Connecting piece intended to electrically connect a first metallic surface to a second metallic surface in an electrochemical generator, generator and associated process

Abstract

Connecting part for electrically connecting a first metallic surface to a second metallic surface in an electrochemical generator, generator, and associated process. The part (12) comprises a metallic body having a first electrical connection portion (30) to the first metallic surface and a second electrical connection portion (32) to the second metallic surface. At least one of the first electrical connection portion (30) and the second electrical connection portion (32) has a mounting face (38) for welding to the first or second metallic surface, respectively, and an opposite face (42) for applying welding power. The opposite face (42) for applying welding power has a roughened region (44). The roughened region (44) has a roughness Ra greater than 10 micrometers according to standard NF EN ISO 21920-3. Figure for the abbreviation: Figure 1

Description

Description Title of the invention: Connection piece intended to electrically connect a first metal surface to a second metal surface in an electrochemical generator, generator and associated processes

[0001] — The present invention relates to a connection part intended to connect elec- trically a first metal surface to a second metal surface in a electrochemical generator, the connecting part comprising a metal body having a first electrical connection part to the first me- metal and a second electrical connection part to the second metal surface- metal, at least one of the first electrical connection part and the second electrical connection part having a fixing face intended to be welded respectively on the first metal surface or on the second surface metallic and an opposite face of application of welding power, the face opposite application of a welding power having a rough region.

[0002] Such an electrical connection part is intended to be fixed in particular by laser welding by transparency between two parts in an electrochemical generator, for example a lithium-ion battery.

[0003] — The connecting part is in particular intended to be welded onto metal surfaces- copper, aluminum, or stainless steel metals of connecting elements, such as a tab and / or an electrode strip of an electrochemical harness, a output terminal, busbar, latch, etc.

[0004] — During laser transparency welding, part of the laser beam is reflected and does not contribute to the welding energy. For example, with the use of a length infrared wavelength (about 1070 nm), only about 5% of the beam energy laser for copper and 10% of the laser beam energy for aluminum is actually transmitted to the material to be welded to initiate the weld pool.

[0005] — In addition, depending on the variability of the surface state of the materials, the conditions delivery and different production batches, the absorption percentage is also variable. These variations in brightness are likely to cause per- heterogeneous welding forms between the different batches. The welding parameters must be adapted according to the different material states to obtain a weld compliant.

[0006] To overcome this problem, the welding energy applied to this part is increased. significantly and may be at the maximum technical limits of the laser (especially in terms of power), leaving no room for adjustment to the welding process. In addition, the risk of burning peripheral parts remains high, due to the significant energy required. A solution to this problem consists, according to EP 3 073 551, in making regularly spaced prints, for example in the shape of an inverted pyramid, in two directions located in a plane defined by the surface on which the laser is applied. This document also describes, for comparison, welds that are made on regions of low roughness and that fail. The creation of periodic patterns significantly reduces the reflections occurring on the surface, and therefore greatly increases the absorptivity of the treated material. Thus, the weld bead can be produced without having to operate the laser near its technical limits, and avoiding burning the peripheral parts. Such a connecting part can be further improved, in particular to simplify the manufacturing process and reduce the probability of having untreated areas. An aim of the invention is therefore to provide an electrical connection part which can be welded robustly between two metal surfaces of an electrochemical generator, without applying excessively high laser power, while simplifying the production of the part. To this end, the invention relates to a connection part of the aforementioned type, characterized in that the rough region has a roughness Ra greater than 10 micrometers according to standard NF EN ISO 21920-3. The connecting part according to the invention may comprise one or more of the following characteristics, taken in isolation or in any technically possible combination: - the rough region has a roughness Ra greater than 20 micrometers, according to standard NF EN ISO 21920-3; - the rough region has a roughness Ra of less than 50 micrometers, in particular less than 40 micrometers according to standard NF EN ISO 21920-3; - the rough region comprises less than 5% of the total surface area of ​​flat areas; - the rough region is devoid of flat areas; - the rough region has irregular roughness; - the metal body is made of copper, aluminum, or stainless steel; - the thickness of the metal body is less than 2 millimeters, and in particular between 200 micrometers and 2 millimeters. The invention also relates to an electrochemical generator, comprising: - a first metallic surface; - a second metal surface; - a connecting part as defined above, electrically connecting the first metal surface to the second metal surface, the fixing face being welded to at least one of the first metal surface and the second metal surface. The electrochemical generator according to the invention may comprise one or more of the following characteristics, taken in isolation or in any technically possible combination: - the first metal surface is defined on an electrical power output terminal, the second metal surface being defined in an electrochemical beam comprising at least one electrode; - the electrode of the electrochemical bundle comprises a strip, the connection part being connected to the strip: - the electrochemical generator is of the lithium-ion type. The invention also relates to a method for connecting a first metal surface to a second metal surface in an electrochemical generator, the method comprising the following steps: - provision of a connection part comprising a metal body having a first electrical connection part to the first metal surface and a second electrical connection part to the second metal surface, at least one of the first electrical connection part and the second electrical connection part having a fixing face intended to be welded respectively on the first metal surface or on the second metal surface and an opposite face for applying a welding power, the opposite face for applying a welding power having a rough region, the rough region having a roughness Ra greater than 10 micrometers according to standard NF EN ISO 21920-3. - application of welding power on the opposite face to achieve the weld between the first metal surface and / or the second metal surface and the connecting part. The method according to the invention may comprise one or more of the following characteristics, taken in isolation or in any technically possible combination: - the application of welding power is carried out by emitting a laser beam directed onto the rough region; - the process includes a preliminary step of forming the rough region, by stamping, by laser treatment, by ultrasonic treatment, and / or by chemical attack. The invention will be better understood by reading the following description, given solely by way of example, and made with reference to the appended drawings, in which: - [Fig.1] [Fig.1] is a simplified sectional view of an electrochemical generator comprising a first metal connection part according to the invention, connecting a coil-type electrochemical beam with an output terminal; - [Fig.2] [Fig.2] is a photograph illustrating a rough region with a roughness Ra greater than 10 micrometers for a connection part according to the invention, made of copper; - [Fig.3] [Fig.3] is a view similar to [Fig.2], the connecting part being made of aluminum; - [Fig.4] [Fig.4] is a schematic sectional view of a laser welding step in a method of connecting the connection part according to the invention; - [Fig.5] [Fig.5] is a view similar to [Fig.1] of the connecting part between a tab of an electrochemical beam of a prismatic element and a terminal of the prismatic element. A first electrochemical generator 10 according to the invention, provided with a connection part 12 according to the invention, is shown schematically in [Fig.1]. In this example, the electrochemical generator 10 comprises at least one electrochemical element 14 which, in the example of [Fig.1], is a cylindrical element. Alternatively, as will be described later with reference to [Fig.5], the electrochemical element 14 is a prismatic element, or a pocket. The electrochemical element 14 is for example of the lithium-ion type. The electrochemical element 14 comprises, in the example of [Fig.1], a bundle 16 of electrodes of opposite polarities. The electrode bundle 16 comprises an alternation of electrodes of a first polarity, for example positive, and electrodes of a second polarity, for example negative, and a separator separating each pair of electrodes of opposite polarities facing each other. In this example, the electrode bundle 16 is wound around a central axis Δ-Δ' and forms a coil. Advantageously, the electrochemical element 14 further comprises a container 20 containing the bundle of electrodes 16 and the connection part 12, and a cover 22, closing the container 20. The electrochemical element 14 further comprises terminals 18A, 18B carried by the cover 22. Terminals 18A, 18B are output terminals for supplying electrical power when the electrochemical generator 10 is discharging, and for receiving electrical power when the electrochemical generator is charging. Advantageously, terminal 18A is connected to the or each electrode of first polarity and terminal 18B is connected to the or each electrode of second polarity. In this example, the first polarity terminal 18A is mounted through the cover 22 while being electrically insulated therefrom by a gasket 24. The terminal 18A is connected to the electrode bundle 16 via a connection piece 12 according to the invention, The second polarity electrode 18B is directly mounted on the cover 22, being in electrical contact with the cover 22. The or each second polarity electrode is electrically connected to the second polarity terminal 18B via the container 20 and the cover 22. The connection part 12 extends here between a first metal surface present on the terminal 18A and a second metal surface present in the bundle 16. It extends in particular between one or more electrodes of first polarity of the bundle 16, and a metal surface of the terminal 18A. The connection part 12 has a first part 30 for electrical connection to the harness 16, welded to the harness 16 and a second part 32 for connection to the terminal 18A, welded to the terminal 18A. The connecting piece 12 is preferably made in the form of a thin metal body, in particular in the form of a metal strip 34. The metal strip 34 is for example formed from copper or a copper alloy. Examples of material forming the metal strip 34 are Cu-type copper (Cu-ETP) having a minimum mass of 99.9% copper, Cu-type copper (Cu-DHP), having a minimum mass of 99.9% copper, with a residual presence of phosphorus, or Cu-type copper (CU-OF), which is deoxidized, and which has a minimum mass of 99.95% copper. Alternatively, the metal strip 34 is made of aluminum, or aluminum alloy, or stainless steel. The thickness of the metal strip 34 is for example less than 2 mm, and is in particular between 200 μm and 2 mm, preferably between 300 μm and 600 μm. In the example shown in [Fig. 1], the metal strip 34 is folded. Here it has an intermediate portion 36 defining a plurality of successive folds. In its second part 32, the metal strip 34 comprises a fixing face 38 welded to a corresponding metal surface 40 of the terminal 18A. The metal strip 34 further has, in its second part 32 opposite the fixing face 38, a face 42 for applying welding power. As will be seen below, the application face 42 is intended, after application of the fixing face 38 to the metal surface 40, to receive a welding power, for example by being illuminated by a laser beam 50 providing a welding light power. The application face 42 thus receives the welding power from an external source, this power then being transmitted through the metal strip 34 to the fixing face 38 and into the metal surface 40. The application face 42 comprises a rough region 44, an example of which is illustrated in [Fig.2] for a copper metal strip 34 and another example is illustrated in [Fig.3] for an aluminum metal strip 34. The second part 32 of the metal strip 34 is fixed to the receiving surface 40 by a weld bead 46 connecting the fixing face 38 and the receiving surface 40. The weld bead 46 is produced by melting metal from the metal strip 34 and the terminal 18A in a contact zone and by solidifying the contact zone. As illustrated by [Fig.4], the weld bead 40 obtained is advantageously reduced in width L compared to its depth P. As seen in [Fig.2], the rough region 44 is formed of an irregular alternation of hollows and bumps. According to the invention, the rough region has a roughness Ra, greater than 20 um, as measured by Standard NF EN ISO 21920-3 of January 2022 (which cancels and replaces Standard NF EN ISO4288 of March 1998). Roughness Ra is defined as the arithmetic mean roughness, which is the arithmetic mean of the deviations from the mean line, over a maximum measuring length, as defined in standard NF EN ISO 21920-3. Preferably, the rough region has a roughness Ra of less than 50 μm, in particular less than 40 μm. The rough region 44 preferably comprises less than 5% of the total surface area of ​​flat areas. In particular, as illustrated in [Fig. 2], the rough region 44 is completely devoid of flat areas. The roughness of the rough region 44 is irregular and random. Thus, the pits and bumps have different direction, extent, and contour shapes, and are not periodic. Surprisingly, the use of such roughness, possibly irregular, and / or associated with an absence of a flat area in the rough region 44, favorably modifies the surface condition of the face 42 at the location where the welding power is applied. This modification significantly increases the percentage of light power absorbed by the application face 42 when a laser beam 50 is directed onto the rough region 44, which increases the energy transmitted to the weld pool. Thus, the power of the laser beam 50 can be reduced to produce a very robust weld bead 46, making it possible not to work at the maximum emission power of the laser beam 50, while avoiding damaging the regions adjacent or close to the rough region 44. The roughness extends only into the rough region 44 on the application face 42, while retaining a fixing face 38 devoid of macroscopic roughness to optimize contact with the metal surface 40. Furthermore, the reliefs formed on the application face 42 do not protrude relative to the periphery of the rough region 44. Such a surface treatment therefore allows a significant reduction in the welding energy required for a compliant weld and therefore less heating of the surrounding parts, as well as a greater margin for adjusting the laser beam parameters. This guarantees better stability of the welding process of the connection part 12. Preferably, the rough region 44 is formed by mechanical stamping, for example with a punch itself provided with a shape matching that of the rough region 44. In an advantageous variant, the connection part 12 is also produced by stamping. In this case, the punch making it possible to obtain the roughness of the rough region 44 is preferably integrated on the stamping tool of the connection part 12 allowing the shaping of the contour of the connection part 12. This makes it possible to obtain a better quality of welding, without affecting the price of the part. Alternatively, the stamping of the rough region 44 is carried out upstream of the actual stamping of the connection part 12, for example during the rolling of a metal strip intended to form the connection part 12 or during the unwinding of the metal strip before stamping. Alternatively, the rough region 44 is formed by laser or ultrasonic treatment, or by chemical etching. A method of electrically connecting a first metal surface to a second metal surface of the electrochemical generator 10, via a connection part 12 according to the invention, will now be described. In this example, the first metal surface is defined on terminal 18A, with the second metal surface being defined in beam 16. Initially, the connecting part 12 is provided. This providing step comprises, for example, providing a metal strip 34 devoid of a rough region 44, and forming a rough region 44 by mechanical stamping, for example using a punch having a shape matching that of the desired roughness. Alternatively, the rough region 44 is formed by laser or ultrasonic treatment, or by chemical etching. This being done, the fixing face 38 is applied to the metal surface 40 on which it is to be welded. The rough region 44 is placed opposite the area of the metal surface 40 in which the weld bead 46 is to be made. As illustrated by [Fig.4], a laser beam 50 is brought opposite the rough region 44. The laser beam 50 is directed and focused on the rough region. The laser beam 50 advantageously emits infrared light, in particular at a wavelength between 900 nm and 1200 nm, preferably between 1050 nm and 1100 nm. The laser beam 50 is for example provided by a Nd:YAG type laser (neodymium-doped yttrium-aluminum garnet). Thanks to the particular roughness of the rough region 44, the reflection of the laser beam 50 on the application face 38 is reduced, and the absorption of the energy of the laser beam 50 through the metal strip 34 and the metal surface 40 is increased. Thus, a weld pool is formed through the entire thickness of the metal strip 34, and partially through the metal surface 40 to which the metal strip 34 is to be welded. The weld pool brings molten metal from the metal strip 34 into contact with molten metal from the metal surface 40. When the weld pool cools, a solid weld bead 46 is thus produced. The particular roughness used at the application face 42 surprisingly leads to an increase in the energy absorbed within the metal strip 34, and beyond, up to the part on which the metal strip 34 is to be welded. Thus, the weld between the metal strip 34 and the part on which it is fixed is particularly robust. The surfaces adjacent to or / and in the vicinity of the rough region 44 are not significantly subjected to the power of the laser beam 50, which prevents them from being damaged. Therefore, it is not necessary to use the laser at maximum power, and the part is made very simply. In a variant, illustrated by [Fig. 5], the electrochemical element 14 is a prismatic element. The electrode bundle 16 comprises a stack of planar electrodes having electrical connection tabs 60A, 60B. The tabs 60A of the electrodes of first polarity are preferably grouped on one side of the prismatic element, while the tabs 60B of the electrodes of second polarity are grouped on another side of the prismatic element. In this example, a connecting piece 12 connects each group of tabs 60A, 60B to a respective terminal 18A, 18B. As previously described, on the connecting piece 12, the fixing face 38 to a metal surface 40 of the terminal 18A is provided with a rough region 44 presenting a roughness Ra, greater than 20 um according to standard NF EN ISO 21920-3. As a further variant, the connection part 12 connects other metal parts within the electrochemical generator 10, for example busbars, a latch or even connects two metal surfaces within the same part of the electrochemical generator 10. In a variant not shown of the previous embodiments, the first part 30 for electrical connection to the first metal surface and the second part 32 for electrical connection to the second metal surface each have a fixing face 38, welded respectively to the first metal surface and to the second metal surface and an opposite face 42 for applying a welding power having a rough region 44, As described previously, the rough region 44 has a roughness Ra greater than 10 micrometers according to standard NF EN ISO 21920-3. This is the case in particular for the welding between the first part 30 and the electrode bundle 16.

Claims

Claims

1. Connection piece (12) intended to electrically connect a first metal surface to a second metal surface in a electrochemical generator (10), the connecting part (12) comprising a metal body having a first connecting part (30) electrical to the first metal surface and a second part (32) electrical connection to the second metal surface, one at less than the first electrical connection part (30) and the second electrical connection part (32) before a face of fixing (38) intended to be welded respectively on the first metal surface or on the second metal surface and one side opposite (42) of application of welding power, the opposite face (42) of application of a welding power having a region rough (44), characterized in that the rough region (44) has a roughness Ra greater than 10 micrometers according to standard NF EN ISO 21920-3.

2. Connection part (12) according to claim 1, in which the region rough (44) has a roughness Ra greater than 20 micrometers, according to standard NF EN ISO 21920-3.

3. A connecting piece (12) according to any one of claims 1 or 2, wherein the rough region (44) has a roughness Ra in- less than 50 micrometers, especially less than 40 micrometers, according to standard NF EN ISO 21920-3.

4. A connecting piece (12) according to any one of the preceding claims. preceding, in which the rough region (44) comprises less than 5% in total surface area of ​​flat areas.

5. A connecting piece (12) according to claim 4, wherein the region rough (44) is devoid of flat areas.

6. A connecting piece (12) according to any one of the preceding claims. preceding, in which the rough region (44) comprises a roughness irregular.

7. A connecting piece (12) according to any one of the preceding claims. preceding, in which the metal body is made of copper, in aluminum, or stainless steel.

8. A connecting piece (12) according to any one of the preceding claims. preceding, in which the thickness of the metal body is less than 2 millimeters, and in particular between 200 micrometers and 2 millimeters meters.

9. Electrochemical generator (10), comprising: - a first metallic surface; - a second metal surface; - a connecting piece (12) according to any one of the claims previous, electrically connecting the first metal surface to the second metal surface, the fixing face (38) being welded on at least one of the first metal surface and the second metal surface.

10. An electrochemical generator (10) according to claim 9, wherein the first metal surface is defined on an output terminal (18A) of electrical power, the second metal surface being defined in an electrochemical beam (16) comprising at least one electrode.

11. Electrochemical generator (10) according to claim 10, wherein the electrode of the electrochemical beam (16) comprises a strip, the connecting piece (12) being connected to the strap.

12. Electrochemical generator (10) according to any one of the claims- indications 9 to 11, in which the electrochemical generator (10) is lithium-ion type.

13. A method of connecting a first metal surface to a second metal surface in an electrochemical generator (10), the process comprising the following steps: - provision of a connection part (12) comprising a me- metal having a first part (30) for electrical connection to the first metal surface and a second part (32) of rac- electrical connection to the second metal surface, at least one of the first electrical connection part (30) and of the second electrical connection part (32) having a fixing face (38) intended to be welded respectively on the first metal surface or on the second metal surface and an opposite face (42) application of welding power, the opposite face (42) application of a welding power having a region rough (44), the rough region (44) having a roughness Ra su- greater than 10 micrometers according to standard NF EN ISO 21920-3. - application of welding power on the opposite face (42) for carry out the welding between the first metal surface and / or the second metal surface and the connecting part (12).

14. | Method according to claim 13, wherein the application of the welding power is achieved by emitting a laser beam (50) directed at the rough region (44).

15. A method according to any one of claims 13 or 14, comprising a preliminary step of forming the rough region (44), by stamping, by laser treatment, by ultrasonic treatment, or / and by chemical attack.