Battery inspection method and battery manufacturing method

Abstract

This invention provides a battery inspection method that can determine whether a battery is good or bad based on the rate of change in voltage. [Solution] A method for inspecting a battery containing an electrolyte, wherein, during charging of the battery, it is determined whether or not the rate of change of voltage at the potential at which impurities in the electrolyte are electrolyzed is below a predetermined threshold.

Description

Technical Field

[0001] The present disclosure relates to a method for inspecting a battery and a method for manufacturing a battery.

Background Art

[0002] Conventionally, as a method for inspecting the amount of moisture contained in a battery, Japanese Patent Application Laid-Open No. 2014-6981 (Patent Document 1) discloses a technique for calculating the amount of moisture remaining in a battery by performing a drying process for removing moisture inside the battery and measuring the weights before and after the drying process.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When impurities such as moisture remain inside the battery, the battery performance may deteriorate. However, if the injection port is not sealed even after the drying process, moisture may reattach. Therefore, the inspection method described in Patent Document 1 is not sufficient for determining whether a battery is a good product or a defective product.

[0005] The present disclosure has been made in view of the above problems, and an object of the present disclosure is to provide a method for inspecting a battery and a method for manufacturing a battery that can determine whether a battery is good or bad based on the rate of change of voltage.

Means for Solving the Problems

[0006] The method for inspecting a battery according to the present disclosure is a method for inspecting a battery containing an electrolytic solution. In this method for inspecting the battery, when the battery is charged, it is determined whether the rate of change of voltage at a potential at which a substance that becomes an impurity with respect to the electrolytic solution is electrolyzed is less than or equal to a predetermined threshold value.

[0007] A method for manufacturing a battery based on this disclosure comprises the steps of preparing a battery into which an electrolyte has been injected, and charging the battery. In the charging step, the battery inspection method described above is performed. [Effects of the Invention]

[0008] According to this disclosure, it is possible to provide a battery inspection method and a battery manufacturing method that can determine whether a battery is good or bad based on the rate of change of voltage. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic cross-sectional view of a battery according to an embodiment. [Figure 2] This is a flowchart showing the manufacturing process for producing the battery according to the embodiment. [Figure 3] This diagram shows the process of charging the battery in the flow shown in Figure 2. [Figure 4] This figure shows the first example of the relationship between voltage and time during the battery charging process shown in Figure 2. [Figure 5] This figure shows a second example of the relationship between voltage and time during the battery charging process shown in Figure 2. [Figure 6] This figure shows an example of the relationship between voltage and capacity during the battery charging process shown in Figure 2. [Modes for carrying out the invention]

[0010] The embodiments of this disclosure will be described in detail below with reference to the drawings. In the embodiments described below, the same or common parts are denoted by the same reference numerals in the drawings, and their descriptions will not be repeated.

[0011] Figure 1 is a schematic cross-sectional view of a battery according to an embodiment. The battery 100 according to the embodiment will be described with reference to Figure 1. In Figure 1, of the mutually orthogonal X, Y, and Z axes, the Z axis indicates the thickness direction of the battery. Hereafter, the direction indicated by the arrows on the X, Y, and Z axes will be indicated with a "+" and the opposite direction with a "-".

[0012] As shown in Figure 1, the battery 100 is a secondary battery, more specifically a bipolar secondary battery. The battery 100 comprises a laminate 10, a sealing portion 3, and a plurality of voltage detection terminals 20. The laminate 10 includes a plurality of electrode plates 1 and a plurality of separators 13.

[0013] Multiple electrode plates 1 and separators 13 are stacked alternately in the stacking direction. In Figure 1, the Z direction is perpendicular to the electrode plates 1 and corresponds to the stacking direction. Figure 1 illustrates a state where the stacking direction is parallel to the vertical direction (up and down direction).

[0014] The multiple electrode plates 1 include one negative terminal electrode 2A, multiple bipolar electrodes 2C, and one positive terminal electrode 2B. The positive terminal electrode 2B constitutes the end of the laminate 10 on one side in the stacking direction. The negative terminal electrode 2A constitutes the end of the laminate 10 on the other side in the stacking direction. The multiple bipolar electrodes 2C are arranged between the positive terminal electrode 2B and the negative terminal electrode 2A in the stacking direction.

[0015] Each bipolar electrode 2C includes a current collector 11, a negative electrode active material layer 12A provided on the +Z side surface (first main surface) of the current collector 11, and a positive electrode active material layer 12B provided on the -Z side surface (second main surface) of the current collector 11. The first main surface and the second main surface are arranged side by side in the stacking direction.

[0016] The negative terminal electrode 2A has a structure in which the positive electrode active material layer 12B is removed from the bipolar electrode 2C. That is, in the negative terminal electrode 2A, the negative electrode active material layer 12A is provided on the +Z side surface of the current collector 11, but the positive electrode active material layer 12B is not provided on the -Z side surface of the current collector 11. An insulating layer 19A is formed on the -Z side surface of the current collector 11 that constitutes the negative terminal electrode 2A. The insulating layer 19A covers the peripheral portion of the negative terminal electrode 2A, and the central portion of the current collector 11 in the negative terminal electrode 2A is exposed from the insulating layer 19A.

[0017] The positive terminal electrode 2B has a structure in which the negative electrode active material layer 12A is removed from the bipolar electrode 2C. That is, in the positive terminal electrode 2B, the positive electrode active material layer 12B is provided on the -Z side surface of the current collector 11, but the negative electrode active material layer 12A is not provided on the +Z side surface of the current collector 11. An insulating layer 19B is formed on the +Z side surface of the current collector 11 that constitutes the positive terminal electrode 2B. The insulating layer 19B covers the peripheral portion of the positive terminal electrode 2B. The central portion of the current collector 11 in the positive terminal electrode 2B is exposed from the insulating layer 19B.

[0018] A unit cell C is formed between each of the plurality of stacked current collectors 11. Specifically, a unit cell C is formed between a certain current collector 11 (the first current collector) and the current collector 11 (the second current collector) adjacent to the first current collector. Further, a unit cell C is also formed between the second current collector and the current collector 11 (the third current collector) adjacent to the second current collector. The unit cell C includes a negative electrode active material layer 12A, a positive electrode active material layer 12B, and a separator 13.

[0019] Two electrode plates 1 adjacent to each other in the stacking direction face each other with a separator 13 interposed between the negative electrode active material layer 12A of the electrode plate 1 located on the lower side and the positive electrode active material layer 12B of the electrode plate 1 located on the upper side.

[0020] The number of unit cells C can be arbitrarily set. The number of unit cells C may be, for example, 3 or more and less than 50, or 50 or more.

[0021] The current collector 11 is, for example, a metal foil. Surface treatment (e.g., plating treatment) may be performed on one or both sides of the metal foil. As the metal foil, a laminated one of aluminum foil and copper foil may be used. In this case, the positive electrode active material layer 12B is formed on the aluminum foil, and the negative electrode active material layer 12A is formed on the copper foil. Note that the metal foil may be a single layer.

[0022] The negative electrode active material layer 12A contains a negative electrode active material. The positive electrode active material layer 12B contains a positive electrode active material. Known negative electrode active materials and positive electrode active materials can be adopted. In one example, the positive electrode active material is olivine-type lithium iron phosphate (LiFePO4), the negative electrode active material is a carbon-based material (e.g., graphite), and the electrolyte is a non-aqueous electrolyte (e.g., an ester-based electrolyte). However, these materials can be appropriately changed.

[0023] Another example of the positive electrode active material includes a composite oxide (such as LiCoO2, LiNiMnCoO2, etc.) containing one or more elements selected from the group consisting of manganese, titanium, nickel, cobalt, and aluminum and lithium. Another example of the negative electrode active material includes silicon and tin. The electrolyte may be an aqueous electrolyte. Also, a gel-like or solid electrolyte may be adopted instead of the electrolyte.

[0024] Examples of the material constituting the separator 13 include polypropylene, polyethylene, polyester, and cellulose. The structure of the separator 13 may be a single-layer structure or a multi-layer structure. The separator 13 may include, for example, a base material layer and a pair of adhesive layers, and may be adhered to the negative electrode active material layer 12A and the positive electrode active material layer 12B by the pair of adhesive layers. The separator 13 may be a porous sheet.

[0025] The sealing portion 3 surrounds the periphery of the plurality of electrode plates 1. The sealing portion 3 seals each internal space formed between two adjacent electrode plates 1 in the stacking direction among the plurality of electrode plates 1. The space surrounded by the sealing portion 3 (each of the above internal spaces) is filled with an electrolyte. The electrolyte is impregnated into the separator 13 and the like.

[0026] The sealing portion 3 includes sealing layers 14 and 15 and insulating layers 19A and 19B. The sealing layers 14 and 15 are arranged around each of the multiple unit batteries C contained in the laminate 10. The sealing layers 14 and 15 are also arranged in the gaps between two adjacent electrodes.

[0027] Any sealing material can be used to constitute the sealing portion 3. Examples of sealing materials include resin materials such as polyethylene, polypropylene, acid-modified polyethylene, or acid-modified polypropylene. The structure of the sealing portion 3 between the current collectors 11 is not limited to a two-layer structure (seal layers 14, 15), but may also be a three-layer structure. The sealing portion 3 may include a spacer. Furthermore, the seal layers 14 and 15 may be integrated by heat welding or the like.

[0028] A voltage detection terminal 20 is connected to each current collector 11. The voltage detection terminal 20 is welded, for example, to the +X side end of the current collector 11. Examples of welding methods include ultrasonic welding or laser welding.

[0029] The voltage detection terminal 20 includes stainless steel (e.g., SUS304). Stainless steel has excellent corrosion resistance, heat resistance, and workability. However, the material of the voltage detection terminal 20 is not limited to the above and can be changed as appropriate. Other metals (e.g., copper) may be used instead of stainless steel.

[0030] Figure 2 is a flowchart showing the manufacturing process for producing the battery according to the embodiment. The manufacturing method for the battery 100 according to the embodiment will be described with reference to Figure 2.

[0031] As shown in Figure 2, in manufacturing the battery 100, first, in process (S10), the battery 100 with the electrolyte injected is prepared.

[0032] Specifically, a laminate 10 is formed by alternately stacking multiple electrode plates 1 and separators 13, to which voltage detection terminals 20 are connected, and the surrounding area is sealed with resin. The portion of the laminate 10 sealed with resin functions as a sealing portion 3. After injecting electrolyte into the battery 100 (specifically into each internal space) through an injection port provided in the sealing portion 3, the injection port is sealed. The battery 100 prepared in step (S10) is not charged.

[0033] Next, in step (S20), the battery 100 is charged. Figure 3 is a diagram showing the battery charging process in the flow shown in Figure 2.

[0034] As shown in Figure 3, the battery 100 is charged using the charging device 300. The charging device 300 applies a voltage between the positive terminal (current collector 11 of the positive terminal electrode 2B) and the negative terminal (current collector 11 of the negative terminal electrode 2A) of the battery 100. As a result, a charging current flows along the stacking direction as indicated by the arrow in the figure, and multiple unit batteries C are charged. The control device 400 controls the operation of the charging device 300 and continues charging until the average voltage value of the multiple unit batteries C reaches a predetermined target value.

[0035] During charging, the inspection method according to this embodiment is used. Specifically, during the charging of the battery 100, step (S21) is performed as an inspection of the battery 100.

[0036] In step (S21), the rate of change of the voltage of each unit battery C is detected. Specifically, a detector 200 is connected to multiple voltage detection terminals 20, and the state of the unit battery C is detected via the voltage detection terminals 20 and the current collector 11. The detector 200 detects the voltage of each unit battery C based, for example, on the potential difference between two current collectors 11 (voltage detection terminals 20) that sandwich each unit battery C.

[0037] Figure 4 shows a first example of the relationship between voltage and time during the battery charging process shown in Figure 2. As shown in Figure 4, during charging, the relationship between voltage and time is such that the voltage rises initially and then converges to a predetermined voltage value.

[0038] Here, when charging battery 100, if it contains no impurities, the voltage of the unit cell C will increase as it charges. On the other hand, if the electrolyte contains impurities, the voltage of the unit cell C will remain approximately constant at the potential at which the impurities are electrolyzed. Examples of impurities include water. The voltage of the battery at which water is electrolyzed is approximately 2.2V.

[0039] Therefore, by determining whether the rate of change of voltage at the potential in which impurities are electrolyzed is below a predetermined threshold, it is possible to determine whether the battery 100 is good or defective. Note that the impurities may be substances other than water, as long as they are electrolyzed.

[0040] In the first example above, as shown within the dashed-dotted ellipse, if the voltage increase per unit time (dv / dt) near a predetermined voltage at which impurities are electrolyzed is below a predetermined threshold, the unit battery C is determined to be defective.

[0041] On the other hand, as shown in the area enclosed by the dashed line, if the voltage increase per unit time (dv / dt) near a predetermined voltage at which impurities are electrolyzed is greater than a predetermined threshold, then unit battery C is judged to be a good product.

[0042] Figure 5 shows a second example of the relationship between voltage and time during the charging process of the battery shown in Figure 2. As shown in the second example in Figure 5, depending on the charging conditions, several hours after the start of charging, differences in the rate of change of voltage may appear in multiple unit batteries C around a predetermined voltage at which impurities are electrolyzed.

[0043] Even in such cases, as shown within the dashed-dotted ellipse, if the voltage increase per unit time (dv / dt) near a predetermined voltage at which impurities are electrolyzed is below a predetermined threshold, the unit battery C is determined to be defective.

[0044] On the other hand, if the voltage increase per unit time (dv / dt) near a predetermined voltage at which impurities are electrolyzed is greater than a predetermined threshold, then unit battery C is judged to be a good product.

[0045] As shown in Figures 5 and 6, the voltage measurement result obtained from the detector 200 is input to the control device 400, and the control device 400 calculates the voltage increase per unit time (dv / dt) near a predetermined voltage at which impurities are electrolyzed from the measurement result. The control device 400 determines whether the voltage increase per unit time (dv / dt) is below a predetermined threshold, and determines that the battery 100 containing a unit battery C below the predetermined threshold is defective.

[0046] On the other hand, the control device 400 determines that battery 100 is a good product if, in all of the multiple unit batteries C, the amount of voltage increase per unit time (dv / dt) near a predetermined voltage at which impurities are electrolyzed is greater than a predetermined threshold.

[0047] In the above example, the rate of change of voltage used in the inspection method is given as the voltage increase per unit time (dv / dt), but it is not limited to this, and may also be the voltage increase per unit capacity (dv / dQ).

[0048] Figure 6 shows an example of the relationship between voltage and capacity during the charging process of the battery shown in Figure 2. During charging, the relationship between voltage and capacity is such that the voltage increases in stages as the capacity increases, as shown in Figure 6.

[0049] In the relationship between voltage and capacity, as shown in the area enclosed by the dashed line, if the voltage increase per unit capacity (dv / dQ) near a predetermined voltage at which impurities are electrolyzed is greater than a predetermined threshold, then the unit battery C is judged to be a good product.

[0050] On the other hand, as shown within the dashed-dotted ellipse, if the voltage increase per unit time (dv / dQ) near a predetermined voltage at which impurities are electrolyzed is below a predetermined threshold, the unit battery C is determined to be defective.

[0051] In this way, the voltage measurement result obtained from the detector 200 is input to the control device 400, and the control device 400 calculates the voltage increase per unit capacity (dv / dQ) near a predetermined voltage at which impurities are electrolyzed from the measurement result. The control device 400 determines whether the voltage increase per unit capacity (dv / dQ) is below a predetermined threshold, and determines that the battery 100 containing a unit cell C below the predetermined threshold is defective.

[0052] By using the inspection method described above, even if moisture adheres to the inside of the battery 100 after the liquid is injected but before the injection port is sealed, it is possible to determine whether the battery 100 is good or bad due to impurities such as moisture.

[0053] As shown again in Figure 2, after process (S20), a subsequent process is carried out as process (S30). In the subsequent process, the batteries 100 that were judged to be good products in process (S21) are shipped out after going through a predetermined process. The batteries 100 are manufactured through the above process.

[0054] The battery 100 may be used individually, or multiple batteries 100 may be combined to form a module. This module may be used individually, or multiple modules may be stacked together so as to be electrically connected in series. For example, a battery pack (energy storage device) may be completed by housing multiple modules together with other components (such as a cooler) in a case. The manufactured energy storage device may be mounted on a mobile vehicle, for example. Examples of mobile vehicles include automobiles (electric vehicles, hybrid vehicles, etc.), vehicles other than automobiles (ships, airplanes, etc.), mobile machinery (agricultural machinery, construction machinery, etc.), and unmanned mobile vehicles (autonomous transport vehicles, robots, etc.). However, the intended use of the manufactured battery is arbitrary, and a stationary battery may also be manufactured by the above method.

[0055] The embodiments disclosed herein are illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, and all modifications are within the meaning and scope equivalent to the claims. [Explanation of symbols]

[0056] 1 Electrode plate, 2A Negative terminal electrode, 2B Positive terminal electrode, 2C Bipolar electrode, 3 Sealing part, 10 Laminate, 11 Current collector, 12A Negative active material layer, 12B Positive active material layer, 13 Separator, 14,15 Seal layer, 19A,19B Insulating layer, 20 Voltage detection terminal, 100 Battery, 200 Detector, 300 Charging device, 400 Control device, C Unit battery.

Claims

1. A method for inspecting batteries containing electrolyte, A battery inspection method for determining whether the rate of change of voltage at the potential in which impurities in the electrolyte are electrolyzed during charging of the battery is below a predetermined threshold.

2. The battery inspection method according to claim 1, wherein the impurity substance is water.

3. The battery inspection method according to claim 1 or 2, wherein the rate of change of the voltage is the amount of voltage increase per unit time (dv / dt).

4. The battery inspection method according to claim 1 or 2, wherein the rate of change of the voltage is the voltage increase per unit capacity (dv / dQ).

5. The process of preparing a battery with electrolyte injected, The process includes a step of charging the aforementioned battery, A method for manufacturing a battery, comprising performing the battery inspection method described in claim 1 or 2 during the charging step.

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