Abstract:
A process for laminating at least one electrode sheet onto an electrically conductive support film is provided. The process comprises heating the electrically conductive support film and laminating the at least one electrode sheet onto at least one side of the heated electrically conductive support film. An apparatus for laminating at least one electrode sheet onto an electrically conductive support film is also provided. The apparatus comprises lamination rollers forming a nip and means for carrying the electrically conductive support film and the at least one electrode sheet to the nip formed by the lamination rollers. The apparatus also comprises a heater for heating the electrically conductive support film before the electrically conductive support film reaches the nip formed by the lamination rollers.

Description:
FIELD OF INVENTION  
       [0001]     The present invention relates generally to lithium polymer batteries and, more particularly, to a process and an apparatus for assembling components of thin film electrochemical cells for lithium polymer batteries.  
       BACKGROUND OF THE INVENTION  
       [0002]     Rechargeable batteries manufactured from laminates of solid polymer electrolytes and sheet-like anodes and cathodes displays many advantages over conventional liquid electrolytes batteries. These advantages include lower overall battery weight, high power density, high specific energy, longer service life, and environmental friendliness since the danger of spilling toxic liquid into the environment is eliminated.  
         [0003]     Lithium polymer battery components include positive electrodes, negative electrodes and an electrolyte separator capable of permitting ionic conductivity, such as an electrolyte consisting of a polymer and a lithium salt, sandwiched between the positive and negative electrodes. The negative electrodes, or anodes, are usually made of light-weight metals such as alkali metals and alloys, typically lithium metal, lithium oxide, lithium-aluminum alloys and the like, or of carboneous material such as coke or graphite intercalated with lithium ion to form Li x C. The composite positive electrodes, or cathodes, are usually formed of a mixture of insertion material, electronic conductive filler, usually carbon or graphite or mixture thereof, and an ionically conductive polymer electrolyte material, the mixture being set on a current collector, for example, a thin sheet of aluminum.  
         [0004]     Composite cathode thin films are usually obtained by solvent coating onto a current collector or by melt extrusion deposited onto the current collector film.  
         [0005]     Similarly, the polymer electrolyte separator layer is typically produced by solvent coating or by melt extrusion. Solid lithium polymer electrochemical cells are typically manufactured by separately preparing the positive electrode, the electrolyte separator and the negative electrode and thereafter laminating each component together to form an electrochemical cell. U.S. Pat. No. 5,536,278 to Armand et al. discloses one method of assembling the various components of a solid lithium polymer electrochemical cell. The positive electrode thin film is coated or layered onto a current collector. The polymer electrolyte is coated onto a plastic substrate such as a film of polypropylene. The positive electrode is thereafter laminated onto one face of the electrolyte, and the plastic substrate is then removed from the other face of the electrolyte and the lithium negative electrode is applied thereon. Although this manufacturing process is reasonably efficient for research and development and small-scale production of lithium polymer electrochemical cells, it is inadequate for large-scale production of such cells.  
         [0006]     U.S. Pat. No. 5,100,746 to Gauthier discloses a method of laminating simultaneously a plurality of layers of components of an electrochemical cell that is adapted to speed up the manufacturing process, wherein double-layer solid polymer electrolyte/composite positive electrode sub-assemblies are subsequently associated with the other constituent layers of the electrochemical cell.  
         [0007]     Co-pending U.S. Patent Application Publication no. 2003/0215710A1 discloses an efficient method of manufacturing a positive electrode film through a single or twin screw extruder and either depositing the positive electrode film directly onto a moving current collector film, or handling the positive electrode film through one or more rollers and thereafter laminating it onto a moving current collector film. To achieve cost-effective production levels and to produce a high quality electrochemical cell, the lamination of the positive electrode film onto the current collector must be fast and the positive electrode film must adhere properly onto a substrate such as a current collector.  
         [0008]     In order to improve the efficiency of the production process for large-scale manufacturing of lithium polymer batteries, there is a need for an improved method and apparatus for laminating a composite positive electrode onto a substrate support film.  
       SUMMARY OF THE INVENTION  
       [0009]     It is an object of the present invention to provide a process for laminating and assembling a composite positive electrode film onto a substrate support film.  
         [0010]     It is another object of the present invention to provide an apparatus for laminating and assembling a composite positive electrode film onto a substrate support film.  
         [0011]     In accordance with a first broad aspect, the invention provides a process for laminating at least one electrode sheet onto an electrically conductive support film. The process comprises heating the electrically conductive support film and laminating the at least one electrode sheet onto at least one side of the heated electrically conductive support film.  
         [0012]     In a specific non-limiting example of implementation, the at least one electrode sheet is also heated prior to lamination. Advantageously, a first electrode sheet is laminated onto a first side of the heated electrically conductive support film and a second electrode sheet is laminated onto a second side of the heated electrically conductive support film. Furthermore, in a specific embodiment, the first side of the electrically conductive support film is first brought into contact with the first electrode sheet and, thereafter, the second side of the electrically conductive support film is brought into contact with the second electrode sheet.  
         [0013]     In a particular example of implementation, the lamination of the electrode sheet or sheets onto the heated electrically conductive support film is carried out through the nip of a pair of rollers. In a specific embodiment, the electrically conductive support film is passed through a series of stabilizing rollers prior to lamination. Also, in a particular embodiment, the at least one electrode sheet is self-supporting.  
         [0014]     In accordance with a second broad aspect, the invention provides an apparatus for laminating at least one electrode sheet onto an electrically conductive support film. The apparatus comprises lamination rollers forming a nip and means for carrying the electrically conductive support film and the at least one electrode sheet to the nip formed by the lamination rollers. The apparatus also comprises a heater for heating the electrically conductive support film before the electrically conductive support film reaches the nip formed by the lamination rollers.  
         [0015]     In a specific example of implementation, the means for carrying the electrically conductive support film and the at least one electrode sheet to the nip formed by the lamination rollers comprises means for carrying a first electrode sheet and a second electrode sheet to the nip. In a specific embodiment, the means for carrying the first electrode sheet and the second electrode sheet to the nip is adapted to laminate the first electrode sheet onto a first side of the electrically conductive support film and to laminate the second electrode sheet onto a second side of the electrically conductive support film. Advantageously, the heater is a first heater and is aimed at a contact point between the electrically conductive support film and the first electrode sheet, and the apparatus said further comprises a second heater aimed at a contact point between the electrically conductive support film and the second electrode sheet.  
         [0016]     In a particular example of implementation, the apparatus further comprises means for applying and controlling a pressure exerted by the lamination rollers at the nip onto the electrically conductive support film and the at least one electrode sheet.  
         [0017]     These and other aspects and features of the present invention will now become apparent to those of ordinary skill in the art upon review of the following description of specific examples of implementation of the invention in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]     A detailed description of specific examples of implementation of the present invention is provided herein below, by way of example only, with reference to the accompanying drawings, in which:  
         [0019]      FIG. 1  is a schematic frontal view of a lamination apparatus according to a first non-limiting example of implementation of the invention;  
         [0020]      FIG. 2  is a schematic frontal view of a lamination apparatus according to a second non-limiting example of implementation of the invention; and  
         [0021]      FIG. 3  is a schematic frontal view of a lamination apparatus according to a third non-limiting example of implementation of the invention. 
     
    
       [0022]     In the drawings, the embodiments of the invention are illustrated by way of examples. It is to be expressly understood that the description and drawings are only for the purpose of illustration and are an aid for understanding. They are not intended to be a definition of the limits of the invention.  
       DETAILED DESCRIPTION  
       [0023]     In general, the production of thin sheets of composite electrode material is most efficiently done by melt extrusion through a slit die. The various constituents of the composite electrode material are fed from one or more hoppers into an extruder where they are melted, mixed and transported through an air-tight cylinder via a mixing screw. The molten material is extruded toward the slit die and discharged through an elongated discharge port of the slit die adjusted to a desired thickness of film or sheet at a constant rate. The production of thin sheets of composite electrode material may also be done by a solvent coating method.  
         [0024]      FIG. 1  illustrates a first specific non-limiting example of implementation of a lamination apparatus in which a composite cathode material is extruded through a slot die  12  and into a nip  14  formed by a pair of rollers  16  and  18  maintained at a certain temperature. For instance, the temperature at which the rollers  16  and  18  are maintained can be of 12° C. or less. The extruded composite cathode material is thereby formed into a sheet or film  20  of a certain thickness. For example, the thickness of the composite cathode sheet  20  may be in the range of about 30 μm to about 100 μm. The composite cathode sheet  20  remains in contact with the roller  18  for approximately 180° of rotation, during which time it is allowed to cool and acquire a solid state.  
         [0025]     The composite cathode sheet  20  is then transferred onto the surface of the roller  22 , which is also maintained at a certain temperature, and remains in contact with the surface of the roller  22  for a portion of its rotation. The composite cathode sheet  20  then follows the path defined by rollers  24 ,  26  and  28  which leads to lamination rollers  30  and  32 . In a particular example of implementation, the composite cathode sheet  20  is self-supporting. That is, it is sufficiently consistent to be self-supporting and does not require a support film, such as, for example, a plastic film, in order to be transported from the slot die  12  to the lamination rollers  30  and  32 .  
         [0026]     In contact with the surface of the lamination roller  30 , the composite cathode sheet  20  follows the rotation of the lamination roller  30  and enters into a nip  34  formed between the lamination rollers  30  and  32 . In the nip  34 , the composite cathode sheet  20  meets and is bonded to an electrically conductive support film  40  under the pressure exerted by the lamination rollers  30  and  32  to form a single side or monoface cathode/current collector laminate  42 . The position of the lamination rollers  30  and  32  is adjustable such that the pressure applied onto the cathode/current collector laminate  42  being formed is also adjustable. Advantageously, the pressure is maintained between about 10 psi and about 30 psi. In a particular example of implementation, the pressure is maintained at about 20 psi. The cathode/current collector laminate  42  is then either rolled up for storage or transported to another processing station.  
         [0027]     In the non-limiting example of implementation shown in  FIG. 1 , the electrically conductive support film  40  is heated by a pair of heaters  45 A and  45 B prior to entering the nip  34  and bonding with the composite cathode sheet  20 . Each one of the heaters  45 A and  45 B may be any type of heating device adapted to direct heat towards a target area, such as, for example, an infrared light or an electrical resistance element with or without air flow ventilation. The surface temperature of the electrically conductive support film  40  is raised by heaters  45 A and  45 B in order to increase the quality of adhesion between the composite cathode sheet  20  and the electrically conductive support film  40 . When the composite cathode sheet  20  contacts the heated surface of the electrically conductive support film  40 , the surface of the composite cathode sheet  20  softens to create an intimate interface with the surface of the electrically conductive support film  40 , thereby forming an intimate bond between the two sheets  20  and  40 . In a particular example of implementation, the electrically conductive support film  40  is heated to a temperature of approximately 40° C. However, it is to be understood that the temperature at which the electrically conductive support film  40  is heated may vary widely depending on the type of material and thickness of the electrically conductive support film  40 .  
         [0028]     Advantageously, in the specific example of implementation shown in  FIG. 1 , the heaters  45 A and  45 B are aimed directly at the nip  34  formed by the lamination rollers  30  and  32 , thereby heating simultaneously the electrically conductive support film  40  and the composite cathode sheet  20 . In so doing, the temperature of the electrically conductive support film  40  is raised and the composite cathode sheet  20  is softened in order to increase the quality of adhesion between the composite cathode sheet  20  and the electrically conductive support film  40 .  
         [0029]     The electrically conductive support film  40  refers to any type of current collector known to those skilled in the art of electrochemical cells. For example, suitable current collectors can be selected from the group consisting of metallic foils in general, and more specifically metallic foils of aluminum, copper, nickel and alloys of those metals, conductive plastics, metal coated polymer sheets, metallic foils or grids coated with adhesion promoters, anti-corrosion protective layers, metal oxides, and various other types of conductive member devised over decades of research and development.  
         [0030]     In the non-limiting example of implementation shown in  FIG. 1 , the electrically conductive support film  40  passes through a series of rollers  47 ,  48  and  49  prior to lamination. The combination of the rollers  47 ,  48  and  49  stabilizes the electrically conductive support film  40  such that it does not waver or seesaw when entering the nip  34  and contacting the composite cathode sheet  20 .  
         [0031]      FIG. 2  illustrates a second specific non-limiting example of implementation of the lamination apparatus in which additional stabilizing rollers  51 ,  52 ,  53 ,  54 ,  55  and  56  define a more intricate path adapted to prevent lateral wavering and zigzagging of the electrically conductive support film  40 . Furthermore, the last stabilizing roller  56  is in an offset position relative to the nip  58  formed by the lamination rollers  60  and  62 . The offset position of the stabilizing roller  56  directs the electrically conductive support film  40  such that the electrically conductive support film  40  meets the composite electrode sheet  50  before entering the nip  58 . The tension of the electrically conductive support film  40  exerts the initial force or pressure which bonds together the electrically conductive support film  40  and the composite electrode sheet  50 .  
         [0032]     The heaters  45 A and  45 B are positioned to accommodate the angular entry of the electrically conductive support film  40  into the nip  58  defined by the lamination rollers  60  and  62 . The heater  45 A is aimed at the meeting point of the electrically conductive support film  40  and the composite electrode sheet  50  such that they are heated simultaneously to promote adhesion at the initial contact point of the composite electrode sheet  50  and the electrically conductive support film  40 . Thereafter, the monoface laminate  64 , comprising the composite electrode sheet  50  and the electrically conductive support film  40 , enters the nip  58  where it is put under pressure applied by the lamination rollers  60  and  62  to securely bond together the two layers of the laminate  64 . The laminate  64  is then carried away for storage or transported to another processing station.  
         [0033]      FIG. 3  illustrates a lamination apparatus in accordance with a third specific non-limiting example of implementation of the invention. A first electrode sheet  70  exiting a slot die is routed through a series of rollers  71 ,  72  and  73  and led to a lamination roller  74 . A second electrode sheet  80  exiting another slot die is routed through a series of rollers  76 ,  77  and  78  and led to a lamination roller  75 .  
         [0034]     An electrically conductive support film  40  is routed through a series of stabilizing rollers  82 ,  84 ,  86 ,  88 ,  90  and  92  which prevent wavering and zigzagging of the electrically conductive support film  40 , thereby ensuring that the electrically conductive support film  40  is stable when it is bonded to the first electrode sheet  70 . The last stabilizing roller  92  is in an offset position relative to a nip  95  formed by the lamination rollers  74  and  75  such that the electrically conductive support film  40  meets and is bonded to the first electrode sheet  70  at an acute angle before entering the nip  95 . The tension of the electrically conductive support film  40  exerts the initial force or pressure which bonds the electrically conductive support film  40  to the first electrode sheet  70 .  
         [0035]     Heaters  45 A and  45 B are positioned to accommodate the angular entry of the electrically conductive support film  40  into the nip  95  formed by the lamination rollers  74  and  75 . The heaters  45 A and  45 B are respectively aimed at the meeting points of the electrically conductive support film  40  and the first and second electrode sheets  70  and  80  such that they are heated simultaneously to promote adhesion at the initial contact points of the electrode sheets  70  and  80  and the electrically conductive support film  40 . The surface temperature of the electrically conductive support film  40  is raised by the heaters  45 A and  45 B and the first and second electrode sheets  70  and  80  are softened in order to increase the quality of adhesion and create an intimate interface between the electrode sheets  70  and  80  and the electrically conductive support film  40 .  
         [0036]     Therefore, one side of the electrically conductive support film  40  is first laminated onto the first electrode sheet  70 . The second electrode sheet  80  is then laminated onto the other side of the electrically conductive support film  40  when entering the nip  95 . The lamination rollers  74  and  75  apply pressure onto a laminate  96 , comprising the first and second electrode sheets  70  and  80  and the electrically conductive support film  40 , in order to increase the adhesion between the components of the laminate  96  and to prevent any air bubbles from forming between the electrode sheets  70  and  80  and the electrically conductive support film  40 . Thereafter, the bi-face laminate  96 , which comprises the electrode sheets  70  and  80  each securely bonded to a respective side of the electrically conductive support film  40 , is carried away for storage or transported to another processing station.  
         [0037]     The heaters  45 A and  45 B heat the electrically conductive support film  40  to a temperature of approximately 40° C. However, this temperature may vary widely depending on the type of material and thickness of the electrically conductive support film  40 .  
         [0038]     The pressure applied by the lamination rollers  74  and  75  may vary widely depending on the type of electrode material being laminated. For instance, in a particular example of implementation in which the electrode sheets  70  and  80  include a material comprising transitional metal oxide as the active material, the pressure exerted by the lamination rollers  74  and  75  is maintained between about 10 psi and about 30 psi. Advantageously, the pressure exerted by the lamination rollers  74  and  75  is maintained at about 20 psi. The application and control of the pressure exerted by the lamination rollers  74  and  75  at the nip  95  is achieved by either an hydraulic or pneumatic system (not shown) or by a mechanical system (not shown) with or without sensors.  
         [0039]     In the particular examples of implementation illustrated in  FIGS. 1, 2  and  3 , the electrode sheets  20 ,  50 ,  70  and  80  are self-supporting and do not require a support film, such as, for example, a plastic film, in order to be transported to the lamination rollers. However, in other examples of implementation, a support film, such as a plastic support film, may be used for transporting each of the electrode sheets.  
         [0040]     Although various examples of implementation have been illustrated, this was for the purpose of describing, but not limiting, the invention. Various modifications will become apparent to those skilled in the art and are within the scope of the present invention, which is defined more particularly by the attached claims.