) to (d) in this order. (a) A metal piece is placed on the outer surface of the electrode body. (b) Press the metal piece into the electrode body. (c) A short circuit is detected by a change in the potential difference between the electrode in the electrode body and the metal piece. (d) Stop pushing the metal piece. The above (b) includes using a pushing jig and a guide jig. The guide jig has a through hole. The pushing jig is inserted into the through hole. The metal piece has a ring shape. The metal piece is placed in the through hole. The pushing jig pushes the metal piece out of the through hole, thereby forcing the metal piece into the electrode body. The pressing jig is conductive and has a hardness equal to or greater than the hardness of the metal piece.

[0011] In the method for evaluating an electricity storage device disclosed herein, a short circuit is detected based on a change in the potential difference between an electrode (positive electrode or negative electrode) and a metal piece (simulated foreign object). The amount of change in the potential difference between an electrode and a metal piece tends to be less affected by the capacity of the electricity storage device. Therefore, even if the capacity of the electricity storage device increases, a single-layer short circuit can be accurately detected.

[0012] In the method for evaluating an electricity storage device according to the present disclosure, the pressing tool is conductive, and the potential of the metal piece can be measured by measuring the potential of the pressing tool in contact with the metal piece.

[0013] Furthermore, the pressing jig has a hardness equal to or greater than that of the metal piece, so the pressing load is less likely to be transferred to the pressing jig, allowing the metal piece to be smoothly pressed into the electrode body. The synergistic effects of the above are expected to improve the reproducibility of single-layer short circuits.

[0014] 2. The method for evaluating an electricity storage device described in "1" above may include the following configuration. The pressing jig is in the form of a hollow rod.

[0015] When a short-circuit current flows through the metal piece, Joule heat is generated. Joule heat causes the separator to melt and spread, centered on the metal piece. Hereinafter, the diameter of the hole formed by the melting and spreading of the separator will also be referred to as the "melt diameter." The larger the melt diameter, the greater the change in the potential difference between the electrode and the metal piece. Therefore, it is expected that the accuracy of short-circuit detection will improve. However, there is a possibility that the melt diameter will become smaller due to heat escaping from the metal piece to the pressing jig. Hollow materials have a smaller heat capacity than solid materials. It is expected that the hollow pressing jig will make it more difficult for heat to escape to the pressing jig. In other words, it is expected that the accuracy of short-circuit detection will improve.

[0016] 3. The method for evaluating an electricity storage device according to "1" or "2" above may include the following configuration: The metal piece has a first end face and a second end face. The second end face is the face opposite to the first end face. In (b) above, the pressing jig contacts the second end face. The contact area between the pressing jig and the second end face is smaller than the area of ​​the second end face.

[0017] By reducing the contact area between the pressing jig and the metal piece, it is expected that heat will be less likely to escape from the metal piece to the pressing jig, which means that the accuracy of short circuit detection is expected to improve.

[0018] 4. The method for evaluating an electricity storage device according to any one of the above items "1" to "3" may include the following configuration: The pressing jig is made of metal.

[0019] It is believed that there is a wide range of choices for metal materials that are harder than the metal piece and have electrical conductivity. Of course, the material of the pressing jig is not limited to metal materials as long as it is harder than the metal piece and has electrical conductivity.

[0020] 5. The jig set is used in the method for evaluating an electricity storage device according to any one of the above items 1 to 4. The jig set includes a pressing jig and a guide jig.

[0021] 6. A method for producing an electricity storage device includes the following steps (A) and (B) in this order: (A) Manufacture an electricity storage device. (B) Evaluate energy storage devices. The above (B) includes the method for evaluating an electricity storage device according to any one of the above items "1" to "4".

[0022] Hereinafter, an embodiment of the present disclosure (hereinafter may be abbreviated as "the present embodiment") and an example of the present disclosure (hereinafter may be abbreviated as "the present example") will be described. However, the present embodiment and the example do not limit the technical scope of the present disclosure. The present embodiment and the example are illustrative in all respects. The present embodiment and the example are non-restrictive. The technical scope of the present disclosure encompasses all modifications within the meaning and scope equivalent to the claims. For example, it is originally intended that any configuration may be extracted from the present embodiment and the example and that they may be arbitrarily combined. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a schematic flowchart of a method for evaluating an electricity storage device according to this embodiment. [Figure 2] FIG. 2 is a conceptual diagram showing the arrangement of the metal pieces. [Figure 3] FIG. 3 is a schematic plan view of a metal piece. [Figure 4] FIG. 4 is a schematic cross-sectional view of a metal piece. [Figure 5] FIG. 5 is an explanatory diagram of the contact area between the pressing jig and the metal piece. [Figure 6] FIG. 6 shows a first example of the shape of the end face of the pressing jig. [Figure 7] FIG. 7 shows a second example of the shape of the end face of the pressing jig. [Figure 8] FIG. 8 is a schematic plan view of the guide jig. [Figure 9] FIG. 9 is a first conceptual diagram showing the detection of a short circuit. [Figure 10] FIG. 10 is a second conceptual diagram showing the detection of a short circuit. [Figure 11] FIG. 11 is a third conceptual diagram showing the detection of a short circuit. [Figure 12] FIG. 12 is a schematic flowchart of a method for manufacturing an electricity storage device according to this embodiment. [Figure 13] FIG. 13 is a schematic diagram of a prismatic battery. [Figure 14] FIG. 14 is a schematic diagram of an electrode winding body. [Figure 15] FIG. 15 is a schematic diagram of an electrode stack. [Figure 16] FIG. 16 is a schematic diagram of a cylindrical battery. [Figure 17] FIG. 17 is a schematic diagram of a pouch-type battery. [Figure 18] FIG. 18 is a schematic diagram showing an example of opening the outer packaging material. [Figure 19] FIG. 19 is a composition table of the test sample. [Figure 20] FIG. 20 is a table showing the experimental results. [Figure 21] FIG. 21 is a graph showing the relationship between the average number of short-circuit layers and the capacity of the electricity storage device. DETAILED DESCRIPTION OF THE INVENTION

[0024] <Terminology> Terms used in this specification are explained below. Terms not explained here may be explained whenever they are used in this specification.

[0025] The terms "comprise," "include," "have," and variations thereof (e.g., "consisting of") are open-ended. Open-ended terms may or may not include additional elements in addition to the required elements. The term "consisting of" is closed-ended. However, even closed-ended terms do not exclude additional elements that are normally incidental impurities or unrelated to the disclosed technology. The term "consisting essentially of..." is semi-closed. Semi-closed terms allow for the addition of elements that do not substantially affect the basic and novel characteristics of the disclosed technology.

[0026] Expressions such as "may" and "may" are used in the permissive sense, meaning "to have the possibility," rather than in the obligatory sense, meaning "to have to."

[0027] Unless otherwise specified, the order of execution of multiple steps, actions, operations, etc. included in various methods is not limited to the order described. For example, multiple steps may proceed simultaneously. For example, multiple steps may occur one after the other.

[0028] Geometric terms (such as "parallel," "perpendicular," and the like) should not be interpreted in a strict sense. For example, "parallel" may deviate slightly from the strict meaning of "parallel." Geometric terms may include, for example, tolerances, errors, and the like in design, work, and manufacturing. The dimensional relationships in each drawing may not match the actual dimensional relationships. To aid the reader's understanding, the dimensional relationships (length, width, thickness, and the like) in each drawing may be changed. Furthermore, some components may be omitted.

[0029] Unless otherwise specified, a numerical range such as "m to n%" includes both the upper and lower limits. That is, "m to n%" indicates a numerical range of "m% or more and n% or less." Furthermore, "m% or more and n% or less" includes "more than m% and less than n%." Furthermore, a numerical value arbitrarily selected from within the numerical range may be set as a new upper or lower limit. For example, a new numerical range may be set by arbitrarily combining a numerical value within the numerical range with a numerical value described elsewhere in this specification, in a table, a figure, or the like.

[0030] All numerical values ​​are modified by the term "about." The term "about" may mean, for example, ±5%, ±3%, ±1%, etc. All numerical values ​​may be approximate values ​​that may vary depending on the application of the disclosed technology. All numerical values ​​may be expressed with significant figures. Unless otherwise specified, measured values ​​may be average values ​​of multiple measurements. The number of measurements may be three or more, five or more, or ten or more. In general, the more measurements are made, the more reliable the average value is expected to be. Measured values ​​may be rounded to the nearest significant figure. Measured values ​​may include errors, such as those associated with the detection limits of the measuring device.

[0031] "Electrode" is a general term for positive and negative electrodes. An electrode may be either a positive electrode or a negative electrode.

[0032] "Hardness" is expressed by a measurable value for both the metal piece and the pressing jig. For example, if the pressing jig is made of metal, the hardness of the metal piece and the pressing jig may be expressed by, for example, Vickers hardness. "Vickers hardness" can be measured by the following procedure. A pyramidal diamond indenter is pressed against the surface of a sample with a test force (F), forming an indentation. The diagonal length of the indentation is measured using a microscope. The surface area (S) of the indentation is calculated from the diagonal length. The Vickers hardness is calculated by dividing the test force (F) by the surface area (S).

[0033] For example, the tensile yield stress may represent the hardness of the metal piece and the pressing jig. The "tensile yield stress" can be measured by the following procedure: A test piece is prepared by forming a sample into a dumbbell shape. Tensile stress is applied along the axial direction (length direction) of the test piece until the test piece breaks. In the stress-strain diagram, the upper yield stress is divided by the cross-sectional area of ​​the test piece to determine the tensile yield stress.

[0034] The term "conductive pressing jig" includes a pressing jig that is entirely conductive and a pressing jig that is partially conductive. For example, only the surface of the pressing jig may be conductive. 8 A pressing tool is considered to be conductive if it has a resistivity of Ωcm or less.

[0035] <Evaluation method for energy storage devices> FIG. 1 is a schematic flowchart of a method for evaluating an electricity storage device according to this embodiment. Hereinafter, the "method for evaluating an electricity storage device according to this embodiment" may be abbreviated as "this evaluation method." This evaluation method includes "(a) placing a metal piece," "(b) pushing the metal piece," "(c) detecting a short circuit," and "(d) stopping the pushing." Each operation in this evaluation method may be performed, for example, in a low dew point environment. Each operation may be performed, for example, in a constant temperature environment.

[0036] <(a) Arrangement of metal pieces> This evaluation method includes placing a metal piece on the outer surface of the electrode body. An electricity storage device to be evaluated is prepared. Details of the electricity storage device will be described later. For example, the SOC of the electricity storage device may be adjusted. "SOC (State Of Charge)" indicates the percentage of remaining capacity relative to the rated capacity of the electricity storage device. The SOC may be adjusted to, for example, 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, or 100% or more. The SOC may be adjusted to, for example, 120% or less, 110% or less, or 100% or less.

[0037] The power storage device includes a packaging material. The packaging material houses the electrode assembly. After adjusting the SOC, the packaging material may be opened to remove the entire electrode assembly from the packaging material. For example, a portion of the packaging material may be hollowed out to expose a portion of the outer surface of the electrode assembly (see FIG. 18).

[0038] FIG. 2 is a conceptual diagram showing the arrangement of metal pieces. The electrode assembly 10 includes a positive electrode 11, a separator 13, and a negative electrode 12. The separator 13 is interposed between the positive electrode 11 and the negative electrode 12. The separator 13 separates the positive electrode 11 from the negative electrode 12. The separator 13 may be exposed on the outer surface of the electrode assembly 10. An insulating film (not shown) may be attached to the outer surface of the electrode assembly 10. In FIG. 2, the outer surface of the electrode assembly 10 is formed by the separator 13. A metal piece 20 is placed on the outer surface of the electrode assembly 10. The attitude (orientation) of the metal piece 20 is adjusted so that the contact area between the metal piece 20 and the electrode assembly 10 is maximized.

[0039] The metal piece 20 may contain any metal material as long as it has a hardness equal to or less than that of the pressing jig 31 (described below). The metal piece 20 may contain, for example, at least one selected from the group consisting of Al, Cu, Fe, Ni, and stainless steel (SUS). The metal piece 20 may be made of SUS. The SUS may be, for example, any of SUS200 series (e.g., SUS201, etc.), SUS300 series (e.g., SUS304, SUS316, etc.), SUS400 series (e.g., SUS403, SUS430, etc.), and SUS600 series (SUS630, SUS631, etc.). Symbols such as "SUS304" indicate the "type symbols" specified in "JIS G 4303."

[0040] 3 is a schematic plan view of a metal piece. Metal piece 20 is ring-shaped. As long as it is ring-shaped, the planar shape of metal piece 20 is not limited to a circle. The planar shape of metal piece 20 may be, for example, a circle, an ellipse, or a polygon (triangle, square, hexagon, etc.). When the planar shape is not a circle, the inner diameter (φ1) and outer diameter (φ2) of metal piece 20 indicate the maximum diameter in the plan view.

[0041] The planar shape of the metal piece 20 may be continuous over the entire periphery, or may be partially discontinuous. For example, the planar shape of the metal piece 20 may be C-shaped.

[0042] The inner diameter (φ1) of the metal piece 20 may be, for example, 0.1 mm or more, 0.3 mm or more, 0.5 mm or more, or 0.7 mm or more. The inner diameter (φ1) of the metal piece 20 may be, for example, 1.5 mm or less, 1.3 mm or less, 1.1 mm or less, or 1.3 mm or less.

[0043] The outer diameter (φ2) of the metal piece 20 may be, for example, 0.3 mm or more, 0.5 mm or more, 0.7 mm or more, or 0.9 mm or more. The outer diameter (φ2) of the metal piece 20 may be, for example, 2 mm or less, 1.8 mm or less, 1.6 mm or less, or 1.4 mm or less.

[0044] The difference between the outer diameter and the inner diameter (φ2-φ1) may be, for example, 0.05 mm or more, 0.1 mm, 0.2 mm or more, 0.3 mm or more, or 0.5 mm or more. The difference between the outer diameter and the inner diameter (φ2-φ1) may be, for example, 0.9 mm or less, 0.8 mm or less, or 0.7 mm or less.

[0045] 4 is a schematic cross-sectional view of the metal piece. The height (h) of the metal piece 20 may be, for example, 0.2 mm or more, 0.3 mm or more, or 0.4 mm or more. The height (h) of the metal piece 20 may be, for example, 0.5 mm or less, or 0.4 mm or less.

[0046] (b) Pushing in a metal piece This evaluation method includes pressing the metal piece 20 into the electrode body 10. In this evaluation method, a jig set 30 is used. The jig set 30 includes a pressing jig 31 and a guide jig 32. The guide jig 32 has a through hole 32a. The guide jig 32 is placed on the outer surface of the electrode body 10 so that the metal piece 20 fits into the through hole 32a. The pressing jig 31 is inserted into the through hole 32a. For example, a servo press or the like drives the pressing jig 31 in the Y-axis direction, causing the pressing jig 31 to press the metal piece 20. The guide jig 32 guides the movement of the pressing jig in the Y-axis direction. The pressing jig 31 pushes the metal piece 20 out of the through hole 32a, thereby pressing the metal piece 20 into the electrode body 10. By the pressing jig 31 pressing the metal piece 20 inside the through-hole 32a, it is possible to reduce unsuccessful pressing due to misalignment between the pressing jig 31 and the metal piece 20, for example.

[0047] The pressing jig 31 is rod-shaped. The pressing jig 31 may be, for example, a round bar, a square bar, or a flat bar. The cross-sectional shape of the pressing jig 31 perpendicular to the axial direction may be similar to the flat shape (end face shape) of the metal piece 20.

[0048] The pressing jig 31 is conductive. The pressing jig 31 may contain at least one material selected from the group consisting of, for example, a metal material, a carbon material, a conductive resin material, and a conductive ceramic material. The conductive resin material may be a conductive resin material. The conductive resin material may be a matrix resin in which a conductive material (such as a carbon material) is dispersed. The conductive ceramic material may be a conductive ceramic material. The conductive ceramic material may be a mixture of a ceramic material and a conductive material (such as a carbon material). The pressing jig 31 may be manufactured by any method. For example, the pressing jig 31 may be manufactured by extrusion, drawing, bending, welding, or the like. The pressing jig 31 may be a composite material. For example, the pressing jig 31 may be manufactured by coating a rod-shaped insulating material with a conductive material.

[0049] The resistivity of the material (component material) included in the pressing jig 31 is, for example, 1 Ωcm or less, 10 -2 Ωcm or less, 10 -4 Ωcm or less, or 10 -6 Any value below Ωcm is acceptable.

[0050] The pressing jig 31 has a hardness equal to or greater than that of the metal piece 20. That is, the relationship of the following formula (1) is satisfied. H0≦H1…(1) H0: Hardness of metal piece 20 H1: Hardness of the pressing jig 31

[0051] The hardness ratio (H1 / H0) is determined by dividing the hardness of the pressing jig 31 by the hardness of the metal piece 20. From the above formula (1), the hardness ratio (H1 / H0) is 1 or greater. The hardness ratio (H1 / H0) may be, for example, 1.1 or greater, 1.2 or greater, 1.5 or greater, 2 or greater, or 3 or greater. The hardness ratio (H1 / H0) may be, for example, 3 or less, 2 or less, 1.5 or less, 1.2 or less, or 1.1 or less.

[0052] H0 and H1 may be Vickers hardness. H0 and H1 may each be 150 HV or more. For example, the relationship of the following formula (2) may be satisfied. 50HV≦(H1-H0) …(2)

[0053] H1 may be, for example, 200HV or more, 300HV or more, or 400HV or more. H1 may be, for example, 600HV or less, 400HV or less, or 300HV or less. H0 may be, for example, 50 to 200HV, 100 to 200HV, or 150 to 200HV.

[0054] The pressing jig 31 may contain any material as long as it has a hardness equal to or greater than that of the metal piece 20. The pressing jig 31 may contain, for example, at least one selected from the group consisting of Al, Cu, Fe, Ni, and SUS. The pressing jig 31 may be formed of, for example, a material different from that of the metal piece 20. The pressing jig 31 may be formed of, for example, the same material as that of the metal piece 20. When the pressing jig 31 is formed of the same material as that of the metal piece 20, the pressing jig 31 may have the same hardness as that of the metal piece 20. For example, both the pressing jig 31 and the metal piece 20 may be made of SUS304. For example, the pressing jig 31 may be made of SUS630 and the metal piece 20 may be made of SUS304. For example, the pressing jig 31 may be made of SUS440C and the metal piece 20 may be made of SUS304. For example, the pressing jig may be made of SUS304 and the metal piece 20 may be made of 2000 series Al. "2000 series Al" refers to Al materials with alloy numbers in the 1000s listed in "JIS H 4000."

[0055] The material of the pressing jig 31 may have a low specific heat. The lower the specific heat of the material, the lower the heat capacity of the pressing jig 31. The smaller the heat capacity, the less heat tends to escape from the pressing jig 31. The specific heat of the material may be, for example, 1 kJ / (kg·K) or less, 0.9 kJ / (kg·K) or less, 0.8 kJ / (kg·K) or less, 0.7 kJ / (kg·K) or less, 0.6 kJ / (kg·K) or less, 0.5 kJ / (kg·K) or less, 0.4 kJ / (kg·K) or less, 0.3 kJ / (kg·K) or less, 0.2 kJ / (kg·K) or less, or 0.1 kJ / (kg·K) or less. The specific heat of the constituent material may be, for example, 0.1 kJ / (kg·K) or more, 0.2 kJ / (kg·K) or more, 0.3 kJ / (kg·K) or more, or 0.4 kJ / (kg·K) or more.

[0056] The pressing jig 31 may have a lower thermal conductivity than the metal piece 20, for example. The lower the thermal conductivity of the pressing jig 31, the less heat tends to escape from the pressing jig 31. The thermal conductivity of the material constituting the pressing jig 31 may be, for example, 100 W / (m·k) or less, 75 W / (m·k) or less, 50 W / (m·k) or less, 25 W / (m·k) or less, or 10 W / (m·k) or less. The thermal conductivity of the material constituting the pressing jig 31 may be, for example, 1 W / (m·k) or more, 5 W / (m·k) or more, or 10 W / (m·k) or more.

[0057] The pressing jig 31 may be either a solid material or a hollow material. For example, if the pressing jig 31 is a hollow material, the heat capacity of the pressing jig 31 can be reduced. The pressing jig 31 may be, for example, a hollow rod-like material. The pressing jig 31 may be, for example, a hollow cylinder-like material. For example, the hollow portion may penetrate the pressing jig 31 in the axial direction (length direction). In the axial direction of the pressing jig 31, the hollow portion may be open at both end faces or at one end face. The pressing jig 31 may press the metal piece 20 at the end face where the hollow portion is open. The pressing jig 31 may have any hollow ratio as long as it is possible to press the metal piece 20. The "hollow ratio" indicates the percentage of the volume of the hollow portion relative to the apparent volume of the pressing jig 31. The apparent volume indicates the volume calculated from the outer diameter dimensions. The apparent volume includes the volume of the hollow portion 31a. The void ratio may be, for example, 1% or more, 5% or more, 10% or more, 25% or more, 50% or more, or 75% or more. The void ratio may be, for example, 75% or less, 50% or less, 25% or less, 10% or less, 5% or less, or 1% or less.

[0058] FIG. 5 is an explanatory diagram of the contact area between the pressing jig and the metal piece. The metal piece 20 includes a first end face 21 and a second end face 22. The second end face 22 is the face opposite the first end face 21. The first end face 21 and the second end face 22 may each independently be flat or curved. The metal piece 20 is pressed into the electrode body 10 from the first end face 21 side. The pressing jig 31 has a hollow portion 31a. The pressing jig 31 contacts the second end face 22. The second end face 22 is pressed by the pressing jig 31. The contact area between the pressing jig 31 and the second end face 22 may be smaller than the area of ​​the second end face 22. In other words, the relationship of the following formula (3) may be satisfied. S1 <S0…(3) S0: Area of ​​the second end face 22 S1: Contact area between the pressing jig 31 and the second end surface 22 In the cross-sectional view of FIG. 5, for convenience, the difference in area is expressed as the difference in length.

[0059] The area ratio (S1 / S0) is determined by dividing the contact area between the pressing jig 31 and the second end surface 22 by the area of ​​the second end surface 22. When the relationship of the above formula (3) is satisfied, the area ratio (S1 / S0) is less than 1. It is expected that the smaller the area ratio, the less heat will escape from the pressing jig 31. The area ratio (S1 / S0) may be, for example, 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, or 0.1 or less. The area ratio (S1 / S0) may be, for example, 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, or 0.9 or more.

[0060] 6 shows a first example of the end face shape of the pressing jig. The pressing jig 31 may have, for example, a single hollow portion 31a. The outer diameter (φ4) of the pressing jig 31 may be equal to the outer diameter (φ2) of the metal piece 20, for example. The outer diameter (φ4) of the pressing jig 31 may be different from the outer diameter (φ2) of the metal piece 20, for example. The inner diameter (φ3) of the pressing jig 31 may be larger than the inner diameter (φ2) of the metal piece 20, for example.

[0061] 7 shows a second example of the shape of the end face of the pressing jig. The pressing jig 31 may have, for example, a plurality of hollow portions 31a. Each hollow portion 31a may extend along the axial direction (y-axis direction) of the pressing jig 31. Each hollow portion 31a may be parallel to one another.

[0062] FIG. 8 is a schematic plan view of the guide jig. The guide jig 32 can be referred to as, for example, a "pressing jig guide" or a "sleeve." The guide jig 32 has a through hole 32a. The planar shape of the guide jig 32 is arbitrary. The guide jig 32 may have a shape and size that makes it easy to stabilize on the outer surface of the electrode body 10. The planar shape of the guide jig 32 may be, for example, rectangular, circular, etc.

[0063] The guide jig 32 has a through hole 32a. The planar shape of the through hole 32a may be similar to the planar shape (end face shape) of the metal piece 20. The planar shape of the through hole 32a may be similar to the end face shape of the pressing jig 31. A clearance may be set within the through hole 32a so that the pressing jig 31 exhibits slidability. The clearance indicates the difference between the outer diameter of the pressing jig 31 and the inner diameter of the through hole 32a.

[0064] The guide jig 32 may include any material. For example, the guide jig 32 may include at least one material selected from the group consisting of a metal material, a ceramic material, and a resin material. For example, the guide jig 32 may include at least one material selected from the group consisting of a phenolic resin (Bakelite), polyvinyl chloride, an acrylic resin, polyethylene terephthalate, a fluororesin, nylon, polypropylene, and polyethylene.

[0065] (c) Detection of short circuits FIG. 9 is a first conceptual diagram illustrating the detection of a short circuit. This evaluation method involves detecting a short circuit based on a change in the potential difference between an electrode in the electrode assembly 10 and the metal piece 20. The potential difference between the positive electrode 11 and the metal piece 20 may be measured, or the potential difference between the negative electrode 12 and the metal piece 20 may be measured. For example, in the electrode assembly 10, the potential difference between the electrode in the second outermost layer and the metal piece 20 may be measured. In FIG. 9, the electrode in the second outermost layer is the positive electrode 11. The potential difference is measured with a voltmeter. When the metal piece 20 is placed on the outer surface of the electrode assembly 10, the potential difference is 0 V.

[0066] 10 is a second conceptual diagram showing the detection of a short circuit. A metal piece 20 is pushed into the electrode body 10. When the metal piece 20 comes into contact with the negative electrode 12, a change occurs in the potential difference. The potential difference at the time when the metal piece 20 comes into contact with the negative electrode 12 is considered to be equal to the voltage between the positive electrode 11 and the negative electrode 12.

[0067] 11 is a third conceptual diagram illustrating the detection of a short circuit. As the metal piece 20 is further pushed in, it penetrates the negative electrode 12. Then, the metal piece 20 penetrates the separator 13. As the metal piece 20 penetrates the separator 13, the metal piece 20 comes into contact with the positive electrode 11. At this time, the metal piece 20 penetrates one layer of the separator 13, causing a short circuit between the negative electrode 12 and the positive electrode 11. In other words, a one-layer short circuit has occurred.

[0068] When the metal piece 20 comes into contact with the positive electrode 11, the potential difference decreases. That is, a one-layer short circuit can be detected based on the change in the potential difference. The decrease in the potential difference is thought to occur when the metal piece 20 and the positive electrode 11 become equipotential. The amount of decrease in the potential difference is thought to be unlikely to depend on the capacity of the electricity storage device. For example, it may be determined that a short circuit has occurred when a decrease of 2 mV or more in the potential difference is confirmed.

[0069] The pushing speed is arbitrary. However, the lower the pushing speed, the shorter the time lag between detecting a short circuit and stopping the pushing tends to be. The pushing speed may be, for example, 1 mm / s or less, 0.1 mm / s or less, 0.05 mm / s or less, or 0.01 mm / s or less. The pushing speed may be, for example, 0.001 mm / s or more, 0.005 mm / s or more, or 0.01 mm / s or more.

[0070] <(d) Stop pushing> The evaluation method includes stopping the indentation of the metal piece, which may be stopped immediately after detecting a short circuit.

[0071] After the pushing stops, the state of the electrode assembly 10 is checked. The state of the electrode assembly 10 can be used to evaluate the power storage device. The state check can be continued for a predetermined period of time. The check time can be, for example, 1 minute or more, 1 hour or more, 3 hours or more, or 6 hours or more. The check time can be, for example, 24 hours or less, or 12 hours or less.

[0072] The "state of the electrode body" may include, for example, at least one selected from the group consisting of appearance, surface temperature, and terminal voltage. The appearance may be confirmed, for example, by visual inspection. The appearance may be recorded in a recording device. Changes in the appearance may occur, such as discoloration and smoking. For example, the quality of the electricity storage device may be evaluated based on the presence or absence of a change in appearance and the degree of the change in appearance.

[0073] The surface temperature can be measured by, for example, a temperature sensor. The temperature sensor may include, for example, a thermocouple, a thermograph, or the like. For example, the quality of the power storage device may be evaluated based on the level of the surface temperature. The voltage between the terminals can be measured by a voltmeter.

[0074] <Method of manufacturing an electricity storage device> 12 is a schematic flowchart of a method for manufacturing an electricity storage device according to this embodiment. Hereinafter, the "method for manufacturing an electricity storage device according to this embodiment" may be abbreviated as "this manufacturing method." This manufacturing method includes "(A) manufacturing an electricity storage device" and "(B) evaluation of the electricity storage device."

[0075] <(A) Manufacturing of Electricity Storage Devices> The manufacturing method includes manufacturing an electricity storage device. One electricity storage device may be manufactured, or multiple electricity storage devices may be manufactured. For example, multiple electricity storage devices with the same specifications may be manufactured. For example, electricity storage devices with different specifications may be manufactured.

[0076] <(B) Evaluation of energy storage devices> The manufacturing method includes evaluating the electricity storage devices. Each of the electricity storage devices is evaluated by the above-described evaluation method. The evaluation method may be used, for example, for sampling inspections in the manufacturing process of electricity storage devices. For example, one or more electricity storage devices may be sampled from a certain manufacturing lot. For example, the quality of the manufacturing lot may be evaluated based on the evaluation results of the one or more electricity storage devices.

[0077] This evaluation method may be used, for example, for examining specifications in the development process of an electricity storage device. For example, a plurality of electricity storage devices having certain specifications may be manufactured. For example, the acceptability of the specifications may be evaluated based on the evaluation results of one or more electricity storage devices.

[0078] <Electricity storage device> The details of the power storage device will be described below. The term "power storage device" refers to a device that can store electrical energy. The specific configuration and structure of the power storage device are arbitrary. The power storage device may be, for example, a "battery." The battery may be, for example, either a primary battery or a secondary battery. The battery may be, for example, any of a lead battery, a nickel-cadmium battery, a nickel-metal hydride battery, a nickel-zinc battery, a lithium-ion battery, a sodium-ion battery, or a lithium primary battery.

[0079] The battery may be, for example, a liquid battery, a polymer battery, or an all-solid-state battery. The battery may contain at least one selected from the group consisting of a liquid electrolyte (electrolytic solution), a gel electrolyte, and a solid electrolyte.

[0080] The power storage device may be, for example, a “capacitor.” The capacitor may be, for example, a lithium ion capacitor or an electric double layer capacitor.

[0081] The power storage device may be, for example, either a monopolar type (unipolar type) or a bipolar type.

[0082] The electricity storage device includes an electrode assembly. The electricity storage device may further include an exterior material. The "exterior material" is a member that can house the electrode assembly. The exterior material may be referred to as, for example, a housing, a case, a can, or the like. The exterior material may include, for example, a metal container. The exterior material may include, for example, a pouch made of a metal foil laminate film, or the like.

[0083] An "electrode body" is an assembly of electrodes. The electrode body can be referred to as, for example, an electrode group, an electrode assembly, an electrode aggregate, an electrode winding, an electrode stack, etc. The electrode body includes a positive electrode, a separator, and a negative electrode. The separator is interposed between the positive electrode and the negative electrode. The separator separates the positive electrode from the negative electrode.

[0084] FIG. 13 is a schematic diagram of a prismatic battery. Prismatic battery 100 is an example of an electricity storage device. Prismatic battery 100 includes an electrode assembly 110 and an exterior material 120. The exterior material 120 is a prismatic container. "Prismatic" refers to a rectangular parallelepiped shape. The exterior material 120 may be made of, for example, a metal material. The exterior material 120 may be made of, for example, Al, an Al alloy, SUS, Fe, or a resin material. The exterior material 120 may include, for example, a liquid injection hole, a gas release valve, a CID (Current Interrupt Device), etc. The exterior material 120 is sealed. The exterior material 120 houses the electrode assembly 110.

[0085] FIG. 14 is a schematic diagram of an electrode winding. The electrode assembly 110 may be an electrode winding 130. The electrode winding 130 includes a positive electrode 131, a negative electrode 132, and a separator 133. The positive electrode 131, the negative electrode 132, and the separator 133 are all strip-shaped sheets. The electrode winding 130 may include two separators 133. For example, the positive electrode 131, the separator 133 (first sheet), the negative electrode 132, and the separator 133 (second sheet) may be stacked in this order to form a laminate. The electrode winding 130 may be formed by spirally winding the laminate. The electrode winding 130 may be formed into a flat shape by, for example, press working. The electrode winding 130 is impregnated with, for example, an electrolyte solution.

[0086] The positive electrode 131 includes, for example, a positive electrode current collector and a positive electrode active material layer. The positive electrode current collector may include, for example, a metal foil or the like. The positive electrode current collector may include, for example, an Al foil or the like. The positive electrode active material layer may be disposed on the surface of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material. The positive electrode active material layer may further include, for example, a conductive material and a binder in addition to the positive electrode active material. For example, in a lithium ion battery, the positive electrode active material is a lithium-containing transition metal composite oxide (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.8 Co 0.15 Al 0.05 It may also contain oxygen (O2, etc.).

[0087] The negative electrode 132 includes, for example, a negative electrode current collector and a negative electrode active material layer. The negative electrode current collector may include, for example, a metal foil or the like. The negative electrode active material layer may be disposed on the surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material. In addition to the negative electrode active material, the negative electrode active material layer may further include, for example, a conductive material and a binder. For example, in a lithium-ion battery, the negative electrode active material may include graphite or the like.

[0088] The separator 133 may include, for example, a porous film. The porous film may be made of, for example, polyethylene (PE), polypropylene (PP), polyamide (PA), or the like. The porous film may have a multi-layer structure. For example, the porous film may be formed by laminating a PP layer, a PE layer, and a PP layer in this order.

[0089] The separator 133 may further include, in addition to the porous film, a ceramic layer, for example. The ceramic layer may be disposed on the surface of the porous film, for example. The ceramic layer includes, for example, a ceramic material and a binder. The ceramic material may include, for example, alumina, boehmite, or the like.

[0090] 15 is a schematic diagram of an electrode stack. The electrode assembly 110 may be an electrode stack 140. The electrode stack 140 includes a positive electrode 141, a negative electrode 142, and a separator 143. The positive electrode 141, the negative electrode 142, and the separator 143 are all rectangular sheets. The electrode stack 140 can be formed by alternately stacking the positive electrodes 141 and the negative electrodes 142. The separators 143 are disposed between the positive electrodes 141 and the negative electrodes 142, respectively. The electrode stack 140 is impregnated with, for example, an electrolyte solution.

[0091] FIG. 16 is a schematic diagram of a cylindrical battery. A cylindrical battery is an example of an electricity storage device. A cylindrical battery 200 includes an electrode assembly 210 and an exterior material 220. The exterior material 220 is a cylindrical container. The exterior material 220 may be made of, for example, SUS, Fe, or a resin material. The exterior material 220 is sealed. The exterior material 220 houses the electrode assembly 210. The electrode assembly 210 includes a positive electrode 211, a negative electrode 212, and a separator 213. The electrode assembly 210 may be, for example, a wound electrode assembly. The electrode assembly 210 may be, for example, wound into a cylindrical shape.

[0092] FIG. 17 is a schematic diagram of a pouch-type battery. A pouch-type battery is an example of an electricity storage device. A pouch-type battery may also be called, for example, a "laminated battery." A pouch-type battery 300 includes an exterior material 320 and an electrode assembly. The exterior material 320 is a pouch made of aluminum laminate film. The pouch is sealed, for example, by thermal welding. The exterior material 320 houses the electrode assembly. The electrode assembly may be, for example, an electrode wound assembly. The electrode assembly may be, for example, an electrode laminate.

[0093] 18 is a schematic diagram showing an example of opening the exterior material. For example, as described above, a portion of the exterior material 320 may be hollowed out to expose a portion of the electrode body 310. A metal piece 20 may be placed in the exposed portion of the electrode body 310. [Example]

[0094] Fig. 19 is a configuration table of the test sample. An electricity storage device having the configuration shown in Fig. 19 was prepared.

[0095] FIG. 20 is a table showing the experimental results. Short-circuit tests were conducted using methods No. 1 to No. 4. The short-circuit tests were conducted on 10 cells of each of the 5 to 200 Ah energy storage devices. After the tests, the energy storage devices were disassembled to evaluate the number of short-circuited layers and the diameter of the molten metal.

[0096] The "number of short-circuited layers" indicates the number of separator layers penetrated by metal fragments. In the "number of short-circuited layers" section of Figure 20, for example, "1 (10 / 10)" indicates that there was one short-circuited layer in all ten of the ten tests. For example, "1 (7 / 10), 0 (3 / 10)" indicates that there was one short-circuited layer in seven of the ten tests, and zero short-circuited layers (no short circuits) in three of the tests.

[0097] In the "Wet diameter" section of Figure 20, for example, the entry "Φ(7 / 10), 0(3 / 10)" indicates that in 7 out of 10 tests, holes with a diameter of Φ (unit: mm) were formed in the separator, and in 3 tests, no holes were formed in the separator. For example, the entry "2Φ(10 / 10)" indicates that in all 10 out of 10 tests, holes with a diameter of 2Φ (twice Φ) were formed in the separator.

[0098] In the "Voltage Drop" section of Figure 20, "δ" indicates a voltage drop of 2 mV or more. "N" indicates that the voltage drop was less than 2 mV. For example, "δ (7 / 10), N (3 / 10)" indicates that a voltage drop of δ (unit: mV) was confirmed in seven of the ten tests, and that the voltage drop was less than 2 mV in three of the tests. For example, "0.5δ" indicates a value 0.5 times δ.

[0099] <No.1> For No. 1, the "Forced Internal Short Circuit Test" described in IEC 62660-3 was used as a reference. The metal piece was L-shaped (made of nickel). The metal piece was 0.2 mm high, with each side of the L-shape measuring 1 mm (total length 2 mm), and the metal piece width 0.1 mm. The pressing tool was an acrylic resin block (5 mm x 5 mm). The pressing speed was 0.01 mm / s. For No. 1, a drop in terminal voltage of 2 mV or more was considered to be a short circuit. However, for No. 1, pressing was stopped when the pressing load reached 400 N, even if the drop in terminal voltage was less than 2 mV. For example, as shown in the "Number of Short-Circuit Layers" in Figure 20, for No. 1, a tendency for short circuits to occur less readily as the capacity of the energy storage device increased.

[0100] <No.2> For No. 2, the evaluation method for electricity storage devices described in Patent Document 1 was used as a reference. The metal piece was ring-shaped (made of stainless steel). The pressing jig was a Bakelite rod. The pressing speed was 0.01 mm / s. For No. 2, a drop in terminal voltage of 2 mV or more was considered to be the occurrence of a short circuit. However, for No. 2, pressing was stopped when the pressing load reached 400 N, even if the drop in terminal voltage was less than 2 mV. As shown in the "Number of short-circuit layers" in Figure 20, for No. 2, there is a tendency for the number of short-circuit layers to increase as the capacity of the electricity storage device increases.

[0101] <No.3> No. 3 was carried out in accordance with this evaluation method. The metal piece was ring-shaped (made of stainless steel). The pressing jig was a solid metal rod. The pressing speed was 0.01 mm / s. In No. 3, a decrease in the potential difference between the positive electrode and the metal piece was considered to be the occurrence of a short circuit. As shown in the "Number of short-circuited layers" in Figure 20, in No. 3, a single-layer short circuit was maintained even as the capacity of the energy storage device increased. In other words, the reproducibility of a single-layer short circuit was improved.

[0102] Figure 21 is a graph showing the relationship between the average number of short-circuited layers and the capacity of the power storage device. In the capacity range of 50 Ah or more, No. 1 and No. 2 show a significant deviation from single-layer short-circuiting. In contrast, No. 3 stably reproduces single-layer short-circuiting.

[0103] <No.4> No. 4 was evaluated according to this evaluation method. The metal piece was ring-shaped (made of stainless steel). The pressing tool was a hollow metal rod. The pressing speed was 0.01 mm / s. In No. 4, a decrease in the potential difference between the positive electrode and the metal piece was considered to be the occurrence of a short circuit. As shown in the "Number of short-circuited layers" in Figure 20, in No. 4, one layer of short circuit remained even as the capacity of the energy storage device increased.

[0104] In No. 3, the pushing jig is solid material. In contrast, in No. 4, the pushing jig is hollow material. No. 4 tends to have a larger molten diameter than No. 3. This is thought to be because it is more difficult for heat to escape from hollow material than from solid material.

[0105] A correlation is observed between the molten diameter and the voltage drop. In other words, the larger the molten diameter, the larger the voltage drop (absolute value) tends to be. It is expected that the greater the voltage drop, the more accurate the short circuit detection. [Explanation of symbols]

[0106] 10,110,210,310 Electrode body, 11,131,141,211 Positive electrode, 12,132,142,212 Negative electrode, 13,133,143,213 Separator, 20 Metal piece, 21 First end surface, 22 Second end surface, 30 Jig set, 31 Pressing jig, 31a Hollow portion, 32 Guide jig, 32a Through hole, 100 Prismatic battery, 120,220,320 Exterior material, 130 Electrode winding body, 140 Electrode laminate, 200 Cylindrical battery, 300 Pouch-shaped battery.

Claims

1. A method for evaluating an electricity storage device including an electrode assembly, comprising: (a) disposing a metal piece on the outer surface of the electrode body; (b) forcing the metal piece into the electrode body; (c) detecting a short circuit based on a change in the potential difference between the electrode in the electrode body and the metal piece; and (d) stopping the pushing of the metal piece; in this order, (b) includes using a pushing jig and a guide jig; The guide jig is provided with a through hole, The pushing jig is inserted into the through hole, the metal piece has a ring shape; the metal piece is disposed within the through hole; The pushing jig pushes the metal piece out of the through-hole, thereby pushing the metal piece into the electrode body, The pressing jig is conductive, and The hardness of the pressing jig is equal to or greater than the hardness of the metal piece. A method for evaluating an energy storage device.

2. The pushing jig is hollow rod-shaped. The method for evaluating an electricity storage device according to claim 1 .

3. the metal piece has a first end surface and a second end surface; the second end surface is an opposite surface to the first end surface, In the step (b), the pushing jig contacts the second end surface, and a contact area between the pressing jig and the second end surface is smaller than an area of ​​the second end surface; The method for evaluating the electricity storage device according to claim 1 or 2.

4. The pressing jig is made of metal. The method for evaluating the electricity storage device according to claim 1 or 2.

5. A jig set used in the method for evaluating an electricity storage device according to claim 4, The pushing jig and the guide jig are included. Jig set.

6. (A) manufacturing an electricity storage device; and (B) evaluating the electricity storage device; in this order, (B) includes the evaluation method for the electricity storage device according to claim 1 or claim 2, A method for manufacturing an electricity storage device.

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