JP2019145453A - Battery pack - Google Patents

Abstract

To provide a battery pack that can detect heat generated by overcharging of cells constituting the battery pack with a simple configuration at an earlier stage.SOLUTION: A battery pack 1 includes a plurality of single cells 2 arranged in the arrangement direction X, a resin sheet 4 disposed between the plurality of unit cells 2 and on at least one of the inside of the unit cells, a load sensor 6 disposed at any position in the arrangement direction X of the unit cell 2 and the resin sheet 4, and a restraining member 8 that restrains the arrayed unit cell 2, the resin sheet 4, and the load sensor 6 by applying a restraint load to the unit cell 2, the resin sheet 4, and the load sensor 6 in the compression direction along the arrangement direction X. The resin sheet 4 is configured to be melt when the unit cell 2 generates heat due to overcharging. The load sensor 6 is configured to be able to detect a change in the restraint load.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an assembled battery in which a plurality of single cells are constrained.

  2. Description of the Related Art In recent years, secondary batteries represented by lithium ion batteries have been used as power sources for driving vehicles such as electric vehicles (EV), hybrid vehicles (HV), and plug-in hybrid vehicles (PHV). Such secondary batteries for applications requiring high output are generally used in the form of assembled batteries in which a plurality of unit cells are electrically connected. In the assembled battery, the battery is restrained in the direction orthogonal to the electrode surface of the cell in order to prevent the displacement of the cell due to vibration, impact, etc. when driving the vehicle, and to ensure the battery characteristics, battery life, etc. A load is applied. As a result, the assembled battery can easily store heat when the unit cell generates heat, and can easily fall into an overheated state during overcharging. Therefore, in order to increase the safety of the vehicle during overcharge, a configuration in which a temperature sensor is provided for each of the cells constituting the assembled battery has been proposed (see, for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 2015-072830 JP 2006-269345 A

  However, if a temperature sensor is provided in each cell, there is a problem that the cost increases. On the other hand, if a temperature sensor is provided for each of several unit cells, there is a possibility that the temperature sensor is installed away from the unit cell that has generated heat due to overcharging, and there is a problem that the timing for detecting heat generation is delayed. In addition, it is not appropriate or practical to use a temperature sensor near an electrode surface that can be a heating point, for example, inside a single cell or between single cells. Therefore, the temperature sensor is installed at a position in the battery case where there is no problem with the arrangement of the cells, typically on the upper surface of the battery case. When the battery case swells, there is a problem that sensitivity further decreases.

  The present invention has been made in view of such a point, and an object of the present invention is to provide a set that can detect heat generation due to overcharging of the cells constituting the assembled battery at an earlier stage and with a simple configuration. It is to provide a battery.

  The assembled battery disclosed herein includes a plurality of unit cells arranged in an arrangement direction, a resin sheet disposed between the plurality of unit cells and at least one inside the unit cell, the unit cell and the resin. A restraint load is applied to the load sensor arranged at any position in the sheet arrangement direction, the unit cells, the resin sheet, and the load sensor arranged in the direction in which the sheet is compressed. A restraining member. The resin sheet is configured to melt when the unit cell generates heat due to overcharging. The load sensor is configured to be able to detect a change in the restraint load.

  In the above configuration, the load sensor detects a restraining load applied to the assembled battery as, for example, a normal state. At the time of overcharging, among the resin sheets arranged between the individual cells or inside the cells, the resin sheet near the heating point of the single cells that have generated heat due to overcharging is melted at an early stage. The molten resin sheet cannot maintain its shape, and is pushed out between the cells or from the stacked layers by the restraining pressure applied to the assembled battery. As a result, leakage (pressure loss) occurs in the restraint pressure applied to the assembled battery. The assembled battery can detect that any single cell is generating heat due to overcharging by detecting the leakage of the restraining pressure applied by the load sensor. According to the technology disclosed herein, it is possible to detect heat generated in any one of a plurality of single cells constituting an assembled battery at an early timing by one load sensor.

It is a front view which shows typically the mode at the time of the normal time of the assembled battery which concerns on one Embodiment. It is a front view which shows typically the mode at the time of the overcharge of the assembled battery which concerns on one Embodiment. It is a graph which shows the relationship between the charging time of the assembled battery of Example 1, current amount, the detection load by a load sensor, and battery internal temperature, respectively. It is a graph which shows the relationship between the charging time of the assembled battery of Example 3, the amount of electric current, the detection load by a load sensor, and battery internal temperature, respectively.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field. In addition, each drawing is drawn typically and does not necessarily reflect a real thing. Each drawing shows only an example, and each drawing does not limit the present invention unless otherwise specified.

  FIG. 1 is a front view schematically showing the structure of the assembled battery 1 according to the present embodiment. In FIG. 1, X indicates the arrangement direction of the cells 2, X <b> 1 indicates the first direction of the arrangement direction X, and X <b> 2 indicates the second direction of the arrangement direction X. As shown in FIG. 1, the assembled battery 1 has a plurality of single cells 2. The plurality of unit cells 2 are arranged along the arrangement direction X, and a resin sheet 4 is arranged between the two unit cells 2 one by one. In addition, a load sensor 6 is disposed at the end of the arranged cells 2 and the resin sheet 4 in the second direction X2. The unit cell 2, the resin sheet 4, and the load sensor 6 are restrained by a restraining mechanism 8. In the assembled battery 1 in the present embodiment, the combination of the resin sheet 4 and the load sensor 6 functions as a heat generation detection mechanism due to overcharging. Hereinafter, each component will be described.

  The restraining mechanism 8 includes a pair of end plates 8a and 8a and a plurality of restraining bands 8b and 8b. The end plates 8a and 8a are arranged at the end portions in the first direction X1 and the end portions in the second direction X2 so as to sandwich the cells 2, the resin sheet 4 and the load sensor 6 to be described later in the arrangement direction X. Has been. The plurality of restraining bands 8b are extended along the arrangement direction X so as to be bridged between the pair of end plates 8a, 8a. In the present embodiment, the number of the restraining bands 8b is four, but is not limited to this. Although the restraint band 8b of the present embodiment is narrower than the dimensions of the battery case, restraint pressure is provided between the end plates 8a and 8a by providing the restraint band 8b evenly on the periphery of the end plate 8a. Applied uniformly.

The restraining band 8b is a substantially U-shaped jig in plan view, and locks the end plates 8a and 8a by a fixing tool (not shown) (for example, a bolt and nut type fastener). The restraint band 8b regulates the distance between the end plates 8a and 8a so that the arrangement of the cells 2, the resin sheet 4 and the load sensor 6 is maintained in a compressed state in the arrangement direction X with a predetermined restraint load. . Further, the restraining band 8b fixes the distance between the end plates 8a and 8a so that the end plates 8a and 8a do not recover in the pulling direction due to a reaction force against the restraining load. For example, the restraining load applied to the assembled battery 1 by the restraining mechanism 8 may be about 20 to 2000 kgf, typically about 20 to 1000 kgf, along the arrangement direction X with respect to the unit cells 2. The compressive stress inherent in the assembled battery 1 by constraining mechanism 8, as the surface pressure (mean of surface pressure applied to the long side), about 0.2~25kgf / cm ^2, for example 0.2~15kgf / cm ² of about It may be.

  The unit cell 2 is a secondary battery that can be repeatedly charged and discharged, for example, a lithium ion battery. Although not specifically shown, the unit cell 2 is hermetically sealed in a battery case in which a laminated electrode body that is a power generation element and a nonaqueous electrolytic solution are accommodated. The dotted line shown in the cell 2 in FIGS. 1 and 2 imagines the presence of the electrode body. The laminated electrode body includes a plurality of positive electrode plates having a porous positive electrode active material layer on both sides of a positive electrode current collector, and a plurality of negative electrode plates having a porous negative electrode active material layer on both sides of the negative electrode current collector Are alternately stacked so as to face each other with a separator interposed therebetween. One positive electrode active material layer on one surface of one positive electrode plate and the negative electrode active material layer on one surface of one negative electrode plate are overlapped with each other through one separator, thereby generating one power generation element. Composed. And the laminated electrode body is comprised by laminating | stacking two or more of these elements in order.

  The non-aqueous electrolyte includes, for example, a lithium salt that serves as a charge carrier and a non-aqueous solvent. The non-aqueous electrolyte is impregnated in the positive electrode active material layer, the negative electrode active material layer, and the separator in the multilayer electrode body. Moreover, the non-aqueous electrolyte is also present in the space between the multilayer electrode body and the battery case, in addition to the one impregnated in the multilayer electrode body. The battery case in the present embodiment is a flat rectangular battery case made of SUS. The plurality of unit cells 2 are arranged such that the lamination direction of the laminated electrode body coincides with the arrangement direction X. The number of the single cells 2 constituting the assembled battery 1 is not limited, and may be 2 to 20, for example, 3 to 10 or the like. The unit cell 2 may include a wound electrode body in which a long positive electrode, a negative electrode, and a separator are wound instead of the stacked electrode body. Alternatively, the unit cell 2 may be an all-solid battery including a solid electrolyte layer or a gel electrolyte instead of the non-aqueous electrolyte and the separator, or may be a fuel cell, a nickel hydride battery, or another secondary battery. .

  The separator is a member that electrically insulates between the positive electrode and the negative electrode and enables movement of charge carriers between the positive electrode and the negative electrode. As the separator, a sheet material that is electrically insulating and is made of a chemically stable material in the battery environment and provided with fine holes can be preferably used. Examples of such a sheet material include those in the form of a microporous resin sheet, a woven fabric, a non-woven fabric, and the like. The material of the separator includes polyolefin resins such as polyethylene (PE) and polypropylene (PP), polyamideimide resins such as polyamide and polyimide, polyvinyl chloride (PVC) resins, polyester resins, and cellulose resins. Can be mentioned. The average thickness of the separator is not particularly limited. The average thickness of the entire separator may be, for example, about 5 μm or more, typically 10 μm or more, for example, 15 μm or more, and may be about 40 μm or less, typically 30 μm or less, for example, 25 μm or less.

This separator is softened or melted by being heated to a predetermined temperature (typically, the melting point T _S of the separator), and shuts down the pores, which are charge transfer paths, while insulating between the positive and negative electrodes. It may have a function. In this case, the separator may have, for example, a three-layer sheet structure made of PP / PE / PP whose adjustment of the melting point is relatively easy. The separator having the three-layer sheet structure is such that, for example, the middle PE sheet (shutdown resin sheet) is melted at a shutdown temperature (ie, T _S ) lower than the PP sheets at both ends, thereby closing the pores of the PP sheets at both ends. It may be configured. As a result, for example, when the positive electrode or negative electrode self-heats to a predetermined temperature or higher, the separator shuts down, while preventing the short circuit between the positive electrode and the negative electrode, while preventing the charge carrier from moving, Can contribute to stopping. As a result, it is possible to suppress an excessive temperature increase due to further self-heating of the electrode. Melting point T _S of the shutdown resin sheet, for example, may the unit cells 2 is set to a safe temperature range that does not lead to excessive temperature rise. In this example, since there is a resin sheet described below, the melting point T _S of the shutdown resin sheet, for example, is exemplified be approximately 140 to 180 ° C..

The resin sheet 4 is arranged between the unit cells 2 and the unit cells 2 in the arrangement direction X so as to contact the long side surfaces of the unit cells 2. The resin sheet 4 functions as a spacer between the single cells 2 when a normal battery is used, and is configured to melt when the single cells 2 generate heat due to overcharging. The resin sheet 4 is typically softened or melted by being heated to a predetermined temperature (typically, the melting point T _F of the resin sheet 4). The resin sheet 4 constitutes a part of the heat generation detection mechanism in the present embodiment. It can be said that the resin sheet 4 is a sensor source that detects heat generation of the unit cell 2 by being softened or melted. Examples of the material of the resin sheet 4 include polyolefin resins such as polyethylene (PE) and polypropylene (PP), polyamideimide resins such as polyamide and polyimide, polyvinyl chloride (PVC) resins, polyester resins, and cellulose resins. Is mentioned. Such a material may be a material common to the above-described known separator, for example. However, the resin sheet 4 is disposed outside the battery case. Therefore, it is preferable that the resin sheet 4 is a material having a predetermined thickness when it is compressed by, for example, normal pressure (25 ° C.) by a restraining pressure described later. For example, the resin sheet 4 may be in a form that does not include pores that allow movement of charge carriers. In this respect, the resin sheet 4 can be a member having a configuration different from that of the separator. The average thickness of the resin sheet 4 is not particularly limited as long as the load sensor 6 described later can detect a load drop due to the disappearance of the resin sheet 4. The average thickness of the resin sheet 4 may be, for example, about 5 μm or more, typically 10 μm or more, for example, 15 μm or more, and may be about 40 μm or less, typically 30 μm or less, for example, 25 μm or less.

The melting point _TF of the resin sheet 4 is set, for example, so as to be included in a temperature range in which it can be determined that the electrode body of the unit cell 2 starts to self-heat due to overcharging. The melting point _TF of the resin sheet 4 can be controlled, for example, by adjusting the material, polymerization degree, and the like of the resin sheet 4. For example, the melting point _TF of the resin sheet 4 may be set to a temperature higher than the environmental temperature range according to the environmental temperature at which the assembled battery 1 is normally used. For example, when the assembled battery 1 is used as a power source for driving a vehicle such as a hybrid vehicle or an electric vehicle, the environmental temperature in the vicinity of the motor of the vehicle can be increased to about 90 ° C. as an example. Therefore, as an example, the melting point T _F of the resin sheet 4 may be higher than the maximum environmental temperature T _M (for example, 90 ° C.) in the use environment of the assembled battery. The melting point _TF of the resin sheet 4 is not limited to this, but in order to suppress the expansion of the micro short circuit and further enhance the safety of the assembled battery 1, the melting point ( may be set to a lower temperature than the shutdown temperature) T _S. The melting point T _F of the resin sheet 4 may satisfy, for example, T _M <T _F <T _S. As an example, the melting point _TF of the resin sheet 4 is preferably about 90 ° C. and lower than 140 ° C. (for example, 95 ° C. or more and 135 ° C. or less).

  The load sensor 6 is configured to be able to detect a change in the restraint load. The load sensor 6 is a pressure sensor, for example. More preferably, the load sensor 6 is a film-shaped pressure distribution measurement sensor having a thickness of about 0.05 to 0.5 mm (for example, 0.1 mm). The load sensor 6 is arranged along the arrangement direction X together with the plurality of single cells 2 and the resin sheet 4. The plurality of single cells 2, the resin sheet 4, and the load sensor 6 are stacked together along the arrangement direction X to form a stack. The load sensor 6 is disposed at any position between the pair of end plates 8a and 8a. The position of the load sensor 6 is not limited as long as it is between the pair of end plates 8a, 8a. In other words, the position of the load sensor 6 is not limited as long as the magnitude of the restraining load contained in the assembled battery 1 or the change thereof can be sensed. In the present embodiment, the load sensor 6 is disposed between the end plate 8a disposed at the end portion in the second direction X2 and the unit cell 2.

  According to the above configuration, the assembled battery 1 can be repeatedly charged and discharged by a plurality of single cells in the same manner as a conventional assembled battery during normal use. For example, it is assumed that any one of the single cells 2 constituting the assembled battery 1 has fallen into an overcharged state due to product variation or the like. When the unit cell 2 is overcharged, the voltage concentrates on the uneven surface such as minute protrusions on the surface of the electrode, and a minute short circuit occurs between the positive and negative electrodes, and heat is easily generated. The self-heating of the unit cell 2 due to overcharging starts from such a small short circuit and expands by melting the surrounding separator. Therefore, for example, as shown in FIG. 2, even if the temperature sensor 9 is provided on the upper surface of the battery case of the unit cell 2, a certain amount of time is required until the temperature sensor 9 detects heat generation based on the micro short circuit. Cost. In other words, a large time lag (delay of heat generation detection) can occur from the heat generation due to a short circuit to the detection of overcharge. Such a delay in detection of heat generation is also observed in the assembled battery 1 in which the temperature sensors 9 are provided in all the unit cells 2, but any one (typically any one) constituting the assembled battery 1. This is more noticeable when the temperature sensor 9 is provided only in the single battery 2. Moreover, the battery in an overcharged state may have a swollen battery case. In a battery in which swelling has occurred, detection of heat generation by the temperature sensor 9 can be further delayed.

  On the other hand, the assembled battery 1 disclosed here is configured such that the resin sheet 4 contacts the long side surfaces of all the unit cells 2. In addition, since the restraint load is applied to the assembled battery 1, the unit cell 2 and the resin sheet 4 are in close contact with each other. Therefore, when any single cell 2 of the assembled battery 1 is overcharged and a micro short circuit occurs, the heat generated due to the micro short circuit is transmitted to the resin sheet 4 located just outside the battery case. heat. Thereby, the resin sheet 4 is softened or melted and can be plastically deformed. Further, since the restraint load is applied to the assembled battery 1 in the direction of compression along the arrangement direction X between the end plates 8a and 8a, the softened or melted resin sheet 4 is pushed out from the stack to the periphery by the single battery 2. It is. As a result, the distance between the end plates 8a is reduced by a dimension corresponding to the thickness of the molten resin sheet 4. Further, when the distance between the end plates 8a is shortened, a part of the restraining load contained in the assembled battery 1 is suddenly released. The load sensor 6 can detect such a rapid change in the load between the end plates 8a and 8a. Thereby, the assembled battery 1 can detect at an early timing that one of the single cells 2 generates heat due to overcharging.

  In the above-described embodiment, the load sensor 6 detects the missing of the restraint load accompanying the softening / melting of the resin sheet 4 installed between the single cells 2 (that is, outside the battery case). However, the configuration of the assembled battery 1 disclosed herein is not limited to this. For example, the load sensor 6 may be configured to detect the leakage of the restraint load accompanying the softening / melting of the shutdown resin sheet of the separator installed inside the unit cell 2 (that is, inside the battery case). . As described above, the plurality of single cells 2 are arranged such that the stacking direction of the positive electrode, the separator, and the negative electrode in the electrode body matches the arrangement direction X. Moreover, the restraint load of the assembled battery 1 is given in the direction which compresses an electrode body along the arrangement direction X (in other words, a lamination direction) so that the battery characteristic of a cell may improve. Therefore, even if the load sensor 6 detects a decrease in the dimension (thickness) of the unit cells 2 in the arrangement direction X due to the softening / melting of the shutdown resin sheet of the separator, the heat generation of the unit cells 2 is similarly detected at an early timing. be able to.

  When the separator has a shutdown function as described above, the shutdown resin sheet of the separator can be used for heat generation detection by the load sensor instead of the resin sheet 4 described above. In other words, the shutdown resin sheet of the separator can constitute a heat generation detection mechanism in combination with the load sensor 6. Either one or both of the resin sheet 4 and the shutdown resin sheet may be provided.

  When the separator is provided with the shutdown resin sheet without including the resin sheet 4, the melting point of the shutdown resin sheet is similar to the melting point of the resin sheet 4 described above, and the electrode body of the unit cell 2 starts to self-heat due to overcharging. It should be set so that it is included in the temperature range where it can be determined that That is, the melting point of the shutdown resin sheet can be set to a temperature range of 95 ° C. or more and 135 ° C. or less, for example. Further, the average thickness of the shutdown resin sheet of the separator in this case is not strictly limited. Since the separator is housed in the battery case, is a microporous structure and is compressed by a restraint load, etc., for example, a configuration capable of generating a leakage of restraint load that can be detected by a load sensor described later and Thickness is good. As an example, the average thickness of the shutdown resin sheet of the separator (the portion that softens and melts in the above temperature range) may be about 5 μm or more, typically 6 μm or more, for example, 7 μm or more, typically about 15 μm or less, Can be 12 μm or less, for example, 10 μm or less. For example, when the separator has a three-layer structure, the other two microporous sheets sandwiching the shutdown resin sheet have a higher melting point so that the total thickness of the two sheets is equal to or less than that of the shutdown resin sheet. It is good to set. As an example, the thicknesses of the other microporous sheets are each independently about 2 μm or more, typically 3 μm or more, for example 3.5 μm or more, and about 7 μm or less, typically 6 μm or less. For example, it can be about 5 μm or less. Thus, it is preferable to make the thickness of the shutdown resin sheet sufficiently thick because it becomes easy to detect the restraint load leakage.

  In a preferred example, the load sensor 6 can detect overcharge when the restraint load applied to the battery stack by the restraining member 8 in the assembled battery 1 increases. That is, in the unit cell 2 in an overcharged state, gas accompanying decomposition of the non-aqueous electrolyte is generated in the battery case, and the battery case may swell. This can increase the restraining load applied to the battery stack. The load sensor 6 can detect the start of overcharge from such an increase in the restraint load. Moreover, in another suitable example, the load sensor 6 can detect the heat generation of the unit cell 2 when the restraint load applied to the battery stack by the restraint member 8 in the assembled battery 1 starts to decrease. This phenomenon may include the case where the restraint load turns from increasing to decreasing. That is, when overcharge is progressing in the assembled battery 1, other pressure detection type safety mechanisms may not operate, or heat generation may proceed more rapidly than the pressure in the battery case increases. In such a case, as described above, since the resin sheet 4 (or the separator shutdown resin sheet) is melted and the restraint load contained in the assembled battery 1 is released, the load sensor 6 reduces the restraint load. From this, the start of heat generation can be detected.

  When the assembled battery 1 detects overcharge, for example, an unillustrated assembled battery charge / discharge control device can stop charging the assembled battery. The configuration of the charge / discharge control device is not particularly limited. For example, the charge / discharge control device may be configured by hardware such as a circuit or a processor, and is functionally realized by a CPU (Central Processing Unit) executing a computer program. You may be comprised so that. Thereby, the assembled battery 1 can stop charging / discharging to the assembled battery 1 safely at an early timing after generation of heat due to overcharge.

Hereinafter, the assembled battery disclosed here was produced as a specific example. It should be noted that the present invention is not intended to be limited to those shown in the specific examples.
(Example)
Carbon powder (C) as the negative electrode active material powder, styrene butadiene rubber (SBR) as the binder, and carboxymethyl cellulose (CMC) as the thickener, C: SBR: CMC = 98: 1: 1 mass A negative electrode paste was prepared by kneading with ion-exchanged water at a ratio. This paste was applied to both surfaces of a copper foil as a negative electrode current collector, dried and pressed to form a negative electrode active material layer, thereby forming a negative electrode.

LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (LNMC) as a positive electrode active material powder, AB as a conductive material, and PVDF as a binder, LNMC: AB: PVDF = 90: 8: 2 A positive electrode paste was prepared by mixing with N-methylpyrrolidone (NMP) at a mass ratio of This paste was applied to both surfaces of an aluminum foil as a positive electrode current collector, dried and pressed to form a positive electrode active material layer, thereby forming a positive electrode.

A plurality of the prepared negative electrodes and positive electrodes were cut out to a predetermined size, overlapped via a microporous separator, and accommodated in a flat rectangular battery case together with a non-aqueous electrolyte, thereby producing a lithium ion secondary battery. . As the separator, a three-layer microporous sheet (shutdown temperature: 160 ° C., shutdown PE sheet thickness: 8 μm, PP sheet thickness at both ends: 4 μm each) made of PP / PE / PP was used. In addition, as a non-aqueous electrolyte, a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of EC: EMC: DMC = 3: 3: 4 is supported. of LiPF ₆ as a salt were used as dissolved at a concentration of 1 mol / L. Further, the aluminum foil and the copper foil were electrically connected to the external positive terminal and the external negative terminal provided in the battery case, respectively, through a current collecting member. Further, in this example, a thermocouple was installed in the vicinity of the center of the surface where the heat at the time of heat generation of each battery case was difficult to draw. Thereby, 15 unit cells for evaluation having a rated capacity of 20 Ah and a smoke generation temperature of 190 ° C. were prepared. Cell surface (pack center)
In particular, there is variation in temperature rise due to heat shrinkage

  Next, a resin sheet and a load sensor were prepared as a heat generation detection mechanism. In this example, the prepared assembled battery is assumed to be used for vehicle driving, and the upper limit of the environmental temperature at the assembled battery installation position of this vehicle is about 90 ° C. Therefore, as shown in Table 1 below, as the resin sheet, (1) a PE sheet having a melting point of 130 ° C., (2) a PVC sheet having a melting point of 85 ° C., and (3) a melting point of 180 ° C. Three types of PP sheets (thickness: 8 μm) were prepared, and six sheets were cut into shapes corresponding to the long side surfaces of the battery case. As a load sensor, a tactile sensor system (film pressure distribution measuring device) having a shape corresponding to the long side surface of the battery case was prepared. Then, six resin sheets and five unit cells are alternately arranged, a tactile sensor is stacked on one end in the arrangement direction to form a battery stack, and the battery stack is constrained by a restraining mechanism. A battery was built. Each unit cell was connected in series.

  The prepared assembled battery was subjected to a predetermined initial charging process, and then charged with a constant current at 3C (60 A) at an environmental temperature of 25 ° C. to overcharge the assembled battery. Then, when the heat generation detection mechanism detects the heat generation of any single cell, the charge / discharge control device is configured to stop charging the assembled battery. In the heat detection test, the relationship between the elapsed time, the battery temperature, and the restraint load was examined, and it was confirmed whether the overcharge of the assembled battery could be safely stopped by the heat detection mechanism. The results of this heat detection test are shown in Table 1 below. Moreover, the result of the heat_generation | fever detection test obtained about the assembled battery of Example 1 and Example 3 was shown in FIG. 3 and FIG. 4, respectively.

  As shown in FIG. 3 and Table 1, in the assembled battery of Example 1, the overheating could be safely stopped by detecting the heat generation of the unit cell due to the overcharging by the load sensor. Specifically, when the temperature of the unit cell that has been overcharged reaches 130 ° C. (P1 in FIG. 3), the resin sheet installed between the unit cells melts, and the binding load of the assembled battery is lost. It was. The load sensor of the assembled battery detected this load loss, and the charge / discharge control device stopped charging the assembled battery. As a result, when the battery temperature slightly exceeded 130 ° C., the temperature was lowered and the battery was cooled to room temperature as it was, and overcharging of the assembled battery was safely stopped.

  On the other hand, in the assembled battery of Example 2 using a resin sheet having a low melting point of 85 ° C., the resin sheet installed between the single cells was melted when the temperature of the unit battery that was overcharged reached 85 ° C. In addition, the load sensor detected a missing load of the assembled battery, and the charge / discharge control device stopped charging the assembled battery. As a result, in a shape similar to the graph shown in FIG. 3, when the battery temperature slightly exceeded 85 ° C., the temperature was lowered and the battery was cooled to room temperature as it was, and overcharging to the assembled battery was safely stopped. However, in this example, since the upper limit of the environmental temperature at the assembled battery installation position is about 90 ° C., if a resin sheet having a melting point of 85 ° C. is used as the heat generation detection mechanism, the environmental temperature of the assembled battery at the normal vehicle operating temperature is When the temperature is raised to about 90 ° C., the resin sheet melts. Thereby, the load sensor may erroneously detect a temperature increase of the single cell in a normal use environment as heat generation due to overcharging. From this, it has confirmed that it was necessary to set melting | fusing point of a resin sheet to the temperature higher than the upper limit of the environmental temperature in the normal use of the said assembled battery.

  On the other hand, in the assembled battery of Example 3 using a resin sheet having a high melting point of 180 ° C., when the temperature of the unit cell that was overcharged was 160 ° C. (P1 in FIG. 4), the vicinity of the heat generating portion. The PE layer of the separator was melted and the separator was shut down. The load sensor detects a decrease in the thickness of the separator due to the shutdown of the separator, in other words, a leakage of the restrained load due to a decrease in the thickness of the battery, and the charge / discharge control device stops charging the assembled battery. However, the temperature at 160 ° C., which is the shutdown of the separator, is too high for the battery temperature in the overcharged state, and the unit cell that has generated heat due to overcharging continues to generate heat, and the restrained load that once decreased increases again. Confirmed to do. And when the temperature of the unit cell reached 180 ° C. (P2 in FIG. 4), the resin sheet installed between the unit cells was melted, and it was confirmed that the restraining load suddenly decreased due to the melting of the resin sheet. It was confirmed that the battery temperature and the restraint load continued to rise, resulting in an excessive temperature rise state (P3 in FIG. 4) exceeding the smoke temperature of the battery.

  From this, a load sensor such as a tactile sensor can detect the melting of the resin sheet provided between the single cells and the leakage of the restraining load accompanying the melting of the shutdown shutdown resin sheet of the separator. It was confirmed that the presence or absence could be detected by one load sensor. The melting points of these resin sheets and shutdown resin sheets are set to a temperature range in which it can be determined that the unit cell has started to generate heat due to overcharge, in other words, the unit cell that has generated heat due to overcharge can be safely stopped. It was confirmed that by setting the temperature range, charging can be safely stopped without causing the assembled battery to overheat. It can be said that the temperature range in which it is determined that the unit cell starts to generate heat due to overcharging is, for example, more than 90 ° C. and less than 160 ° C. (for example, 95 ° C. or more and 140 ° C. or less).

  As mentioned above, although this invention was demonstrated in detail, the said embodiment and Example are only illustrations and what changed and changed the above-mentioned specific example is contained in the invention disclosed here. For example, although not specifically illustrated, the resin sheet 4 in FIG. 1 includes a plurality of arranged single cells 2 and an end portion in the first direction X1 of the resin sheet 4 and an end portion in the second direction X2. May be arranged respectively. In other words, the resin sheet 4 may be disposed adjacent to the end plates 8a and 8a or between the end plates 8a and 8a and the unit cell 2. Thereby, the detection system when the single battery arrange | positioned at the both ends of a stack falls into an overcharge can be improved. Further, the plurality of single cells 2 are arranged in the arrangement direction X in an electrically connected state. The unit cells 2 may be electrically connected in series or in parallel. Between the plurality of unit cells 2, a unit other than the unit cell 2 and a resin sheet 4 described later (for example, a cooling plate or the like) may be interposed.

1 assembled battery 2 single cell 4 resin sheet 6 pressure sensor 8 restraint mechanism

Claims (1)

A plurality of cells arranged in the arrangement direction;
A resin sheet disposed between at least one of the plurality of unit cells and inside the unit cell;
A load sensor disposed at any position in the arrangement direction of the unit cells and the resin sheet;
A restraint member that restrains the arrayed cells, the resin sheet, and the load sensor by applying a restraint load in a direction of compression along the array direction, and
With
The resin sheet is configured to melt when the unit cell generates heat due to overcharging,
The assembled battery is configured such that the load sensor can detect a change in the restraint load.

Images