Battery pack

Abstract

The invention discloses a battery pack, and belongs to the technical field of batteries. According to the battery pack disclosed by the invention, when c / d-2. 8 is greater than or equal to 0.2 and less than or equal to 9, and / or l / d-6. 4 is greater than or equal to 0.3 and less than or equal to 13, the value range of the thickness of the heat insulation pad is 0.2 mm-6 mm, so that the heat insulation pad can block heat transfer between the two battery monomers, and the risk of thermal runaway of the other battery monomer after thermal runaway of one battery monomer in the two battery monomers is reduced; the thermal safety performance of the battery pack is improved, the setting form of the thermal insulation pad can be quickly determined when the battery packs of different models are developed, the research and development efficiency can be improved, and the cost can be reduced; meanwhile, the situation that heat transfer between every two adjacent single batteries cannot be effectively blocked due to the fact that the thickness of the heat insulation pad is too small can be avoided, and the situation that the heat insulation pad is prone to deformation due to the fact that the single batteries are prone to squeezing the adjacent heat insulation pad in the charging and discharging use process due to the fact that the thickness of the heat insulation pad is too large can be avoided; and the deformation quantity of the battery shell is too large.

Description

Technical Field

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

[0002] Lithium iron phosphate battery is a new type of lithium-ion battery widely used in fields such as electric vehicles and energy storage systems. Lithium iron phosphate battery has the characteristics of low capacity, good thermal stability, more stable chemical structure and not easy to decompose. During the charging process, it has a smaller expansion rate and lower heat generation, so it has higher thermal safety performance and is not easy to have thermal runaway.

[0003] In the prior art, heat insulation pads are usually arranged between any two adjacent battery cells of lithium iron phosphate batteries to prevent heat transfer between adjacent battery cells through the heat insulation pads and improve the thermal safety performance of lithium iron phosphate batteries. In order to meet different needs of customers, there are various models of lithium iron phosphate batteries, and the lengths, widths and heights of the battery cells of different models of lithium iron phosphate batteries are different. It is difficult to match suitable heat insulation pads for different models of lithium iron phosphate batteries, which can not only ensure the heat insulation performance but also will not occupy too much space inside the battery case, which is not conducive to the rapid research and development of different models of lithium iron phosphate batteries. Summary of the Invention

[0004] The purpose of the present invention is to provide a battery pack, which can meet the heat insulation requirements of the battery pack, ensure the thermal safety performance of the battery pack, and facilitate the development of different models of batteries.

[0005] To achieve the above object, the following technical solutions are provided:

[0006] A battery pack, the battery pack includes a plurality of battery cells stacked along a first direction, and a heat insulation pad arranged between two of the battery cells; the positive electrode material of the battery cell is lithium iron phosphate; the thickness of the battery cell along the first direction is d; the width of the battery cell along a second direction is l; the capacity of the battery cell is c; the first direction is perpendicular to the large surface of the battery cell, and the first direction is perpendicular to the second direction;

[0007] When 0.2 ≤ c / d - 2.8 ≤ 9, and / or 0.3 ≤ l / d - 6.4 ≤ 13, the value range of the thickness of the heat insulation pad is 0.2 mm to 6 mm.

[0008] Compared with the prior art, the beneficial effects of the present invention:

[0009] For the battery pack of the present invention, by defining that when 0.2 ≤ c / d - 2.8 ≤ 9 and / or 0.3 ≤ l / d - 6.4 ≤ 13, the thickness of the heat insulation pad ranges from 0.2 mm to 6 mm, the heat insulation pad can block the heat transfer between two battery cells, thereby reducing the risk of thermal runaway of one battery cell causing thermal runaway of another battery cell, improving the thermal safety performance of the battery pack, and facilitating the rapid determination of the setting form of the heat insulation pad when developing different models of battery packs, which is beneficial to improving the R & D efficiency and reducing the cost.

[0010] When 0.2 ≤ c / d - 2.8 ≤ 9 and / or 0.3 ≤ l / d - 6.4 ≤ 13, making the thickness of the heat insulation pad range from 0.2 mm to 6 mm can effectively prevent the heat transfer between two adjacent battery cells. It can not only avoid the thickness of the heat insulation pad being too small to effectively block the heat transfer between two adjacent battery cells, but also avoid the thickness of the heat insulation pad being too large, which may cause the battery cell to easily squeeze the adjacent heat insulation pad during the charge and discharge process, resulting in the deformation of the heat insulation pad and further causing excessive deformation of the battery housing.

[0011] The battery pack of the present invention can not only avoid the heat insulation pad occupying too much space inside the battery pack, thereby reducing the energy density of the battery pack, but also avoid the heat insulation pad being unable to effectively isolate the heat transfer between battery cells, resulting in potential safety hazards in the battery pack. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a schematic structural diagram of the battery pack in an embodiment of the present invention;

[0013] Figure 2 is a schematic structural diagram of a battery cell and the adjacent heat insulation pad in an embodiment of the present invention;

[0014] Figure 3 is a schematic structural diagram of the heat insulation pad and two adjacent battery cells in an embodiment of the present invention.

[0015] Reference Numerals:

[0016] 1, battery cell; 11, large surface; 2, heat insulation pad; 21, first end; 22, second end; 23, connecting portion; 3, explosion-proof valve. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Usually, the components of the embodiments of the present invention described and illustrated herein can be arranged and designed in various different configurations.

[0018] Accordingly, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0019] It should be noted that like reference numerals and letters denote like items in the following figures, and thus, once an item is defined in one figure, it is not necessary to further define and explain it in subsequent figures.

[0020] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the inventive product is customarily placed during use. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation of the present invention. In addition, the terms "first", "second", "third", etc. are only used for descriptive distinction and should not be construed as indicating or implying relative importance. In the description of the present invention, unless otherwise specified, the meaning of "a plurality" is two or more.

[0021] In the description of the present invention, it should also be noted that unless otherwise clearly defined and limited, the terms "arranged" and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0022] In the present invention, unless otherwise clearly defined and limited, the first feature being "above" or "below" the second feature may include direct contact between the first and second features, or may include the first and second features not being in direct contact but being in contact through additional features therebetween. Moreover, the first feature being "above", "over" and "on" the second feature includes the first feature being directly above and obliquely above the second feature, or merely indicating that the first feature has a higher horizontal height than the second feature. The first feature being "below", "beneath" and "under" the second feature includes the first feature being directly below and obliquely below the second feature, or merely indicating that the first feature has a lower horizontal height than the second feature.

[0023] Embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are only used to explain the present invention and should not be construed as limiting the present invention.

[0024] As Figures 1 - 3 shown, this embodiment provides a battery pack, which includes a plurality of battery cells 1 stacked along a first direction, and a heat insulation pad 2 disposed between two battery cells 1; the first direction is perpendicular to the large surface 11 of the battery cell 1. It should be noted that the battery cell 1 includes a plurality of outer surfaces, and the large surface 11 of the battery cell 1 is the outer surface with the largest area among the plurality of outer surfaces of the battery cell 1.

[0025] Specifically, the battery cell 1 includes an electric core and a housing, and the electric core is placed inside the housing to be isolated from the outside world. The electric core is the basic unit for storing and releasing electric energy, which is usually composed of a positive electrode, a negative electrode, an electrolyte and a separator, and realizes the storage and release of electric energy through chemical reactions. In this embodiment, the positive electrode material of the battery cell 1 is lithium iron phosphate. The heat insulation pad 2 is used to block the heat transfer between two battery cells 1, and the material of the heat insulation pad 2 is generally aerogel, ceramicized foam, silicone foam, ceramicized silicone rubber, or PO foam, etc.

[0026] In this embodiment, the thickness of the battery cell 1 along the first direction is d; the width of the battery cell 1 along the second direction is l; the first direction is perpendicular to the second direction; the capacity of the battery cell 1 is c; when 0.2 ≤ c / d - 2.8 ≤ 9, and / or 0.3 ≤ l / d - 6.4 ≤ 13, the value range of the thickness of the heat insulation pad 2 is 0.2 mm to 6 mm.

[0027] Optionally, the thickness of the heat insulation pad 2 can be 0.2 mm, 0.3 mm, 0.4 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, 5.5 mm or 6 mm.

[0028] It should be noted that when the value of c / d - 2.8 and / or the value of l / d - 6.4 are relatively small, it indicates that the energy density of the battery cell 1 is relatively low, and the risk that one battery cell 1 has a thermal runaway and spreads to other battery cells 1 is relatively low. At this time, if a heat insulation pad 2 is provided between two battery cells 1, it will cause the heat insulation pad 2 to occupy too much space inside the battery pack, thereby reducing the energy density of the battery pack. When the value of c / d - 2.8 and / or the value of l / d - 6.4 are relatively large, it indicates that the energy density of the battery cell 1 is relatively high. Setting a heat insulation pad 2 between two battery cells 1 cannot effectively isolate the heat transfer between the battery cells 1, and there are potential safety hazards in the battery pack.

[0029] For the battery pack of this embodiment, by defining that when 0.2 ≤ c / d - 2.8 ≤ 9 and / or 0.3 ≤ l / d - 6.4 ≤ 13, the thickness of the heat insulation pad 2 ranges from 0.2 mm to 6 mm, the heat insulation pad 2 can block the heat transfer between the two battery cells 1, thereby reducing the risk that one battery cell 1 causes the other battery cell 1 to thermally runaway after thermal runaway of one of the two battery cells 1, improving the thermal safety performance of the battery pack, and facilitating quickly determining the setting form of the heat insulation pad 2 when developing different models of battery packs, which is beneficial to improving the R & D efficiency and reducing the cost.

[0030] That is to say, the battery pack of this embodiment can not only avoid the heat insulation pad 2 occupying too much space inside the battery pack, thereby reducing the energy density of the battery pack, but also avoid the heat insulation pad 2 being unable to effectively isolate the heat transfer between the battery cells 1, resulting in potential safety hazards in the battery pack.

[0031] When 0.2 ≤ c / d - 2.8 ≤ 9 and / or 0.3 ≤ l / d - 6.4 ≤ 13, making the thickness of the heat insulation pad 2 range from 0.2 mm to 6 mm can effectively prevent the heat transfer between two adjacent battery cells 1. It can not only avoid the thickness of the heat insulation pad 2 being too small to effectively block the heat transfer between two adjacent battery cells 1, but also avoid the thickness of the heat insulation pad 2 being too large, which makes the battery cell 1 easily squeeze the adjacent heat insulation pad 2 during the charge and discharge process, resulting in the heat insulation pad 2 being easily deformed and further resulting in too large a deformation amount of the battery case.

[0032] It should be noted that when evaluating the energy density of the battery cell 1 by c / d - 2.8 and l / d - 6.4, for the convenience of description, the two battery cells 1 are respectively denoted as battery cell one and battery cell two. When c / d - 2.8 of battery cell one is equal to l / d - 6.4 of battery cell two, the unit thickness capacity of battery cell one is greater than that of battery cell two. The battery has a larger unit thickness capacity and more heat during thermal runaway. Therefore, in this embodiment, the upper limit value of c / d - 2.8 is defined to be less than the upper limit value of l / d - 6.4, and the lower limit value of c / d - 2.8 is less than the lower limit value of l / d - 6.4.

[0033] Optionally, the width l of the battery cell 1 in the second direction ranges from 100 mm to 400 mm. If the value range of l is too small, it means that the size of the battery cell 1 is small and the energy density is low, making it difficult to meet the user's needs; if the value range of l is too large, it means that the size of the battery cell 1 is large and the energy density is high. Even if a heat insulation pad 2 is provided between two battery cells 1, it is impossible to effectively isolate the heat transfer between the battery cells 1, and there are safety hazards in the battery pack. By limiting the value range of l to 100 mm to 400 mm, it is possible to balance the energy density of the battery pack to meet the user's needs and ensure the thermal safety performance of the battery pack.

[0034] Optionally, the width l of the battery cell 1 in the second direction can be 100 mm, 150 mm, 200 mm, 250 mm, 300 mm, 350 mm or 400 mm.

[0035] Optionally, the thickness d of the battery cell 1 in the first direction ranges from 10 mm to 80 mm. If the value range of d is too small, it means that the size of the battery cell 1 is small and the energy density is low, making it difficult to meet the user's needs; if the value range of d is too large, it means that the size of the battery cell 1 is large and the energy density is high. Even if a heat insulation pad 2 is provided between two battery cells 1, it is impossible to effectively isolate the heat transfer between the battery cells 1, and there are safety hazards in the battery pack. By limiting the value range of d to 10 mm to 80 mm, it is possible to balance the energy density of the battery pack to meet the user's needs and ensure the thermal safety performance of the battery pack.

[0036] Optionally, the thickness d of the battery cell 1 in the first direction can be 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, 35 mm, 40 mm, 45 mm, 50 mm, 55 mm, 60 mm, 65 mm, 70 mm, 75 mm or 80 mm.

[0037] Optionally, the capacity c of the battery cell 1 ranges from 30 Ah to 380 Ah. If the value range of c is too small, it means that the energy density of the battery cell 1 is low and it is difficult to meet the user's needs; if the value range of c is too large, it means that the energy density of the battery cell 1 is high. Even if a heat insulation pad 2 is provided between two battery cells 1, it is impossible to effectively isolate the heat transfer between the battery cells 1, and there are safety hazards in the battery pack. By limiting the value range of c to 30 Ah to 380 Ah, it is possible to balance the energy density of the battery pack to meet the user's needs and ensure the thermal safety performance of the battery pack.

[0038] Optionally, the capacity c of the battery cell 1 can be 30 Ah, 40 Ah, 50 Ah, 100 Ah, 150 Ah, 200 Ah, 250 Ah, 300 Ah, 350 Ah or 380 Ah.

[0039] Optionally, a plurality of heat insulation pads 2 are provided between two adjacent battery cells 1, thereby improving the heat insulation performance between two adjacent battery cells 1 and enhancing the thermal safety performance of the battery pack.

[0040] Optionally, a heat insulation pad 2 is provided between any two adjacent battery cells 1, and at least two heat insulation pads 2 have different thicknesses. By increasing the thickness of the heat insulation pad 2, the heat insulation effect of the heat insulation pad 2 can be improved. For the convenience of description, the heat insulation pad 2 with a larger thickness is denoted as the thickened heat insulation pad. When a thermal runaway occurs in the battery cell 1 on one side of the thickened heat insulation pad, the risk of the thermal runaway spreading to the battery cell 1 on the other side of the thickened heat insulation pad can be reduced through the thickened heat insulation pad.

[0041] Optionally, the plurality of battery cells 1 include a first battery cell, a second battery cell, and a third battery cell arranged in sequence along a first direction. Along the first direction, the distance between the first battery cell and the second battery cell is greater than the distance between the second battery cell and the third battery cell; there are a plurality of heat insulation pads 2, and the plurality of heat insulation pads 2 include a first heat insulation pad provided between the first battery cell and the second battery cell, and a second heat insulation pad provided between the second battery cell and the third battery cell. The thickness of the first heat insulation pad is less than the thickness of the second heat insulation pad. By making the distance between the first battery cell and the second battery cell greater than the distance between the second battery cell and the third battery cell, the heat transfer between the first battery cell and the second battery cell can be made less than the heat transfer between the second battery cell and the third battery cell. At this time, the thickness of the first heat insulation pad can be made less than the thickness of the second heat insulation pad to reduce the internal space of the battery pack occupied by the heat insulation pad 2, which is beneficial to improving the energy density of the battery pack.

[0042] Optionally, the plurality of battery cells 1 are divided into a plurality of battery cell groups, and each battery cell group includes at least two battery cells 1; there are a plurality of heat insulation pads 2, and the plurality of heat insulation pads 2 include a first heat insulation pad provided between two adjacent battery cell groups, thereby blocking the heat transfer between two adjacent battery cell groups through the first heat insulation pad, reducing the risk of one battery cell group causing thermal runaway of another battery cell group after thermal runaway, and being beneficial to improving the thermal safety performance of the battery pack.

[0043] Specifically, as Figure 1 shown, each battery cell group includes three battery cells 1, a first heat insulation pad is provided between two adjacent battery cell groups, and no second heat insulation pad is provided between two adjacent battery cells 1 within the same battery cell group, thereby not only improving the thermal safety performance of the battery pack to a certain extent, but also being beneficial to reducing the internal space of the battery pack occupied by the heat insulation pad 2 and improving the energy density of the battery pack.

[0044] Optionally, the plurality of heat insulation pads 2 includes a second heat insulation pad disposed between two adjacent battery cells 1 of the same battery cell group, thereby blocking the heat transfer between the two adjacent battery cells 1 through the second heat insulation pad, reducing the risk of thermal runaway of another battery cell 1 caused by thermal runaway of one battery cell 1, and being conducive to improving the thermal safety performance of the battery cell group.

[0045] Optionally, the thickness of the first heat insulation pad is not less than that of the second heat insulation pad. Thus, when thermal runaway occurs in one battery cell 1, the heat generated by the thermal runaway is transferred as much as possible within the battery cell group where the battery cell 1 is located, without affecting another battery cell group, so as to further improve the thermal safety performance of the battery pack.

[0046] Optionally, the thermal conductivity of the heat insulation pad 2 ranges from 0.01 W / (m·K) to 0.2 W / (m·K). Thus, on the premise of ensuring the heat insulation reliability of the heat insulation pad 2, the thickness or the number of settings of the heat insulation pad 2 can be reduced, which is conducive to reducing the internal space occupied by the heat insulation pad 2 in the battery pack and improving the energy density of the battery pack.

[0047] Optionally, the thermal conductivity of the first heat insulation pad is not greater than that of the second heat insulation pad. Thus, the heat insulation performance of the first heat insulation pad is better than that of the second heat insulation pad. When thermal runaway occurs in one battery cell 1, the heat generated by the thermal runaway is transferred as much as possible within the battery cell group where the battery cell 1 is located, without affecting another battery cell group, so as to further improve the thermal safety performance of the battery pack.

[0048] Optionally, the area of the large surface 11 of the battery cell 1 is S1; the projected area of the heat insulation pad 2 on the large surface 11 of the battery cell 1 is S2; the value range of S2 / S1 is 0.5 to 1.2; the value range of the thickness of the heat insulation pad 2 is 0.2 mm to 4 mm. When the value range of S2 / S1 is 0.5 to 1.2, the insulation performance between two adjacent battery cells 1 can be improved, and the heat transfer between the two battery cells 1 during thermal runaway can be reduced. At this time, the thickness of the heat insulation pad 2 can be appropriately reduced to improve the energy density of the battery pack.

[0049] Optionally, as Figure 3As shown in the figure, an explosion-proof valve 3 is provided on one side of the battery cell 1 along the third direction; the first direction, the second direction and the third direction are perpendicular to each other in pairs; the heat insulation pad 2 includes a first end 21 and a second end 22 arranged opposite to each other along the third direction. The first end 21 is arranged between two battery cells 1, and the second end 22 protrudes from the surface of the side of the battery cell 1 where the explosion-proof valve 3 is located; the thickness of the heat insulation pad 2 ranges from 0.2 mm to 4 mm. When the second end 22 of the heat insulation pad 2 protrudes from the surface of the side of the battery cell 1 where the explosion-proof valve 3 is located, when a battery cell 1 adjacent to the heat insulation pad 2 is out of control thermally, the second end 22 of the heat insulation pad 2 can block the spread of the hot substances ejected by the explosion-proof valve 3 to other battery cells 1. At this time, in order to ensure the overall energy density of the battery pack, the thickness of the heat insulation pad 2 can be reduced.

[0050] Optionally, connection parts 23 are provided on both sides of the second end 22 of the heat insulation pad 2 along the first direction. The connection parts 23 are connected to the surface of the side of the explosion-proof valve 3 of the battery cell 1 on the same side as the heat insulation pad 2, which is convenient for fixing the heat insulation pad 2 and can avoid problems such as bending and deformation of the protruding second end 22 of the heat insulation pad 2, thereby affecting the blocking effect on the hot substances ejected by the explosion-proof valve 3.

[0051] Exemplarily, the connection part 23 is a hem. In other words, hems are provided on both sides of the second end 22 of the heat insulation pad 2 along the first direction. The hems are overlapped and fixed to the surface of the side of the explosion-proof valve 3 of the battery cell 1, improving the convenience of fixing the heat insulation pad 2.

[0052] Optionally, the battery cell 1 further includes a terminal post. The explosion-proof valve 3 and the terminal post are both located on the same side of the battery cell 1; the thickness of the heat insulation pad 2 ranges from 2 mm to 6 mm. When the explosion-proof valve 3 and the terminal post are both located on the same side of the battery cell 1, the assembly efficiency of the battery pack can be improved. However, when the terminal post and the explosion-proof valve 3 are on the same side, the thermally out-of-control substances of one battery cell 1 will affect the terminal posts and the explosion-proof valve 3 of other batteries. At this time, the thickness of the heat insulation pad 2 needs to be increased to further improve the thermal safety performance.

[0053] In other embodiments, the explosion-proof valve 3 and the terminal post are respectively located on both sides of the battery cell 1; the thickness of the heat insulation pad 2 ranges from 2 mm to 5 mm. When the explosion-proof valve 3 and the terminal post are respectively located on both sides of the battery cell 1, the thermally out-of-control substances of one battery cell 1 will not affect the terminal posts of other batteries, improving the thermal safety performance of the battery pack. At this time, the thickness of the heat insulation pad 2 can be reduced to increase the energy density of the battery pack.

[0054] Next, the heat insulation performance test and the battery deformation test of the battery pack in this embodiment are carried out. The test steps and test results are as follows:

[0055] In the heat insulation performance test, the specifications of the two battery cells 1 of the same embodiment are the same; for the battery cells 1 of different embodiments, the capacity c, the thickness d in the first direction, and the width l in the second direction of the battery cell 1 are shown in the following table respectively. Except for this, the remaining parameters of the battery cells 1 of different embodiments are the same. Further, the two battery cells 1 of the same embodiment are stacked in a manner of large surface 11 against large surface 11, and a heat insulation pad 2 is placed between the two battery cells 1. The thickness of the heat insulation pad 2 between the two battery cells 1 of each embodiment is shown in the following table. Further, after one of the battery cells 1 in each embodiment is thermally out of control, the temperature of the other battery cell 1 is monitored. If the temperature is greater than or equal to 100 °C, it is unqualified; if the temperature is less than 100 °C, it is qualified.

[0056] In the battery deformation test, twenty battery cells 1 with the same specifications are taken for each embodiment, and the specifications of the battery cells 1 of the same embodiment are the same; for the battery cells 1 of different embodiments, the capacity c, the thickness d in the first direction, and the width l in the second direction of the battery cell 1 are shown in the following table respectively. Except for this, the remaining parameters of the battery cells 1 of different embodiments are the same. Further, in the same embodiment, the twenty battery cells 1 are stacked in a manner of large surface 11 against large surface 11, and a heat insulation pad 2 is placed between any two adjacent battery cells 1. The thickness of the heat insulation pad 2 between the two battery cells 1 of each embodiment is shown in the following table; then a total pressure of 5000 N is applied to the large surfaces 11 of the battery cells 1 at both ends, the output ends of the twenty battery cells 1 are welded with busbars, connected in series to form a battery pack, the battery pack is charged and discharged in cycles, discharged at 1C to 0% SOC, left standing for 5 min, then charged at 2C to 100% SOC, left standing for 5 min, then discharged at 1C to 0% SOC, left standing for 5 min, then charged at 2C to 100% SOC, left standing for 5 min,... After such cycling for two hundred circles, the battery cells 1 are disassembled, and the deformation of the large surface 11 of the battery cells 1 is observed. If the deformation amount is greater than 1 mm, it is unqualified; if it is less than or equal to 1 mm, it is qualified. It should be noted that the test method for the deformation amount of the large surface 11 of the battery cell 1 is the prior art and will not be elaborated here.

[0057]

[0058] In summary, from the experimental data of Embodiment 1 to Embodiment 24, it can be obtained that when 0.2 ≤ c / d - 2.8 ≤ 9, and / or 0.3 ≤ l / d - 6.4 ≤ 13, by setting a heat insulation pad 2 between the large surfaces 11 of two adjacent battery cells 1, and the value range of the thickness of the heat insulation pad 2 is 0.2 mm to 6 mm, the heat transfer between two adjacent battery cells 1 can be effectively blocked by the heat insulation pad 2, and the risk of thermal runaway spread can be reduced.

[0059] It can be concluded from Comparative Examples 2 to 4 that when c / d - 2.8 > 9 and / or l / d - 6.4 > 13, the setting of the heat insulation pad cannot effectively block the heat transfer between two adjacent battery cells, thus unable to effectively prevent thermal runaway. It can be concluded from Comparative Example 5 that when the thickness of the heat insulation pad is too small, it cannot effectively block the heat transfer between two adjacent battery cells, thus unable to effectively prevent thermal runaway. It can be concluded from Comparative Example 1 that when c / d - 2.8 < 0.2 and l / d - 6.4 < 0.3, the housing is prone to being crushed under overpressure and cannot return to the normal state, affecting the lifespan of the battery cell and the battery pack. It can be concluded from Example 6 that when the heat insulation pad is too thick, the constraint between the battery cells is insufficient, and the battery cells are prone to bulging and deformation.

[0060] Note that the above are only the preferred embodiments of the present invention and the applied technical principles. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein. Various obvious changes, re-adjustments, and substitutions can be made by those skilled in the art without departing from the protection scope of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments only. Without departing from the inventive concept of the present invention, it can also include more other equivalent embodiments, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A battery pack, characterized in that: The battery pack includes a plurality of battery cells stacked along a first direction, and a heat insulating pad disposed between two of the battery cells; the positive electrode material of the battery cell is lithium iron phosphate; the thickness of the battery cell along the first direction is d; the width of the battery cell along the second direction is l; the capacity of the battery cell is c; the first direction is perpendicular to the large surface of the battery cell, and the first direction is perpendicular to the second direction; When 0.2≤c / d-2.8≤9, and / or 0.3≤l / d-6.4≤13, the thickness of the thermal insulation pad ranges from 0.2mm to 6mm.

2. The battery pack according to claim 1, characterized in that: A plurality of the thermal insulation pads are arranged between two adjacent battery cells.

3. The battery pack according to claim 1, characterized in that: The thermal insulation pad is arranged between any two adjacent battery cells, and at least two of the thermal insulation pads have different thicknesses.

4. The battery pack according to claim 1, characterized in that: The area of ​​the large surface of the battery cell is S1; the projected area of ​​the thermal insulation pad on the large surface of the battery cell is S2; The value range of S2 / S1 is 0.5 to 1.2; the value range of the thickness of the thermal insulation pad is 0.2 mm to 4 mm.

5. The battery pack according to claim 1, characterized in that: An explosion-proof valve is provided on one side of the battery cell along the third direction; the first direction and the second direction are perpendicular to the third direction in pairs; The thermal insulation pad comprises a first end and a second end which are arranged opposite to each other along the third direction, wherein the first end is arranged between the two battery cells, and the second end protrudes from the surface of the battery cell on the side where the explosion-proof valve is located; The thickness of the thermal insulation pad ranges from 0.2 mm to 4 mm.

6. The battery pack according to claim 5, characterized in that: The second end of the thermal insulation pad is provided with connecting parts on both sides along the first direction, and the connecting parts are connected to the surface of the battery cell on the same side as the thermal insulation pad at the side where the explosion-proof valve is located.

7. The battery pack according to claim 1, characterized in that: The battery cell comprises an explosion-proof valve and a pole, and the explosion-proof valve and the pole are both located on the same side of the battery cell; The thickness of the thermal insulation pad ranges from 2 mm to 6 mm.

8. The battery pack according to claim 1, characterized in that: The battery cell comprises an explosion-proof valve and a pole, wherein the explosion-proof valve and the pole are respectively located on two sides of the battery cell; The thickness of the thermal insulation pad ranges from 2 mm to 5 mm.

9. The battery pack according to any one of claims 1 to 8, characterized in that: The thermal conductivity of the thermal insulation pad ranges from 0.01 W / (m·K) to 0.2 W / (m·K).

10. The battery pack according to any one of claims 1 to 8, characterized in that: The width l of the battery cell along the second direction ranges from 100 mm to 400 mm.

11. The battery pack according to any one of claims 1 to 8, characterized in that: The thickness d of the battery cell along the first direction ranges from 10 mm to 80 mm.

12. The battery pack according to any one of claims 1 to 8, characterized in that: The capacity c of the battery cell ranges from 30Ah to 380Ah.

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