Abstract:
A stacking apparatus and a method for assembly of electrochemical cells. The stacking apparatus includes at least one stacking head having an adjustable holding member adapted to hold an electrochemical laminate of a pre-determined length and means for adjusting the shape of the electrochemical laminate of the pre-determined length during stacking of a plurality of electrochemical laminates. The electrochemical laminates are assembled in a way that prevents air entrapment between the electrochemical laminates.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. Patent Application Ser. No. 10/666,045 filed on Sep. 22, 2003 now U.S Pat. No. 7,000,665, which is a continuation of International Application No. PCT/CA2003/001489 filed on Sep. 18, 2003 and designating the United States of America, both of which are hereby incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to the manufacturing of polymer batteries and more specifically to an apparatus and method for stacking polymer electrochemical laminates to form polymer electrochemical cells that are constituents of a polymer battery. 
     BACKGROUND OF THE INVENTION 
     Rechargeable batteries manufactured from laminates of solid polymer electrolytes and sheet-like anodes and cathodes display many advantages over conventional liquid electrolyte batteries. These advantages include lower overall battery weight, high power density, high specific energy, longer service life, as well as being environmentally friendly since the danger of spilling toxic liquid into the environment is eliminated. 
     Solid polymer electrochemical cell components include positive electrodes, negative electrodes and a separator material capable of permitting ionic conductivity such as a solid polymer electrolyte sandwiched between each anode and cathode. The anodes (or negative electrodes) and cathodes (or positive electrodes) are made of material capable of reversibly intercalating alkali metal ions. 
     Such an advanced battery system typically consists of a series of extremely thin film laminates of anode material, polymer electrolyte separator, cathode material and current collector assembled together as a multi-layer construction in either a flat roll configuration, a jelly roll configuration or a flat stack configuration to form a battery. Individual electrochemical laminates are typically mono-face or bi-face. A mono-face electrochemical laminate consists of a current collector, a cathode, a polymer electrolyte separator, and an anode covered with an insulating polypropylene film to insulate the electrochemical laminate from the adjacent one for preventing short circuits. A bi-face electrochemical laminate consists of a central current collector having a cathode layer on both sides, a polymer electrolyte separator adjacent each cathode layer, and an anode layer adjacent each electrolyte separator. In a bi-face laminate, the insulating polypropylene film is eliminated since the risk of short-circuits between the anode and the cathode of adjacent laminates is removed. A bi-face laminate assembly typically provides a higher energy density. 
     For large batteries (500 gr or more), the preferred configuration is a flat stacked multi-layer assembly of bi-face laminate for its high energy density and for its ability to be shaped into a limited volume. 
     Numerous methods of assembling laminates into cells and batteries have been devised and/or investigated. U.S. Pat. No. 5,100,746 discloses a method of assembling the anode, cathode, current collector and electrolyte separator layers are co-laminated using a series of pressure rollers, the assembly thereafter being coiled to form a battery; however, the assembly could be cut and stacked. 
     U.S. Pat. No. 6,030,421 discloses a previously laminated mother-battery containing an anode of metallic lithium or sodium, a composite cathode, a polymer electrolyte that acts as a separator between the electrodes, and a current collector. The laminated mother-battery is thereafter subjected to a sharp mechanical cutting out to give thin polymer electrolyte batteries. 
     These documents disclose how to assemble the laminates themselves but do not teach precisely how to properly superpose or flat-stack the laminates to form batteries. 
     U.S. Pat. No. 6,547,229 discloses a stacking apparatus and method employing one or more stations, each including a stationary stacking platform or a conveyor upon which spaced-apart pucks are coupled for travel thereon. A product delivery apparatus drives one or more movable webs to which segmented product sheets are removably affixed. The product delivery apparatus includes one or more rotatable lamination interfaces associated with each of the stations for transferring product sheets from the webs to the pucks on a repetitive basis to produce a stack of product sheets on the respective pucks. Each of the segmented product sheets may define. all or a portion of an electrochemical cell, the latter including layers of film or sheet material, wherein a portion of each of the layers is provided with a bonding feature. A puck need not be in motion during the transfer of the product sheet from the lamination roll to the puck. The puck may or may not be attached to a conveyor, but the conveyor need not be in motion during the lamination or stack building process. In this case, a roller is moved across the puck and simultaneously rotated so a point on the surface of the roller interfaces with the puck at the same location on each pass. 
     WO 02/43179 discloses an apparatus and method for rotatably cutting and/or laminating layered structures or sheet material supported by webs. A rotary converting apparatus and method converts a web comprising a cathode layered structure and a web comprising an anode layered structure into a series of layered electrochemical cell structures supported by a release liner. Employment of a rotary converting process provides for the creation of a product having a finished size, without need for downstream or subsequent cutting. 
     These two documents disclose methods of stacking components of laminates using a rotary device. This type of rotating mechanism is however often unreliable to produce precise assembly. 
     There are numerous difficulties to overcome when stacking extremely thin sheets together to produce electrochemical cells. First, each layer must be precisely aligned with the other layers in order to have a properly assembled stack that can be electrically connected with ease and within which no electrical short circuit will occur due to misalignment of the plurality of layers. A rotary system is inherently unable to provide the precise stacking of each layer required for electrochemical cell assembly. Secondly, when stacking the various layers of the electrochemical cell together, it is imperative that air not be trapped between two layers. Air entrapment will prevent proper contact between the various layers thereby reducing the capacity of the electrochemical cell as well as creating uneven surfaces that may cause further problems in subsequent assembly steps. Thirdly, the components, i.e. thin films of cathode, anode and electrolyte separator, are sticky and are difficult to handle without ripping or corrupting. 
     Thus there is a need in the polymer battery industry for an efficient method and apparatus for stacking polymer electrochemical laminates and constituents thereof to form polymer electrochemical cells and batteries. 
     STATEMENT OF THE INVENTION 
     It is therefore an object of the present invention to provide a stacking apparatus for assembly of electrochemical cells comprising:
         a supporting structure;   at least one stacking head having an adjustable holding member adapted to hold an electrochemical laminate of a pre-determined length and having means for adjusting the shape of the electrochemical laminate;   the stacking head being operative to stack a plurality of electrochemical laminates of the pre-determined length one on top of the other, during stacking the adjustable holding member holding each particular electrochemical laminate of the pre-determined length in a shape such that a central portion of the particular electrochemical laminate of the pre-determined length is deposited first, followed by a motion of the adjustable holding member that progressively lowers the remainder of the particular electrochemical laminate of the pre-determined length, thereby preventing air entrapment between adjacent electrochemical laminates of the pre-determined length in the stack.       

     Advantageously, the adjustable holding member comprises a substantially flat plate made of a micro-porous material through which a vacuum system generates a negative pressure that holds the pre-determined length of electrochemical laminate. 
     As embodied and broadly described, the invention further provides a process for assembling a plurality of electrochemical laminates to form a battery comprising the steps of:
         laminating a continuous length of anode film with a continuous length of pre-assembled half cell comprising a current collector, a cathode film and an electrolyte separator film;   cutting the laminate into pre-determined lengths of laminates;   stacking the pre-determined lengths of laminates one on top of the other in a shape such that a central portion of each pre-determined length of laminate is deposited first, followed by a motion that lowers the remainder of the pre-determined length of laminate, thereby preventing air entrapment between adjacent pre-determined lengths of laminate in the stack.       

     As embodied and broadly described, the invention also provides a process for assembling a plurality of electrochemical laminates to form a battery wherein the electrochemical laminates are in a charged state when being assembled one above the other. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood and other advantages will appear by means of the following description and the following drawings in which: 
         FIG. 1  is a partial perspective view of a plurality of stacked electrochemical laminates forming an electrochemical cell according to one embodiment of the invention; 
         FIG. 2  is a schematic cross-sectional view of a bi-face electrochemical laminate according to one embodiment of the invention; 
         FIG. 3  is a schematic cross-sectional view of a pre-assembly of an electrochemical laminate according to one embodiment of the invention; 
         FIG. 4  is a schematic front elevational view of a stacking apparatus according to one embodiment of the invention; 
         FIGS. 5A and 5B  are enlarged schematic front elevational views of two embodiments of a component of the stacking apparatus according to the invention; and 
         FIGS. 6   a ,  6   b  and  6   c  illustrate schematic front elevational views of three different positions assumed by the component illustrated in  FIG. 5A  throughout one assembly cycle of the assembly process according to the invention; 
     
    
    
     DETAILED DESCRIPTION 
     In  FIG. 1 , there is shown for illustrative purposes a specific embodiment of a Lithium polymer electrochemical cell  10  comprising a prismatic assembly of a plurality of electrochemical laminates  12  stacked together. With reference to  FIG. 2 , in a preferred configuration, each individual electrochemical laminate  12  comprises a central cathode current collector  14 , a cathode film  16  and  18  layered on both sides of cathode current collector  14 , a polymer electrolyte separator film  20  and  22  layered over each cathode film  16  and  18 , and an anode thin sheet  24  and  26  layered over each polymer electrolyte separator film  20  and  22 , which together form a bi-face electrochemical laminate  12 . As shown in  FIG. 2 , the anode sheets  24  and  26  are offset relative to the central current collector  14  such that the cathode current collector  14  extends on one side of the electrochemical laminate  12  and the anode thin sheets  24  and  26  extend on the opposite side of the electrochemical laminate  12 . When a plurality of laminates  12  are stacked together, the anode sheets of all laminates  12  may be electrically connected together on one side  13  of the electrochemical cell  10  and the cathode current collectors  14  of all laminates  12  may be electrically connected together on the opposite side  11  of the electrochemical cell  10  as shown in  FIG. 1 . Each electrochemical laminate  12  generally has a thickness in the range of 80 to 300 microns. 
     In order to efficiently assemble electrochemical cell  10 , the central portion of the electrochemical laminate  12  is first assembled. Cathode films  16  and  18  are applied on both sides of a continuous length of current collector sheet or foil  14  which is typically a metal foil, such as an aluminum foil, to form a continuous length of cathode films coated on both sides of current collector  14 . Subsequently, polymer electrolyte separator films  20  and  22  are layered over each continuous length of cathode films  16  and  18  to form the core or half-cell  25  of laminate  12 . Hereafter, an anode thin sheet  26  is applied to only one side of half-cell  25  of laminate  12  as illustrated in  FIG. 3  to form a pre-assembly  30  of laminate  12 . The pre-assembly  30  therefore consists of a continuous length comprising a central cathode current collector  14  having a layer of cathode material  16  and  18  on each side thereof, each cathode layer  16  and  18  being covered by polymer electrolyte separator films  20  and  22 , and one anode sheet  26  on one side of pre-assembly  30 . By continuous lengths, we understand long lengths of materials extending from a few meters in length to hundreds of meters in length. 
     The continuous length of pre-assembly  30  is then brought to a stacking apparatus where it is cut in appropriate lengths ranging from 10 cm to 80 cm depending on the electrochemical cell configuration and thereafter stacked one on top of each other to form an electrochemical cell  10 . 
       FIG. 4  illustrates schematically a stacking apparatus  40  adapted to handle a continuous length of pre-assembly  30 , cut the pre-assembly  30  to length and stack the cut lengths of the pre-assembly  30  to form an electrochemical cell  10 . In a preferred embodiment, a continuous length of half-cell  25  is brought together with a lithium metal anode sheet  26  on an assembly roll  60  which presses the lithium metal anode sheet  26  onto the half-cell  25  to form the pre-assembly laminate  30 . Once the lithium metal anode sheet  26  is assembled to one side of the half-cell  25 , one side of the pre-assembly electrochemical laminate  30  is live and by definition charged and voltage measurements may be taken to ensure that no short-circuits occurred in the assembly. As illustrated, when the continuous half-cell  25  is unrolled, a protective polypropylene sheet  62  is removed. The pre-assembly laminate  30  is wound through a series of cylindrical rolls  64  adapted to maintain the pre-assembly laminate  30  under a pre-determined tension and brought to the stacking apparatus  40 . 
     In a one specific embodiment, the stacking apparatus  40  comprises a stacking head  45  slideably mounted on a upper girder  46  itself mounted on a fixed supporting structure  47  and adapted to move forward and backward on the fixed supporting structure  47 . The stacking head  45  is adapted to move sideways and vertically relative to the girder  46 . In combination with the forward and backward movement of the girder  46 , the stacking head  45  is adapted to move along all three axes X, Y and Z. The movements of the stacking head  45  along the various axes are effected by sliding or rolling connections and are powered by any means know to the person skilled in the art, for example by pneumatic, hydraulic or precision electric motors. All through the assembly process, the movements of stacking head  45  are controlled precisely by a positioning system of coordinates X, Y and Z. The stacking head  45  comprises a pair of holding members  48  adapted to securely hold pre-assembly laminate  30  without damaging its fragile layers. Each holding member  48  is mounted onto a rotating bracket  50  rotatably mounted on the stacking head  45  through a slot system  82 ,  84 . The rotating brackets  50  are adapted to control the angular positions of each holding member  48  relative to one another and relative to the horizontal axis. A mechanical, hydraulic or pneumatic system (not shown) controls the rotation of rotating brackets  50  and therefore the angular positions of each holding member  48 . 
     As illustrated in  FIGS. 5A and 5B , holding members  48  consists of a flat or curvilinear plate  52  made of a micro-porous material compatible with lithium which means that it does not adhere to the lithium sheet  26 . The upper portion of plate  52  comprises a vacuum chamber  56  that is connected through the rotating brackets  50  to a pneumatic vacuum system, via a conduit  58 . In operation, the vacuum system generates a vacuum within vacuum chamber  56 , which in turn generates a negative pressure on the lower surface  70  of plate  52  through the micro-pores or capillaries of the micro-porous material such that the holding member  48  can lift and securely hold the pre-assembly laminate  30 . The micro-pores of the material ensures that the pre-assembly laminate  30  and more specifically the upper lithium sheet  26  will not be damaged by the vacuum force applied thereto. If plate  52  comprised a series of small apertures through which the vacuum force was applied, the lithium sheet  26  could be deformed to a mirror image of plate  52  which would be detrimental to the subsequent assembly of the electrochemical cell  10 . The micro-pores are sufficiently small that the vacuum force does not affect the surface of the lithium sheet  26 . 
     Referring back to  FIG. 4 , in operation, an end  42  of the continuous length of pre-assembly laminate  30  is gripped by a pincer  44  having soft jaws with flat surfaces which then pulls a pre-determined length of the pre-assembly laminate  30  into position in front of stacking head  45  and onto a smooth surface  72  located immediately in front of stacking, head  45 . Aligned with the end of surface  72 , a rotary knife  76  and anvil  74  assembly is provided. Rotary knife  76  and anvil  74  are adapted to move together perpendicular to the end of surface  72  to effectively cut the pre-assembly laminate  30  to its pre-determined length. In operation, the stacking head  45  is moved forward over pre-assembly laminate  30  and surface  72  and is lowered onto the pre-assembly laminate  30  which it holds securely onto surface  72  while the rotary knife  76 /anvil  74  assembly is rolled onto the pre-assembly laminate  30  to cut the pre-assembly laminate  30  to a pre-determined length. Thereafter, the stacking head  45  lifts the cut pre-assembly  30  using the negative force generated on the lower surface  70  of holding members  48  by the vacuum system through vacuum chamber  56 . 
     Stacking head  45  is then moved forward and is positioned over a carriage platform  80 . The surface  86  of the carriage platform  80  is treated with plasma deposition to prevent the pre-assembly laminate  30  from sticking to it. Stacking head  45  then moves down and deposits the pre-assembly laminate  30  onto the carriage platform  80  to form the first layer of the electrochemical cell  10 . Stacking head  45  then moves back to its initial position where the cycle previously described is repeated. A second pre-assembly laminate  30  is deposited onto the previously laid pre-assembly laminate  30  to form a complete bi-face electrochemical laminate  12  as illustrated in  FIG. 2 . The cycle is repeated until a predetermined number of electrochemical laminates are assembled to form an electrochemical cell  10 . The carriage platform  80  is then moved to another station (not shown) for further processing; an empty carriage platform  80  is positioned in its place and the entire cycle is repeated for assembling a new electrochemical cell  10 . 
       FIG. 6  illustrates the various positions holding members  48  assume at various points during the assembly cycle.  FIG. 6a  illustrates the position of the holding members  48  when stacking head  45  is lowered onto the pre-assembly laminate  30  to hold it securely onto surface  72  while it is being cut to the pre-determined length. The holding members  48  form between them a substantially flat surface with an angle of approximately 180°. At this stage, the vacuum system is turned on which generates a negative pressure at the surface  70  which enables holding members  48  to gently lift the cut length of laminate  30 . Thereafter, the holding members  48  assume the position illustrated in  FIG. 6b , where the rotating brackets  50  are rotated inwardly such that the holding members  48  form between them an angle of less the 180° and the pre-assembly laminate  30  assumes a somewhat angular or curvilinear shape. The rotating brackets  50  are pivoted or rotated via precisely shaped slots  82  and  84  to prevent the surfaces  70  of the holding members  48  from moving marginally away from each other and creating a pulling force on the pre-assembly laminate  30  that could rip or damage it. The pre-assembly laminate  30  is carried to a position above the carriage platform  80  onto which another pre-assembly laminate  30  has been previously laid down. The stacking head  45  lowers the pre-assembly laminate  30  onto the previously laid component in this angular or curvilinear position such that the central or middle portion of laminate  30  touches the previously laid component first. The rotating brackets  50  are then rotated outwardly as shown in  FIG. 6c , in order to lower and at the same time spread the remainder of the pre-assembly laminate  30  onto the previously laid component thereby driving out air and preventing air entrapment between the components during assembly. Simultaneously, the negative pressure is released from vacuum chambers  56  to release the pre-assembly  30  while it is being spread onto the previously laid component. Stacking head  45  then moves back to its initial position where the entire cycle previously described is repeated until the predetermined number of electrochemical laminates are assembled to form an electrochemical cell  10 . When the predetermined number of assembled electrochemical laminates is reached, the carriage platform  80  is moved away and replaced with an empty one and the assembly cycle begins again. 
     Stacking apparatus  40  is shown and described with a single stacking head  45 ; however, a plurality of stacking-heads  45  may be installed side by side in the supporting structure  47  such that a plurality of electrochemical cells  10  may be assembled simultaneously. In this embodiment, there are as many rotary knife  76 /anvil  74  assemblies as there are stacking heads  45 . The continuous length of pre-assembly laminate  30  is gripped by the pincer  44  and pulls a pre-determined length of the pre-assembly laminate  30  into position in front of the plurality of stacking heads  45  and onto a plurality of aligned smooth surfaces  72  located immediately in front of each of the plurality of stacking heads  45 . One rotary knife  76 /anvil  74  assembly is positioned adjacent each of the plurality of stacking heads  45 . In operation, the stacking heads  45  are then moved forward over the length of pre-assembly laminate  30  and are lowered onto the pre-assembly laminate  30  which it holds securely onto surfaces  72  while the rotary knife  76 /anvils  74  assemblies are rolled onto the pre-assembly laminate  30  adjacent each stacking head  45  to cut the, pre-assembly laminate  30  to pre-determined lengths. Thereafter, the stacking heads  45  lift their respective portion of the cut pre-assembly laminate  30  as previously described and stack them onto a plurality of carriage platforms  80 , one for each stacking head  45  in the same manner previously described. In this embodiment of the stacking apparatus  40 , the movements of the plurality of stacking heads  45  are also controlled precisely by a positioning system of coordinates X, Y and Z throughout the assembly process. 
     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.