Apparatus for forming a stack of electrodes for use in manifacturing electric energy storage devices

Abstract

The apparatus for forming a stack of electrodes is associated with a machine for manufacturing electrical energy storage devices, of the type comprising a stack of electrodes formed by folding a flexible strip (2) comprising at least one separator element (20), a series of anode elements (21) and a series of cathode elements (22), applied alternately on said separator element (20). The apparatus comprises feed means (10) for advancing said flexible strip (2) along a feed direction (A) on a feed plane and folding means (3) suitable to be operated in a suitable step relationship to perform a series of folds orthogonal to the feed direction on said flexible strip (2) and to deposit the flexible strip (2) thus folded on a stacking plane (4). The apparatus comprises rotatable means (5) capable of being driven in continuous rotation and having distributed peripherally a plurality of devices (55, 56) for collecting and transferring said anode and cathode elements (21, 22) on the flexible strip (2) in the folding step onto the stacking plane (4).

Description

[0001] Description

[0002] APPARATUS FOR FORMING A STACK OF ELECTRODES FOR USE IN MANIFACTURING ELECTRIC ENERGY STORAGE DEVICES

[0003] Technical field

[0004]

[0001] The present invention relates to an apparatus for forming a stack of electrodes for use in a machine for manufacturing electrical energy storage devices, such as electric batteries.

[0005] Prior art

[0006]

[0002] In the field of electrical energy storage devices, it is currently known to use electric batteries consisting of a plurality of electrodes forming alternately an anode and a cathode, arranged in a stack. The electrodes forming the anode and cathode are separated by a separator element. The separator element is made, for example, of polymeric material.

[0007]

[0003] To make the aforementioned electric batteries, a known system provides, for example, for the use of a separator element formed by a single continuous strip, with the anode and cathode elements applied to the opposite faces and alternating between them. In particular, according to a known embodiment, known as Z-folding, the separator strip is folded several times in alternating directions to form individual portions on which the anode and cathode elements are applied alternately.

[0008]

[0004] A machine for manufacturing electric batteries of this type is illustrated, for example, in European patents EP 2 569 816 and EP 2 856 552 and in US patent application 2019 / 0229360.

[0009]

[0005] The known apparatus for forming a stack of electrodes for use in electrical energy storage devices generally has a relatively low production speed.

[0010]

[0006] It is also complained that the known apparatuses are often highly complex, inefficient and expensive to manufacture.

[0011] Disclosure

[0012]

[0007] The task of the present invention is to solve the aforementioned problems by providing an apparatus for optimally forming an electrode stack for use in electrical energy storage devices, such as electric batteries.

[0013]

[0008] Within the scope of this task, a further aim of the invention is to provide an apparatus for forming a stack of electrodes for use in electrical energy storage devices which ensures that a high production speed is achieved.

[0014]

[0009] A further purpose of the invention is to provide an apparatus for forming a stack of electrodes intended for use in electrical energy storage devices, which is simple in design and function, has a reliable mode of operation, is versatile in use and is relatively inexpensive.

[0015]

[0010] The above objectives are achieved, according to the present invention, by the apparatus for forming a stack of electrodes for use in electrical energy storage devices according to claim 1.

[0016]

[0011] In particular, said electrical energy storage devices comprise a stack of electrodes formed by folding a flexible strip comprising at least one separator element, on which a series of anode elements and a series of cathode elements are alternately applied in an ordered sequence.

[0017]

[0012] The apparatus in question comprises feed means for advancing said flexible strip in a feed direction on a feed plane and folding means operable in a suitable stepwise manner to perform a series of folds orthogonal to the feed direction on said flexible strip and to deposit the flexible strip thus folded on a stacking plane.

[0018]

[0013] According to the present invention, the apparatus in question comprises rotatable means capable of being driven in continuous rotation and bearing, distributed peripherally, a plurality of collecting and transfer devices for said anode and cathode elements on the flexible strip during the folding step on the stacking plane.

[0019]

[0014] In particular, the apparatus in question comprises a first rotatable member capable of being rotated in a continuous manner about a first axis of rotation and having a plurality of first gripping members distributed peripherally, each of which is tiltable about an axis parallel to said first axis of rotation; a second rotatable member capable of being rotated in a continuous manner about a second axis of rotation and having a plurality of second gripping members distributed peripherally, each of which is tiltable about an axis parallel to said second axis of rotation; each gripping member of said first rotatable member and of said second rotatable member being configured to pick up and transfer said anode elements and said cathode elements onto said flexible strip, respectively.

[0020]

[0015] The first rotatable member and the second rotatable member are suitably arranged on opposite sides with respect to the flexible strip feed plane.

[0021]

[0016] The first and second axes of rotation of the first and second rotatable members are suitably parallel to each other.

[0022]

[0017] According to one aspect of the invention, said collecting and transferring devices for said anode and cathode elements on the flexible strip are tiltable about a respective tilting axis parallel to the axes of rotation of said rotatable members.

[0023]

[0018] Preferably, said anode and cathode element collecting and transfer devices consist of lever mechanisms having gripping members at their ends for gripping the anode and cathode elements in succession.

[0024]

[0019] Preferably, said lever mechanisms comprise respectively a rocker member mounted tiltable about said tilting axis and having, at its free end, a rotatable body bearing a respective gripping member, which is pivoted about an axis parallel to the tilting axis of the rocker member.

[0025]

[0020] Preferably, said gripping member is articulated to said rotatable body according to an axis parallel to the axes of rotation of said rotatable members.

[0026]

[0021] According to one embodiment of the invention, said folding means comprise a pair of rollers arranged side by side, between which the flexible strip to be folded unfolds, said folding rollers being adapted to be driven in alternating motion above said stacking plane so as to perform said series of folds on the flexible strip and deposit the flexible strip thus folded on the same stacking plane.

[0027]

[0022] In particular, said folding rollers are configured to impose a succession of rotations on said flexible strip with respect to said flexible strip feed plane, in order to perform the accordion folding of the same flexible strip.

[0028]

[0023] Preferably, said folding rollers are arranged with horizontal axes, parallel to each other, orthogonal to the direction of development of the flexible strip to be folded.

[0029]

[0024] According to one embodiment of the invention, said folding rollers are suitably motorized.

[0030]

[0025] According to one embodiment of the invention, said folding rollers are driven in a pendulum motion above the stacking plane.

[0031]

[0026] According to a different embodiment of the invention, said folding means comprise pushing means configured to act from opposite sides on said flexible strip to perform said folding perpendicular to the direction of advance.

[0032]

[0027] In particular, said pushing means are associated respectively with said collecting and transfer devices of the anode and cathode elements.

[0033]

[0028] Preferably, said pushing means consist of cylindrical elements of thin diameter, each fixed to the free end of said gripping members of the collecting and transfer assemblies, with axes horizontally parallel to the axis of rotation of said rotatable members.

[0034]

[0029] According to a further aspect of the invention, the apparatus comprises a feeding device capable of sequentially collecting individual anode and cathode elements and transferring them to said collecting and transfer devices.

[0035]

[0030] Advantageously, said feeding device comprises a distribution wheel, rotated about an axis parallel to the axis of said rotatable members, configured to sequentially pick up and transfer said individual anode and cathode elements.

[0036]

[0031] Advantageously, said feeding device comprises sensor means for checking the correct positioning of said individual anode and cathode elements and means for discharging and removing waste products.

[0037]

[0032] The present invention also relates to a method for forming an electrode stack for use in electrical energy storage devices, such as electric batteries and the like, of the type comprising an electrode stack formed by folding a flexible strip comprising at least one separator element, on which a series of anode elements and a series of cathode elements are applied alternately in an orderly sequence.

[0038]

[0033] The method in question comprises the steps of a. feeding said flexible strip forming said separator element along a feed direction; b. operating, in a suitable step relationship, folding means for performing a series of folds orthogonal to the feed direction on said flexible strip and to deposit the flexible strip thus folded on a stacking plane; c. rotating, in continuous movement, rotatable means, bearing distributed peripherally a plurality of collecting and transfer devices of said anode and cathode elements on the flexible strip in the folding step on said stacking plane; d. progressively depositing the accordion-folded flexible strip on said stacking plane; e. in a suitable step relationship, alternately transfer said anode elements and said cathode elements onto the overlapping portions of said accordion-folded flexible strip.

[0039]

[0034] Preferably, said step of e. alternately transferring said anode elements and said cathode elements onto the overlapping portions of said accordion-folded flexible strip comprises e1. feeding said anode elements and said cathode elements in sequence to a first and a second distribution wheel, respectively, rotated in a suitable step relationship with said rotatable means; e2. checking the correct positioning of said anode and cathode elements on said first and second distribution wheels; e3. removing any waste products from said first and second distribution wheels and sending them to discharge and removal means; e4. alternately collecting said anode and cathode elements from said first and second distribution wheels by said collecting and transfer devices to transfer them in ordered sequence onto said overlapping portions of said accordion-folded flexible strip.

[0040] Brief description of the drawings

[0041]

[0035] The details of the invention will be more evident from the detailed description of a preferred embodiment of the apparatus for forming a stack of electrodes for use in a machine for manufacturing electrical energy storage devices, such as electric batteries and the like, illustrated by way of example in the accompanying drawings, in which:

[0042] Figure 1 shows a schematic side view of the apparatus for forming a stack of electrodes according to the present invention;

[0043] Figures 2 and 3 show, respectively, a schematic side view of a form of the apparatus for forming a stack of electrodes in question, in different operating steps;

[0044] Figures 4 and 5 show, respectively, a schematic side view of a different embodiment of the apparatus in question, in different operating steps.

[0045] Description of embodiments of the invention

[0036] With particular reference to these figures, the apparatus for forming a stack of electrodes for use in a machine for manufacturing electrical energy storage devices, such as electric batteries, is indicated as a whole by 1 .

[0046]

[0037] In particular, these electrical energy storage devices comprise a stack of electrodes formed by folding a flexible strip 2 comprising at least one separator element 20, on which a series of anode elements 21 and a series of cathode elements 22 are alternately applied in an ordered sequence. Said separator element 20 is made, for example, of polymeric material.

[0047]

[0038] In particular, said anode elements 21 and said cathode elements 22 are applied to opposite faces of the separator element 20 and are offset with respect to each other along the flexible strip 2 when the separator element 20 is folded substantially in an accordion fashion.

[0048]

[0039] The apparatus in question comprises feed means 10 for advancing the separator element 20 along a feed plane of the separator element 20 itself. In the case illustrated, this feed plane is arranged substantially vertically. In particular, said feed means 10 cause the separating element 20 to be unwound from a reel, not shown, and cause the same separating element 20 to advance in a downward direction, preferably vertical.

[0049]

[0040] The feed means 10 comprise a pair of counter-rotating rollers 11 , suitably motorized, configured to act on the flexible strip 2 from opposite sides with respect to the feed plane.

[0050]

[0041] The apparatus comprises folding means 3 designed to be operated in a suitable stepwise manner to perform a series of folds orthogonal to the direction of advance on the flexible strip 2 and to deposit the flexible strip 2 thus folded on a stacking plane 4. As specified below, the stacking plane 4 is movable vertically step-by-step to follow the formation of the stack of electrodes.

[0051]

[0042] According to a first embodiment of the invention, the folding means 3 comprise a pair of rollers 30 arranged side by side between which the flexible strip 2 to be folded is fed, downstream of the feeding means 10. More specifically, the rollers 30 are arranged with horizontal axes, parallel to each other, perpendicular to the direction of development of the flexible strip 2 to be folded.

[0052]

[0043] The folding rollers 30 are configured to be driven in an alternating motion above the stacking plane 4 so as to perform said series of folds on the flexible strip 2 and deposit the flexible strip 2 thus folded on the same stacking plane 4. Suitable stopping means 40 can be activated to hold the individual folded sections of the flexible strip 2 on the stacking plane 4.

[0053]

[0044] According to a particular embodiment, illustrated in Figures 2 and 3, the folding rollers 30 are driven with a pendular motion above the stacking plane 4. For this purpose, the folding rollers 30 are freely rotatable at the free end of a tilting arm 31 on a vertical plane perpendicular to the folding rollers 30 themselves.

[0054]

[0045] The tilting arm 31 is suitably articulated at the top to an angularly rotatable lever 32 to follow the pendular movement of the arm 31. The lever 32 also carries a further pair of rollers 33 for guiding the unwinding flexible strip 2.

[0055]

[0046] The apparatus comprises rotatable means 5 configured to be driven in continuous rotation and bearing, distributed peripherally, a plurality of devices 55, 56 for collecting and transferring the said anode and cathode elements 21 , 22 on the flexible strip 2 during the folding step on the stacking plane 4.

[0056]

[0047] The rotatable means 5 comprise a first rotatable member 51 capable of being driven in rotation with continuous movement according to a first axis of rotation 53 and a second rotatable member 52 capable of being driven in rotation with continuous movement according to a second axis of rotation 54, parallel to said first axis of rotation 53 of the first rotatable member 51. The axes of rotation 53, 54 of the rotatable members 51 , 52 are suitably defined by the respective drive shafts arranged coplanar on a horizontal plane orthogonal to the feed plane of the flexible strip 2. The drive shafts are driven in rotation continuously by appropriate drive members, which are known per se and therefore not shown.

[0057]

[0048] In particular, the first rotatable member 51 and the second rotatable member 52 are driven in rotation in opposite directions, with equal peripheral speed, from opposite sides with respect to the vertical plane of feed of the flexible strip 2.

[0058]

[0049] The first rotatable member 51 and the second rotatable member 52 are constructed in a similar manner from a structural and functional point of view. In particular, the first rotatable member 51 and the second rotatable member 52 are similarly made up of a pair of drums of equal dimensions, suitably spaced apart from each other, mounted on the drive shaft that defines the respective axis of rotation 53, 54.

[0059]

[0050] The collecting and transfer devices 55, 56 of the anode and cathode elements 21 , 22, distributed peripherally on the rotatable members 51 , 52, are tiltable about a respective tilting axis 550, 560 parallel to the axes of rotation 53, 54 of the rotatable members 51 , 52. In the case illustrated, there are three collecting and transfer assemblies 55, 56 for each of the rotatable members 51 , 52, but it is obviously possible to provide for a different number, in particular one or more.

[0060]

[0051] The collecting and transfer devices 55, 56 consist of lever mechanisms having gripping members 551 , 561 at their ends, which are configured to grasp the anode and cathode elements 21 , 22 in succession. These lever mechanisms comprise, respectively, a rocker member 552, 562 mounted tiltable about said tilt axis 550, 560 and having, at its free end, a pivotable body 554, 564 parallel to the tilt axis 550, 560 of the rocker member 552, 562, bearing a respective gripping member 551 , 561. The gripping member 551 , 561 is articulated to the rotatable body 554, 564 according to an axis 555, 565 which is also parallel to the axes of rotation 53, 54 of the rotatable members 51 , 52 respectively.

[0061]

[0052] Essentially, the gripping member 551 , 561 of each of the collecting and transfer assemblies 55, 56 has three degrees of freedom with respect to the drum of the rotatable member 51 , 52, defined by rotation around the respective axes 550, 560 of the rocker member 552, 562, the axis 553, 563 of the rotatable body 554, 564 and the axis 555, 565 of the gripping member 551 , 561 itself. The movement of the collecting and transfer devices 55, 56 bearing the gripping members 551 , 561 , during the continuous rotation of the rotatable members 51 , 52, is preferably effected by means of suitable cams, not shown.

[0062]

[0053] The anode elements 21 and the cathode elements 22 are fed to the collecting and transfer assemblies 55, 56 bearing the gripping members 551 , 561 by means of a respective feed device 71 , 72 comprising a respective distribution wheel 710, 720, rotated about an axis 711 , 721 parallel to the axis 53, 54 of the rotatable members 51 , 52. The distribution wheel 710, 720 is configured to pick up the individual anode and cathode elements 21 , 22 in sequence and transfer them to the respective gripping members 551 , 561 .

[0063]

[0054] The anode elements 21 and cathode elements 22 are obtained respectively from a strip material 210, 220 fed by an electrically driven unwinding member 712, 722. Appropriate cutting means 713, 723 sequentially cut the individual anode and cathode elements 21 , 22 from the strip material 210, 220 to be supplied to the distribution wheel 710, 720. Preferably, the feed device 71 , 72 is equipped with a photocell sensor 714, 724 to control the position of the anode and cathode elements 21 , 22. If irregularities are detected in the positioning of the anode and cathode elements 21 , 22 or if one of these anode 21 and cathode 22 elements is defective, this element is rejected and deposited in a respective gathering container 716, 726 by means of a respective conveyor 715, 725.

[0064]

[0055] The operation of the apparatus for forming a stack of electrodes in a machine for manufacturing electrical energy storage devices, such as electric batteries and the like, is easily understood from the above description.

[0065]

[0056] The flexible strip 2 intended to form the separator element 20 of the stack of electrodes is fed continuously along the direction of advance on the vertical unwinding plane, arranged in a central position between the first rotatable member 51 and the second rotatable member 52. In particular, the flexible strip 2 at the outlet of the feeding means 10 is guided by the pair of rollers 33 to engage the rollers 30 driven with a pendular motion above the stacking plane 4. This pendular motion transmitted to the flexible strip 2 causes a series of folds to form on the flexible strip 2, perpendicular to the direction of travel. The formation of these perpendicular folds causes the newly folded portion of the flexible strip 2 to rest on the stack of electrodes forming above the stacking plane 4.

[0057] In a suitable step relationship, when the folded portion of the flexible strip 2 is placed on the stack of electrodes being formed, in practice on the stacking plane 4, a gripping member 551 , 561 carried by a relative collecting and transfer device 55, 56, through the combined movement imposed by the lever mechanism, deposits the electrode element 21 , 22 previously picked up on said folded portion of the strip (see in particular fig. 2).

[0066]

[0058] The electrode is held on the work plane, while the gripping member 551 , 561 is lifted and rotated to a position where it does not interfere with the folding rollers 30 that are folding a new portion of the strip (see fig. 3). This new portion of the strip overlaps the electrode previously deposited on the stack being formed.

[0067]

[0059] It should be noted that at each electrode addition cycle, the stacking plane 4 is lowered by a predetermined step height in order to maintain the same stacking plane 4 at the same working height.

[0068]

[0060] At the same time, the rotation of the opposite rotatable member 51 , 52 prepares a relative collecting and transfer device 55, 56 for the deposition of a subsequent electrode 21 , 22 on the stack being formed (see again fig. 3).

[0069]

[0061] When the stack of electrodes has been completed with the required number of electrodes, appropriate cutting means, not shown as they are known per se, arranged upstream of the feed means 10, cut the flexible strip 2 to size. Appropriate unloading means, not shown, then remove the stack of electrodes formed towards the further manufacturing steps.

[0070]

[0062] According to a different embodiment of the invention, illustrated in Figures 4 and 5, the means for folding the flexible strip 2 forming the separator element 20 comprise pushing means 35, 36 configured to act on opposite sides of said flexible strip 2 to perform the required folds perpendicular to the direction of advance.

[0071]

[0063] Advantageously, said pushing means 35, 36 are respectively associated with said collecting and transfer devices 55, 56 of the anode and cathode elements 21 , 22. In particular, said pushing means 35, 36 consist of cylindrical elements each fixed to the free end of the gripping members 61 of the picking and transfer devices 6, with axes horizontally parallel to the axis of rotation 53, 54 of the rotatable members 51 , 52. Preferably, said cylindrical elements have a diameter that is small compared to the overall dimensions of the rotatable members 51 , 52.

[0072]

[0064] In use, the rotary-translational movement of the collecting and transfer device 55, 56 during the transfer of an electrode onto the stack being formed causes the respective pushing member 35, 36 integral with the end of the gripping member 551 , 561 to engage on one side of the flexible strip 2. The strip 2 thus extends over the stack being formed, where it is suitably retained (fig. 4).

[0073]

[0065] As in the solution illustrated above, the gripping member 551 , 561 then lifts and rotates to a position where it does not interfere with the stacking area. The flexible strip 2 is engaged by the respective pushing member 35, 36 located on the opposite side and integral with the end of the gripping member 551 , 561 which is bringing a new electrode 21 , 22 to the stacking area (fig. 5).

[0074]

[0066] This solution has the advantage of not requiring the presence of folding means such as the tiltable rollers described above, which require specific drive means. This simplifies the structure of the apparatus and speeds up the strip folding step.

[0075]

[0067] The apparatus described therefore achieves the purpose of optimally forming a stack of electrodes intended for the manufacture of electrical energy storage devices, such as electric batteries and the like, consisting of a stack of electrodes. The stack is formed by accordion folding a flexible strip comprising at least one separator element on which a series of anode elements and a series of cathode elements are applied alternately in an ordered sequence.

[0076]

[0068] In particular, the apparatus for forming a stack of electrodes for the manufacture of electrical energy storage devices according to the present invention allows a high production speed to be ensured.

[0077]

[0069] This is made possible by the inventive idea of feeding the anode and cathode elements to be applied to the flexible strip acting as a separator by means of folding devices carried by rotatable members driven in continuous rotation, in a suitable phase relationship with the accordion folding of the flexible strip itself.

[0078]

[0070] Essentially, according to the solution of the present invention, there is no downtime during the step of transferring the electrodes onto the separator element. This naturally results in higher operating speed and, consequently, a significant increase in machine productivity.

[0079]

[0071] The apparatus described by way of example is susceptible to numerous modifications and variations depending on different requirements.

[0080]

[0072] In the practical implementation of the invention, the materials used, as well as the shape and dimensions, may be any depending on the requirements.

[0081]

[0073] Where the technical features mentioned in each claim are followed by reference signs, these reference signs have been included for the sole purpose of increasing the understanding of the claims and consequently have no limiting effect on the scope of each element identified by way of example by these reference signs.

Claims

Claims1. An apparatus for forming a stack of electrodes formed by folding a flexible strip (2) comprising at least one separator element (20), a series of anode elements (21 ) and a series of cathode elements (22), said anode elements (21) and said cathode elements (22) being applied alternately, in ordered sequence, on said separator element (20), said apparatus comprising:- a stacking plane (4);- feed means (10) suitable for advancing said flexible strip (2) along a feed direction;- folding means (3) configured to be operated in a suitable step relationship to perform a series of folding lines orthogonal to the direction of advance on said flexible strip (2) while it is deposited on said stacking plane (4);- a first rotatable member (51 ) configured to be rotated in a continuous movement about a first axis of rotation (53); and a second rotatable member (52) configured to be rotated in a continuous movement about a second axis of rotation (54); characterized in that said first rotatable member (51 ) carries a plurality of first collecting and transfer devices (55), distributed peripherally, tiltable respectively according to a respective first tilting axis (550), and in that said second (52) rotatable member carries a plurality of second collecting and transfer devices (56), distributed peripherally, tiltable respectively according to a respective second tilting axis (560); each of said first and second collecting and transferring devices (55, 56) being configured to be actuated so as to collect and transfer directly onto said flexible strip (2) at said stacking plane (4) said anode elements (21) and said cathode elements (22), respectively.

2. The apparatus of claim 1 , wherein said first rotatable member (51) and said second rotatable member (52) are arranged on opposite sides with respect to a feed plane parallel to said direction of advance of the flexible strip (2).

3. The apparatus of claim 1 or 2, wherein the first and second axes of rotation (53, 54) of the first and second rotatable members (51 , 52) are parallel to each other.

4. The apparatus of any one of the preceding claims, wherein the first (550) and second (560) tilting axes are parallel to the rotation axes (53, 54) of the first (53) and second (54) rotation axes, respectively.

5. The apparatus of any one of the preceding claims, wherein the first (55) and second (56) collecting and transfer devices consist of respective lever mechanisms having respective gripping members (551 , 561) capable of gripping in succession the anode and cathode elements (21 , 22) respectively.

6. The apparatus of any one of the preceding claims, wherein the folding means (3) comprise a pair of rollers (30) arranged side by side, between which the flexible strip to befolded (2) unwinds, said folding rollers (30) being adapted to be driven in reciprocating motion along a linear path above the stacking plane (4) so as to fold the flexible strip (2) and deposit the folded flexible strip (2) on the same stacking plane (4).

7. The apparatus of claim 6, wherein said folding rollers (30) are driven along a path adapted to impose on said flexible strip (2) a succession of rotations with respect to said flexible strip feed plane, in order to perform the accordion folding of the same flexible strip (2).

8. The apparatus of any one of claims 1 to 5, wherein the folding means (3) comprise pushing means (35, 36) configured to act from opposite sides on the flexible strip (2) to perform said folds perpendicular to the direction of advance.

9. The apparatus of claim 8, wherein said pushing means (35, 36) are associated, respectively, with said first (55) and second (56) collecting and transfer devices.

10. The apparatus of claim 9, when dependent on claim 5, wherein said pushing means (35, 36) are positioned at a respective free end of the respective gripping member (551 , 561 ).

11. The apparatus of any one of the preceding claims, wherein it further comprises stop means (40) configured to be actuated to retain the individual folded sections of the flexible strip (2) on the stacking plane (4).

12. The apparatus of any one of the preceding claims, wherein it further comprises a first and a second feed device (71 , 72) for sequentially collecting individual anode and cathode elements (21 , 22) and transferring them to said respective first (55) and second (56) collecting and transferring devices.

13. The apparatus of claim 12, wherein the first (71 ) and second (72) feed devices comprise a respective distribution wheel (710, 720), rotatable about a respective axis (711 , 721) parallel to the first and second axis of rotation (53, 54), respectively, and configured to sequentially pick up and transfer said respective individual anode and cathode elements (21 , 22).

14. The apparatus of claim 12 or 13, wherein said first (71 ) and second (72) feed devices comprise respective sensor means (714, 724) for checking the correct positioning of said respective individual anode and cathode elements (21 , 22) and respective discharge means (715, 725) and removal means (716, 726) for the incorrectly positioned elements.

15. A method for forming a stack of electrodes formed by folding a flexible strip (2) comprising at least one separator element (20), a series of anode elements (21) and a series of cathode elements (22), said anode elements (21) and said cathode elements (22) being applied alternately, in ordered sequence, on said separator element (20), said method comprising the steps of a. feeding said flexible strip (2) forming said separator element (20) along a feed direction;b. operating, in a suitable phase relationship, folding means (3) to perform a series of folds orthogonal to the direction of advance on said flexible strip (2) and to deposit the flexible strip thus folded on a stacking plane (4); c. rotating a first (51) and a second (52) rotatable member in continuous movement to transport said anode elements (21 ) and said cathode elements (22), respectively; d. progressively depositing the accordion-folded flexible strip (2) on said stacking plane (4); characterized in that the first (51) rotatable member has a plurality of first collecting and transferring devices (55), and the second (52) rotatable member has a plurality of second collecting and transferring devices (56), and in that during said step c. said anode elements (21) and said cathode elements (22) are collected and transferred directly onto said flexible strip (2) at said stacking plane (4) respectively by means of said first (55) and second (56) collecting and transfer devices, so as to transfer, in a suitable step relationship, alternately said anode elements (21 ) and said cathode elements (22) onto the overlapping portions of said accordion-folded flexible strip (2).

16. The method of claim 15, wherein it further comprises the steps of: e1. feeding said anode elements (21) and said cathode elements (22) in sequence to a first and a second distribution wheel (710, 720), rotated in a suitable step relationship; e2. checking the correct positioning of said anode and cathode elements (21 , 22) on said first and second distribution wheels (710, 720); e3. removing any waste products from said first and second distribution wheels (710, 720); e4. alternately collecting said anode and cathode elements (21 , 22) from the respective first (710) and second (720) distribution wheels by means of the respective collecting and transfer device (55, 56) to transfer them in ordered sequence onto said overlapping portions of said accordion-folded flexible strip (2).

17. The method of claim 15 or 16, wherein it further comprises a step f. of cutting the flexible strip (2) once the stack has been completed on the stacking plane (4) and a step g. of removing the completed stack from the stacking plane to start again with the formation of a new stack.

18. The method of any one of claims 15 to 17, wherein said folding means (3) comprise pushing means (35, 36) positioned on the collecting and transfer devices (55, 56) of the respective first (51) and second (52) rotatable members, wherein said step b. of actuating said folding means (3) consists in alternately engaging the flexible strip (2) with the pushing means (35, 36) integral with the collecting and transfer equipment (55, 56) of the first (51) and second (52) rotatable members, so as to fold said strip (2) in an accordionmanner during step c. of actuating, while the transfer is taking place, the anode (21 ) and cathode (22) elements on the strip (2).

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