CN219534725U

CN219534725U - Battery pack

Info

Publication number: CN219534725U
Application number: CN202320031503.XU
Authority: CN
Inventors: 齐紫玉; 郑娅敏; 廖思航; 董红伟; 王华文
Original assignee: Sunwoda Electric Vehicle Battery Co Ltd
Current assignee: Xinwangda Power Technology Co ltd
Priority date: 2023-01-06
Filing date: 2023-01-06
Publication date: 2023-08-15
Anticipated expiration: 2033-01-06

Abstract

The utility model discloses a battery pack, which comprises a first electric core group and a second electric core group, wherein the first electric core group comprises two first electric cores and at least one second electric core positioned between the two first electric cores, the second electric core group comprises two third electric cores and at least one fourth electric core positioned between the two third electric cores, the thermal stability of the first electric core group is higher than that of the second electric core group, and the thermal expansibility of the first electric core group is smaller than that of the second electric core group. According to the utility model, the battery packs with different thermal stabilities and different thermal expansions are introduced into the battery pack, the expansion and deformation of the first battery pack are small, the expansion of the whole battery pack in the working process can be reduced, the safety problems of ignition and thermal runaway caused by excessive expansion and mutual extrusion of the battery packs are avoided, the first battery pack is not easy to generate thermal runaway, and the thermal runaway area adjacent to the first battery pack in the battery pack can be blocked from spreading, so that the safety performance of the battery pack is improved.

Description

Battery pack

Technical Field

The utility model relates to the technical field of energy storage devices, in particular to a battery pack.

Background

The battery pack is a main energy storage device of the new energy automobile, in the related technology, batteries of different types are arranged in the battery pack to balance the performances of the battery pack in different aspects, and in order to meet the requirements of the new energy automobile on the endurance mileage, a large number of high-capacity batteries are usually arranged in the battery pack, so that the heat stability performance cannot be considered, the safety performance of the battery pack is reduced, and the thermal runaway is easy to occur.

Disclosure of Invention

The present utility model aims to solve at least one of the technical problems existing in the prior art. Therefore, the utility model provides the battery pack, which can improve the thermal stability and the safety performance of the battery pack.

The battery pack according to an embodiment of the present utility model includes:

the first battery cell group comprises two first battery cells and at least one second battery cell positioned between the two first battery cells, and the first battery cells and the second battery cells are battery cells of different chemical systems;

the second battery cell group comprises two third battery cells and at least one fourth battery cell positioned between the two third battery cells, and the third battery cells and the fourth battery cells are battery cells of different chemical systems;

the thermal stability of the first battery cell group is higher than that of the second battery cell group, and the thermal expansibility of the first battery cell group is smaller than that of the second battery cell group.

The battery pack according to the embodiment of the utility model has at least the following beneficial effects:

according to the utility model, the battery packs with different thermal stability and different thermal expansibility are introduced into the battery pack, the expansion and deformation of the first battery pack in the charging and discharging process of the battery pack are small, the expansion of the whole battery pack in the working process can be reduced, the situation that the battery packs are mutually extruded with other components in the battery pack or are mutually extruded with each other due to excessive expansion to cause leakage of the battery packs is avoided, so that the safety problems of ignition and thermal runaway are caused, the thermal stability of the first battery pack is high, the thermal runaway is not easy to occur, and the thermal runaway area adjacent to the first battery pack in the battery pack can be prevented from spreading to other positions, so that the safety performance of the battery pack is improved.

According to some embodiments of the utility model, the first battery cell group and the second battery cell group are arranged along at least one preset direction, and in the preset direction, the first battery cell group is arranged at the head end, or the first battery cell group is arranged at the tail end, or the first battery cell group is arranged at the head end and the tail end at the same time.

According to some embodiments of the utility model, the first cell group is disposed around the periphery of the second cell group;

or the second electric core group is arranged in an annular shape, and the first electric core group is arranged on the inner side and the outer side of the second electric core group;

or, in the arrangement direction of the first electric core group and the second electric core group, the first electric core group is arranged on two opposite sides of the second electric core group.

According to some embodiments of the utility model, the first cell has a thermal expansion that is less than a thermal expansion of the second cell, and the third cell has a thermal expansion that is less than a thermal expansion of the fourth cell.

According to some embodiments of the utility model, the first cell and the fourth cell are cells of the same chemical system, and the second cell and the third cell are cells of the same chemical system.

According to some embodiments of the utility model, the second cells have a larger capacity than the first cells, and the second cells have a larger number than the fourth cells.

According to some embodiments of the utility model, the battery pack further comprises at least one third cell group comprising at least one fifth cell, at least one of the first, second, third and fourth cells being a cell of a different chemical system than the fifth cell.

According to some embodiments of the utility model, the third cell group is located between the adjacent first cell and the second cell in the first cell group, or between two adjacent second cells;

or the third cell group is positioned between the adjacent third cell and the fourth cell in the second cell group or between the two adjacent fourth cells;

or the third cell group is positioned at the side part of the first cell group and is arranged adjacent to the first cell group;

or the third cell group is positioned at the side part of the second cell group and is arranged adjacent to the second cell group.

According to some embodiments of the utility model, the battery pack further comprises an electrical isolation plate, a first bus bar and a second bus bar, wherein adjacent first cells are connected with the second cells and two adjacent second cells through the first bus bar, adjacent third cells are connected with the fourth cells and two adjacent fourth cells through the second bus bar, the electrical isolation plate is located between the first bus bar and the first cell group, and between the second bus bar and the second cell group, and the electrical isolation plate is provided with a first limit structure limiting the first bus bar and a second limit structure limiting the second bus bar.

According to some embodiments of the utility model, the first and fourth cells are lithium iron phosphate cells, and the second and third cells are one of lithium nickel cobalt manganese oxide cells and lithium nickel cobalt aluminate cells.

Additional aspects and advantages of the utility model will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the utility model.

Drawings

The utility model is further described with reference to the accompanying drawings and examples, in which:

FIG. 1 is a schematic view of one embodiment of a battery pack of the present utility model;

FIG. 2 is a schematic layout diagram of an embodiment of a first cell set and a second cell set;

FIG. 3 is a schematic layout diagram of another embodiment of the first and second battery cell groups;

FIG. 4 is a schematic layout diagram of an embodiment of a third cell set;

FIG. 5 is a schematic diagram of an embodiment of an electrical isolator plate;

FIG. 6 is a cross-sectional view of FIG. 5;

fig. 7 is an enlarged view at a in fig. 6.

Reference numerals:

a first cell group 100, a first cell 110, a second cell 120; the second cell set 200, the third cell 210, the fourth cell 220, the case 300; a third cell set 400, a fifth cell 410; an electrical isolation board 500, a first limit structure 510, a second limit structure 520; a first bus 600; and a second bus bar 700.

Detailed Description

Embodiments of the present utility model are described in detail below, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to like or similar elements or elements having like or similar functions throughout. The embodiments described below by referring to the drawings are illustrative only and are not to be construed as limiting the utility model.

In the description of the present utility model, it should be understood that references to orientation descriptions such as upper, lower, front, rear, left, right, etc. are based on the orientation or positional relationship shown in the drawings, are merely for convenience of description of the present utility model and to simplify the description, and do not indicate or imply that the apparatus or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus should not be construed as limiting the present utility model.

In the description of the present utility model, the meaning of a number is one or more, the meaning of a number is two or more, and greater than, less than, exceeding, etc. are understood to exclude the present number, and the meaning of a number is understood to include the present number. The description of the first and second is for the purpose of distinguishing between technical features only and should not be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated or implicitly indicating the precedence of the technical features indicated.

In the description of the present utility model, unless explicitly defined otherwise, terms such as arrangement, installation, connection, etc. should be construed broadly and the specific meaning of the terms in the present utility model can be reasonably determined by a person skilled in the art in combination with the specific contents of the technical scheme.

In the description of the present utility model, the descriptions of the terms "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present utility model. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiments or examples. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

In order to overcome the defect that the safety performance of the battery pack is low and thermal runaway is easy to occur in the prior art, as shown in fig. 1, a first battery cell group 100 and a second battery cell group 200 are provided in the battery pack, the first battery cell group 100 includes two first battery cells 110 and at least one second battery cell 120 located between the two first battery cells 110, the first battery cell 110 and the second battery cell 120 are battery cells with different chemical systems, the second battery cell group 200 includes two third battery cells 210 and at least one fourth battery cell 220 located between the two third battery cells 210, and the third battery cell 210 and the fourth battery cell 220 are battery cells with different chemical systems, the first battery cell group 100 and the second battery cell group 200 are both provided with battery cells with different chemical systems, and the thermal stability of the first battery cell group 100 is higher than the thermal stability of the second battery cell group 200, and the thermal expansion of the first battery cell group 100 is smaller than the thermal expansion of the second battery cell group 200.

The chemical reaction in the charging and discharging process of the battery cell generates gas and heat, when the gas and the heat are excessive, the battery cell expands and deforms to break the explosion-proof valve, and after the electrolyte is sprayed out, the electrolyte and the anode material of the battery cell are high in temperature, and are easy to burn and fire, so that the battery pack is out of control. According to the utility model, the battery packs with different thermal stabilities and different thermal expansions are introduced into the battery pack, so that the thermal stability of the battery pack is improved, the expansion and deformation of the first battery pack 100 in the charge and discharge process of the battery pack are small, the expansion of the whole battery pack in the working process can be reduced, the situation that the battery packs are mutually extruded with other components in the battery pack or are mutually extruded with each other due to excessive expansion is avoided, the battery packs are prevented from leaking, the safety problems of ignition and thermal runaway are further caused, the thermal stability of the first battery pack 100 is high, the thermal runaway in the battery pack adjacent to the first battery pack 100 is prevented from spreading to other positions, and the safety performance of the battery pack is improved.

The thermal stability of the battery cell group can be detected by a thermogravimetric analysis method, a differential thermal analysis method or a differential scanning calorimetry method, and the thermal expansibility of the battery cell group can be calculated according to the volume ratio of the expansion amount of the battery cell group in unit time to the battery cell group. It should be noted that, in the embodiment of the present utility model, the first battery cell group 100 and the second battery cell group 200 are both provided with battery cells of different chemical systems, and the battery cells of different chemical systems have different energy densities, thermal stability, thermal expansibility and other performances, and by changing the types, the numbers, the arrangement positions and the like of the battery cells in the battery cell group, the battery cell group can have different chemical and physical performances; for example, providing a larger number of cells with low expansibility and high thermal stability in the first cell stack 100 can increase the thermal stability of the first cell stack 100 and decrease the thermal expansibility of the first cell stack 100.

As a specific embodiment for improving the thermal stability, the thermal stability of the first battery cell 110 in the first battery cell group 100 is higher than that of the second battery cell 120, for example, the first battery cell 110 may be a lithium iron phosphate battery cell, the second battery cell 120 may be a ternary battery cell, the first battery cell 110 is not easy to generate thermal runaway, and the first battery cell 110 can prevent thermal runaway from forming thermal runaway due to the arrangement of the first battery cell 110 at the end of the first battery cell group 100, so as to play a role in blocking fire, so that the first battery cell group 100 has better thermal stability, and after the first battery cell group 100 is applied to a battery pack, the first battery cell group 100 can block fire and thermal runaway, avoid expansion of a thermal runaway area in the battery pack, and improve the safety performance of the battery pack. As a specific embodiment for reducing the thermal expansion, the thermal expansion of the first cell 110 in the first cell group 100 is lower than that of the second cell 120, for example, the first cell 110 may be a lithium iron phosphate cell, the second cell 120 may be a ternary cell, the thermal expansion of the first cell 110 is lower, and since the first cell 110 is located at the end of the first cell group 100, the deformation of the first cell 110 towards the outside of the first cell group 100 is small, the overall expansion of the first cell group 100 may be reduced, so that the first cell group 100 has lower thermal expansion, and after the first cell group 100 is applied to a battery pack, the first cell group 100 may not excessively squeeze with other components in the battery pack due to the larger expansion, so as to avoid the situations of cell leakage and component deformation caused by extrusion, thereby improving the safety performance of the battery pack.

The battery pack further comprises a box 300, wherein the first battery cell set 100 and the second battery cell set 200 are both accommodated in the box 300, and the box 300 is used for accommodating and fixing the first battery cell set 100 and the second battery cell set 200 and protecting the first battery cell set 100 and the second battery cell set 200. The box 300 is further provided with electrical components such as a battery management system and a signal acquisition component, and is electrically connected with the first electric core set 100 and the second electric core set 200 through a bus bar, a wire harness and the like.

As a specific embodiment of the arrangement manner of the first battery cell group 100 and the second battery cell group 200, the first battery cell group 100 and the second battery cell group 200 are arranged along at least one preset direction, and in the preset direction, the first battery cell group 100 is arranged at the head end, or the first battery cell group 100 is arranged at the tail end, or the first battery cell group 100 is arranged at the head end and the tail end. Because the thermal stability of the first electric core group 100 is higher than that of the second electric core group 200, the first electric core group 100 is not easy to generate thermal runaway, and the thermal runaway area in the battery pack can be prevented from spreading to the outside, so that the thermal runaway range is reduced; in addition, since the thermal expansibility of the first battery cell group 100 is smaller than that of the second battery cell group 200, the expansion amount of the first battery cell group 100 is smaller, the pressure applied by the first battery cell group 100 on the components at the end part and the side part of the battery pack box 300 can be reduced, and the situation that the components in the battery pack box 300 are excessively pressed to deform or the battery cells leak due to the extrusion of the battery cell group to cause safety accidents is avoided.

Further, the preset direction may be a width direction or a length direction of the case 300. In this embodiment, as shown in fig. 1, the first battery cell group 100 and the second battery cell group 200 are arranged along the width direction and the length direction of the case 300 at the same time, and are distributed in multiple rows and multiple columns in the case 300, so as to improve the power storage capability of the battery pack.

Referring to fig. 2, as another embodiment of the arrangement manner of the first battery cell group 100 and the second battery cell group 200, the first battery cell group 100 (blank area) is surrounded on the periphery of the second battery cell group 200 (shadow area), so that the battery pack has higher thermal stability and the battery cell group with lower expansion is located in the edge area of the battery pack, on one hand, the first battery cell group 100 with lower expansion has small pressure on the components in the edge area of the box 300, so that the excessive extrusion of the battery cell group and the components in the box 300 is avoided, and on the other hand, the first battery cell group 100 has higher thermal stability, and can prevent other thermal runaway areas of the box 300 from spreading outwards, thereby improving the safety performance of the battery pack.

Alternatively, referring to fig. 3, the second battery cell groups 200 are arranged in a ring shape, and the inner side and the outer side of the second battery cell groups 200 are provided with the first battery cell groups 100, that is, the first battery cell groups 100 are located at the center and the periphery of the second battery cell groups 200 in a ring shape; because the central area and the edge area of the battery pack are the areas easy to generate thermal runaway, the first battery cell group 100 with high stability and low expansibility is arranged at the center and the edge of the battery pack, so that the thermal runaway of the battery pack can be prevented to a greater extent, the overall expansion of the first battery cell group 100 and the second battery cell group 200 is reduced, and the extrusion effect of the battery cell group and the inner members of the battery pack is reduced.

Or, referring to fig. 2, in the arrangement direction of the first battery cell group 100 and the second battery cell group 200, the first battery cell group 100 is disposed on two opposite sides of the second battery cell group 200, so that at least one first battery cell group 100 is located at the head end and the tail end in the arrangement direction of the first battery cell group 100 and the second battery cell group 200, thereby reducing the thermal runaway range of the battery pack, and reducing the mutual extrusion force of the battery cell group and the internal components of the box 300, so as to further improve the safety performance of the battery pack.

In one embodiment of the present utility model, the thermal expansion of the first cell 110 is less than the thermal expansion of the second cell 120, the expansion of the first cell 110 is less than the expansion of the second cell 120, the thermal expansion of the third cell 210 is less than the thermal expansion of the fourth cell 220, and the expansion of the third cell 210 is less than the expansion of the fourth cell 220. When the first battery cell group 100 is distributed at the edge position of the box 300, since the first battery cell 110 is located at the outer side of the second battery cell 120 and the expansion amount of the first battery cell 110 is smaller, the extrusion force between the first battery cell group 100 and other components in the box 300 can be reduced, so that the stress of the components is released conveniently; similarly, when the second battery cell group 200 is distributed at the edge of the case 300, since the third battery cell 210 is located outside the fourth battery cell 220 and the expansion amount of the third battery cell 210 is smaller, the extrusion force between the second battery cell group 200 and other components in the case 300 can be reduced, and the safety performance of the battery pack can be improved.

In an embodiment of the present utility model, the first electric core 110 and the fourth electric core 220 are electric cores of the same chemical system, the first electric core 110 and the fourth electric core 220 have the same performances of thermal stability, thermal expansion, energy density, etc., the second electric core 120 and the third electric core 210 are electric cores of the same chemical system, and the second electric core 120 and the third electric core 210 have the same performances of thermal stability, thermal expansion, energy density, etc. By introducing the electric cores of two different chemical systems into the battery pack and grouping the two electric cores in different arrangement modes, the first electric core group 100 and the second electric core group 200 are respectively formed, so that the first electric core group 100 has higher thermal stability and lower thermal expansibility compared with the second electric core group 200, the first electric core group 100 and the second electric core group 200 can be grouped through the two electric cores, and the arrangement of the electric core groups in the battery pack is more convenient.

The first and fourth electric cores 110 and 220 may be configured as lithium iron phosphate electric cores, the second and third electric cores 120 and 210 may be configured as ternary electric cores, for example, the second and third electric cores 120 and 210 are one of lithium nickel cobalt manganese oxide electric cores and lithium nickel cobalt aluminate electric cores, the second electric core 120 has a higher energy density and a capability of adapting to a low-temperature environment compared with the first electric core 110, and the first electric core 110 has a higher thermal stability and a lower thermal expansibility compared with the second electric core 120. So, all be provided with lithium iron phosphate electric core and ternary electric core in first electric core group 100 and the second electric core group 200, lithium iron phosphate electric core can reduce the holistic expansion volume of electric core in the battery package to promote the thermal stability of battery package, ternary electric core can improve the holistic capacity of electric core in the battery package, and make the battery package satisfy the user demand of low temperature environment, thereby through introducing above-mentioned two kinds of electric cores in the battery package, make the battery package have higher thermal stability and security performance.

Further, the capacity of the second electric core 120 is larger than the capacity of the first electric core 110, and since the first electric core 110 and the fourth electric core 220 are the same type of electric core, the capacity of the fourth electric core 220 is smaller than the capacity of the third electric core 210, and the capacity of the second electric core 120 is larger than the capacity of the fourth electric core 220, in this embodiment, the number of the second electric cores 120 is larger than the number of the fourth electric core 220, so that the number of electric cores with high capacity in the battery pack can be increased, and the battery pack can simultaneously meet the requirements of safety performance and high capacity.

In the present utility model, referring to fig. 4, the battery pack further includes at least one third cell group 400, where the third cell group 400 includes at least one fifth cell 410, and at least one of the first cell 110, the second cell 120, the third cell 210 and the fourth cell 220 is a cell with a different chemical system from the fifth cell 410, so that other types of cells are introduced into the battery pack, the chemical system of the fifth cell 410 can be selected according to the requirement of the battery pack, and the fifth cell 410 is disposed at a corresponding position, so that the third cell group 400 is matched with the first cell group 100 and the second cell group 200, so as to improve the performance of the battery pack in terms of thermal stability, capacity, thermal expansion and the like.

The third cell set 400 may be disposed inside the first cell set 100, inside the second cell set 200, or between the first cell set 100 and the second cell set 200. Specifically, the third cell group 400 may be located between the adjacent first cells 110 and the second cells 120 in the first cell group 100, or between the two adjacent second cells 120, or the third cell group 400 may also be located between the adjacent third cells 210 and the fourth cells 220 in the second cell group 200, or between the two adjacent fourth cells 220, or the third cell group 400 may also be located at a side portion of the first cell group 100 and disposed adjacent to the first cell group 100, or the third cell group 400 may also be located at a side portion of the second cell group 200 and disposed adjacent to the second cell group 200.

The position and type of the third battery cell group 400 can be reasonably set according to the overall performance requirement of the battery pack. If the thermal stability of the battery pack needs to be improved, a third cell set 400 with higher thermal stability than the first cell set 100 is selected, one or more fifth cells 410 may be disposed in the third cell set 400, the third cell set 400 is distributed between the first cell set 100 and the second cell set 200, or the third cell set 400 is distributed in the first cell set 100 or the second cell set 200; if the overall expansion of the battery pack needs to be reduced, selecting a third cell set 400 with thermal expansion lower than that of the first cell set 100, wherein one or more fifth cells 410 may be disposed in the third cell set 400, and the third cell set 400 is distributed on one side of the first cell set 100 close to the side wall or the end wall of the case 300; for example, when the overall capacity of the battery pack needs to be increased, a third battery cell group 400 with a capacity greater than that of the first battery cell group 100 or the second battery cell group 200 is selected, one or more fifth battery cells 410 may be disposed in the third battery cell group 400, and the third battery cell group 400 is distributed between the first battery cell group 100 and the second battery cell group 200, or the third battery cell group 400 is distributed inside the first battery cell group 100 or the second battery cell group 200.

Referring to fig. 5 to fig. 7 (fig. 7 illustrates the limitation of the first bus bar), the battery pack further includes an electrical isolation board 500, a first bus bar 600 and a second bus bar 700, the first bus bar 600 is used for connecting the first cell 110 and the second cell 120 in the first cell set 100, the second bus bar 700 is used for connecting the third cell 210 and the fourth cell 220 in the second cell set 200, and the electrical isolation board 500 is used for limiting the first bus bar 600 and the second bus bar 700 and realizing electrical isolation between the bus bars and the cells. Specifically, the adjacent first cells 110 are connected with the second cells 120 and the two adjacent second cells 120 through the first bus bar 600, so that the first cells 110 and the second cells 120 are connected through the first bus bar 600 to form a first cell group 100, the adjacent third cells 210 are connected with the fourth cells 220 and the two adjacent fourth cells 220 through the second bus bar 700, so that the third cells 210 and the fourth cells 220 are connected through the second bus bar 700 to form a second cell group 200, and the electric isolation plate 500 is positioned between the first bus bar 600 and the first cell group 100 and between the second bus bar 700 and the second cell group 200 to realize electric isolation between the bus bars and the cell groups; the electrical isolation board 500 is provided with a first limiting structure 510 for limiting the first bus bar 600 and a second limiting structure 520 for limiting the second bus bar 700, wherein the first limiting structure 510 and the second limiting structure 520 can be protrusions protruding from the surface of the electrical isolation board 500, or grooves concavely arranged on the surface of the electrical isolation board 500, limit the bus bar through the first limiting structure 510 and the second limiting structure 520, so that the positioning and connection of the bus bar and the battery core are facilitated, and the assembly convenience and the assembly precision of the battery pack are improved.

The embodiments of the present utility model have been described in detail with reference to the accompanying drawings, but the present utility model is not limited to the above embodiments, and various changes can be made within the knowledge of one of ordinary skill in the art without departing from the spirit of the present utility model. Furthermore, embodiments of the utility model and features of the embodiments may be combined with each other without conflict.

Claims

1. A battery pack, comprising:

2. The battery pack according to claim 1, wherein the first cell group and the second cell group are arranged along at least one preset direction, and in the preset direction, the first cell group is arranged at a head end, or the first cell group is arranged at a tail end, or the first cell group is arranged at both the head end and the tail end.

3. The battery pack of claim 1, wherein the first cell stack is disposed around the outer periphery of the second cell stack;

4. The battery pack of claim 2 or 3, wherein the first cell has a thermal expansion that is less than the thermal expansion of the second cell and the third cell has a thermal expansion that is less than the thermal expansion of the fourth cell.

5. The battery pack of claim 1, wherein the first cell and the fourth cell are cells of the same chemical system and the second cell and the third cell are cells of the same chemical system.

6. The battery pack of claim 5, wherein the second cells have a greater capacity than the first cells, and the number of second cells is greater than the number of fourth cells.

7. The battery pack of claim 1, further comprising at least one third cell group comprising at least one fifth cell, at least one of the first, second, third, and fourth cells being a cell of a different chemical system than the fifth cell.

8. The battery pack of claim 7, wherein the third cell group is located between adjacent ones of the first cells and the second cells in the first cell group or between two adjacent ones of the second cells;

9. The battery pack of claim 1, further comprising an electrical isolation plate, a first bus bar and a second bus bar, adjacent ones of the first cells and the second cells and two adjacent ones of the second cells being connected by the first bus bar, adjacent ones of the third cells and the fourth cells and two adjacent ones of the fourth cells being connected by the second bus bar, the electrical isolation plate being located between the first bus bar and the first cell group and between the second bus bar and the second cell group, the electrical isolation plate having a first limit structure limiting the first bus bar and a second limit structure limiting the second bus bar.

10. The battery pack of claim 1, wherein the first and fourth cells are lithium iron phosphate cells and the second and third cells are one of lithium nickel cobalt manganese oxide cells and lithium nickel cobalt aluminate cells.