SE2350757A1

SE2350757A1 - Current collector for battery cell

Info

Publication number: SE2350757A1
Application number: SE2350757A
Authority: SE
Inventors: Sanz Daniel Garcia; Danny Naar; Hong Hyeon Lee
Original assignee: Northvolt Ab
Priority date: 2023-06-20
Filing date: 2023-06-20
Publication date: 2024-12-21
Also published as: WO2024261057A1

Abstract

There is disclosed herein a current collector (114), a method (300) of manufacturing such a current collector (114), and a battery cell (100) comprising such a current collector (114). The current collector (114) comprises a first plate (114a) having a first side (114a) and a second side (114w) adjacent the first side (114l), a second plate (114b) extending from the first side (114w) of the first plate (114a) and perpendicular to the first plate (114a), and a third plate (114c) extending from the second side (114l) of the first plate (114a) and away from the second plate (114b).

Description

Technical Field The present disclosure relates to components for battery cells. ln particular, the present disclosure relates to an improved current co||ector for a battery cell, a method for manufacturing such a current co||ector from sheet metal, and a battery cell comprising such an improved current co||ector.

Background ln addressing climate change, there is an increasing demand for rechargeable batteries, e.g., to enable electrification of transportation and to supplement renewable energy. Such batteries typically comprise a number of battery cells coupled together to provide the desired voltage and current.

Rechargeable or 'secondary' batteries find widespread use as electrical power supplies and energy storage systems. For example, in automobiles, battery packs formed of a plurality of battery modules, wherein each battery module includes a plurality of electrochemical cells, are provided as a means of effective storage and utilization of electric power.

Several different form factors exist for the electrochemical cells applied in secondary batteries depending on their intended application field. ln automotive applications, the most common cell types are cylindrical, prismatic and pouch cells.

A battery cell stores electrical energy in an electrode assembly, which may be stacked, and referred to as an 'electrode stack', or rolled, and referred to as an 'electrode roll' or a 'jelly roll'. Stored electrical energy may then be collected and transferred to the terminals of the battery cell via current collectors, which may be adapted for (electrical) connection to the terminal(s) and to the electrode assembly. One current co||ector may connect between an anode of the electrode assembly and an anode terminal (or negative electrode), while another current co||ector may connect between a cathode of the electrode assembly and a cathode terminal (or positive electrode).

Summary lt is realized as a part of the present disclosure that various Iimitations are placed upon the dimensions of current collectors if they are to be used in cells having only a single electrode assembly ('jelly roll'). ln such cells, the electrical energy stored in the jelly roll is transferred via a current collector to the terminal using a single electrical connection (current path) therebetween. Thus, the Iimitations placed upon the dimensions of the current collectors include the space available within the confines of the battery cell's casing (e.g. maximum width or height), an anticipated current flow through the current collector, a heat generation from Ohmic heating, etc.

However, it is further appreciated as part of the present disclosure that a single current path may be advantageously provided by the current collector while abiding by these Iimitations.

To address these considerations and others, according to an aspect of the present disclosure, there is provided a current collector for a battery cell, comprising a first plate having a first side and a second side adjacent the first side. The current collector further comprises a second plate extending from the first side of the first plate and perpendicular to the first plate.

When installed into a battery cell having an electrode assembly, the first plate is arranged along an edge of the electrode assembly, preferably in a manner that presents a flat surface to the edge of the electrode assembly. The third plate, extending from the first side of the first plate, is configured for attachment to the electrode assembly, e.g., by presenting an attachment surface to which electrode tabs extending from the electrode assembly can be welded or otherwise attached.

The second plate is arranged along a second side of the electrode assembly, configured for attachment to a terminal of the cell. ln this way, a current path is formed from the electrode assembly (e.g., the cathode or anode sheets thereof), to the current collector via the connection therewith of the electrode tabs, and therefrom to the terminal of the cell, which may be the positive or negative terminal. 3 Prior art cells (particularly prismatic cells) contain a plurality of electrode assemblies, each being connected (via anode and cathode connections) to respective current collectors. Accordingly, current collectors in such prior art cells typically comprise a plurality of 'legs' (being essentially different attachment plates) which each require attaching to corresponding electrode tabs from each respective electrode assembly of the plurality of electrode assemblies. That is, for each of the cathode and anode sides of such prior art cells, a plurality of welding connections are required between the electrode assemblies and the current collector.

By contrast, the current collector described herein advantageously allows for a single electrode assembly - i.e., an electrode assembly consisting of a single jelly roll. Thus, only one current path (per side) is required, thereby greatly simplifying a welding attachment process between the electrode assembly and the current collector.

The arrangement of the first and second plates perpendicular to each other may allow for the installation of the current collector around a corner, such as a right-angled corner. For example, in a prismatic cell having a substantially cuboidal shape and containing a substantially cuboidal electrode assembly, the current collector may be welded, clamped, slotted, or otherwise attached to the electrode assembly, via electrode tabs protruding from an edge thereof (e.g. along a height of the prismatic cell).

The current collector may then connect at the other end to the terminal of the prismatic cell which may be arranged at an adjacent side of the electrode assembly (e.g., along a length of the prismatic cell). Such current collectors may be referred to by those skilled in the art as 'side current collectors". When referring to prismatic cells in this way, the battery cell preferably has a length greater than its height.

A current path is thus defined from the first end to the second end such that electrical energy stored in the electrode assembly can be transferred to the terminal of the cell via the current collector. Similarly, electrical energy for storage in the electrode assembly can be provided thereto via the current collector by connecting a source of electrical energy to the terminal. 4 lt is often desirable to maximize the current flow in the current path while minimizing the space taken up by the current collector in the casing, to be able to provide a battery cell with improved efficiency, which is of high relevance in applications using a single jelly roll, as well as a capability of fast charging and discharging.

With one jelly roll, the current flow has only one current path, while the requirements of battery efficiency and fast charging may be maintained. Thus, the heat generation in the current collector may increase in comparison to the heat generated in a cell having multiple current paths. An increased heat generation leads to an increased risk of damaging the cell. Moreover, it is appreciated as a part of the present disclosure that attempting to mitigate this risk by increasing the size of the current collector, a size of the battery cell may be undesirably increased.

Therefore, it is realized as a part of the present disclosure that an advantageous configuration of the current collector, to address these desires and limitations, comprises the first and second plates as mentioned, the second plate extending from the first side of the first plate and being perpendicular to the first plate, and a third plate extending from the second side of the first plate and away from the second plate.

Thus, a surface of the first plate may present an abutment surface to the electrode assembly, that is preferably flush against the edge of the electrode assembly, to thereby reduce the internal volume of the casing required to house the current collector. The first plate is preferably substantially flat, such that the surface of the first plate presenting the abutment surface may be the substantial entirety of the face of the first plate. ln the event of a crush event along the edge of the electrode assembly, for example caused by dropping of the battery cell or an external impact such as during a car crash, etc, the current collector may be pushed into the electrode assembly. However, it will be appreciated that the abutment surface of the first plate may push the electrode assembly rather than penetrate it, due to it being formed as a plate and being positioned to abut the edge electrode assembly. Therefore, the external force acting on the first side of the battery cell, may be advantageously distributed over the area of the abutment surface and/or the entire area of the first plate. Thus, during a crush event, a penetrating damage to the electrode assembly is advantageously mitigated. ln one example, the first plate may have a substantially rectangular shape. This is advantageous for example in the case where the current collector is used in a prismatic cell with a substantially cuboidal shape. Furthermore, a rectangular shape is easy to manufacture, and thus facilitates production of the current collector. The rectangular shape of the first plate may then be dimensioned such that its height and/or width are maximized and correspond to a shape of the edge of the electrode assembly, thereby enhancing protection during a crush event, without excessive uptake of the cell's internal volume.

Further, the maximized dimensions may further enable an increased heat dissipation of the first plate and a reduced electrical resistance for the current path, i.e., the current collector may work as a heat sink for the electrode assembly. Thus, an advantage of the present disclosure is that it may mitigate the risk of overheating the electrode assembly, potentially causing damage to the cell. ln some refinements, at least the first plate may comprise a ribbing or corrugation to enhance the structural rigidity of the first plate and to further enhance the performance of the first plate as a heat sink.

As the third plate extends from the first plate along the second side thereof, and away from the second plate, the third plate will extend away from the electrode assembly when the current collector is arranged in the cell, e.g., around a corner of an electrode assembly having a substantially cuboidal shape.

The third plate may thus increase the structural resiliance of the current collector. Further, it may ensure the position of the current collector in the cell in the length direction, and may to this end engage with or abut a side insulator arranged between the current collector and the casing of the cell. ln preferred examples, the current collector is formed as a bent metal sheet. The current collector may be formed by bending the metal sheet such 6 that the first side of the first plate is formed together with the second plate, wherein the second plate extends from the first plate along the first side thereof. ln other words, the first plate may be bent in one direction to form the second plate, perpendicular to the first plate. Further, the metal sheet may be bent along the second side of the first plate in a second direction different from the first direction, to form the third plate, e.g., as a flange along the first plate. The third plate may thus extend away from the second plate.

Put another way, the first plate may have two opposite surfaces, where the second and third plates may extend from opposite sides of said surfaces. By forming the first, second and third plates of the current collector from a single bent metal sheet, an increased consistency of electrical impedance throughout the current collector along the current path may be maintained. Further, assembling the current collector does not require joining of any separate pieces together, or additional machining steps such as riveting or welding, thereby simplifying the construction of the current collector. Moreover, any such joins in a multi-part current collector may risk forming thermal or electrical 'hot-spots', which are thus mitigated through the forming of the current collector as a single piece.

A flange form for the third plate may advantageously be formed through conventional mass production techniques, known to those skilled in the art. Further, the third plate may form a reinforcement structure for the first plate, to thereby mitigate deformation of the current collector during a crush event. The third plate may further act to reinforce the casing of the cell along the side said third plate extends. Forming the third plate as a flange may thus provide structural stability in terms of distributing the force over the first and third plates during impact of an external force acting on the battery cell, and current collector.

The third plate may be perpendicular to the first plate. A perpendicular arrangement of the first and third plates increases the structural stability offered by the third plate to the first plate, and thus current collector, and furthermore enables an ease of connection between the electrode assembly and the current collector, if the electrode assembly is formed as an electrode 7 stack having stacked electrode sheets that extend in the same direction as the third plate (i.e., perpendicular to the first plate, which is substantially flush against the edge of the electrode assembly). ln a preferred example, the first plate and the second plate are joined along a substantial majority of the first side of the first plate. The current flowing through the current collector from the first plate to the second plate may thus flow substantially unimpeded. Hence, bottlenecks or uneven heat generation along the current path formed by the current collector can be advantagouesly mitigated. ln preferred examples, the joins between the plates are merely bends of an integrally formed, bent metal sheet. Thus, according to a further aspect of the present disclosure, there is provided a method of manufacturing the current collector from sheet metal, which may comprise machining a piece of sheet metal and then folding the sheet metal to provide the first, second and third plates, to thereby form the current collector. The machining of the sheet metal may comprise laser cutting, etching, drilling, sanding, stamping, and/or any other suitable machining process. The folding may then be performed manually or automatically using one or more folding machines. According to yet a further aspect of the present disclosure, there is provided a battery cell, comprising an electrode assembly and a current collector connecting the electrode assembly and a terminal of the battery cell.

The battery cell may be prismatic, having a length L greater than its height H, and a height H greater than its width W (i.e., W < H < L).

Electrode tabs (and/or additional foil tabs attached thereto) may protrude from a first edge of the electrode assembly, at a first side of the cell (along the height), and the terminals may be arranged at a second (i.e., top) side of the cell, the second side being adjacent to the first side.

The electrode assembly may thus have a substantially rectangular profile (e.g. as a result of having a substantially cuboidal shape), and the current collector may be arranged around a corner of the substantially rectangular profile of the electrode assembly. lt will be appreciated that, according to such an example, the current collector may preferably have the 8 first plate and the second plate angled at substantially 90 degrees to each other such that the vertex formed at their meeting may conform to the outer profile of the electrode assembly. Therefore a space efficient configuration of the current collector may be achieved. ln some further examples, the current collector may be arranged with a small gap to the electrode assembly. Such an arrangement may advantageously allow for the current collector to avoid colliding with (e.g. and risk causing damage to) the electrode assembly during normal movement or vibration of the cell.

The width of the first plate along the first side preferably substantially spans a width of the electrode assembly and/or a width of the casing. Such an embodiment of the current collector may advantageously improve the thermal properties as well as the electrical properties of the current collector, since a surface of the first plate may be maximized, as discussed above. ln any event, numerous advantages, some of which are described above, may be realized through a current collector as disclosed herein. These advantages as well as others, may be further appreciated through a description of specific illustrated embodiments.

Brief Description of the Drawings One or more embodiments will be described, by way of example only, and with reference to the following figures, in which: Figures 1A to 1D schematically show various views of a prismatic cell according to an example embodiment of the present disclosure; Figure 2 schematically shows a perspective view of a current collector according to aspects of the present disclosure; Figure 3 illustrates a method of manufacturing a current collector according to aspects of the present disclosure; and Figure 4 shows a piece of machined sheet metal for folding into a current collector according to aspects of the present disclosure.

Detailed Description 9 The present disclosure is described in the following by way of a number of illustrative examples. lt will be appreciated that these examples are provided for illustration and explanation only and are not intended to be limiting on the scope of the disclosure. Furthermore, although embodiments be presented individually for the sake of focused discussion of particular features, it will be recognized that the present disclosure also encompasses combinations of the embodiments described herein.

Figure 1A schematically shows a battery cell 100 according to aspects of the present disclosure, also referred to herein as simply a 'cell 100". ln the illustrated example, a prismatic battery cell 100 is shown having a cuboidal casing 102 that is longer that it is tall, and taller than it is wide. The height of the cell 100 may be referred to as the 'short side' of the cell 100. lt will be appreciated that the illustrated prismatic cell 100 is purely illustrative and that the presently disclosed aspects could, with appropriate adaptations, be applied to cylindrical secondary cells.

The cell 100 has terminals 104 on a same side, i.e., the top side of the cell 100 as illustrated, a failure vent 106 for venting gases from the cell 100, and an injection port 108 for introducing an electrolyte, also shown in figure 1B. The failure vent 106 and the injection port 108 are not discussed in detail herein and are not shown in figure 1C.

Figure 1C is a cross-sectional view of the cell 100, taken along line A-A shown in figure 1B, and shows the connection of the terminals 104 to an electrode stack 110 (which may also be referred to as an 'electrode assembly') comprised in the cell 100, via current collectors 114.

Particularly, the current collectors 114 are arranged around corners of the electrode stack 110 such that a first extension of each of the current collectors 114 extends along the top side of the electrode stack 110 (as illustrated) to connect to a terminal 104 electrically and mechanically on the top side of the cell 100. A second extension of each of the current collectors 114, angled relative to the first extension (i.e., at substantially 90 degrees), extends along the short side of the electrode stack 110 (i.e., the height) and is connected to the electrode stack 110 via electrode tabs 112 (also referred to herein as simply 'tabs 112') extending from the short sides of the electrode stack 110, as shown in more detail in figure 1D.

The arrangement of the current collectors 114 on the sides of the electrode stack 110, rather than, e.g., on an upper side thereof, allows for the height of the electrode stack to be increased and thus improves the energy density of the cell 100.

The cell 100 further comprises a number of spacers/insulators 116 configured to properly space the internal components of the cell 100 from one another and/or electrically and/or thermally insulate the internal components from the casing 102, which may be made from metal such as nickel-plated steel or aluminum, depending on the implementation of the aspects of the present disclosure.

During assembly of the cell 100, the upper end of the casing 102 may be a lid that is arranged to close an opening in the casing 102 after arrangement of the electrode stack 110 and the current collectors 114, welded thereto, into the opening of the casing 102.

Figure 1D schematically shows the connection of the electrode stack 110 to the current collector 114 in more detail, showing the region B indicated in figure 1B, taken along the cross-sectional line C-C as shown in figure 1C.

As shown in figure 1D, the electrode assembly 110 consists of a single electrode stack 110 having a stacking direction along the width of the cell 100. From an edge of the electrode stack 110, a plurality of electrode tabs 112 extend. The tabs 112 may be extensions of electrode sheets in the stack 110 (e.g., cathode or anode sheets) or may be attached to the electrode sheets, depending on the implementation.

The tabs 112 correspond to a single polarity of the electrode stack 110, such as the cathode or the anode, such that their connection together allows for a common cathode or anode connection. For example, if the tabs 112 are extensions from cathode sheets in the electrode stack 110, then the connection of the cathode sheets to the current collector 114 provides a cathode connection point at the terminal 104 to which said current collector 114 is connected. 11 The current collector comprises a section formed of the first and third plates, which has an extension in the height direction H of the cell 100, wherein the third plate extends in the length direction L of the cell 100 to thereby provide a surface to which the electrode tabs 112 can be welded. ln the illustrated example, the electrode assembly consists of a single electrode stack, and thus all of the tabs 112 extending from the electrode stack 110 are welded to the current collector 114, onto the surface of the third plate which faces the casing 102. lt will be appreciated that the shape and configuration of the tabs 112 is purely schematic in figure 1D. lt can be appreciated from this view that during a crush event, which pushes the current collector into the electrode stack 110, the first plate of the current collector 114 will present an abutment surface to the edge of the electrode stack 110. The abutment surface thus abuts the edge of the electrode stack 110 during the crush event and distributes the crushing force without risk of penetrating the electrode stack 110, thereby mitigating the risk of short circuiting during a crush event.

Moreover, it can be appreciated from this view how a connection of the electrode tabs 112 to the surface of the third plate simplifies a pre-welding process for the tabs 112 and/or the welding of the tabs 112 to the current collector 114, as the tabs 112 extend in the same direction as the extension of the third plate. During a crush event, it can be seen that a tearing of the electrode tabs 112 is mitigated, in synergy with the abutment of the first plate against the electrode stack 110, as the flange-like configuration of the third plate advantageously provides a reinforced structure with the first plate.

Figure 2 schematically shows, in isolation, the current collector 114 shown in figures 1C and 1D. The current collector 114 comprises a first plate 114a formed as a rectangle having a width along a first side 114w and a length along a second side 114l.

A second plate 114b extends at a right-angle from the first plate 114a, the second plate 114b and the first plate 114a being joined along the first side 114w of the first plate 114a. The second plate is also rectangular, but may in 12 other examples be configure for attachment to a terminal of a cell, e.g., through the provision of a through-hole or the like.

A third plate 114c extends as a ﬂange from the first plate 114a, the third plate 114c and the first plate 114a being joined along the second side 114l of the first plate 114a. The third plate 114c defines an angle ß to the first plate 114a which, in this angle, is substantially 90 degrees.

The width of the first plate 114a, i.e., along the first side 114w, preferably extends along a maximal width of the electrode stack. Thus, the resistance of the current path provided by the first plate 114a can be reduced, the thermal dissipation of the first plate 114a can be increased, and the protection offered by the first plate 114a during a crush event can be enhanced.

The connection of the first plate 114a to the second plate 114b is along the entirety of the first side 114w of the first plate 114a in the illustrated example. ln preferred examples, this connection is along at least a majority of the first side 114w, as this mitigates the formation of a 'bottleneck' along the current path provided by the current collector 114, which may place a limitation on a maximum possible current flow through the current collector 114. The same applies to the connection of the third plate 114c along the second side 114l of the first plate 114a.

The current collector 114 is formed as a single piece of folded sheet metal, as discussed in more detail in relation to figures 3 and 4. By forming the current collector 114 from a single piece of sheet metal, that is folded to thereby form the plates 114a, 114b, 114c as shown in figure 2, advantageous thermal, mechanical, and electrical properties are provided, as joins between separate pieces may be localized areas of higher resistance or weak spots.

A method 300 of manufacturing a current collector such as that shown in figures 1C, 1D, and 2 is illustrated in figure 3. As shown therein, the method 300 may first comprise machining 310 the sheet metal. Machining 310 the sheet metal may comprise any number of processes such as cutting, (e.g. using waterjets, lasers, etc.), drilling, shaving, stamping, and the like. The sheet metal may be provided with a constant width and/or thickness. 13 The method may then comprise a step of folding 320 the sheet metal, to thereby form a current collector, such as the current collector 114 shown in figures 1C, 1D and 2. The folding 320 may be performed manually or by automatic folding machines, depending on the implementation. Moreover, the folding 320 may be performed in one combined step or as a series of folding steps, depending on the implementation. Once folded, the current collector 114 may thereby comprise a first 114a and a second 114b plate perpendicular to each other for arranging around a corner of an electrode assembly 110 of a battery cell 100, and a third plate 114c, extending from the second side 114l of the first plate 114a, and extending away from the second plate 114b, as described above.

By manufacturing the current collector 114 according to such a method 300, a current collector 114, having many advantageous features as described above, may be produced rapidly at a large scale and for a low cost. The method may be readily automated as part of a wider cell manufacture and assembly process, for example.

Figure 4 illustrates a piece of sheet metal 400, according to an example implementation of the method 300 described above. The sheet metal 400 has been machined 310 according to the method 300 described above, and shown in a state prior to the folding 320 of the piece of sheet metal 400. The sheet metal comprises a first portion 401, a second portion 402 and a third portion 403. The figure further illustrates folding lines 404 and 405.

The sheet metal 400 is to be folded along the folding line 404 in a first direction, until the section 402 is perpendicular to the section 401, forming two joining plates. The first and second sections 401 and 402 may thus correspond to the first 114a and second 114b plates of the current collector 114. Further, the folding line 404 may correspond to the first side 114w of the first plate 114a.

Moreover, the sheet metal 400 is folded along the folding line 405 in a second direction, different from the first direction, until the third section 403 is substantially perpendicular to the first section 401. The section 403 may thus 14 correspond to the third plate 114c of the current collector 114 as shown in figures 1C, 1D and 2, and the folding line 405 may correspond to the second side 114| of the first plate 114 of the current collector 114.

While the present disclosure is susceptible to various modifications and alternative forms, specific embodiments are shown and described above by way of example in relation to the drawings, with a view to clearly explaining the various advantageous aspects of the present disclosure. lt should be understood, however, that the detailed description herein and the drawings attached hereto are not intended to limit the disclosure to the particular form disclosed. Rather, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the following claims.

Claims

1. A current collector (114) for a battery cell (100), comprising; a first plate (114a) having a first side (114w) and a second side (114l) adjacent the first side (114w); a second plate (114b) extending from the first side (1 14w) of the first plate (114a) and perpendicular to the first plate (114a); and a third plate (114c) extending from the second side (1 14l) of the first plate (114a) and away from the second plate (114b).

2. The current collector (114) according to claim 1, wherein the current collector (114) is formed as a bent metal sheet.

3. The current collector (114) according to claim 1 or 2, wherein the third plate (114c) is formed as a flange along the second side (1 14l) of the first plate (114a).

4. The current collector (114) according to any preceding claim, wherein the third plate (114c) is perpendicular (ß) to the first plate (114a).

5. The current collector (114) according to any preceding claim, wherein the first plate (114a) and the second plate (1 14b) are joined along a substantial majority of the first side (1 14w) of the first plate (114a). 16

6. The current collector (114) according to any preceding claim, wherein the first plate (114a) has a substantially rectangular shape.

7. A method (300) of manufacturing the current collector (114) according to claim 1, comprising: machining (310) a piece of sheet metal; folding (320) the sheet metal to provide the first (114a), second (114b) and third (114c) plates, and thereby form the current collector (114).

8. A battery cell (100), comprising: an electrode assembly (110); a current collector (114) according to any of claims 1 to 6, connecting the electrode assembly (110) and a terminal (104) of the battery cell (100).

9. The battery cell (100) according to claim 8, wherein: the electrode assembly (110) has a substantially rectangular profile; and the current collector (114) is arranged around a corner of the substantially rectangular profile of the electrode assembly (110).

10. The battery cell (100) according to claim 9, wherein: the second plate (114b) of the current collector (114) extends along the length of the electrode assembly (110). 5

11. The battery cell (100) according to claim 9 or claim 10, wherein: the first plate (1 14a) of the current collector (114) extends along the height of the electrode assembly (110).

12. The battery cell (100) according to any of claims 9 to 11, wherein: 10 the third plate (114c) extends away from the electrode assembly (110).

13. The battery cell (100) according to claim 11 or claim 12, wherein: the battery cell (100) comprises a casing (102); and the width of the first plate (1 14a) along the first side (114w) 15 substantially spans a width of the electrode assembly (110) and/or a width of the casing (102).

14. The battery cell (100) according to any of claims 8 to 13, wherein the battery cell (100) is substantially prismatic, having a length (L) greater than its 20 height (H); and the first plate (114a) and the third plate (1 14c) of the current 18 collector (114) are arranged to extend along the height of the electrode assembly (110).