Connecting outer flags of battery cell electrodes to clamps using pulsed laser

Abstract

A method for connecting outer tabs of a battery cell to a terminal comprises providing a battery cell stack comprising C cathode electrodes, A anode electrodes, and S separators, where C, S, and A are integers greater than one. The method comprises arranging a stack of outer tabs of one of the C cathode electrodes and the A anode electrodes on a terminal; and laser-welding W weld segments at each of L weld points on the stack of outer tabs of one of the C cathode electrodes and the A anode electrodes to connect the outer tabs of one of the C cathode electrodes and the A anode electrodes to the terminal, where W and L are integers greater than one.

Description

INITIATIONThe information provided in this section is to generally illustrate the context of the disclosure. Work of the present inventors, insofar as described in this section, as well as aspects of the description that may not otherwise be considered prior art at the time of filing, is neither expressly nor silently admitted as prior art against the present disclosure.The present disclosure relates to battery cells, and more particularly to connecting the outer tabs of electrodes of battery cells to the terminals using pulsed laser.Electric vehicles (EVs), such as battery-powered 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 packs. 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, a cathode active layer disposed on the cathode current collector, and an outer tab extending from the anode current collector, A anode electrodes including an anode current collector, an anode active layer disposed 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 a stack of the outer tabs of one of the C cathode electrodes and the A anode electrodes on a clamp; and laser welding W welding segments at each of L welds on the stack of the outer tabs of one of the C cathode electrodes and the A anode electrodes to connect the outer tabs of the one of the C cathode electrodes and the A anode electrodes to the clamp, where W and L are integers greater than one.In other features, for each of the L welds, the W weld segments are arranged parallel to each other in a first diagonal direction. For each of the L welds, the W weld segments include a first group arranged parallel to each other in a first diagonal direction and a second group arranged parallel to each other in a second diagonal direction and overlapping the first group. For each of the L welds, the W weld segments are arranged parallel to each other in a first direction parallel to an outer edge of the stack including the outer tabs. For each of the L welds, the W weld segments are arranged parallel to each other in a first direction perpendicular to an outer edge of the stack including the outer tabs.In other features, the W weld segments include, for each of the L welds, a first group arranged parallel to each other in a first direction parallel to an outer edge of the stack including the outer fins and a second group arranged parallel to each other in a second direction perpendicular to an outer edge of the stack including the outer fins and overlapping the first group. The L welds are arranged in a row positioned parallel to and spaced from an outer edge of the stack including the outer tabs. The L welds are arranged in a row positioned parallel to and overlapping an outer edge of the stack including the outer tabs.In other features, the W weld segments are created at each of the L welds in a predetermined sequence without sequentially welding immediately adjacent W weld segments at each of the L welds. The L welds are created on the stack of outer fins in a predetermined sequence without immediately adjacent L welds being welded sequentially. The L welds are generated in a predetermined sequence including laser welding the outer L welds before the inner L welds.In other cases, the stack of outer fins is trimmed at an acute angle to form a beveled edge, and the L welds are arranged in a row along the beveled edge. The anode current collector of the A anode electrodes and / or the cathode current collector of the C cathode electrodes is made of foil.A battery cell includes a terminal. A battery cell stack includes C cathode electrodes each including a cathode current collector, a cathode active layer disposed on the cathode current collector, and an outer tab extending from the cathode current collector, A anode electrodes including an anode current collector, an anode active layer disposed on the anode current collector, and an outer tab extending from the anode current collector, and S separators, where C, S, and A are integers greater than one. A stack of the outer tabs of one of the C cathode electrodes and the A anode electrodes is laser welded to the clamp. A laser weld between the outer tab stack of one of the C cathode electrodes and the A anode electrodes and the clamp comprises W weld segments at each of the L welds, where W and L are integers greater than one.In other features, for each of the L welds, the W weld segments are arranged parallel to each other in at least one of a first diagonal direction and a second diagonal direction. For each of the L welds, the W weld segments are arranged parallel to each other in a first direction of at least one of parallel and perpendicular to an outer edge of the stack including the outer tabs of one of the C cathode electrodes and the A anode electrodes. The L welds are arranged in a row positioned parallel to and spaced from an outer edge of the stack including the outer tabs. The L welds are arranged in a row positioned parallel to and overlapping an outer edge of the stack including the outer tabs.In other cases, the stack of outer fins is trimmed at an acute angle to form a beveled edge, and the L welds are arranged in a row along the beveled edge. The anode current collector of the A anode electrodes and / or the cathode current collector of the C cathode electrodes is made of foil.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 become more fully understood from the detailed description and the accompanying drawings, wherein: 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 according to the present disclosure; FIG. 1D is a side cross-sectional view of an example of inner and outer terminals of a prismatic battery cell according to the present disclosure; FIG. 2 is a perspective view illustrating an example of a method of connecting a stack of outer tabs of cathode or anode electrodes to a terminal according to the present disclosure; FIG. 3 illustrates an example of a welding sequence for creating weld segments at a weld location according to the present disclosure; FIG. 4 illustrates further examples of welding sequences for providing welds for joining a stack of outer tabs of cathode or anode electrodes to a clamp in accordance with the present disclosure; FIGS. 5A to 5F are examples of welding patterns for the welding segments at each of the welds according to the present disclosure; FIGS. 6 and 7 are perspective views illustrating examples of methods for connecting the stacks of outer tabs to the terminals according to the present disclosure; and FIG. 8 is a side cross-sectional view illustrating one of the weld segments connecting the outer tab stack and the clamp according to the present disclosure.In the drawings, reference numerals may be reused to identify similar and / or identical elements.DETAILED DESCRIPTIONAlthough the battery cells are shown with laser welded terminals in the context of electric vehicles, the battery cells, including laser welded terminals, may also be used in stationary applications and / or other applications.The present disclosure addresses quality issues of welds between outer tabs extending from current collectors of anode electrodes and / or cathode electrodes and terminals of a battery cell. In some examples, the terminals correspond to the inner terminals of the battery cell that 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 electrodes and / or anode electrodes.When welding multiple layers of outer tabs (e.g., outer tabs extending from foil current collectors) in an overlapping joint, the weld may be porous and peeling may occur at a melt boundary. The present disclosure relates to methods for joining outer tabs of electrodes of battery cells at multiple welds. Each weld comprises weld segments formed by a series of short laser pulses. The weld segments are generated in a predetermined welding sequence and arranged in a predetermined welding pattern. Using the predetermined welding sequence and / or the predetermined welding pattern helps to control the heat generated during welding and reduce the interaction time between the laser beam and the material. This approach also reduces shrinkage and minimizes detachment in a seam region of the lap joint. The energy, frequency, velocity, and location of the pulsed laser beam are optimized to provide sufficient energy to penetrate the stack of outer tabs and the clamp and create a robust weld while preventing delamination and / or reducing thermal distortion. In some examples, each of the weld segments 132 is shorter than the width, height, or diagonal length of an outer edge of the weld 130. In some examples, the outer edge of the weld 130 is rectangular, although other edge shapes may also be used.Referring now 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 housed in a case 50, where A, C, and S are integers greater than one. The C cathode electrodes 20-1, 20-2,..., and 20-C (where C is an integer greater than one) include cathode active material layers 24 disposed on one or both sides of the cathode current collectors 26. The A anode electrodes 40-1, 40-2,..., and 40-A (where A is an integer greater than one) include anode active material layers 42 disposed on one or both sides of the anode current collectors 46. For example, S separators 32 are disposed between the C cathode electrodes 20 and the A anode electrodes 40.The C cathode electrodes 20 and the A anode electrodes 40 each include outer tabs 28 and 48 corresponding to portions of the cathode current collectors 26 and the anode current collectors 46 that extend beyond the cathode active material layer 24 and the anode active material layer 42, respectively. In some examples, the outer tabs 28 of the C cathode electrodes 20 are laser welded to a first terminal and the outer tabs 48 of the A anode electrodes 40 are laser welded to a second terminal, as described below. In some examples, the terminals are inner terminals connected to outer terminals of the battery cell. The outer tabs 28 and 48 in FIG. 1A may extend a longer distance if necessary for laser welding or other purposes.The outer tabs 28 and 48 may comprise a single outer tab per current collector or multiple outer tabs per current collector to provide redundant connection(s). The outer tabs 28 and 48 may extend across the entire width of the current collectors or only across a portion of the width of the current collectors.In some examples, the cathode current collectors 26 and the anode current collectors 46 comprise foil layers. In some examples, the cathode current collector 26 and the anode current collectors 46 are made of one or more materials selected from a group consisting of copper, stainless steel, brass, bronze, zinc, aluminum, and alloys thereof. In some examples, the cathode active material layers 24 and / or the anode active material layers 46 include a coating on one or both sides of the cathode current collector 26 and the anode current collector 46, respectively. In some examples, the electrodes are prepared by applying a slurry to coat the current collectors in a roll-to-roll process.Referring now to FIG. 1B, a pouch battery cell 52 includes a pouch housing 53 including a stack 56. As described below, the outer tabs 57 of the anode and cathode electrodes are laser welded to the terminals 54 and 55, respectively, which extend through the pouch housing 53.Referring now to FIG. 1C, the battery cell may be a prismatic battery cell 58 that includes a housing 60. Although a prismatic battery cell is shown for purposes of illustration, other types of battery cells may also be used. 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 below, the outer tabs 28 and 48 of the cathode current collectors and / or the anode current collectors are laser welded to the respective terminals. In some examples, the terminals are disposed in contact with the outer terminals 62 and 64 of the battery cell 10 to provide external connections for the anode electrodes and cathode electrodes.Referring now to FIG. 1D, examples of the internal terminals 84 and 86 of a prismatic battery cell in the housing 60 are illustrated. 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 optionally folded and laser welded to the inner terminals 84 and 86, respectively, as described below. The inner clamps 84 and 86 are shown as "L" shaped clamps, but planar clamps or clamps having other shapes may also be used.Referring now to FIG. 2, a stack 110 includes the C cathode electrodes 20, the A anode electrodes 40, and the S separators 32 as described above. The stack 110 includes a stack of outer tabs 112 extending from the current collectors of the anode electrodes or the cathode electrodes. The stack of outer tabs 112 is positioned adjacent to the active material regions 114 of the anode electrodes or the cathode electrodes. The stack of outer tabs 112 is disposed on a terminal 116, such as an inner or outer terminal of a battery cell.A laser 120 directs short laser pulses to the stack of outer tabs 112 of the anode or cathode electrodes to generate weld segments 132 from a plurality of welds 130-1, 130-2,..., and 130-L (collectively or individually referred to as welds 130), where L is an integer greater than zero. In some examples, the welds 130 are aligned in a row on the stack of outer tabs 112 across a width of the stack 110. Alternatively, the welds 130 may also include an array of welds having more than one row. In still other examples, the welds 130 may be arranged in other regular or irregular patterns.Each of the welds 130 includes a plurality of weld segments 132 arranged in a predetermined pattern. For example, in FIG. 2, the plurality of weld segments 132 include P diagonally oriented laser pulse welds, where P is an integer (e.g., P=5). The laser 120 heats and melts the weld segments 132 at the welds 130 and joins the stack of outer tabs 112 to the clamp 116.In some examples, the laser 120 or other laser (not shown) performs a first pass using other laser welding parameters or other laser to preheat the weld segments and / or welds before laser welding is performed. Examples of laser operating parameters that can be varied for preheating and / or laser welding are laser power, laser scanning speed, laser oscillation pattern, laser focus / defocus, workpiece speed, pulse frequency and / or pulse shape. Using a different laser and / or changing the operating parameters of the laser may be used to change the amount of heating that occurs at a particular location during preheating compared to welding.Referring now to FIG. 3, a welding sequence at one of the welds 130 is illustrated. In some examples, the welding segments 132 are welded in a non-sequential manner. For example, the weld 130 includes weld segments 132- 1, 132- 2, 132- 3, 132- 4, and 132- 5 arranged in the order of -1 to -5 from bottom left to top right at the weld. In some examples, the welding sequence according to the present disclosure does not generate the welding segments sequentially, such that two adjacent welding segments are not welded sequentially. This approach reduces overheating, distortion and / or shrinkage by distributing the heat in the outer fins and the terminals. In the non-sequential welding sequence, for example, the welding segments are generated at the odd welding positions from bottom left to top right, and then the welding segments are generated at the even positions from bottom left to top right.Referring now to FIG. 4, a sequence for laser welding welds 130- 1, 130- 2,..., and 130-L is shown, where L is an integer greater than 2. In this example, L=7, although L may also be set equal to other integers. In some examples, adjacent welds 130 are welded in a non-sequential order. In a first welding sequence at 180, the weld segments 132 are created at the welds 130 alternately at the outermost welds and then at the next inner welds, etc. In some examples, the weld segments are executed at the welds 130 in the following order: 130- 1, 130- 7, 130- 2, 130- 6, 130- 3, 130- 5, and 130- 4.In a second welding sequence at 190, the welding segments 132 are executed at the welds 130 from an outermost weld on one side to a middle weld, to an outermost weld on the other side to a middle weld, etc. In some examples, the weld segments are executed at the welds 130 in the following order: 130- 1, 130- 4, 130- 7, 130- 2, 130- 5, 130- 3, and 130- 4. As can be appreciated, other laser welding sequences may also be performed at the welds and / or weld segments.Referring now to FIGS. 5A through 5F, various arrangements of the weld segments 132 at the welds 130 are illustrated. In FIG. 5A, the weld segments 132 extend diagonally and parallel from a left side upward to a right side of the weld in the weld 130. In some examples, the weld segments extend diagonally at a predetermined angle in a range of 30° to 60° (e.g., 45°) relative to an outer edge 192 of the stack of outer tabs 112. In FIG. 5B, the weld segments 132 extend diagonally and parallel from a right side upward to a left side of the weld in the weld 130. In FIG. 5C, the weld segments 132 extend diagonally in two directions at the weld 130 to produce a cross-hatched pattern.In FIG. 5D, the weld segments 132 extend in a first direction (e.g., perpendicular to the outer edge 192 of the stack of outer tabs 112) at the weld location 130 and are parallel to each other. In FIG. 5E, the weld segments 132 extend in a second direction (e.g., parallel to the outer edge 192 of the stack of outer tabs 112) at the weld location 130 and are parallel to each other. In FIG. 5F, the weld segments 132 extend in the first direction and in the second direction (transverse to the first direction) at the weld 130 to produce a cross-hatched pattern.The welds may be located within the outer edges of the stack of outer fins, as shown in FIG. 2. In other examples, the welds may be located between the outer edge 192 of the stack of outer tabs 112 and an edge of the active material layer 114, as shown in FIG. 6. In other examples, the stack of outer tabs 112 may be trimmed at an acute angle along the outer edge 192 of the stack of outer tabs 112 to form a beveled edge 200. The welds 130 are positioned along the chamfered edge 200 of the stack of outer tabs 112 as shown in FIG. 7.Referring now to FIG. 8, a cross-section through one of the weld segments 132 is shown. The penetration of the weld at weld segments 132 extends partially or completely through the thickness of clamp 116, thereby ensuring a robust weld.The foregoing description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or its use. The broad teachings of the disclosure may be practiced in a wide variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be limited to the same as other changes will become apparent after studying the drawings, the specification, and the following claims. It should be appreciated that one or more steps within a method may be performed in different order (or simultaneously) without altering the principles of the present disclosure. Further, although the embodiments are each described above as being provided with certain features, any one or more of those features described with respect to an embodiment of the disclosure may be implemented with and / or combined with features of any of the other embodiments, even if that combination is not expressly described. In other words, the described embodiments are not mutually exclusive, and replacement of one or more embodiments with each other remains within the scope of this disclosure.Spatial and functional relationships between elements (e.g., between modules, circuit elements, semiconductor layers, etc.) are described with various terms including "connected," "engaged," "coupled," "adjacent," "next," "top-on," "over," "under," and "arranged.". Where a relationship between first and second elements is not expressly described as "direct" in the foregoing disclosure, this relationship may be a direct relationship in which no other intervening elements are present between the first and second elements, but also an indirect relationship in which one or more intervening elements are present (either spatially or functionally) between the first and second elements. As used herein, the term "A, B, and / or C" should be construed as being logical (A ORed with B ORed with C) using a non-exclusive logical OR operation and should not be understood as "at least one of A, at least one of B, and at least one of C.".In the figures, the direction of an arrow as indicated by the arrow head generally illustrates the flow of information (e.g., data or instructions) of interest for the illustration. For example, if element A and element B exchange a plurality of information, but the information sent 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 mean that no other information is sent from element B to element A. Further, for information sent from element A to element B, element B may send requests or acknowledgements for the information to element A.

Claims

A method of joining outer tabs of a battery cell to a terminal, comprising: providing a battery cell stack comprising: C cathode electrodes each comprising a cathode current collector, a cathode active layer disposed on the cathode current collector, and an outer tab extending from the cathode current collector; A anode electrodes comprising an anode current collector, an anode active layer disposed 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 a stack of the outer tabs of one of the C cathode electrodes and the A anode electrodes on a terminal; and laser welding W welding segments at each of L welds on the stack of outer tabs of one of the C cathode electrodes and the A anode electrodes to connect the outer tabs of the one of the C cathode electrodes and the A anode electrodes to the terminal, where W and L are integers greater than one.The method of claim 1, wherein for each of the L welds, the W weld segments are arranged parallel to each other in a first diagonal direction.The method of claim 1, wherein for each of the L welds, the W weld segments include a first group arranged parallel to each other in a first diagonal direction and a second group arranged parallel to each other in a second diagonal direction, and overlap the first group.The method of claim 1, wherein for each of the L welds, the W weld segments are arranged parallel to each other in a first direction parallel to an outer edge of the stack including the outer tabs.The method of claim 1, wherein for each of the L welds, the W weld segments are arranged in a first direction parallel to each other perpendicular to an outer edge of the stack including the outer tabs.The method of claim 1, wherein for each of the L welds, the W weld segments comprise a first group arranged parallel to each other in a first direction parallel to an outer edge of the stack including the outer fins and a second group arranged parallel to each other in a second direction perpendicular to the outer edge of the stack including the outer fins, and overlapping the first group.The method of claim 1, wherein the L welds are arranged in a row positioned parallel to and spaced from an outer edge of the stack including the outer tabs.The method of claim 1, wherein the L welds are arranged in a row positioned parallel to and overlapping an outer edge of the stack including the outer tabs.The method of claim 1, wherein the W weld segments are created at each of the L welds in a predetermined sequence without sequentially welding immediately adjacent W weld segments at each of the L welds.The method of claim 1, wherein the L welds are created on the stack of outer fins in a predetermined sequence without sequentially welding immediately adjacent L welds.

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