Patent Application
20200388798
Lithium ion battery packs for vehicle and other high-power applications typically include multiple lithium ion battery pouch cells that are electrically connected together. Each pouch cell includes a plurality of lithium ion battery unit cells enclosed within a sealed pouch envelope. Each lithium ion battery unit cell, in turn, includes a negative electrode, a positive electrode, and a separator that physically separates and electrically isolates the negative and positive electrodes. To facilitate lithium ion mobility, an electrolyte that conducts lithium ions may be present within the separator. The electrolyte allows lithium ions to pass through the separator between the opposed electrodes in order to counterbalance the flow of electrons that, during charge and discharge cycles of the lithium ion battery unit cell, circumvent the separator and move between the electrodes through an external circuit. Depending on their chemistry, each lithium ion battery unit cell has a maximum or charging voltage (voltage at full charge) as a result of the difference in electrochemical potentials of the electrodes. For example, each lithium ion battery cell may have a charging voltage in the range of 3 V to 5 V and nominal open circuit voltage (midpoint between charging voltage and cell cutoff) in the range of 3.5 V to 4 V.
The lithium ion battery pouch cells may be connected in series, in parallel, or in series and in parallel depending on the specified battery pack design. To that end, each of the lithium ion battery pouch cells includes a negative terminal tab and a positive terminal tab. The two tabs extend through the sealed pouch envelope so that current can be delivered to and from pouch cells. Within the pouch cell, the negative terminal tab electrically communicates with the negative current collectors that contact and exchange electrons with the negative electrodes of the lithium ion battery unit cells, and, likewise, the positive terminal tab electrically communicates with the positive current collectors that contact and exchange electrons with the positive electrodes of the lithium ion battery unit cells. The negative current collectors and the negative terminal tabs have typically been composed of copper, and the positive current collectors and the positive terminal tabs have typically been composed of aluminum. Aluminum generally cannot be used to form the negative current collectors since aluminum will react with lithium ions at the negative electrode within the unit cell charging voltage range.
Bus bars have conventionally been used to connect the lithium ion battery pouch cells together. Aluminum is a particularly good candidate for constructing the bus bars. Indeed, aluminum is a highly electrically conductive and lightweight metal that is easy to process and also happens to be relatively inexpensive. However, the negative terminal tabs of the lithium ion battery pouch cells, which have conventionally been composed of copper, are not easily weldable to an aluminum bus bar. In particular, when a copper negative terminal tab is laser welded to an aluminum bus bar, brittle Al—Cu intermetallic compounds, such as Al2Cu, tend to form at the aluminum-copper interface. These brittle Al—Cu intermetallic compounds are susceptible to fracture when the laser weld joint is loaded and, thus, may adversely affect the mechanical properties of the joint under various loading conditions, especially the lap shear strength of the joint. One proposed solution to the problem of welding aluminum and copper is to employ a bimetal bus bar comprised of an aluminum portion (for welding to the aluminum positive terminal tabs) and a copper portion (for welding to the copper negative terminal tabs). But such a bus bar is fabricated of copper and aluminum, thereby increasing the cost of the bus bar, and still requires its aluminum and copper portions to be joined, which is problematic for the reasons just mentioned. The ability to connect lithium ion battery pouch cells while avoiding the need to fusion weld aluminum and copper would be a noteworthy development.
A lithium ion battery pack according to one embodiment of the present disclosure includes a first group of lithium ion battery pouch cells and a second group of lithium ion battery pouch cells. Each of the lithium ion battery pouch cells in the first group comprises a negative terminal tab and a positive terminal tab. The negative terminal tab of each lithium ion battery pouch cell in the first group has an exterior portion that includes a joining region, and the positive terminal tab of each lithium ion battery pouch cell in the first group has an exterior portion that includes a joining region. The exterior portion of the positive terminal tab of each lithium ion battery pouch cell in the first group is composed of aluminum, and at least the joining region of the exterior portion of the negative terminal tab of each lithium ion battery pouch cell in the first group is composed of aluminum or nickel-coated aluminum. Similarly, each of the lithium ion battery pouch cells in the second group comprises a negative terminal tab and a positive terminal tab. The negative terminal tab of each lithium ion battery pouch cell in the second group has an exterior portion that includes a joining region, and the positive terminal tab of each lithium ion battery pouch cell in the second group has an exterior portion that includes a joining region. The exterior portion of the positive terminal tab of each lithium ion battery pouch cell in the second group is composed of aluminum, and at least the joining region of the exterior portion of the negative terminal tab of each lithium ion battery pouch cell in the second group is composed of aluminum or nickel-coated aluminum. The positive terminal tabs of the first group of lithium ion battery pouch cells are electrically connected to the negative terminal tabs of the second group of lithium ion battery pouch cells.
The lithium ion battery pack of the aforementioned embodiment may include additional features or be further defined. For example, the lithium ion battery back may further comprise an aluminum bus bar. The joining region of the exterior portion of the positive terminal tab of each lithium ion battery pouch cell in the first group may be welded to the aluminum bus bar, and the joining region of the exterior portion of the negative terminal tab of each lithium ion battery pouch cell in the second group may also be welded to the aluminum bus bar. Further, the joining regions of the exterior portions of the positive terminal tabs of the lithium ion battery pouch cells in the first group may be stacked together and overlap, and a weld joint may weld the joining regions of the exterior portions of the positive terminal tabs of the lithium ion battery pouch cells in the first group to each other as well as to the aluminum bus bar. Likewise, the joining regions of the exterior portions of the negative terminal tabs of the lithium ion battery pouch cells in the second group may be stacked together and overlap, and a weld joint may weld the joining regions of the exterior portions of the negative terminal tabs of the lithium ion battery pouch cells in the second group to each other as well as to the aluminum bus bar. In another example, the joining regions of the exterior portions of the positive terminal tabs of the lithium ion battery pouch cells in the first group are welded directly to the joining regions of the exterior portions of the negative terminal tabs of the lithium ion battery pouch cells in the second group.
In still another example, the negative terminal tab of each lithium ion battery pouch cell of the second group may include a nickel segment and an aluminum segment. The nickel segment may be electrically connected to a plurality of lithium ion battery unit cells within an envelope of its respective lithium ion battery pouch cell and may further extend through the envelope of its respective lithium ion battery pouch cell. The aluminum segment may be joined to and extend from the nickel segment to provide the joining region of the exterior portion of the negative terminal tab of its respective lithium ion battery pouch cell. Additionally, the aluminum segment of the negative terminal tab of each lithium ion battery pouch cell may comprise a majority of the exterior portion of the negative terminal tab of its respective lithium ion battery pouch cell. In yet another example, at least the interior portion of the negative terminal tab of each lithium ion battery pouch cell of the second group is composed of nickel-coated aluminum. To that end, in one implementation, the negative terminal tab of each lithium ion battery pouch cell of the second group may be composed entirely of nickel-coated aluminum.
The lithium ion battery pack of the aforementioned embodiment may additionally include a third group of lithium ion battery pouch cells. Each of the lithium ion battery pouch cells in the third group comprises a negative terminal tab and a positive terminal tab. The negative terminal tab of each lithium ion battery pouch cell in the third group has an exterior portion that includes a joining region, and the positive terminal tab of each lithium ion battery pouch cell in the third group has an exterior portion that includes a joining region. The exterior portion of the positive terminal tab of each lithium ion battery pouch cell in the third group is composed of aluminum, and at least the joining region of the exterior portion of the negative terminal tab of each lithium ion battery pouch cell in the third group is composed of aluminum or nickel-coated aluminum. The positive terminal tabs of the second group of lithium ion battery pouch cells are electrically connected to the negative terminal tabs of the third group of lithium ion battery pouch cells.
A lithium ion battery pack according to another embodiment of the present disclosure includes a first group of lithium ion battery pouch cells and a second group of lithium ion battery pouch cells. Each of the first group of lithium ion battery pouch cells has a positive terminal tab that includes an exterior portion composed of aluminum, and, likewise, each of the second group of lithium ion battery pouch cells has a negative terminal tab that includes an exterior portion. At least part of the exterior portion of the negative terminal tab of each lithium ion battery cell in the second group is composed of aluminum or nickel-coated aluminum. Also, the exterior portion of each positive terminal tab and the part of the exterior portion of each negative terminal tab that is composed of aluminum or nickel-coated aluminum are welded to a common aluminum bus bar or are directly welded together.
The lithium ion battery pack of the aforementioned embodiment may include additional features or be further defined. For example, the negative terminal tab of at least one lithium ion battery pouch cell of the second group may include a nickel segment and an aluminum segment. The nickel segment may be electrically connected to a plurality of lithium ion battery unit cells within an envelope of its respective lithium ion battery pouch cell and may further extend through the envelope of its respective lithium ion battery pouch cell. The aluminum segment may be joined to and extend from the nickel segment. In another example, the negative terminal tab of at least one lithium ion battery pouch cell of the second group may be entirely composed of nickel-coated aluminum. In yet another example, the negative terminal tab of at least one lithium ion battery pouch cell of the second group may include an interior portion, and at least the interior portion of the negative terminal tab may be composed of nickel-coated aluminum. And, in still another example, each of the lithium ion battery pouch cells in the second group may further comprise a positive terminal tab that includes an exterior portion composed of aluminum, and the lithium ion battery may further comprise a third group of lithium ion battery pouch cells. Each of the third group of lithium ion battery pouch cells may have a negative terminal tab that includes an exterior portion. At least part of the exterior portion of the negative terminal tab of each lithium ion battery pouch cell in the third group may be composed of aluminum or nickel-coated aluminum. The exterior portions of positive terminal tabs of the second group of lithium ion battery pouch cells and the parts of the exterior portions of the negative terminal tabs of the lithium ion battery pouch cells in the third group that are composed of aluminum or nickel-coated aluminum may be welded to a common aluminum bus bar or may be directly welded together.
A lithium ion battery pouch cell is also disclosed. According to one embodiment of the present disclosure, the lithium ion battery pouch cell comprises an envelope. The pouch cell also comprises a plurality of lithium ion battery unit cells enclosed within the envelope. Each of the lithium ion battery unit cells comprises a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrodes. The pouch cell additionally comprises a plurality of positive-side metal current collectors that are in contact with and exchange electrons with the positive electrodes of the plurality of lithium ion battery unit cells, and a plurality of negative-side metal current collectors that are in contact with and exchange electrons with the negative electrodes of the plurality of lithium ion battery unit cells. Still further, the pouch cell comprises a positive terminal tab that electrically communicates with the positive-side metal current collectors inside the envelope. The positive terminal tab extends through the envelope and has an exterior portion outside of the envelope, and is further composed of aluminum. The pouch cell also includes a negative terminal tab that electrically communicates with the negative-side metal current collectors inside the envelope. The negative terminal tab extends through the envelope and has an exterior portion outside of the envelope. At least a part of the exterior portion of the negative terminal tab is composed of aluminum or nickel-coated aluminum.
The lithium ion battery pouch cell of the aforementioned embodiment may include additional features or be further defined. For instance, the negative terminal tab may include a nickel segment and an aluminum segment. The nickel segment may be electrically connected to the negative-side metal current collectors within the envelope and may further extend through the envelope to provide part of the exterior portion of the negative terminal tab, and the aluminum segment may be joined to and extend from the nickel segment to provide a remainder of the exterior portion of the negative terminal tab. As another example, the negative terminal tab may be composed of nickel-coated aluminum.
The present disclosure is directed to a lithium ion battery pouch cell and a larger lithium ion battery pack that includes a plurality of individual pouch cells electrically connected together. The lithium ion battery pouch cell includes a negative terminal tab and a positive terminal tab. An exterior portion of the positive terminal tab, and preferably the entire positive terminal tab, is composed of aluminum, while at least a part of an exterior portion of the negative terminal tab is composed of aluminum or nickel-coated aluminum. The negative terminal tab and the positive terminal tab can thus be welded to a common aluminum bus bar, or directly welded to each other in the absence of an aluminum bus bar, without having to weld dissimilar aluminum and copper materials or contend with the resultant brittle Al—Cu intermetallics that are formed in the process. As such, a lithium ion battery pack is less susceptible to failure or certain performance declines that may result when an individual pouch cell becomes disconnected from the rest of the pouch cells. The battery pack is also simpler in design and less expensive to manufacture. The lithium ion battery pack may contain enough lithium ion battery pouch cells and be configured to present the voltage, energy density, and power needed to propel various types of electric vehicles—most notably battery electric vehicles (BEVs) and hybrid electric vehicles (HEVs)—among other high-power applications.
A lithium ion battery pouch cell 10 according to one embodiment of the present disclosure is illustrated in in
The negative electrode 16 and the positive electrode 18 of each lithium ion battery unit cell 14 is comprised of an electrode material that is able to intercalate and deintercalate lithium ions. The electrode materials of the two electrodes 16, 18 are formulated to store intercalated lithium at different electrochemical potentials relative to a common reference electrode (typically lithium). In the construct of the lithium ion battery unit cell 14, the negative electrode 16 stores intercalated lithium at a lower electrochemical potential (i.e., a higher energy state) than the positive electrode 18 such that an electrochemical potential difference exists between the electrodes 16, 18 when the negative electrode 16 is lithiated. The electrochemical potential difference for each lithium ion battery cell 14 results in a charging voltage in the range of 3 V to 5 V and nominal open circuit voltage in the range of 3.5 V to 4 V. These attributes of the negative and positive electrodes 16, 18 permit the reversible transfer of lithium ions between the two electrodes 16, 18 either spontaneously (discharge phase) or through the application of an external voltage (charge phase) during operational cycling of the unit cell 14. The thickness of each electrode 16, 18 typically ranges from 30 μm to 150 μm.
The negative electrode 16 comprises a lithium host material such as, for example, graphite, silicon, or lithium titanate. The lithium host material may be intermingled with a polymeric binder material to provide the negative electrode 16 with structural integrity and, optionally, a conductive fine particle diluent. The lithium host material is preferably graphite and the polymeric binder material is preferably one or more of polyvinylidene fluoride (PVdF), an ethylene propylene diene monomer (EPDM) rubber, styrene butadiene rubber (SBR), a carboxymethyl cellulose (CMC), polyacrylic acid, or mixtures thereof. Graphite is normally used to make the negative electrode 16 because, on top of being relatively inert, its layered structure exhibits favorable lithium intercalation and deintercalation characteristics which help provide the lithium ion battery unit cell 14 with a suitable energy density. Commercial forms of graphite that may be used to construct the negative electrode 16 are available from Timcal Graphite and Carbon (headquartered in Bodio, Switzerland), Lonza Group (headquartered in Basel, Switzerland), and Superior Graphite (headquartered in Chicago, Ill.). The conductive diluent may be very fine particles of, for example, high-surface area carbon black.
The positive electrode 18 comprises a lithium-based active material that stores intercalated lithium at a higher electrochemical potential (relative to a common reference electrode) than the lithium host material used to make the negative electrode 16. The same polymeric binder materials (PVdF, EPDM, SBR, CMC, polyacrylic acid) and conductive fine particle diluent (high-surface area carbon black) that may be used to construct the negative electrode 16 may also be intermingled with the lithium-based active material of the positive electrode 18 for the same purposes. The lithium-based active material is preferably a layered lithium transition metal oxide, such as lithium cobalt oxide (LiCoO2), a spinel lithium transition metal oxide, such as spinel lithium manganese oxide (LiMn2O4), a lithium polyanion, such as a nickel-manganese-cobalt oxide [Li(NiXMnYCOZ)O2], lithium iron phosphate (LiFePO4), or lithium fluorophosphate (Li2FePO4F). Some other suitable lithium-based active materials that may be employed as the lithium-based active material include lithium nickel oxide (LiNiO2), lithium aluminum manganese oxide (LiXAlYMn1-YO2), and lithium vanadium oxide (LiV2O5), to name but a few alternatives. Mixtures that include one or more of these recited lithium-based active materials may also be used to make the positive electrode 18.
The separator 20 comprises one or more porous polymer layers 26 that, individually, may be composed of any of a wide variety of polymers. Only one such polymer layer 26 is shown here for simplicity. Each of the one or more polymer layers 26 may be a polyolefin. Some specific examples of a polyolefin are polyethylene (PE) (along with variations such as HDPE, LDPE, LLDPE, and UHMWPE), polypropylene (PP), or a blend of PE and PP. The polymer layer(s) 26 function to electrically insulate and physically separate the negative and positive electrodes 16, 18. The separator 20 may further be infiltrated with a liquid electrolyte throughout the porosity of the polymer layer(s) 26. The liquid electrolyte, which also wets both electrodes 16, 18, preferably includes a lithium salt dissolved in a non-aqueous solvent. The lithium salt may be LiClO4, LiAlCl4, LiI, LiBr, LiSCN, LiBF4, LiB(C6H5)4, LiAsF6, LiCF3SO3, LiN(CF3SO2)2, LiPF6, or a mixture that includes one or more of these salts, and the non-aqueous solvent may be a cyclic carbonate (i.e., ethylene carbonate, propylene carbonate), an acyclic carbonate (i.e., dimethyl carbonate, diethyl carbonate, ethylmethylcarbonate), an aliphatic carboxylic ester (i.e., methyl formate, methyl acetate, methyl propionate), a γ-lactone (i.e., γ-butyrolactone, γ-valerolactone), an acyclic ether (i.e., 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane), a cyclic ether (i.e., tetrahydrofuran, 2-methyltetrahydrofuran), or a mixture that includes one or more of these solvents. The thickness of the separator 20 typically ranges from 10 μm to 50 μm.
The descriptions set forth above pertaining to the negative electrode 16, the positive electrode 18, the separator 20, and the electrolyte included within the separator 20 are intended to be non-limiting examples of those aspects of the lithium ion battery unit cell 14. It should be appreciated that many variations on the chemistry of each component 16, 18, 20 are known and may be applied in the context of the lithium ion battery pouch cell 10 of the present disclosure. For example, the lithium host material of the negative electrode 16 and lithium-based active material of the positive electrode 18 may be compositions other than those specific electrode materials listed above, particularly as lithium ion battery electrode materials continue to be researched and developed. Additionally, the polymer layer(s) 26 and/or the electrolyte contained within the polymer layer(s) 26 of the separator 20 may also include other polymers and electrolytes than those specifically listed above. In one variation, the separator 20 may be a solid polymer electrolyte that includes a polymer layer—such polyethylene oxide (PEO), polypropylene oxide (PPO), polyacrylonitrile (PAN), or polyvinylidene fluoride (PVdF)—that is complexed with a lithium salt or swollen with a lithium salt solution. However constructed and whatever materials are used, the lithium ion battery unit cell 14 need only be able to reversibly exchange lithium ions through the separator 20 and a flow of electrons around the separator 20 during applicable discharge and charge cycles.
The negative-side and positive-side metal current collectors 22, 24 may be thin metallic foils that contact their respective negative and positive electrodes 16, 18 over an appreciable interfacial surface area. The purpose of these metal current collectors 22, 24 is to exchange free electrons with their respective positive and negative electrodes 16, 18 during discharging and charging of the lithium ion battery unit cells 14. The thickness of each of the negative-side and the positive-side metal current collectors 22, 24 is typically between 5 μm and about 25 μm. To facilitate the collective distribution and flow of electrons, each of the negative-side metal current collectors 22 includes a negative connection tab 28, and each of the positive-side metal current collectors 24 includes a positive connection tab 30. As shown representatively in
The lithium ion battery pouch cell 10 includes a negative terminal tab 32 and a positive terminal tab 34. Within the pouch envelope 12, the negative terminal tab 32 electrically communicates with the negative-side current collectors 22 and the positive terminal tab 34 electrically communicates with the positive-side current collectors 24. Specifically, in this particular embodiment, an interior portion 36 of the negative terminal tab 32 is connected to the negative connection tabs 28 and an interior portion 38 of the positive terminal tab 34 is connected to the positive connection tabs 30. The interior portions 36, 38 of the negative and positive terminal tabs 32, 34 are those portions of the tabs 32, 34 that are contained within the sealed pouch envelope 12 of the lithium ion battery pouch cell 14. The interior portions 36, 38 of the negative and positive terminal tabs 32, 34 are preferably connected to the negative and positive connection tabs 28, 30, respectively, by a weld joint 40, 42 (
The negative and positive terminal tabs 32, 34 also extend through the sealed envelope 12 so that external electrical connections can be made to the pouch cell 14. To that end, the negative terminal tab 32 includes an exterior portion 44 disposed outside of the sealed pouch envelope 12, and the positive terminal tab 34 includes an exterior portion 46 disposed outside of the sealed pouch envelope 12. Each of the exterior portion 44 of the negative terminal tab 32 and the exterior portion 46 of the positive terminal tab 34 contains a joining region 48, 50, as shown best in
The negative-side metal current collectors 22 are preferably composed of copper, and the negative terminal tab 32 is constructed so that at least the joining region 48 of the exterior portion 44 of the tab 32 is composed of aluminum or nickel-coated aluminum. For instance, in one embodiment, which is shown best in
In another embodiment, and as shown in
The negative terminal tab 132 may be manufactured to ensure that no portion of the aluminum core 56 is uncovered by the nickel coating 58. In current manufacturing processes, negative terminal tabs are cut to the desired length from a larger sheet metal substrate. If the larger sheet metal substrate is an aluminum sheet that is coated with nickel prior to cutting, the negative terminal tabs would include edges obtained from previously-interior portions of the sheet substrate that present bare aluminum. This would be problematic within the sealed pouch envelope since lithium would react with the exposed aluminum of the negative tabs. To address this potential issue, an aluminum sheet metal substrate can be unwound from a reel and punched or stamped to define individual negative terminal tabs that are connected along an edge of the substrate but are otherwise separated by notches. The sheet substrate is then pulled through an electroplating bath or other thin-film coating station and, at that time, a nickel coating is applied to the negative terminal tabs contained in the sheet substrate. The negative terminal tabs can then be cut from the edge of the sheet substrate with the end that is opposite from the end that was cut from the sheet substrate edge being disposed within the sealed pouch envelope and joined to the negative connection tabs. As such, no surface of the interior portion 136 of the negative terminal tab 132 is left uncovered by the nickel coating 58.
In still another embodiment, and as shown in
The negative terminal tab 32, 132 can be joined to the negative connection tabs 28 by way of ultrasonic welding, as described above, and can additionally be fusion or solid-state welded to a common aluminum bus bar, or directly fusion welded to each other, to build a lithium ion battery pack. Two examples of a lithium ion battery pack 60, 160 that includes a plurality of lithium ion battery pouch cells 14 electrically connected together is shown schematically in
Referring to the embodiment of the lithium ion battery back 60 shown in
Still further, the joining regions 48 of the exterior portions 44 of the negative terminal tabs 32 of the third group 66 of lithium ion battery pouch cells 14 are fusion welded to the third aluminum bus bar 683, and the joining regions 50 of the exterior portions 46 of the positive terminal tabs 34 of the third group 66 of lithium ion battery cells 14 are fusion welded to a fourth aluminum bus bar 684 to connect the pouch cells 14 of the third group 64 in parallel and also to connect the second and third groups 64, 66 of lithium ion battery pouch cells 14 in series. The fusion welding of the various negative and positive terminal tabs 32, 34 to their respective aluminum bus bars 681, 682, 683, 684 is easier to accomplish and more reliable than attempting to weld both aluminum (positive) and copper (negative) terminal tabs to bimetallic aluminum/copper bus bars, or to weld both aluminum and copper terminal tabs to a common aluminum or a common copper bus bar, in accordance with conventional procedures. Not only does the presently-disclosed battery pack architecture avoid having to weld aluminum to copper within the bimetallic bus bars, which results in the formation of brittle Al—Cu intermetallic compounds at the joint interface, but it also avoids having to weld copper-to-copper. This is noteworthy since aluminum has a higher energy absorptivity at laser beam wavelengths than copper and also has a lower melting point than copper. In that regard, aluminum can be welded using a comparatively lower energy input, which helps prevent thermal damage to the battery pack.
The weld joints 70, 72, 74, 76, 78, 80 that fusion weld the negative and positive terminal tabs 32, 34 of each group 62, 64, 66 of pouch cells 14 to their respective aluminum bus bars 68 (681, 682, 683, 684) may be formed by laser welding. And since the pouch cells 14 within each group 62, 64, 66 are connected in parallel, the joining regions 48 of the exterior portions 44 of the negative terminal tabs 32 of each group 62, 64, 66 may be stacked together so that they overlap. By stacking the negative terminal tabs 32, the laser welding process can be performed so that the weld joints 70, 74, 78 extend through the joining regions 48 of the stacked exterior portions 44 of the tabs 32 of each group 62, 64, 66 and into their respective aluminum bus bars 681, 682, 683, as shown here. This results in a single weld joint 70, 74, 78 fusion welding all of the negative terminal tabs 32 within each group 64, 64, 66 of pouch cells 14 to the applicable aluminum bus bars 681, 682, 683. The same stacking and welding practice may also be carried out with the positive terminal tabs 34 of each group 62, 64, 66 of lithium ion battery pouch cells 14. That is, the exterior portions 46 of the positive terminal tabs 34 within each group 62, 64, 66 may be stacked together so that they overlap, and the laser welding process may be performed so that the weld joints 72, 76, 80 extend through the joining regions 50 of the stacked exterior portions 46 of the tabs 34 and into their respective aluminum bus bars 682, 683, 684.
In another embodiment, and referring now to
While only the first, second, and third groups 62, 64, 66 of lithium ion pouch cells 14 are shown electrically connected together either by aluminum bus bars 68 or through direct fusion welding, additional groups of lithium ion battery pouch cells 14 may be electrically connected to the groups 62, 64, 66 shown in
The above description of preferred exemplary embodiments and specific examples are merely descriptive in nature; they are not intended to limit the scope of the claims that follow. Each of the terms used in the appended claims should be given its ordinary and customary meaning unless specifically and unambiguously stated otherwise in the specification.
