Abstract:
Production apparatus and method for producing devices for storing electric energy are disclosed, wherein stacks of flat cathodes r and anodes that face one another alternately with the interposition of a separator are produced, and in which the separator is formed by a single continuous strip folded several times in a single folding direction.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to an apparatus and method for manufacturing devices for storing electric energy, in particular storage devices having a stack of cathodes and anodes that face one another alternatively with an interposed dielectric separator. 
         [0002]    Specifically, but not exclusively, the invention may relate to the production of various types of storage devices—such as lithium batteries, electric double-layer capacitors, units for electrochemical treatment of liquids (for example oxygenators for water), electrostatic capacitors, fuel cells, etc—in which an electrode separator consists of a single continuous strip folded several times in the same folding direction. 
         [0003]    Amongst known electric energy storage devices, lithium batteries are able to supply a relatively high voltage with an optimal energy-weight ratio. Various systems are known for manufacturing lithium batteries having a stack of flat cathodes and anodes that face one another alternatively and separated by a separator. In particular, producing a lithium battery with a separator consisting of a continuous single strip is known. In certain known manufacturing methods, adhesive means is used to join the electrodes to the separator, in particular on both the sides of a separating strip. In some embodiments forming the stack of electrodes by folding a separating strip several times in a zigzag is known; for example, using an apparatus is known that folds the strip in alternate directions (“z-folding”). A method is also known, for example from US 2006/0088759, for folding a separating strip in a single folding direction. 
         [0004]    Patent publication WO 2002/095858 A1 shows an apparatus according to the preamble of claim  1 . Patent publication WO 2003/100901 A1 shows a method according to the preamble of claim  14 . 
         [0005]    Systems known for manufacturing storage devices comprising a stack of electrodes that face one another and are separated by a separator consisting of a single continuous strip are improvable in various aspects. 
         [0006]    In the first place, it is desirable to reduce the cost of manufacturing the storage device. Further, producing storage devices with relatively high capacity and performance is desirable. One of the drawbacks of assembling a stack of electrodes with the “z-folding” system is the reduced productivity. One of the drawbacks of the production of a storage device with a lamination system of the electrodes via adhesive means are the high costs (which are in particular due to the cost of the adhesive means) and the relatively low performance of the storage device (in particular because of the reduced ionic transfer between the electrochemical cells that is due to the adhesive means). 
       SUMMARY OF THE INVENTION 
       [0007]    One object of the invention is to provide an apparatus and/or a method for producing devices for storing electric energy comprising a stack of electrodes facing and separated from one another by a continuous single strip. 
         [0008]    One advantage is to produce energy storage devices in a simple and cheap manner. 
         [0009]    One advantage is to make an apparatus and/or a method available that is able to produce devices for storing electric energy in a precise and reliable manner. 
         [0010]    One advantage is giving rise to an electric energy storage device that is of simple construction and great reliability. 
         [0011]    One advantage is to produce a storage device having a stack of electrodes assembled by folding a continuous separating strip in a single folding direction. 
         [0012]    One advantage is to enable a stack of electrodes to be formed without the need to use adhesive means to maintain the electrodes in the desired position during assembly of the stack. 
         [0013]    Such objects and advantages and still others are achieved by the apparatus and/or by the method of one or more of the claims set out below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The invention can be understood and implemented better with reference to the attached drawings, which show an embodiment thereof by way of non-limiting example. 
           [0015]      FIG. 1  is a diagram, in a vertical elevation, of an apparatus for manufacturing devices for storing electric energy. 
           [0016]      FIG. 2  is a top plan view of the apparatus diagram in  FIG. 1 . 
           [0017]      FIG. 3  is an enlarged detail of  FIG. 1  comprising the advancing path of the separating strip  5  bearing the electrodes from the rollers  9  to the winding device  16  that forms the electrode stack and to the cutting device  17  that separates the stack formed from the rest of the strip  5 . 
           [0018]      FIGS. 4   a  to  4   d  are four top plan views that show four possible manners of arrangement of the electrodes (cathodes C and anodes A) along the advancing path in  FIG. 3  (with the strip  5  below not shown for sake of clarity). 
           [0019]      FIG. 5  is an enlarged detail of  FIG. 3  comprising the zone where the winding device  16  for forming the electrode stack performs a series of overturnings of the stack P being formed by means of which the separating strip is wound around the electrodes. 
           [0020]      FIG. 6  is  FIG. 5  from which some parts have been removed to show better the pressure elements  23  and  24 , which contribute to the stability of the stack P being assembled during the overturning thereof, and the cutting elements (blade and counterblade) of the cutting device  17 , that separate the already formed stack from the strip  5 . 
           [0021]      FIG. 7  is  FIG. 5  from which some parts have been removed to show better the end portion of the supporting device  12  of the strip  5  bearing the electrodes A and C and a part of the rotating support (with a movable rotation axis) that rotates the members that overturn the stack P during assembly thereof. 
           [0022]      FIG. 8  is a diagram of a sequence of positions numbered i to x, adopted by the first electrode during the first overturning at the start of assembly of the stack P, to highlight the movement R of the median zone of the electrode and the movement T of the end of the electrode arranged near the folding line of the strip. 
           [0023]      FIG. 9  is a frontal view of the winding device  16  at the start of assembly of the stack, with some dashed and interrupted lines that show the disengagement position of some operating members of the device at the end of the construction of the stack. 
           [0024]      FIG. 10  is a detail of  FIG. 9 . 
           [0025]      FIG. 11  is a top plan view of the winding device  16  of  FIG. 9 . 
           [0026]      FIG. 12  is a detail of  FIG. 11 . 
           [0027]      FIG. 13  is a frontal view of the winding device  16 , like that of  FIG. 9 , at the end of assembly of the stack, before the gripping elements  25  have been removed from inside the stack by moving some operating members to the disengagement position. 
           [0028]      FIGS. 14 to 16  show three operating steps of the pressure elements  23  and  24 . 
           [0029]      FIG. 17  shows the electrode stack with the rotation axis of the first electrode highlighted that, during assembly of the stack, is grasped and rotated by the winding device  16 , and at the end of assembly of the stack, is located in the centre of the stack. 
           [0030]      FIG. 18  is a top plan view of the stack in  FIG. 17 . 
           [0031]      FIG. 19  is an enlargement of the already assembled stack in  FIG. 17 . 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    With reference to the aforesaid figures, overall with  1  there has been indicated an apparatus for the manufacture of devices for storing electric energy comprising a stack of cathodes C and anodes A that alternate and face one another with an interposed separator. 
         [0033]    With  2  the magazines have been indicated where the electrodes (cathodes C and anodes A) are arranged that will form the stack of the storage device. With  3  there has been indicated a conveying device (of known type) of the (flat) electrodes which may comprise, as in the specific case, a closed-loop flexible member (for example a conveyor belt). It is possible that, as in the specific case, the conveying device is provided with pneumatic means for keeping the electrodes in position (via suction), such as, for example, a conveyor belt with suction means to make the electrodes adhere to the belt. With  4  there has been indicated a loading device (of known type) to remove the electrodes from the magazines (also two or more electrodes at a time, in the specific case four electrodes at a time) and transfer the electrodes to the conveying device. The loading device  4  may comprise, as in the specific case, a transferring device of the “pick-and-place” type, which may operate, for example, with suction cup means to take the electrodes from the magazines and deposit the electrodes on the conveyor belt. 
         [0034]    With  5  a continuous strip has been indicated, which is made of dielectric material (of known type), which will act as a separator interposed between the electrodes inside the stack. The strip  5  is unwound, in a known manner, from a reel  6 . 
         [0035]    With  7  there has been indicated an inserting device (of known type, for example of the gripper type) configured for removing the electrodes (cathodes C and anodes A) that advance supplied by the conveying device  3  and for placing the electrodes (cathodes C and anodes A) on the continuous separating strip  5  whilst the latter is unwound continuously from the reel  6 . The inserting device  7  can be configured for transferring the electrodes one at a time by a reciprocating forward and backward movement (coordinated with an opening and closing movement of the gripping means that grasps the electrode) between a position of withdrawing the electrode (from the conveying device  3 ) and a releasing position (to enable the electrode to be inserted and laminated on the strip  5 ). With  8  there has been indicated a sensor (of known type) for detecting the position of the electrodes to be placed on the strip  5 . The sensor  8  may comprise, as in the specific case, a sensor of optical type, for example a viewing system, that operates in an (end) zone of the conveying device  3 . The sensor  8  and the inserting device  7  are connected to a control unit configured for controlling (in a known manner) the inserting device  7  on the basis of a signal emitted by the sensor  8 , in such a way as to correct possible positioning errors of the electrodes. With  9  there have been indicated rollers between which the continuous strip  5  is passed and between which the electrodes are also inserted (one by one). 
         [0036]    With  10  there has been indicated a protective film (made of plastics) for protecting the electrodes arranged on the upper side of the advancing strip  5 . The protective film  10  is unwound continuously from a reel  11 . 
         [0037]    With  12  there has been indicated a supporting device of the continuous separating strip  5  that advances by bearing on the upper side the electrodes (cathodes C and anodes A according to a set sequence). The supporting device may comprise a movable element that will define a (horizontal) movable supporting plane for supporting the strip  5 . In particular, the supporting device  12  may comprise, as in the specific case, a closed-loop flexible member (for example a slidable supporting belt) having driving means for sliding the flexible member. The flexible member can have a (horizontal) upper branch configured for defining the (slidable) conveying plane on which the strip  5  bearing the electrodes can advance. 
         [0038]    With  13  there has been indicated a stabilising device that stabilises the electrodes carried by the continuous separating strip  5 . This stabilising device operates, amongst other things, to enable undesired air to be evacuated that may remain interposed between the electrodes and the separating strip  5 . The stabilising device  13  may comprise a sliding element that will define a (horizontal) plane parallel to and superimposed on the supporting plane defined by the supporting device  12 . The stabilising device may comprise, as in the specific case, a closed-loop flexible member (for example of the slidable belt type) having driving means for sliding the flexible member. The flexible member may have a lower (horizontal) slidable branch that is configured for cooperating with the (slidable) conveying plane in such a way as to exert slight stabilising (and air evacuating) pressure on the electrodes carried by the strip  5 . This stabilising pressure can enable possible air bubbles between the electrodes and the separating strip  5  to be eliminated. Between the electrodes on the strip  5  and the stabilising device  13  the protective film  10  is interposed, which is also slidable. 
         [0039]    With  14  there has been indicated a sensor for detecting the position of the electrodes arranged on the separating strip  5 . In particular, the sensor  14  is configured for measuring the distance between two consecutive electrodes. The sensor  14  may comprise, as in the specific case, a sensor of optical type, for example a viewing system, that operates on the advancing strip  5  bearing the electrodes. With  15  there has been indicated a reel for rewinding the protective film  10 . 
         [0040]    With  16  there has been indicated a winding device for forming the electrode stack (cathodes C and anodes A) from the product (supplied in the advancing direction X) formed by the strip  5  and by the electrodes C and A carried by the strip. The winding device  16  performs a series of overturnings of a stack P during the assembly step in such a manner as to wind the separating strip  5  around the electrodes C and A. At the start of stack assembly operations, the stack under construction will consist of a sole electrode (the first electrode of the arrangement of electrodes), which will be the first to be overturned. At the first overturning the first electrode will be overturned on an empty strip region (having dimensions that are such as to be able to receive an electrode, but are initially not occupied by any electrode). At the end of each successive overturning (performed, like the first, by performing a 180° rotation in the direction F around a movable rotation axis, still in the same overturning direction F, as will be better explained below), the stack under construction will be imposed on the subsequent electrode (cathode C or anode A) that will then be added to the stack under construction, which will then be overturned in the subsequent 180° rotation. 
         [0041]    As said, the winding device  16  and the operation thereof will be disclosed in greater detail below. The sensor  14  and the winding device  16  can be connected to a control unit configured for controlling the winding device  16  on the basis of a signal emitted by the sensor  14 , in such a manner as to take account of possible positioning errors of the electrodes, in particular of errors in the distance between two consecutive electrodes. 
         [0042]    With  17  there has been indicated a cutting device, of known type, for separating the already assembled stack from the rest of the continuous separating strip  5 . The cutting device  17  may comprise, as in the specific case, a blade and a counter blade that are movable in relation to one another and cooperate together for the transverse cut of the strip  5  to enable the already assembled stack to be detached and subsequently removed and the subsequent stack to be formed. 
         [0043]    With  18  there has been indicated a transferring device (of known type) for transferring the stack that has already been assembled (and separated from the strip  5 ) to the subsequent work stations. The transferring device  18  may comprise a gripping member (for example of the gripper type) to grasp the stack. The gripping member can be movable (for example carried by an element rotating around a horizontal axis) in such a manner as to adopt a stack withdrawal position (for example immediately downstream of the cutting device  17 ) and a position of delivery of the stack to a conveying system. The delivery position can be, as in the specific case, rotated by 180° with respect to the withdrawal position. The conveying system can be configured for supplying the stacks that have already been assembled through a preset path along which possible further work stations are arranged, such as, for example, a welding station  19  of the separator, a station  20  for running an electric test, a station  21  for running a dimensional test, as far as an outlet  22 . 
         [0044]    In  FIGS. 4   a  and  4   b  there are illustrated two possible manners of arranging the electrodes (cathodes C and anodes A) on the continuous separating strip  5  (which is not illustrated for the sake of clarity). In  FIG. 4   a , the first electrode of the row of electrodes with which the electrode stack will be formed is a cathode, followed by an empty space that is not occupied by an electrode, which is in turn followed by a succession of two anodes and two cathodes. In  FIG. 4   b , the first electrode of the row is an anode, followed by an empty space that is not occupied by an electrode, which is in turn followed by a succession of two cathodes and two anodes. In the specific case the electrodes are flat and rectangular. Between each electrode and the next electrode, a strip folding line is provided (only between the first and the second electrode are two folding lines provided that bound the empty strip space that is not occupied by an electrode). The distance between the electrodes is chosen in such a manner as to take account of the fact that, continuing with winding, the stack increases thickness, so this distance will increase progressively from the first to the last electrode of the sequence of electrodes. Each electrode has an electric terminal (or collector), for example in the shape of a tab protruding from a (short) side of the electrode. The arrangement of the electrodes on the strip  5  is made in such a way that, once the stack has been constructed, each anode A faces and alternates with a cathode C (with the interposition of a single layer of the separating strip), and in such a way that (in the examples of  FIGS. 4   a  and  4   b ) the electric terminals of the anodes A are all aligned on one another on one part of a side of the stack, whilst the electric terminals of the cathodes C are aligned on one another and arranged on an opposite part of the side of the stack at a certain distance from the terminals of the anodes A. In the examples of  FIGS. 4   c  and  4   d , once the stack is assembled, the electric terminals of the anodes A will be aligned on one another on a side of the electrode, whilst the electric terminals of the cathodes C will be aligned on one another and arranged on the opposite side of the stack. It is possible to provide other manners of arranging the electrodes. In particular, it is possible to provide that between the first electrode and the second electrode there is no empty strip  5  portion, in which case the first electrode will already be supplied with a separating layer (for example a sheet of dielectric material), applied to the upper face of the electrode (this upper separating layer can be applied before placing of the electrodes on the strip  5 , in the apparatus  1  or outside the apparatus  1 , or can be applied by folding on the first electrode a front end portion of the strip  5  that is not occupied by an electrode). 
         [0045]    The winding device  16  is illustrated in greater detail in  FIGS. 5 to 16 . The winding device  16  comprises a rotating support S (rotated during winding always in the same rotation direction indicated by the arrow F) around a (horizontal) rotation axis z-z that is perpendicular to the advancing direction of the strip  5  on the supporting device  12  (this rotation axis z-z being movable, as will be explained below). The rotating support S rotates two pressure devices that operate reciprocally on the stack P during assembly thereof. Each pressure device is configured for applying slight stabilising pressure to a side of the stack P during the assembly step (in particular the side where the last electrode is located that is added to the stack under construction during winding). Substantially, the pressure devices exert slight pressure to ensure adhesion and compaction between the separating strip  5  and the stack P being formed, so that the most advanced part of the strip is rotated during winding. 
         [0046]    The first pressure device comprises a first pair of pressure elements  23  and the second pressure device comprises a second pair of pressure elements  24 . Each pair of pressure elements is configured for operating on side portions opposite the stack under construction P ( FIG. 11 ). 
         [0047]    The rotating support S further rotates a gripping device which is configured for taking the first electrode of the arrangement of electrodes on the strip  5 . The gripping device can operate, as in the specific case, with a gripping mechanism of the gripper type. The gripping device may comprise a pair of gripping elements  25  operating on side portions opposite the first electrode (i.e. operating on opposite sides of the first electrode with reference to the advancing direction X of the strip  5 ). Each gripping element  25  may comprise, as in the specific case, two active portions  25   a  and  25   b  that operate on front and back end portions (with reference to the advancing direction X of the strip  5 ), of the respective side portion of the first electrode. The gripping elements  25  collaborate together to grasp the first electrode (together with the strip  5  portion below the first electrode) and to rotatingly drive the first electrode (together with the strip  5 ) during formation of the stack (i.e. during the various overturnings). 
         [0048]    As said, the strip  5  that advances carrying the electrodes C and A is transformed in the stack P of electrodes by means of a series of overturnings (in direction F) of the stack under construction P. The stack P is assembled in the most advanced portion of the strip  5 . In  FIGS. 5 and 7  (with greater clarity in  FIG. 8 ) there is illustrated the sequence of the positions (numbered with Roman numerals from i to x) adopted by the first electrode, at the start of assembly of the stack, during overturning thereof by 180°. The first electrode (together with the strip  5 ) is then grasped laterally by the gripping elements  25 , whilst the pressure elements  23  press the strip  5  against the first electrode in such a manner as to ensure the compactness of the electrode-strip assembly. Both the gripping elements  25  and the pressure elements  23  are rotated in the direction F (and are carried by the support S). With R ( FIG. 8 ) there are indicated the various positions adopted in sequence by the median axis of the first electrode during overturning from position i to position x. With T there are indicated the corresponding positions adopted in sequence, during overturning by 180°, by the end of the first electrode around which folding of the separating strip  5  occurs. The positions T correspond, substantially, to the positions adopted by the folding line of the strip  5  during overturning of the first electrode and, substantially, also for the subsequent electrodes, i.e. in the course of each subsequent overturning until the end of assembly of the stack. 
         [0049]    Each successive overturning will comprise a folding (in the same folding direction) of the strip  5  around a respective folding line arranged between the stack P being assembled and the immediately subsequent electrode (i.e. the electrode that will be the lower electrode of the stack at the start of the subsequent overturning). At the end of each overturning in fact the stack being assembled P will be superimposed on the immediately subsequent electrode that will thus be part of the stack being assembled in the subsequent overturning. As said, folding of the strip  5  has a folding direction (shown by arrow F) that is the same for each overturning. It is seen clearly from  FIG. 8  that during overturning the folding line (corresponding to position T) advances in the advancing direction of the strip  5 , remaining substantially in the (horizontal) advancing plane defined by the product (strip  5  bearing the electrodes C and A) which advances, in such a manner as to avoid irregular movements (jolts) of the strip  5  that could modify the correct position of the electrodes C and A. 
         [0050]    The rotating support S that rotates the gripping elements  25  and the pressure elements  23  and  24  can rotate by varying the position of the rotation axis z-z thereof, in particular in such a manner that the folding line (position T) of the strip  5  remains, at each overturning of the stack being formed, substantially in the strip  5  advancing direction X or in the advancing plane of the strip  5  (for example with the aim that the preset position of the electrodes arranged on the moving strip is not lost through irregular movements of the strip). In particular, the rotation axis z-z of the rotating support S will be able to perform a trajectory (orbit or at least partial orbit) having at least one of the trajectory portions with an ascending and descending vertical motion (transverse to the advancing direction X of the strip  5 ) and/or trajectory portions with horizontal motion (parallel to the advancing direction X of the strip) forwards and backwards (where forwards and backwards is defined with reference to the advancing direction X of the strip  5 ). 
         [0051]    As said, during winding (i.e. the various overturnings by 180° of the stack under construction around the subsequent folding lines of the strip  5 ) the first electrode (i.e. the electrode that has been overturned first at the start of formation of the stack) is maintained grasped by the gripping device (comprising in this case the lateral gripping elements  25 ). The gripping elements  25  are provided with the possibility of disengaging from the stack assembled at the end of winding. The disengagement may comprise opening the gripping elements (for example in the case of gripping elements of the gripper type), with a slight movement in order not to damage the stack that has just been assembled in which the gripping elements are located, followed by a removal movement that may comprise, as in the specific case, reciprocal moving away of the two gripping elements  25  in a horizontal direction (in  FIG. 9  there is indicated by a dashed line the position of reciprocal moving away of the two opposite rotating semi-elements that comprise the support S and support the gripping elements  25  and, also, the pressure elements  23  and  24 ). 
         [0052]    In  FIGS. 14 to 16  there is illustrated schematically the operation of the pressure elements  23  and (in these figures the separating strip that advances in the advancing direction X has not been illustrated for the sake of greater clarity). At the start of overturning, one of the pairs of pressure elements (in the illustrated example the pair indicated by  23 ) operates on the front portion (with reference to the advancing direction X) of the stack P being assembled, by pressing from the bottom up. The first pressure elements  23  are commanded to adopt an active locking position (see  FIG. 10  or  12 ) in which they can interact in contact with the stack P being assembled, whilst the second pressure elements  24  are in an inactive non-interference position (see  FIG. 10  or  12 ) in which they do not interfere with the stack and can rotate without interfering with the separating strip. 
         [0053]    In  FIG. 15 , after rotation by a set amount (greater than 90°, the same as, for example, approximately 145° as in the specific example), the first pressure elements  23  start to move towards the inactive non-interference position in which they do not interfere with the stack. In  FIG. 16 , after rotation by a set amount (greater than 90°, equal, for example, to about 172° as in the specific example), the second pressure elements  24  start to move towards the active or locking position in which they can interact in contact with the stack P under construction. After which, after a 180° rotation has terminated, it starts another overturning with the pressure elements  23  and  24  that operate reciprocally. The closing movement (towards locking) of a pressure element may be commanded after the opening movement (towards non interference) of the other pressure element, as in the specific example. The opening and closing movements of the pressure elements  23  and  24  can be driven mechanically, for example by a cam mechanism  26  having a cam guiding profile with a circular base that is coaxial with the rotation axis z-z. 
         [0054]    In  FIGS. 14 to 16  the movement is clearly visible of the (horizontal) rotation axis z-z of the winding device in a (vertical) direction that is perpendicular to the (horizontal) advancing direction X of the separating strip  5 . 
         [0055]    In greater detail, each pressure element  23  or  24  comprises, in the specific example illustrated here, a carriage  27 , an arm  28  and a contact member  29 . The carriage  27  is coupled with the rotating support S and is movable (for example may comprise a slide that is slidable along sliding guides) in a direction that is parallel to the rotation axis z-z of the rotating support (to enable the rotating support to move towards or away from the side of the stack P). The arm  28  is pivoted on the carriage  27  around a rotation pivot (with an axis that is horizontal and transverse to the rotation axis z-z) with the possibility of moving towards or away from a (flat) face of the stack. The contact member  29  is an end element of the arm  28 , configured for contact with the stack P being assembled. The contact member  29  can be coupled with the arm  28  by a rotation pivot. Each gripping element  25  may comprise a gripper carried by a further carriage  30  coupled with the rotating support S (for example a slide that is slidable along sliding guides). The further carriage  30  is movable in a direction that is parallel to the rotation axis z-z of the rotating support S, to enable, at the end of the formation of the stack, the removal of the gripper from the stack by moving away from the side of the stack. 
         [0056]    In  FIG. 19  there is illustrated the stack of electrodes C and A made with the apparatus and the method disclosed above. The various electrodes face one another. The cathodes C and the anodes A are arranged alternately. The dielectric separator comprises a single strip  5  wound around the electrodes, in which the initial end strip (shown with  51 ) of the strip is situated in the centre of the stack (near or interposed between the two most central electrodes inside the stack), and the final end strip (indicated by  52 ) of the strip is located outside the stack. The separating strip  5  is wound, from the initial end to the outside of the stack, always in the same winding direction.