Method for producing an electric battery cell

Abstract

Method for producing an electric battery cell, said method comprising: - stacking in an interleaved manner a plurality of first sheets (1 ) in a first electrically conductive material and a plurality of second sheets (2) in a second electrically conductive material, wherein each first sheet (1 ) comprises a first tab (5) and wherein the first tabs form a first stack (7) in which the first tabs are in mutual contact; and - directly modulating a laser source to generate a pulsed laser beam (10; 16) and mutually welding the first tabs (5) in the first stack (7) by means of the pulsed laser beam (10).

Description

[0001] DESCRIPTION

[0002] Title: METHOD FOR PRODUCING AN ELECTRIC BATTERY CELL

[0003] Technical field of the invention

[0004] The present invention relates to a method for producing an electric battery cell, for example a solid-state battery or a lithium-ion battery.

[0005] State of the art

[0006] The industrial production of electric batteries, for example lithium-ion batteries, comprises the production of the main component thereof, namely battery cells, which may be cylindrical, pouch (or bag-type), prismatic, etc. Each cell comprises first sheets (e.g. forming the cathode) and second sheets (e.g. forming the anode) made of electrically conductive material (which acts as a current collector, typically aluminum for the cathode and copper for the anode), which are interleaved with one another and aligned so as to form a stack, and which are separated by a separator sheet normally composed of a plastic polymer or ceramic material that has the function of an insulator between two adjacent sheets.

[0007] Each sheet is coated with active material, except for a portion, referred to as a tab, which protrudes from the stack proper to ensure electrical contact.

[0008] Once the stack of first sheets, second sheets, and separator sheets has been assembled, the stack is inserted into a container (or “case”). The stacks of tabs respectively of the cathode and the anode are connected, by means of ultrasonic welding, respectively to the two electrical contacts of the cell that extend out of the container.

[0009] The container is then filled with an electrolyte liquid, for example by injection. The electrolyte, e.g. containing lithium salts, wets the first and second sheets in order to transfer electrical charges between the first and second sheets.

[0010] Summary of the invention

[0011] In the above context, the Applicant has ascertained that the correct assembly of the battery cells that make up an electric battery, whether prismatic, cylindrical, or pouchtype, is an extremely complex operation, which requires long chains of machinery and stages and maximum precision at each stage thereof, in order to ensure safety, quality, and reliability over time.

[0012] The Applicant has addressed the problem of carrying out the welding of the stacks of cathode and / or anode tabs in such a manner as to weld the entire stack over the whole thickness thereof (i.e. involving all the sheets), with high welding process speed, with ease of automation, with low mechanical stress, with the ability to access joints that are difficult to reach, with low heat input and distortion, and / or with a wide range of possible welding geometries, while ensuring high repeatability of the pre-welding in order to reduce defects and irregularities in the finished cells and / or to ensure limited costs, both in terms of investment and operation.

[0013] According to the Applicant one or more of the above-mentioned problems is solved by a method for producing an electric battery cell in accordance with the appended claims and / or having one or more of the following features.

[0014] According to one aspect the invention relates to a method for producing an electric battery cell.

[0015] Preferably the method comprises stacking in an interleaved manner a plurality of first sheets in a first electrically conductive material and a plurality of second sheets in a second electrically conductive material.

[0016] Preferably each first sheet comprises a first tab.

[0017] Preferably said first tabs form a first stack in which said first tabs are in mutual contact.

[0018] Preferably the method comprises directly modulating a laser source to generate a pulsed laser beam.

[0019] Preferably the method comprises mutually welding said first tabs to each other in said first stack by means of said pulsed laser beam.

[0020] The Applicant has discovered that the pulsed laser beam mode with respect to a continuous laser beam reduces the overall thermal input to the material while keeping the welding in a conduction regime in which melting of the material occurs only by heat conduction from the energy of the laser beam thereby maximizing welding productivity and welding quality.

[0021] The Applicant has verified that in a comparative solution, in which the laser beam is not pulsed (that is at substantially continuous power), the high energy overall transferred to the material can facilitate vaporization of the material, in particular of the sheets first impinged by the laser beam, thereby triggering a welding pool (“keyhole”) surrounded by molten material that flows and fills the void while the laser beam sinks into the material, sealing the welding (resulting in a welding having a very deep and narrow profile). Such a keyhole welding mode can entail the formation of voids and other defects. For example, the interstitial air between the sheets that is incorporated into the molten welding pool can lead to porosity and to ejection of molten material (“spattering”).

[0022] The present invention, on the contrary, makes it possible to weld all the tabs of the stack of tabs, in at least one or more points of the stack, avoiding or limiting the formation of consequent defects, for example, due to vaporization or displacement of material.

[0023] Moreover, directly modulating the laser source to generate the pulsed laser beam makes it possible, especially for pulses of limited duration and / or for frequencies lower than those of typical pulsed lasers (e.g. on the order of kHz), to generate the pulsed laser beam in a simple and economical manner, in that a laser source designed to emit in continuous mode (and therefore typically less expensive than a pulsed laser) can be used but operated according to the present invention in direct power modulation, without the need for additional external devices.

[0024] Directly modulating, as known (see for example “Directly Modulated Semiconductor Lasers”, IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 24, NO. 1 , JANUARY / FEBRUARY 2018 by Ning Hua Zhu et al.), consists in a modulation of the laser carried out directly on the optical source, without using an external modulator, for example, wherein the analog electronic signal is transposed onto the optical carrier by modulating the laser current with the analog electronic signal to be transposed directly onto the optical carrier. An alternative to direct modulation of the laser is to operate the laser in continuous mode (so-called CW) and delegate to a further downstream device (modulator) the transposition onto the optical carrier, with higher costs and technological and constructive complications.

[0025] The present invention, in one or more of the aspects thereof, may have one or more of the following preferred features.

[0026] In one embodiment the method comprises (e.g. in a second station) positioning a first electrical contact in contact with said first stack and said mutually welding said first tabs to each other comprises, simultaneously, welding said first stack of first tabs to said first electrical contact to create an electrical connection between all said first sheets and said first electrical contact. In this manner electrical connection of the whole stack of sheets is ensured.

[0027] In one embodiment the method comprises, prior to said mutually welding said first tabs to each other in said first stack by means of said pulsed laser beam, mutually pre-welding said first tabs to each other in said first stack to spatially fix said first tabs to each other. Preferably during said pre-welding mutually pre-welding only said first tabs to each other in said first stack is provided. In other terms the pre-welding does not involve further elements to be welded other than the first tabs.

[0028] Preferably said mutually pre-welding is performed in a first station and the method comprises, subsequent to said pre-welding, moving said first and second sheets interleaved from said first station to a second station.

[0029] Preferably the method comprises, in said second station, performing said mutually welding of said first tabs to each other in said first stack by means of said pulsed laser beam.

[0030] The Applicant has ascertained that it is advantageous to subject the stacks of tabs that act as current collectors to a pre-welding, subsequent to the step of forming the stack of sheets and before (hence the prefix pre-) one or more subsequent operations, including the above-mentioned welding of the stacks of tabs, e.g. to the electrical contacts of the cell. The primary function of such pre-welding is to join the tabs to each other, fixing and compacting the tabs reciprocally, in order to improve handling of the semi-finished product, in particular in view of high-speed movements thereof that could induce uncontrolled fluttering of the tabs. In this manner the quality of the subsequent operations is improved, such as for example the subsequent welding of the stack of tabs with further conductive elements, such as those forming part of the external electrical contacts of the cell. In this context the pre-welding promotes electrical contact of all the tabs, and therefore of all the current collector sheets, with the external contacts.

[0031] Said pre-welding can be performed with any suitable welding technique, for example by means of ultrasonic welding or, preferably, by laser beam welding, continuous or pulsed. In the latter case preferably the pre-welding is performed with the modes described herein for the welding.

[0032] In one embodiment said mutually pre-welding said first tabs to each other is performed by means of ultrasonic welding. Such technique is a reliable and consolidated technique. In one embodiment said mutually pre-welding said first tabs to each other is performed by means of a further pulsed laser beam, more preferably obtained by directly modulating a further laser source. It is observed that the term further does not necessarily imply a laser source distinct from the above-mentioned laser source. The Applicant observes that the pre-welding presents specific criticalities, since the pre-welding is a welding of extremely thin sheets (e.g. having the thickness indicated below) stacked one on top of the other and typically without other elements being involved in the welding, as instead occurs for example in the subsequent welding in which, in addition to the tabs, also the external electrical contact is welded (where the presence of the latter relaxes some of the above-mentioned criticalities). In this context, the Applicant has found that pulsed laser pre-welding, with respect for example to ultrasonic welding, is overall fast, is easily automatable, reduces mechanical stress (being a contactless process), makes it possible to access joints that are difficult to reach (since accessibility from two sides as required for the anvil and the sonotrode of ultrasonic welding is not necessary), and / or makes it possible to achieve a wide range of possible welding geometries.

[0033] Preferably each second sheet comprises a second tab, wherein said second tabs form a second stack in which said second tabs are in mutual contact.

[0034] Preferably the method comprises performing on said second tabs and / or said second stack, the operations described herein for said first tabs and, respectively, said first stack. Preferably the method comprises mutually welding said second tabs to each other in said second stack by means of said pulsed laser beam.

[0035] Preferably the method comprises, e.g. in said first station, mutually pre-welding said second tabs to each other in said second stack to spatially fix said second tabs to each other.

[0036] Preferably said welding and / or said mutually pre-welding said second tabs is performed with the same modes described herein for respectively welding and pre-welding said first tabs.

[0037] Preferably the method comprises (e.g. in said second station) positioning a second electrical contact in contact with said second stack and said mutually welding said second tabs to each other comprises welding said second stack of second tabs to said second electrical contact to create an electrical connection between all said second sheets and said second electrical contact. In this manner the electrical connection also with all the second sheets is completed.

[0038] In one embodiment said first and / or second electrical contact is a metal sheet, preferably respectively in the first and / or second material, more preferably having a thickness greater than 100 pm.

[0039] In one embodiment said first and / or second electrical contact is a further stack of first and / or second tabs belonging respectively to further first and / or second sheets reciprocally stacked.

[0040] Preferably the method comprises providing a plurality of separator sheets, preferably in an electrically insulating material, for example a plastic polymer or ceramic material, each separator sheet being interposed between each pair of consecutive first and second sheets.

[0041] Preferably each first and / or second sheet, more preferably except for the respective tabs, is coated, more preferably on both faces, with an active material.

[0042] Preferably the method comprises, subsequent to said welding, inserting said first and second sheets (and preferably said separator sheets) into a container (or “case”), and more preferably filling said container with an electrolyte liquid. In this manner the battery cell is completed.

[0043] Preferably said plurality of first and / or second sheets, and / or said plurality of separator sheets, consists of a number of respective sheets greater than or equal to thirty, more preferably greater than or equal to forty, and / or less than or equal to two hundred, more preferably less than or equal to one hundred.

[0044] Preferably said first and / or second material is a metal or a metal alloy.

[0045] Preferably said first material is copper and / or said second material is aluminum.

[0046] Preferably each first and / or second sheet has a respective thickness greater than or equal to 1 pm and / or less than or equal to 30 pm. Preferably said thickness of each first and / or second sheet is greater than or equal to 2 pm, more preferably greater than or equal to 5 pm, and / or less than or equal to 20 p, more preferably less than or equal to 15pm.

[0047] Preferably said welding by means of said pulsed laser beam comprises directing said pulsed laser beam onto, and preferably substantially perpendicularly to, a face of said first stack, and preferably also of said second stack, more preferably said face being substantially parallel to a prevailing development plane of said tabs. In other terms the laser beam preferably impinges on the free face of an end tab of the stack of tabs. The Applicant observes that incidence of the laser beam directly on the ultra-thin tabs, rather than on more robust and / or resistant elements such as an electrical terminal having a thickness of some hundreds of microns, entails specific criticalities solved by the present invention.

[0048] With “substantially perpendicularly” it is meant for example that an angle formed by said laser beam with a projection thereof on said face is greater than or equal to 75°, and less than or equal to 105°, for example greater than or equal to 85° and less than or equal to 95°, for example 90°.

[0049] Preferably said welding comprises emitting said pulsed laser beam from an optical fiber, which can be single mode (in which a single guided mode or a plurality of guided modes propagate) or multimode.

[0050] Preferably the method comprises, during at least part of said welding by means of said pulsed laser beam, mutually translating (more preferably the laser beam is translated while keeping the stack of tabs stationary) said pulsed laser beam with respect to said first and / or second tabs with a translation speed, v, more preferably along a predetermined trajectory, e.g. rectilinear, on a face of said first stack, and preferably also of said second stack. In other terms the spot of the laser beam moves on the surface of the stack of tabs (e.g. said free face) with speed v.

[0051] Preferably said translation speed is greater than or equal to 60 mm / s, more preferably greater than or equal to 80 mm / s, and / or less than or equal to 500 mm / s. In this manner the welding is fast.

[0052] Preferably said pulsed laser beam has a pulse frequency, f, a pulse intensity, I, and / or a pulse duration, d.

[0053] By pulse frequency it is meant the inverse of the repetition period T of the pulse.

[0054] By pulse intensity, I, or peak intensity, it is meant the ratio between the peak pulse power, Ph, and the area of the cross section of the laser beam (or “spot”), As, according to the formula

[0055] It is observed that the power may not be homogeneous over the whole spot. The power density distribution within the spot can be of a quasi-Gaussian type, especially in the case of single-mode lasers, can be homogeneously distributed over the area of the spot, or can be distributed over two or more concentric laser beams propagated by the same optical fiber. In the latter case the power can be distributed in variable percentages among the various laser beams and such percentages can be dependent on each other (with discrete combinations of power values on the various beams) or independent (on each beam any power up to the maximum value allowed by the source can be delivered).

[0056] It is further observed that the power may not be homogeneous within the duration time of the pulse itself, for example with a ramp variation of the power within the pulse duration. Preferably said pulse frequency is greater than or equal to 1 kHz and / or less than or equal to 2 MHz.

[0057] Preferably said pulse duration, d, is greater than or equal to 10 ns and / or less than or equal to 1 ms.

[0058] Preferably said pulse intensity is greater than or equal to 5 MW / cm2and / or less than or equal to 150 MW / cm2.

[0059] The Applicant has experimentally verified that by selecting the values of the above- mentioned fundamental process parameters of the pulsed laser beam within the above- mentioned ranges it is possible to weld the stack over the whole thickness thereof reducing to a minimum or eliminating vaporization of one or more tabs.

[0060] The Applicant observes that selection of the specific values of the above-mentioned parameters within the above-mentioned ranges depends on the specific operating conditions, in particular the number and thickness of the tabs in each stack, the translation speed of the laser beam, the power distribution on the laser spot, etc, according to the considerations set out below. The person skilled in the art, starting from a choice of values for one or more parameters within the ranges described herein, is able to select the remaining parameters, within the above-mentioned ranges, on the basis of the interrelation among the process parameters.

[0061] The duration, the frequency, and the period T are correlated to the duty cycle, De, defined as the percentage of the period T in which emission of the pulse occurs, according to the formula 100 = d * f * 100.

[0062] Preferably the duty cycle is less than or equal to 50%, more preferably less than or equal to 40%, and / or greater than or equal to 10%, more preferably greater than or equal to 20%. It is observed that the duty cycle is always lower than 100 (and therefore the duration is always lower than the inverse of the frequency).

[0063] By percentage overlap O it is meant the parameter defined by the formula: where dsis the equivalent diameter of the spot, assuming a circular spot, given by the formula ds= In the case of a circular spot, the equivalent diameter coincides with the real diameter.

[0064] It is observed that the real overlap, Or, between two successive pulses can be different from (typically greater than) the above-mentioned overlap. For example, in the case of a circular spot, the real overlap can be given by the formula:

[0065] As can be seen, with increasing frequency and spot diameter, and / or with decreasing translation speed, the overlap between successive pulses increases.

[0066] Preferably a percentage overlap (0) between successive pulses is less than or equal to 60%, more preferably less than or equal to 40%, even more preferably less than or equal to 30%.

[0067] The Applicant has experimentally verified that such lower limits of the overlap, on the one hand, provide a satisfactory welding in terms of welding of the entire stack over the whole thickness thereof in at least one or more points, and, on the other hand, avoid the abovedescribed phenomenon.

[0068] In some embodiments, the theoretical overlap, and possibly also the real overlap, is positive, that is the pulses maintain a certain degree of overlap. In such case the welding results continuous along the translation direction of the pulsed laser beam, at least in the portion of the stack facing the beam and possibly over the entire thickness of the stack of tabs.

[0069] In other embodiments, the theoretical overlap, and possibly also the real overlap, is negative, for example less than or equal to -20%, or less than or equal to -40%.

[0070] Preferably said welding comprises creating on said first stack, and preferably also said second stack, of tabs a spatial succession of welding points, more preferably as deep as the entire stack, distinct from one another. The Applicant has in fact discovered that the present invention provides satisfactory results also in the case of welding by spatially separated points on the welding face (“tack welding”), and / or in the case of welding of the entire thickness of the stack only at points spatially separated from one another.

[0071] It is observed that the pulse intensity increases with increasing pulse power and decreases with increasing equivalent diameter.

[0072] Preferably the equivalent diameter of the spot, ds, is greater than or equal to 40 pm, and / or less than or equal to 200 pm.

[0073] Preferably the peak pulse power, Ph is greater than or equal to 500 W, and / or less than or equal to 5000 W.

[0074] Preferably the energy per pulse, E, given by the formula E = Ph* d, is greater than or equal to 0.1 mJ and / or less than or equal to 1 J.

[0075] By power P effectively emitted during the process it is meant P=E*f.

[0076] In one embodiment, said pulse frequency is less than or equal to 30 kHz, more preferably less than or equal to 20 kHz, even more preferably less than or equal to 10 kHz, said pulse duration is greater than or equal to 50 ns, more preferably greater than or equal to 100 ns, and less than or equal to 300 ns, more preferably less than or equal to 200 ns, and said pulse intensity is greater than or equal to 10 MW / cm2, more preferably greater than or equal to 20 MW / cm2, and less than or equal to 100 MW / cm2, more preferably less than or equal to 50 MW / cm2.

[0077] In such embodiment, preferably the peak pulse power, Ph is greater than or equal to 1000 W, and / or less than or equal to 1500 W. In such embodiment, preferably the equivalent diameter of the spot, ds, is greater than or equal to 50 pm, and / or less than or equal to 100 pm.

[0078] In such embodiment, preferably the energy per pulse is greater than or equal to 0.1 J and / or less than or equal to 0.5 J.

[0079] In such embodiment, preferably the duty cycle is greater than or equal to 10%, more preferably greater than or equal to 20%, and / or less than or equal to 50%, more preferably less than or equal to 40%.

[0080] In such embodiment, preferably the overlap is greater than zero, more preferably greater than or equal to 10%, and / or less than or equal to 30%.

[0081] In such embodiment, preferably the translation speed is greater than or equal to 50 mm / s, and / or less than or equal to 200 mm / s.

[0082] In one embodiment said pulse frequency is greater than or equal to 500 kHz, more preferably greater than or equal to 800 kHz, even more preferably greater than or equal to 1000 kHz, said pulse duration is less than or equal to 120 ns, more preferably less than or equal to 80 ns, and / or greater than or equal to 20 ns, and said pulse intensity is greater than or equal to 10 MW / cm2, more preferably greater than or equal to 20 MW / cm2, and / or less than or equal to 100 MW / cm2, more preferably less than or equal to 50 MW / cm2.

[0083] In such embodiment, preferably the peak pulse power, Ph is greater than or equal to 1200 W, and / or less than or equal to 1800 W.

[0084] In such embodiment, preferably the equivalent diameter of the spot, ds, is greater than or equal to 50 pm, and / or less than or equal to 100 pm.

[0085] In such embodiment, preferably the energy per pulse is less than or equal to 0.2 J.

[0086] In such embodiment, preferably the duty cycle is greater than or equal to 20%, more preferably greater than or equal to 30%, and / or less than or equal to 60%.

[0087] In such embodiment the translation speed can be the maximum made available by the movement system, for example greater than or equal to 10 m / s, in order to carry out a spot welding, that is spatially discontinuous as described above.

[0088] In a further aspect, the invention relates to a method for producing an electric battery cell, said method comprising:

[0089] - stacking in an interleaved manner a plurality of first sheets in a first electrically conductive material and a plurality of second sheets in a second electrically conductive material, wherein each first and second sheet has a respective thickness greater than or equal to 1 pm and less than or equal to 30 pm, wherein each first sheet comprises a first tab and wherein said first tabs form a first stack in which said first tabs are in mutual contact;

[0090] - mutually welding said first tabs to each other in said first stack by means of a pulsed laser beam to spatially fix said first tabs to each other;

[0091] - during at least part of said welding by means of said pulsed laser beam, mutually translating said laser beam with respect to said first tabs with a translation speed; wherein said pulsed laser beam has a pulse frequency (f), a pulse intensity (I), and a pulse duration (d), and wherein said pulse frequency is greater than or equal to 1 kHz and less than or equal to 2 MHz, wherein said pulse duration is greater than or equal to 10 ns and less than or equal to 1 ms and wherein said pulse intensity is greater than or equal to 5 MW / cm2and less than or equal to 150 MW / cm2.

[0092] In a further aspect, the invention relates to a method for producing an electric battery cell, said method comprising:

[0093] - stacking in an interleaved manner a plurality of first sheets in a first electrically conductive material and a plurality of second sheets in a second electrically conductive material, wherein each first sheet comprises a first tab and wherein said first tabs form a first stack in which said first tabs are in mutual contact;

[0094] - in a first station, mutually pre-welding said first tabs to each other in said first stack by means of a laser beam to spatially fix said first tabs to each other;

[0095] - subsequently, moving said first and second sheets interleaved from said first station to a second station; and

[0096] - in said second station, performing an operation on said first and second sheets interleaved, wherein said operation in said second station comprises welding said first stack of first tabs to a first electrical contact to create an electrical connection between all said first sheets and said first electrical contact.

[0097] Preferably said laser beam is a pulsed laser beam.

[0098] Preferably said pre-welding comprises directly modulating a laser source to generate said pulsed laser beam.

[0099] Preferably during at least part of said pre-welding by means of said laser beam, it is provided to mutually translate said laser beam with respect to said first tabs with a translation speed (v), wherein said pre-welding comprises creating on said first stack of tabs a spatial succession of welding points distinct from one another.

[0100] Preferably said pre-welding comprises directing said laser beam onto a face of said first stack substantially parallel to a prevailing development plane of said tabs, wherein said laser beam is more preferably substantially perpendicular to said face of said first stack. Preferably said pre-welding comprises emitting said laser beam from an optical fiber.

[0101] Preferably during said pre-welding it is provided to mutually pre-weld only said first tabs to each other in said first stack.

[0102] Preferably said welding in said second station is performed by laser beam welding, more preferably by pulsed laser beam welding.

[0103] With regard to the latter two aspects of the invention, one or more of the preferred features and the considerations set out above apply.

[0104] It is specified that some steps of the method described above may be independent of the order of execution reported, except where a sequence or simultaneity between two or more steps is expressly indicated.

[0105] Moreover, some steps may be optional. Moreover, some steps may be carried out iteratively or may be carried out in series or in parallel with other steps of the method. Brief description of the figures

[0106] Figure 1 shows a semi-finished product of a battery cell in the pre-welding step of the method according to one embodiment of the present invention;

[0107] Figure 2 shows the semi-finished product of Figure 1 in the subsequent welding step of the method according to one embodiment of the present invention.

[0108] Detailed description of some embodiments of the invention

[0109] The features and advantages of the present invention will be further clarified by the following detailed description of some embodiments, provided by way of example and not limitation of the present invention, with reference to the accompanying figures.

[0110] The method for producing an electric battery cell initially comprises stacking in an interleaved manner a plurality of first sheets 1 in a first electrically conductive material, for example copper, and a plurality of second sheets 2 in a second electrically conductive material, for example aluminum, as schematically shown in Figure 1. Between each pair of consecutive first and second sheets a separator sheet 3 made of an electrically insulating material is interleaved.

[0111] As for example known, each first and second sheet is coated, preferably on both faces, with an active material 4 (represented by the black strips in the figures).

[0112] Stacking of the sheets 1 , 2 and of the separator sheets 3 can take place by means of different construction methodologies, per se known, such as stacking of individual precut sheets, z-folding of a continuous separator sheet between pre-cut anode and cathode sheets, or rolling (or winding), in which the continuous precursor sheets of the sheets are first stacked one on top of the other and then continuously wound on a base.

[0113] Each first and second sheet 1 , 2 comprises respectively a first tab 5 and a second tab 6, not coated with active material (that is, in the example, only metal), which protrudes from the stack of interleaved first and second sheets to form respectively a first stack 7 and a second stack 8 of first and second tabs 5, 6, respectively, in which the tabs are in mutual contact or in close proximity.

[0114] Although in the figures the stacks of tabs 7 and 8 are schematically shown on opposite sides of the stack of interleaved sheets, in some embodiments the stacks of tabs can be located on the same side of such stack.

[0115] In one embodiment, the first tabs 5 and the second tabs 6 are mutually pre-welded to each other respectively in the first stack 7 and the second stack 8 to spatially fix to each other respectively all the first tabs and the second tabs of each stack. To this end any welding technique can be used, such as for example ultrasonic welding (not shown).

[0116] In a preferred embodiment, such pre-welding is carried out by means of a laser beam 10, continuous or preferably pulsed.

[0117] To this end a single source (not shown) emitting a single laser beam 10 can be used to pre-weld both the first tabs and the second tabs in distinct time phases, or a dedicated laser source can be used for each first and second stack (in which case the two weldings can take place simultaneously).

[0118] Preferably the laser beam is guided by means of an optical fiber 11 , which can be single mode or preferably multimode. The present invention encompasses any power distribution on the spot: uniform or non-uniform, radially uniform or non-uniform, top hat, Gaussian, ring-shaped, etc.

[0119] Preferably it is provided to mutually translate the stack of tabs and the laser beam (preferably the latter is moved while keeping the stack of tabs stationary), so that the spot of the laser beam moves on the face of the respective stack with a translation speed, v, for example along a rectilinear segment.

[0120] Preferably the laser beam is directed onto, for example substantially orthogonally to, a free end face of the uppermost tab of the respective stack of tabs, such face being substantially parallel to the development plane of the tabs, as shown in Figure 1.

[0121] In other embodiments, not shown, the laser beam can be directed (exclusively or in addition to the above-mentioned face) onto the end face of the stack orthogonal to the development plane of the tabs (that is on the thickness side). Thanks to the transfer of energy from the laser beam, the material melts and, following re-solidification, a welding 12 is obtained that, at least in one or more points, involves all the tabs of the respective stack, that is extends along the entire thickness of the stack. As explained above, the pulsed nature of the laser can limit or avoid vaporization of the material, inducing substantially only conduction melting.

[0122] In a first example, each stack of tabs contains fifty tabs (and therefore fifty first sheets and fifty second sheets) having a thickness equal to 6 pm for the copper tabs and 12 pm for the aluminum tabs.

[0123] Preferably a laser source is used, for example a multimode fiber laser marketed by n Light Inc., power 2.5 kW, wavelength 1070 nm, normally operating in continuous mode being designed for such use, directly modulating (e.g. with ON / OFF mode) the supply current to the pump diodes that provide energy to the resonator of the laser source (operation made possible thanks to the limited pulse frequency, for example up to 100 kHz).

[0124] The parameters used are exemplarily the following:

[0125] Subsequent to the pre-welding (possibly with the interposition of further steps, not described herein as for example known), it is provided, as shown in Figure 2, to weld the first and second stacks of tabs respectively to a first electrical contact 13 and a second electrical contact 14 (shown only schematically) in order to create an electrical connection between all the first and second sheets 1 , 2 and the first and second electrical contacts 13, 14, respectively.

[0126] Preferably such welding takes place in a second station distinct from a first station in which the pre-welding takes place, the stack of interleaved first and second sheets being moved from the first station to the second station (not shown).

[0127] The welding to the electrical contacts 13, 14, which constitute or are electrically connected to the electrical terminals accessible from the outside of the cell, is carried out with a pulsed laser beam 16 obtained by direct modulation of a laser source (not shown, coinciding with or distinct from the above-mentioned laser source used for the prewelding, for example with a laser source and the process parameters described above), delivered through an optical fiber 15. The result is a welding 17 that involves the whole thickness of the stack of tabs and the electrical contact.

[0128] In an alternative embodiment, not shown, the mutual welding of the first tabs 5 in the first stack 7, and of the second tabs 6 in the second stack 8, and the welding of the first stack 7 and the second stack 8 with respectively the first and second electrical contacts 13, 14, takes place in a single solution by means of the above-mentioned pulsed laser beam 16 through direct modulation. This single-solution welding can take place both in the absence of a previous pre-welding, and in applications in which a pre-welding is provided (the latter carried out by laser or ultrasonic welding). In such case the laser source and the laser process parameters can exemplarily be those described above.

[0129] Typically it is therefore provided to insert the stack of interleaved first and second sheets and with the tabs pre-welded into a container (or “case”), not shown, and to fill the container with an electrolyte liquid.

[0130] Production of battery cells can comprise further steps before and / or after those described above, for example as per se known.

Claims

CLAIMS1 . Method for producing an electric battery cell, said method comprising:- stacking in an interleaved manner a plurality of first sheets (1 ) in a first electrically conductive material and a plurality of second sheets (2) in a second electrically conductive material, wherein each first sheet (1 ) comprises a first tab (5) and wherein said first tabs form a first stack (7) in which said first tabs are in mutual contact; and- directly modulating a laser source to generate a pulsed laser beam (10; 16) and mutually welding said first tabs (5) to each other in said first stack (7) by means of said pulsed laser beam (10).

2. Method according to claim 1 , said method comprising positioning a first electrical contact (13) in contact with said first stack (7), wherein said mutually welding said first tabs (5) to each other in said first stack (7) comprises, simultaneously, welding said first stack (7) of first tabs (5) to said first electrical contact (13) to create an electrical connection between all said first sheets and said first electrical contact (13) by means of said pulsed laser beam (10; 16).

3. Method according to any one of the previous claims, comprising, prior to said mutually welding said first tabs (5) to each other in said first stack (7) by means of said pulsed laser beam (10; 16), mutually pre-welding said first tabs (5) to each other in said first stack (7) to spatially fix said first tabs (5) to each other.

4. Method according to claim 3, wherein said mutually pre-welding is performed in a first station, the method comprising:- subsequent to said pre-welding, moving said first (1 ) and second (2) sheets interleaved from said first station to a second station; and- in said second station, performing said mutually welding of said first tabs (5) to each other in said first stack (7) by means of said pulsed laser beam (10; 16).

5. Method according to any one of the previous claims, wherein said pulsed laser beam has a pulse frequency (f), a pulse intensity (I), and a pulse duration (d), wherein said pulse frequency is greater than or equal to 1 kHz and less than or equal to 2 MHz, wherein said pulse duration is greater than or equal to 10 ns and less than or equal to 1 ms, and wherein said pulse intensity is greater than or equal to 5 MW / cm2and less than or equal to 150 MW / cm2.

6. Method according to any one of the previous claims, comprising, during at least part of said welding by means of said pulsed laser beam (10; 16), mutually translating said pulsed laser beam with respect to said first tabs (5) with a translation speed (v), whereinsaid welding comprises creating a spatial succession of distinct welding points on said first stack (7) of tabs.

7. Method according to any one of the previous claims, wherein each first sheet (1 ) has a respective thickness greater than or equal to 1 pm and less than or equal to 30 pm, and wherein said plurality of first sheets consists of a number of respective sheets greater than or equal to thirty.

8. Method according to any one of the previous claims, wherein said welding by means of said pulsed laser beam (10; 16) comprises directing said pulsed laser beam (10; 16) onto a face of said first stack (7) substantially parallel to a prevailing development plane of said tabs (5).

9. Method according to claim 8, wherein said pulsed laser beam (10; 16) is substantially perpendicular to said face of said first stack (7).

10. Method according to any one of the previous claims, wherein said welding comprises emitting said laser beam (10; 16) from an optical fiber (11 ).11 . Method for producing an electric battery cell, said method comprising:- stacking in an interleaved manner a plurality of first sheets (1 ) in a first electrically conductive material and a plurality of second sheets (2) in a second electrically conductive material, wherein each first and second sheet (1 , 2) has a respective thickness greater than or equal to 1 pm and less than or equal to 30 pm, wherein each first sheet (1 ) comprises a first tab (5) and wherein said first tabs form a first stack (7) in which said first tabs are in mutual contact;- mutually welding said first tabs (5) to each other in said first stack (7) by means of a pulsed laser beam (10) to spatially fix said first tabs (5) to each other;- during at least part of said welding by means of said pulsed laser beam (10), mutually translating said laser beam with respect to said first tabs (5) with a translation speed (v); wherein said pulsed laser beam has a pulse frequency (f), a pulse intensity (I), and a pulse duration (d), and wherein said pulse frequency is greater than or equal to 1 kHz and less than or equal to 2 MHz, said pulse duration is greater than or equal to 10 ns and less than or equal to 1 ms and wherein said pulse intensity is greater than or equal to 5 MW / cm2and less than or equal to 150 MW / cm2.

12. Method for producing an electric battery cell, said method comprising:- stacking in an interleaved manner a plurality of first sheets (1 ) in a first electrically conductive material and a plurality of second sheets (2) in a second electrically conductivematerial, wherein each first sheet (1 ) comprises a first tab (5) and wherein said first tabs form a first stack (7) in which said first tabs are in mutual contact;- in a first station, mutually pre-welding said first tabs (5) to each other in said first stack (7) by means of a laser beam (10) to spatially fix said first tabs (5) to each other;- subsequently, moving said first (1 ) and second sheets (2) interleaved from said first station to a second station; and- in said second station, performing an operation on said first and second sheets (1 , 2) interleaved, wherein said operation in said second station comprises welding said first stack (7) of first tabs (5) to a first electrical contact (13) to create an electrical connection between all said first sheets (1 ) and said first electrical contact (12).

13. Method according to claim 12, wherein said laser beam (10) is a pulsed laser beam.

14. Method according to claim 13, wherein said pre-welding comprises directly modulating a laser source to generate said pulsed laser beam.

15. Method according to claim 13 or 14, wherein said pulsed laser beam has a pulse frequency (f), a pulse intensity (I) and a pulse duration (d), wherein said pulse frequency is greater than or equal to 1 kHz and less than or equal to 2 MHz, wherein said pulse duration is greater than or equal to 10 ns and less than or equal to 1 ms and wherein said pulse intensity is greater than or equal to 5 MW / cm2and less than or equal to 150 MW / cm2.

16. Method according to any one of the claims from 13 to 15, comprising, during at least part of said pre-welding by means of said laser beam (10), mutually translating said laser beam with respect to said first tabs with a translation speed (v), wherein said pre-welding comprises creating on said first stack of tabs a spatial succession of welding points distinct from one another.

17. Method according to any one of the claims from 13 to 16, wherein each first sheet (1 ) has a respective thickness greater than or equal to 1 pm and less than or equal to 30 pm and wherein said plurality of first sheets consists of a number of respective sheets greater than or equal to thirty.

18. Method according to any one of the claims from 13 to 17, wherein said pre-welding comprises directing said laser beam (10) onto a face of said first stack substantially parallel to a prevailing development plane of said tabs.

19. Method according to claim 18, wherein said laser beam (10) is substantially perpendicular to said face of said first stack.

20. Method according to any one of the claims from 13 to 19, wherein said pre-welding comprises emitting said laser beam (10) from an optical fiber (11 ).

21. Method according to any one of the claims from 13 to 20, wherein during said pre- welding it is provided to mutually pre-weld only said first tabs (5) to each other in said first stack (7).

22. Method according to any one of the claims from 13 to 21 , wherein said welding in said second station is performed by laser beam welding.

23. Method according to claim 22, wherein said welding is pulsed laser beam welding.

24. Method according to claim 15, wherein said pulse frequency is less than or equal to 20 kHz, wherein said pulse duration is greater than or equal to 50 ns and less than or equal to 300 ns and wherein said pulse intensity is greater than or equal to 10 MW / cm2and less than or equal to 100 MW / cm2.

Images