Cylindrical secondary cell

Abstract

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, a second terminal electrically insulated from the first terminal, an electrode assembly within the cylindrical housing, and a current collector electrically interconnecting the electrode assembly and the first terminal. The first end includes a first end breakable portion (120) configured to rupture to provide an opening in the first end if the pressure within the cylindrical housing reaches a threshold value. The current collector includes a first current collector part (124) directly electrically connected to the electrode assembly, a second current collector part (126) directly electrically connected to the first terminal, and a current collector breakable portion interconnecting the first current collector part and the second current collector part. The current collector breakable portion is configured to be broken by the rupture of the first end breakable portion to disconnect the first current collector part and the second current collector part.

Description

[0001] CYLINDRICAL SECONDARY CELL

[0002] Technical field

[0003] 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.

[0004] 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.

[0006] 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.

[0007] 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. It is desirable to improve the performance of vents in secondary cells, and / or to increase the ease of manufacturing of such secondary cells.

[0008] Summary

[0009] 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; a second terminal electrically isolated from the first terminal; an electrode assembly within the cylindrical housing; and a current collector electrically interconnecting the electrode assembly and the first terminal; wherein the first end includes a first end breakable portion configured to rupture to provide an opening in the first end if the pressure within the cylindrical housing reaches a threshold value; wherein the current collector includes a first current collector part directly electrically connected to the electrode assembly, a second current collector part directly electrically connected to the first terminal, and a current collector breakable portion interconnecting the first current collector part and the second current collector part; wherein the current collector breakable portion is configured to be broken by the rupture of the first end breakable portion to disconnect the first current collector part and the second current collector part.

[0010] As the current collector is broken when the vent opens, current will no longer be able to flow to the first terminal after breakage of the vent, since the part of the first current collector part and the second current collector part are separated. This provides an added advantage over known venting arrangements and may enhance the safety of the cell.

[0011] The first current collector part and second current collector part may be flexible. This may enable easier opening of the vent prior to separation of the two parts. Furthermore, the breakable portion between the first current collector part and the second current collector part may function as a fuse when a larger current than a predetermined threshold is applied in this portion. The first current collector part and the second current collector part may be integrally formed. This ensures that the current collector is a single piece until such a time as it is broken during operation of the device. Providing the current collector as a single piece may ensure optimal conduction of the current collector during normal usage, prior to it being broken.

[0012] There may be notches between the first current collector part and the second current collector part. This may help to ensure that the breakable portion of the current collector is broken when the event occurs.

[0013] The first current collector part may be welded to one of a positive electrode and a negative electrode of the electrode assembly. The second current collector part may be welded to the first terminal. Welding provides good conduction between the electrically conductive parts, and has good characteristics for ensuring ease of manufacture and assembly.

[0014] The first terminal may comprise a recess via which the second current collector part is welded to the first terminal. The provision of a recess may help to ensure that the first terminal is not so thick as to prevent proper welding of the two components. The recess can be sized and shaped so as to give optimal access for the welding operation, such that the power and time of welding can be selected to provide a good weld that prevents or limits collateral damage of adjacent components.

[0015] The first terminal may further comprise a cap to close the recess. The cap may form a flat surface with an upper surface of the first terminal. Closing the recess can help to provide a better welding surface for connection of a load to the first terminal. A flat surface is further desirable to ensure a good welding surface.

[0016] In an alternative, the first terminal may be joined to the second current collector part from an alternative position that does not require a recess in the first terminal. For example, the first terminal may be joined by welding from below, through a centre of the electrode assembly. In such an assembly, the first terminal need not include a recess or an associated cap.

[0017] The first terminal may comprise a terminal rivet. A terminal rivet may close the cell housing during manufacture by being deformed around the first end of the cell housing. Use of a terminal rivet is well-known in the art.

[0018] The first end breakable portion may surround or substantially surround the first terminal. By surrounding or substantially surrounding the first terminal, the size of the rupture of the first end breakable portion can be improved, which will in turn provide more movement of the first terminal, which will subsequently impart more motion to the current collector to break it more easily.

[0019] Alternatively, the first end breakable portion may extend around at least 60%, at least 70%, at least 80%, or at least 90% of the circumferential extent of the first terminal. A longer first end breakable portion may provide a more efficient breakage of the current collector breakable portion.

[0020] The current collector may comprise a plate-like structure. For example, the first current collector part and the second current collector part may be co-planar. In an alternative, the first current collector part may be in a first plane and the second current collector part may lie in a second plane that is different from the first plane.

[0021] The current collector may be disc shaped. It may further include one or more cut-out portions. The disc shape may help provide a large welding surface for connecting to the electrode roll. Cutout portions may provide enhanced flow of gas and / or electrolyte within the cell, both during assembly and during use. The first end breakable portion may be proximal to the first terminal. A first end breakable portion that is proximal to the first terminal may cause a greater upward movement of the first terminal when the first end breakable portion opens, which will impart a greater movement to help break the current collector breakable portion.

[0022] The first end breakable portion may be positioned less than 50% of the distance from the first terminal to an edge of the first end. Alternatively, the first end breakable portion may be positioned less than 40%, less than 30%, less than 25%, or less than 20% of the distance from the first terminal to the edge of the first end.

[0023] According to a second aspect, there is provided a system comprising a plurality of cylindrical secondary cells according to the first aspect and at least one electrical connector configured to electrically interconnect the plurality of cylindrical secondary cells.

[0024] 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.

[0025] According to a third aspect, there is provided an energy storage system comprising the system of the second aspect.

[0026] According to a fourth aspect, there is provided a vehicle comprising the system of the second aspect.

[0027] Brief summary of the drawings

[0028] Different aspects are now described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a secondary cell in accordance with the first aspect;

[0029] Figure 2 is a top view of the secondary cell of Figure 1;

[0030] Figure 3 is a cross-sectional view of an upper portion of the secondary cell of Figure 1;

[0031] Figure 4 is a plan view of the current collector shown in Figure 3;

[0032] Figure 5 is a simplified view of a system comprising a plurality of secondary cells that are electrically connected; and

[0033] Figure 6 shows a vehicle comprising the system of Figure 5.

[0034] Detailed description

[0035] The disclosure is not limited to the embodiments disclosed but may be varied and modified within the scope of the claims.

[0036] 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.

[0037] As used herein, the terms "comprise / comprises" or "include / includes" do not exclude the presence of other elements or steps.

[0038] 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 106.

[0039] 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. Part of the first end 104 of the cell housing 102 is integrally formed with the side wall 108. The first end breakable portion 120 is arranged on the part of the first end 104 of the cell housing 102 that 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.

[0040] 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 3, 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.

[0041] 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.

[0042] 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 first end breakable portion 120. The first end breakable portion 120 is depicted as a broken line on the first end 104. In this example, the first end breakable portion 120 is circular and completely surrounds the first terminal 110. The first end breakable portion 120 is shown in cross-section through the cell in Figure 3.

[0043] The first end breakable portion 120 comprises a weakened portion of the first end 104. In the example shown in Figure 3, the weakened portion comprises a notch 122, which is in this case pointed. When the pressure within the cell 100 increases above a threshold, the weakened portion will cause the cell 100 to break in a predictable manner. The skilled person will be aware of ways in which the weakened portion may be adapted to break at different threshold pressures dependent on design requirements.

[0044] In other examples, the first end breakable portion need not extend to completely surround the first terminal. It may extend to substantially surround the first terminal, such as where the first end breakable portion does not form a complete ring around the first terminal. Alternatively, it may extend around a proportion of the circumferential extent of the first terminal. This proportion may be at least 50% of the circumferential extent of the first terminal, or at least 60% of the circumferential extent of the first terminal, or at least 70% of the circumferential extent of the first terminal, or at least 80% of the circumferential extent of the first terminal, or at least extent of the first terminal.

[0045] The first end breakable portion 120 may comprise a notch 122, as in Figure 3, or may comprise other types of weakening, such as a groove, thinning portion, partial-depth perforation, or any other such weakening of the material. Options for providing breakable portions in a cell housing are well-known to the skilled person and need not be discussed in further detail.

[0046] The first current collector 116 is shown in more detail in Figure 4, where it is viewed from the top down. The first current collector 116 comprises a first current collector part 124, which is substantially annular and is configured to be directly electrically connected to either a positive electrode or negative electrode of the electrode roll 114, as mentioned above. The first current collector 116 also comprises a second current collector part 126, which is substantially circular and is surrounded by the first current collector part 124. The second current collector part 126 is configured to be directly electrically connected to the first terminal 110. In the present example, welds are used to connect the first current collector 116 to the respective parts, and these are visible in Figures 3 and 4. First weld portions 128 provide a direct electrical connection between the first current collector part 124 and the electrode roll 114, whilst a second weld portion 130 provides direct electrical connection between the second current collector part 126 and the first terminal 110.

[0047] The first weld portions 128 are provided as four groups of three welds, where each weld is radial and each group of three welds is at 90 degrees to the next. The second weld portion 130 comprises only a single, circular weld, which is central on the second current collector part 126.

[0048] Methods of providing the direct electrical connection other than welding, such as soldering or brazing, may be used in place of welding, if so desired. In addition, the number of weld portions may differ for both of the first weld portions 128 and second weld portions 130, and may be adapted based on design and manufacturing desire. The first current collector part 124 and the second current collector part 126 are connected by a current collector breakable portion 132, which forms the only connection between the first current collector part 124 and the second current collector part 126. As such, if the current collector breakable portion 132 were to break, current would no longer be able to flow between the first current collector part 124 and the second current collector part 126.

[0049] Although a single current collector breakable portion 132 is shown in Figure 4, multiple current collector breakable portions may be provided. For example, two breakable portions may be provided, side by side, opposing each other, or spread around the second current collector portion. Alternatively, multiple breakable portions may be provided, for example side-by-side creating a perforated region. Many different options are possible and may be utilised.

[0050] Furthermore, the single current collector breakable portion 132 may have notches between the first current collector part and the second current collector. This ensures that the breakable portion of the current collector is broken when the event occurs.

[0051] In use, an overpressure within the cell housing 102 will cause the opening of the first end breakable portion 120. As this opens, the first terminal 110 will be moved upwards, away from the second end 106 of the cell 100. Because the first terminal 110 is connected to the second current collector part 126, it will also pull this part with it, causing the breaking of the current collector breakable portion 132. The opening of the first end breakable portion 120 will therefore allow the pressure in the cell housing 102 to be decreased through venting, whilst the current through the first terminal 110 is removed due to the break of the current collector breakable portion 132 in the first current collector 116 disconnecting the first terminal 110 from the electrode roll 114.

[0052] It will be apparent from the above examples that the weakened portion 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. A weakened portion may comprise a continuous feature, a non-continuous feature, or a combination of the two.

[0053] Although the current collector breakable portion 132 is provided as a narrow strip of material, in the depicted embodiment, it may also be provided as a weakened portion in the first current collector 116, similarly to how the first end breakable portion 120 is formed as a weakened portion in the first end 104. The current collector breakable portion 132 may therefore be formed using notches, grooves, perforations, or any other suitable manner of providing a breakable portion in the first current collector 116.

[0054] Figure 5 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.

[0055] Figure 6 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

Claims1. A cylindrical secondary cell comprising: a cylindrical housing comprising a first end and an opposing second end; a first terminal at the first end; a second terminal electrically insulated from the first terminal; an electrode assembly within the cylindrical housing; and a current collector electrically interconnecting the electrode assembly and the first terminal; wherein the first end includes a first end breakable portion configured to rupture to provide an opening in the first end if the pressure within the cylindrical housing reaches a threshold value; wherein the current collector includes a first current collector part directly electrically connected to the electrode assembly, a second current collector part directly electrically connected to the first terminal, and a current collector breakable portion interconnecting the first current collector part and the second current collector part; wherein the current collector breakable portion is configured to be broken by the rupture of the first end breakable portion to disconnect the first current collector part and the second current collector part.

2. A cylindrical secondary cell according to claim 1, wherein the first current collector part and the second current collector part are integrally formed.

3. A cylindrical secondary cell according to claim 1 or claim 2, wherein the first current collector part is welded to one of a positive electrode and a negative electrode of the electrode assembly.

4. A cylindrical secondary cell according to any preceding claim, wherein the second current collector part is welded to the first terminal.

5. A cylindrical secondary cell according to claim 4, wherein the first terminal comprises a recess via which the second current collector part is welded to the first terminal, optionally wherein the first terminal further comprises a cap to close the recess, which optionally forms a flat surface with an upper surface of the first terminal.

6. A cylindrical secondary cell according to any preceding claim, wherein the first terminal comprises a terminal rivet.

7. A cylindrical secondary cell according to any preceding claim, wherein the first end breakable portion surrounds or substantially surrounds the first terminal.

8. A cylindrical secondary cell according to any of claims 1 to 6, wherein the first end breakable portion extends around at least 50%, at least 60%, at least 70%, at least 80%, or at least 90% of the circumferential extent of the first terminal.

9. A cylindrical secondary cell according to any preceding claim, wherein the first current collector part and the second current collector part are co-planar.

10. A cylindrical secondary cell according to any of claims 1 to 9, wherein the first end breakable portion are positioned less than 50% of the distance from the first terminal to an edge of the first end.

11. A system comprising a plurality of cylindrical secondary cells according to any of the preceding claims and at least one electrical connector configured to electrically interconnect the plurality of secondary cells.

12. An energy storage system comprising the system of claim 11.

13. A vehicle comprising the system of claim 11.

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