WELDING OF ELECTRODE OUTER LAB STACKS WITH CONNECTIONS IN A TWO-STAGE LASER PROCESS TO REDUCE DEFECTS

Abstract

A method for joining outer tabs of a battery cell to a terminal comprises providing a battery cell stack containing C cathode electrodes, A anode electrodes, and S separators, where C, S, and A are integers greater than one. The method comprises arranging an outer tab stack of one of the C cathode electrodes and the A anode electrodes at a terminal; creating a junction in the outer tab stack of one of the C cathode electrodes and the A anode electrodes at a weld point during a first laser processing step; and welding the outer tab stack of one of the C cathode electrodes and the A anode electrodes at the weld point during a second laser processing step.

Description

INITIATIONThe information provided in this section is for the purpose of generally presenting the context of the disclosure. Both the work of the presently named inventors, to the extent it is described in this section, and the aspects of the description that cannot otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.The present disclosure relates to battery cells, and more particularly to laser welding electrode outer tab stacks to the terminals of battery cells.Electric vehicles (EVs) such as battery electric vehicles (BEVs), hybrid vehicles, and / or fuel cell vehicles include one or more electric machines and a battery system including one or more battery cells, modules, and / or blocks. A power control system is used to control charging and / or discharging of the battery system during charging and / or driving.SUMMARYA method of connecting outer tabs of a battery cell to a terminal includes providing a battery cell stack including C cathode electrodes each including a cathode current collector made of a foil, a cathode active layer located on the cathode current collector, and an outer tab extending from the cathode current collector, A anode electrodes including an anode current collector made of a foil, an anode active layer located on the anode current collector, and an outer tab extending from the anode current collector, and S separators, wherein C, S, and A are integers greater than one. The method includes disposing an outer tab stack of one of the C cathode electrodes and the A anode electrodes at a terminal; creating a joint in the outer tab stack at the one of the C cathode electrodes and the A anode electrodes at a weld location during a first laser processing step; and welding the outer tab stack of the one of the C cathode electrodes and the A anode electrodes at the weld location during a second laser processing step.In other features, both the first laser processing step and the second laser processing step are performed using a first laser. After the first laser processing step is performed, the method for the second laser processing step includes adjusting the laser power and / or the laser scanning speed and / or the laser focusing / defocusing and / or the laser oscillation pattern and / or the workpiece speed and / or the pulse frequency and / or the pulse shape of the first laser. The first laser processing step and the second laser processing step are performed using a first laser and a second laser, respectively. The first laser is operated using different laser operating parameters than the second laser. The laser power and / or the laser scanning speed and / or the laser focusing / defocusing and / or the workpiece speed and / or the laser oscillation pattern and / or the pulse frequency and / or the pulse shape of the second laser differ from those of the first laser.In other features, the first laser is operated at a first focus setting and a first scan speed and the second laser is operated at a second focus setting and a second scan speed. The first focus setting is less focused than the second focus setting and the first scan speed is greater than the second scan speed. At least some defects generated during the first laser processing step are repaired during the second laser processing step.In other features, the first laser includes a cutting laser and the second laser includes a welding laser. The first laser includes a welding laser and the second laser includes a welding laser. The method includes disposing filler material in the groove after the first laser processing step and before the second laser processing step.A method for connecting outer tabs of a battery cell to a terminal includes providing a battery cell stack including C cathode electrodes each including a cathode current collector made of a foil, a cathode active layer located on the cathode current collector, and an outer tab extending from the cathode current collector, A anode electrodes including an anode current collector made of a foil, an anode active layer located on the anode current collector, and an outer tab extending from the anode current collector, and S separators, wherein C, S, and A are integers greater than one. The method includes disposing an outer tab stack of one of the C cathode electrodes and the A anode electrodes at a terminal; creating a joint in the outer tab stack of the one of the C cathode electrodes and the A anode electrodes at a weld location during a first laser processing step; and welding the outer tab stack of the one of the C cathode electrodes and the A anode electrodes at the weld location during a second laser processing step.In other features, the first laser and the second laser are operated using at least one different laser operating parameter. The at least one different laser operating parameter is selected from a group consisting of laser power, laser scanning speed, laser focusing / defocusing, workpiece speed, pulse frequency and pulse shape.In other features, the first laser includes a cutting laser and the second laser includes a welding laser. The first laser includes a welding laser and the second laser includes a welding laser. The first laser is operated at a first focus setting and a first scan speed and the second laser is operated at a second focus setting and a second scan speed.In other features, the first focus setting is less focused than the second focus setting. The first scanning speed is higher than the second scanning speed. At least some defects generated by the first laser during the first laser processing step are repaired by the second laser during the second laser processing step.Further, areas of applicability of the present disclosure will become apparent from the detailed description, claims, and drawings. The detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure.BRIEF DESCRIPTION OF THE DRAWINGSThe present disclosure will be more fully understood from the detailed description and the accompanying drawings, in which: FIG. 1A is a side cross-sectional view of an example of a battery cell including cathode electrodes, anode electrodes, and separators according to the present disclosure; FIG. 1B is a side view of an example of a pouch battery cell according to the present disclosure; FIG. 1C is a perspective view of an example of a prismatic battery cell according to the present disclosure; FIG. 1D is a side cross-sectional view of an example of inner terminals and outer terminals of a prismatic battery cell according to the present disclosure; FIG. 2 is a side view of an example of the outer tabs of the electrodes disposed at a terminal of a battery cell according to the present disclosure; FIG. 3 is a side view showing an example of a first laser processing step for laser welding the electrode outer tab stack to the terminal of the battery cell according to the present disclosure; FIG. 4 is a side view showing an example of defects of a joint at a welding site after the first laser processing step according to the present disclosure; FIG. 5 is a side view showing an example of a second laser processing step for laser welding the electrode outer tab stack to the terminal of the battery cell according to the present disclosure; FIG. 6 is a side view of an example of the outer tab stack and the terminal after the second laser processing step according to the present disclosure; FIG. 7 is a side view of another example of laser welding the outer tab stack to a terminal of a battery cell according to the present disclosure; FIG. 8 is a side view showing another example of a first laser processing step for laser welding the outer tab stack to the terminal of the battery cell according to the present disclosure; FIG. 9 is a side view showing another example of defects of a joint at a welding site after the first laser processing step according to the present disclosure; and FIG. 10 is a side view showing another example of a second laser processing step for laser welding the outer tab stack to the inner terminal of the battery cell according to the present disclosure.In the drawings, reference numerals may be used multiple times to identify similar and / or similar elements.DETAILED DESCRIPTIONAlthough battery cells including laser welded interior terminals have been shown in the context of electric vehicles, the battery cells including laser welded interior terminals may be used in stationary applications and / or other applications.The present disclosure addresses the quality issues of welds between the current collectors of anode and / or cathode electrodes and the terminals of a battery cell. According to some examples, the terminals of the battery cell are embodied as inner terminals which, in the case of prismatic battery cells, are in contact with the outer terminals of the battery cell. In other words, the outer terminals are in contact with the inner terminals that are laser welded to the outer tabs of the cathode and / or anode electrodes. As can be seen, separate terminals are used to connect the cathode and anode electrodes to external devices.When welding the outer tabs in multiple layers (e.g., outer tabs extending from the current collectors made of foil) in an overlap joint, the weld may be porous and peeling may occur at a melting boundary. Defects may be generated when laser welding is used. The present disclosure relates to joining the outer tabs of the current collectors of anode and / or cathode electrodes to the terminals using two-step laser machining to reduce or eliminate defects and improve weld quality. According to some examples, laser welding is performed without ultrasonic welding.Referring to FIG. 1A, a battery cell 10 includes C cathode electrodes 20, A anode electrodes 40, and S separators 32 arranged in a predetermined sequence in a stack 12 located in a case 50. The cathode electrodes 20- 1, 20- 2,..., and 20- C (where C is an integer greater than one) include cathode active layers 24 located on one or both sides of the cathode current collector 26. The anode electrodes 40- 1, 40- 2,..., and 40- A (where A is an integer greater than one) include anode active layers 42 located on one or both sides of the anode current collector 46.Typically, there are connections to the C cathode electrodes 20 and the A anode electrodes 40 with terminals. The C cathode electrodes 20 and the A anode electrodes 40 include outer tabs 28 and 48, respectively, that correspond in portions to the current collectors of the C cathode electrodes 20 and the A anode electrodes 40 that extend beyond the cathode and anode active material layers 24 and 42. According to some examples, the outer tabs 28 of the C cathode electrodes 20 are connected to one inner terminal and the outer tabs 48 of the A anode electrodes 40 are connected to another inner terminal. The inner terminals are connected to the outer terminals of the battery cell. Although the length of the outer flaps 28 and 48 is shown as relatively small in FIG. 1A, the outer flaps 28 and 48 may extend any distance needed for welding or other purposes. The outer tabs 28 and 48 may include a single outer tab per electrode or multiple outer tabs per electrode to provide a redundant connection. The outer tabs 28 and 48 may extend across the width of the current collectors or only across a portion of the width of the current collectors.According to some examples, the cathode current collectors 26 and the anode current collectors 46 include foil layers. In some examples, the current collectors are made of one or more materials selected from a range of materials consisting of copper, stainless steel, brass, bronze, zinc, aluminum, and alloys thereof. According to some examples, the anode active layers 42 and / or the cathode active layers 24 include coatings including one or more active materials, one or more conductive fillers / additives, and / or one or more binders. According to some examples, the battery cells and / or electrodes are produced by applying a slurry to coat the current collectors in a roll / roll process.Referring to FIG. 1B, a pouch battery cell 52 includes a pouch housing 53 that includes a stack 56. As will be described below, the outer tabs 57 of the anode and cathode electrodes are laser welded to the terminals 54 and 55, or extend through the pouch housing 53.Referring to FIG. 1C, a prismatic battery cell 58 includes a housing 60. Although a prismatic battery cell is shown for purposes of illustration, two-stage laser machining according to the present disclosure may be used to laser weld the outer tabs to the terminals of cylindrical, pouch or other battery cell shape factors. In some examples, the housing 60 has rectangular cross-sections in the planes of the x, y, and z axes. The prismatic battery cell 58 includes outer terminals 62 and 64, and a vent cap 66. As will be described further below, outer tabs of the anode current collectors and / or the cathode current collectors are laser welded to the corresponding terminals. The terminals are disposed in contact with the external terminals 62 and 64 of the battery cell 10 and provide the external connections to the anode electrodes and the cathode electrodes.In FIG. 1D, examples of prismatic battery cell inner terminals 84 and 86 are shown in the housing 60. The stack 12 of the A anode electrodes or the C cathode electrodes includes outer tabs 88. the outer tabs 88 of the A anode electrodes and / or the C cathode electrodes are laser welded to the inner terminals 84 and 86, respectively, as described further below. Although the inner terminals 84 and 86 are shown as "L"-shaped terminals, planar terminals or terminals having other shapes may be used.Referring now to FIGS. 2 to 4, there is shown an example of a first step of a two-stage laser processing method. As can be appreciated, the two-step laser processing method can be used to connect the outer tabs of the anode or cathode electrodes to the terminals (e.g., in a prismatic battery cell or other forms of battery cells). Referring to FIG. 2, a stack of outer tabs 110 extending from either the current collectors of the cathode or the current collectors of the anode electrodes is disposed at a terminal 114 of a battery cell.In FIG. 3, a laser 120- 1 is directed at a weld 118 to create a joint 119 in the outer flap stack 110. The laser 120- 1 cuts and / or melts the outer flap stack 110. According to some examples, material may be removed at the weld 118 of the outer flap stack 110 to form the joint 119. According to some examples, laser 120- 1 may also penetrate and / or ablate a portion of internal terminal 114 that is below weld 118, as shown at 121. According to some examples, a vacuum source 124 including a vacuum tube 126 may be used to remove molten film, debris, or other material from the joint 119 formed at the weld joint 118 during the first laser processing step to clean the weld joint 118 prior to the second laser processing step.In FIG. 4, the outer flap stack 110 is shown after the first laser processing step. Defects 130, such as voids or cracks, may form on the inner surfaces or the outer surfaces of the outer flap stack 110 inside and / or near the joint 119 at the weld site 118 during the first laser processing step. The defects are repaired during the second laser processing step.FIGS. 5 and 6 show a second laser processing step for welding the outer tab stack 110 of the anode or cathode electrode to the inner terminal of the battery cell. A laser 120- 2 re-heats the weld 118, the material melts, and the defects 130 are removed. The laser 120- 2 heats a region slightly wider than the laser 120- 1, and penetrates a part or the entire thickness of the terminal 114.Prior to initiating the second laser processing step, the joint 119 at the weld site 118 may be at least partially filled with a weld filler material 133 compatible with the material of the foil and / or the interior port 114 being welded. The weld filler material 133 may be used to replace material lost during the first laser processing step. After the second laser processing step, the film material, the inner lead, the filler material and / or the lead are refilled and a final weld 143 with few or no defects is created, as shown in FIG. 6.In some examples, lasers 120- 1 and 120- 2 are similar lasers. In some examples, lasers 120- 1 and 120- 2 are different. For example, the two lasers 120- 1 and 120- 2 may be welding lasers that operate with different operating parameters. According to other examples, laser 120- 1 is a cutting laser and laser 120- 2 is a welding laser. Examples of laser operating parameters include laser power, laser scan speed, laser oscillation patterns, laser focusing / defocusing, workpiece speed, pulse frequency, and / or pulse shape. The laser operating parameters are used to vary the amount of heating that occurs at a particular location. A laser oscillation pattern of the laser (e.g., about a numeral 8, a zigzag pattern, or other patterns) may be used to adjust heating at the weld site.As can be seen, the final weld is only slightly larger than the seam 119 created during the first laser processing step. The increase in weld area during the second laser processing step melts defects at the edges of the weld site 118 and typically does not produce new defects.Referring now to FIGS. 7 to 9, there is shown a first laser processing step of another two-stage laser processing process. In FIG. 7, a stack 210 is disposed on an inner terminal 214 of a battery cell. In FIG. 8, a laser 220- 1 heats the material at a weld 218. According to some examples, the laser 120 penetrates a portion of the internal terminal 214 below the weld 218. Referring to FIG. 9, during the first laser processing step, a cavity is created at the weld 218 and material may be ablated and / or defects 230 may form in the weld 218.In FIG. 10, a second laser processing step for connecting the foil of the outer tabs to the inner terminal of the battery cell is shown. According to some examples, a cavity at the weld location may be at least partially filled with the weld filler material compatible with the film prior to the second laser processing step. The laser 120 heats the weld 218 and the defects 230 are repaired. After further heating, a final weld 243 is created as shown in FIG. 10.According to some examples, lasers 220- 1 and 220- 2 correspond to a single laser operating with identical or different operating parameters. According to some examples, lasers 220- 1 and 220- 2 are different and both are welding lasers. Examples of laser operating parameters include laser power, laser scan speed, laser oscillation patterns, laser focusing / defocusing, workpiece speed, pulse frequency, and / or pulse shape. According to some examples, during the first laser processing step, the laser 220- 1 uses a defocusing laser beam and laser scanning at a first speed. According to some examples, during the second processing step, the laser 220- 2 uses a focused laser beam and laser scanning at a second speed that is slower than the first speed.As can be seen, the final weld is only slightly larger than the seam 119 created during the first laser processing step. The increase in the welding area during the second laser processing step melts defects and typically does not produce new defects.The foregoing description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure may be implemented in various forms. Therefore, while this disclosure includes specific examples, the true scope of the disclosure should not be so limited as other modifications will become apparent upon a study of the drawings, the specification, and the following claims. It should be understood that one or more steps within a method may be performed in different order (or overlapping in time) without altering the principles of the present disclosure. Further, although each of the embodiments has been described above with certain features, one or more of those features described with respect to any embodiment of the disclosure may be implemented in any of the other embodiments and / or combined with their features, even if that combination is not explicitly described. In other words, the described embodiments are not mutually exclusive, and permutations of one or more embodiments with each other remain within the scope of this disclosure.Spatial and functional relationships between elements (e.g., between modules, circuit elements, semiconductor layers, etc.) are described using various terms, e.g., "connected," "engaged," "coupled," "adjacent," "next," "top-on," "over," "under," and "disposed.". Unless expressly described as "direct", when a relationship between first and second elements is described in the above-described disclosure, this relationship may be a direct relationship in which no other intervening elements are present between the first and second elements, but may also be an indirect relationship in which one or more intervening elements (either spatially or functionally) are present between the first and second elements. As used herein, the term at least one of A, B, and C is intended to mean a logical (A OR B OR C) using a non-exclusive logical OR, and is not intended to mean "at least one of A, at least one of B, and at least one of C.".In the figures, the direction of an arrow indicated by the arrow head generally demonstrates the flow of information (such as data or commands) that is of interest for purposes of illustration. For example, if element A and element B exchange different information, but the information transmitted from element A to element B is relevant for illustration, the arrow may point from element A to element B. This unidirectional arrow does not imply that no further information is sent from element B to element A. Further, for the information transmitted from the element A to the element B, the element B may transmit requests of or reception acknowledgments of the information to the element A.

Claims

A method of connecting outer tabs of a battery cell to a terminal, comprising: providing a battery cell stack comprising: C cathode electrodes each including a cathode current collector made of foil, a cathode active layer located on the cathode current collector, and an outer tab extending from the cathode current collector; A anode electrodes each including an anode current collector made of foil, an anode active layer located on the anode current collector, and an outer tab extending from the anode current collector; and S separators, wherein C, S, and A are integers greater than one; and disposing an outer tab stack of one of the cathode electrodes C and the anode electrodes A at a terminal; creating a joint in the outer-tab stack of the one of the C cathode electrodes and the A anode electrodes at the weld location during a first laser processing step; and welding the outer-tab stack of the one of the C cathode electrodes and the A anode electrodes at the weld location during a second laser processing step.The method of claim 1, wherein each of the first laser processing step and the second laser processing step is performed using a first laser.The method according to claim 2, further comprising, after the first laser processing step is performed, adjusting the laser power and / or the laser scanning speed and / or the laser focusing / defocusing and / or the laser oscillation pattern and / or the workpiece speed and / or the pulse frequency and / or the pulse shape of the first laser for the second laser processing step.The method of claim 1, wherein the first laser processing step and the second laser processing step are performed using a first laser and a second laser, respectively.The method of claim 4, wherein the first laser is operated using laser operating parameters other than the second laser.The method of claim 5, wherein the laser power and / or the laser scanning speed and / or the laser focusing / defocusing and / or the workpiece speed and / or the laser oscillation pattern and / or the pulse frequency and / or the pulse shape of the second laser are different from those of the first laser.The method of claim 4, wherein the first laser is operated at a first focus setting and a first scan speed and the second laser is operated at a second focus setting and a second scan speed.The method of claim 7, wherein: the first focus setting is less focused than the second focus setting, and the first scan speed is greater than the second scan speed.The method of claim 1, wherein at least some defects generated during the first laser processing step are repaired during the second laser processing step.The method of claim 4, wherein the first laser includes a cutting laser and the second laser includes a welding laser.

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