JP7639635B2 - Battery module and its cushioning sheet - Google Patents

Description

The technology disclosed in this specification relates to a battery module and its cushioning sheet.

Patent Document 1 describes a battery module. This battery module includes a plurality of stacked battery cells and a plurality of buffer sheets arranged alternately with the battery cells. Each battery cell is a rectangular non-aqueous secondary battery cell, and each buffer sheet has a two-layer structure in which an elastic layer and a heat insulating layer are stacked along the stacking direction.

International Publication No. 2020/194939

When the buffer sheet has a two-layer structure of an elastic layer and a heat insulating layer, as in the battery module described above, it is possible to provide both elasticity and heat insulation to the buffer sheet. However, it is difficult to provide both elasticity and heat insulation appropriately to a single buffer sheet. In particular, in non-aqueous secondary battery cells, it is known that the internal electrode body expands (hereinafter referred to as swelling) with charging and deterioration. At this time, if the spring constant of the elastic layer is too high, the pressing force on the electrode body becomes excessive, and the electrolyte is pushed out from the electrode body, which may increase the internal resistance of the battery cell. On the other hand, if the spring constant of the elastic layer is too low, the swelling cannot be sufficiently regulated, and openings may occur in the current collecting sheets stacked on the electrode body, which may lead to capacity deterioration of the battery cell. In order to suppress such problems caused by swelling of the battery cell, it is necessary to appropriately adjust the elasticity given to the buffer sheet.

In addition, the swelling of the battery cell described above is also related to the aspect ratio of the battery cell. When the aspect ratio of a rectangular battery cell is 1.5 or more, the distance from the end to the center of the electrode body is relatively long, and the moment of inertia relative to swelling becomes high, making the structure more susceptible to swelling. In addition, in a battery cell with an aspect ratio of 10 or more, the aspect ratio is too high, so the rigidity of the short side increases and the force restricting the electrode body becomes weak, making it easier for capacity reduction to occur due to the opening of the current collecting sheet. Therefore, in order to suppress deterioration of the performance of the battery cell, it is necessary to take into account the aspect ratio of the battery cell.

In addition, in a structure in which multiple battery cells are stacked, it is known that when heat is generated in one battery cell due to a short circuit, the heat is transferred to adjacent battery cells, inducing self-heating in the adjacent cells. In order to avoid such a chain of heat generation (hereinafter referred to as chain heating), it is effective to increase the insulation properties of the insulating layer, and for this purpose, it is considered to increase the thickness of the insulating layer. However, there is a limit to the thickness of the buffer sheet, and in order to increase the thickness of the insulating layer, the thickness of the elastic layer needs to be reduced, and as a result, the elasticity of the buffer sheet as a whole decreases. If the elasticity of the buffer sheet decreases, the pressing force acting on the electrode body becomes excessive, and if chain heating occurs in this state, the separator in the electrode body of the adjacent cell may break even at a relatively low temperature, causing a short circuit.

In view of the above, this specification provides a technology that can suppress performance degradation and failure of battery cells in a battery module in which multiple battery cells are stacked with buffer sheets interposed between them.

The technology disclosed in this specification is embodied in a battery module. The battery module includes two or more battery cells arranged in a stacked manner, and at least one buffer sheet arranged alternately with the two or more battery cells. The battery cells are rectangular non-aqueous secondary battery cells, and the aspect ratio of the main surface intersecting the stacking direction is within a range of 1.5 to 10.0. The buffer sheet has a structure in which an elastic layer and a heat insulating layer are stacked along the stacking direction. The spring constant of the elastic layer in the stacking direction is within a range of 0.03 MPa/mm to 4.3 MPa/mm. The heat transfer coefficient of the heat insulating layer in the stacking direction is within a range of 0.012 W/mK to 0.1 W/mK. The thickness of the heat insulating layer in the stacking direction is within a range of 12.5% to 69% of the distance between two adjacent battery cells via the buffer sheet.

According to the above configuration, the buffer sheet having an elastic layer and a heat insulating layer can have both appropriate elasticity and heat insulating properties for rectangular battery cells having an aspect ratio of 1.5 to 10.0. This makes it possible to effectively suppress the expansion of the battery cell without increasing the internal resistance of the battery cell. It also makes it possible to suppress chain heating and to avoid short circuits caused by separator breakage of adjacent cells due to chain heating.

The elasticity of the elastic layer does not necessarily have to have ideal linearity. That is, the spring constant of the elastic layer may change according to the strain occurring in the elastic layer. In this regard, the elasticity of the elastic layer may satisfy the following relationship. That is, when the distance between two adjacent battery cells is D, the thickness of the battery cells in the stacking direction is d, the surface pressure generated in the elastic layer when the buffer sheet is compressed to a thickness of D-0.001×d is α1, and the surface pressure generated in the elastic layer when the buffer sheet is compressed to a thickness of D-0.002×d is α2, the spring constant γ1 of the elastic layer, defined by the formula (α2-α1)/(d(0.002-0.001))=γ1, may satisfy the relationship of 0.03 MPa/mm<γ1.

In addition to or instead of the above, the elasticity of the elastic layer may satisfy the following relationship. That is, if the distance between two adjacent battery cells is D, the thickness of the battery cells in the stacking direction is d, the surface pressure generated on the elastic layer when the buffer sheet is compressed to a thickness of D-0.100 x d is β1, and the surface pressure generated on the elastic layer when the buffer sheet is compressed to a thickness of D-0.101 x d is β2, the spring constant γ2 of the elastic layer, defined by the formula (β2-β1)/(d(0.101-0.100))=γ2, may satisfy the relationship γ2<4.3 MPa/mm.

Note that the external shape of a rectangular battery cell is usually not necessarily a strict rectangular parallelepiped. Therefore, the above-mentioned distance D and thickness d may vary slightly depending on the position at which they are measured. For this reason, in this specification, the dimensions such as distance D and thickness d are measured at the position of the surface (e.g., the top surface) on which the external terminals of the battery cell are provided. That is, in this specification, the distance D between two adjacent battery cells means the distance between the surface on which the external terminals of one battery cell are provided and the surface on which the external terminals of the other battery cell are provided, and particularly means the distance in the stacking direction. Similarly, the thickness d of the battery cell in the stacking direction means the dimension of the surface on which the external terminals of the battery cell are provided, and particularly means the dimension in the stacking direction.

FIG. 1 is a front view showing a schematic configuration of a battery module 10 according to an embodiment of the present invention. FIG. 1 is a plan view showing a schematic configuration of a battery module 10 according to an embodiment of the present invention. FIG. 2 is an enlarged view of a portion III in FIG. 1, showing the configuration of a buffer sheet 20. Experimental data for some examples is presented. Experimental data for some examples is presented. Experimental data for some examples is presented. FIG. 4 is a diagram showing a typical range of values according to a preferred embodiment;

An embodiment of a battery module 10 will be described with reference to the drawings. The battery module 10 of this embodiment can be used, for example, in an electric vehicle to supply power to a traction motor that drives the wheels. However, the use of the battery module 10 is not limited to electric vehicles.

1 and 2, the battery module 10 includes a plurality of battery cells 12 and a plurality of buffer sheets 20. The battery cells 12 are stacked along the X direction in the figure. Hereinafter, the X direction may be referred to as the stacking direction. The buffer sheets 20 are alternately arranged with the battery cells 12. That is, one buffer sheet 20 is interposed between two adjacent battery cells 12. The battery cells 12 are also called a cell stack (or battery stack). Although not shown, both ends of the cell stack are restrained, and a compressive force is applied to the battery cells 12 along the stacking direction. The number of battery cells 12 and buffer sheets 20 is not particularly limited. The battery module 10 may include two or more battery cells 12 and at least one buffer sheet 20.

The battery cell 12 is a non-aqueous secondary battery cell, and in particular, a rectangular battery cell. Although not particularly limited, the battery cell 12 in this embodiment is a lithium ion battery cell. The battery cell 12 includes an electrode body 14, a rectangular housing 16 that houses the electrode body 14, and a pair of external terminals 18p, 18n. The electrode body 14 has a structure in which a positive electrode current collector sheet and a negative electrode current collector sheet are stacked with an insulating separator interposed therebetween. These current collector sheets and separators are stacked along the X direction, and the stacking direction of the current collector sheets in the electrode body 14 coincides with the stacking direction of the multiple battery cells 12. As described above, the battery cell 12 is a non-aqueous secondary battery cell, and the inside of the housing 16 is filled with a non-aqueous electrolyte.

A pair of external terminals 18p, 18n are provided on the upper surface 16b of the housing 16. The pair of external terminals 18p, 18n are electrically connected to the electrode body 14 inside the housing 16, and a portion of each is exposed to the outside at the upper surface 16b of the housing 16. Although not shown, the external terminals 18p, 18n of each battery cell 12 are electrically connected to the external terminals 18p, 18n of the adjacent battery cells 12. As a result, the multiple battery cells 12 are electrically connected in series. Note that, in another embodiment, some or all of the multiple battery cells 12 may be electrically connected in parallel.

The aspect ratio of the battery cell 12 is in the range of 1.5 to 10.0. The aspect ratio here refers to the aspect ratio of the main surface 16a of the battery cell 12 that intersects with the stacking direction. In other words, when the length of the short side of the main surface 16a is h and the length of the long side of the main surface 16a is w, the aspect ratio can be expressed by the formula w/h. Note that the length h of the short side and the length w of the long side of the main surface 16a are sufficiently larger than the thickness d of the battery cell 12. Note that the thickness d here refers to the dimension of the top surface 16b on which the external terminals 18p, 18n are provided, and specifically refers to the dimension in the stacking direction.

The buffer sheet 20 is a sheet-like member, and the area of the buffer sheet 20 is approximately equal to the main surface 16a of the battery cell 12. The presence of the buffer sheet 20 provides a predetermined distance D between two adjacent battery cells 12. Note that the distance D here refers to the distance between the top surface 16b of one battery cell 12 and the top surface 16b of the other battery cell 12, and specifically refers to the distance in the stacking direction.

As shown in FIG. 3, the buffer sheet 20 includes an elastic layer 22 and a heat insulating layer 24, and has a structure in which the elastic layer 22 and the heat insulating layer 24 are laminated along a lamination method (i.e., the X direction). The elastic layer 22 is made of an elastic material such as rubber or resin. The heat insulating layer 24 is made of an insulating material such as a porous material. The materials constituting the elastic layer 22 and the heat insulating layer 24 are not particularly limited. The elastic layer 22 only needs to have a higher elasticity (i.e., a lower spring constant) than the heat insulating layer 24, and the heat insulating layer 24 only needs to have a higher elasticity (i.e., a lower spring constant) than the elastic layer 22.

The above-mentioned structure allows the buffer sheet 20 to have both elasticity and heat insulation. The elasticity of the buffer sheet 20 is mainly exerted by the elastic layer 22 and changes depending on the spring constant of the elastic layer 22. As mentioned above, the elasticity of the buffer sheet 20 suppresses the expansion of the battery cell 12. However, if the spring constant of the elastic layer 22 is too high, the internal resistance of the battery cell 12 increases and there is a high possibility of short-circuiting adjacent cells during chain heating. Conversely, if the spring constant of the elastic layer 22 is too low, the expansion of the battery cell 12 cannot be sufficiently suppressed, and there is a high possibility of causing capacity deterioration of the battery cell 12. On the other hand, the heat insulation of the buffer sheet 20 is mainly exerted by the heat insulation layer 24 and changes depending on the heat transfer rate of the heat insulation layer 24. As mentioned above, the chain heating of the battery cell 12 is suppressed. The higher the heat insulation of the elastic layer 22, the more preferable it is, and at least the heat insulation that can avoid short-circuiting of adjacent cells caused by chain heating is required.

In addition, the elasticity and heat insulation of the buffer sheet 20 also change depending on the thickness A of the elastic layer 22 in the stacking direction and the thickness B of the elastic layer 22 in the stacking direction. For example, even if the spring constant of the elastic layer 22 and the heat transfer coefficient of the heat insulating layer 24 are constant, if the thickness A of the elastic layer 22 is increased and the thickness B of the elastic layer 22 is decreased accordingly, the elasticity of the buffer sheet 20 improves, but the heat insulation of the buffer sheet 20 decreases. Conversely, if the thickness A of the elastic layer 22 is decreased and the thickness B of the elastic layer 22 is increased accordingly, the elasticity of the buffer sheet 20 decreases, but the heat insulation of the buffer sheet 20 improves. Therefore, in the design of the buffer sheet 20, not only the spring constant of the elastic layer 22 and the heat transfer coefficient of the heat insulating layer 24, but also the proportion of the elastic layer 22 and the heat insulating layer 24 in the buffer sheet 20 are important parameters. Furthermore, the expansion of the battery cell 12 is also related to the aspect ratio (w/h) of the battery cell 12. Therefore, when designing the buffer sheet 20, the aspect ratio (w/h) of the battery cell 12 must also be taken into consideration.

Based on the above findings, Figures 4 to 6 show the results of cycle tests carried out on various embodiments of the battery module 10. In this cycle test, the battery module 10 was repeatedly charged and discharged 200 cycles to verify the presence or absence of smoke in the battery cells 12 (adjacent cells), the rate of increase in the internal resistance of the battery cells 12, and the capacity degradation of the battery cells 12. The charging conditions were constant current and constant voltage charging with a charging voltage of the battery cells 12 of 4.25 V, a C rate of 0.5 C, and a cutoff current of 0.1 C. The discharging conditions were constant current discharging with a discharging voltage of the battery cells 12 of 2.8 V and a C rate of 0.5 C.

4 to 6, "Insulation ratio" indicates the ratio B/D of the thickness B of the insulation layer 24 to the distance D between the two battery cells 12. "Heat transfer coefficient" indicates the heat transfer coefficient (W/mK) in the stacking direction of the insulation layer 24. This heat transfer coefficient is measured when a heater of 500°C is applied from one side of the insulation layer 24 for 50 seconds with a pressure of 2 MPa applied. "Aspect ratio" indicates the aspect ratio w/h of the main surface 16a of the battery cell 12. "Smoke generation from adjacent cells" indicates the presence or absence of smoke generation in adjacent cells and the time required for smoke generation. In "Presence/absence", "◯" indicates that there was no smoke generation, and "×" indicates that there was smoke generation. In "Time", for example, "12:29" means 12 hours and 29 minutes. "Spring constant" indicates the spring constant (MPa/mm) in the stacking direction of the elastic layer 22. "Resistance increase rate" indicates the rate of change in the internal resistance of the battery cell 12 due to the cycle test. In addition, "〇" in "Judgment" indicates that the "resistance increase rate" is 106 percent or less, and "×" indicates anything other than that. "Cycle maintenance rate" indicates the rate of change in the capacity of the battery cell 12 due to the cycle test. In addition, "〇" in "Judgment" indicates that the "cycle maintenance rate" is 95 percent or more, and "×" indicates anything other than that.

From the test results shown in Figures 4 to 6, the following technical insights can be obtained when the aspect ratio of the battery cell 12 is between 1.0 and 10.0. That is, as shown in Figure 7, it is preferable that the spring constant of the elastic layer 22 in the stacking direction is within the range of 0.03 MPa/mm to 4.3 MPa/mm. In particular, when the spring constant is in the range exceeding 4.3 MPa/mm, the pressing force acting on the battery cell 12 becomes excessive, and there is a risk of short-circuiting of adjacent cells during chain heating. To avoid this, it is necessary to limit the C rate during charging and discharging to a low value, and the desired characteristics cannot be obtained ("High rate NG" in Figure 7). On the other hand, when the spring constant is in the range below 0.03 MPa/mm, the pressing force acting on the battery cell 12 is insufficient, and capacity deterioration of the battery cell 12 becomes a problem ("Electrode opening NG" in Figure 7).

The thermal conductivity of the insulating layer 24 in the stacking direction is preferably in the range of 0.012 W/mK to 0.1 W/mK. The thickness B of the insulating layer 24 in the stacking direction is preferably in the range of 12.5% to 69% of the distance D between two adjacent battery cells 12 via the buffer sheet 20. In particular, if the ratio of the insulating layer 24 is less than 12.5%, the insulation of the buffer sheet 20 as a whole is insufficient, making it difficult to suppress chain heating ("Chain NG" in Figure 7). On the other hand, if the ratio of the insulating layer 24 is more than 69%, the elasticity of the buffer sheet 20 as a whole is poor (i.e., the spring constant increases), which may lead to a short circuit of adjacent cells during chain heating. In this case, it is necessary to limit the C rate during charging and discharging to a low value, and the desired characteristics cannot be obtained ("High Rate NG" in Figure 7).

As described above, when the spring constant of the elastic layer 22 is within the range of 0.03-4.3 MPa/mm, the thermal conductivity of the insulating layer 24 is within the range of 0.012-0.1 W/mK, and the proportion of the insulating layer 24 is within the range of 12.5-69 percent, the buffer sheet 20 can have both appropriate elasticity and insulating properties for battery cells 12 with aspect ratios of 1.5 to 10.0. This makes it possible to effectively suppress the expansion of the battery cells 12 without increasing the internal resistance of the battery cells 12. It also makes it possible to suppress chain heating of the battery cells 12, and does not cause short circuits of adjacent cells during chain heating.

Here, the elasticity of the elastic layer 22 does not necessarily have to have ideal linearity. That is, the spring constant of the elastic layer 22 may change according to the strain occurring in the elastic layer 22. In this regard, the elasticity of the elastic layer 22 may satisfy the following relationship. That is, with respect to the distance D between two adjacent battery cells 12 and the thickness d of the battery cells 12 in the stacking direction, when the surface pressure occurring in the elastic layer 22 when the buffer sheet 20 is compressed to a thickness of D-0.001×d is α1, and the surface pressure occurring in the elastic layer 22 when the buffer sheet 20 is compressed to a thickness of D-0.002×d is α2, the spring constant γ1 of the elastic layer 22 defined by the formula (α2-α1)/(d(0.002-0.001))=γ1 may satisfy the relationship of 0.03 MPa/mm<γ1. If this relationship is satisfied, it is possible to prevent the spring constant of the elastic layer 22 from falling below 0.03 MPa/mm in the expected normal usage of the battery module 10.

In addition, or instead, the elasticity of the elastic layer 22 may satisfy the following relationship. That is, if the surface pressure generated on the elastic layer 22 when the buffer sheet 20 is compressed to a thickness of D-0.100 x d is β1, and the surface pressure generated on the elastic layer 22 when the buffer sheet 20 is compressed to a thickness of D-0.101 x d is β2, the spring constant γ2 of the elastic layer 22, defined by the formula (β2-β1)/(d(0.101-0.100))=γ2, may satisfy the relationship γ2<4.3 MPa/mm. If this relationship is satisfied, it is possible to avoid the spring constant of the elastic layer 22 exceeding 4.3 MPa/mm in the expected normal usage form of the battery module 10.

Although the embodiments of the present technology have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. The technical elements described in this specification or drawings exert technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technology exemplified in this specification or drawings achieves multiple objectives simultaneously, and achieving one of those objectives is itself technically useful.

10: Battery module 12: Battery cell 14: Battery cell electrode body 16: Battery cell housing 18p, 18n: Battery cell external terminals 20: Cushioning sheet 22: Elastic layer of cushioning sheet 24: Heat insulating layer of cushioning sheet

Claims (4)

Two or more battery cells arranged in a stack;
at least one buffer sheet arranged alternately with the two or more battery cells;
the battery cell is a rectangular nonaqueous secondary battery cell, and the aspect ratio of a main surface intersecting a stacking direction is within a range of 1.5 to 10.0;
The buffer sheet has a structure in which an elastic layer and a heat insulating layer are laminated along the lamination direction,
The spring constant of the elastic layer in the stacking direction is in the range of 0.03 MPa/mm to 4.3 MPa/mm,
The thermal insulation layer has a thermal conductivity in the stacking direction in a range of 0.012 W/mK to 0.1 W/mK;
a thickness of the insulating layer in the stacking direction is within a range of 12.5% to 69% of a distance between two adjacent battery cells via the buffer sheet;
Battery module. The battery module according to claim 1, wherein the spring constant γ1 of the elastic layer, defined by the formula (α2-α1)/(d(0.002-0.001))=γ1, satisfies the relationship 0.03 MPa/mm<γ1, where D is the distance between the two adjacent battery cells, d is the thickness of the battery cell in the stacking direction, α1 is the surface pressure generated on the elastic layer when the buffer sheet is compressed to a thickness of D-0.001×d, and α2 is the surface pressure generated on the elastic layer when the buffer sheet is compressed to a thickness of D-0.002×d. The battery module according to claim 1 or 2, wherein the spring constant γ2 of the elastic layer, defined by the formula (β2-β1)/(d(0.101-0.100))=γ2, satisfies the relationship γ2<4.3 MPa/mm, where D is the distance between the two adjacent battery cells, d is the thickness of the battery cell in the stacking direction, β1 is the surface pressure generated on the elastic layer when the buffer sheet is compressed to a thickness of D-0.100×d, and β2 is the surface pressure generated on the elastic layer when the buffer sheet is compressed to a thickness of D-0.101×d. A buffer sheet arranged alternately with two or more stacked battery cells,
the battery cell is a rectangular nonaqueous secondary battery cell, and the aspect ratio of a main surface intersecting a stacking direction is within a range of 1.5 to 10.0;
The buffer sheet has a structure in which an elastic layer and a heat insulating layer are laminated along the lamination direction,
The spring constant of the elastic layer in the stacking direction is in the range of 0.03 MPa/mm to 4.3 MPa/mm,
The thermal insulation layer has a thermal conductivity in the stacking direction in a range of 0.012 W/mK to 0.1 W/mK;
a thickness of the insulating layer in the stacking direction is within a range of 12.5% to 69% of a distance between the two adjacent battery cells via the buffer sheet;
Cushioning sheet.

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