METHOD FOR WELDING CELL INTERCONNECTORS AND WELDING ELECTRODE ARRANGEMENT FOR THIS PURPOSE

Description

[0001] The present patent application relates to a method for welding interconnectors of a lead-acid accumulator, the lead-acid accumulator, and a welding electrode arrangement therefor.

[0002] Conventionally, a lead-acid battery or a lead-acid accumulator for a vehicle has a housing comprising a plurality of chambers. These chambers are separated from one another by means of housing partitions. In each chamber (when the lead-acid accumulator is installed), an electrochemical cell is accommodated or arranged, wherein each electrochemical cell has a plurality of positive and negative electrode plates, which are separated from one another by means of a separator, in particular electrically separated from one another, and an electrolyte. The positive and negative electrode plates can be covered with a positive or negative pasty active mass, respectively, and optionally a pasting fleece can be arranged on the active mass, which holds the active mass on the respective electrode plate and prevents the active mass from detaching from the electrode plate.In order to tap or supply electrical current via the terminals of the lead-acid battery, the individual electrochemical cells are electrically connected to one another, allowing a series and / or parallel connection of the plurality of electrochemical cells to be formed. For this purpose, interconnectors of two adjacent electrochemical cells are welded together through the housing partition separating the adjacent electrochemical cells. The interconnectors are designed to be electrically connected to the plurality of positive electrode plates or the plurality of negative electrode plates, respectively.

[0003] Because the housing of lead-acid batteries is predominantly made of plastic to save weight, and the melting point of interconnectors made of lead or a lead alloy is higher than the melting point of the plastic material, plastic inclusions occur in the weld surface when the interconnectors of two adjacent electrochemical cells are welded. Such plastic inclusions represent a qualitative defect in the weld surface and thus reduce the strength of the weld surface. In conventional lead-acid batteries, the proportion of plastic inclusions in the weld surface is approximately 50% of the weld surface.

[0004] US 4 429 208 A relates to a conventional welding electrode arrangement for welding two interconnectors of two adjacent battery cells, wherein the welding electrodes have a circular conical welding projection and a circular ring-shaped forging area with a contacting surface concentrically surrounding the latter.

[0005] DE 24 55 348 A1 relates to another conventional method and a conventional device for producing an intercell connection in electrical accumulators by means of two opposing circular electrodes.

[0006] US 4,485,959 A relates to a conventional apparatus for forming through-the-partition intercell connection welds. The conventional welding electrodes are designed as circular welding protrusions.

[0007] The object of the invention is therefore to provide a method for welding interconnectors which reduces the proportion of enclosed plastic inclusions in the welding surface and which is at the same time simple and cost-effective to implement.

[0008] The object underlying the present invention is achieved in particular by a welding electrode arrangement according to the subject matter of independent patent claim 1 and by a method for welding one interconnector each of two adjacent electrochemical cells according to the subject matter of patent claim 7. Advantageous further developments are specified in the dependent patent claims.

[0009] In particular, the subject matter of the independent patent claim 1 relates to a welding electrode arrangement for welding one interconnector each of two adjacent electrochemical cells of an accumulator, in particular a lead-acid accumulator.

[0010] The interconnectors are separated from one another by means of a housing partition wall and are arranged opposite one another on opposite sides of the housing partition wall, wherein the housing partition wall has an opening in a region where the interconnectors are opposite one another.

[0011] For this purpose, the welding electrode arrangement has at least one pair of welding electrodes, wherein each welding electrode of the at least one pair of welding electrodes has an insert part which is designed to contact a corresponding interconnector and to weld the interconnectors through the opening in the housing partition wall in such a way that a surface proportion of plastic inclusions in the welding surface amounts to a maximum of 8% of the welding surface.

[0012] The insert part has a welding plate on the front side of which a welding projection is formed, which extends from the welding plate and has a recess.

[0013] The advantages of the present invention are obvious. In particular, by using an insert according to the invention for a welding electrode assembly, the quality of the weld can be increased. In particular, the strength of the connection and electrical conductivity are improved.

[0014] The recess helps to bypass the detected weak points of the conventional welding projection, thus creating a weld that has both higher or better mechanical and higher or better electrical properties.

[0015] Furthermore, only the insert needs to be replaced, while the remaining elements of the conventional welding electrode assembly can continue to be used.

[0016] This allows welding electrode assemblies that are already in operation to be retrofitted easily, cost-effectively, and quickly, which can reduce manufacturing, production, and assembly costs. Furthermore, downtime can be limited to less than 5 minutes, minimizing interruptions to the operation of the welding electrode assembly, further contributing to a reduction in assembly costs, which also include the costs for necessary downtime.

[0017] This also allows the quality of the battery to be increased and improved.

[0018] The insert can be calculated and simulated using a finite element method. This allows weak points in the conventional insert to be easily and cost-effectively identified and prevented. This leads to an improved weld surface and thus to higher weld quality.

[0019] According to a further aspect of the invention, the welding projection has at least substantially the shape of a prism with a base area of ​​a round-end rectangle and the recess has at least substantially the shape of a prism with a trapezoidal base area.

[0020] According to a further aspect of the invention, the welding projection has a contacting surface for contacting the interconnector, wherein the welding projection is tapered towards the contacting surface.

[0021] According to a further aspect of the invention, the contacting surface has an at least substantially U-shaped or C-shaped cross-section.

[0022] According to a further aspect of the invention, a protrusion is arranged on the back of the welding plate for inserting the insert part into a groove in the welding electrode that is designed complementarily to the protrusion, wherein the insert part can be or is fastened to the welding electrode by means of a fastening bore that is arranged on the back of the welding plate.

[0023] This allows for easy (and, above all, detachable) replacement of the insert, which can reduce assembly costs and time. It also simplifies centering of the insert.

[0024] According to a further aspect of the invention, the welding projection and / or the protrusion are formed integrally with the welding plate.

[0025] This advantageously reduces the manufacturing costs of the insert part, as it can be manufactured cost-effectively, for example, using a casting process with optional subsequent post-processing.

[0026] Furthermore, the subject matter of independent patent claim 7 relates to a method for welding interconnectors of two electrochemical cells of a lead-acid accumulator spaced apart from one another by a housing partition.

[0027] The two electrochemical cells are separated from each other by a housing partition, with the interconnectors arranged facing each other on two opposite sides of the housing partition. In other words, the two interconnectors are arranged on two opposite sides of the housing partition such that they are at least substantially congruent with each other. An opening is arranged in a region of the housing partition where the interconnectors are opposite each other. The method comprises the following steps: contacting the interconnectors with a welding electrode arrangement and welding the interconnectors.

[0028] The welding electrode assembly comprises at least one pair of welding electrodes, with each welding electrode of the at least one pair of welding electrodes contacting one of the interconnectors by means of an insert. The welding of the interconnectors is carried out in such a way that, by means of a pressure applied by the inserts of the welding electrodes and a current applied to the welding electrode assembly, the material of the interconnectors melts at least partially and forms a material bond through the opening in the housing partition wall, such that the resulting weld surface has a maximum area of ​​plastic inclusions of 8% within the weld surface.

[0029] The insert part has a welding plate, on the front side of which a welding projection is formed, which extends from the welding plate and has a recess.

[0030] In particular, by using an insert according to the invention for a welding electrode, the quality of the weld can be increased. In particular, the strength of the connection and electrical conductivity are improved.

[0031] Furthermore, only the insert needs to be replaced, while the remaining elements of the conventional welding electrode assembly can continue to be used.

[0032] This allows welding electrode assemblies that are already in operation to be retrofitted easily, cost-effectively, and quickly, which can reduce manufacturing, production, and assembly costs. Furthermore, downtime can be limited to less than 5 minutes, minimizing interruptions to the operation of the welding electrode assembly, further contributing to a reduction in assembly costs, which also include the costs for necessary downtime.

[0033] This also allows the quality of the battery to be increased and improved.

[0034] The recess helps to bypass the detected weak points of the conventional welding projection, thus creating a weld that has both higher or better mechanical and higher or better electrical properties.

[0035] According to a further aspect of the invention, the area proportion of plastic inclusions in the welding surface is less than 8%, in particular less than 4%.

[0036] This allows the quality of the weld - and in particular the electrical conductivity and strength of the connection - to be further improved, ensuring a more robust connection with better electrical properties.

[0037] The insert can be calculated and simulated using the finite element method. This allows weak points in the conventional insert to be easily and cost-effectively identified and prevented. This leads to an improved weld surface and thus to higher weld quality.

[0038] According to a further aspect of the invention, the welding projection has a shape which has been calculated and simulated such that the area proportion of plastic inclusions in the welding surface is a maximum of 8%, preferably less than 8%, particularly preferably less than 4%, of the welding surface.

[0039] This ensures that less waste is produced, which further reduces manufacturing costs.

[0040] According to a further aspect of the invention, the welding projection has the recess such that the cross section of the welding projection is at least substantially U-shaped or C-shaped.

[0041] This avoids the weak points caused by the conventional insert or conventional welding projection, which leads to an increase in quality.

[0042] According to a further aspect of the invention, the welding projection has a contacting surface which has an at least substantially U-shaped or C-shaped cross section, wherein the welding projection is tapered towards the contacting surface.

[0043] This avoids the weak points caused by the conventional insert or conventional welding projection, which leads to an increase in quality.

[0044] According to a further aspect of the invention, the interconnectors are welded using a through-the-partition (TTP) welding process.

[0045] This is a simple process that can further reduce manufacturing costs.

[0046] According to a further aspect of the invention, the interconnectors are welded at a welding temperature of 300°C to 380°C, in particular 300°C to 360°C, preferably 300°C to 340°C, particularly preferably 300°C to 320°C.

[0047] In particular, the welding temperature is in the range of the melting point of the interconnectors (±5°C) or only slightly (i.e., approximately 5°C to 15°C) above the melting point of the interconnectors, thereby advantageously reducing negative influences on the housing partition material, which has a lower melting point than the material of the interconnectors. This ensures that less stress is generated in the housing partition during the welding process and thus fewer plastic inclusions in the weld surface.

[0048] According to a further aspect of the invention, the housing partition wall is made of plastic having a melting point of 200°C to 250°C, in particular 220°C.

[0049] According to a further aspect of the invention, the housing partition wall is made of polyethylene, polypropylene, polyamide, polyoxymethylene or a copolymer thereof.

[0050] This ensures electrical insulation of the battery in a simple and cost-effective way and at the same time the weight of the battery can be reduced.

[0051] The welded interconnectors can withstand a torque of at least 12 Nm, and in particular at least 16 Nm. This allows the quality of the weld to be further improved.

[0052] According to a further aspect of the invention, a lead-acid accumulator is provided which comprises a housing with a plurality of chambers which are separated from one another by means of a plurality of housing partition walls, and a plurality of electrochemical cells, wherein in each case an electrochemical cell is arranged in a corresponding chamber, and wherein each electrochemical cell has two interconnectors for forming an electrical connection,

[0053] In this case, an interconnector of a first electrochemical cell and an interconnector of a second adjacent electrochemical cell are arranged opposite each other on two opposite sides of a housing partition wall, which spatially separates or divides the first and second electrochemical cells from each other. Furthermore, the housing partition wall has an opening in a region where the interconnectors are opposite each other, through which the interconnectors are connected or, in particular, welded to each other using the method described above. The connecting surface or, in particular, the welding surface has a surface proportion of plastic inclusions of a maximum of 8% of the welding surface.

[0054] This has the advantageous consequence that a lead-acid accumulator with improved electrical and mechanical properties can be provided, which is also simple and cost-effective to manufacture.

[0055] According to a further aspect of the invention, the welded interconnectors withstand a torque of at least 12 Nm, in particular of at least 16 Nm.

[0056] The invention is explained in more detail below, also with regard to further features and advantages, by means of the description of embodiments with reference to the accompanying drawings.

[0057] These show in: FIG. 1 shows a schematic representation of a vehicle; FIG. 2 shows a schematic representation of an insert part according to the invention for a welding electrode; FIG. 3 shows a schematic representation of a front view of the insert part according to the invention for a welding electrode; FIG. 4 shows a detailed view of the welding projection according to the invention; FIG. 5 shows a schematic representation of a side view of an insert part according to the invention for a welding electrode; FIG. 6 shows a schematic representation of a rear view of the insert part according to the invention for a welding electrode; and FIG. 7 shows a schematic representation of a front view of a conventional insert part for a welding electrode.

[0058] The method according to the invention and the welding electrode arrangement according to the invention are described below with reference to the illustrations in FIGS. 1 bis 7 described in more detail. Identical or equivalent elements and functions are provided with the same or similar reference symbols.

[0059] The supply of energy, especially electricity, to a vehicle is playing an increasingly important role with the ever-increasing number of energy consumers, especially electricity consumers, both in combustion engine-based vehicles and in electric vehicles and hybrid vehicles. In particular, starting a combustion engine generates high currents, which are provided by the vehicle's starter battery.

[0060] The vehicle can be an aircraft or watercraft, a tracked vehicle, an off-road vehicle, or preferably a road vehicle, where a road vehicle can be understood as a passenger car, a truck, a bus, or a mobile home. Furthermore, hybrid vehicles can be understood as any vehicle that has both an internal combustion engine and an electric motor as a power source. Hybrid vehicles can be subdivided into micro-hybrid, mild-hybrid, full-hybrid, and plug-in-hybrid vehicles.

[0061] Lead-acid batteries, or lead-acid accumulators, are primarily used as starter batteries. These are designed to provide the electrical power needed to start the engine. One type of lead-acid accumulator, for example, is an Absorbent Glass Mat (AGM) accumulator, in which the electrolyte is bound in a fiberglass mat. Compared to wet accumulators, in which the electrolyte is in liquid form, AGM accumulators have the advantage that no electrolyte can leak out, even if the accumulator is tipped over. AGM accumulators are also characterized by low internal resistance.

[0062] In the following, the lead-acid battery and the welding electrode assembly are described in such a way that relative terms refer to the installation state of the lead-acid battery. For example, "in an upper area" means an upper area as seen in the installed state of the lead-acid battery; "in a side area" means a front, rear, left, or right area as seen in the installed state and in the direction of travel; and "in a lower area" means a lower area as seen in the installed state.

[0063] FIG. 1 shows a schematic representation of a vehicle V. The lead-acid accumulator 10 can be arranged in a front area of ​​the vehicle V in the direction of travel, in a rear area of ​​the vehicle V and / or in an area below the seats, in particular below the driver's seat.

[0064] According to the presentation in FIG. 1 the lead-acid accumulator 10 is arranged in a front region of the vehicle, in particular in a front engine compartment below the front flap.

[0065] The lead-acid storage battery 10 has a housing configured to accommodate a plurality of electrochemical cells. For this purpose, the housing comprises a lower housing part defining an interior space, the upper side or upper side surface of which is open in the installed state, and a cover configured to close the upper side of the lower housing part, which is open in the installed state.

[0066] The housing base further comprises a plurality of housing partition walls arranged such that the interior of the housing base is divided into a plurality of chambers, each of which is designed to accommodate an electrochemical cell.

[0067] The housing base and the cover can be connected or joined to each other, in particular welded or welded, in such a way that a connection sealed against liquids and gases or gas mixtures can be created. For this purpose, the cover can be connected to the housing base, in particular, by a material and / or force fit. For example, the cover can be connected to the housing base via a screw connection.

[0068] The cover can have a positive terminal and a negative terminal, which can be electrically and mechanically connected to electrical consumers or loads. However, instead of the positive and negative terminals, the cover can equally well have at least substantially flat positive and negative electrical contact surfaces. This advantageously allows the size and, in particular, the height of the lead-acid battery 10 to be reduced.

[0069] The housing, i.e., the lower housing section including the housing partitions and the cover, can be made at least partially, in particular entirely, of plastic in order to make the lead-acid accumulator 10 as lightweight as possible. The material selected can be, for example, polyolefin, acrylonitrile butadiene styrene, polycarbonate, polyamide, polyvinyl chloride, polyethylene terephthalate, polyoxymethylene, or a copolymer thereof. In particular, the housing of the lead-acid accumulator 10 can be made of polyamide, polypropylene, or polyethylene, or a copolymer thereof.

[0070] The housing material has a melting point of 120°C to 260°C, in particular 150°C to 250°C, preferably 200°C to 250°C, particularly preferably 220°C to 240°C, in particular approximately 220°C. Approximately 220°C, in the context of the present application, means 220°C ±5°C.

[0071] However, it is equally conceivable to manufacture only the enclosure partitions from a plastic material described above. The enclosure base and / or cover can be made of metal or a metal alloy. However, in this case, electrical insulation of the enclosure must also be provided, arranged, and ensured.

[0072] Each electrochemical cell has a plurality of positive electrode plates and a plurality of negative electrode plates, wherein the plurality of positive electrode plates and the plurality of negative electrode plates are arranged alternately and spaced from one another and electrically separated by means of a separator.

[0073] The positive electrode plates can be covered with a positive paste-like active mass, which can optionally be covered with a pasting fleece that holds the positive paste-like active mass to the positive electrode plate and prevents the positive paste-like active mass from detaching. Similarly, the negative electrode plates can be covered with a negative paste-like active mass, which in turn can be covered with a pasting fleece that holds the negative paste-like active mass to the negative electrode plate and prevents the negative paste-like active mass from detaching from the negative electrode plate.

[0074] The electrochemical cell also contains an electrolyte. This can be in liquid form. It is also possible to use an electrolyte bound in a fiberglass mat. When an electrolyte is bound in a fiberglass mat, it is also referred to as an Absorbent Glass Mat (AGM) battery.

[0075] Each electrochemical cell further comprises a pair of interconnectors. Specifically, each electrochemical cell comprises a positive interconnector, which is electrically connected to the plurality of positive electrode plates, and a negative interconnector, which is electrically connected to the plurality of negative electrode plates. An electrical current is drawn from or supplied to the corresponding electrochemical cell by means of the positive and negative interconnectors.

[0076] The interconnectors of two adjacent electrochemical cells separated from each other by a housing partition are electrically connected to each other via the partition, in particular through an opening in the partition, so that the plurality of electrochemical cells are connected to each other in series and / or in parallel. This connection determines the total current or total voltage that can be delivered by the lead-acid battery 10. The nominal voltage of the lead-acid battery 10 is in particular approximately 12 V. For this purpose, the plurality of electrochemical cells are electrically connected to each other, in particular in series.

[0077] To connect the plurality of electrochemical cells in series, the positive interconnector of a first cell is electrically connected to the negative interconnector of a second adjacent electrochemical cell. Similarly, the positive interconnector of the second electrochemical cell is electrically connected to the negative interconnector of a third electrochemical cell adjacent to the second electrochemical cell, and so on. The negative interconnector of the first cell is electrically connected to the negative terminal of the lead-acid battery 10. Similarly, the positive interconnector of the last electrochemical cell is electrically connected to the positive terminal of the lead-acid battery 10, so that the accumulated voltage of the individual electrochemical cells can be tapped via the negative and positive terminals of the lead-acid battery 10.

[0078] To electrically connect the interconnectors of two adjacent electrochemical cells, an opening is provided or arranged in the housing partition wall through which the interconnectors of the adjacent electrochemical cells are electrically connected. In particular, a welded connection is formed between the interconnectors of the adjacent electrochemical cells.

[0079] For this purpose, an interconnector of a first electrochemical cell is welded through the opening in the housing partition to an interconnector of a second electrochemical cell spaced from the first electrochemical cell by the housing partition using a through-the-partition (TTP) welding process.

[0080] In particular, the electrical contacting of two interconnectors of two adjacent electrochemical cells, which are separated from each other by a housing partition, is carried out in such a way that an opening is arranged in the housing partition at the point at which the two interconnectors of the respective cells are opposite each other.

[0081] In other words, the interconnectors to be connected or welded are arranged at least substantially congruently on two opposite sides of the housing partition in a welding area of ​​the housing partition. In this context, "substantially congruent" means that the outlines of the interconnectors on two opposite sides of the housing partition overlap by at least 90% of the area they enclose, or that the outlines of the interconnectors are arranged (completely) congruently on the two opposite sides of the housing partition.

[0082] The opening is also located in the welding area. The opening has the contour of a rectangle with rounded corners or a rounded-end rectangle. A rounded-end rectangle is understood to be a rectangle whose end faces or shorter sides are at least substantially semicircular or rounded. In particular, the opening is shaped such that the longer side of the opening is smaller than the width of the interconnectors, so that the opening is completely covered and closed by the interconnectors.

[0083] For example, the opening may have an area of ​​80 mm 2< to 120 mm 2<, in particular 90 mm 2< to 100 mm 2<.

[0084] The interconnectors of many electrochemical cells are made of lead or a lead alloy. The melting point of lead or lead alloy is in the range of approximately 300°C to 350°C.

[0085] To carry out the method known as TTP welding, a welding assembly according to the invention is used. The welding assembly comprises at least one pair of welding electrodes according to the invention. Each pair of welding electrodes is designed to produce a welded joint; i.e., with a welding electrode assembly comprising six pairs of welding electrodes, six welded joints can be produced, particularly simultaneously. Each pair of welding electrodes can be assigned a control unit for monitoring and controlling the welding process. It is equally conceivable to provide or arrange a (central) control unit that monitors and controls all pairs of welding electrodes.

[0086] The method according to the invention and the welding electrode arrangement according to the invention are explained in more detail below using an example with a pair of welding electrodes. Of course, this embodiment is purely exemplary and also applies accordingly to welding electrode arrangements with at least one pair or more pairs of welding electrodes according to the invention.

[0087] In an exemplary embodiment, the welding electrode assembly comprises a pair of welding electrodes. Each welding electrode has a specifically designed insert 100 at a distal end. In particular, the welding electrode assembly is arranged such that each welding electrode with a specifically designed insert 100 engages a corresponding interconnector, specifically such that the inserts 100 of the welding electrodes contact and press the interconnectors together.

[0088] In particular, the pair of welding electrodes can be designed as a type of clamp that can apply a predetermined force to the interconnectors. For example, the interconnectors can be pressed together with a force of 4 kN to 10 kN, in particular 5 kN to 6 kN.

[0089] An electric current is then supplied to the welding electrodes in such a way that a welding temperature of approximately 300°C to 380°C, in particular 300°C to 360°C, and particularly preferably 300°C to 320°C, is achieved. This can be easily monitored using suitable sensors and maintained by means of a control unit connected to and communicating with the pair of welding electrodes.

[0090] When the welding temperature is reached, the interconnectors are melted, at least in part, at the point where the insert 100 rests against the interconnectors. The pressure applied by the welding electrodes forces at least a portion of the melted material of the interconnectors into the opening in the housing partition, so that the interconnectors arranged on both sides of the housing partition fuse together.

[0091] After a predetermined melting time, the welding electrode is held against the interconnectors for a defined holding time without current supply but with the application of a predetermined contact pressure, ensuring the melting or material bond of the interconnectors in the opening. This creates a weld between the interconnectors after the melted material of the interconnectors has solidified. For the purposes of this application, welding refers to the material bond between the interconnectors after the welding process has been carried out, with the connection being defined or distinguished by a weld surface created between the interconnectors.

[0092] The resulting welding surface corresponds at least substantially to the area of ​​the opening in the housing partition and preferably lies in a plane therewith. Furthermore, the welding surface has a contour that at least substantially corresponds to the circumference of the opening.

[0093] Since the melting temperature of the housing, and in particular of the housing partition, is significantly below the welding temperature or the welding temperature range, the housing partition is melted at least partially in an area around the opening during welding. In this context, the term "significantly below" refers to a temperature difference of at least 100°C, in particular approximately 100°C to 150°C, between the material of the interconnectors and the material of the housing partition.

[0094] Due to the pressure applied by the welding electrodes and the resulting stresses, parts of the molten material of the housing partition may migrate into the opening.

[0095] This can lead to plastic inclusions in the welding surface, which reduce the quality of the weld.

[0096] On the one hand, the strength of the weld is reduced by a high plastic inclusion and, on the other hand, the electrical conductivity is also reduced.

[0097] In this context, FIG. 7 a conventional insert 100' for a welding electrode. The conventional insert 100' has a welding plate 140' on which a conventional welding projection 110' is arranged. The conventional welding projection 110' contacts the element to be welded, namely an interconnector, with a contact surface 120'.

[0098] The conventional contact surface 120' has at least substantially the shape of a rectangle with rounded corners or the shape of a rectangle with a rounded end. This means that the end faces, i.e., the short sides of the rectangle, are particularly semicircular.

[0099] In other words, the conventional contacting surface 120' has at least substantially a shape that corresponds to the contour of the opening.

[0100] During the welding process, the material of the housing partition wall around the opening increasingly melts. In particular, performing the TTP welding process with a conventional 100' insert increasingly leads to plastic inclusions in the weld surface.

[0101] In particular, when using the conventional insert 100', the area proportion of the plastic inclusions after the welding process is 50% or more of the welding area.

[0102] This represents a significant quality problem, as both the strength of the weld (i.e. the welded elements) and the electrical conductivity of the weld or the welded interconnectors are negatively affected and, in particular, reduced.

[0103] In order to reduce the surface area of ​​plastic inclusions, an insert part 100 according to the invention is hereby specified, which in FIG. 2 bis 6 is shown.

[0104] In particular, the TTP welding process was simulated using a finite element method (FEM), and the weak points of the conventional insert part 100' were optimized in such a way that lower stresses are applied to the area around the opening in the housing partition during the welding process or are present in the area around the opening in the housing partition, which leads to reduced plastic inclusion in the resulting welding surface.

[0105] In particular, the contact surface 120 according to the invention is optimized using the finite element method, starting from the conventional contact surface 120', such that the surface area of ​​the plastic inclusions in the resulting weld surface is at most 8%, in particular less than 8%, preferably less than or equal to 4%, of the total weld surface. Particularly preferably, the surface area of ​​the plastic inclusions in the resulting weld surface is at least substantially 0%; i.e., no plastic inclusions are present in the resulting weld surface.

[0106] This has the advantage of improving both the electrical conductivity of the weld or the welded interconnectors and increasing the strength of the weld. In particular, the weld should be able to withstand a (torsional) torque of at least 12 Nm before the weld fails.

[0107] For this purpose, the contact surface 120 of the welding projection 110 according to the invention on the welding plate 140 can have at least substantially the shape of a short-legged "U" or at least substantially the shape of a banana or boomerang.

[0108] In other words, in comparison to the conventional at least substantially round-end rectangular contacting surface 120', the contacting surface 120 according to the invention has a recess 130, so that the welding temperature generated during the welding process is at least partially lower, whereby the stresses between the opening in the housing partition wall and the interconnector are reduced during welding.

[0109] Preferably, the recess 130 is arranged at a location where the highest stresses and temperatures were detected and determined in the simulation using the FEM method during the welding process with a conventional welding electrode or with a conventional insert part 100'. In other words, the recess 130 is arranged at a location where the majority of plastic inclusions occur in the welding surface. Such an optimized insert part 100 can, in particular, reduce or minimize the contact of the melted material of the interconnectors with the material of the housing partition in a region around the opening, which leads to lower stresses in the housing partition and to less melting of the housing partition.

[0110] This allows the area fraction of plastic inclusions in the resulting weld surface to be reduced, while at the same time, the strength of the weld or the welded interconnectors is not negatively affected. In particular, the interconnectors welded using an insert according to the invention can withstand a (torsional) torque between the interconnectors that exceeds the specified value of 11 Nm. In particular, the weld surface between the interconnectors only fails at approximately 16 Nm.

[0111] In particular, the outline of the contacting surface 120 is continuous; that is, at least substantially without corners and angles. For this purpose, all (acute) corners and angles are rounded, so that the outline of the contacting surface 120, as well as the lateral surface of the welding projection 110, has a smooth contour. A smooth contour means that no corners, sharp edges, and / or angles occur in a surface, outline, or perimeter. This prevents stresses from being applied to the housing partition during a welding process, or at least reduces them.

[0112] FIG. 2 shows a schematic representation of an insert part 100 according to the invention, which has a welding plate 140. On the front side of the welding plate 140, which faces the element to be welded (in this case an interconnector), the welding projection 110 according to the invention is arranged, which essentially has the contour of the contact surface 120 according to the invention. The welding projection 110 according to the invention extends from the front side of the welding plate 140 to the contact surface and is in particular tapered towards this. The welding projection 110 has on the FIG. 2 lower side has a recess 130, whereby the contacting surface 120 receives the above-mentioned specific shape according to the invention.

[0113] As in FIG. 2 As shown, the recess 130 has a substantially prismatic shape with a symmetrical trapezoid as its base. The welding projection 110 has at least a substantially prismatic shape with a round-ended rectangle as its base, a portion of which is missing from the shape of the recess 130 such that the welding projection 110 has the contact surface 120 with a cross-section of an (upside-down) short-legged "U." The contact surface 120 can equally well have a substantially C-shape or a U-shape.

[0114] However, it is equally conceivable for the contact surface 120 to have a different shape. In this context, it is only important that a weld of interconnectors can be achieved in which the surface area of ​​plastic inclusions is less than 8%, in particular less than (or equal to) 4%, of the total weld surface, and wherein the weld can withstand a (torsional) torque of at least 12 Nm. In other words, the weld surface may have a maximum surface area of ​​8%, preferably less than 4%, of plastic inclusions and must withstand a torsional moment of at least 12 Nm before the weld fails.

[0115] This is done in particular by simulating the welding process with the conventional insert part 100' using an FEM method, in which the weak points of the conventional welding projection 110' and the conventional contact surface 120' are detected and evaluated. This is done in particular by determining a relationship between the stresses and temperatures generated during the welding process and the plastic inclusions occurring in the resulting welding surface (and their position in the welding surface). Based on these results, an alternative shape of the contact surface 120 according to the invention is then determined, in which the weak points can be prevented or at least reduced.In this context, weak points are understood to be areas where high stresses and / or temperatures occur during the welding process in an area around the opening in the housing partition, and where plastic inclusions are increasingly found in the created welding surface after the welding process has been carried out.

[0116] FIG. 3 shows the front view of an insert 100 according to the invention for the welding electrode. The welding plate 140 has essentially the shape of a "T." Such a shape can, in particular, already provide or form an alignment of the insert 100 according to the invention to the welding electrode.

[0117] Furthermore, FIG. 3 A circle indicates an area which is FIG. 4 is shown in more detail in a detailed view IV.

[0118] FIG. 4 shows the FIG. 3 indicated detailed view IV of the welding projection 110 according to the invention with the recess 130 and the contact surface 120 according to the invention.

[0119] FIG. 5 shows a side view of the insert part 100 according to the invention. It can be seen that on a rear side of the welding plate 140, namely the side which is opposite the welding projection 110, a protrusion 160 is formed, which essentially has the shape of a key with a round end on one side.

[0120] Furthermore, a fastening bore 150 with a thread is arranged in the insert part 100, passing through the protrusion 160 and ending in the welding plate 140, by means of which the insert part 100 can be fastened to the welding electrode, namely by means of a screw.

[0121] As a result, the insert part 100 can be changed or replaced easily and quickly, which on the one hand reduces tool costs because the entire welding electrode arrangement or the entire welding electrode does not have to be replaced, and on the other hand reduces the time required to replace or change the insert part 100, which can reduce production costs and, for example, prevent or at least shorten a production stoppage.

[0122] In particular, the fastening bore 150 is arranged substantially at the level of the welding projection 110.

[0123] FIG. 6 shows a rear view of the insert 100, on which the back of the welding plate 140 can be seen. In FIG. 6 Furthermore, the shape of the protrusion 160 can be seen more precisely, which is semicircular at an upper end and has a chamfer at a lower end.

[0124] The protrusion 160 can be inserted into a correspondingly complementary groove in the welding electrode, allowing the insert 100 to be centered on the welding electrode. Subsequently, to secure the insert 100 to the welding electrode, a screw can be screwed through the welding electrode into the mounting hole 150 of the insert 100.

[0125] Thus, the insert part 100 according to the invention can be easily mounted and dismounted on welding electrodes, which leads to improved handling and thus reduced assembly costs and the susceptibility to errors during assembly. Furthermore, welding electrodes already in operation can be easily, cost-effectively, and quickly retrofitted with the insert part 100 according to the invention. In particular, it is not necessary to replace the entire welding electrodes; it is sufficient to simply replace the conventional insert part 100' with the insert part 100 according to the invention. This can be done, in particular, within a replacement time of less than 5 minutes.

[0126] With the aid of the insert part 100 according to the invention, the interconnectors of the electrochemical cells of the lead-acid accumulator 10 can be welded in such a way that in the welding surface between the interconnectors, the area proportion of plastic inclusions is a maximum of 8%, in particular less than 8%, particularly preferably a maximum of or less than 4% of the total welding surface, wherein at the same time the strength of the weld between the interconnectors is designed such that the weld withstands a torsional moment of at least 12 Nm, in particular at least 16 Nm (without failing).

[0127] For example, by using the insert part 100 according to the invention in an opening with an area in the order of 90 mm 2< to 100 mm 2<, the area proportion of plastic inclusions in the welding surface can be reduced from 36 mm 2< to 51 mm 2< to 0 mm 2< to 15 mm 2<, preferably to 0 mm 2< to 5 mm 2<. Bezuaszeichenliste

[0128] VVehicle 10Battery 100Insert for a welding electrode 110Welding projection 120Contact surface 130Recess 140Welding plate 150Mounting hole 160Highlight 100'Conventional insert for a welding electrode 110'Conventional welding projection 120'Conventional contact surface 140'Conventional welding plate

Claims

1. Welding electrode arrangement for welding in each case one interconnector of two adjacent electrochemical cells of a rechargeable battery, in particular a lead acid rechargeable battery (10), wherein the interconnectors are disposed so as to be separated from one another by means of a housing partition and so as to be opposite one another on opposite sides of the housing partition, wherein the housing partition has an opening in a region in which the interconnectors lie opposite one another, wherein the welding electrode arrangement has at least one pair of welding electrodes, wherein at least one, in particular each, of the welding electrodes of the at least one pair of welding electrodes has an insert part (100) which is conceived to contact a corresponding interconnector, and to weld the interconnectors through the opening in the housing partition in such a manner that an area proportion of plastics inclusions in the welding area is at most 8% of the welding area, wherein the insert part (100) has a welding plate (140), on the front side of which is formed a welding protrusion (110) that extends from the welding plate (140), and wherein the welding protrusion (110) has a recess (130).

2. Welding electrode arrangement according to Claim 1, wherein the welding protrusion (110) has at least substantially the shape of a prism with a footprint of a round-fronted rectangle, and the recess (130) has at least substantially the shape of a prism with a trapezoidal footprint.

3. Welding electrode arrangement according to Claim 1 or 2, wherein the welding protrusion (110) has a contacting face (120) for contacting the interconnector, wherein the welding protrusion (110) is configured so as to taper toward the contacting face (120).

4. Welding electrode arrangement according to Claim 3, wherein the contacting face (120) has an at least substantially U-shaped or C-shaped cross section.

5. Welding electrode arrangement according to one of Claims 1 to 4, wherein disposed on the rear side of the welding plate (140) is an elevation (160) for introducing the insert part (100) into a groove, configured in the welding electrode so as to be complementary to the elevation (160), wherein the insert part (100) by means of a fastening bore (150) which is disposed on the rear side of the welding plate is able to be fastened to, or is fastened to, the welding electrode.

6. Welding electrode arrangement according to one of Claims 1 to 5, wherein the welding protrusion (110) and / or the elevation (160) are / is configured so as to be integral to the welding plate (140).

7. Method for welding in each case one interconnector of two adjacent electrochemical cells of a rechargeable battery, in particular a lead acid rechargeable battery (10), by means of a welding electrode arrangement according to one of Claims 1 to 6, wherein the two electrochemical cells are disposed so as to be separated from one another by means of a housing partition, wherein the interconnectors are disposed so as to face one another on two opposite sides of the housing partition, wherein an opening is disposed in a region of the housing partition where the interconnectors are opposite one another, and wherein the method comprises the following steps: - contacting the interconnectors with a welding electrode arrangement, wherein the welding electrode arrangement has at least one pair of welding electrodes, wherein one welding electrode of the at least one pair of welding electrodes contacts in each case one of the interconnectors by means of an insert part (100); - welding the interconnectors in such a manner that, by means of a pressure applied by the insert parts (100) of the welding electrodes and a current applied to the welding electrode arrangement, the material of the interconnectors melts at least in regions and is connected in a materially bonded manner through the opening in the housing partition, specifically so that the generated welding area has an area proportion of plastics inclusions of at most 8% in the welding area, wherein the insert part (100) has a welding plate (140), on the front side of which is formed a welding protrusion (110) that extends from the welding plate (140), and wherein the welding protrusion (110) has a recess (130).

8. Method according to Claim 7, wherein the area proportion of plastics inclusions in the welding area is less than 8%, in particular less than 4%.

9. Method according to Claim 7 or 8, wherein the welding protrusion (110) has a shape which has been calculated and simulated in such a manner that the area proportion of plastics inclusions in the welding area is at most 8%, preferably less than 8%, particularly preferably less than 4%, of the welding area.

10. Method according to Claim 9, wherein the welding protrusion (110) has the recess (130) in such a manner that the cross section of the welding protrusion (110) is at least substantially U-shaped or C-shaped.

11. Method according to Claim 9 or 10, wherein the welding protrusion (110) has a contacting face (120) which has an at least substantially U-shaped or C-shaped cross section, wherein the welding protrusion (110) is configured so as to taper toward the contacting face (120).

12. Method according to one of Claims 7 to 11, wherein the interconnectors are welded by means of a through-the-partition (TTP) welding method.

13. Method according to one of Claims 7 to 12, wherein the interconnectors are welded at a welding temperature of 300°C to 380°C, in particular 300°C to 360°C, preferably 300°C to 340°C, particularly preferably 300°C to 320°C.

14. Method according to one of Claims 7 to 13, wherein the housing partition is made of plastics material which has a melting point of 200°C to 250°C, in particular 220°C, wherein the housing partition is preferably made of polyethylene, polypropylene, polyamide, polyoxymethylene or a copolymer thereof.

15. Lead acid rechargeable battery (10) which has the following: - a housing with a multiplicity of chambers which are separated from one another by means of a multiplicity of housing partitions; - a multiplicity of electrochemical cells, wherein one electrochemical cell is in each case disposed in a corresponding chamber, and wherein each electrochemical cell has two interconnectors for configuring an electrical connection; wherein one interconnector of a first electrochemical cell and one interconnector of a second adjacent electrochemical cell are in each case disposed opposite one another on two opposite sides of a housing partition that spatially separates the first and second electrochemical cells from one another, wherein the housing partition in a region where the interconnectors are located opposite one another has an opening by way of which the interconnectors, by means of a method as claimed in one of Claims 7 to 14, are connected, in particular welded, to one another, wherein the connecting face, in particular the welding area, has an area proportion of plastics inclusions of at most 8% of the welding area.