CN110890509A

CN110890509A - Method for connecting individual film-shaped films of a stack of battery films

Info

Publication number: CN110890509A
Application number: CN201910830929.XA
Authority: CN
Inventors: A.米哈洛夫斯基; M.鲁斯费尔德
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2018-09-05
Filing date: 2019-09-04
Publication date: 2020-03-17
Also published as: DE102018215069A1

Abstract

The invention relates to a method for connecting individual film-like individual films of a stack of battery films by means of a laser radiation source by means of a material-locking joint. Performing at least the following method steps: a) producing a channel in the cell film stack (10) by means of a short or ultrashort laser pulse (50) with the laser radiation source, b) wherein the removed material of the individual film-shaped films is partially evaporated and a melt pool is formed partially in the channel bottom of the channel, c) causing a pressure increase in the melt pool by means of an ultrashort laser pulse and discharging the melt from the melt pool by means of steam formation in the transport direction in the direction of the channel inlet, and d) producing a thin, continuous contact layer of the melt on the channel walls for the material-locking connection of the individual film-shaped films to one another.

Description

Method for connecting individual film-shaped films of a stack of battery films

Technical Field

The invention relates to a method for connecting individual film-like films of a battery film stack by means of a laser radiation source by means of a material-locking joint and to the use of the method for producing a battery film stack.

Background

Within the field of battery technology, the electrodes stacked in a battery cell, here typically 30 to 70 anodes and cathodes each, are connected to an electrical conductor by means of appropriately shaped elements, known as Flags (Fähnchen) or Flags (Flags), each flag having a typical thickness of 6 to 20 μm, the electrical conductor having a thickness between 300 and 800 μm, the total stack to be contacted consisting of Flags and electrical conductors having a thickness of 0.5 to 2mm, the Flags and electrical conductors generally consisting of aluminum for the cathode or copper for the anode, the Flags and electrical conductors consisting of copper for the anode, other materials such as nickel or lithium can also be considered depending on the battery design, the central requirement for the connection is an electrical contact and the stability with respect to mechanical forces acting on the individual films during manufacture and during operation (Beständigkeit), in particular the small positional requirement of the joints, the duration of the process which can be about 3s, the limited handling time for the joining process and the low handling of the mechanical forces and the post-clamping overhead.

From the prior art of previous battery production, it is known to connect the materials of the mating parts by means of an ultrasonic method in a cohesive manner. However, in this case, a large structural space of a Sonotroden (Sonotroden) for coupling in ultrasonic waves should be provided. Due to mechanical movements during the joining process, tearing of the flag may also occur at the joining point (ansissen). These flags can fail during operation of the battery, especially in the event of large volume changes during the charging process. In addition to this, chip formation (Fliterbildung) occurs during the process.

In contrast, the laser joining method is characterized by contactless supply of energy for the form-locking joining. Only for clamping and orientation forces have been applied to the component.

When joining the individual films of a battery film stack by means of a laser, various method alternatives are conceivable.

For the lap joint of a stack of cell films, a plurality of individual films are lapped one on top of the other. In a first embodiment variant of laser bonding, the contacting of the total stack takes place perpendicular to the surface of the flag.

As an alternative, a lap joint can be provided for the stack of cell membranes, for which the severing of the membranes is effected simultaneously. Also referred to herein as "cutting contact". The contacting of the cell film stack is performed perpendicular to the flag-raised surface. The process is performed such that the flag is cut off and brought into contact therewith at the cutting edge.

Another embodiment variant of the laser joining method is a lap joint of individual films; the flag projections are brought into contact with the respective flag projections lying therebelow successively perpendicularly to the film surface until they are completely in contact with the entire cell film stack. The consequence is a correspondingly high outlay for guiding the laser beam source.

Furthermore, the cell film stack can be contacted at the end faces. The cell film stack is bonded to the end faces perpendicular to the flag. Before contacting, the cell film stack has to be separated on the side perpendicular to the flag convex surface for generating a flat-running end face.

In the first-mentioned alternative to the laser method, a weld pool of great thickness is produced relative to the flag, which is inclined to the instability, which in turn can lead to uneven welds. In addition, the individual flags were observed to tear from the seam. In a second embodiment of the laser method, insufficient contact of the flag on the electrical conductor occurs due to the small bath size. In addition, the second method entails a significant limitation in the freedom of design, since the flag and the conductor are each cut flush.

In the third mentioned method, the size of the molten pool is significantly reduced. However, a multi-stage process (more than 130 welding processes for a common film stack with 69 anodes and 68 cathodes) requires a very complex design of the stack unit.

Finally, in the last-mentioned embodiment of the method, i.e. in the fourth embodiment, a very complex pretreatment is required for producing flush stack edges due to the production of the accessible end faces. In this respect, it is assumed that the process duration is several minutes.

US 2010/247992 a1 relates to a secondary battery and a method for manufacturing a sealed secondary battery. US 2004/127952 a1 relates to a method for manufacturing a battery stack. The cell stack comprises a plurality of alternating anode layers and cathode layers, which are separated from each other by separators, respectively. The electrode layers arranged in an alternating sequence are oriented and interconnected in the case of a stack in order to place the largest electrode area in the smallest volume without wasting installation space.

Disclosure of Invention

According to the invention, a method for connecting individual film-like films of a battery film stack by means of a laser radiation source by means of a cohesive bonding is proposed, with at least the following method steps:

a) passing said laser radiation source through a short (10)^-9s to 10^-7s) ultra short (10)^-13s to 10^-11s) laser pulses create channels in the cell thin film stack,

b) wherein the removed material of the individual film-like film is partially evaporated and a melt pool is partially formed in the channel bottom of the channel,

c) the pressure increase is caused in the molten bath by the laser pulse and the melt is discharged from the molten bath by steam formation in a conveying direction in the direction of the channel inlet and

d) a thin, continuous contact layer of melt is produced on the channel walls for the cohesive connection of the individual films in the form of films to one another.

Further according to the proposed solution, the pulse duration of the short laser pulse is 10^-9s and 10^-7s in between. In particular, the pulse duration of the laser pulses of the laser radiation source can also be set such that the pulse duration of the laser pulses is 10^-13s to 10^-11s (ultra short).

When a channel is produced in the cell stack, the channel is connected in a bonded manner to the electrical conductor in the contact region. In the method according to the invention, therefore, not only the individual films in the form of films are connected to one another, but also the electrical conductors in the stack of battery films are connected to the individual films.

The channels produced in the cell film stack are produced continuously by successive laser pulses. The channel bottom of the channel then erodes the cell film stack more and more deeply, whereby a new, deep melt pool corresponding to the penetration depth is always created, from which melt particles are thrown out by the steam generated as a result of the pressure increase and accumulate on the channel walls in the form of a continuous thin layer. Depending on the pulse duration of the ultrashort laser pulse of the laser radiation source, the channel erodes up to the electrical conductor arranged on the lower side of the cell film stack. The method steps a) to d) are therefore carried out several times, as long as the channel base forms a contact region with the electrical conductor and there forms a cohesive connection with it.

In the method according to the invention, one or more of the following listed parameters can be changed for the purpose of adjusting the method:

-the pulse duration of the laser pulse,

-the pulse frequency of the laser pulses,

-the pulse energy of each laser pulse,

-a focal position and

-spot size.

In an advantageous embodiment of the method according to the invention, a plurality of side-by-side channels can be produced simultaneously on the stack of cell membranes starting from the uppermost membrane-like individual membrane. The channels can be arranged in a pattern or matrix, for example in rows and/or columns produced alongside one another or above one another.

Finally, the invention relates to the use of the method for bringing individual films in the form of films into cohesive contact with one another and with the electrical conductors of a stack of battery films.

The method proposed according to the invention is distinguished in particular by the relatively small volume of the melt pool which accumulates on the channel walls of the channel and solidifies immediately after processing and forms a thin, continuous contact layer between the individual film-like individual films arranged one above the other in the cell film stack. Due to the locally very limited machining zone, the power input and heating of the entire component is very low. A large degree of freedom is created in the design of the method due to variations in process parameters in pulse duration, pulse frequency, pulse energy, focal position and spot size. Thus, there is an adjustable energy input together with a direct influence on the melt generation and on the diameter of the channel and the achievable depth. In addition, the method can be flexibly adapted to new designs of cell film stacks by adjusting the parameters.

In the method according to the invention, it is also possible to consider the implementation 10 in particular^-9s to 10^-7s pulse duration is a low cost short pulse laser.

The method proposed according to the invention has the advantage in terms of design freedom that both the efficiency of the mechanical contact and the efficiency of the electrical contact can be adjusted in small increments by introducing a plurality of channels arranged next to one another.

For a single joint, such defects may lead to rejects (Ausschuss) or field failures (feldaufälle).

The method proposed according to the invention provides a possible solution for mass production, i.e. for the industrial laser welding of individual films in the form of films, which avoids the disadvantages of ultrasonic methods. The solution proposed according to the invention provides an alternative procedure for ultrasonic joining, which enables a significantly stronger cohesive connection to be produced.

Drawings

The invention is described in detail below with the aid of the figures.

Figures 1.1 to 1.4 show different variants of the laser contacting method of the individual films of a stack of battery films (battierefoliensis),

FIG. 2 shows a schematic sketch of the drilling contact by means of a short-pulse or ultrashort-pulse laser on a cell film stack consisting of a single film in the form of a film and an electrical conductor, and

fig. 3 shows the arrangement of the channels as seen from the upper side of the cell membrane stack.

Detailed Description

To briefly describe below with the aid of the sequence of fig. 1.1 to 1.4, experiments have been carried out to date on laser contacting methods for producing an adhesive connection in a cell film stack 10.

Fig. 1.1 shows a cell film stack 10 comprising a plurality of individual films, the individual films of the cell film stack 10 are brought into contact perpendicular to the surface in a lapping arrangement 14 according to fig. 1.1 by means of a laser radiation source 12, in the variant of the laser contact method shown in fig. 1.2, the individual films are likewise received inside the cell film stack 10 in a lap-up manner (ü berlappendend), the individual films are cut 16, also referred to as "cutting contact", in accordance with the contact of the individual films of the cell film stack 10 of fig. 1.2 perpendicular to the surface, the process control (Prozessf ü hrng) is carried out in such a way that the cutting takes place and the contact is set at the cutting edge (gesetztt).

Fig. 1.3 shows a variant of the laser contacting method, according to which the individual films are contacted individually perpendicularly to their surfaces with the individual films lying underneath in each case until the entire battery film stack 10 is in full contact. The path of movement of the laser radiation source 12 is outlined by an arrow 18 and shows the sequential contacting of the individual films of the cell film stack 10 with one another.

Fig. 1.4 shows a further embodiment variant of the laser contact method. The cell film stack 10 is brought into end-face contact according to fig. 1.4. For this purpose, the cell film stack 10 is subjected to a vertical cut 20. The end face on which the contacting 22 of the end face is carried out is produced by a perpendicular cut 20. For this purpose, the laser radiation source 12 must be turned around by approximately 90 °. Furthermore, a clean cut is required in order to produce a uniformly smooth end face by the perpendicular cut 20, which particularly meets the high requirements for flatness.

A disadvantage of the laser contact method according to fig. 1.1 is that a large weld pool is formed, which is prone to instabilities, which may lead to uneven joints. Furthermore, tearing of the individual films may occur from the seams.

In the laser contact method illustrated in fig. 1.2, insufficient contact with the electrical conductor can occur in a simultaneously large melt pool surface due to the low melt pool depth. Furthermore, in the method according to fig. 1.2, there are limitations on the degree of freedom of design.

In the method shown in fig. 1.3, despite the considerable reduction in the size of the weld pool, the multi-stage process requires a large number of joining processes, which are very cumbersome and extend the process duration. In the laser contact method shown in fig. 1.4, a cumbersome pretreatment is required for producing flush stack edges. This results in an excessively long process duration, which in extreme cases may no longer be an acceptable few minutes.

Fig. 2 shows the laser contacting of the individual film-like films 30 and the electrical conductors 46 with one another within the cell film stack 10.

As can be gathered from fig. 2, a laser radiation source 12 is arranged above the cell thin-film stack 10. The laser is produced at 10^-9s and 10^-7Laser pulses 50 with pulse durations between s either at 10^-13s and 10^-11s, if such a laser pulse 50 impinges on the upper side of the cell film stack 10, which comprises a plurality of film-like individual films 30 and electrical conductors 46 layered one above the other, a channel 32 is produced in the cell film stack starting from a channel inlet 58, in the case of short and ultrashort laser pulses 50, the channel 32 is usually produced gradually by a sequence of a plurality of laser pulses 50, for which a portion of the irradiated material is converted into the molten (schmelzfl ü) phase at the channel wall 36 and in particular at the channel bottom 34 and a portion of the material is evaporated almost directly, by the successive execution of a plurality of laser pulses 50 with an intermediate gap, the depth of the channel 32 is advanced in the direction of the electrical conductor (Ableiter) 46, in the melt channel 40 formed in each case on the channel bottom 34 in question, the pressure is increased by the sequence of the laser pulses 50 having an ultrashort pulse duration, whereby steam 42 is formed in the channel bottom 40, by the steam forming channel 42, and the melt channel 32 is formed in the direction of the molten pool 32, by the molten metal layer 60, which is drawn up in the molten pool 32, and the molten metal melt is solidified in the direction of the molten pool 32, which is formed in the molten metal layer 60, the molten metal layer 32, which is drawn up in the molten pool 32, and the molten metal layer is drawn up in the molten metal layer of the molten metal layer, which is drawn up in the molten metal layer of the molten metal which is drawn up, and solidified by the molten metal layer, and the molten metal layer, which is drawn up in the molten metal layer of molten metal which is drawn up in the molten metal layer of molten metal which is drawn up in the molten metal which is drawn up inContact areas 54 are formed between the surfaces of the electrical conductors 46 on the underside of the stack 10. The contact region between the surface 56 of the electrical conductor 46 and the melt pool 40 or the thin continuous contact layer 52 is designated by reference numeral 54 in the illustration according to fig. 2.

Due to the continuous deepening of the channel 32, which is carried out by the successive sequence of laser pulses 50, the melt pool 40 moves deeper and deeper in the direction of the channel bottom 34. Since the melt pool 40 has a rather small volume, the local heating of the cell thin film stack 10 is very limited. There is another reason for the small volume of the molten bath 40, namely: as a result of the pressure increase in the melt pool 40 and the accompanying vapor formation 42, the melt is transported from the melt pool in the direction of the channel inlet 58 as a function of the number of laser pulses 50, and solidifies along the channel wall 36 and forms a thin continuous contact layer 52. The construction is performed until the height 48 of the stack of battery films 10 and the electrical conductors 46 is reached.

The arrangement of the channels formed on the upper side of the cell film stack 10 can be seen from the illustration according to fig. 3.

Fig. 3 shows the uppermost film-like individual film 72. On this single film there is a matrix 62 of joints 64. The individual junctions 64 corresponding to the channels 32 extend from the uppermost film-like individual film 72 into the plane of the drawing, i.e. towards the underlying film-like individual film 30, as far as the current conductors 46, from which the cell film stack 10 is formed.

As can be gathered from fig. 3, the individual joints 64 are spaced apart from one another by horizontal spacings 70 (rows) and vertical spacings 71 (columns). The matrix 62 of joints 64 comprises a plurality of joints 64, which can be arranged alongside one another or above one another in the form of rows 66 or in the form of columns 68.

The method proposed according to the invention is distinguished by a relatively small volume in the melt pool 40, which is continuously distributed along the channel wall 36 of the channel 32, which is continuously formed by the sequence of laser pulses 50 in the individual film-like films of the cell film stack 10, until the electrical conductor 46 is reached, there is a greater freedom in the process design due to the locally very limited treatment area, than due to the variation of parameters such as the pulse duration of the laser pulses 50, the pulse frequency of the laser pulses 50, the pulse energy, the focal position and the spot size, and therefore a greater freedom in the design of the process is possible, in particular the energy input can be adjusted, which leads to a direct influence on the melt generation and on the diameter and achievable depth of the channel 32. in the method proposed according to the invention, by introducing a plurality of channels 32 arranged side by side as outlined in the illustration according to fig. 3, there is a great advantage in terms of design freedom, as a result of which not only the efficiency of the mechanical contact (leitsunksf ä) but also the adjustment of the electrical contact geometry of the other joint geometry shown in fig. 64 can be adjusted in the diagram 64.

The present invention is not limited to the embodiments described herein and the aspects emphasized therein. Rather, a number of modifications are possible within the scope of the claims and within the reach of the person skilled in the art.

Claims

1. Method for connecting (30) individual film-like films of a stack of battery films (10) by means of a laser radiation source (12) by means of a cohesive bonding, comprising at least the following method steps:

a) generating a channel (32) in the cell thin film stack (10) by means of a short or ultrashort laser pulse (50) with the laser radiation source (12),

b) wherein the removed material of the individual film (30) in the form of a film is partially evaporated and a melt pool (40) is formed partially in the channel bottom (34) of the channel (32),

c) a pressure increase is caused in the melt pool (40) by the laser pulse (50) and the melt is discharged (44) from the melt pool (40) by steam formation (42) in a conveying direction (60) in the direction of a channel inlet (58) and

d) a thin, continuous contact layer (52) made of the melt is produced on the channel walls (36) for the cohesive connection of the individual film webs (30) to one another.

2. Method according to claim 1, characterized in that the short laser pulse (50) has a pulse duration of 10^-9s and 10^-7s in between.

3. The method according to claim 1, wherein the ultrashort laser pulse (50) has a pulse duration of 10^-13s and 10^-11s in between.

4. Method according to claim 1, characterized in that the channels (32) are brought into cohesive engagement with the electrical conductors (46) within the contact regions (54) when the channels are produced in the stack (10) of cell films.

5. Method according to claim 1, characterized in that according to method step a) channels (32) are created in the cell thin-film stack (10) gradually by means of a plurality of laser pulses (50).

6. Method according to claim 1, characterized in that the method steps a) to d) are carried out a plurality of times, as long as the channel bottom (34) forms a contact area (54) with the electrical conductor (46).

7. The method of claim 1, wherein one or more of the following process parameters are changed for tuning the method:

-the pulse duration of the laser pulse (50),

-the pulse frequency of the laser pulses (50),

-a pulse energy of each laser pulse (50),

-a focal position and

-spot size.

8. The method according to claim 1, characterized in that a plurality of side-by-side channels (32) are produced on the cell film stack (10) starting from the uppermost film-like individual film (72).

9. Method according to claim 8, characterized in that the channels (32) are produced in rows (66) or columns (68) alongside one another or above one another.

10. Method according to claim 1, characterized in that the channels (32) are arranged in a construction space optimized form.

11. Use of the method according to one of claims 1 to 10 for bringing film-like individual films (30) into cohesive contact with one another and with electrical conductors (46) of a stack of battery films (10).