JP6248751B2 - Power storage device inspection method - Google Patents

Description

  The present invention relates to an inspection method for a power storage device that performs a short circuit inspection on an electrode assembly in the process of manufacturing a power storage device including an electrode assembly having a positive electrode, a negative electrode, and a separator.

  The power storage device is configured such that an electrode assembly in which a positive electrode and a negative electrode are stacked via a separator is accommodated in a case. If foreign matter enters between the positive electrode and the separator of this electrode assembly or between the negative electrode and the separator, the separator may be stretched and broken by the foreign matter. When the separator breaks, an internal short circuit occurs in the electrode assembly. Therefore, a short circuit inspection is performed on the electrode assembly (laminated body) before being housed in the case, and an internal short circuit (and hence a foreign object) is detected. Patent Document 1 discloses a battery short-circuit inspection method for performing a short-circuit inspection while pressurizing an electrode plate group before inserting the electrode plate group in which a positive electrode plate and a negative electrode plate are laminated via a separator into a battery case. Yes.

JP 2001-236985 A

  In some cases, a power storage device uses a separator having a large allowable amount of elongation so that the separator is not easily broken even if foreign matter enters between the electrode and the separator. When such a separator is used, the separator does not break even if foreign matter of a certain size is contained. In this case, the electrode assembly does not cause an internal short circuit, and a short circuit (and hence a foreign object) cannot be detected by a short circuit inspection. Even when a separator having a large allowable amount of elongation is not used, the separator may not be broken if a foreign substance having a small size enters. Also in this case, the electrode assembly does not cause an internal short circuit, and a short circuit cannot be detected by a short circuit inspection. Even in the short circuit inspection method disclosed in the above-mentioned Patent Document 1, a short circuit cannot be detected in such a case.

  Therefore, in this technical field, there is a demand for a method for inspecting a power storage device that can improve the detection accuracy of foreign matter that has entered between an electrode and a separator.

  An inspection method for a power storage device according to an aspect of the present invention performs a short circuit inspection on an electrode assembly in a process of manufacturing a power storage device including an electrode assembly having a positive electrode, a negative electrode, and a separator between the positive electrode and the negative electrode. The inspection method includes a temperature adjustment step of adjusting the temperature of the electrode assembly to a predetermined temperature or less, and a short-circuit inspection step of performing a short-circuit inspection of the electrode assembly during the temperature adjustment in the temperature adjustment step.

  The electrode assembly of this power storage device includes a positive electrode and a negative electrode as electrodes, and a separator is disposed between the positive electrode and the negative electrode. The glass transition temperature of the separator is determined by the material used, and when the separator is below the glass transition temperature, it enters a glass state. Therefore, when performing a short circuit inspection on the electrode assembly, the temperature of the electrode assembly is adjusted to a predetermined temperature or lower to perform a short circuit inspection. The predetermined temperature is lower than the glass transition temperature of the separator of the electrode assembly. By adjusting the temperature of the electrode assembly (and hence the separator) to a predetermined temperature or lower, the separator changes to a glass state, and the separator is prevented from being stretched (the allowable elongation of the separator is reduced). For this reason, even when a small-sized foreign substance is present between the positive electrode or the negative electrode and the separator, the separator is easily broken by the foreign substance. When the separator breaks, the positive electrode and the negative electrode are short-circuited directly or via conductive foreign matter, and a short-circuit (and hence foreign matter) can be detected by a short-circuit inspection. As described above, this power storage device inspection method detects a foreign matter that has entered between the electrode and the separator by adjusting the temperature of the electrode assembly (and thus the separator) to a predetermined temperature or less and performing a short circuit inspection. Accuracy can be improved.

  Note that the electrode assembly to be inspected may be in a state where the tabs of the electrodes are not welded, or may be in a state where the tabs of the electrodes are welded. Further, the electrode assembly to be inspected may be a laminated body or a wound body.

  In the power storage device inspection method according to the embodiment, the predetermined temperature may be set based on the glass transition temperature of the separator. By setting a predetermined temperature based on the glass transition temperature of the separator, when the temperature is adjusted to the predetermined temperature or lower, the separator can be reliably transferred to the glass state and the temperature does not have to be lowered more than necessary. The optimum predetermined temperature can be set.

  ADVANTAGE OF THE INVENTION According to this invention, the detection precision of the foreign material which entered between the electrode and the separator can be improved.

It is a figure which shows typically the structure of the short circuit test | inspection system used for the test | inspection method of the electrical storage apparatus which concerns on one Embodiment.

  Hereinafter, an inspection method for a power storage device according to an embodiment of the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected about the element which is the same or it corresponds in each figure, and the overlapping description is abbreviate | omitted.

  A power storage device inspection method according to an embodiment is applied to an inspection step of performing a short circuit inspection on an electrode assembly (laminated body) stacked in a stacking step in the process of manufacturing a power storage device. In this inspection process, a short circuit inspection system is used. The power storage device is a power storage device such as a secondary battery or an electric double layer capacitor. The secondary battery is, for example, a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery. In this embodiment, the power storage device is applied to a lithium ion secondary battery.

  With reference to FIG. 1, a power storage device inspection method (inspection process) according to an embodiment will be described. FIG. 1 is a diagram schematically illustrating a configuration of a short circuit inspection system used in a method for inspecting a power storage device according to an embodiment.

  Before describing the inspection process, the configuration of the power storage device will be described. The power storage device is a rectangular power storage device. In the power storage device, an electrode assembly, an electrolytic solution, and the like are accommodated in a case. Here, only the electrode assembly to be inspected will be described in detail. The electrode assembly includes a positive electrode, a negative electrode, and a separator, and is a laminate in which the positive electrode and the negative electrode are stacked with a separator interposed therebetween.

  The positive electrode includes a metal foil and a positive electrode active material layer formed on at least one surface of the metal foil. The positive electrode has a tab on which the positive electrode active material layer is not formed at the end of the metal foil. The tab extends to the upper edge of the positive electrode and is connected to the positive terminal via a conductive member. The metal foil is, for example, an aluminum foil or an aluminum alloy foil. The positive electrode active material layer includes a positive electrode active material and a binder. The positive electrode active material layer may contain a conductive additive. The positive electrode active material is, for example, a composite oxide, metallic lithium, or sulfur. The composite oxide includes at least one of manganese, nickel, cobalt, and aluminum and lithium. The binder is, for example, a fluorine-containing resin such as polyvinylidene fluoride, polytetrafluoroethylene, or fluororubber, a thermoplastic resin such as polypropylene or polyethylene, an imide resin such as polyimide or polyamideimide, or an alkoxysilanol group-containing resin. . Examples of the conductive auxiliary agent include carbon black, graphite, acetylene black, and ketjen black (registered trademark).

  The negative electrode includes a metal foil and a negative electrode active material layer formed on at least one surface of the metal foil. The negative electrode has a tab on which the negative electrode active material layer is not formed at the end of the metal foil. The tab extends to the upper edge of the negative electrode and is connected to the negative electrode terminal via a conductive member. The metal foil is, for example, a copper foil or a copper alloy foil. The negative electrode active material layer includes a negative electrode active material and a binder. The negative electrode active material layer may contain a conductive additive. Examples of the negative electrode active material include graphite, highly oriented graphite, carbon such as mesocarbon microbeads, hard carbon, and soft carbon, alkali metals such as lithium and sodium, metal compounds, and SiOx (0.5 ≦ x ≦ 1.5). ) And the like, and boron-added carbon. As the binder and the conductive additive, for example, the same binder and conductive additive exemplified in the positive electrode can be applied. As the binder, carboxymethyl cellulose, methyl cellulose, styrene butadiene rubber, alkoxysilyl group-containing resin, and the like can be applied in addition to the positive electrode examples.

  The separator separates the positive electrode and the negative electrode and allows lithium ions to pass while preventing a short circuit due to contact between the two electrodes. The separator is, for example, a porous film made of a polyolefin resin such as polyethylene (PE) or polypropylene (PP), a woven fabric or a nonwoven fabric made of polypropylene, polyethylene terephthalate (PET), methylcellulose or the like. The separator has a glass transition temperature determined by the materials used, and enters a glass state when the temperature falls below the glass transition temperature.

  In the laminating step, a predetermined number of sheet-like positive electrodes and sheet-like negative electrodes are laminated via a separator. In particular, as for the lamination of the separators, sheet-like separators may be laminated one by one, or a bag-like separator in which two sheets are welded, other than a tab of one electrode (for example, positive electrode). You may laminate | stack in the state which wrapped the part. After this lamination process, an inspection process is performed on the electrode assembly (laminated body) laminated in the lamination process. The inspection process is performed on the electrode assembly in which the tabs of the electrodes are not welded to each other.

  Now, the inspection process will be described. In the inspection process, the short-circuit inspection is performed by pressurizing (adding a load) the electrode assembly (laminated body) S using the short-circuit inspection system 1 shown in FIG. This short circuit inspection in the pressurized state is the same as the conventional well-known short circuit inspection. In particular, in the inspection process, in order to detect whether a foreign substance is contained with high accuracy (in order to easily break the separator due to the foreign substance), the temperature of the electrode assembly S is adjusted to a predetermined temperature or less to perform a short circuit inspection. For this purpose, the short-circuit inspection system 1 includes a tester 2, a pressure member 3, a load generator 4, and a constant temperature bath 5.

  The tester 2 is a tester that measures a resistance value. The tester 2 is a conventional tester used for well-known short-circuit inspection. In the tester 2, when the positive electrode tab Tp of the electrode assembly S is connected to the positive measurement terminal 2a and the negative electrode tab Tn of the electrode assembly S is connected to the negative measurement terminal 2b, the positive electrode tab Tp A predetermined voltage (for example, several V) is applied between the negative electrode tab Tn and the resistance value between the positive electrode tab Tp and the negative electrode tab Tn is measured. When the positive electrode and the negative electrode are not short-circuited, the measured resistance value is an infinite resistance value. On the other hand, when an internal short circuit occurs, the measured resistance value is a very low value (for example, several kΩ). Therefore, a resistance value (for example, several tens of MΩ, several MΩ, several thousand kΩ, and several hundred kΩ) that can detect the difference between the resistance values is set in advance as a threshold value. The tester 2 determines whether or not the measured resistance value is equal to or less than a threshold value, and provides information indicating an internal short circuit (for example, lamp lighting) if the measured resistance value is equal to or less than the threshold value. Note that the tester 2 does not perform the determination up to whether or not it is equal to or less than the threshold, but may perform the measurement of the resistance value. In this case, the person determines from the resistance value measured by the tester 2.

  The pressing member 3 is a member that applies (presses) a load generated by the load generating device 4 to the electrode assembly S. As the pressure member 3, a pressure member used in a conventional well-known short circuit inspection is applied. The pressurizing member 3 is, for example, a flat plate having a predetermined thickness, and has a sufficient size to apply a load to the side surface in the stacking direction of the electrode assembly S. The pressing member 3 is disposed so as to contact each side surface of the electrode assembly S in the stacking direction. As shown in FIG. 1, the pressure members 3 may be arranged on opposite side surfaces in the stacking direction of the electrode assembly S, or one side surface in the stacking direction of the electrode assembly S is used as a base. The pressure member 3 may be placed only on the other side surface.

  The load generating device 4 is a device that generates a load for pressurization. As the load generating device 4, a load generating device used in a conventional well-known short circuit inspection is applied. A pressure member 3 is attached to the load generator 4. The load generator 4 generates a predetermined weight (for example, several kN, several tens kN) during the short circuit inspection. This load is applied to the electrode assembly S via the pressure member 3. In addition, as shown in FIG. 1, the load generating device 4 may be provided on both side surfaces facing each other in the stacking direction of the electrode assembly S, and the load may be applied from both side surfaces. The assembly S may be provided only on one side surface in the stacking direction, and a load may be applied only from one side surface.

  Note that the short-circuit inspection is performed while applying pressure (adding a load) to the electrode assembly S because, for example, the maximum load that may be applied to the power storage device after shipment is applied before shipment. This is because the air between the three-dimensional layers is removed so that the electrode assembly can be stored in the case. The predetermined load generated by the load generator 4 is set based on this maximum load and the like.

  The thermostatic bath 5 is a bath capable of maintaining the inside of the bath at a constant temperature. The thermostat 5 is a conventional well-known thermostat. The thermostat 5 is substantially rectangular and has a space inside. The thermostat 5 has a size that can sufficiently accommodate the electrode assembly S pressurized by the pressure member 3 and the load generator 4. In the thermostatic bath 5, the temperature in the bath is adjusted to the set temperature during the short circuit inspection. Below, the set temperature at the time of performing this short circuit inspection is demonstrated.

  As described above, the separator has a glass transition temperature, and when the temperature falls below the glass transition temperature, the separator enters a glass state. When the temperature in the bath of the thermostatic bath 5 (and hence the temperature of the electrode assembly S) is adjusted to bring the separator to a glass transition temperature or lower, the separator enters a glass state. When the glass state is reached, the elongation of the separator is suppressed (the allowable amount of elongation of the separator is reduced). When the elongation of the separator is suppressed, even when a foreign matter is present between the positive electrode or the negative electrode and the separator, the separator is easily broken even with a small foreign matter. When the separator breaks, the positive electrode and the negative electrode are short-circuited directly or through a foreign substance, and the short-circuit can be detected by measurement using the tester 2. Therefore, the set temperature of the thermostatic chamber 5 is set based on the glass transition temperature of the separator used in the electrode assembly S. In particular, in order to reliably lower the temperature of the separator to the glass transition temperature or lower, a temperature lower than the glass transition temperature by a certain temperature is set as the set temperature. For example, in the case of polypropylene (PP), the glass transition temperature is around 0 ° C., so the set temperature is about −20 ° C. By adjusting the temperature in the thermostatic chamber 5 to the set temperature, the temperature of the electrode assembly S (and thus the temperature of the separator) is lowered to the glass transition temperature or lower.

  The inspection process using this short circuit inspection system 1 will be described. When the laminating process is completed, the electrode assembly S is placed in the thermostat 5 and the pressure member 3 is disposed on each side surface of the electrode assembly S in the laminating direction. The positive measurement terminal 2 a of the tester 2 is connected to the positive electrode tab Tp of the electrode assembly S, and the negative measurement terminal 2 b is connected to the negative electrode tab Tn of the electrode assembly S.

  The load generator 4 generates a predetermined load. Then, the load is applied from the side surface of the electrode assembly S through the pressing member 3, and the electrode assembly S is in a pressurized state. In the thermostatic bath 5, the temperature in the bath is adjusted to a set temperature, and the temperature is maintained (temperature adjusting step). As a result, the temperature of the electrode assembly S decreases, and the temperature of the separator decreases. When the temperature of the separator is equal to or lower than the glass transition temperature, the separator is in a glass state and the allowable amount of elongation of the separator is reduced. Even when a separator having a large allowable elongation at room temperature is used, since the separator is in a glass state, the allowable elongation of the separator is small.

  During pressurization and low temperature, the tester 2 applies a predetermined voltage between the measurement terminals 2a and 2b (that is, between the positive electrode tab Tp and the negative electrode tab Tn), and the positive electrode tab Tp and the negative electrode The resistance value between the tab Tn is measured, and it is determined whether or not a short circuit has occurred (short circuit inspection step). When the resistance value measured by the tester 2 is equal to or greater than the threshold value, it is determined that the short circuit has not occurred, and when the resistance value measured by the tester 2 is less than the threshold value, the short circuit has occurred (as a result, the positive electrode or the negative electrode is separated from the separator). It is determined that there is a foreign object in between.

  Even if there is a small size foreign material between the positive electrode or negative electrode and the separator, and the amount of elongation of the separator is small due to the foreign material, the separator is in a glass state (because the allowable amount of elongation of the separator is small). The separator is likely to break. When the separator breaks, the positive electrode and the negative electrode are short-circuited, so that even a small foreign object can be detected. The minimum size of foreign matter that can be detected in this inspection process is, for example, 100 to several hundreds of micrometers.

  In addition, when the hardness of the active material layer of a positive electrode and a negative electrode differs, when a foreign material enters, there exists a possibility that the elongation of a separator may become large and it may fracture | rupture. For example, in the case of a power storage device in which the active material layer of the positive electrode is harder than that of the negative electrode, if a foreign object enters between the positive electrode and the separator having the hard active material layer, the hard active material layer on the positive electrode side is hard to be dented by the foreign object. The soft active material layer on the negative electrode side is greatly dented by foreign matter, and the amount of elongation of the separator increases. On the other hand, if a foreign substance enters between the negative electrode and the separator having the softer active material layer, the soft active material layer on the negative electrode side tends to be dented by the foreign substance. The amount of elongation is small. In other words, the amount of elongation of the separator is greater when the foreign material enters between the negative electrode and the separator with the softer active material layer than when the foreign material enters between the positive electrode and the separator with the harder active material layer. Is small. In this way, even when foreign matter enters between the electrode having the softer active material layer and the separator and the amount of elongation of the separator becomes small, the short circuit inspection is performed with the separator in the glass state, so that the foreign matter can be detected.

  According to the inspection process (inspection method) using the short-circuit inspection system 1, the temperature of the electrode assembly (and thus the separator) is adjusted to a predetermined temperature or lower (low temperature) and the short-circuit inspection is performed. A short circuit can be inspected in a glass state, and the detection accuracy of foreign matter that has entered between the electrode and the separator can be improved. In particular, even when a small-sized foreign object that cannot be detected by a conventional short-circuit inspection is contained, the separator is broken even by the small-sized foreign object, and the foreign object can be detected. Even when a separator having a large allowable elongation at room temperature is used, the allowable amount of elongation in the glass state is small, so that foreign matter can be detected.

  Moreover, according to this inspection process (inspection method), by determining the set temperature of the thermostat 5 based on the glass transition temperature of the separator, the temperature of the thermostat 5 is adjusted to be equal to or lower than the set temperature, so that the separator is reliably transferred to the glass state. And it is not necessary to lower the temperature more than necessary, so that the optimum set temperature can be set.

  As mentioned above, although one Embodiment of this invention was described, it is implemented with various forms, without being limited to the said embodiment.

  For example, in the above embodiment, the present invention is applied to a rectangular power storage device (lithium ion secondary battery), but the present invention can also be applied to a power storage device having another shape such as a cylindrical (winding body). Moreover, it is applicable also to electrical storage apparatuses other than a lithium ion secondary battery.

  In the above embodiment, the short circuit inspection is performed while the electrode assembly is pressurized (applied with a load) using the pressure member and the load generator. However, the short circuit inspection is performed without pressing the electrode assembly. You may go.

  Moreover, in the said embodiment, although it was set as the structure which utilizes a thermostat in order to adjust the temperature of an electrode assembly (especially separator) below to predetermined temperature, it is an electrode assembly (separator) using another temperature adjustment means. The temperature may be adjusted to a predetermined temperature or lower.

  Moreover, in the said embodiment, although it was set as the structure which performs a short circuit inspection with respect to the electrode assembly (laminated body) in the state where the tabs of each electrode are not welded, the electrode of the state in which the tabs of each electrode are welded A short circuit inspection may be performed on the assembly.

  DESCRIPTION OF SYMBOLS 1 ... Short-circuit inspection system, 2 ... Tester, 2a, 2b ... Measurement terminal, 3 ... Pressure member, 4 ... Load generator, 5 ... Constant temperature bath.

Claims (1)

An inspection method for performing a short circuit inspection on the electrode assembly in a process of manufacturing a power storage device including a positive electrode and a negative electrode and an electrode assembly having a separator between the positive electrode and the negative electrode,
A temperature adjustment step of adjusting the temperature of the electrode assembly to be equal to or lower than the glass transition temperature of the separator ;
During temperature adjustment in the temperature adjustment step, a short-circuit inspection step for performing a short-circuit inspection of the electrode assembly,
A method for inspecting a power storage device.

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