Battery pack

Abstract

The invention belongs to the technical field of batteries, and discloses a battery pack, the battery pack comprises a plurality of single batteries and heat exchange parts, the proportion of the heat exchange area of the heat exchange parts and the single batteries to the surface of the single batteries is a, under the condition of the temperature of 25 DEG C, when the state of charge of the single batteries is 40%, the direct current internal resistance is R0, and when the state of charge of the single batteries is 80%, the direct current internal resistance is R0. And a, R0 and R1 meet the relational expression that R1-R0 / a is greater than or equal to 0.01117 and less than or equal to 0.076. According to the battery pack, the contact area of the single batteries and the heat exchange pieces can be set according to the DCR change of the single batteries, stable cooling of the battery pack is achieved, it is ensured that the temperature change of the battery pack in the working process is not too large, and therefore the probability of thermal runaway of the battery pack is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a battery pack. Background Art

[0002] In order to ensure a long life of the battery pack, it is necessary to control the maximum temperature and maximum temperature difference during the battery cycle in the battery pack. In the prior art, a cold plate is usually provided at the bottom of the battery pack to cool the single cells.

[0003] Different DCRs (direct current internal resistance) of single cells will lead to different heat generation during the charging and discharging process. If the DCR of a single cell changes from empty to fully charged during the charging process, the greater the heat generation, the existing cold plate heat dissipation structure cannot effectively meet the heating problem caused by the change of single cell DCR. Summary of the Invention

[0004] The object of the present invention is to provide a battery pack that can set the contact area between the single cell and the heat exchange element according to the DCR change of the single cell, thereby achieving stable cooling of the battery pack and ensuring that the temperature change of the battery pack during operation will not be too large, thereby reducing the probability of thermal runaway of the battery pack and extending the cycle life of the battery pack.

[0005] To achieve this object, the present invention adopts the following technical solutions:

[0006] A battery pack includes multiple single cells and a heat exchange element. The ratio of the heat exchange area between the heat exchange element and the single cells to the surface area of ​​the single cells is a. At a temperature of 25°C, when the state of charge of the single cells is 40%, the DC internal resistance is R0. When the state of charge of the single cells is 0%, the DC internal resistance is R1. a, R0, and R1 satisfy the relationship: 0.0117≤|R1-R0| / a≤0.076.

[0007] Beneficial effects of the battery pack of the present invention: The battery pack provided by the present invention determines the ratio a of the heat exchange area of ​​the heat exchange component and the single cell to the surface area of ​​the single cell 100 according to the absolute value of the difference between the DC internal resistance R0 of the single cell when the state of charge is 40% and the DC internal resistance R1 of the single cell when the state of charge is 80%. This can ensure that the ratio a of the heat exchange area of ​​the heat exchange component and the single cell to the surface area of ​​the single cell 100 can not only ensure the heat exchange effect, improve the cooling effect of the single cell, avoid excessive temperature rise inside the battery pack, reduce the probability of thermal runaway of the battery pack, and extend the cycle life of the battery pack, but also can control the size of the heat exchange component and the space occupied by the heat exchange component, which is beneficial to improving the space utilization inside the battery pack, thereby helping to improve the energy density of the battery pack.

[0008] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a schematic structural diagram of a first battery pack according to an embodiment of the present invention;

[0010] Figure 2 is a schematic structural diagram of a second battery pack according to an embodiment of the present invention;

[0011] Figure 3 1 is a schematic structural diagram of a third battery pack according to an embodiment of the present invention.

[0012] Reference numerals:

[0013] 100, single cell; 110, terminal;

[0014] 200, heat exchange element; 210, first heat exchange part; 220, second heat exchange part. DETAILED DESCRIPTION

[0015] The present invention will be further described in detail below with reference to the accompanying drawings and examples. It will be understood that the specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention. It should also be noted that, for ease of description, the accompanying drawings only illustrate portions relevant to the present invention, not all structures.

[0016] In the description of the present invention, unless otherwise expressly specified or limited, the terms "connected," "connected," and "fixed" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integration; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention in specific circumstances.

[0017] In the description of this embodiment, terms such as "upper," "lower," "left," "right," "front," and "rear" are used to refer to positions or locations based on the positions or locations shown in the accompanying drawings. These terms are intended solely to facilitate description and simplify operation, and are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the present invention. Furthermore, the terms "first" and "second" are used solely for descriptive purposes and have no special meaning.

[0018] The present invention discloses a battery pack, referring to Figure 1 and Figure 3As shown, a plurality of single cells 100 and a heat exchange element 200 are included. The ratio of the heat exchange area of ​​the heat exchange element 200 and the single cell 100 to the surface area of ​​the single cell 100 is a. Under the condition of a temperature of 25°C, when the state of charge of the single cell 100 is 40%, the DC internal resistance is R0. When the state of charge of the single cell 100 is 80%, the DC internal resistance is R1. a, R0 and R1 satisfy the relationship: 0.0117≤|R1-R0| / a≤0.076.

[0019] First, it should be noted that differences in the DC internal resistance of the cell 100 result in different heat generation during the charging and discharging process. The greater the change in the DC internal resistance of the cell 100 from empty to fully charged during charging, the greater the heat generation. Therefore, corresponding to a larger change in DC internal resistance, the larger the heat exchange area of ​​the cell 100 needs to be to improve heat dissipation and prevent excessive temperature differences within the battery pack. Furthermore, for the same cell 100, the larger the ratio (a) of the heat exchange area of ​​the heat exchange element 200 to the cell 100 to the cell 100's surface area, the better the heat exchange effect. However, the heat exchange element 200 occupies a larger space, resulting in wasted space within the battery pack and hindering the improvement of the battery pack's energy density. The smaller the ratio (a) of the heat exchange area of ​​the heat exchange element 200 to the cell 100 to the cell 100's surface area, the poorer the heat exchange effect, which can easily lead to excessive temperature rise within the battery pack, thereby increasing the probability of thermal runaway.

[0020] It should be noted that the heat exchange element 200 of this embodiment is used to perform heat exchange with the battery cells 100. A heat exchange medium, such as a liquid or gas, can flow through the interior of the heat exchange element 200. Alternatively, the heat exchange element 200 can be directly made of a thermally conductive material or a phase-change material. Furthermore, the heat exchange area mentioned above refers to the contact area between the housing surface of the battery cell 100 and the heat exchange element 200. This contact can be direct or adhesively bonded via a thermally conductive adhesive.

[0021] It is understandable that after the single cell 100 is manufactured, the DC internal resistance of the single cell 100 will be tested through a DCR test and a corresponding curve will be drawn. In this embodiment, the ratio a of the heat exchange area of ​​the heat exchange component 200 and the single cell 100 to the surface area of ​​the single cell 100 is determined according to the absolute value of the difference between the DC internal resistance R0 of the single cell 100 when the state of charge is 0 and the DC internal resistance R1 of the single cell 100 when the state of charge is 100%. This can ensure that the ratio a of the heat exchange area of ​​the heat exchange component 200 and the single cell 100 to the surface area of ​​the single cell 100 can not only ensure the heat exchange effect, improve the cooling effect of the single cell 100, avoid excessive temperature rise inside the battery pack, and reduce the probability of thermal runaway of the battery pack, but also control the size of the heat exchange component 200 and the space occupied by the heat exchange component 200, which is beneficial to improving the space utilization inside the battery pack, thereby facilitating improving the energy density of the battery pack.

[0022] Optionally, |R1-R0| / a can be 0.0117, 0.012, 0.013, 0.014, 0.015, 0.016, 0.017, 0.018, 0.019, 0.02, 0.021, 0.022, 0.023, 0.024, 0.025, 0.026, 0.027, 0.028, 0.029, 0.03, 0.031, 0.032, 0.033, 0.034, 0.035, 0.036, 0.037, 0.038, 0.039 , 0.04, 0.041, 0.042, 0.043, 0.044, 0.045, 0.046, 0.047, 0.048, 0.049, 0.05, 0.051, 0.052, 0.053, 0.054, 0.055, 0.056, 0.057, 0.058, 0.059, 0.06, 0.061, 0.062, 0.063, 0.064, 0.065, 0.066, 0.067, 0.068, 0.069, 0.07, 0.076. Of course, other values ​​within the range of 0.0117-0.076 are also possible, and are not limited to the above examples.

[0023] Optionally, the range of R0 is 0.35mΩ-1.60mΩ.

[0024] Optionally, the range of R1 is 0.6mΩ-2.9mΩ.

[0025] Optionally, the ratio a of the heat exchange area to the surface area of ​​the single cell 100 is in a range of 8%-40%. Optionally, the ratio a of the heat exchange area to the surface area of ​​the single cell 100 can be 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 20%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, or 40%. Other values ​​within the range of 8%-40% are also possible.

[0026] In some embodiments, reference Figure 1 and Figure 2 As shown, multiple battery cells 100 are stacked along a predetermined direction, with at least a portion of the heat exchange element 200 located between two adjacent battery cells 100, and a, R0, and R1 satisfying the relationship: 0.02 ≤ |R1-R0| / a ≤ 0.076. It is understood that at least a portion of the heat exchange element 200 is located between two adjacent battery cells 100, allowing the two adjacent battery cells 100 to share a portion of the heat exchange element 200, which is beneficial for improving the heat exchange efficiency of the heat exchange element 200. Under this premise, if the absolute value of the difference between R1 and R0 is fixed, a smaller ratio a (the ratio of the heat exchange area of ​​the heat exchange element 200 to the surface area of ​​the battery cell 100) can be selected, which is beneficial for improving the space utilization within the battery pack and thus the energy density of the battery pack.

[0027] In some embodiments, reference Figure 1 and Figure 2As shown, the cell 100 has two first sidewalls, two second sidewalls, and two third sidewalls. The area of ​​the first sidewall is greater than that of the second and third sidewalls. The heat exchange element 200 is located between the two first sidewalls, and a, R0, and R1 satisfy the relationship: 0.025≤|R1-R0| / a≤0.076. It is understood that the cell 100 typically has one large face and two small faces. The large faces are the two faces along the thickness of the cell 100, which are the first sidewalls mentioned above. One small face is the two faces along the height of the cell 100, which are the second sidewalls mentioned above. The other small face is the two faces along the width of the cell 100, which are the third sidewalls mentioned above. In this embodiment, since the heat exchange element 200 is located between the two first side walls with larger areas, the heat exchange element 200 has a better heat dissipation effect on the single battery 100 under the same heat exchange area. Under this premise, when the absolute value of the difference between R1 and R0 is fixed, a smaller ratio a of the heat exchange area of ​​the heat exchange element 200 and the single battery 100 to the surface area of ​​the single battery 100 can be selected. On the one hand, the space occupied by the heat exchange element 200 is further reduced, which is beneficial to improving the space utilization inside the battery pack, thereby helping to improve the energy density of the battery pack. On the other hand, it prevents the contact area between the single battery 100 and the heat exchange element 200 from being too large, thereby preventing the insulation performance from being affected.

[0028] In some embodiments, reference Figure 2 As shown, the heat exchange element 200 includes a first heat exchange portion 210 and a second heat exchange portion 220. The first heat exchange portion 210 is sandwiched between two adjacent single cells 100, and the second heat exchange portion 220 is disposed on one side of the multiple single cells 100 in a direction perpendicular to a predetermined direction. Compared to a heat exchange element 200 that merely abuts against one sidewall of a single cell 100, in this embodiment, the heat exchange element 200 includes a first heat exchange portion 210 and a second heat exchange portion 220. The first heat exchange portion 210 is sandwiched between two adjacent single cells 100, and the second heat exchange portion 220 is disposed on one side of the multiple single cells 100 in a direction perpendicular to the predetermined direction. With the same heat exchange area, the heat exchange element 200, which contacts two surfaces of the single cells 100, achieves a better heat dissipation effect for the single cells 100.

[0029] In some embodiments, reference Figure 3As shown, a single cell 100 includes a terminal 110. The terminal 110 and the heat exchange element 200 are disposed on two opposing side walls of the single cell 100, and a, R0, and R1 satisfy the relationship: 0.028≤|R1-R0| / a≤0.076. Because the terminal 110 is disposed on two opposing side walls of the single cell 100, the required heat dissipation effect is smaller than that of a structure with a terminal 110 on the same side. Under this premise, if the absolute value of the difference between R1 and R0 is fixed, a smaller ratio a of the heat exchange area of ​​the heat exchange element 200 and the single cell 100 to the surface area of ​​the single cell 100 can be selected. This further reduces the space occupied by the heat exchange element 200, thereby improving the space utilization within the battery pack and thus the energy density of the battery pack. It also prevents the excessive contact area between the single cell 100 and the heat exchange element 200 from affecting insulation performance.

[0030] In some embodiments, a single battery cell 100 includes a housing and a battery cell disposed within the housing. The heat exchange element 200 abuts against the side wall of the housing. The distance between the battery cell and the side wall of the housing abutting the heat exchange element 200 is 0.5 mm to 5 mm. It is understood that during operation, heat from the battery cell is removed by the heat exchange element 200 through the housing. Excessive or insufficient distance between the battery cell and the side wall of the housing abutting the heat exchange element 200 will affect the heat dissipation efficiency of the heat exchange element 200. Controlling the distance between the battery cell and the side wall of the housing abutting the heat exchange element 200 to between 0.5 mm and 5 mm can meet the heat exchange requirements of the single battery cell 100, avoid excessive temperature rise within the battery pack, and reduce the probability of thermal runaway of the battery pack. Optionally, the distance between the battery cell and the shell and the side wall of the heat exchanger 200 can be 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm, 1mm, 1.1mm, 1.2mm, 1.3mm, 1.4mm, 1.5mm, 1.6mm, 1.7mm, 1.8mm, 1.9mm, 2mm, 2.1mm, 2.2mm, 2.3mm, 2.4mm, 2.5mm, 2.6mm, 2.7mm, 2.8mm, 2.9mm, 3mm, 3.1mm, 3.2mm, 3.3mm, 3.4mm, 3.5mm, 3.6mm, 3.7mm, 3.8mm, 3.9mm, 4mm, 4.1mm, 4.2mm, 4.3mm, 4.4mm, 4.5mm, 4.6mm, 4.7mm, 4.8mm, 4.9mm, or 5mm. Of course, it can also be other values ​​within the range of 0.5mm-5mm, and is not limited to the above examples.

[0031] In some embodiments, the single cell 100 has a pole 110 and an explosion-proof valve, which are arranged on the same side wall of the single cell 100. The heat exchange element 200 is stopped on the side wall of the single cell 100 where the pole 110 and the explosion-proof valve are arranged, and a, R0 and R1 satisfy the relationship: 0.03≤|R1-R0| / a≤0.076. It is understandable that, in actual operation, the temperature of the side wall of the single cell 100 where the pole 110 and the explosion-proof valve are provided is relatively higher than that of the other side walls. Therefore, if the heat exchange component 200 is stopped against this side wall, a relatively large heat exchange area is required. When the absolute value of the difference between R1 and R0 is fixed, determining the ratio a of the heat exchange area of ​​the heat exchange component 200 and the single cell 100 to the surface area of ​​the single cell 100 within the range of 0.03-0.076 can better meet the heat exchange requirements of the single cell 100, avoid excessive temperature rise inside the battery pack, and reduce the probability of thermal runaway of the battery pack.

[0032] In some embodiments, the heat exchange element 200 has a flow channel for circulating coolant, with the cross-sectional area of ​​the flow channel being S1 and the cross-sectional area of ​​the heat exchange element 200 being S0. S1 and S0 satisfy the relationship: 0.4 ≤ S1 / S0 ≤ 0.9. It is understood that, in actual operation, the greater the ratio of the cross-sectional area S1 of the flow channel to the cross-sectional area S0 of the heat exchange element 200, the greater the volume of the flow channel in the heat exchange element 200, the more cooling medium circulates in the same amount of time, and the better the heat exchange effect of the heat exchange element 200 on the battery cells 100. A ratio of the cross-sectional area S1 of the flow channel to the cross-sectional area S0 of the heat exchange element 200 that is too large can result in the wall thickness of the heat exchange element 200 being too small, which can easily cause deformation. In this embodiment, the ratio of the cross-sectional area of ​​the flow channel (S1) to the cross-sectional area of ​​the heat exchange element 200 (S0) is controlled between 0.4 and 0.9. This ensures the heat exchange effect of the heat exchange element 200 on the single cells 100 while reducing the probability of deformation of the heat exchange element 200, thereby extending the service life of the battery pack. Optionally, the S1 / S0 ratio can be 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9. Other values ​​within the range of 0.4-0.9 are also possible and are not limited to the above examples.

[0033] In some embodiments, an insulating layer is provided on the surface of the heat exchange element 200, and a, R0, and R1 satisfy the relationship: 0.025≤|R1-R0| / a≤0.076. It is understood that providing an insulating layer on the surface of the heat exchange element 200 can significantly reduce the probability of a short circuit between two adjacent single cells 100. However, the presence of the insulating layer will affect the heat exchange performance of the heat exchange element 200. When the absolute value of the difference between R1 and R0 is fixed, the ratio a of the heat exchange area between the single cell 100 and the heat exchange element 200 to the surface area of ​​the single cell 100 can be readjusted based on whether or not an insulating layer is provided. This can better meet the heat exchange requirements of the single cell 100, prevent excessive temperature rise within the battery pack, and reduce the probability of thermal runaway. It can also significantly reduce the probability of a short circuit between two adjacent single cells 100.

[0034] In some specific embodiments, the thickness of the insulating layer ranges from 0.3 mm to 2 mm, and a, R0, and R1 satisfy the relationship: Z3 ≤ |R1-R0| / a ≤ Z4. It is understood that if the insulating layer is too thick, the insulation effect is better, but the heat exchange effect of the heat exchange element 200 is relatively significantly affected. If the insulating layer is too thin, the insulation effect is relatively poor, but the heat exchange effect of the heat exchange element 200 is less affected. In this embodiment, the insulating layer thickness is controlled within the range of 0.3 mm to 2 mm. On the one hand, it can better meet the heat exchange requirements of the single cell 100, avoid excessive temperature rise within the battery pack, and reduce the probability of thermal runaway of the battery pack. On the other hand, it can also greatly reduce the probability of short circuits between two adjacent single cells 100. Optionally, the thickness of the insulating layer may be 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm, 1.6 mm, 1.7 mm, 1.8 mm, 1.9 mm, or 2 mm. Of course, other values ​​within the range of 0.3 mm to 2 mm are also possible, and are not limited to the above examples.

[0035] The relationship between the temperature rise of the battery pack according to the embodiment of the present invention and the temperature rise of the battery pack according to the comparative example will be described below with reference to a data table.

[0036] The internal resistance of the single cell 100 is tested by discharging the single cell 100 at 0.33C to 0% SOC, then charging it at 0.33C to 100% SOC, obtaining a charging curve. During this period, the temperature of the single cell 100 is controlled at 25±1°C. The voltage U0 and the current I0 when charging to 40% SOC are obtained and recorded from the charging curve; the voltage U1 and the current I1 when charging to 80% SOC are obtained and recorded. According to the resistance formula R=U / I, the resistance at 40% SOC is calculated to be R0, and the resistance at 80% SOC is calculated to be R1.

[0037] RO R1 R1-RO a(％) R1-RO / a Temperature (℃) Cycle life (cycles) Example 1 0.35 0.62 0.27 23.17 0.0117 28.4 1042 Example 2 0.58 2.44 1.86 37.73 0.0493 39.2 1173 Example 3 0.85 1.98 1.13 27.16 0.0416 36.2 1158 Example 4 1.04 1.16 0.12 8.03 0.0149 29.1 1054 Example 5 1.21 2.05 0.84 21.31 0.0394 35.7 1161 Example 6 1.46 1.86 0.4 14.26 0.0281 31.2 1176 Example 7 1.58 2.23 0.65 18.91 0.0344 33.5 1182 Example 8 1.41 2.86 1.45 24.38 0.0595 42.5 1135 Example 9 0.56 1.83 1.27 30.26 0.0420 36.8 1192 Example 10 0.73 1.75 1.02 16.56 0.0616 47.6 1114 Example 11 1.03 2.65 1.62 31.34 0.0517 42.2 1125 Example 12 0.62 2.86 2.24 29.51 0.0759 54.2 1084 Example 13 0.61 2.63 2.02 39.23 0.0515 43.1 1124 Example 14 1.84 4.03 2.19 37.42 0.0585 45.4 1118 Example 15 0.35 2.85 2.5 47.64 0.0525 44.3 1128 Comparative Example 1 1.26 2.63 1.37 15.03 0.0912 58.9 1002 Comparative Example 2 0.85 1.12 0.27 28.83 0.0094 29.4 975 Comparative Example 3 1.73 4.42 2.69 31.52 0.0853 57.3 993 Comparative Example 4 2.91 3.02 0.11 39.25 0.0028 28.3 946

[0038] Table 1

[0039] The heat dissipation performance test method for the group of single cells 100 in Table 1 is as follows: 10 single cells 100 are taken from each group, and a heat exchanger 200 is placed on the surface of each cell 100 and bonded to the surface of the cell housing 100 using thermally conductive adhesive. The relationship between the ratio a of the contact area between the heat exchanger 200 and the single cell 100 to the surface area of ​​the cell housing 100 and the change in the internal resistance |R1-R0| of the single cell 100 is shown in Table 1. The single cells 100 are discharged at 0.33C to 0% SOC at 25°C, allowed to stand for 20 minutes, and then charged at 2C to 100% SOC. The temperature at this point is measured as t1. After 10 measurements, the average value is taken. The specific results are shown in Table 1. If the temperature is greater than or equal to 60°C, it is unqualified; if the temperature is less than 60°C, it is qualified.

[0040] The cycle life test method for the group of single cells 100 in Table 1 is as follows: For each embodiment and comparative example, 10 single cells 100 are taken, and a heat exchanger 200 is set on the surface of the single cell 100 and bonded to the shell surface of the single cell 100 using thermal adhesive. The relationship between the ratio a of the contact area between the heat exchanger 200 and the single cell 100 to the shell surface area of ​​the single cell 100 and the internal resistance change |R1-R0| of the single cell 100 is shown in the following table. Other than this, all other conditions are the same; the single cell 100 is discharged at 0.33C at 45°C to 0% SoC, and the static After standing for 20 minutes, charge to 100% SOC at 1C, stand for 10 minutes, and then discharge to 0% SOC at 1C. Record the capacity at this time as C1. Stand for 10 minutes. Charge the single battery 100 to 100% SOC at 1C at 45°C, stand for 10 minutes, and then discharge to 0% SOC at 1C. Stand for 10 minutes. If the discharge capacity of the cycle value is less than 0.8 times of C1, record the number of cycles at this time. Measure 10 times and take the average value. If the number of cycles is less than 1000, it is unqualified. If it is greater than 1000, it is qualified. See Table 1 for the specific structure.

[0041] From the comparison of the experimental data of Examples 1-15 and Comparative Examples 1-4, it can be found that when the relationship between |R1-R0| and a is within an appropriate range, the temperature rise of the single cell 100 during the charging process is small, and the charge and discharge cycle life is good. In Comparative Example 1, the ratio of |R1-R0| to a is too large. Although the charge and discharge cycle life of the single cell 100 is good, the temperature rise is too high. In Comparative Example 2, the ratio of |R1-R0| to a is large, the charge and discharge cycle life of the single cell 100 is poor, and the temperature rise is too high. In Comparative Examples 3 and 4, the ratio of |R1-R0| to a is small. Although the temperature rise of the single cell 100 during the charging process is small, the charge and discharge cycle life of the single cell 100 is poor.

[0042] Throughout this specification, references to "some embodiments," "other embodiments," and the like indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0043] Obviously, the above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention and are not intended to limit the embodiments of the present invention. A person skilled in the art would be able to make various obvious changes, readjustments, and substitutions without departing from the scope of protection of the present invention. It is not necessary and impossible to enumerate all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. A battery pack, characterized in that: The invention comprises a plurality of single cells (100) and a heat exchange element (200), wherein the ratio of the heat exchange area of ​​the heat exchange element (200) and the single cells (100) to the surface area of ​​the single cells (100) is a, and under the condition of a temperature of 25°C, when the state of charge of the single cells (100) is 40%, the DC internal resistance is R0, and when the state of charge of the single cells (100) is 80%, the DC internal resistance is R1, and a, R0 and R1 satisfy the relationship: 0.0117≤|R1-R0| / a≤0.

076.

2. The battery pack according to claim 1, wherein: A plurality of the single cells (100) are stacked along a preset direction, at least a portion of the heat exchange element (200) is located between two adjacent single cells (100), and a, R0, and R1 satisfy the relationship: 0.02≤|R1-R0| / a≤0.

076.

3. The battery pack according to claim 2, wherein: The single cell (100) has two first side walls, two second side walls, and two third side walls, the area of ​​the first side wall is greater than the areas of the second side wall and the third side wall, the heat exchange element (200) is located between the two first side walls, and a, R0, and R1 satisfy the relationship: 0.025≤|R1-R0| / a≤0.

076.

4. The battery pack according to claim 2, wherein: The heat exchange component (200) comprises a first heat exchange portion (210) and a second heat exchange portion (220), wherein the first heat exchange portion (210) is sandwiched between two adjacent single batteries (100), and along a direction perpendicular to the preset direction, the second heat exchange portion (220) is arranged on one side of the plurality of single batteries (100).

5. The battery pack according to claim 1, wherein: The single cell (100) comprises a pole (110), the pole (110) and the heat exchange element (200) are arranged on two opposite side walls of the single cell (100), and a, R0 and R1 satisfy the relationship: 0.028≤|R1-R0| / a≤0.

076.

6. The battery pack according to claim 1, wherein: The single battery (100) comprises a shell and a battery core arranged in the shell, the heat exchange element (200) abuts against a side wall of the shell, and the distance between the battery core and the shell abutting against the side wall of the heat exchange element (200) is 0.5 mm to 5 mm.

7. The battery pack according to claim 1, wherein: The single cell (100) comprises a pole (110) and an explosion-proof valve, the pole (110) and the explosion-proof valve being arranged on the same side wall of the single cell (100), the heat exchange element (200) abuts against the side wall of the single cell (100) where the pole (110) and the explosion-proof valve are arranged, and a, R0, and R1 satisfy the relationship: 0.03≤|R1-R0| / a≤0.

076.

8. The battery pack according to claim 1, wherein: The heat exchange element (200) has a flow channel for circulating cooling liquid, the cross-sectional area of ​​the flow channel is S1, the cross-sectional area of ​​the heat exchange element (200) is S0, and S1 and S0 satisfy the relationship: 0.4≤S1 / S0≤0.

9.

9. The battery pack according to claim 1, wherein: The surface of the heat exchange element (200) is provided with an insulating layer, and a, R0 and R1 satisfy the relationship: 0.025≤|R1-R0| / a≤0.

076.

10. The battery pack according to claim 9, wherein: The thickness of the insulating layer ranges from 0.3 mm to 2.0 mm.

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