Battery Pack and Jig for Battery Pack Manufacture

A battery pack designed for disassembly and maintenance comprises a plurality of battery cells. Each battery cell has a set of battery terminals, and ones of the set of battery terminals are connected electrically to supply collective power. A set of battery pack terminals receives and conveys the collective power. The battery pack includes a flexible outer sheathing secured around it that rigidifies the battery pack. For example, one or more foils may connect ones of the sets of battery terminals, and layers of electrical insulation may be included within the outer sheathing, for example, interposed between the anodes and the cathodes of the battery cells and the foils. The outer sheathing may comprise shrink wrap. A battery assembly jig for assembling the battery pack is also disclosed. The assembly jig is both modular and symmetrical, allowing the battery cells to be easily welded.

TECHNICAL FIELD

The invention relates to a multi-cell battery pack, and to a jig for manufacturing the battery pack.

BACKGROUND

A battery is an electrochemical cell that can store and discharge current at an operating voltage. Batteries are ubiquitous in modern life, found in everything from small consumer electronics to electric cars. Even if a system is powered in some other way, a battery or batteries may still be present as a backup, or to store generated power and provide it at a different time or in a different condition. For example, batteries are often present in solar power systems to store power as it is generated and to provide power when the sun is not available. As another example, uninterruptible power supplies (UPSes) are used with computer, Internet, and telecommunications infrastructure to provide power when a main power supply becomes unavailable or unsuitable for the needs of the equipment. In some data centers and other industrial settings, if the local electrical power grid fails, batteries may be used to supply power temporarily until backup electrical generators can be started.

The operating voltage of most battery cells is relatively low, usually on the order of a few volts, and each cell holds only a relatively small amount of current. Thus, the power that can be delivered by a single battery cell is small. Most devices require more power than a single battery cell can supply. Thus, many devices will use multiple battery cells connected together to supply the necessary power. If the number of battery cells is relatively few, a user may simply install those individual battery cells in a device one-by-one, as in the battery compartment of a flashlight or a portable music player. However, as the number of battery cells grows, dealing with those cells individually may be time consuming and inconvenient, and the amount of stored energy may require special handling precautions to prevent accidental discharge, fire, and other problems. In these situations, battery packs are frequently used.

A battery pack is an assemblage of individual battery cells along with other components needed to connect the battery cells together and to connect the battery pack to the device or devices that it is intended to power. Other components may be included to electrically insulate the battery cells, to prevent accidental discharges, and to allow the health and performance of the battery cells to be monitored, either individually or collectively.

In a typical battery pack, the terminals of the battery cells are tack-welded together. Electrically, the individual cells are usually placed in series with one another, which increases the output voltage of the battery pack, but series-parallel combinations may be used, because parallel connections between subsets of cells increase the current storage capacity of the battery pack for a particular voltage. The tack-welded battery cells are then placed in an enclosure or casing, which is typically rigid.

While battery packs are effective, the physical assembly of battery packs and their maintenance can be problematic. The sheer number of cells in a battery pack makes assembly a daunting challenge, particularly in placing and preparing battery cells for welding to electrical contacts. Additionally, the failure of a single battery cell within a battery pack can cause that battery pack to perform sub-optimally or to fail entirely. Yet battery packs are generally not assembled in ways that make them easy to disassemble. This makes it hard to diagnose and replace failing battery cells, and discarding an entire battery pack is undesirable and often infeasible.

BRIEF SUMMARY

One aspect of the invention relates to a battery pack. The battery pack comprises a plurality of battery cells. Each of the battery cells has an anode and a cathode on opposite faces thereof. Opposite inner insulation layers cover the anodes and the cathodes of the plurality of battery cells. The inner insulation layers have openings provided to expose the anodes and the cathodes to allow for electrical connection. Opposite sets of one or more foils are electrically connected to the anodes and the cathodes of the plurality of battery cells over the inner insulation layers so as to connect the plurality of battery cells in series, in parallel, or in some combination of series and parallel to produce a collective power. At least one set of battery pack terminals is electrically and mechanically connected to the opposite sets of one or more foils to receive and convey at least some of the collective power of the plurality of battery cells. A flexible outer sheathing is secured around the plurality of battery cells to rigidify the battery pack.

Another aspect of the invention relates to a battery pack assembly jig. The jig comprises a lower plate, an upper plate, and a central bar. The lower plate, the upper plate, and the central bar are releasably connectable with one another in an I-beam configuration when connected.

The lower plate includes at least one battery compartment. The at least one battery compartment includes at least two through holes extending from an outer surface of the lower plate through to an inner surface of the lower plate. First engaging structures are associated with the at least two through-holes. The first engaging structures are constructed and adapted to engage and support a conductive foil in drop-in fashion over the at least two through-holes.

The upper plate has at least one access opening in a defined relationship relative to the at least one battery compartment of the lower plate. The at least one access opening extends from an outer surface through to an inner surface of the upper plate and has second engaging structures constructed and adapted to engage and support a conductive foil in drop-in fashion.

The battery pack assembly jig may be symmetrical about multiple axes, and the outwardly-facing surfaces of is upper and lower plates may be generally flat, with connecting structure recessed into the plates. This symmetry may provide advantages in manufacturing.

The battery pack assembly jig may be made of a thermoplastic, and the upper plate and the lower plate may each include two or more sections. In some cases, the assembly jig may be made by additive manufacturing.

Other aspects, features, and advantages of the invention will be set forth in the following description.

DETAILED DESCRIPTION

FIG.1is a perspective view of a battery pack, generally indicated at10, according to one embodiment of the invention. The battery pack10is covered by an outer sheathing12that leaves only anode and cathode terminals14,16visible. In the view ofFIG.1, the sheathing12is illustratively cut away to show that the battery pack10comprises a number of individual battery cells18.

As used here, the term “battery pack” refers to an assemblage of individual battery cells that are electrically and mechanically connected together to operate collectively. A battery pack10may have as few as two battery cells18or as many battery cells18as are required to produce a particular output voltage or to store sufficient current for the application. For example, a typical battery pack might include 10-30 battery cells18electrically in series, in parallel, or in some combination of series and parallel. For example, subsets of two or four battery cells18may be connected electrically in parallel in a many-celled battery pack10, with each subset of parallel-connected battery cells18connected to other subsets in series. The chemistry of the individual battery cells18is not critical and may be of any type, although much of this description will assume that the battery cells18are rechargeable, and certain portions of this description will assume that the battery cells18are of a lithium-based chemistry, e.g., lithium ferrophosphate, lithium iron phosphate (LFP), lithium nickel manganese cobalt oxide (NMC), or lithium nickel cobalt aluminum oxide (NCA). This description also assumes that the battery cells18are in a standard form and/or standard size. In this description, each of the battery cells18has a cylindrical form with the anode and cathode terminals14,16disposed on opposite end faces.

As was described briefly above, battery packs10according to embodiments of the invention may be used in a vast number of applications, including consumer electronics; backup applications like uninterruptible power supplies (UPSes); power storage for power generating systems, like solar power systems; as direct primary power for electric vehicles, etc. Battery packs10for different applications may vary in the number of battery cells18that are used in the battery pack10, in the type of battery cell18, and in how those battery cells18are electrically connected together (i.e., in series, in parallel, or in some combination of series and parallel). Generally speaking, the disclosure provided here is equally applicable to battery packs10of all sizes and for all sorts of applications.

The outer sheathing12of the battery pack10is the primary mechanical support for the battery pack10and the primary means by which the individual cells18are held together. However, the outer sheathing12itself is not rigid. Rather, the outer sheathing12is thin and flexible, yet it binds the cells18together and harnesses their inherent rigidity in order to make the battery pack10a cohesive block. Thin films are particularly suitable for the outer sheathing12. In the illustrated embodiment, the outer sheathing12comprises a tubular heat-shrink wrap that is slid over the assembled battery pack10and shrunk by application of heat (e.g., by hot air) until it is tensioned and taut against the battery cells18. In other embodiments, other types of elements may be used as an outer sheathing12, including various adhesive tapes and films, elastic bands, and the like.

There are several potential advantages to using thin films as the outer sheathing12. First, such films are generally well-known, have been used widely in industry, behave in ways that are predictable, and are available in forms that would meet regulatory requirements for application in a battery pack10. For example, heat shrink wraps that meet the flammability standards of UL 94 (UL, Inc., “Tests for Flammability of Plastic Materials for Parts in Devices and Appliances,” Standard 94, Edition 7, February 2023) are available. Thin films are also available in a variety of different sizes to accommodate battery packs10of different sizes. Finally, and as will be discussed below, should a battery pack10experience a cell failure or another type of maintenance problem, a thin-film outer sheathing12can easily be cut into and removed, exposing the problem and allowing for maintenance and repair. For example, as will be described below in more detail, a malfunctioning battery cell18can be easily removed and replaced. Once repairs are complete, new shrink wrap can be placed over battery pack10and shrunk into place as the outer sheathing12.

The outer sheathing12will generally cover at least a portion of the battery pack10, and it may cover substantially the entirety of the battery pack10. However, the outer sheathing12need not cover the entirety of the battery pack10in all cases. As shown inFIG.1, when the outer sheathing12is shrunk into shape around the battery pack10, it may leave openings13.

As can be seen inFIG.1, the terminals14,16in the illustrated embodiment are short, threaded posts. In other embodiments, any type of terminal14,16may be used, so long as it can be used to make an electrical connection. As one of skill in the art might surmise, the terminals14,16are usually made of copper or some other conductive metal, and they are thick enough (i.e., have enough ampacity) to carry the full current supplied by the battery pack10, typically plus some safety margin. The outer sheathing12is cut or punched in the areas around the terminals14,16, leaving openings19that allow the terminals14,16to protrude. As will be explained below in more detail, the outer sheathing12may be placed over the battery pack10, including the terminals14,16and then cut or punched to form the openings19. While any form of cutting sufficient to penetrate the outer sheathing12will function to create openings19, it may be helpful to punch the openings with a shaped tool, in order to avoid creating a tear that will enlarge or propagate over the life of the battery pack10. In some cases, openings19may be punched before the outer sheathing12is shrunk and tensioned, but if that is done, care should be taken to ensure that the final openings19are properly sized, positioned, and dimensioned for the terminals14,16.

FIG.2is a perspective view of the battery pack10with the outer sheathing12removed to illustrate its interior arrangement, andFIGS.3and4are side elevational and end elevational views, respectively, of the battery pack10. In this embodiment, the battery pack10has a width just greater than the width of two cells18placed side-by-side. The tops and bottoms of the cells18, where their contact terminals are located, are covered by several layers of electrically insulative and fire-retardant material to prevent accidental discharges, sparks, and fires. The outer layers of material20,22are visible in the views ofFIGS.2-4. In one embodiment, these layers of material20,22may be insulation papers, such as NOMEX® 410 insulation paper (DuPont de Nemours, Inc., Wilmington, Delaware, United States). While other insulating and fire-retardant materials may be used, this kind of insulation paper has the advantages of being thin, light, and easily removed and replaced, which facilitates maintenance in the same way as the easily cut-and-replaced outer sheathing12.

As can be appreciated fromFIGS.2-4, the insulation paper20,22is not planar; rather, it is cut to a larger size and folded over the sides of the battery cells18, such that the insulation papers20,22together cover the tops and a substantial portion of the sides of the battery cells18. However, as can be seen inFIG.2, in the illustrated embodiment, the corners and edges of the insulation paper20,22are not bonded or otherwise permanently secured. Instead, the corners are loose-when installed, the outer sheathing12keeps the insulation paper20,22in shape and in place against the cells18. Of course, if it is necessary or convenient, the insulation paper20,22may have edges or corners that are bonded or otherwise secured to keep the insulation paper20,22in a particular shape. Sheets of insulation paper20,22may be cut or punched with any necessary or desirable features. As shown inFIG.2, flaps24are cut or punched in the upper insulation paper20and folded back to allow the terminals14,16to protrude.

The full arrangement and configuration of the battery pack10can be appreciated fromFIG.5, an exploded perspective view showing all of the components except for the outer sheathing12. The battery cells18are cylindrical in overall shape, with electrical terminals26,28at the top and bottom faces. In this embodiment, the battery cells18are 26650 lithium iron phosphate cells, although the chemistry, style, size, and capacity of the cells18will vary from embodiment to embodiment.

Inner insulation papers30,32are placed over the bottoms and the tops, respectively, of the battery cells18. These inner insulation papers30,32may be made of the same material as the outer layers of material20,22, and are folded down over the sides of the battery cells18much like the outer layers of material20,22. However, unlike the outer layers of material20,22, the inner insulation papers30,32have cut openings34at predefined spacings that expose the terminals26,28of the battery cells18.

The inner insulation papers30,32, with their cut openings34, help to ensure that although the terminals26,28of the battery cells18are exposed for electrical connection, the areas between adjacent terminals26,28are insulated, such that electrical shorts are less likely to develop. Additionally, the insulation papers30,32may prevent sparks from spreading, either during welding or during operation of the battery pack10.

The inner insulation papers30,32and the outer layers of insulating material20,22provide double insulation, making it less likely that sparks will catch, or a short circuit will occur. However, double insulation is optional; it may not be necessary in some applications. For example, in some applications and circumstances, it may be possible to omit the outer layers of insulating material20,22, particularly if the outer sheathing12has appropriate electrical insulating properties and fire-resistant or fire-retardant properties.

In the illustrated embodiment, thin conductive foils are used to connect the battery cells18in series, in parallel, or in some combination of series and parallel. The term “foil” is used here because, as a general matter, the foils have a much greater width and depth than their thickness. The foils used in embodiments of the invention are generally as thin as possible while still having the ampacity necessary to function in the battery pack10(i.e., they can carry the necessary current with some safety margin). The precise number and configuration of the foils will vary depending on the configuration of the battery pack10. In typical embodiments, the foils may be, e.g., stamped and punched from sheet metal, although they may be made in other ways. The foils may be designed such that if the current or total power is over the safety margin, the foil will melt. This can be construed as a safety feature—e.g., in a short-circuit situation, the foils may act like fuses and melt, thereby disconnecting and remedying the short-circuit situation before a complete meltdown or total energy discharge.

In the illustrated embodiment of the battery pack10, sets of two battery cells18are connected in parallel, and fourteen sets of two parallel-connected battery cells18are connected in series. Thus, the battery pack10has a total of 28 individual battery cells. To support this parallel-series connection scheme, the battery pack10ofFIG.5uses two distinct types of foils. Specifically, atop the inner insulation paper32at each end of the battery pack10, a bar foil36connects the last row of two end battery cells18in parallel. Each of the two bar foils36is adapted to connect electrically with a thicker metal bus bar38that lies overtop of the bar foil36. The bus bars38carry the terminals14,16that connect the battery pack10to its load or loads. As can be seen inFIG.5, the bus bars38have depending portions that contour around the battery cells18, improving the physical connection between the battery cells18and the bus bars38.

The connections between most battery cells18are made by foils40that have the shape of a hollow square. These foils40are adapted to connect with four terminals26,28simultaneously, one terminal26,28at each corner of the hollow square of the foil40, placing the two battery cells18in each row in parallel with one another, and placing each row of battery cells18in series with the row(s) adjacent to it. As can be seen inFIG.5, six foils40are used atop the battery cells18on top, and seven foils40are used in the bottom of the battery cells18. As will be described below in more detail, during assembly, the bar foil36and square foil40are tack-welded to the terminals26,28of the battery cells18that lie beneath or overtop of them. Thus, in this embodiment, the last row of battery cells18at each end of the battery pack10has a bar foil36tack-welded to the top terminals26,28and one-half of a square foil40tack-welded to the bottom terminals26,28.

Each of the square foils40has a protruding tab42. The tabs42connect to wiring harnesses (not shown in the figures) and serve as low-current voltage taps for a battery monitoring system, i.e., to measure output voltage and other metrics indicative of battery cell18charge and health.

The bar foils36have a straight horizontal section44with a depending leg46,48on each end. The horizontal section44is what is tack-welded to the upper terminals26through the openings34in the inner insulation paper32. One depending leg48has a section50that folds back up and in, and terminates in a forked end52that fits over the top of the bus bar38and the terminal12,14that is fixed to it. (In this case, the terminals14,16are conductive threaded rods press-fit into appropriate openings in the bus bars36.) The section50of the bar foil36that inserts over the terminals14,16ensures secure electrical contact with the bus bar38.

With this arrangement, should any of the battery cells18within the battery pack10require replacement, the outer sheathing12can be cut into to expose the battery cells18. In typical embodiments, the foils36,40are thin enough to be cut through with hand tools, e.g., wire cutters or sheet metal cutters, like tin snips. Thus, once the battery cells18and the foils36,40are exposed, the foils36,40can be cut through to release the affected battery cells18from the battery pack10. New battery cells18can then be put in place and covered with new inner insulation papers30,32. The foils36,40are thin enough that new foils36,40can be welded overtop of the foils36,40that were cut to remove the affected battery cells18without significantly affecting fit or performance. New outer sheathing12can then be installed.

If the battery pack10is particularly small, it may be possible to make an assemblage like that shown inFIGS.1-5without any special tooling or support structure. However, with almost any size of battery pack10, it is generally useful to have some sort of jig or support.

FIG.6is a perspective view of a jig, generally indicated at100, for constructing a battery pack10like the one described above. The jig100ofFIG.6has an upper plate102and a lower plate104with a central bar106sandwiched between them in an I-beam configuration. The I-beam configuration can be seen most clearly inFIG.7, an end-elevational view of the jig100, illustrating the relationship between the upper plate102, lower plate104and central bar106.

A jig100according to an embodiment of the present invention may be configured to make more than one battery pack10at once. This may improve the efficiency of manufacture. Moreover, there is no particular limit on the number of battery packs10that any one jig may be adapted to hold simultaneously for manufacture, although one would generally seek to keep the size and weight of a fully-loaded jig manageable. In the illustrated embodiment, the jig100is adapted to hold and make two battery packs10simultaneously, one battery pack10on each side of the central bar106.

The upper plate102has openings108,110adapted to expose the terminals26,28of the battery cells18for welding. These openings108,110generally correspond with the shape of the foils36,40that are used to connect the battery cells18. That is, the openings108allow access to the two parallel-connected battery cells18at each end of the battery pack; these are bar-shaped, broadening into circular areas to expose the terminals26,28of the two battery cells18. The remainder of the openings110in the upper plate102have a broad, cloverleaf shape, roughly rectangular, like the foils40they accommodate, with rounded corners that correspond to the shapes of the four battery cells18that the foils40connect. These openings110expose the terminals26,28of four battery cells18and the foil40that is installed overtop of them so that the terminals26,28of the four battery cells18can be welded to the foil40.

The lower plate104has a shaped compartment112for each battery cell18that is accommodated by the jig100. In the illustrated embodiment, the shaped compartments112are cylindrical, as the battery cells18are cylindrical.

The upper plate102and the lower plate104each have structure to accommodate foils38,40and to ensure that those foils38,40can be dropped into place and easily aligned. In the lower plate104, a set of recesses114connects between the compartments112. These recesses114include sets of flat, parallel sides113, corresponding to the hollow square shape of the foils40. The shape of the recesses114is such that a foil40dropped into them will be easily aligned with the terminals28to which it is intended to connect.

This feature—easy drop-in and alignment of foils36,48—is shared by the upper plate102. The openings110of the upper plate102are more open than the corresponding structure on the lower plate104but have similar foil-alignment structure: inwardly-extending portions on each side that terminate in flat sides116. The size of the openings110and the positions of the flat sides116are set so as to assist in the placement and alignment of the square foils40. Similar flat sides118in the openings108are sized and arranged to align the bar foils36.

FIG.8is an exploded perspective view illustrating the jig100as used, showing how the components of the battery pack10are inserted into it. InFIG.8, to avoid crowding the view, the components of only one battery pack100are shown, although the jig100can be used to assemble two battery packs simultaneously.

As can be appreciated fromFIG.8, the jig100itself is designed to be disassembled into its three major components102,104,106. Bolts120insert through holes in the underside of the lower plate104, and into corresponding, aligned holes122in the central bar106. In the illustrated embodiment, there are four bolts120inserted through corresponding holes122, although more or fewer may be used in other embodiments. On the top side of the upper plate102, thumb nuts124are positioned to be inserted over the threaded ends of the bolts122to secure the components102,104,106of the jig100together. Recesses126are provided on the top side of the upper plate102for the thumb nuts124. The recesses126are larger than the diameter of the thumb nuts124to allow the thumb nuts124to be manipulated with fingers. In fact, the recesses126intersect with the openings110, reducing the wall height of the openings110at the positions of intersection.

With this configuration, one opens the jig100by removing the thumb nuts124and lifting the upper plate102from the central bar106. The square foils40are dropped into the recesses114in the lower plate, aligned so that the tabs42protrude from the sides of the jig100. The lower, inner insulation paper30is laid on top of the square foils40, and the battery cells18are arranged on top of the inner insulation paper30so that their lower terminals28are accessible through the openings34in the lower, inner insulation paper30. The upper, inner insulation paper32is laid overtop of the battery cells18. The jig100is closed by installing the upper plate102and tightening the thumb nuts124. The square and bar foils36,40are laid overtop of the inner insulation paper32by dropping them into the openings108,110in the upper plate102of the jig100. The tabs42of the upper foils40also protrude from the side of the jig100.

As shown inFIG.8, in addition to its role connecting the upper plate102and the lower plate104, the central bar106has substantial thickness, and on each side has an appropriately sized and shaped recess107for each battery cell18. This is an optional feature but may aid in securing the battery cells18.

Once the upper plate102is installed and the thumb nuts124are tightened, the battery cells18and other components are held in place in part by compressive force. Additionally, the upper plate102has depending sides127,128that prevent the components from moving out of alignment in the jig100, and the lower plate has corresponding upwardly-extending sides130,132. With the components properly arranged and the jig100closed, the foils36,40can be tack-welded to the terminals of the battery cells18through the openings110,112.

To finish the assembly of the battery pack10, the tabs42are connected to wires, e.g., by soldering. With the battery pack10removed from the jig100, the outer insulation papers20,22are installed, and the outer sheathing12is installed. If the outer sheathing12is shrink wrap, it would be slid over the battery pack10and then shrunk into place, as described above.

As may be apparent fromFIGS.6-8, when properly assembled and secured, the jig100holds the individual cells18in an arrangement that is symmetrical along X, Y, and Z axes. With reference to the coordinate system of the jig100itself, the jig100is symmetrical about its long axis and its short axis. If those two axes are defined as X and Y, the jig100is also symmetrical about the Z axis, i.e., an axis mutually perpendicular to X and Y.

Additionally, with the thumb nuts124recessed into the jig100, both the top and bottom of the jig100are generally flat. These features may have any number of advantages in the manufacturing process. For example, an inexpensive and non-product-specific locating method can be used to position the jig100in a welding machine. Additionally, the same computer-numerically-controlled (CNC) welding program may be used to weld both the top and bottom sides of the jig100. With the jig100and its symmetry, a jig100may be placed in a welding machine, have one side welded, be flipped over, and have the other side welded using the same locating structures.

The jig100itself is also designed to be modular, so as to be easily manufactured. The jig100may be made of a thermoplastic material, such as poly (lactic acid), poly (vinyl alcohol), polycarbonate, or acrylonitrile-butadiene-styrene (ABS) plastic by additive manufacturing (i.e., 3D-printing) or injection molding. As can be seen inFIGS.6and8, the upper plate102and the lower plate104are designed to be manufactured in sections, and include cooperating engaging structure, like tongue134and groove136structure, to connect adjacent sections. This allows a jig100to be manufactured using an additive manufacturing system with a small working volume. In the illustrated embodiment, the upper plate102and the lower plate104are each comprised of two sections, although more or fewer sections may be used. Before the jig100is used, the sections can be bonded together by any number of techniques, including thermal fusing, solvent bonding, sonic welding, adhesives, and the like. In some cases, the sections may simply be made with very tight tolerances and press-fit together.

Of course, additive manufacturing and injection molding are not the only ways in which a jig100can be made, and neither the method of manufacture nor the material are particularly limited, although it may be helpful if the jig100is either made of an electrically insulative material or coated with one. Beyond thermoplastic manufacturing methods100, a jig100may be cast, machined, stamped from sheet metal and bent into shape, etc. If the battery pack that is to be made is particularly large, or there are a number of battery packs, the upper and lower plates102104could be made as single pieces to improve strength, or any joints between sections could be reinforced.

While the invention has been described with respect to certain embodiments, the description is intended to be exemplary, rather than limiting. Modifications and changes may be made within the scope of the invention, which is defined by the appended claims.