DE102022132904A1 - WELDING CLAMP, METHOD FOR CONTACTING BATTERY CELLS AND CELL COMPOSITES - Google Patents

Abstract

The present invention relates to a welding clamp (110) for pressing contact lugs (106) of battery cells (102) onto a cell connector (108), wherein the welding clamp (110) has a pressure surface (114) and at least two elastic spring arms (116), wherein the spring arms (116) are bent in a U-shape and are arranged opposite the pressure surface (114), wherein the spring arms (116) are designed to be pushed onto a rear side (118) of the cell connector (108) and elastically deformed, while the pressure surface (114) is pushed onto the contact lugs (106) arranged on a contact surface (112) of the cell connector (108), wherein the pressure surface (114) is designed to press the contact lugs (106) onto the contact surface (112) of the cell connector (108).

Description

Technical area

The present invention relates to a welding clamp for pressing contact tabs of battery cells onto a cell connector, a method for contacting battery cells and a cell assembly of battery cells with at least one such welding clamp.

State of the art

The present invention is described below mainly in connection with the manufacture of batteries with pouch cells.

Pouch cells have contact tabs. To create a cell assembly, the pouch cells are stacked and their contact tabs are welded to cell connectors. To weld them, the contact tabs are pressed onto the cell connector using a holding-down device of a welding device and are connected to the cell connector, in particular by laser welding.

Laser welding allows heat input to be controlled and difficult material combinations, such as aluminum alloys and copper alloys, to be welded together.

Since welded joints of difficult material combinations have a reduced mechanical load-bearing capacity compared to welded joints of favorable material combinations, the pouch cells can be fixed in holding frames to minimize movements of the pouch cells.

Description of the invention

One object of the invention is therefore to provide an improved method for contacting battery cells and an improved cell assembly of battery cells using the simplest possible construction means. An improvement can, for example, relate to an improved durability of a cell assembly.

The object is solved by the subject matter of the independent claims. Advantageous developments of the invention are specified in the dependent claims, the description and the accompanying figures.

In the approach presented here, contact tabs of battery cells are clamped to the cell connector by a welding clamp, with which they are welded. The welding clamp is elastically deformed when pushed onto the contact tabs and the cell connector, thus pressing the contact tabs against the cell connector with a resulting spring force.

The approach presented here eliminates the need for hold-down clamps and allows a simplified welding device to be used. The welding clamp can press the contact tabs together in such a way that there are essentially no gaps between the contact tabs and the cell connector. This state can be referred to as zero gap.

When the cell assembly is in operation, the contact tabs can continue to be pressed against the cell connector by the weld clamp. Mechanical loads can be at least partially diverted from the weld seam by the weld clamp. The weld seam can therefore be subjected to less load. The durability of the cell assembly can be improved by the weld clamp. For example, battery cells with an increased change in volume during charging and discharging can be welded to the cell connector using such a weld clamp and can be used safely with the weld clamp.

According to a first aspect of the invention, a welding clamp for pressing contact lugs of battery cells onto a cell connector is proposed, wherein the welding clamp has a pressure surface and at least two elastic spring arms, wherein the spring arms are bent in a U-shape and are arranged opposite the pressure surface, wherein the spring arms are designed to be pushed onto a rear side of the cell connector and elastically deformed, while the pressure surface is pushed onto the contact lugs arranged on a contact surface of the cell connector, wherein the pressure surface is designed to press the contact lugs onto the contact surface of the cell connector with a spring force resulting from the elastic deformation of the spring arms.

According to a second aspect of the invention, a method for contacting battery cells is proposed, wherein a welding clamp according to the first aspect is pushed onto contact lugs of the battery cells and a cell connector, wherein during the pushing on, elastic spring arms of the welding clamp are elastically deformed when pushed onto a rear side of the cell connector and contact lugs of the battery cells are pressed by a resulting spring force from a pressure surface of the welding clamp onto a contact surface of the cell connector and clamped between the contact surface and the pressure surface. whereby the contact lugs pressed onto the contact surface are welded to the contact surface.

In other words, the pressure surface of the welding clamp is pushed onto the contact lugs of the battery cells, while the elastic spring arms of the welding clamp are pushed onto the back of the cell connector resting on the contact lugs and are elastically deformed in the process, whereby the contact lugs and the cell connector are clamped between the pressure surface and the spring arms with the resulting spring force, whereby the contact lugs pressed against the contact surface are welded to the contact surface.

According to a third aspect of the invention, a cell assembly of battery cells with at least one welding clamp according to the first aspect is proposed, wherein the welding clamp is pushed onto a cell connector of the cell assembly and contact lugs of the battery cells, wherein the spring arms of the welding clamp rest against a rear side of the cell connector and the pressure surface of the welding clamp presses the contact lugs onto a contact surface of the cell connector, wherein the pressed contact lugs are welded to the contact surface.

A battery cell can be a cell sealed in foil. The battery cell can be referred to as a pouch cell. The battery cell can have a positive pole and a negative pole. The positive pole and the negative pole can be designed as contact lugs made of metal foil or very thin metal strip. The contact lugs can be, for example, between 0.1 millimeters and 0.8 millimeters, in particular between 0.3 millimeters and 0.6 millimeters thick. The contact lugs can be referred to as tabs. The contact lugs can protrude from a weld seam in the foil. The contact lugs of the positive pole and the negative pole can be made of different metal materials. For example, the contact lugs of the positive pole can be made of an aluminum material, while the contact lugs of the negative pole can be made of a copper material.

A cell connector can be a plate made of metal material. The cell connector can be referred to as a busbar. The cell connector can in particular be made of a copper material. The cell connector can provide a large conductor cross-section for conducting high currents without increased losses. The cell connector can be about two millimeters thick, for example. The cell connector can be designed as a base for welding the contact lugs. A contact surface of the cell connector can be a top side of the cell connector. The back side can be an opposite surface of the cell connector.

The contact tabs can be welded to the cell connector by laser welding. The contact tabs can be connected to the cell connector in an electrically conductive manner by welding. The contact tabs can be connected to the cell connector by at least one weld seam that runs across approximately the entire width of the contact tabs. Several parallel weld seams can also be used. The weld seam can go through all the contact tabs into the cell connector. The battery cells can be connected electrically in parallel by welding. For example, between two and ten battery cells can be connected in parallel by a cell connector. In particular, between three and six battery cells can be connected in parallel.

A cell assembly can comprise a plurality of battery cells. The battery cells of the cell assembly can be stacked. The battery cells can be arranged in a frame or housing. The contact tabs can protrude from the frame or housing. The cell connector can be arranged on the side of the frame or housing. The cell assembly can be referred to as a battery module or as a battery.

A welding clamp can be a stamped and bent part made of a metal material. The welding clamp can be made of an iron material or bronze material, for example. The welding clamp can be wider than the contact lugs. A pressure surface can be substantially rectangular. The pressure surface can be at least as wide as the contact lugs. A spring arm can be aligned substantially transversely to the pressure surface. The spring arms can be connected to the pressure surface at opposite ends of the pressure surface. The spring arms can be bent out of a plane of the pressure surface by more than 180 degrees. The spring arms can be bent with a predefined radius. The spring arms can be bent away from the pressure surface at a free end to have an insertion bevel for sliding onto the back of the cell connector.

The contact tabs can be aligned transversely to the cell connector before the welding clamp is pushed on. When pushed on, the contact tabs can be bent by the pressure surface on the cell connector.

The pressure surface can be formed by at least one rib aligned transversely to the pressure surface be stiffened. A rib can be aligned essentially transversely to the plane of the pressure surface. The rib can significantly increase the bending resistance of the pressure surface. The rib enables the welding clamp to transfer the spring force across the entire width of the contact lugs. The rib can be bent out of the plane of the pressure surface. The rib can be bent out of the plane of the pressure surface in a direction opposite to the spring arms. The rib can define an edge of the pressure surface. The rib can be bent out of the pressure surface with a radius. The radius can make it easier to slide the pressure surface onto the contact lugs. The radius can lead the insertion bevel of the spring arms. This means that the pressure surface can be placed on the contact lugs first before the contact arms slide onto the back.

The pressure surface can be stiffened by two substantially parallel ribs. The ribs can run along two opposite sides of the pressure surface.

The pressure surface can have an elongated welding window for welding the contact lugs to the contact surface. The contact lugs pressed against the contact surface can be welded through the welding window of the welding clamp arranged in the pressure surface. A welding window can be a recess or a through-opening in the pressure surface. The contact lugs can be welded to the cell connector through the welding window. The welding clamp can remain unwelded. The welding window allows the welding clamp to apply the spring force to opposite sides of a welding area of the contact lugs. Small distances between the contact lugs can be achieved through the welding window.

The at least one rib can run parallel to an edge of the welding window. The rib can distribute the spring force evenly along the edge of the welding window.

The spring arms can be spaced apart from each other by at least one width of the contact lugs. The contact lugs can be arranged between the spring arms. The spring arms can act as a side stop when sliding on the welding clamp. The spring arms can specify a lateral position of the welding clamp.

The welding clamp can remain pushed onto the contact tabs and the cell connector after welding. The welding clamp can serve as a strain relief for the weld seam between the contact tabs and the cell connector. The welding clamp can increase the durability of the cell assembly.

The contact lugs can be inserted into an undercut on the spring arms before the welding clamp is pushed on. The undercut can prevent the welding clamp from being removed after welding. An undercut on the spring arms can locally make a distance between the spring arms smaller than the width of the contact lugs. When the contact lugs are welded to the cell connector, the undercut can be caught behind the contact lugs. This means that the welding clamp can no longer be removed after the contact lugs have been welded to the cell connector.

The undercut can also be formed by a strip of metal material connecting the spring arms in the area of the free ends. The contact lugs can then be threaded into an opening in the welding clamp defined by the spring arms, the pressure surface and the strip. The strip can be enclosed behind the contact lugs after welding.

Further contact tabs of further battery cells can be clamped between the contact surface of the cell connector and a further pressure surface of the further welding clamp by means of a further pushed-on welding clamp according to the first aspect. The further contact tabs pressed against the contact surface can also be welded to the contact surface. The further contact tabs can be arranged on an opposite side of the cell connector. The further welding clamp can be pushed onto the further contact tabs and the cell connector from an opposite direction to the first welding clamp. The further contact tabs can be pressed onto the cell connector in the direction of the first welding clamp. The welding clamps can also be pushed onto the cell connector and their respective contact tabs at the same time. The resulting forces when pushed on can compensate for each other. By welding contact tabs to both sides of the cell connector, the groups of battery cells connected in parallel can be electrically connected in series.

The additional welding clamp can be pushed onto the first welding clamp so that it touches it. The welding clamps can be welded together. By welding the welding clamps, the welding clamps can be arranged on the cell connector so that they cannot be lost. In particular, the stiffening ribs can be welded together during welding.

Short character description

• 1 zeigt eine räumliche Darstellung eines Zellverbunds gemäß einem Ausführungsbeispiel; und
• 2 zeigt eine Schnittdarstellung durch einen Zellverbund gemäß einem Ausführungsbeispiel.

Advantageous embodiments of the invention are explained below with reference to the accompanying figures. They show:

• 1 shows a spatial representation of a cell assembly according to an embodiment; and
• 2 shows a sectional view through a cell composite according to an embodiment.

The figures are schematic representations and serve only to explain the invention. Identical or equivalent elements are provided with the same reference numerals throughout.

Detailed description

1 shows a spatial representation of a cell assembly 100 according to an embodiment. The cell assembly 100 can be referred to as a battery module or as a battery. The cell assembly 100 has a plurality of battery cells 102 that are stacked within a housing 104 to form a stack. The battery cells 102 are pouch cells sealed in foil. Contact tabs 106 of the battery cells 102 protrude outwards through recesses in the housing 104. The contact tabs can be referred to as tabs of the battery cells 102. A group of four contact tabs 106 protrudes from each of the recesses. The contact tabs 106 of a group are electrically connected in parallel by a cell connector 108. For this purpose, a cell connector 108 is arranged between each two of the groups of four contact tabs 106. The contact lugs 106 of one of the groups are the positive poles of their battery cells 102 and the contact lugs 106 of the other group are the negative poles of their battery cells 102. The cell connector 108 arranged between the groups connects the groups electrically in series. The contact lugs 106 of the positive poles are made of an aluminum material. The contact lugs 106 of the negative poles are made of a copper material. The cell connectors 108 are made of a copper material.

The contact lugs 106 of one group are pressed onto one side of a contact surface 112 of the adjacent cell connector 108 by a pushed-on welding clamp 110. The contact lugs 106 of the other group are pressed onto the other side of the contact surface 112 by another welding clamp 110. To do this, the contact lugs 106 have been bent from the sides of the cell connector 108 onto the contact surface 112 by the welding clamp. The contact lugs 106 of both groups have therefore been bent towards each other by a welding clamp 110 each. In this position, the contact lugs 106 of both groups are welded to the cell connector 108.

The contact lugs 106 are clamped between a pressure surface 114 of their welding clamp 110 and the contact surface 112 in such a way that they lie directly against one another and have almost no air gaps. The air gaps are in particular smaller than 50 µm. The contact lugs 106 are pressed onto the contact surface 112 with a spring force that results from a restoring force of an elastic deformation of spring arms 116 of the welding clamps 110. The spring arms 116 are bent in an arc shape by more than 180 degrees in the direction of a rear side 118 of the cell connector 108. The deformation is caused by the ends of the spring arms 116 being pushed onto the rear side 118 of the cell connector 108. When pushed on, the pressure surface 114 and the ends of the spring arms 116 are pressed apart by a combined material thickness of the contact lugs 106 and the cell connector 108.

In one embodiment, the pressure surface 114 is arranged between the spring arms 116 and is stiffened by two ribs 120. The ribs 120 are bent essentially perpendicularly from a plane of the pressure surface 114 away from the contact lugs 106 or from the spring arms 116.

In one embodiment, the pressure surfaces 114 each have a welding window 122. The contact tabs 106 are welded to the cell connector 108 by laser welding through the welding window 122. In this case, all contact tabs 106 are welded through to the cell connector 108 without any additional material. The cell connector 108 serves as a weld pool protector and protects the battery cells 102 from damage.

The welding clamps 110 remain pushed onto the contact lugs 106 and the cell connector 108 even after the contact lugs 106 have been welded to the cell connector 108. After welding, the spring force relieves the weld seam of mechanical stress and thus increases the durability of the cell assembly 100.

In one embodiment, the contact lugs 106 of a group are inserted behind an undercut of the welding clamp 110 before the welding clamp 110 is pushed on. As a result, the undercut is locked between the contact lugs 106, the cell connector 108 and the housing 104 when the contact lugs 106 are welded to the cell connector 108 and can no longer be pulled off the contact lugs 106 and the cell connector 108. The undercut serves as a loss protection for the welding clamp 110.

2 shows a sectional view through a cell assembly 100 according to an embodiment. The cell assembly 100 essentially corresponds to the cell assembly in 1 Here, the contact lugs 106 of one group have a higher material thickness than the contact lugs 106 of the other group. As a result, the thicker contact lugs 106 would be pressed against the cell connector 108 with a higher contact force than the thinner contact lugs 106. In order to obtain approximately the same contact forces, a welding clamp 110 with a larger opening width between the pressure surface 114 and the spring arms 116 is used for the group of thicker contact lugs 106 than for the group of thinner contact lugs 106.

In one embodiment, free ends of the spring arms 116 are slightly bent to obtain insertion bevels for sliding on. When sliding on, the insertion bevels slide along an edge of the rear side 118 and thus cause the elastic deformation of the spring arms 116.

In order to simplify the sliding and bending of the contact lugs into a plane of the contact surface 112, at least the front rib 120 in one embodiment has a bending radius along its bending edge from the plane of the pressure surface 114.

In the following, possible embodiments of the invention are summarized again or presented using slightly different wording.

A securing clamp for welding tabs of pouch cells is presented.

The electrical contact elements of pouch cells are called tabs. These are thin metal strips that are often made of copper or aluminum. When building a module or a battery system, i.e. a cell assembly made of individual pouch cells, the tabs are bonded to one another. The bonded connection can be made by laser welding. In this joining process, a so-called zero gap is created between the joining partners before welding begins. After welding, mixed joints in particular, in which copper and aluminum are joined together, for example, have little mechanical strength.

Especially when using new types of lithium-ion batteries, the cells are subject to constant changes in thickness due to swelling, which exerts a permanent mechanical alternating load on the tabs.

The approach presented here describes a clamp around the welded connection of the tabs, the function of which is to create a zero gap during laser welding and then remain there. This also provides mechanical strain relief for the tabs during operation. This also protects a mixed material connection against material fatigue and failure under alternating mechanical loads.

Up to now, the zero gap has been created using a hold-down device that is only put in place during the welding process. Up to now, the alternating mechanical load during operation has been reduced by using inserts that compensate for the swelling. In addition, previous pouch cells have significantly reduced swelling, which means that the problem can also be minimized by using plastic molded parts or cell holding frames.

With new types of cells with significantly greater swelling, this is no longer possible or requires greater construction and material effort.

The safety clip can be used, for example, on modules for super-fast charging. The safety clip can also be used on any other module with pouch cells.

In production, the laser welding of pouch cells is simplified because there is no need to handle a complicated welding device. At the same time, the welded joint is protected from mechanical alternating stress during operation. The safety clip reduces the design effort, particularly when using the new cell chemistry with large swelling. In addition, the safety clip can be designed in such a way that it grips behind the tabs and cannot be removed or come off again after the tabs have been welded (loss protection).

A safety clip is presented in the welding area of contact elements in pouch cells, whereby the safety clip is attached before the welding process and then remains there during operation of the battery. The pouch cells are rechargeable pouch cells with lithium-ion chemistry. The safety clip can be shaped in such a way that it is secured against loss after the welding process. The safety clip has a recess for the welding area. Several pouch cells form a module or a battery system. The module or battery system is in a vehicle. The locking clip is made of steel or spring bronze.

Since the devices and methods described in detail above are exemplary embodiments, they can be modified to a large extent by those skilled in the art in the usual way without departing from the scope of the invention. In particular, the mechanical arrangements and the size relationships of the individual elements to one another are merely exemplary.

LIST OF REFERENCE SYMBOLS

100

Cell network

102

Battery cell

104

Housing

106

Contact flag

108

Cell connectors

110

Welding clamp

112

Contact surface

114

Pressure surface

116

Spring arm

118

back

120

rib

122

Welding window

Claims (12)

Welding clamp (110) for pressing contact lugs (106) of battery cells (102) onto a cell connector (108), wherein the welding clamp (110) has a pressure surface (114) and at least two elastic spring arms (116), wherein the spring arms (116) are bent in a U-shape and are arranged opposite the pressure surface (114), wherein the spring arms (116) are designed to be pushed onto a rear side (118) of the cell connector (108) and elastically deformed, while the pressure surface (114) is pushed onto the contact lugs (106) arranged on a contact surface (112) of the cell connector (108), wherein the pressure surface (114) is designed to press the contact lugs (106) onto the contact surface (112) of the cell connector (108) with a spring force resulting from the elastic deformation of the spring arms (116). to press. Welding clamp (110) according to Claim 1 , in which the pressure surface (114) is stiffened by at least one rib (120) aligned transversely to the pressure surface (114). Welding clamp (110) according to one of the preceding claims, wherein the pressure surface (114) has an elongated welding window (122) for welding the contact lugs (106) to the contact surface (112). Welding clamp (110) according to Claim 2 and 3 in which the rib (120) runs parallel to an edge of the welding window (122). Welding clamp (110) according to one of the preceding claims, in which the spring arms (116) are spaced from each other by at least one width of the contact lugs (106). Method for contacting battery cells (102), wherein a welding clamp (110) according to one of the Claims 1 until 5 is pushed onto contact lugs (106) of the battery cells (102) and a cell connector (108), wherein during the pushing on, elastic spring arms (116) of the welding clamp (110) are elastically deformed when pushed onto a rear side (118) of the cell connector (108), and contact lugs (106) of the battery cells (102) are pressed by a resulting spring force from a pressure surface (114) of the welding clamp (110) onto a contact surface (112) of the cell connector (108) and are clamped between the contact surface (112) and the pressure surface, wherein the contact lugs (106) pressed onto the contact surface (112) are welded to the contact surface (112). Procedure according to Claim 6 , in which the welding clamp (110) remains pushed onto the contact lugs (106) and the cell connector (108) after welding. Method according to one of the preceding claims, in which the contact lugs (106) are inserted into an undercut on the spring arms (116) before the welding clamp (110) is pushed on, the undercut preventing removal of the welding clamp (110) after welding. Method according to one of the preceding claims, in which the contact lugs (106) pressed against the contact surface (112) are welded by a welding window (122) of the welding clamp (110) arranged in the pressure surface (114). Method according to one of the preceding claims, in which further contact lugs (106) of further battery cells (102) are connected by a further pushed-on welding clamp (110) according to one of the Claims 1 until 5 between the contact surface (112) of the cell connector (108) and a further pressure surface (114) of the further welding clamp (110) and the further The contact lugs (106) are also welded to the contact surface (112). Procedure according to Claim 10 , in which the further welding clamp (110) is pushed onto the welding clamp (110) when pushed on and the welding clamps (110) are welded together. Cell assembly (100) of battery cells (102) with at least one welding clamp (110) according to one of the Claims 1 until 5 , wherein the welding clamp (110) is pushed onto a cell connector (108) of the cell assembly (100) and contact lugs (106) of the battery cells (102), wherein the spring arms (116) of the welding clamp (110) rest against a rear side (118) of the cell connector (108) and the pressure surface (114) of the welding clamp (110) presses the contact lugs (106) onto a contact surface (112) of the cell connector (108), wherein the pressed-on contact lugs (106) are welded to the contact surface (112).

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