Abstract:
The present invention pertains to lightweight, hard and leakproof prismatic packaging structures for electrochemical devices and economical method of assembly and hermetic sealing of said structures by plastic layers attached to their metal walls. Metal welding is avoided and superior protection of lithium polymer cells and other cells is thus provided at lesser cost.

Description:
CROSS REFERENCE TO RELATED DOCUMENTS  
         [0001]    The subject matter of the invention is shown and is described in the Disclosure Document of Joseph B. Kejha Ser. No 490,164 filed on Mar. 8, 2001, and entitled “Packaging of Lithium Based Polymer Cells and Batteries” 
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention pertains to construction of lightweight, leakproof, and moisture-proof packaging enclosures for various electrochemical devices, such as lithium-ion-polymer batteries, ultracapacitors and other kinds of batteries and devices, in which said enclosures, have hard metal walls joined and sealed by heat welding of plastic layers attached to them This invention also describes the method of assembly of said enclosures.  
           [0004]    2. Description of the Prior Art  
           [0005]    Prior art lithium polymer prismatic cells are usually heat sealed in a soft and thin aluminum, plastic coated foil pouches or bags, which may be later inserted into a hard box to create a multi-celled battery with the cells in series, as described in the U.S. Pat. No. 5,057,385 (claim 1), and U.S. Pat. No. 5,422,200 of Hope at al. The polymer cells do not require hard casings to hold them together because they are laminated, (welded or glued) The aluminum foil protects the cells from moisture, and the plastic layer is used for heat weld seal Major problem is with the sealing of the cell terminals existing from the pouch, due to the steps in the thickness of the seal, caused by the flat foil terminals presence. The plastic layers during welding do not always flow into the gaps created by the terminals, which creates openings and leaks of the electrolyte, or a moisture entry into the pouch, and thus spoilage of the cell. The aluminum pouch is also a poor protector of the cell, since it can be easily punched through by a sharp object, also bends easily or cracks at the corners when the seal is folded, which again creates leaks and/or spoilage of the cell. Sometimes the terminals during the seal welding cut through the plastic layer and touch the aluminum foil, which causes electronic shorts and damage to the cells and thus a low production yield.  
           [0006]    The prismatic, liquid electrolyte lithium based cells, nickel metal hydride cells, or prismatic capacitors, ultracapacitors or other electrochemical devices are usually inserted into a rectangular hard metal vessel having a metal lid with insulated terminals welded to the vessel which seals the devices therein. The hard casing is necessary to hold the cells or devices tightly together, and to create a pressure on the stack of the cells for proper functioning.  
           [0007]    The described prior art hard casings are expensive, heavy, slow to weld, and have size limitations, due to the limited stiffness of the casings and their ability to maintain pressure on the stack. The heavy casings decrease the energy density of the devices.  
           [0008]    Prismatic packaging structure for electrochemical devices of this invention does not suffer from prior art problems and provides superior cell protection, energy density improvements, reduced cost, and many other positive advantages.  
         SUMMARY OF THE INVENTION  
         [0009]    It has now been found, that a hard, lightweight and sealed structure of prismatic packaging enclosure for electrochemical devices, such as lithium-ion-polymer cells, various batteries, capacitors, ultracapacitors and other kind of electrochemical devices can be made by heat-welding plastic coated or claded, preferably aluminum tubing extrusions, or metal sheets formed into “u” channels and then into rectangular tubing, and that the tubing&#39;s both ends can be closed and heat-sealed by plastic end plugs with a metal layer attached to them. Selected plastic end plugs may have embedded-in them and sealed metal terminals, preferably ultrasonically welded to metal terminal tabs of the particular device&#39;s electrodes, and may have also embedded in an electrolyte filling connectors. The enclosure can be also made from a plastic coated deep drawn metal vessel and sealed by a similar plastic plug with a metal layer attached, and with embedded-in metal terminals insulated from the metal layer. The preferred plastic is “Surlyn” as manufactured by DuPont Corp., or other plastic which attaches easily to the metals. The plugs may be also hollow or relieved to save weight.  
           [0010]    Because the lithium polymer based electrochemical devices are laminated together and do not require the holding pressure by their outside casings, the described had and punch-proof enclosure of the invention in this case can be relatively thin, lightweight, and of unlimited size, but should be thicker than the prior art soft aluminum pouch, to provide a good protection to the cells. Other devices may require thicker enclosures.  
           [0011]    Method of assembly of the enclosure has been also found in order to provide a leak-proof seal-weld of the square or rectangular end plugs to the square or rectangular tubing: The hot clamping device providing heat and pressure on the joint should be preferably pressing in the direction of two opposing corners of the square or rectangular tubing (45° to the tubing walls), in two steps. The tubing may be rotated 180° lengthwise and the heat-sealing is then repeated against the other two corners.  
           [0012]    The principle of the invention is to use only the plastic attached to metal for fast and economical welding, sealing and holding the hard metal structure together, while avoiding slow and expensive metal welding. The metal layers protect the cells from moisture.  
           [0013]    The principal object of this invention is to provide a lightweight, more reliable and economical packaging structure for lithium based prismatic cells and batteries, as well as other electrochemical devices.  
           [0014]    Another object of this invention is to provide reliable and economical method of assembly of the packaging structure for various and preferably prismatic electrochemical devices. Other objects and advantages of the invention will be apparent from the description and claims.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    The nature and characteristic features of the invention will be more readily understood from the following description taken in connection with the accompanying drawing forming part hereof in which:  
         [0016]    [0016]FIG. 1 is a diagrammatic, side elevational, sectional view of the enclosure, illustrating its components and their layers.  
         [0017]    [0017]FIG. 2 is a diagrammatic, front view of the enclosure, illustrating plastic coated tubing, plastic plug and terminal.  
         [0018]    [0018]FIG. 3 is a diagrammatic back elevational, sectional view of the enclosure, at the line  3 - 3  of FIG. 1, illustrating tubing, end plug and their plastic coating layers.  
         [0019]    [0019]FIG. 4 is a diagrammatic, side elevational, partially sectional view of the enclosure containing a stack of cells connected to the terminals.  
         [0020]    [0020]FIG. 5 is a diagrammatic front elevational view of another embodiment of the enclosure&#39;s tubing, formed from two plastic coated channels sealwelded together.  
         [0021]    [0021]FIG. 6. is a diagrammatic, side elevational, sectional view of the enclosure&#39;s tubing at the line  6 - 6  of FIG. 5.  
         [0022]    [0022]FIG. 7 is a diagrammatic, side elevational view of heat sealing press fixture, with two channels being fastened together by welding their plastic coatings.  
         [0023]    [0023]FIG. 8 is a diagrammatic, front sectional view of the heat sealing press fixture and two channels at the line  8 - 8  of FIG. 7.  
         [0024]    [0024]FIG. 9 is a diagrammatic side elevational view of another heat sealing press fixture with the enclosure&#39;s tubing and end plug being fastened together by welding of their plastic interfaces.  
         [0025]    [0025]FIG. 10 is a diagrammatic, front elevational view of the heat sealing press fixture, the enclosure&#39;s tubing and end plug at the line  10 - 10  of FIG. 9.  
         [0026]    [0026]FIG. 11 is a diagrammatic, side elevational, sectional view of the enclosure&#39;s deep drawn vessel with front end plastic plug and terminals.  
         [0027]    [0027]FIG. 12 is a diagrammatic, back elevational view of the enclosure&#39;s deep drawn vessel.  
         [0028]    [0028]FIG. 13 is a diagrammatic, side elevational, partially sectional view of the enclosure&#39;s tubing or vessel with plastic coated metal front end plug having sealed-in terminals by an insulating substance. 
     
    
       [0029]    Like numerals refer to like parts throughout the several views and figures.  
         [0030]    It should, of course, be understood that the description and the drawings herein are merely illustrative, and it will be apparent that various modifications, combinations and changes can be made of the structures and the systems disclosed without departing from the spirit of the invention and from the scope of the appended claims.  
       DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0031]    When referring to the preferred embodiments, certain terminology will be utilized for the sake of clarity. Use of such terminology is intended to encompass not only the described embodiment, but also all technical equivalents which operate and function in substantially the same way to bring about the same results.  
         [0032]    Packaging enclosures for prismatic electrochemical devices, and for example lithium-ion batteries, nickel metal hydride batteries, and ultracapacitors usually employ a hard metal box structure which is sealed by a metal welding method, such as laser welding. Lithium polymer batteries are usually heat sealed in a soft plastic coated metal foil pouch, which requires an additional protection by a non-sealed, hard box. The present invention employs a novel prismatic enclosure structure, which is more reliable and less costly and its method of assembly results in improved cells or devices with many advantages.  
         [0033]    Referring now in more detail, particularly to the drawings of this patent and FIGS.  1 - 4  inclusive, one embodiment of this invention is enclosure  1  comprising hard rectangular or square cross section metal tubing  2 , which may be an extrusion of aluminum, coated or claded on the inside and optionally also on the outside by a heat sealable plastic layer  3 , a rectangular or square metal back plug  4 , which may be a deep drawn cup, and which is coated or claded or encapsulated by a heat sealable plastic layer  5 , and a solid plastic rectangular or square front plug  6 , which has embedded-in and sealed metal terminals  7  and  8 .  
         [0034]    The plastic plug  6  may have also a metal plate  9  attached to it, which plate covers the entire side of the plug  6 , but does not touch the terminals  7  and  8  due to larger openings  7 A and  8 A. The terminals  7  and  8  may be electroconductively attached and preferably by ultrasonic welds to terminal tabs  10  of at least one or several cells  11 , which cells may be as described in our prior patent application Ser. No. 10/119,220, and may be inserted into the enclosure  1 , prior to sealing, as shown in FIG. 4. The plastic plugs  4  and  6  are then heat welded (sealed) and bonded to the plastic layer  3  attached to the tubing  2 , by a method to be described.  
         [0035]    The tubing  2  may be a seamless metal extrusion, or it may have a seam or seams, preferably on the vertical side(s).  
         [0036]    Either plug  4  or  6  may have also embedded-in or sealwelded a safety vent, and a closeable or sealable tubing, or an orifice for filling the enclosure with an electrolyte (not shown). Both plugs  4  and  6  should be made to fit snugly into the tubing  2 , or may be press-fitted. The tubing  2  and coating  3  may have also inside corners with radii to fit the radii on the plug  4  with coating  5 , and the plug  6 .  
         [0037]    Optionally, the cells  11  may be tightly fitted into the enclosure  1  with the help of a shim  12 , which shim may be of a fabric, such as a glass non-woven or a woven fabric, or other flexible or compressible material, as shown in FIG. 4.  
         [0038]    The preferred plastic material of the layers  3  and  5  and the plug  6  is polymeric plastic material sold under the name of “Surlyn”, as manufactured by DuPont Corp., Wilmington, Del. Any polymeric material, which attaches easily and strongly to metals, which may be due to an acid salt groups presence, is also suitable, such as (poly) vinylacetate, polyethylene, polypropylene, or (PVDF) polyvinylidene fluoride, their alloys and copolymers.  
         [0039]    The preferable metal for the tubing  2 , plug  4  and plate  9  is aluminum, and preferably should be at least 0.015 of inch thick, or more. Other metals like magnesium, titanium or stainless steel are also suitable, depending on the product application. Preferable thickness of layers  3  and  5  is 0.001 to 0.010 of inch. The polymeric plastic material should be the same in both layers and in the plugs.  
         [0040]    It should be noted that the plug  4  may be replaced by plug  4 B also of solid plastic like the plug  6 , or may be hollow or with a relief to reduce its weight. In this case the plug  4 B should have attached a metal layer  13  similar to the plate  9 , which layers may be foils and can be attached to the plugs by well known means of heat and pressure, as shown in FIG. 4A. The metal layers  9  and  13  should be a little smaller than the plugs  4 B and  6  to permit compression of the plugs during welding under pressure. Preferable depth “x” or thickness of the plug is from ⅛″ to ½″, and more preferably about ¼″. Both plugs may be molded and mass produced. Production of both plugs&#39; subassembles with the terminals embedding and the plates attachment can be fully automated by well known means.  
         [0041]    Referring now to FIGS. 11 and 12, which represent another embodiment of the invention, and in which the enclosure  14  comprises: metal vessel  15 , which may be deep drawn and having rectangular or square cross section, with inside coated plastic layer  16 , which may be the same or similar to the plastic coatings described above, and the plug  6  with the plate  9  and terminals  7  and  8 . The cells  11  may be similarly inserted-in before the sealing, as shown in FIG. 4. The plastic coating may be also applied to the vessel  15  by a dip-coating method in which the vessel  15  is completely coated inside and outside (not shown). Similarly, the tubing  2  and the plug  4  in FIG. 1 may be also dip coated (not shown). The plug  6  is then heat sealed and bonded to the plastic layer  16  by a method to be described.  
         [0042]    Another embodiment of the invention is shown in FIGS. 5 and 6, which illustrates rectangular or square tubing assembly  2 A, constructed from two metal channels  17  and  18 , with heat sealable plastic layers  19  and  20 , which plastic may be identical to the plastic in layers  3  and  5 , as described above in FIGS.  1 - 4 . The channels  17  and  18  may be also dip-coated, or coated on both sides, or encapsulated by said plastic (not shown). The channels  17  and  18  are first heat welded and sealed together by the layers  19  and their flanges  17 A and  18 A to form a rectangular or square tubing assembly  2 A. The tubing assembly  2 A can be then rotated 180° to heatweld and seal also the other flanges  17 B and  18 B of said channels. The tubing  2 A can replace the tubing  2  in the enclosure assembly  1  shown in FIGS.  1 - 4 . The channels&#39;  17  and  18  thickness may be even thinner than the tube  2  walls or the deep drawn vessel  15  walls, because the metal sheets are possible to be made thinner than the extrusion walls. The “y” dimension of the flanges should be at least ⅛″.  
         [0043]    This construction of the tubing permits more design flexibility in changing the thickness of the cells or cell packs and their footprint, because the channels can be easily custom bent from flat, claded metal stock to fit the required dimensions.  
         [0044]    In all described structures, the plastic plug  6  and plate  9  may be also replaced by a metal plug  6 A, having heat sealable plastic layer  6 B on its outside surface, and having metal terminals  7  and  8  sealed-in by an electrically insulating substance  6 C, such as a plastic or glass material, as shown in FIG. 13. The metal terminals  7  and  8  are not in contact with the metal plug  6 A.  
         [0045]    The same enclosure construction as shown in FIGS.  1 - 6  inclusive and in FIGS. 11, 12, and  13 , may be also used for the construction of the main battery box with cells, or packs of cells electrically connected in series. Each cell or parallel pack of cells can be sealed in a plastic bag or pouch to separate the electrolytes of each cell and thus built up voltage, and may be stacked similarly as shown in FIG. 4. In case of lithium batteries requiring electronic circuit protection of each cell, each cell or cell pack may have also separate and individually sealed terminals embedded-in and passing through the plug  6  (not shown). Although the described packaging structures are intended mostly for enclosing of prismatic electrochemical devices, cylindrical or any other shape cells or devices  11 A may be also inserted therein, as shown in FIG. 12, and connected to the terminals. It is apparent that all the described types of plugs may be used in any suitable combination with said tubings or vessels, including two plugs  6  or  6 A with terminals electroconductively connected to the devices and being at both ends of the tubing  2  or  2 A as shown in FIG. 13, which is another embodiment of the invention. The heat sealed plastic layers serve also as an insulation to prevent electrical shorts. When the heat sealable plastic layers  3 ,  16 , and  20 , or  5  and  6 B are omitted, the enclosure  1  or  14  is still heat sealable, because the only one heat sealable plastic layer between the metal parts, or the heat sealable plastic plugs alone are good enough to be attached to the metal tubing  2  or  2 A, or vessel  15 . This construction is useable in case when the cells or cell packs can touch the metal enclosure, and it is another embodiment of the invention. The terminals  7  and  8  may have any desirable shape, and are not limited to just flat shapes as shown.  
         [0046]    Another embodiment of the invention is illustrated in FIGS. 7 and 8, showing one method of heat sealing and welding channels  17  and  18  together, in hot clamping fixture or device  20 A comprising: hard, preferably aluminum metal support  22  of cantilever construction having compliant layer  24  on top, which may be of silicone rubber or teflon, and metal clamp  21  with electric heaters  23 . Clamp  21  may have also a compliant layer, similar to layer  24  (not shown). Controlled heat and pressure by well known means is applied to the assembly for a controlled time period, to melt and then to cool the plastic layer  19  and thus bond and seal the channels  17  and  18  together to form the tube  2 A. The layers  19  and  20  serve as an electrical insulation inside of the enclosure, and later to heatweld the tube  2 A to the plugs  6  or  6 A and  4  or  4 B. Optionally, the support  22  may have also embedded-in or otherwise attached electric heaters, like flat blanket heaters, (not shown). The clamp  21  is removable, preferably in upward direction.  
         [0047]    Another embodiment of the invention is illustrated in FIGS. 9 and 10, showing one method of heat sealing and welding the plastic coated or claded tube  2  or  2 A, or vessel  15  to the plastic plugs  6  or  6 A, or  4  or  4 B in hot clamping fixture or device  24 , comprising: hard, preferably aluminum metal support clamp  25  having inserted heaters  26  therein, and optionally a compliant layer  27  attached as shown, which layer may be of silicone rubber or teflon; vertically removable, hard and preferably of aluminum metal clamp  28  having additional heaters  26  inserted therein and optionally compliant layer  29  attached as shown, which layer may be of the same material as the layer  27 ; and optional filler arbor  30 , which is horizontally removable and may be of heat insulating tough plastic composite. The arbor  30  is not used when the plug  6  or  6 A, or  4 B are welded to the tube  2  or  2 A. After aligning the parts as shown in FIGS.  1 - 4  or  11 ,  12 , and  13 , and  9 - 10 , controlled heat and pressure by well known means is applied to the particular assembly for controlled “on” time period, to melt and then to cool the plastic layers. The pressure is then released and the plugs at their interfaces with the plastic layer are thus welded, bonded and hermetically sealed together with the plastic layers of the tubing to form the enclosure  1 . It should be noted that the hot clamping fixture or device  24  as shown in FIGS. 9 and 10 provides for even pressure and heat onto the enclosure sides and corners. The pressure is applied approximately in 45° direction to the tubing&#39;s or vessel&#39;s walls and the plug&#39;s surface as shown in the front view (FIG. 10), which makes a good sealing of the corners possible. This method is another embodiment of the invention. After applying heat and pressure on the corners “a” and “b”, the enclosure is rotated 180° lengthwise and the heat sealing step is repeated to apply the heat and pressure on the corners “c” and “d”. Temperature, pressure and minimum weld time should be custom adjusted to match the selected plastic of the coatings and plugs, for proper welding. Although the FIGS. 9 and 10 show heat sealing of the only one plug at a time, it is apparent to a person skilled in the art that the hot clamping device  24  can be modified to heatseal both plugs at once, and for example by doubling the components of the clamping device. The heaters  26  may be also replaced by an ultrasonic welding system with modified support  25  and clamp  28  for such welding.  
         [0048]    Example of the Enclosure Manufacture and Pack Assembly:  
         [0049]    1. The enclosure size was designed to accept snugly desired prismatic electrochemical device, which was a stack of parallel connected hybrid lithium-ion-polymer cells, as described in our prior patent application Ser. No. 10/119,220.  
         [0050]    2. Solid plastic plugs  6  and  4 B were molded from Surlyn resin as manufactured by DuPont Corp. Wilmington, Del. and as shown in FIGS. 1, 2 and  4 A. The plugs  6  was made from two halves in order to encapsulate and trap-in two terminals  7  and  8 , by heat-weld and pressure.  
         [0051]    3. Aluminum metal foils  9  and  13  were fabricated and attached to corresponding plugs  6  and  4 A by heat and pressure, as shown in FIGS. 1, 2 and  4 A.  
         [0052]    4. Two aluminum metal sheets 0.015″ thick were cut into desired rectangular sections and each was laminated together with 3 mils thick Surlyn film on its entire one side surface, using commercially available laminator and a polyester film folder.  
         [0053]    5. Two laminated sheets were bent on sheet metal brake to form two channels  17  and  18  as shown in FIG. 5.  
         [0054]    6. The channels of item  5  were assembled together as shown in FIGS. 5 and 6 and two times heat bonded together in the fixture as shown in FIGS. 7 and 8 to form the tube  2 A.  
         [0055]    7. The plug  4 B with foil  13  was assembled into the tube  2 A as shown in FIG. 4A and two times heat bonded together in the fixture as shown in FIGS. 9 and 10.  
         [0056]    8. Plug  6  with terminals  7  and  8  embedded-in and foil  9  attached was ultrasonically welded to terminal tabs  10  of cells in the stack, by the terminals  7  and  8 , and this subassembly was vacuum dried and inserted into the tube  2 A, as shown in FIG. 4, under argon atmosphere.  
         [0057]    9. Plug  6  was then heat bonded and sealed to the tube  2 A in the fixture shown in FIGS. 9 and 10, under argon atmosphere, to form the sealed enclosure of cells.  
         [0058]    10. Metered amount of well known electrolyte was injected through a small hole drilled in the back plug  4 B and the hole was then closed with a press fit pin and heat sealed by hot iron.  
         [0059]    Because the lithium polymer based electrochemical deices are laminated together, they do not require the holding pressure by their outside casings. The described had and punch-proof enclosure of the invention in case of lithium polymer cells can be relatively thin, lightweight, and of unlimited size, but should be thicker than the prior art soft aluminum foil pouch, to provide a good protection to the cells. Other devices may require thicker enclosures.  
         [0060]    It should, of course, be understood that the description and the drawings herein are merely illustrative and it will be apparent that various modifications, combinations and changes can be make of the structures disclosed without departing from the spirit of the invention and from the scope of the appended claims.  
         [0061]    It will thus be seen that a more economical and reliable method for electrochemical devices&#39; prismatic packaging, and improved enclosure&#39;s structures have been provided with which the objects of the invention are achieved.