WO2017157794A1

WO2017157794A1 - Method for welding a conductive element to a battery terminal

Info

Publication number: WO2017157794A1
Application number: PCT/EP2017/055700
Authority: WO
Inventors: Michel Combier
Original assignee: Accuwatt
Priority date: 2016-03-17
Filing date: 2017-03-10
Publication date: 2017-09-21
Also published as: FR3048906A1; FR3048906B1

Abstract

The present application relates to a process for welding a conductive element (100a) to a terminal (202; 204) of a battery (200), the process comprising respectively firing (T1a) at least once a laser beam (302) at at least one point of impact (402) located on an edge face (102a) of the conductive element (100a), the edge face (102a) making contact with the terminal along a line of contact (104), the conductive element (100a) being made of copper or a copper alloy and the laser beam (302) having a wavelength comprised between 500 and 560 nm.

Description

WELDING METHOD BETWEEN A CONDUCTIVE ELEMENT AND

A BATTERY POLE

Introduction

The present invention relates to a method of welding between a conductive element and a battery pole, preferably electrochemical (also called electrochemical accumulator), in particular a battery of small dimensions, such as a 26650 battery of cylindrical conformation of 26. mm diameter by 65 mm length.

The present invention also relates to an assembly formed of a battery and a conductive element, said assembly being obtained by welding, according to the invention, between a conductive element and a battery pole.

Prior art

The small size batteries according to the state of the art are typically stainless steel containers and are well suited to the production of batteries of all sizes by series or parallel association of said batteries.

The formats referenced 18650, of cylindrical conformation of 18 mm in diameter by 65 mm in length, and 26650 have the advantage of being manufactured by many manufacturers and to be easily integrated because of their small sizes. It is thus possible to make battery sets of any shape and power, also called "pack" batteries.

Such battery assemblies can be used statically, for example to supply an electrical network of a dwelling, possibly as backup from a main supply or as a primary supply source, or dynamically, for example to power, continuously or intermittently, the electrical circuit of a vehicle such as a hybrid automobile. The use of these battery formats requires the need to associate a large number of batteries to obtain sufficient capacity for the aforementioned uses, which requires the realization of many electrical interconnections of said batteries.

The interconnection of a first pole of a battery and a second pole of another battery is usually achieved by means of resistance welding. Resistance welding is a process without a filler metal that uses the combined effects of mechanical pressure and electrical current passing through the parts. The parts to be welded are superimposed and are clamped locally between two electrodes to create a preferred contact area which constitutes an electrical resistance. The assembly formed by the parts and electrodes is traversed by a very strong welding current, under a low voltage, which causes a strong rise in temperature by the Joule effect. The heating results in the localized fusion of the two parts in the preferred contact area, followed by the formation of a recrystallized metal core. In the application of the resistance welding process to the battery interconnection, a conductive element soldered to the battery poles is constituted by a metal strip.

For each embodiment of a connection between a conductive element and a battery, a welding head is lowered, the welding is performed, then the welding head is raised. The operation typically takes one second. The resistance welding of 10,000 conductive elements requires about 40,000 connections, or about 11 hours of welding. The continuing decline in the price of batteries makes the relative cost of the welding step relative to the cost of assembly increasingly important.

Furthermore, the resistance welding requires the use of metal strips sufficiently fine to allow said welding. Such metal strips are fragile, which limits the intensity of currents that can circulate. Finally, resistance welding generates significant contact resistances, typically of the order of 120 μΩ per connection.

An object of the invention is to propose a method of welding between a conductive element and a pole of a battery:

which is faster than that of the prior art, and / or

which is mechanically simpler than that of the prior art, and / or,

which makes it possible to circulate currents of greater intensity in the connectors than in those implemented in the prior art, and / or

which makes it possible to use connectors that are more robust than those used in the prior art, and / or

for which the conductive element has a thickness greater than that of a pole of a battery, without damaging the pole of the battery, and / or

which has connection resistances lower than those generated in the prior art.

Presentation of the invention

According to a first aspect of the invention, at least one of the abovementioned objectives is reached with a welding method between a conductive element and a pole of a battery, said method comprising at least one firing of a laser beam on respectively at least one impact point located on a wafer of the conductive element, said wafer being in contact with said pole along a nip, said conducting element being made of copper or a copper alloy and said laser beam having a wavelength of between 500 and 560 nm.

Preferably, the laser beam has a wavelength of between 531 and 533 nm. Even more preferably, the laser beam has a wavelength of 532 nm. Such a laser may be called a green laser. In one embodiment of the method according to the invention, the contact line belongs to a region of the pole extending in a plane, called plane of the pole, and the laser beam of each shot forms an angle less than 90 ° with said plane of the pole, preferably less than 60 °. Advantageously, the conductive element may extend towards the wafer in a direction, called wafer direction, and the laser beam may propagate, at the point of impact, in a direction of propagation, said propagation direction being at least partly opposed to said slice direction.

More preferably, each shot is preferably made by emitting a pulse of the laser beam by a laser.

The method according to the invention may further comprise, for each point of impact, an emission of an argon flow in the direction of this point of impact.

Preferably, each shot hits the pole at the same time as it hits the edge.

Advantageously, each shot can hit the pole and then be reflected by said pole and then hit the edge.

According to one possibility, no shot hits the pole.

In one embodiment, each shot, the laser is focused on the point of impact.

Preferably, the at least one shot comprises several shots on several impact points located on the edge of the conductive element, said plurality of shots being distributed along the line of contact.

The pole may be nickel or a nickel alloy.

Advantageously, the conductive element may have a thickness at each point of impact which is greater than a thickness of the battery pole at this point of impact, the thickness of the conductive element preferably being greater than at 0.5 mm and the thickness of the pole being preferably less than 0.2 mm. Preferably, the laser beam has a wavefront dimension (called "waste" in English), at the point of impact, set substantially equal to the thickness of the conductive element.

According to one possibility, the wafer has a decreasing thickness in the direction of the nip.

According to one embodiment, the conductive element is in the form of a plate, said plate having two faces connected by a border, said border comprising the edge.

According to a second aspect of the invention, there is provided a method of assembling two batteries by means of a conducting element comprising copper or a copper alloy, said method comprising:

a welding step, according to the first aspect of the invention, or one or more of its improvements, between a wafer of said conductive element and a pole of a battery of said two batteries, and

a welding step, according to the first aspect of the invention, or one or more of its improvements, between another wafer, or said wafer, of said conducting element and a pole of the other battery of said two batteries.

According to a third aspect of the invention, there is provided a method of assembling several batteries, in which each pole of a battery is electrically connected to one pole of each of the other batteries, by a plurality of implementations of the method assembly according to the second aspect of the invention.

The at least two implementations of the assembly method according to the second aspect of the invention can be carried out in parallel with time.

According to a fourth aspect of the invention, there is provided a set of several batteries assembled by a method assembly of several batteries according to the third aspect of the invention, or one or more of its improvements.

Description of figures

Other features and advantages of the invention will appear on reading the detailed description of implementations and non-limiting embodiments, with reference to the appended figures in which:

- Figure 1 is a perspective diagram of an embodiment of a welding method P according to the invention;

FIG. 2 comprises four perspective diagrams, each illustrating a firing configuration of a laser beam of the implementation of FIG. 1;

- Figure 3 is a sectional diagram of a profile of a conductive element during the implementation of the welding process P; FIG. 4 illustrates a plurality of shots implemented in one embodiment of the method according to the invention;

FIG. 5 is a perspective diagram of the result of an implementation of the method of assembling several batteries according to the invention;

- Figure 6 is a perspective diagram of the result of another implementation of the method of assembling several batteries according to the invention.

detailed description

These embodiments being in no way limiting, it will be possible in particular to make variants of the invention comprising only a selection of characteristics described hereinafter, as described or generalized, isolated from the other characteristics described, if this selection of characteristics is sufficient to confer a technical advantage or to differentiate the invention from the state of the art.

It is illustrated in Figure 1 a conductive element 100a and a pole 202 of a battery 200. By conductive element, the present invention is preferably directed at a current-conducting element, ie a conductive element having a resistivity of less than 100 × 10 ^-9 Ω-m at 300 K (Kelvin).

By battery, the present invention is preferably a cylindrical container battery. The invention does not preferably target a battery of prismatic type or of polymer plate type.

By battery, the present invention is intended, preferably, in particular batteries comprising containers comprising, in all or part, stainless steel.

Different types of electrochemical accumulators of batteries are envisaged. Electrochemical accumulators of lithium-ion, lithium-titanate, lithium-iron phosphate, lithium-sulfur, sodium-ion type are in particular envisaged.

In Figure 1, the battery 200 is of cylindrical conformation, 18 mm in diameter by 65 mm in length.

The conductive member 100a is preferably made of copper or copper alloy.

By copper alloy, the present description is preferably an alloy in which the copper content is predominant, that is to say at least half of the atoms are copper atoms.

The copper or copper alloy connectors are preferably chosen to be more robust (because they are thicker) than the connectors used in the prior art. Such connectors allow the circulation of currents of greater intensity than those which can circulate in the connectors implemented in the prior art.

The pole 202 is, in Figure 1, the negative pole of the battery 200, also called anode, and is preferably made of nickel. The pole could be made of nickel alloy. By nickel alloy, the present description is aimed preferably at an alloy in which the nickel content is predominant, that is to say of which at least half of the atoms are nickel atoms.

The nickel or a nickel alloy reflects a laser beam having a wavelength such as that used by the method P.

A shot on the edge of the conductive element allows a large thickness H of the conductive element 100a outside this wafer.

The green wavelength makes it possible to melt the copper alloy without damaging the nickel pole, and thus to draw with the laser beam at the junction between the element 100a and the pole 202.

In the diagram shown, the conductive element 100a is made in the form of a copper plate, said plate having two faces 108 and 110, parallel to each other and connected by a border 112.

One end of the conductive element 100a is laid flat on the pole 202, and partially covers the pole 202. In this implementation, each of the faces 108 and 110 is parallel to a plane 400 of the pole 202.

As shown in FIG. 1, a wafer 102a of the edge 112 of the conductive member 100a is in contact with the pole 202 along a nip 104.

The other end of the copper plate rests partly on another anode of another battery.

A laser 300 is shown in FIG. 1. The laser 300 is configured to transmit and fire a laser beam 302 in the form of pulses. The laser beam 302 has a wavelength of 532 nm.

The use of a laser in pulse mode makes it possible to avoid an excessive depth of fusion of an impact point during a shot. The method comprises at least one shot T1a of the laser beam 302 at an impact point 402 located on the wafer 102a of the conductive member 100a. The firing Tla forms a weld between the conductive element 100a and the pole 202. The weld is located on and around the point of impact 402, that is to say on and around the nip 104.

The wavelength of the laser beam is selected to form a weld between the battery pole material and the copper, or copper alloy of the conductor.

The power of the laser can be between 50 W and 100 W.

Laser welding achieves electrical continuity of the conductive element and the battery.

In the present description, the expression "at least one point of impact on the slice" means that there may be, for the same shot, other points of impact, for example on line 104 and / or on pole 202.

The welding method P does not include, for making each weld, mechanical displacement of a welding head. In particular, it does not require an approach phase and removal of the laser head 300. The welding process P is faster than that of the prior art. Typically, the welding time of the method P is 0.1 seconds.

Not requiring pressurization of the two materials to be welded, the welding process P is mechanically simpler than that of the prior art.

The connection resistances generated by the welding method P are lower than those generated in the prior art. Resistances twice lower than those generated in the prior art could be measured, of the order of 60 μΩ per connection.

A laser head 300 comprises an optical deflection system 304, well known in the field of laser devices (for example a pair of moving mirrors and / or lenses), to deviate the laser beam 302 without moving the laser head 300. Thus, the laser that is heavy is not mobile, but simply and quickly moves a lens and / or a mirror to move the beam emitted by the laser.

As illustrated in FIG. 4, the method P may also comprise several shots. The shot Tla and a shot T2a are made on several points of impact located on the edge 102a of the conductive element 100a. The shots T1a and T2a are distributed parallel or along the contact line 104. Only two shots are shown in FIG. 4, but other shots can be made. These shots form several welds, preferably joined, all of which is called weld seam.

These shots can be carried out continuously by the laser 300, for example at a transmission frequency of several tens of pulses per second, for example at a frequency greater than 90 Hz.

It is also illustrated in Figure 1, for each point of impact, an emission of an argon flow 502 towards this point of impact. This flow of argon 502 aims to prevent the oxidation of copper during welding.

Figure 2 illustrates four firing patterns, Tla, Tlb, Tic and Tld of the laser beam 302, respectively on the upper left, upper right, lower left and lower right sides of the figure.

In the Tla and Tic firing configurations, the firing hits the pole 202 at the same time as it hits the wafer 102a. Only the size of the laser beam 302 at the point of impact 402 changes. The size of the laser beam 302 is smaller than the thickness of the wafer in the first configuration and greater than the thickness of the wafer in the second configuration.

In the present description, a thickness preferably denotes a thickness along an axis perpendicular to the plane 400 of the pole 202 comprising the contact line 104. In the Tlb firing configuration, the firing strikes the pole 202, then is reflected by the pole 202 to hit the edge 402.

In the firing configuration Tld, no firing hits the pole 202. In the examples shown in FIGS. 1, 2 and 4, the contact line 104 belongs to a region Z (FIG. 1) of the pole extending along the plane 400. The laser beam of each firing Tla, T2a, Tlb, Tic, Tld forms an angle approximately equal to 45 ° with the plane 400.

This angle has the advantage of allowing the use of a reflection of the laser beam by the pole of the battery. Indeed, nickel or a nickel alloy reflect a laser beam having a wavelength such as that used by method P. The nickel reflection coefficient of such a laser beam is of the order of 60% . This angle also has the advantage of avoiding reflection of the laser beam towards the laser head.

In the examples shown in Figures 4 and 6, the conductive element 100a extends in the direction of the wafer 102a in a direction dTl, said slice direction. In these examples, the laser beam propagates, at the point of impact, along a propagation direction d1 (FIG. 4). The propagation direction dP1 comprises a component opposite to said dT1 slice direction.

In each of the illustrated examples, the conductive element has a thickness H 1 which is greater than a thickness H2 of the battery pole at the level of the contact line 104:

the thickness H 1 of the conductive element is preferably greater than 0.3 mm, more preferably greater than 0.5 mm, more preferably greater than 0.8 mm, the thickness H 2 of the battery pole. is preferably less than 0.5 mm, more preferably less than 0.3 mm,

in the examples shown, the plate has a thickness of about 0.5 mm at the point impact 402. The pole of the battery has a thickness of about 0.25 mm at said point of impact.

Thus, the method P allows welding between a pole and a connector, said pole having a thickness less than that of the conductive element, without damaging said pole of the battery.

The size of the wavefront (denoted "waste" in English) of the laser beam at the point of impact, is set substantially equal to the thickness Hl of the conductive element. Thus, the size of the weld is maximum, for example 0.5 mm in the examples shown. The connection resistance thus generated is minimal.

Figure 3 illustrates a sectional diagram of a second conductive element 100b. In the example shown, the conductor 100b has a wafer 102b located at one end of the conductive element 100b which has a decreasing thickness in the direction of the nip 104.

What is described with reference to FIGS. 1, 2 and 4, also applies to the second conductive element 102b.

In FIG. 3, there is furthermore shown a shot Tle taken perpendicular to the pole 202. In the example shown, the shot Tle does not touch the pole 202.

The example of FIG. 5 illustrates an assembly of several batteries, numbered B1 to B12 implementing a method P.

Each pole of one of the batteries B1 to B12 is connected to one pole of each of the other batteries by soldering of conductive elements.

The example of FIG. 5 illustrates the possibility of using a conductor, here the conductor C2, to connect two batteries, here the batteries B3 and B4.

The example of FIG. 5 also illustrates the possibility, according to the invention, of using the same conductor, here the conductor C1, to connect three batteries, here the batteries B1, B5 and B9. More than three batteries could be connected by the method P using the same conductor. Figure 6 illustrates a possibility of welding a multitude of batteries, that is to say a "pack" of batteries, using only one driver.

Six batteries Al to A6 are partially visible in Figure 6. The six batteries are held parallel to each other and staggered by means of two holding plates M l and M2 plastic.

For this purpose, the two holding plates each comprise six through holes arranged parallel to each other and staggered arranged to accommodate and block a battery end, that is to say a battery pole.

A conductive element 100c, made of copper, is disposed in contact with the poles, respectively PI to P6 of the six batteries A1 to A6, the poles being disposed on the other side of the body of the batteries relative to the holding plate M .

Six welds S1 to S6 are produced in accordance with the method P, respectively between the batteries B1 to B6 and the conductive element 100c, thereby electrically connecting the batteries together by a conductive element made in the form of a copper plate. It is noted that the copper plate has a better resistance to the passage of strong currents than a metal strip, that each weld performed by the laser has a lower contact resistance to a weld performed by a resistance welding and that the time of manufacturing is faster than that required for resistance welding.

Of course, the invention is not limited to the examples that have just been described and many adjustments can be made to these examples without departing from the scope of the invention. In addition, the various features, shapes, variants and embodiments of the invention may be associated with each other in various combinations to the extent that they are not incompatible or exclusive of each other. It is shown in Figures 4 and 6 a second slice direction dT2 which is orthogonal to the direction dTl. It is further shown in Figure 4 a wafer 102c which is orthogonal to wafer 102a. The conductor 100a (FIG. 4) also extends in the direction of the wafer 102c along the second direction dT2, shown in dashed line. It is possible to propagate a laser beam, at a point of impact on the wafer 102c, in a propagation direction dP2, said propagation direction dP2 having a component opposite to the second wafer direction dT2. It is thus possible to weld the conductive element between the pole and the wafer 102c of the conductive element.

Claims

claims

A method of welding between a conductive member (100a, 100b, 100c) and a pole (202; 204, PI - P6) of a battery (200; B1, B2; B1 - B12, B1 - B6); method comprising at least one firing (Tla; T2a; Tlb; Tic; Tld; Tle) of a laser beam (302) on respectively at least one impact point (402) located on a wafer (102a; 102b; 102c ) of the conductive element, said wafer being in contact with said pole along a nip (104), said conductive element being made of copper or a copper alloy and said laser beam having a wavelength comprised between 500 and 560 nm.

2. Method according to claim 1, wherein the nip belongs to a region (Z) of the pole extending in a plane

(400), said plane of the pole, and wherein the laser beam of each shot forms an angle (a) less than 90 ° with said plane of the pole, preferably less than 60 °.

3. The method of claim 1 or 2, wherein the conductive element extends towards the wafer in a direction (dTl, dT2), said wafer direction, and wherein the laser beam propagates at the impact point, according to a propagation direction (dP1, dP2), said propagation direction having at least one component opposite said wafer direction.

4. A method according to any one of the preceding claims, further comprising, for each point of impact, an emission of an argon stream (502) towards this point of impact.

5. A method according to any one of the preceding claims, wherein each shot (T1a, T2a, Tic) strikes the pole at the same time as it strikes the wafer (102a, 102b).

6. Method according to any one of the preceding claims, wherein each shot (Tlb) strikes the pole and is reflected by said pole to then hit the wafer (102a).

7. A method according to any one of the preceding claims, wherein the at least one shot comprises several shots (Tla, T2a) on several impact points located on the wafer (102a) of the conductive element (100a), said shots being distributed along the line of contact.

The method of any of the preceding claims, wherein the conductive member has a thickness (106) at each point of impact that is greater than a thickness (206) of the battery pole at that point of contact. point of impact.

The method of any of the preceding claims, wherein the wafer (102b) has a decreasing thickness toward the nip.

A method of assembling two batteries (B1, B2) by means of a conductive element (100a) comprising copper or a copper alloy, said method comprising:

- A welding step according to any one of the preceding claims between a wafer of said conductive element and a pole (202) of a battery (Bl) of said two batteries, and - A welding step according to any one of the preceding claims between another wafer, or said wafer, said conductive element and a pole (2022) of the other battery (B2) of said two batteries.

11. A method of assembling a plurality of batteries (Bl-B12), wherein each pole of a battery is electrically connected to a pole of each of the other batteries, by a plurality of implementations of the assembly method according to the claim previous.