Abstract:
A method and an apparatus for manufacturing through an extruder a composite positive electrode film having a thickness of less than 50 μm and having a high solid content.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     The present application claims priority from U.S. provisional application No. 60/535,828 filed on Jan. 13, 2004. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to polymer batteries and, more specifically, to a method and an apparatus for making positive electrode films for polymer batteries.  
       BACKGROUND  
       [0003]     Rechargeable batteries manufactured from laminates of polymer electrolytes and sheet-like electrodes display many advantages over conventional liquid electrolyte batteries. These advantages include lower overall battery weight, high power density, high specific energy, and longer service life. In addition, they are more environmentally friendly since the danger of spilling toxic liquid into the environment is eliminated.  
         [0004]     Polymer battery components generally include positive electrodes (also referred to as cathodes), negative electrodes (also referred to as anodes), and an insulating material capable of permitting ionic conductivity, such as an electrolyte separator, sandwiched therebetween. The negative electrodes are usually made of light-weight metal foils, such as alkali metals and alloys thereof typically lithium metal, lithium oxide, lithium-aluminum alloys and the like or insertion materials such as carbon or graphite. The composite cathodes or positive electrodes are usually formed of a mixture of active material such as a transitional metal oxide, an electronically conductive filler, usually carbon particles, an ionically conductive polymer electrolyte material, and a current collector, usually a thin sheet of aluminum.  
         [0005]     Composite cathode films are usually obtained by coating onto a current collector a mixture of a solvent and cathode materials with a doctor blade, for instance, and evaporating the solvent. This process is inefficient for the mass production of cathode films since it requires recycling the. solvent evaporated and the resulting cathode films have a relatively high porosity, and therefore decreased density.  
         [0006]     One of the most efficient manufacturing processes for obtaining thin films is the process of continuous extrusion. However, the extrusion of positive electrode material into thin films is rendered extremely difficult by the high percentage of solids (active material and conductive filler) necessary to produce high energy density cathode films. The difficulty increases dramatically when attempting to directly extrude cathode films of less than 50 μm. The pressure required to extrude cathode material with over 40% solid content through a sheet die opening of less than 50 μm is such that the die itself may not resist and a gear pump capable of generating the required pressure may not be available on the market and therefore must be custom built.  
         [0007]     In automotive applications such as hybrid vehicle applications, it is highly desirable to assemble very thin films of less than 50 μm and preferably less than 30 μm. Unfortunately, it is extremely difficult to process through an extruder cathode materials having a high solid content of active cathodic material and conductive filler (above 30%) to form a thin positive electrode composite film of less than 50 μm and preferably less than 30 μm.  
         [0008]     Thus, there is a need for a method and an apparatus for manufacturing thin positive electrode films of less than 50 μm and preferably less than 30 μm having a high solid content.  
       SUMMARY OF THE INVENTION  
       [0009]     In accordance with a first broad aspect, the invention seeks to provide a method for manufacturing through an extruder a composite positive electrode film of less than 50 μm having a high solid content.  
         [0010]     In accordance with a second broad aspect, the invention seeks to provide an apparatus which can be combined with an extruder to manufacture a composite positive electrode film of less than 50 μm having a high solid content.  
         [0011]     In accordance with a third broad aspect, the invention seeks to provide a method of making a positive electrode film having a thickness of less than 50 μm. The method comprises compounding in an extruder a composite positive electrode mixture of active cathode material, an electronically conductive additive, and an ionically conductive polymer electrolyte. The method also comprises extruding the composite positive electrode mixture through a sheet die into a film having a thickness of more than 50 μm. The method further comprises reducing the thickness of the extruded film through at least one pair of nip rollers to obtain a composite positive electrode film having a thickness of less than 50 μm.  
         [0012]     In a particular example of implementation, the thickness of the extruded film is reduced to less than 30 μm.  
         [0013]     In accordance with a fourth broad aspect, the invention seeks to provide an apparatus for reducing a thickness of an extruded positive electrode film to less than 50 μm. The apparatus comprises a pair of nip rollers defining a nip distance of less than 50 μm, at least one nip roller of the pair of nip rollers being adapted to be heated.  
         [0014]     In accordance with a fifth broad aspect, the invention seeks to provide an apparatus for reducing a thickness of an extruded positive electrode film to less than 50 μm. The apparatus comprises a series of at least two pairs of nip rollers. The at least two pairs of nip rollers include a first pair of nip rollers defining a first nip distance, at least one nip roller of the first pair of nip rollers being adapted to be heated. The at least two pairs of nip rollers also include a second pair of nip rollers defining a second nip distance less than the first nip distance, at least one nip roller of the second pair of nip rollers being adapted to be heated.  
         [0015]     In a particular example of implementation, the apparatus further comprises a pair of cooling nip rollers, positioned after the first and second pair of nip rollers and adapted to solidify the extruded positive electrode film when the latter has reach a desired thickness of less than 50 μm.  
         [0016]     The apparatus may further comprise a belt connecting the nip rollers of each side of the at least two pairs of nip rollers or in another embodiment a polypropylene film to separate the extruded film from the nip rollers.  
         [0017]     The apparatus may also comprise a dispenser for applying lubricant to a surface of at least one nip roller of the pairs of nip rollers.  
         [0018]     The rotational speed of the second pair of nip rollers may be set to exceed the rotational speed of the first pair of nip rollers in order to control the width of the extruded film being processed.  
         [0019]     Advantageously, during the process of calendering or thickness reduction through the nip rollers, the extruded film is maintained at or above the melting point of its polymer electrolyte constituent in order to prevent separation of the polymer electrolyte from the active cathode material.  
         [0020]     In one embodiment, the positive electrode film comprises more than 40%/wt of active cathode material and electronically conductive additive. The positive electrode film may be laminated onto a current collector when it has reached a desired thickness of less than 50 μm.  
         [0021]     The active cathode material may be selected from cobalt oxide, nickel oxide, nickel cobalt oxide, nickel cobalt aluminum oxide, manganese oxide (LiMn 2 O 4 ) or their analogs for so-called 4 V cathodes or among cathodes of less than 4 V such as phosphates or other polyanions of transition metals such as LiFePO 4 , Nasicon structures also including V 2 O 5 , LiV 3 O 8  and MnO 2 . Various other choices are possible as the nature of the active material is not a limitation of the present invention.  
         [0022]     Advantageously, a lubricant is used on the surfaces that directly contact the positive electrode film in order to prevent or at least inhibit adhesion of the positive electrode film to the contact surfaces. In a particular embodiment, the lubricant has the chemical formula of C 7 H 16 .  
         [0023]     The apparatus may comprise a plurality of nip rollers wherein the nip distance between pairs of rollers is progressively smaller. A metallic belt surrounding the rollers of each side of the nips may be used as contact surfaces. In one specific embodiment, a polypropylene film is used to separate the positive electrode film from the contact surfaces.  
         [0024]     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 embodiments of the invention in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]     A detailed description of embodiments of the present invention is provided herein below with reference to the following drawings, in which:  
         [0026]      FIG. 1  is a schematic perspective view of a simplified calendering apparatus combined with an extrusion machine, according to a first embodiment of the invention;  
         [0027]      FIG. 2  is a schematic perspective view of a simplified calendering apparatus combined with an extrusion machine, according to a second embodiment of the invention;  
         [0028]      FIG. 3  is a schematic side elevational view of a calendering apparatus combined with an extrusion machine, according to a third embodiment of the invention;  
         [0029]      FIG. 4  is a schematic top plan view of the calendering apparatus/extrusion machine combination shown in  FIG. 3 ;  
         [0030]      FIG. 5  is a schematic side elevational view of a calendering apparatus combined with an extrusion machine, according to a fourth embodiment of the invention;  
         [0031]      FIG. 6  is a schematic top plan view of the calendering apparatus/extrusion machine combination shown in  FIG. 5 ;  
         [0032]      FIG. 7  is a schematic perspective view of a calendering apparatus combined with an extrusion machine, according to a fifth embodiment of the invention; and  
         [0033]      FIG. 8  is a schematic side elevational view of a calendering apparatus combined with an extrusion machine, according to a sixth embodiment of the invention. 
     
    
       [0034]     In the drawings, embodiments of the invention are illustrated by way of examples. It is to be expressly understood that the description and the drawings are only for the purpose of illustration and as an aid to understanding. They are not intended to be a definition of the limits of the invention.  
       DETAILED DESCRIPTION  
       [0035]     With reference to  FIG. 1 , there is shown a sheet die  10  of a typical single or twin screw extruder (not shown) and a calendering apparatus  12 . Calendering apparatus  12  comprises a first pair of nip rollers  14 A and  14 B and a second pair of nip rollers  16 A and  16 B. The various component materials of a composite positive electrode are mixed and compounded in the screw section of the extruder and exit under pressure though the sheet die  10  in the form of a sheet or film  20  of a thickness of about 75 μm to 125 μm. The composite positive electrode sheet  20  exits the sheet die  10  at a temperature according to the melting point of the polymer binder used and is taken up by the first pair of cylindrical nip rollers  14 A and  14 B. The distance ‘x’ between rollers  14 A and  14 B is set at a desired thickness (for instance, x&lt;30 μm). When composite positive electrode sheet  20  is passed through the nip rollers  14 A and  14 B, its thickness is reduced directly to the desired thickness ‘x’.  
         [0036]     In a particular embodiment, in order for the composite positive electrode sheet  20  to maintain some malleability which enables it to be calendered with minimum stress, at least one of the nip rollers  14 A and  14 B is heated to a temperature near the temperature of the composite positive electrode sheet  20  when it exits the sheet die  10 . Advantageously, both nip rollers  14 A and  14 B are heated to a temperature near the temperature of the composite positive electrode sheet  20  when it exits the sheet die  10 . Maintaining the composite positive electrode sheet  20  at a temperature near the temperature when it exits the sheet die  10  maintains the electrochemical integrity of the composite positive electrode sheet  20  by preventing microscopic separation of the polymer electrolyte constituent from the active cathode material. If the composite positive electrode sheet  20  is allowed to cool substantially, its polymer constituent may harden enough that it loses its malleability and pliability such that when it is deformed through the nip rollers  14 A and  14 B, its bond with the solid active cathode material may be severed, thereby partially breaking the electrochemical link between the polymer and the active cathode material.  
         [0037]     The second pair of cylindrical nip rollers  16 A and  16 B picks up the composite positive electrode sheet  20  of reduced thickness and moves it to a further processing station. At least one of the nip rollers  16 A and  16 B (and advantageously both rollers  16 A and  16 B) is maintained at a cool temperature such that, when the composite positive electrode sheet  20  passes through, it is cooled down to a temperature that allows it to maintain its physical integrity. In this example, the distance between rollers  16 A and  16 B is set at the same distance as the distance ‘x’ between the rollers  14 A and  14 B (x&lt;30 μm) such that no reduction of thickness occurs at the second pair of nip rollers  16 A and  16 B.  
         [0038]     In one example of implementation, a lubricant is used on the surfaces of nip rollers  14 A,  14 B and  16 A,  16 B which directly contact the positive electrode film  20  in order to inhibit adhesion of the positive electrode film  20  to the surfaces of the nip rollers. The lubricant is dispensed by any method known to those skilled in the art. In a specific embodiment, the lubricant has the chemical formula of C 7 H 16 .  
         [0039]     In a variant of the process, the composite positive electrode sheet  20  exiting nip rollers  16 A and  16 B may be maintained in contact with the surface of one of the cylindrical rollers  16 A or  16 B in order to increase the cooling time.  
         [0040]     In the specific embodiment of  FIG. 1 , the rotational speed of nip roller  14 A is equal to the rotational speed of nip roller  14 B, and the rotational speed of nip roller  16 A is equal to the rotational speed of nip roller  16 B. However, the relation between the rotational speed ω 1  of the first pair of cylindrical nip rollers  14 A and  14 B and the rotational speed  62  of the second pair of nip rollers  16 A and  16 B may vary. In this particular example where the second pair of nip rollers  16 A and  16 B apply no pressure onto the composite positive electrode sheet  20 , if ω 1  is equal to ω 2 , the width of the composite positive electrode sheet  20  will increase proportionally to its thickness reduction such that the composite positive electrode sheet  20  will be wider after it has passed through nip rollers  14 A and  14 B and remain the same width before and after it passes through nip rollers  16 A and  16 B. It is however possible to reduce the width of the composite positive electrode sheet  20  after it passes through nip rollers  14 A and  14 B by increasing the rotational speed ω 2  relative to the rotational speed ω 1  such that nip rollers  16 A and  16 B pull and stretch the composite positive electrode sheet  20  thereby reducing its width. In this case the relation between the rotational speeds ω 2 /ω 1  is greater than one (ω 2 /ω 1 &gt;1). This relation ω 2 /ω 1  may be calculated relative to the thickness reduction occurring at the nip rollers  14 A and  14 B such that the width of composite positive electrode sheet  20  exiting nip rollers  16 A and  16 B will be the same as the width of composite positive electrode sheet  20  exiting sheet die  10 .  
         [0041]     In  FIG. 2 , there is shown a second embodiment of the invention in which a calendering apparatus  22  is juxtaposed to a sheet die  10  of a typical single or twin screw extruding machine (not shown). Calendering apparatus  22  comprises a first pair of cylindrical nip rollers  24 A and  24 B and a second pair of cylindrical nip rollers  26 A and  26 B. In this specific embodiment, nip rollers  24 A and  26 A are joined by a metallic belt  28 A that remains in contact with the composite positive electrode sheet  20  as it is being calendered. Similarly, nip rollers  24 B and  26 B are joined by a metallic belt  28 B that remains in contact with the composite positive electrode sheet  20  as it is being calendered. The metallic belts  28 A and  28 B impose that the rotational speeds of nip rollers  24 A and  26 A and of nip rollers  24 B and  26 B are equal such that ω 1 =ω 2 .  
         [0042]     In one example of implementation, the distance x 1  between nip rollers  24 A and  24 B is set at the final desired thickness of composite positive electrode sheet  20  of less than 30 μm (x 1 &lt;30 μm) and the distance x 2  between nip rollers  26 A and  26 B is set at the same distance (x 1 =x 2 ) such that all the thickness reduction work is performed at the first pair of nip rollers  24 A and  24 B. As previously described for the example of implementation shown in  FIG. 1 , at least one but advantageously both of the nip rollers  24 A and  24 B are heated to a temperature that maintains the composite positive electrode sheet  20  soft and malleable to prevent separation of the polymer electrolyte constituent from the active cathode material and maintain electrochemical integrity. By conduction, the metallic belts  28 A and  28 B are also heated to the temperature of the nip rollers  24 A and  24 B. At least one but advantageously both of the nip rollers  26 A and  26 B are cooled to a temperature that at least partially solidifies the composite positive electrode sheet  20  before releasing it.  
         [0043]     In another example of implementation, the distance x 1  between nip rollers  24 A and  24 B is set at an intermediate distance (for example, x 1 =40 μm) and the distance x 2  between nip rollers  26 A and  26 B is set at the final desired thickness for the composite positive electrode sheet  20  (for example, x 2 =20 μm). In such an example of implementation, the thickness reduction work is performed at the first pair of nip rollers  24 A and  24 B and at the second pair of nip rollers  26 A and  26 B. The nip rollers  24 A and  24 B and the nip rollers  26 A and  26 B are heated to a temperature that maintains the composite positive electrode sheet  20  soft and malleable. The metallic belts  28 A and  28 B are also heated by conduction throughout the thickness reduction process. The composite positive electrode sheet  20  of reduced thickness is cooled by any means known to those skilled in the art, such as through a series of cooling rollers.  
         [0044]     It will be appreciated that, in the embodiment illustrated in  FIG. 2 , because ω 1 =ω 2 , the width of composite positive electrode sheet  20  will increase at each pass through the nip rollers where its thickness is reduced.  
         [0045]     In a particular example of implementation, a lubricant is used on the surfaces of the metallic belts  28 A and  28 B which directly contact the composite positive electrode film  20  in order to prevent adhesion of the composite positive electrode film  20  to the surfaces of the metallic belts  28 A and  28 B. The lubricant is dispensed by any method known to those skilled in the art. In a specific embodiment, the lubricant has the chemical formula of C 7 H 16 .  
         [0046]     In  FIGS. 3 and 4 , there is shown respectively a side elevational view and a top plan view of a third embodiment of the invention in which a calendering apparatus  30  is juxtaposed to a sheet die  10  of a typical single or twin screw extruding machine (not shown). Calendering apparatus  30  comprises a series of cylindrical nip rollers  32 A,  32 B,  34 A,  34 B,  36 A,  36 B,  38 A and  38 B arranged in pairs and adapted to progressively reduce the thickness of a composite positive electrode sheet  20  passing through the calendering apparatus  30 . In this embodiment, the distances x 1 , x 2  and x 3  between the nip rollers  32 A and  32 B,  34 A and  34 B, and  36 A and  36 B, respectively, gradually decrease such that x 1 &gt;x 2 &gt;x 3  and the thickness reduction, work performed on the composite positive electrode sheet  20  is also more gradual than in the previous embodiments shown in  FIGS. 1 and 2 . As an example only, the composite positive electrode sheet  20  may exit die  10  at a thickness of 75 μm, the distances x 1 , x 2  and x 3  between the nip rollers  32 A and  32 B,  34 A and  34 B, and  36 A and  36 B, respectively, may be set at 55 μm, 35 μm, and 25 μm, respectively. To facilitate the performance of the thickness reduction work, at least one but preferably both rollers of each pair of nip rollers  32 A- 32 B,  34 A- 34 B, and  36 A- 36 B are heated to a temperature that maintains the composite positive electrode sheet  20  soft and malleable to prevent separation of the polymer electrolyte constituent from the active cathode material and maintain electrochemical integrity. In this example, the distance x 4  between nip rollers  38 A and  38 B remains at 25 μm and at least one but preferably both of nip rollers  38 A and  38 B are cooled to a temperature that at least partially solidifies the composite positive electrode sheet  20  before it is released.  
         [0047]      FIG. 4  illustrates the process of thickness reduction through the series of pairs of nip rollers  32 A- 32 B,  34 A- 34 B,  36 A- 36 B, and  38 A- 38 B, wherein the rotational speed of the nip rollers is progressively faster such that ω 1 &lt;ω 2 &lt;ω 3 . The increase in rotational speed between successive pairs of nip rollers  32 A- 32 B,  34 A- 34 B, and  36 A- 36 B, respectively, stretches the composite positive electrode sheet  20 , thereby offsetting the increase in width of the sheet  20  that typically occurs if the rotational speeds of nip rollers  32 A and  32 B,  34 A and  34 B, and  36 A and  36 B remain the same (ω 1 =ω 2 =ω 3 ). As illustrated schematically, the widths d 1 , d 2 , d 3 , d 4  and d 5  of composite positive electrode sheet  20  remain substantially equal because the rotational speeds of nip rollers  32 A and  32 B,  34 A and  34 B, and  36 A and  36 B are such that ω 1 &lt;ω 2 &lt;ω 3 . In this specific example, ω 3 =ω 4  since x 3 =x 4  and no reduction of thickness occurs at the pair of nip rollers  38 A and  38 B. It is to be understood that various variations are possible without departing from the scope of the invention. For instance, the widths d 1 , d 2 , d 3  and d 4  may keep increasing (d 1 &lt;d 2 &lt;d 3 &lt;d 4 ) yet the rotational speeds may still be such that ω 1 &lt;ω 2 &lt;ω 3  or the rotational speeds may be equal (ω 1 =ω 2 =ω 3 ).  
         [0048]     In a particular example of implementation, a lubricant is used on the surfaces of nip rollers  32 A and  32 B,  34 A and  34 B,  36 A and  36 B, and  38 A and  38 B, which directly contact the composite positive electrode film  20  in order to prevent adhesion of the composite positive electrode film  20  to the surfaces of the nip rollers. The lubricant is dispensed by any method known to those skilled in the art. In a specific embodiment, the lubricant has the chemical formula of C 7 H 16 .  
         [0049]     In  FIGS. 5 and 6 , there is shown respectively a side elevational view and a top plan view of a fourth embodiment of the invention in which a calendering apparatus  40  is juxtaposed to a sheet die  10  of a typical single or twin screw extruding machine (not shown). Calendering apparatus  40  comprises a series of pairs of cylindrical nip rollers  42 A- 42 B,  44 A- 44 B,  46 A- 46 B, and  48 A- 48 B, as well as two metallic belts  50 A and  50 B respectively circumscribing and joining together the two banks of nip rollers  42 A- 44 A- 46 A- 48 A and  42 B- 44 B- 46 B- 48 B. Calendering apparatus  40  is adapted to progressively reduce the thickness of a composite positive electrode sheet  20  passing through the calendering apparatus  40 . In this embodiment, the distances x 1 , x 2  and x 3  between the nip rollers  42 A and  42 B,  44 A and  44 B, and  46 A and  46 B, respectively, gradually decrease such that x 1 &gt;x 2 &gt;x 3  and the thickness reduction work performed on the composite positive electrode sheet  20  is also more gradual than in the previous embodiments shown in  FIGS. 1 and 2 . For the sake of simplification, the same exemplary distances x 1 , x 2 , x 3  and x 4  will be used here as for  FIGS. 3 and 4 . Composite positive electrode sheet  20  exits die  10  at a thickness of about 75 μm, the distances x 1 , x 2  and x 3  between the nip rollers  42 A and  42 B,  44 A and  44 B, and  46 A and  46 B, respectively, are set at 55 μm, 35 μm, and 25 μm, respectively. Similarly, in order to facilitate the performance of the thickness reduction work, at least one but preferably both rollers of each pair of nip rollers  42 A- 42 B,  44 A- 44 B and  46 A- 46 B are heated to a temperature sufficient to transfer to the metallic belts  50 A and  50 B enough heat to maintain the composite positive electrode sheet  20  soft and malleable as it passes through the pairs of nip rollers  42 A- 42 B,  44 A- 44 B and  46 A- 46 B. In this example, the distance x 4  between the nip rollers  48 A and  48 B remains at 25 μm and at least one but preferably both of nip rollers  48 A and  48 B are cooled to a temperature sufficient to draw enough heat from metallic belts  50 A and  50 B to at least partially cool and solidify the composite positive electrode sheet  20  before it is released.  
         [0050]     The metallic belts  50 A and  50 B circumscribing the two banks of nip rollers impose that the rotational speeds of nip rollers  42 A and  42 B,  44 A and  44 B,  46 A and  46 B, and  48 A and  48 B are equal (ω 1 =ω 2 =ω 3 =ω 4 ). As such, the width of the composite positive electrode sheet  20  will increase with each step of reduction of thickness through the pairs of nip rollers  42 A- 42 B,  44 A- 44 B and  46 A- 46 B such that d 1 &lt;d 2 &lt;d 3 &lt;d 4 . However, since no work is performed at the pair of nip rollers  48 A- 48 B other than cooling of composite positive electrode sheet  20 , the width d 5  should be substantially equal to the width d 4 .  
         [0051]     In a particular example of implementation, a lubricant is used on the surfaces of metallic belts  50 A and  50 B which directly contact the composite positive electrode film  20  in order to prevent adhesion of the composite positive electrode film  20  to the surfaces of the metallic belts  50 A and  50 B. The lubricant is dispensed by any method known to those skilled in the art. In a specific embodiment, the lubricant has the chemical formula of C 7 H 16 .  
         [0052]     In  FIG. 7 , there is shown a fifth embodiment of the invention in which a calendering apparatus  55  is juxtaposed to a sheet die  10  of a typical single or twin screw extruder (not shown). Calendering apparatus  55  comprises a series of cylindrical nip rollers arranged in pairs  56 A- 56 B,  58 A- 58 B,  60 A- 60 B, and  62 A- 62 B, and adapted to progressively reduce the thickness of a composite positive electrode sheet  20  passing through calendering apparatus  55 . Calendering apparatus  55  also comprises a pair of polypropylene sheets  64  and  66  which separate the composite positive electrode sheet  20  from the surfaces of nip rollers  56 A,  56 B,  58 A,  58 B,  60 A,  60 B,  62 A and  62 B. In this embodiment, the distances x 1 , x 2  and x 3  between the nip rollers  56 A and  56 B,  58 A and  58 B, and  60 A and  60 B, respectively, gradually decrease such that x 1 &gt;x 2 &gt;x 3  and the thickness reduction work performed on the composite positive electrode sheet  20  is also more gradual than in the previous embodiments shown in  FIGS. 1 and 2 . As described in previous examples, x 3 =x 4  and the last pair of nip rollers  62 A- 62 B is used to cool the composite positive electrode sheet  20  before releasing it. To facilitate the performance of the thickness reduction work, at least one but preferably both rollers of each pair of nip rollers  56 A- 56 B,  58 A- 58 B, and  60 A- 60 B are heated to a temperature sufficient to transfer to the polypropylene sheets  64  and  66  enough heat to maintain the composite positive electrode sheet  20  soft and malleable as it passes through the pairs of nip rollers  56 A- 56 B,  58 A- 58 B, and  60 A- 60 B. The polypropylene sheets  64  and  66  are dispensed from rolls  70  and  72  and are removed and collected onto rolls  74  and  76 . Due to the presence of the polypropylene sheets  64  and  66 , the rotational speeds of the nip rollers  56 A,  56 B,  58 A,  58 B,  60 A,  60 B,  62 A and  62 B are equal such that there will be an increase in the width of the composite positive electrode sheet  20  as it passes through the pairs of nip rollers  56 A- 56 B,  58 A- 58 B, and  60 A- 60 B.  
         [0053]     In a particular example of implementation, a lubricant is used on the surfaces of polypropylene sheets  64  and  66  which directly contact the composite positive electrode film  20  in order to prevent adhesion of the composite positive electrode film  20  to the surfaces of polypropylene sheets  64  and  66 . The lubricant is dispensed by any method known to those skilled in the art. In a specific embodiment, the lubricant has the chemical formula of C 7 H 16 .  
         [0054]     In  FIG. 8 , there is shown a sixth embodiment of the invention in which a calendering apparatus  75  is juxtaposed to a sheet die  10  of a typical single or twin screw extruding machine (not shown). Calendering apparatus  75  comprises a series of cylindrical nip rollers  76 ,  78 ,  80  and  82  adapted to progressively reduce the thickness of a composite positive electrode sheet  20  passing through calendering apparatus  75 . In this embodiment, the extruded composite positive electrode sheet  20  snakes it way in between the nip rollers  76 ,  78 ,  80  and  82 . The composite positive electrode sheet  20  is taken by nip x 1  defined by the pair of rollers  76 - 78  which are advantageously heated to facilitate the work of compressing the positive electrode sheet  20  to reduce its thickness and to prevent separation of the polymer electrolyte constituent from the active cathode material and maintain electrochemical integrity. The positive electrode sheet  20  then moves into a second nip x 2  defined by the pair of rollers  78 - 80 , roller  80  also being advantageously heated to facilitate the work of compressing the positive electrode sheet  20  between the pair of rollers  78 - 80 . The positive electrode sheet  20  then follows the contour of cylindrical roller  80  and passes through a third nip x 3  defined by the pair of rollers  80 - 82  which further reduces its thickness. Advantageously, the last roller  82  is maintained at a cool temperature such that the composite positive electrode sheet  20  is also cooled and at least partially solidified before being released.  
         [0055]     In a particular example of implementation, a lubricant is used on the surfaces of rollers  76 ,  78 ,  80  and  82  which directly contact the composite positive electrode film  20  in order to prevent adhesion of the composite positive electrode film  20  to the surfaces of rollers  76 ,  78 ,  80  and  82 . The lubricant is dispensed by any method known to those skilled in the art. In a specific embodiment, the lubricant has the chemical formula of C 7 H 16 .  
         [0056]     In each of the previously described embodiments, the sheet die and calendering apparatus may be oriented horizontally or vertically without departing from the scope of the invention. Furthermore, the width of the composite positive electrode film  20  when exiting the calendering apparatus may further be controlled by a slitting process to ensure an exact width of the final product without departing from the scope of the invention.  
         [0057]     It should be expressly understood that various mechanical and/or hydraulic means for mounting and adjusting the position of the nip rollers relative to each other to define the nip distances ‘x’ are contemplated and within the reach of a person skilled in the art, and as such are within the scope of the present invention.  
         [0058]     Although the present invention has been described in relation to particular variations thereof, other variation and modifications are contemplated and are within the scope of the present invention Therefore, the present invention is not to be limited by the above description but is defined by the appended claims.