Housing for electrochemical reactor of redox flow battery, electrochemical reactor of redox flow battery, electrochemical reactor frame, redox flow battery

Abstract

Housing for a redox-flow battery reactor comprising a body, the body being made of at least two parts constituting a first part (2) and a second part (3) having a circular cross- sectional shape, which are detachably connected to each other by known means, preferably by means of at least one protrusion (8) or recess (9) formed on the first part, and correspondingly, at least one recess (9) formed on the second part and shaped to match the protrusion of the first part, or at least one protrusion (8) formed on the second part and shaped to match the recess (9) of the first part. An external thread (7) is formed on the outer surface of the first part (3), and furthermore, the housing comprises a tightening- sealing clamp (1) which tightly connects both parts of the housing from the outside by compression, preferably in the form of a tightening-sealing ring (1), such that the tightening-sealing clamp (1) has an internal thread (6) formed on its inner part, the internal thread (6) being shaped to match the thread (7) formed on the first part (3) of the housing in a manner enabling the closing of the body parts by twisting.

Description

[0001] Housing for electrochemical reactor of redox flow battery, electrochemical reactor of redox flow battery, electrochemical reactor frame, redox flow battery

[0002] The invention refers to housing - casing, enclosure for a reactor of redox flow battery, the electrochemical reactor of a redox flow battery, with a stacked arrangement - layered - of its main components, a membrane frame in housing, as well as redox flow battery with electrochemical reactor and membrane frame within - in its housing. The invention provides durable, flexible and effective means of electrical energy storage, featuring independent power to capacity regulation.

[0003] Redox flow batteries and its electrochemical reactor constitute one of the high capacity battery types. Said batteries comprise of an electrochemical reactor, positive electrolyte reservoir for storing the positive electrolyte intended to be transported to the reactor, negative electrolyte reservoir for storing the negative electrolyte intended to be transported to the reactor, and piping (fluid lines), that is connected to the cell of the battery and the reservoirs of the positive and negative electrolyte, configured for circulating the positive and negative electrolyte.

[0004] In the simplest embodiment, as described by Yu Zhao et al. in Chem. Soc. Rev., 2015,44, 7968-7996, one pair of electrodes of high surface area in contact with the electrolyte is utilized, made for example from carbon felt. Ion-conducting membrane separates the electrode compartments, preventing any direct contact between the electrodes as well as physical mixing of the solutions that wash the positive and negative electrode. An electric current is supplied to and collected from two collectors, usually in the form of plates made of conducting materials, such as copper, which are not in a direct contact with electrodes and electrolytes. The electrical contact between a collector and an electrode is provided by a chemically resistant and electrically conductive bipolar plate, typically made of a carbon-poly mer composite. During the battery operation the electrolyte continuously flow through the electrode compartments. The electrolyte is transported between a reservoir and a reactor by suitable tubing, and in the reactor itself the liquid electrolyte is supplied to the electrode compartments by a system of canals in a corresponding frame that ensures an uniform inflow and outflow of the fluid. Every electrode has its own electrolyte distribution frame.

[0005] From U. S. Patent No. 6,475,661 Bl and European Patent Application No. EP3716383A1, a redox flow battery is known that comprises three main components: an electrochemical reactor, electrolyte reservoirs, and pumps providing controlled electrolyte flow between a reservoir and a reactor. During cell operation, the reactor converts electrical energy into chemical energy and vice-versa due to chemical reactions occurring at the electrodes involving electrons. A reactor comprises a single pair of electrodes or a multiple thereof. EP3716383B describes a redox flow battery comprising the following components: battery cell- designated as an electrochemical reactor; reservoir, in which an electrolyte is stored that is further transported to the battery cell; a tube connected to the battery cell and the reservoir configured to allow electrolyte circulation; a container housing together the battery cell, the reservoir and the piping; a partition wall positioned inside the container, in order to prevent electrolyte leakage outside the container, wherein the height of said partition wall is equal to or greater than the height of the liquid level at the time a predetermined amount of electrolyte leaks into the container due to piping damage, and wherein the predetermined amount corresponds to the sum of the volume of the battery cell and the volume of the piping.

[0006] Redox flow battery according to the disclosed invention comprises a battery cell, a reservoir for storing an electrolyte to be transported to the cell, tubing connected to the battery cell and the reservoir, configured to allow electrolyte circulation, a container housing the battery cell, the reservoir, and the tubing, as well as a partition wall positioned within the container to prevent electrolyte leakage outside the container. The height of the partition wall is equal to or greater than the height of the liquid level at the time a predetermined amount of electrolyte leaks into the container due to piping damage, and wherein the predetermined amount corresponds to the sum of the volume of the battery cell and the volume of the piping.

[0007] U. S. Patent No. 6,475,661 Bl describes the operation and construction of a redox flow battery comprising a plurality of cells connected in series, defined by a stacked and repeating arrangement of a conductive inter-cell separator having a substantially bipolar function, a positive electrode, an ion exchange membrane, a negative electrode, and another conductive inter-cell separator. Each electrode is disposed in a flow compartment, and the battery implements the flow of the positive half-cell electrolyte, containing the reducible and oxidizable ions of a first redox couple, through the compartments containing said positive electrodes; and implements the flow of the negative half-cell electrolyte, containing the reducible and oxidizable ions of a second redox couple, through the compartments containing said negative electrodes, wherein each of the negative half-cell electrolyte and the positive half-cell electrolyte flows separately through the corresponding compartments of said stack, serially through the plurality of cells by introducing each electrolyte at a given state of charge into the corresponding compartment of the first cell at one end of the stack, and recovering each electrolyte from the corresponding compartment of the last cell of the stack, at the opposite end thereof, at a modified state of charge dependent on the magnitude and direction of the electrical current flowing through the battery during the flow of a predetermined volume of the electrolyte.

[0008] A redox flow battery therefore comprises a plurality of flat components which must be precisely fitted to ensure complete sealing of the reactor. For this purpose seals are used / are employed between individual components and their number and type depend on the material properties of the individual components and the internal pressure of the system. The compression of all the mentioned before elements, parts (current collectors, bipolar plates, electrodes, flow frames, membrane, and the seals) is achieved by the compression between two rigid plates utilizing a plurality of bolts, which, however, does not guarantee tightness - sealing and durability in the known solutions. Sealing - tightness and mechanical durability of the construction would be ensured by uniform distribution of contact stress. In the known solutions it can be only partially achieved with a dedicated stack assembly technique - twisting the reactor, unfortunately based on multi-stage, sequential tightening of the bolts with the use of specified force set on a torque wrench. Therefore, in known solutions a sealed - strongly tight and mechanically durable housing of the electrochemical reactor of the redox flow cell is not achieved.

[0009] A further disadvantage, however, of known solutions concerning the connection of components - so in creating tight, sealed housing that has been not used so far, for redox flow battery reactor is that the assembly and disassembly of the cell is time-consuming and labor-intensive and requires specific expertise for this operation. Moreover, uniform contact stress distribution in such an assembled reactor can never be guaranteed, and the utilized bolts are prone to gradual loosening during operation, which further degrades the uniformity of the compression across the reactor. The use of a plurality of bolts requires the use of a massive housing with significantly larger surface area than the utilized electrodes, causing its size and weight are substantially greater compared to the cell of the proposed construction that utilize electrodes of the same size. An additional drawback of the known construction is the requirements of employing multiple seals between reactor components. Furthermore, ensuring stable securement of the membrane of the electrochemical reactor is vital, that set goal of the invention.

[0010] Consequently, there is requirements - an ongoing search for provision of solutions in the fields of tightens - sealing, mechanical durability, and uniform - regular, even -contact stress distribution in the constructions of redox flow battery housings and its electrochemical reactors. The reduction in the size of cell housings, redox-flow reactors and redox-flow batteries is also essential. An ensuring a stable securement of the membrane of reactor. According to the invention, these goals have been especially achieved by means of the provision of not used before housing for the redox flow battery, that is a two-part housing construction with a ring - sealing-tightening clamp - ensuring durable, thought coupling - connecting - of the battery reactor. Furthermore a stable securement, coupling, fitting - of the membrane between the housing parts coupled by said clamp — ring is provided by positioning it within a frame comprising two self-locking rings. Reactor membrane frames have not been known in the prior art.

[0011] The scope of the invention is defined in the patent claims.

[0012] Detailed description of the redox flow reactor

[0013] The designations, terms of “lower” and “upper” part are conventional and are not restrictive, limited to the invention’s application - they are thus to be understood as part one and second part so two disposed arbitrarily, order parts (top-bottom-up, left-right). The terms housing body - casing - for the whole reactor, and reactor body - housing, are used in the description. The electrochemical reactor of the redox flow battery is understood to be two parts of the housing coupled by the sealing-tightening clamp, otherwise referred to as the ring, while the remaining components of the battery reactor are located - disposed between the parts of the housing - inside the housing. In the description a term self-locking ring is also used in the context of the element of reactor frame. Body is also known as a corps.

[0014] The electrochemical reactor of the redox flow battery has a stacked arrangement of the main components, wherein within its body (reactor housing) the elements -components of the respective half-cells are separated by a membrane permeable by the selected ions and impermeable to the active species, and each half-cell comprises a current collector, preferably a flat, thin copper sheet, which is in direct electrical contact with a bipolar plate, for example made of carbon-polymer composite, and at least one electrode, preferably made of carbon felt. The reactor housing body comprises the upper part of the body adjacent to the clamping ring with an internal thread. Furthermore, the reactor housing body comprises a lower body part having a thread directly on its outer surface that mates with the internally threaded section, and wherein this lower body part is detachably connected to the ring by means of a direct thread. The reactor body also comprises an inner body part having a recess in which at least one electrode is mounted, wherein each electrode contacts a bipolar plate on one side, which is in electrical contact with a current collector supplying or collecting current from the electrodes, and wherein the current collector is covered by an insulating mounting plate. On the other side of the electrode, there is a membrane separating the half-cell components. The inner part of the reactor body includes flow channels and ports supplying and exhausting the electrolyte that bathes the electrodes.

[0015] Redox flow battery comprises a reservoir with at least one electrolyte and means of electrolyte transport, reservoir with positive electrolyte for storing the positive electrolyte that is transported to the battery cell, reservoir with negative electrolyte for storing the negative electrolyte that is transported to the battery cell, housing, membrane frame, and the previously described reactor comprising the membrane within the frame.

[0016] The redox flow battery reactor housing - housing for reactor, according to the invention offers the following advantages. The provided housing also known as a casing provides adequate compression, sealing - tightness, and uniform - regular - contact stress distribution, while being an easily and quickly assembled solution that does not require specific expertise, and that allows for a significant reduction in the size and weight of the battery reactor due to the housing construction according to the invention.

[0017] The reactor with the provided during the study housing according to the invention, especially due to the use of the threaded connection and the ring, allows for its rapid and easy assembly or disassembly by means of the direct thread, wherein the inner surface of the ring and the outer surface of one of the body parts are threaded. The membrane is placed between self-locking rings that form the frame facilitating easy assembly or replacement with the same or different type. System is suitable for membranes of varying thickness, does not require additional seals, and enables quick, simple and precise positioning of the membrane within the reactor. Precise relative positioning of the cell components during the assembly of the redox flow battery electrochemical reactor is ensured by two parts of the reactor housing body (one and two) coupled via the housing ring, that is assembly of the parts of the housing can be ensured by utilizing at least one protrusion or recess located on part one with a matching recess or protrusion respectively located on part two in a form of parallel key connection or a spline connection if there is more than one protrusion / recess. This can be implemented via a system of one or more positioning pins and corresponding sockets on the adjacent surfaces. The described system of the reactor assembly via the developed reactor housing as well as utilization of the selflocking membrane frame, according to the invention, allows for exceptionally rapid reactor opening, membrane replacement and reactor reassembly of the redox flow battery. The use of the two-part reactor housing, coupled by means of protrusions (e.g., positioning pins) and recesses, as well as the use of the ring, ensure precise and proper relative positioning of the reactor components, guaranteeing its correct operation. The connection of the housing parts provides stable coupling of the reactor components and operates on the principle of twisting. The membrane frame according to the invention provides the following advantages: (i) quick membrane replacement; (ii) precise membrane positioning; (iii) absolute certainty of correct membrane placement during reactor assembly.

[0018] The subject matter of the invention is shown in an exemplary embodiment - examples and in the drawing, wherein fig. 1 shows the housing and the redox flow battery electrochemical reactor with the threaded sealing ring – in a disassembled view. fig. 2 shows a cross-section of the housing and the redox flow battery electrochemical reactor with the threaded sealing ring, with the disassembled subcomponents considered, together with a cross-section of the redox flow battery reactor with the threaded sealing ring in an assembled view. fig. 3 shows the membrane frame prior to its assembly within the reactor and the housing. The electrochemical reactor of the redox-flow battery, in an exemplary embodiment, as shown in Fig. 1, is described within the example below:

[0019] Example 1 the general construction

[0020] Construction of the reactor housing:

[0021] As shown in Figs. 1 and 2, the reactor housing is a body composed of two circular parts: a first part 2 and a second part 3, each having a corresponding recess and a system of channels connecting the recess to inlet and outlet ports located on the outer surface of the housing part. On the outer surface of both housing parts, two ports 10 for electrolyte transport are provided in the assembled view. The housing also comprises the clamping ring 1, which connects both body parts, i.e., the sealing-clamping clamp 1. The clamping ring 1 has a thread on its inner wall that mates with the thread on the outer wall of one of the body parts. The ring is mounted onto the body from the side of the unthreaded body part as a clamp for the two reactor housing parts, the first part 2 and the second part 3. The coupling of the two reactor housing parts is achieved by means of four protrusions 8 (pins) on the first part 2, and four corresponding recesses 9 (sockets) on the second part 3, which are shaped to match the protrusions 8. In this example, a system with positioning pins 8 (protrusions) and their sockets 9 (recesses) is utilized. The dimensions of the first part 2 in this example are 63 mm in diameter and 10 mm in height; the second part 3 is 68 mm in diameter and 17 mm in height; and the ring is 88 mm in diameter and 15 mm in height. Components of the reactor body comprises- inner part of the body 15 is made of a transparent material: Anycubic ABS-Like Pro 2 Clear resin, and the housing parts 1, 2, and 3 are made of opaque material: PET-G Dark Gray.

[0022] Construction of the redox flow battery electrochemical reactor with the reactor housing.

[0023] Redox flow battery electrochemical reactor possesses a stacked arrangement of its main components. In both halves of the reactor body, a current collector 12 is disposed in a form of flat copper sheet with dimensions 25 x 25 mm and thickness of 0.2 mm. Collector 12 is in direct contact with a bipolar plate 13 made of carbon-polymer composite with matching dimensions and thickness of 0.6 mm, which is further in contact with an electrode, preferably made of carbon felt, of dimensions 24 x 25 mm and thickness of 5 mm. In the whole reactor at least one pair of such electrodes is disposed and separated by a membrane 5, which is selectively ion-permeable, and impermeable to the active species.

[0024] Construction of the reactor membrane frame

[0025] The membrane 5 is disposed within a frame 4 which comprises two self-locking rings 4, with a set of positioning pins 8 and corresponding receptacles 9 (four of each in this example). The membrane used is a cation-exchange polymer membrane—a sulfonated tetrafluoroethylene copolymer having conductive properties, known as Nafion 117. As the electrolyte, a commercially available acidic solution of vanadium sulfate at the +3 and +4 oxidation states is used. The frame 4 has overall dimensions of 56 x 56 mm, a wall width of 7 mm, and a thickness of 3 mm.

[0026] The ring 1, body parts 2, 3 and 15, inflow and outflow ports 10 and membrane frame 4 were made with 3D printing technology.

[0027] Construction of redox flow battery

[0028] The reactor, described in the section above, is connected via tubing to electrolyte reservoirs containing electrochemically active species. Peristaltic pump ensures continuous circulation of electrolyte between the reservoirs and the electrodes. Redox flow battery comprises reservoir with at least one electrolyte and means of electrolyte transport, positive electrolyte reservoir for storing the positive electrolyte intended to be transported to the reactor, negative electrolyte reservoir for storing the negative electrolyte intended to be transported to the reactor, reactor housing and the reactor which contains the membrane inside the previously described self-locking membrane frame (achieved by key way connection) as shown in fig. 3. The achieved effects: The reactor constructed according to the present description, when incorporated into a functioning flow battery, is characterized by a significantly smaller size, namely 80 mm in diameter and 43 mm in height, as well as a weight orders of magnitude lower than commercially available reactors of this type. Additionally, its assembly is much quicker and simpler, which ensures uniform contact stress distribution, a feature essential for ensuring sealing integrity and greater mechanical durability of the reactor. The entire solution is lightweight, and the housing is manufactured from resins suitable for 3D printing.

[0029] Example 2

[0030] The housing, the reactor, and the membrane frame are made similarity to those in example 1. Redox flow battery electrochemical reactor comprises a stacked arrangement of its main components. The components of the half-cells are disposed within the reactor body and are separated by a membrane (5), which is selectively ion-conductive and impermeable to the active species. Each of the half-cells comprises a current collector 12 in the form of flat and thin copper sheet. Collector 12 is in direct contact with a bipolar plate 13 made of carbon-polymer composite. At least one pair of electrodes, made of carbon felt, is present within the reactor.

[0031] The reactor body comprises an upper body part 2 adjacent to the tightening ring 1, which has a threaded internally threaded side 6. The body also includes the lower body part 3 with an external thread directly on its surface 7, matching the internal threaded side 6. The lower body part 3 is detachably connected to the ring 1 via the direct threaded connection 17. The body also comprises an inner body part 15, in the recess of which at least one pair of electrodes 11 is disposed. Each electrode 11 contacts the bipolar plate 13 on one side, which in turn contacts the current collector 12, responsible for supplying or collecting current to the electrodes 11. The current collector 12 is covered by an insulating mounting plate 14, while the membrane 5, separating the half-cell components, is located on the opposite side of the electrode 11. The inner part 15 includes a set of channels 16 and ports 10 for supplying and collecting electrolyte that flows over the electrodes 11. The membrane 5 is mounted inside frame 4, which is made of two self-locking rings, spawning a set of miniature positioning pins and their sockets. Membrane is a cation-exchange polymer membrane—a sulfonated tetrafluoroethylene copolymer having conductive properties, known as Nafion 117.

[0032] Example 3

[0033] Construction of the housing:

[0034] Using 3D printing technology, the ring 1, body parts 2, 3, and 15, the inlet / outlet ports 10, and the membrane frame 4 (as previously described) were manufactured. The current collectors 12 were manufactured from a copper sheet having a thickness of 0.2 mm, while the bipolar plates were prepared from a polymer-carbon composite with a thickness of 0.6 mm. As electrodes, 5 mm thick thermally activated carbon felt was utilized, and a cation-exchange polymer membrane (Nafion 117) was utilized as the membrane, mounted within the self-locking frame 4.

[0035] In the constructed flow battery, the individual components are arranged in layers, as shown in Fig. 2. Within the reactor, two symmetrically constructed electrode spaces are separated by ion-permeable membrane 5. On both sides of said membrane, electrodes 11 are disposed, which subsequently are in contact with bipolar plates 13, that are in turn in contact with current collectors 12, which supply or collect the current to and from the electrodes. The current collector 12 is covered from the outside by an isolating mounting plate 14. Electrode 11 is disposed within the recess of the body 15, where the electrolyte is supplied or discharged via the system of channels 16 through the ports 10, flowing over the electrode.

[0036] The compression of the reactor, ensuring its tightness and adequate contact between electrodes and bipolar plates, is achieved by using ring 1 possessing thread 6 on its internal wall, which maches the outer thread of the reactor body part 3. Sucha a connection via the direct threaded connection 17 enables very rapid assembly and ensures uniform contact stress distribution, as well as proper sealing during the battery assembly. As the electrolyte, a commercially available acidic solution of vanadium sulfate at the +3 and +4 oxidation states was used. Liquid electrolyte was transported from the external reservoirs to the reactor using a peristaltic pump via flexible tubing connected to the ports 10. A battery constructed in this manner allowed for energy conversion, achieving work parameters comparable to other lab-scale flow batteries.

[0037] Description of the reference numerals:

[0038] 1 - tightening ring, that is tightening and sealing clamp, sealing-clamping clamp connecting two parts of the housing for the reactor - further described as a ring

[0039] 2 - the upper part of the housing, that is part of the reactor body adjacent to the sealingclamping - clamp- ring 1 - the first part of the housing

[0040] 3 - the lower part of the housing, in the threaded connection with the ring 1- the second part of the housing

[0041] 4 — membrane frame

[0042] 5 - membrane

[0043] 6 - internal threaded part of the ring 1 - the threaded surface - threading surface connecting parts of the housing

[0044] 7 - outer - external threaded side - external thread - threading surface of the housing part 3 - threaded surface - surface where threaded is made - matching, adjusted threaded internal part 6 of the ring 1, intended to seal the housing by twisting, thus ensuring compression and uniform - regular contact stress distribution

[0045] 8 - protrusions for connecting parts of the housing - positioning pins in the example

[0046] 9 - recesses- sockets for connecting the housing parts with positioning pins 8

[0047] 10 - inflow and outflow port intended for liquid electrolyte, made on the outer surface of the assembled housing 11 – electrodes

[0048] 12 – current collector

[0049] 13 – bipolar plate

[0050] 14 – external isolating mounting plate

[0051] 15 – internal body part

[0052] 16 – canals for electrolyte transport to the electrode

[0053] 17 – direct threaded connection

Claims

Claims1. Housing for a redox-flow battery reactor comprising a body, characterized in that the body comprises at least two parts constituting a first part (2) and a second part (3) having a circular cross-sectional shape, which are detachably connected to each other by known means, preferably by means of at least one protrusion (8) or recess (9) formed on the first part, and correspondingly, at least one recess (9) formed on the second part and shaped to match the protrusion of the first part, or at least one protrusion (8) formed on the second part and shaped to match the recess (9) of the first part, wherein the first part (3) has an external thread (7) formed on its outer surface, while the housing comprises a tightening-sealing clamp (1) which tightly connects both parts of the housing from the outside by compression, preferably in the form of a tightening-sealing ring (1), such that the tightening-sealing clamp (1) has an internal thread (6) formed on its inner part that is being shaped to match the thread (7) formed on the first part (3) of the housing in a way enabling the closing of the body parts by twisting.

2. Housing according to claim 1, wherein it is made from plastic material such as ABS and / or PET.

3. Housing according to claim 1, wherein the protrusions (8) and recesses (9) comprise at least one positioning pin (8) or at least one socket (9).

4. The housing according to claim 1, wherein at least two ports (10) for transporting the redox-flow battery electrolyte are formed in both parts of the housing, preferably on the external surface of the housing.

5. An electrochemical reactor for a redox-flow battery having a layered arrangement of main components, characterized in that in the main part the reactor housing comprises a body, in which at least two parts having a circular cross-sectional shape are made, whichare detachably connected to each other by means of at least one protrusion or recess formed on the first part, and correspondingly, at least one recess or protrusion formed on the second part with has adjusted shape to the protrusion or recess of the first part, wherein on the first part external thread is formed on its outer surface, and furthermore, the housing comprises a tightening-sealing clamp (1) which tightly connects both parts of the reactor body by compression, preferably in the form of a tightening-sealing ring, such that the tightening-sealing clamp (1) has an internal thread formed on its inner part, the internal thread being shaped to match the thread on the first part of the housing in a manner enabling the closing of the body parts by twisting, and wherein the reactor comprises at least two electrodes (11), a current collector (12), preferably in the form of a flat copper sheet, which is in direct contact with a bipolar plate (13), preferably made of a polymercarbon composite, the bipolar plate (13) being adjacent to at least one electrode (11), preferably made of carbon felt, and two adjacent electrodes (11) are separated by an ion-conductive reactor membrane (5) impermeable to active species, and furthermore, electrolyte is supplied to the electrode space through at least one port (10) in one part of the housing (preferably located on the external surface of the housing) connected to at least one channel (16), and is discharged through at least one port (10) in the second part of the reactor housing.

6. A membrane frame for the electrochemical reactor, characterized in that it comprises at least two self-locking rings (4) between which the membrane (5) is detachably mounted, and preferably wherein on the surface of the first self-locking ring (4) at least one connecting socket is formed, and on the second ring (4) at least one connecting pin is formed, the pin being shaped to match the socket.

7. The frame according to claim 6, wherein the opening formed in its center has a rectangular cross-sectional shape adapted to the shape of the membrane (5).

8. A redox-flow battery comprising a reservoir with at least one electrolyte and means for electrolyte transport, a reservoir storing positive electrolyte, and a reservoir storing negative electrolyte, characterized in that it contains the housing described inclaims 1-4, the reactor described in claim 5, the membrane (5) being clamped between at least two self-locking rings (4) detachably mounted between the parts of the housing and the tightening-sealing clamp (1), wherein the housing parts are preferably connected by means of at least one protrusion and one recess, preferably in the form of at least one positioning pin (8) and at least one socket (9).

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