Secondary cell

Abstract

A secondary cell 100 is provided comprising a housing 102, and an electrode assembly 104 arranged in the housing 102. The secondary cell 100 further comprises a current collector plate 106 directly connected to an electrode 105 of the electrode assembly, and a lid structure 108 which comprises a lid plate 110 and a terminal part 112. A surface portion of the terminal part is configured for attachment to an external load. The terminal part 112 is provided with at least one fracturable portion 124 outside the surface portion configured for attachment to the external load, and the terminal part 112 is directly connected to the current collector plate 106.

Description

[0001] Secondary cell

[0002] Technical field

[0003] The present disclosure relates to a secondary cell, and to an energy storage system and a vehicle comprising a secondary cell.

[0004] Background

[0005] The transition from fossil fuels towards renewable energy has gained considerable momentum. One of the most important contributing factors is the development of better and cheaper rechargeable battery cells, also referred to as secondary cells. Currently, lithium-ion battery cells are becoming increasingly popular. They represent a type of cell in which lithium ions move from the negative electrode to the positive electrode during discharge and back when charging.

[0006] An electric vehicle typically comprises a large number of secondary cells (often hundreds or even thousands) arranged in a module and / or pack. In case of a short circuit or other malfunction (e.g. due to external crushing due to a crash), the temperature may increase inside the cell causing development of gases and an increase of pressure. If this reaction is not controlled, it may lead to thermal runaway which could also propagate to neighboring cells, in the worst case causing a fire and / or explosion.

[0007] To prevent such events from occurring, secondary cells are generally provided with safety features. One commonly applied safety feature is to provide the cell with a vent for releasing gas and / or other ejecta when the pressure inside the cell rises above a threshold value. Venting contributes to slowing down or stopping a thermal runaway event as well as directing the ejected material away from neighboring cells.

[0008] Such a vent may be provided as a weakened portion, for example a notch, designed to fracture at a defined threshold pressure and provide an opening for gases and material. The weakened portion may be stamped into the housing or lid of the cell, or the vent may be provided as a separate component inserted into an opening of the cell. This may however require additional cell components or special assembly methods to ensure that the venting channels are not blocked. There is a general need in the art for secondary cells that provide sufficient safety while also allowing for flexibility when assembling the cells into vehicles or packs, and without sacrificing the total energy capacity of the cell.

[0009] Summary

[0010] A secondary cell 100 is provided comprising a housing 102, and an electrode assembly 104 arranged in the housing 102. The housing 102 may be a cylindrical can. The cell 100 further comprises a current collector plate 106 which is directly connected to an electrode 105 of the electrode assembly. The secondary cell 100 further comprises a lid structure 108 comprising a lid plate 110 and a terminal part 112, wherein a surface portion of the terminal part 112 is configured for attachment to an external load. The terminal part 112 is provided with at least one fracturable portion 124 outside the surface portion configured for attachment to the external load. Further, the terminal part 112 is directly connected to the current collector plate 106.

[0011] The fracturable portion may be configured to break when the pressure inside the cell reaches a threshold value.

[0012] Locating the fracturable portion 124 outside the portion where the external load is attached reduces the risk of an external connector or bus bar interfering with the venting function. Thereby, more efficient venting may be achieved without the need for additional cell components.

[0013] In some variants, the at least one fracturable portion 124 surrounds the surface portion. The at least one fracturable portion 124 may be circular or annular in shape. In further variants, the at least one fracturable portion 124 is rotationally symmetric around the surface portion. In specific variants, a plurality of fracturable portions 124 are symmetrically arranged around the surface portion configured for attachment to the external load. Having the fracturable portion 124 rotationally symmetric may further facilitate the assembly of the cells with the external load, since it allows the cell 100 to be placed in any rotational position. The terminal part 112, or more specifically the surface portion of the terminal part 112, may be raised relative to the lid plate 110. In some variants, the fracturable portion 124 may be located proximal to the raised edge 126 of the terminal part 112. More specifically, the fracturable portion 124 may be located at least 2 / 3 of the radial distance from the center of the terminal part 112 to the raised edge 126 of the terminal part 112. In further variants, the diameter of the terminal part 112 is at least 2 / 3 of the diameter of the lid plate 110.

[0014] The current collector plate 114 may comprise a protrusion 116 toward the lid structure 122, and the terminal part 112 may comprise a corresponding recess 114. In some variants, the current collector plate 106 and the terminal part 112 may be electrically connected at the interface between the recess 114 and the protrusion 116.

[0015] Brief summary of the drawings

[0016] Different aspects are now described, by way of example, with reference to the accompanying drawings, in which:

[0017] Fig. 1 shows a secondary cell according to some examples.

[0018] Fig. 2 shows a secondary cell according to some examples.

[0019] Fig. 3a - 3c shows top views of different arrangements of a fracturable portion.

[0020] Fig. 4 shows an energy storage system according to some examples.

[0021] Fig. 5 shows a vehicle according to some examples.

[0022] Detailed description

[0023] In the context of this disclosure, "terminal" refers to a portion of the cell which is configured to be connected to an external load.

[0024] "Electrode" refers to a foil or other substrate coated with active material. When this disclosure refers to connecting to an electrode, this means making an electrical connection to an electrode tab, which may either be an uncoated portion of the foil, or a separate tab attached to the foil. Figure 1 shows a secondary cell 100 according to some embodiments. The cell 100 comprises a cylindrical can 102, and an electrode assembly 104 arranged in the can 102. The can 102 may be made of steel, aluminium, or any other suitable material. The electrode assembly 104, which can alternatively be referred to as a jelly roll or electrode roll, comprises a negative electrode and a positive electrode. The negative electrode will be interchangeably referred to as the "anode electrode" in this disclosure, and the positive electrode will be interchangeably referred to as the "cathode electrode". The anode and cathode electrode sheets are rolled together with a separator sheet (not shown) in between. The separator is a thin sheet of electrically insulating material, typically a polyolefin, which prevents physical contact between anode and cathode as this would lead to a short circuit. Each electrode comprises a foil substrate (typically copper foil on the anode side, and aluminium foil on the cathode side) which is coated with active material. The type of active material can vary as different cell chemistries may be applied depending on the desired cell characteristics. One commonly used anode active material is graphite, which may be mixed with silicon particles. Commonly used cathode active materials are NMC (Lithium nickel manganese cobalt oxides) and LFP (Lithium iron phosphates).

[0025] The edge of the foil is uncoated and functions as a tab 105 for electrical connection to an external terminal of the cell, which will be further described below. It is however also possible to attach a separate tab to the foil, e.g. by welding, in which case the separate tab will provide the electrical connection.

[0026] The positive electrode (sometimes referred to as the cathode side) is connected to a current collector plate 106, which in this example is a circular disc. However it should be appreciated that other shapes are possible, for example an oval or polygonal disc, or a structure with one more arms extending from a central portion. Advantageously, the current collector plate is large enough to cover the electrode assembly, in order to maximize electrical contact. When the current collector plate is a circular disc, the diameter of the disc may be at least the same size as the diameter of the electrode assembly.

[0027] Physical contact between the electrode 105 and the current collector plate 106 can be achieved by pressing the plate 106 against the electrode 105 and then welding in one more positions from the top of the current collector plate 106, for example by laser welding. It's also possible to slit the electrode 105 in one or more positions before applying the current collector plate 106, to improve physical contact and reduce resistance.

[0028] The can 102 is closed by a lid structure 108, which comprises a lid plate 110 with a terminal portion 112. The terminal portion 112 protrudes from the lid plate 110, or stated differently, the terminal portion 112 is raised in relation to the lid plate 110. This can be achieved for example by stamping the lid plate 110.

[0029] In this example, the lid structure 108 is also provided with a recess 114 on the side facing the electrode assembly 104. A corresponding protrusion 116 is provided on the current collector plate 106. This provides an advantageous welding point for attaching the lid structure 108 to the current collector plate 106, as the recess 116 creates an additional distance from the electrode assembly 104 thereby reducing the risk of damaging the electrode assembly 104 during welding. Preferably, the recess 116 and protrusion 114 are provided in the center of the lid structure 108 to provide an easy reference point for welding. However, it should be appreciated that the recess / protrusion are not required and both the current collector plate 106 and the underside of the lid structure 108 could be flat. However, an advantage of the recess / protrusion is that the thinning of the lid plate 110 allows for improved welding thickness ratios. Stated differently, when the current collector plate 106 and the lid plate 110 are of a similar thickness, it may be easier to achieve a successful weld.

[0030] The terminal part 112 functions as the positive terminal of the cell 100 and can be attached to an external load by connecting a bus bar to the outer surface of the terminal part 112, for example by laser welding.

[0031] To prevent the electrode assembly 104 from moving inside the cylindrical can 102, a beading groove 118 is optionally provided around the circumference of the can 102. The beading groove 118 also provides a shelf for positioning the lid structure 108. Hence, the beading groove 118 is advantageously provided near the can opening, adjacent to or just below the lid structure 108. The can 102 is closed by crimping the can edge over the lid structure 108 and gasket 122, thereby forming a closed can.

[0032] The negative terminal may be provided by an additional terminal structure on the other end of the can (not shown), which is electrically connected to the negative electrode. Alternatively, the negative electrode may be connected to the can, such that the entire surface of the can functions as the negative terminal. To avoid a short circuit between the negative can and positive lid structure, gasket 122 may then be provided around the edge of the lid plate 110.

[0033] It should be noted that when the negative electrode is connected to the can 102, the crimped edge 120 will also form part of the negative terminal. This provides the possibility to connect the external load to both terminals on the same side of the cell 100, which may facilitate the assembly of large numbers of cells into e.g. modules or packs.

[0034] As mentioned above, secondary cells are typically provided with a safety vent to allow gases to escape the cell in a controlled manner in case of a thermal event. In known solutions, the vent may be placed on the bottom of the can (i.e. the side opposite to the lid structure in Figure 1). However, venting on the bottom may not always be desirable as it may interfere with other components in the energy storage system or vehicle. Alternatively, a circular or oval rupture disc may be provided in a vent opening on the positive lid. A rupture disc on the positive lid may however require additional venting channels or spacing between the lid components to ensure sufficient venting area. Such a solution may also require a more complicated assembly process when connecting of the cell to the external load, to avoid the vent being blocked by connectors or bus bars.

[0035] According to some examples, a secondary cell 100 as illustrated in Figure 1 is therefore provided, wherein a surface portion of the terminal part 112 is configured for attachment to the external load, and the terminal part 112 is provided with at least one fracturable portion 124 outside the portion where the external load is attached. The fracturable portion 124 is configured to break when the pressure reaches a threshold level, thereby allowing gases and other ejecta to vent outside the cell 100. Because the fracturable portion 124 is located outside the portion where the external load is attached, there is less risk of the external connector or bus bar interfering with the venting function. Preferably, the fracturable portion 124 is rotationally symmetric around the portion where the external load (e.g. bus bar) is attached. This further facilitates the assembly of the cells with the external load (e.g. in a module, pack or vehicle), since the cell 100 can be placed in any rotational position before being connected.

[0036] In some variants, the fracturable portion 124 is provided around the connection portion between the terminal part 112 and the current collector plate 106, e.g. as an annular notch surrounding the welding area between the terminal part 112 and current collector plate 106. In this case, opening of the vent will also lead to a break in the connection between the current collector plate 106 and the terminal part 112. This will interrupt the current through the cell, thereby stopping or at least mitigating further thermal reaction. If the reaction inside the cell is more violent, driving a higher flow of gases and / or material, the current collector plate 106 itself or a portion thereof may also rupture, providing additional space for gases and material to vent outside the cell 100. Hence, an additional benefit of these variants is that there is no need for additional spacing or venting channels between the current collector plate 106 and lid structure 108. This reduces the need for additional components and increases the space available for the electrode assembly 104, thereby enabling a higher energy capacity without increasing the outer cell dimensions.

[0037] Although Figure 1 schematically illustrates the notch or weakened portion 124 provided on both sides of the terminal part 112, it should be understood that it is equally possible to provide the notch on only one side, as long as the properties of the notch (e.g. depth and width) are adapted to provide the desired opening behaviour.

[0038] In order to provide sufficient room for attaching the external load (e.g. bus bar or other connector), the fracturable portion 124 is in some variants located proximal to the raised edge 126 of the terminal part 112. For example, if the fracturable portion 112 is an annular notch, the diameter of the notch may be close to the diameter of the raised terminal part 112, so that a relatively large area is provided in the center of the terminal surface where the connector can be welded. In some examples, this means that the fracturable portion 124 is located in the range of 65-95% of the radial distance from the center of the terminal part 112 to the raised edge 126 of the terminal part 112, for example 2 / 3 of the radial distance from the center of the terminal part 112 to the raised portion of the disc.

[0039] The terminal part 112 may also be dimensioned such that it is relatively wide in relation to the diameter of the can 102. This further contributes to providing a sufficient welding area for the external load. In some variants, the diameter of the terminal part 112 is at least 50% of the diameter of the lid plate 110, preferably in the range of 50-75% of the diameter of the lid plate 110. In a particular example, the diameter of the terminal part 112 is 2 / 3 of the diameter of the lid plate 110. These variants may be combined with positioning the fracturable portion proximal to the raised edge 126 of the terminal part 112, as described in the previous paragraph, thereby providing an even larger surface for attaching the external load.

[0040] Figure 2 shows a secondary cell 200 similar to the one illustrated in Figure 1. However, in this example the terminal portion 112 is insulated toward the lid plate 110 by insulating portion 202. Insulating portion 202 may for example be comprised of a glass or ceramic material which can be interposed between and fused with both the lid plate 110 and the terminal portion 112. In this example the lid plate 110 is in electrical contact with the crimped portion 120, and thereby forms part of the negative terminal of the cell 200. This may advantageously provide a larger area for connecting to the negative side of the external load. An additional insulator 204 is provided between the lid plate 110 and the positive current collector plate 106 to avoid a short circuit. The additional insulator 204 may be a substantially ring-shaped structure of e.g. a rubber material. Optionally (not shown), the additional insulator 204 may extend partially down along the inside of can, providing additional insulation between the electrode 105 and the inside wall of the can 102. In a variant of this example, the can 102 is closed by laser welding instead of crimping. In this variant there is no crimping potion 120. Instead, the edge of the lid plate 110 is brought in contact with the can 102 and the border between lid plate and can is closed with a laser weld. Optionally the outer rim of the lid plate may be bent upwards so that the outer edge of the lid plate 110 meets the upper edge of the can 102, before laser welding the edge. Figures 3a, 3b and 3c illustrate different variants for providing the fracturable portion 124, which apply to the examples of both Figure 1 and Figure 2. Generally, the fracturable portion 124 can be a weakened portion or region, such as a notch. As shown in Figure 3a, the fracturable portion 124 may be provided in an annular shape around the center of the terminal portion 112. In another variant, illustrated in Figure 3b, the fracturable portion 124 comprises several weakened parts or regions which are positioned around the circumference of the terminal portion 112. A yet further variant is shown in Figure 3c. Here, the fracturable portion 124 forms a partial circle or C-shape, which will cause the vent to open like a door on a hinge. In this variant, the fractured part of the vent will stay connected to the lid structure instead of detaching and potentially damaging other cells or components.

[0041] Figure 4 illustrates an energy storage system comprising a plurality of secondary cells as described above in connection with Figures 1-3. The cells may be arranged in modules and / or packs within the energy storage system (not shown) and connected to a battery management system (not shown) which controls the operation of the cells.

[0042] Figure 5 illustrates an electric vehicle comprising a plurality of secondary cells as described above in connection with Figures 1-3. The cells may be arranged in modules and / or packs (not shown) within the vehicle and connected to a battery management system (not shown) which controls the operation of the cells.

[0043] While the above examples have described the solution in the context of a positive terminal structure, it should be appreciated that the polarity of the cell terminals could also be reversed. Hence, the examples apply equally well to a lid structure with a negative terminal part.

[0044] 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. Furthermore, the word "comprising" does not exclude the presence of other elements or steps than those listed. The disclosure is not limited to the embodiments disclosed but may be varied and modified within the scope of the claims.

Claims

Claims1. A secondary cell (100) comprising: a housing (102); an electrode assembly (104) arranged in the housing (102); a current collector plate (106) directly connected to an electrode (105) of the electrode assembly; a lid structure (108) comprising a lid plate (110) and a terminal part (112), wherein a surface portion of the terminal part is configured for attachment to an external load; the terminal part (112) is provided with at least one fracturable portion (124) outside the surface portion configured for attachment to the external load; and the terminal part (112) is directly connected to the current collector plate (106).

2. The secondary cell (100) according to claim 1, wherein the at least one fracturable portion (124) is rotationally symmetric around the surface portion.

3. The secondary cell (100) according to any one of claims 1-2, wherein the at least one fracturable portion (124) is a notch.

4. The secondary cell (100) according to any one of claims 1-3, wherein the at least one fracturable portion (124) is annular or circular in shape.

5. The secondary cell according to any one of claims 1-3, wherein a plurality of fracturable portions (124) are rotationally symmetrically arranged around the surface portion.

6. The secondary cell (100) according to any one of claims 1-5, wherein the surface portion of the terminal part (112) is raised relative to the lid plate (110).

7. The secondary cell (100) according to claim 6, wherein the fracturable portion (124) is located proximal to the raised edge (126) of the terminal part (112).

8. The secondary cell (100) according to any one of claims 6 or 7, wherein the fracturable portion (124) is located between 65-95% of the radial distance from the center of the terminal part (112) to the raised edge (126) of the terminal part (112).

9. The secondary cell (100) according to any one of claims 1-8, wherein the diameter of the terminal part (112) is between 50-75% of the diameter of the lid plate (110).

10. The secondary cell (100) according to any one of claims 1-9, wherein the current collector plate (114) comprises a protrusion (116) toward the lid structure (122), and the terminal part (112) comprises a corresponding recess (114).

11. The secondary cell (100) according to claim 10, wherein current collector plate (106) and the terminal part (112) are electrically connected at the interface between the recess (114) and the protrusion (116).

12. The secondary cell (100) according to any one of claims 1-11, wherein the housing (102) is a cylindrical can.

13. An energy storage system comprising the secondary cell of any one of claims 1-12.

14. A vehicle comprising the secondary cell of any one of claims 1-12.

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