SE548019C2

SE548019C2 - Cylindrical secondary cell

Info

Publication number: SE548019C2
Application number: SE2330604A
Authority: SE
Inventors: Calum Bradbury
Original assignee: Northvolt Ab
Priority date: 2023-12-21
Filing date: 2023-12-21
Publication date: 2026-01-13
Also published as: SE2330604A1

Abstract

A cylindrical secondary cell (100) is disclosed. The cell (100) comprises a cylindrical housing (102) comprising a first end (104) and an opposing second end (106), a first terminal (110) at the first end (104), and a second terminal electrically insulated from the first terminal (110). The first end (104) further comprises a venting region (120) configured to rupture to provide an opening in the first end (104) if the pressure inside the cylindrical housing reaches a threshold value. The venting region (120) extends between an inner boundary (122) and an outer boundary (124) and extends

Description

[0001] The present disclosure relates to a cylindrical secondary cell. It further relates to a system comprising a plurality of secondary cells, and an energy storage system and vehicle including such a system.

[0003] Background

[0005] To address climate change, there is an increasing demand for rechargeable batteries, for example to enable electrification of transportation and to supplement renewable energy. Currently, lithium-ion batteries are becoming increasingly popular. They represent a type of rechargeable battery in which lithium ions move from the negative electrode to the positive electrode during discharge and in reverse when charging.

[0007] A rechargeable battery, often referred to as a secondary battery, typically comprises one or more secondary cells electrically connected to each other. Some secondary cells have at least one vent for releasing gas and/or other ejecta when the pressure inside the batteries rises above an allowed level. This release of pressure helps to lower the risk of explosion due to uncontrolled pressure rise within the cell. Typically, venting is provided by forming a weakened seam, which therefore splits under increased pressure.

[0009] When used to form a battery, secondary cells are connected using electrical connectors. These electrical connectors are used to connect a plurality of cells in series, parallel, or a combination of the two. Typically, these electrical connectors are attached at one end of the cells, requiring the terminals of the cell to each be accessible from that one end.

[0010] It is desirable to improve the performance of vents in secondary cells, and/orto increase the ease of manufacturing of such secondary cells.

[0012] Summary

[0014] According to a first aspect, there is provided a cylindrical secondary cell comprising: a cylindrical housing comprising a first end and an opposing second end; a first terminal at the first end; and a second terminal electrically insulated from the first terminal; wherein the first end further comprises a venting region configured to rupture to provide an opening in the first end if the pressure inside the cylindrical housing reaches a threshold value; wherein the venting region extends between an inner boundary and an outer boundary, the venting region extending around the first terminal to surround or substantially surround the first terminal, and wherein the inner boundary and the outer boundary are separate from one another, and the inner boundary and the outer boundary are concentric.

[0016] The use of a venting region with inner and outer boundaries enables the venting region to be ejected from the surrounding part of the housing during venting. This provides an increased area for venting of both gases and ejecta compared to a split in the housing as in other known vents. Moreover, in the event that an electrical connector is connected to the first terminal, the venting region may break from the first end without any associated movement of the first terminal. This may also enable the pressure required to open the vent to be more predictable due to the isolation of the vent from the first terminal and any connected electrical connection, as deformation of the remainder of the first end is not required.

[0018] The inner boundary and outer boundary may each comprise a weakened portion. Each weakened portion may be formed by, for example, a groove, notch, thinning of material, or other weakening in the material making up the first end.

[0019] Rupture of both the inner boundary and outer boundary may cause the venting region to be disconnected from a remainder of the first end.

[0021] The inner boundary and outer boundary may be separate from one another. The inner boundary and outer boundary may be concentric. In the case where the inner boundary and outer boundary are concentric, the venting portion may completely surround the first terminal.

[0023] The inner boundary and outer boundary may each be circular. Optionally, the inner boundary and the outer boundary may each be centred on the first terminal. In such an arrangement, the venting region may be formed as an annulus around the first terminal. Such an arrangement will ensure that the venting region has full rotational symmetry around a longitudinal axis of the secondary cell. This can help with ease of manufacture and assembly, as the rotational position of the cell during these processes will be less important.

[0025] The inner boundary and the outer boundary may together define at least part of a continuous boundary of the venting region. The continuous boundary of the venting region may further comprise at least one additional boundary portion. The inner boundary and outer boundary may therefore form inner and outer edges, which may be joined directly or which may alternatively include additional portions that, for example, join the inner boundary to the outer boundary. The at least one additional boundary portion may, for example, comprise a straight boundary portion, such as a radial boundary portion extending in a radial direction of the cylindrical housing, or may comprise a curved boundary portion.

[0027] The venting region may have a perimeter that is weakened around its entire length. The perimeter may be defined by the inner boundary, the outer boundary, and optionally any additional boundary portions. In some examples, the perimeter of the venting region may be weakened around substantially its entire length, but with a small portion that is not weakened. This non-weakened portion may help to tether the venting region to the cell housing once it has been opened.

[0028] The weakened portions may be continuous, formed, for example, by a continuous notch, groove, thinning of material, or other weakening feature. Alternatively, the weakened portions may be discontinuous, for example, by a partial thickness perforation or 'dotted' notch, groove, or thinning of material.

[0030] Each of the boundaries may be configured to break at the same threshold pressure. Alternatively, each boundary may be configured to break at a different threshold pressure. In this way, the mechanics of opening the vent may be adjusted as desired, by modification of the boundaries.

[0032] According to a second aspect, there is provided a system comprising a plurality of secondary cells according to the first aspect and at least one electrical connector configured to electrically interconnect the plurality of secondary cells.

[0034] The at least one electrical connector may be configured to electrically interconnect a first terminal of a first secondary cell of the plurality of secondary cells and a first terminal or a second terminal of a second secondary cell of the plurality of secondary cells.

[0036] According to a third aspect, there is provided an energy storage system comprising the system of the second aspect.

[0038] According to a fourth aspect, there is provided a vehicle comprising the system of the second aspect.

[0040] Brief summary of the drawings

[0042] Different aspects are now described, by way of example, with reference to the accompanying drawings, in which:

[0043] Figure 1 shows a secondary cell in accordance with the first aspect;

[0044] Figure 2 is a top view of the secondary cell of Figure 1;

[0045] Figure 3a is a vertical sectional view of the top of the secondary cell of Figure 1;

[0046] Figure 3b is the same vertical sectional view of Figure 3, after an increase in internal pressure of the secondary cell;

[0047] Figure 4 is a top view of another secondary cell in accordance with the first aspect;

[0048] Figures 5a to 5c are alternative examples of the boundaries of the venting region of Figure 3a;

[0049] Figure 6 is a top view of the secondary cell of claim 1 attached to an electrical connector; Figure 7 is a simplified view of a system comprising a plurality of secondary cells that are electrically connected; and

[0050] Figure 8 shows a vehicle comprising the system of Figure 7.

[0052] Detailed description

[0054] The disclosure is not limited to the embodiments disclosed but may be varied and modified within the scope of the claims.

[0056] The terminology used herein is for the purpose of describing particular aspects of the disclosure only and is not intended to limit the invention. The singular forms "a", "an" and "the" are intended to include plural forms as well, unless the context clearly indicates otherwise.

[0058] As used herein, the terms "comprise/comprises" or "include/includes" do not exclude the presence of other elements or steps.

[0060] Figure 1 shows an example of a cylindrical secondary cell 100, hereinafter referred to as a cell 100. The cell comprises a cylindrical cell housing 102 having a first end 104 and a second end 106 opposite the first end 104. A side wall 108 interconnects the first end 104 and the second end In the depicted example, the first end 104 and the second end 106 are circular, with the interconnecting side wall 108 having a circular cross-section. In other examples, it may be desirable to have the first end 104 and second end 106 as different shapes, with the side wall 108 having a corresponding shape able to interconnect the two.

[0062] Part of the first end 104 of the cell housing 102 is integrally formed with the side wall 108. In the present example, the first end 104 and side wall 108 are formed by a drawing process to create the cylindrical shape. The second end 106 is provided as a separate part that is then connected to the remainder of the cell housing 102 during a further manufacturing step, such as crimping or welding. In some cases, the second end 106 is electrically insulated from the side wall 108, or alternatively the second end 106 may be welded or otherwise bonded to form an electrical connection with the rest of the cell housing 102. The present example has the second end 106 electrically connected to the side wall 108.

[0064] The first end 104 also includes a first terminal 110. In the depicted embodiment, the first terminal 110 is electrically isolated from the rest of the cell housing 102. As shown in Figure 3a, the first terminal 110 is in electrical communication with an electrode assembly 112 of the cell 100. The electrode assembly 112 includes positive and negative electrodes forming an electrode roll 114, and a first current collector 116, which is electrically connected to one of the positive and negative electrodes. The first terminal 110 is then electrically connected to the first current collector 116. A second current collector (not shown), is situated at the other end of the electrode roll 114 and is electrically connected to the other of the positive and negative electrodes. The second current collector is in electrical communication with the cell housing 102, such that the cell housing 102, excluding the first terminal 110, forms a second terminal of the cell 100. The first terminal 110 is electrically insulated from the second terminal by an insulator 118. In the depicted arrangement, the first terminal 110 is formed by a terminal rivet, which is inserted through the cell housing 102, isolated by the insulator 118, and deformed to form a seal with the cell housing 102. Thus, the terminal rivet is held in place and maintains the integrity of the cell housing 102.

[0066] Alternative arrangements for electrically connecting the electrode assembly to the first and second terminal will be known to the skilled person, and the specific arrangement used does not impact the present invention. As such, any such arrangement may be used. It will also be clear to the skilled person that the electrical insulation of the first terminal may be provided in different positions. For example, the entire first side of the cell housing may form the first terminal, with an insulator being positioned between the first side and the side wall. In another example, the first terminal may include all of the first side and the side wall, with the second end being electrically insulated from this first terminal. The skilled person will be aware of other arrangements. Of course, the first terminal should be electrically insulated from the second terminal in these arrangements.

[0068] Referring now to Figure 2, a top-down view of the cell 100 is shown. Within the area of the first end 104, surrounding the first terminal 110, is a venting region 120. The venting region 120 is defined by an inner boundary 122 and an outer boundary 124, each depicted as broken lines on the first end 104. As such, in this example, the venting region 120 is annular and completely surrounds the first terminal 110. The venting region 120 is shown in cross-section through the cell in Figure 3a.

[0070] Each of the inner boundary 122 and outer boundary 124 comprise a weakened portion of the first end 104. In the example shown in Figure 3a, each weakened portion comprises a notch 126, which is in this case pointed. When the pressure within the cell 100 increases above a threshold, the weakened portions will cause the cell 100 to break in a predictable manner. The threshold pressure of weakened portions may be adapted differently in each inner boundary 122 and outer boundary 124. For example, in some embodiments, the threshold pressure may be higher for the outer boundary than the inner boundary, such that they break at different times, or that the second boundary opens only at very high internal pressures. In other embodiments, the threshold pressure may be made the same for both boundaries, such that the boundaries are configured to rupture at the same time or at substantially the same time. The skilled person will be aware of ways in which the weakened portions may be adapted to break at different threshold pressures dependent on design requirements.

[0072] As the venting region 120 is a region having an area, rather than simple a single point or line, an area of the first end 104 is caused to separate from the rest of the first end 104 when the pressure is increased to the threshold. This has a number of advantages over a vent formed by a single weakened point or line. Firstly, the separated area may leave a large area though which gas and/or ejecta can leave the cell 100, increasing the efficiency of the vent. Secondly, the opening may be provided without substantial deformation of the first end 104 itself. This can be particularly advantageous when the first terminal 110 is connected to other cells 100 via an electrical connector, shown in Figure 6. Here, a first electrical connector 128 is attached to the first terminal 110 and can then be used to provide electrical connection to a second cell (not shown), and a second electrical connector 130 is attached to the second terminal, isolated from the first terminal 110, and can provide an electrical connection to a third cell (not shown). The use of the venting region 120 can limit or prevent deformation of the first end 104 of the cell 100, allowing venting without disrupting the electrical connectors 128, 130, and may allow the opening of the venting region 120 without being directly affected by the electrical connectors 128, 130.

[0074] Figure 4 shows a second example of a venting region 220 on a first end 204 of a cell 200. In the second example, rather than the inner boundary 222 and outer boundary 224 being separate, they form part of a continuous boundary around the venting region 220. In this example, the inner boundary 222 and outer boundary 224 are connected at each end by an additional boundary portion 232. Each additional boundary portion 232 is also weakened, such that an entire perimeter of the venting region 220 is weakened. The venting region 220 of this example extends to substantially surround the first terminal 210. In practice, the venting region 210 of Figure 4 therefore acts in substantially the same or a similar way and has the same or similar advantages to the venting region 120 of Figure 2.

[0076] In each example, the venting region extends to surround or to substantially surround the first terminal. The venting region may extend around at least 80% of the circumference of the first terminal, for example. In other examples, the venting region may extend around at least 85%, at least 90%, at least 95%, or at least 98% of the circumference of the first terminal.

[0078] Figures 5a to 5c show some alternative options for the weakened portion. These options are not exhaustive and the skilled person will be aware of other options that function in the same way as the options disclosed in the present disclosure.

[0080] Figure 5a shows an example of a weakened portion whereby each of the inner boundary 322 and the outer boundary 324 comprises a thinned portion 334, where the material is thinner than that of the surrounding region. The weakened portion operates in the same way as that of Figure 2 by breaking once the pressure within the cell housing reaches the threshold pressure.

[0082] Figure 5b is a further example of a weakened portion. In this example, the inner boundary 422 and outer boundary 424 are again formed by notches 426, but on the inner side of the first end 404, facing into the cell housing.

[0084] Figure 5c is a further example of a weakened portion. In this example, the inner boundary 522 is formed by a notch 526 on the outer side of the first end 504 and the outer boundary 524 is formed by a notch 526 on the inner side of the first side 504.

[0086] It will be apparent from the above examples that the weakened portions may be formed in different ways, with different material profiles, and in different positions, but retaining the same operating characteristics. It should be noted that the term "weakened portion" is considered to include not only a continuous feature, such as a groove or notch in the material that extends around the whole weakened portion, but also a non-continuous feature, such as a repeating pattern of short grooves or notches, similar to a perforation but through only a partial thickness of the material. Each weakened portion may comprise a continuous feature, a non-continuous feature, or a combination of the two.

[0088] Figure 7 depicts a system 1000 comprising a plurality of cells 100 connected together. These cells 100 are interconnected using one or more electrical connectors 1002, and the system 1000 can be attached to an external load (not shown) using terminals 1004. The system 1000 may further include control electronics 1006 such as a cell sensing board or battery management system, which can operate to provide features such as cell balancing, or sensing such as voltage sensing or temperature sensing. Such control electronics 1006 are well-known in the art and will not be described in more detail in this disclosure. The system 1000 may be utilised as an energy storage system, for example, as large-scale energy storage in a battery farm, or alternatively as energy storage in other applications such as vehicles.

[0090] Figure 8 shows a vehicle 2000 including the system 1000 of Figure 7. The vehicle 2000 may use energy from the system 1000 to provide propulsive force to the vehicle 2000.

Claims

1. A cylindrical secondary cell (100) comprising: a cylindrical housing (102) comprising a first end (104) and an opposing second end (106); a first terminal (110) at the first end (104); and a second terminal electrically insulated from the first terminal (110); wherein the first end (104) further comprises a vent region (120) configured to rupture to provide an opening in the first end (104) if the pressure within the cylindrical housing reaches a threshold value; wherein the vent region (120) extends between an inner boundary (122) and an outer boundary (124), wherein the vent region (120) extends around the first terminal (110) to surround or substantially surround the first terminal (110); characterized in that: the inner boundary (122) and the outer boundary (124) are separated from each other; and the inner boundary (122) and the outer boundary (124) are concentric.

A cylindrical secondary cell (100) according to claim 1, wherein the inner boundary (122) and the outer boundary (124) each include a weakened portion.

A cylindrical secondary cell (100) according to claim 2, wherein rupture of the weakened portion of both the inner boundary (122) and the outer boundary (124) causes the ventilation region (120) to be disconnected from a remainder of the first end (104).

A cylindrical secondary cell (100) according to claim 1, wherein the inner boundary (122) and the outer boundary (124) are each circular, optionally wherein the inner boundary (122) and the outer boundary (124) are each centered about the first terminal (110).

5. A cylindrical secondary cell (100) according to any preceding claim, wherein the ventilation area (120) comprises a perimeter, and that perimeter is weakened around its entire length.

6. A system (1000) comprising a plurality of secondary cells (100) according to any one of claims 1 to 5 and at least one electrical contact (1002) configured to electrically interconnect the plurality of secondary cells (100).

7. A system according to claim 6, wherein the at least one electrical contact is configured to electrically interconnect a first terminal (110) of a first secondary cell (100) of the plurality of secondary cells (100) and a first terminal (110) or a second terminal of a second secondary cell (100) of the plurality of secondary cells (100).

8. An energy storage system comprising the system according to claim 7.

9. A vehicle comprising the system according to claim 7.