JP7174326B2 - assembled battery - Google Patents

Description

The present invention relates to an assembled battery. Specifically, it relates to an assembled battery including a plurality of cells.

Lithium-ion secondary batteries, nickel-metal hydride batteries, other secondary batteries, or storage elements such as capacitors are used as single cells, and assembled batteries equipped with a plurality of such single cells are important as power sources for vehicles, personal computers, mobile terminals, etc. sexuality is increasing. In particular, assembled batteries in which lithium-ion secondary batteries, which are lightweight and provide high energy density, are used as single cells are preferably used as high-output power sources for vehicles. In such an assembled battery, a constraining plate is arranged between each unit cell for the purpose of improving heat dissipation characteristics by avoiding direct contact between the cells and applying a constraining pressure evenly to each unit cell. may be

The above-described secondary battery and the like may generate excessive heat (excessive temperature rise) due to overcharging, breakage of the electrode body, or the like. When the above-described excessive temperature rise occurs in an assembled battery in which a plurality of such secondary batteries or the like are arranged as single cells, the heat of the excessive temperature rise is transmitted to the other single cells, causing a chain reaction in which the single cells heat each other. Fever may progress. Patent Document 1 describes an example of a technique for preventing the chain reaction of heat generation. In the assembled battery described in Patent Document 1, a conductive pin is embedded inside a constraining plate arranged between cells, and when a predetermined cell is overheated, the cell The constraining plate adjacent to the battery is melted, and the electrically conductive pin is pierced into the cell that has excessively risen in temperature. This forcibly stops the charging and discharging of the unit cell in which the temperature has risen excessively, thereby preventing a chain reaction of heat generation.

JP 2018-73576 A

However, due to the increasing demand for safety in recent years, there is a demand for a technique for suppressing the chain reaction of heat generation by a safer means than that of Patent Document 1. The present invention has been made in response to such a demand, and its main object is to provide an assembled battery capable of suppressing the chain reaction of heat generation between cells without short-circuiting the cells. and

In order to achieve the above objects, the present invention provides an assembled battery having the following configuration.

The assembled battery disclosed here is constructed by arranging a plurality of unit cells along a predetermined arrangement direction and binding each unit cell along the arrangement direction. In this assembled battery, a constraining plate made of a thermoplastic resin is arranged between each of the plurality of arranged unit cells, and an elastic body that generates an elastic force along the arrangement direction inside the constraining plate. is buried.

In the assembled battery disclosed herein, when a predetermined unit cell is overheated, the constraining plate adjacent to the overheated unit cell melts and the elastic body in the constraining plate is exposed. The elastic force of this elastic body keeps the cell that has overheated away from the other cells, making it difficult for the heat from the overheating to reach the other cells, thereby preventing a chain reaction of heat generation. can be suppressed. As described above, according to the assembled battery disclosed herein, it is possible to suppress the chain reaction of heat generation by a safe means that does not short-circuit the cells.

1 is a perspective view schematically showing a unit cell that constitutes an assembled battery according to an embodiment of the present invention; FIG. 1 is a perspective view schematically showing an electrode body in one embodiment of the present invention; FIG. FIG. 4 is an explanatory view schematically showing each member that constitutes an electrode assembly in one embodiment of the present invention; 1 is a perspective view schematically showing an assembled battery according to one embodiment of the present invention; FIG. 1 is a side view schematically showing an assembled battery according to one embodiment of the present invention; FIG. FIG. 4 is a side view illustrating a case where one cell is overheated in the assembled battery according to one embodiment of the present invention.

Hereinafter, as one embodiment of the present invention, a lithium ion secondary battery is used as a unit cell, and an assembled battery in which a plurality of such lithium ion secondary batteries are arranged will be described. In the drawings below, members and portions having the same function are denoted by the same reference numerals. The dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect the actual dimensional relationships. Matters other than those specifically mentioned in this specification, which are necessary for carrying out the present invention, can be grasped as design matters by those skilled in the art based on the prior art in the relevant field.

1. Configuration of Single Cell First, the single cell that constitutes the assembled battery according to the present embodiment will be described. FIG. 1 is a perspective view schematically showing a unit cell that constitutes an assembled battery according to this embodiment. FIG. 2 is a perspective view schematically showing the electrode body in this embodiment. Moreover, FIG. 3 is an explanatory view schematically showing each member constituting the electrode body in this embodiment.

In this embodiment, a flat rectangular lithium ion secondary battery as shown in FIG. 1 is used as the cell 20 . The unit cell 20 is configured by accommodating an electrode assembly and an electrolytic solution inside the battery case 50 .

(a) Battery Case The battery case 50 in this embodiment is a flat, rectangular case having a predetermined rigidity. The battery case 50 includes a rectangular case body 52 with an open upper surface and a flat lid 54 that closes the opening of the upper surface. From the viewpoint of obtaining a predetermined rigidity, the case body 52 and the lid 54 are preferably made of a metal material such as aluminum. A positive electrode terminal 60 and a negative electrode terminal 62 are provided on the lid body 54 . Although not shown, the positive terminal 60 and the negative terminal 62 are electrically connected to an electrode body housed in the battery case 50 . The positive electrode terminal 60 is preferably made of aluminum, an aluminum alloy, or the like, and the negative electrode terminal 62 is preferably made of copper, a copper alloy, or the like.

(b) Electrode Body As the electrode body, those conventionally used in lithium ion secondary batteries can be used without particular limitation. As an example of such an electrode body, there is a laminated electrode body 30 as shown in FIG. This laminated electrode body 30 is formed by alternately laminating positive electrode sheets 31 and negative electrode sheets 35 with separators 38 interposed therebetween, as shown in FIG.

The positive electrode sheet 31 includes a foil-shaped positive electrode current collector 32 made of aluminum or the like, and a positive electrode active material layer 33 provided on the surface of the positive electrode current collector 32 . The positive electrode active material layer 33 contains a positive electrode active material and other additives. A lithium-containing compound (lithium-transition metal composite oxide) containing a lithium element and one or more transition metal elements is used as the positive electrode active material. Examples of this lithium-transition metal composite oxide include lithium-nickel composite oxide (eg, LiNiO ₂ ), lithium-nickel-cobalt-manganese composite oxide (eg, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ), and the like. mentioned.
Further, other additive materials include a conductive material, a binder, and the like. Examples of the conductive material include carbon powder such as carbon black and carbon materials such as carbon fiber. Examples of binders include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), carboxymethylcellulose (CMC), styrene-butadiene rubber (SBR), and the like.

The negative electrode sheet 35 includes a foil-shaped negative electrode current collector 36 made of copper or the like, and a negative electrode active material layer 37 provided on the surface of the negative electrode current collector 36 . The negative electrode active material layer 37 contains a negative electrode active material and other additives. For the negative electrode active material, for example, graphite, non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon), carbon nanotubes, or a carbon material combining these can be used. Other additives include binders, thickeners, dispersants, and the like. Note that the same binder as that used for the positive electrode active material layer can be used as the binder. Moreover, carboxymethyl cellulose (CMC), methyl cellulose (MC), etc. can be used for a thickener.

The separator 38 is a porous insulating sheet that insulates the positive electrode sheet 31 and the negative electrode sheet 35 and allows charge carriers (lithium ions) in the electrolyte to pass through. An example of the separator 38 is a resin porous sheet having a three-layer structure in which polypropylene (PP), polyethylene (PE), and polypropylene (PP) are laminated in order.

It should be noted that the electrode body used in the assembled battery disclosed herein is not limited to the above-described laminated electrode body 30 . Another example of this electrode body is a wound electrode body in which a positive electrode sheet and a negative electrode sheet which are superimposed with a separator interposed therebetween are wound.

(c) Electrolyte As in the case of the electrode assembly, any electrolyte that has been conventionally used in lithium-ion secondary batteries can be used without particular limitation. As an example of such an electrolytic solution, LiPF ₆ is added to a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) (for example, a volume ratio of 3:4:3) at a concentration of about 1 mol/L. A non-aqueous electrolytic solution contained therein may be mentioned.

2. Structure of Assembled Battery Next, the assembled battery 10 including a plurality of the unit cells 20 described above will be described. FIG. 4 is a perspective view schematically showing the assembled battery according to this embodiment, and FIG. 5 is a side view schematically showing the assembled battery according to this embodiment. Moreover, FIG. 6 is a side view for explaining a case where the temperature of one unit cell is excessively increased in the assembled battery according to the present embodiment.

(a) Overall Configuration of Assembled Battery As shown in FIG. 4, in the assembled battery 10 according to the present embodiment, four cells 20A to 20D are arranged along the arrangement direction x. Specifically, as shown in FIG. 5, the cells 20A to 20D are arranged adjacent to each other so that the side walls 50a of the rectangular battery case 50 face each other. In this embodiment, the arrangement direction x of the cells 20A to 20D is the same as the stacking direction y of the positive electrode sheet 31 and the negative electrode sheet 35 (see FIG. 2).

As shown in FIG. 4, in this assembled battery 10, each of the cells 20A to 20D is electrically connected. Specifically, the positive electrode terminal 60 of one of the two adjacent cells and the negative electrode terminal 62 of the other cell are connected by a bus bar 64 . The negative terminal 62 of the cell 20A arranged at one end in the arrangement direction x is not connected to the positive terminals of other cells. A negative electrode terminal 62 of the cell 20A is connected to an external device (for example, a vehicle motor, etc.) as a negative electrode output terminal 62a. Similarly, the positive terminal 60 of the cell 20D arranged at the other end in the arrangement direction x is not connected to the negative terminals of other cells. A positive electrode terminal 60 of the cell 20D is connected to an external device as a positive electrode output terminal 60a.

Further, in the assembled battery 10 according to this embodiment, the cells 20A to 20D are constrained along the arrangement direction x. Specifically, the assembled battery 10 includes a pair of plate members 70A and 70B, a tightening beam member 72, and a screw 74. As shown in FIG. Plate members 70A and 70B are arranged on the outermost sides in the arrangement direction x so as to sandwich the cells 20A to 20D, and a clamping beam member 72 is attached so as to bridge the plate members 70A and 70B. Then, by tightening the screws 74 and fixing the tightening beam material 72 to the plate members 70A and 70B, the arrayed unit cells 20A to 20D are restrained. A binding load F (see FIG. 5) along the arrangement direction x is applied to the unit cells 20A to 20D bound in this manner.

(b) Constraining Plate As shown in FIG. 5, a constraining plate 40, which is a rectangular plate member, is arranged between each of the cells 20A to 20D. It is preferable that the restraining plate 40 is adjusted in size and arrangement position so that a uniform restraining load F is applied to the electrode assembly housed in the battery case 50 .
The constraining plate 40 in this embodiment is made of thermoplastic resin. As used herein, the term “thermoplastic resin” refers to a resin having a melting point _TB lower than the maximum temperature _TA of the unit cell when the temperature is excessively raised (i.e., a resin that satisfies _TB < _TA ). . By using such a thermoplastic resin as the material of the constraining plate 40, the constraining plate 40 adjacent to the unit cell whose temperature has risen excessively can be melted to expose an elastic body (spring 42), which will be described later. . For example, when the cells 20A to 20D are general lithium ion secondary batteries, the maximum temperature T _A is 200° C. to 300° C. (for example, about 250° C.), so the melting point T _B is 100° C. to 190° C. (preferably 130° C. to 180° C.) is preferably used for the restraining plate 40 . Examples of such thermoplastic resins include polyethylene (melting point: 130° C.) and polypropylene (melting point: 180° C.).

(c) Elastic Body In the assembled battery 10 according to the present embodiment, an elastic body (spring 42 ) is embedded inside the restraint plate 40 . The spring 42 is arranged so as to generate an elastic force along the arrangement direction x of the cells 20A to 20D. In other words, the spring 42 is embedded in the restraining plate 40 so that the axial direction extends along the arrangement direction x. As a result, it is possible to suppress the chain reaction of heat generation without short-circuiting the cells 20A to 20D. Specifically, as shown in FIG. 6, in the assembled battery 10 according to the present embodiment, when a predetermined unit cell 20B is overheated, the thermoplastic resin constraining plate 40 melts and the spring 42 is released. expose. The elastic force of the springs 42 along the arrangement direction x can keep the cell 20B overheated away from the other cells 20A and 20C. This makes it difficult for the heat due to the excessive temperature rise of the cell 20B to be transmitted to the other cells 20A and 20C, and it is possible to suppress the progression of chain heat generation among the cells 20A to 20D.

In addition, using the restraining plate 40 with the spring 42 embedded as in the present embodiment can contribute to improving the battery performance in a mode of use where the installation space is limited (for example, a vehicle power source). Specifically, conventionally, in order to prevent chain heat generation, the constraining plates are thickened to widen the intervals between the cells. On the other hand, in the present embodiment, since the interval between the cells can be widened when the temperature is excessively increased, the constraining plate is made thinner than in the conventional case, and the single cells can be kept in the same position when the temperature is not excessively increased. The interval can be made narrower than before. As a result, the number of cells constituting the assembled battery can be increased without changing the size of the entire assembled battery, which contributes to improving the performance of the assembled battery in a mode of use where the installation space is limited.

It should be noted that the spring 42 in this embodiment is preferably made of a material that can maintain a sufficient elastic force even when the cell 20B is heated due to an excessive temperature rise. For example, when a lithium ion secondary battery is used as a single cell, the maximum temperature T _A when an excessive temperature rise occurs is 200° C. to 300° C. (for example, about 250° C.). In this case, it is preferable that the spring 42 is made of a heat-resistant material that can maintain an elastic force of 400 kgf or more even when heated to 350° C. or higher (for example, about 450° C.). Examples of such heat-resistant materials include nickel, chromium, iron, and alloys containing these metal elements. In the following description, the upper limit temperature at which the spring can maintain sufficient elastic force is referred to as the "use upper limit temperature".

Further, in the assembled battery 10 according to the present embodiment, it is preferable that the relationship between the elastic force FA of the spring 42 when the temperature is excessively increased and the binding load _FB when the temperature is excessively increased satisfies _{FB ≦ FA} . As a result, the other cells 20A and 20C can be appropriately kept away from the cell 20B in which the temperature has risen excessively, and the progression of chain heat generation can be suitably suppressed. It should be noted that the "elastic force F _A of the spring when the temperature rises excessively" takes into account the decrease in elastic force due to heat. This "elastic force F _A of the spring at excessive temperature rise" is obtained by heating the spring to the maximum temperature (about 250 ° C. in the case of a lithium ion secondary battery) at the time of excessive temperature rise of the unit cell, and It can be obtained by measuring the elastic force of the spring. The "restraint load F _B at excessive temperature rise" takes into consideration changes in the restraint load F due to expansion of the battery case and melting/softening of the restraint plates during excessive temperature rise. This "restraining load F _B at excessive temperature rise" is obtained by overheating a predetermined unit cell with respect to the assembled battery to which the present invention is applied and measuring the restraining load F at the maximum temperature. be able to. For example, as a result of the above preliminary test, when it is assumed that the binding load F _B at the time of excessive temperature rise is about 200 kgf to 400 kgf (for example, 300 kgf), the elastic force F _A at the time of excessive temperature rise is 400 kgf or more (for example, A 500 kgf) spring 42 is preferably used.

3. Other Embodiments The assembled battery according to one embodiment of the present invention has been described above. In addition, above-described embodiment is not intended to limit this invention.

For example, the assembled battery 10 according to the above-described embodiment includes four cells 20A to 20D, but the number of cells constituting the assembled battery is not particularly limited as long as it is two or more. Further, although the assembled battery 10 according to the embodiment described above uses lithium ion secondary batteries as the cells 20A to 20D, batteries used as the cells are not limited to lithium ion secondary batteries. The single cell may be, for example, a nickel-metal hydride battery or other secondary battery, or may be an electric storage element such as a capacitor.

Further, in the above-described embodiment, a metal rectangular case is used as the battery case 50, but the shape and material of the battery case are not particularly limited. For example, even when a laminate film or the like is used as the battery case, the effects of the present invention can be exhibited. If a case with low rigidity such as a laminate film is used, the part not in contact with the elastic body (spring) may expand due to the increase in internal pressure when the temperature rises excessively, and may come close to other cells. Therefore, when using a battery case with low rigidity, it is preferable to adjust the length of the spring in consideration of the amount of deformation of the case. Specifically, it is preferable to make the length _LA of the spring longer than half (L _B /2) of the amount of deformation L _B of the case at the time of excessive temperature rise (L _A >L _B /2). As a result, even if the battery case with low rigidity expands, the other batteries can be kept away from the excessively heated unit cell.

[Test example]
Test examples relating to the present invention will be described below, but the following test examples are not intended to limit the present invention.

1. Fabrication of assembled battery (1) Example 1
A unit cell (width 150 mm×thickness 15 mm×height 75 mm) having an aluminum rectangular battery case was prepared. The cells used in this test example used a nickel-cobalt-manganese composite oxide as the positive electrode active material, carbon as the negative electrode active material, and a PP/PE/PP three-layer resin sheet as the separator. It is a lithium ion secondary battery (battery capacity: 20 Ah). Six of these cells were prepared and arranged so that the side walls of the battery case faced each other, and then a constraining plate (thickness: 3 mm) with a spring embedded therein was placed between each cell. Then, the arrayed unit cell group was restrained with a restraining load of 300 kgf to construct an assembled battery for testing.
The constraining plate used in this example is made of polyethylene (melting point: 130°C). Also, the spring embedded in the restraining plate is made of nickel-chromium-iron alloy (NCF) (upper limit temperature for use: 450° C.). This spring has a length of 4 mm and an elastic force of 500 kgf. The above-mentioned "restraint load on each unit cell" and "elastic force of spring" are values at the temperature (250°C) when the temperature of the lithium ion secondary battery is excessively increased.

(2) Example 2
An assembled battery was produced under the same conditions as in Example 1, except that the material of the restraining plate was changed to polyimide (melting point: 500° C.), which is a heat-resistant resin.

(3) Example 3
An assembled battery was produced under the same conditions as in Example 1, except that the material of the spring was changed to SWOSC (silicon chromium steel oil-tempered wire for spring). The operating condition temperature of this spring is 120°C.

(4) Examples 4 to 6
An assembled battery was produced under the same conditions as in Example 1, except that the battery case was changed to a laminate film and the length of the spring was changed. In Examples 4 to 6, the thickness of the laminate film was changed in each example, and the amount of deformation of the case when the temperature was excessively increased was varied. Table 1 shows the "spring length" and "1/2 of the amount of deformation of the case" in each example.

(5) Examples 7 to 9
An assembled battery was produced under the same conditions as in Example 1, except that the elastic force of the spring and the binding load were changed as shown in Table 1.

(6) Example 10
An assembled battery was produced under the same conditions as in Example 1, except that a constraining plate in which no spring was embedded was used.

2. Evaluation test It was examined whether chain heat generation progresses when the temperature of the unit cell is excessively increased for the assembled battery of each example. In this evaluation test, first, a nail made of nickel was pierced into the unit cell arranged at one end in the arrangement direction to damage the electrode body so as to cause an excessive temperature rise. Charging and discharging were performed in this state, and the temperature of the unit cells at both ends in the arrangement direction was measured during the charging and discharging. As a result, the temperature of the unit cell (the unit cell into which the nail was stuck) placed at one end in the arrangement direction was about 250° C. in any of Examples 1 to 10. On the other hand, the temperature of the cells arranged at the other end was different in each case, and whether chain heat generation was progressing was evaluated based on the temperature of the cells at the other end. Specifically, when the temperature of the cell at the other end is less than 50 ° C., it is evaluated as "no chain heat generation (good)", and when it is 50 ° C. or higher and less than 200 ° C., it is evaluated as "chain heat generation. The progress of heat generation is suppressed (acceptable)", and the case of 200°C or higher is evaluated as "a chain reaction of heat generation is occurring (impossible)". Table 1 shows the evaluation results.

As shown in Table 1, in the assembled batteries of Examples 1 and 3 to 9, progression of chain heat generation was suppressed. From this, by using a thermoplastic resin restraint plate with a spring embedded inside, it is possible to keep the other cells away from the cell in which the temperature has risen excessively, thereby suppressing the chain reaction of heat generation. confirmed. In particular, in the assembled batteries of Examples 1, 4, 7, and 8, the chain reaction of heat generation was suppressed more favorably.

Although the present invention has been described in detail with reference to specific embodiments, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the embodiments described above.

REFERENCE SIGNS LIST 10 assembled battery 20, 20A to 20D cell 30 laminated electrode body 31 positive electrode sheet 32 positive electrode current collector 33 positive electrode active material layer 35 negative electrode sheet 36 negative electrode current collector 37 negative electrode active material layer 38 separator 40 restraint plate 42 spring 50 battery Case 50a Side wall of battery case 52 Case main body 54 Lid 60 Positive electrode terminal 60a Positive output terminal 62 Negative electrode terminal 62a Negative output terminal 64 Bus bar 70A, 70B Plate-like member 72 Beam material for tightening 74 Screw F Restraining load x Direction of unit cell arrangement y stacking direction of the electrode body

Claims (3)

An assembled battery in which a plurality of unit cells are arranged along a predetermined arrangement direction and each unit cell is constrained along the arrangement direction,
A thermoplastic resin restraint plate is arranged between each of the plurality of arranged cells,
An elastic body is embedded in the constraining plate to generate an elastic force along the arrangement direction ,
The assembled battery, wherein a relationship between an elastic force _{F A} of the elastic body when the temperature is excessively increased and a binding load F B applied to the unit cell when the temperature is excessively increased satisfies _{FB ≦} FA . 2. The assembled battery according to claim 1 , wherein the elastic force F _A of the elastic body when the temperature rises excessively is 400 kgf or more, and the binding load F _B applied to the unit cell when the temperature rises excessively is 200 kgf to 400 kgf. . The assembled battery according to claim 2 , wherein the elastic body is made of a heat-resistant material that maintains an elastic force of 400 kgf or more when heated to 350°C or more.

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