Method for the fabrication of electrochemical cells

- 28036 Madrid

IS 2 175 165 T3

DESCRIPTION

Method for the manufacture of electrochemical cells.

The present invention relates to a method for the manufacture of electrochemic cells and, in particular, to a method for the manufacture of industrial electrolytic or galvanic cells comprising a plurality of components joined together in a stack.

Industrial electrolytic or galvanic cells, such as auxiliary batteries, fuel cells, and electrolysers, typically consist of modules each comprising several components stacked in layers that are pressed together in a stack. For example, in a redox flow (reducing-oxidizing) type auxiliary battery, the components typically consist of electrically insulating flow-frames, each containing an electrode, a plurality of such flow-frames being sandwiched together. with other components, such as membranes and meshes. Auxiliary batteries of this type are well known to one of ordinary skill in the art.

In assembling the modules from their component parts, the most important considerations are:

i) In order to ensure that the fluids within the stack are isolated from each other and successfully contained with minimal leakage to the outside, it is necessary that satisfactory seals are provided between the individual layers of the stack and between the individual compartments. within the stack, for example, by sealing a frame around the perimeter of each electrode;

ii) each component layer of the stack should be positioned precisely in relation to the adjacent components; and iii) the interleaved arrangement of electrodes, membranes and meshes should remain intact and undisturbed while the remainder of the stack is formed and the unit is sealed. Some membranes may have a tendency to tear, wrinkle, fold or puncture and / or may be highly sensitive to partial water pressure.

Usually, fluid seals have been achieved, for example, by employing an elastomeric sealing arrangement between each flow frame, such as a toric ring or flat gasket. Conventional locating and retention devices can be used to position individual components relative to their neighbors and then fix them in place to form a partial module. However, when the stack consists of a large number of components, a reliable assembly of the stack with a plurality of theoretical rings is still difficult to achieve and is labor intensive. Elastomeric materials that are chemically resistant to aggressive electrolyte chemicals are relatively expensive and can account for a significant proportion of the total cost of such assembly. In addition, the requirement for toric ring grooves may conflict with the easy and reliable fulfillment of the other frame functions, such as liquid electro-cell flow distribution, especially with stacks containing thin frames, for example, when the thickness of the frame approaches less than 2.5 times the thickness of the electrolyte feed channel.

It has also been proposed to create fluid seals, avoiding the cumbersome and expensive assembly of theoretical rings, by welding the layers together, for example, using friction welding for frame-to-frame seals and / or laser welding for electrode-to-frame seals. Disadvantages of this method include the possible disruption of carefully placed and conditioned membranes by movement and / or heat during frame-to-frame sealing, the need to have compatible materials that can be successfully welded together, the inability to disassemble and the method to ensure the reliability of the weld.

A further type of sealing arrangement has been proposed, in which a sealing mechanism in the form of a flow frame is incorporated and in which a flexible sheet with a special channel is placed, specifically in order to complete the sealing. Such a sealing arrangement is described in US-A-4,640,876. The flexible sheet that completes the seal is, however, difficult to manufacture and, due to its flexion, will be susceptible to environmental and mechanical degradation.

FR-A-2,292,345 describes a tongue and groove arrangement for joining the frame components of an electrical cell. The tab on one frame fits into the corresponding groove on an adjacent frame, and the frames are attached together using adhesives, solvents, or ultrasonic welding.

Document FR-A-2,700,639 describes a seal formed by trapping a flat metal sheet between a tongue and a groove formed, one opposite the other, in adjacent frames, the sheet being pressed under the action of the means for compressing the stacking of elements. The seal between adjacent frames is maintained by compression of the flat sheet metal.

We have now developed an improved method for the manufacture of an electrochemic cell comprising a plurality of electrochemic components joined in a stack, a method in which the tasks of positioning, sealing and securing the stacking components are accomplished by a single one-piece sealing arrangement. .

Accordingly, the present invention provides a method for manufacturing an electrochemic or galvanic cell comprising a plurality of electrochemic components, electrochemic components that are joined in a stack, which method comprises:

i) providing a first component formed from a deformable polymeric material, with at least one groove

ES 2 175 165 T3 substantially continuous comprising a female opening having a width w and a depth h;

ii) providing a second component with at least one substantially continuous erect portion having a width> w and a height <h;

iii) pressing the first and second components against each other in order to provide an integral seal between the erect part in the second component and the opening in the first component, the seal between the parts being provided by interference between the sides of the erect part and the sides of the opening, deforming the components into tight conformity with each other; and iv) joining a plurality of first and second components to form a stack.

In carrying out the method of the present invention, the first component is formed from a deformable polymeric material so that, when the first and second components are brought together, an appropriate distribution of deformations is obtained, so that sealing can be obtained. required between the first and second components. Suitable polymeric materials from which the first component may be made include here those capable of resisting continuous tensile stresses and providing local compressive deformation without catastrophic failure, particularly semi-crystalline polymers, such as most kinds of polyethylene, polypropylene and their substances. copolymer blends, acetal, nylons, poly (ethylene terephthalate), poly (vinylidene fluoride), poly (vinyl chloride), polytetrafluoroethylene, fluorinated ethylene-propylene copolymer, polyfluoroamide, chlorinated polyoxymethylene, plus many others. In order to provide the first component with the desired configuration, these polymeric materials can be machined, injection molded, compression molded, or otherwise formed.

The material from which the second component is formed can be a deformable polymeric material, for example, it can be formed from the same polymeric material as the first component, although the second component does not have to be formed from a polymeric material. deformable. Additional materials that can therefore be used in the construction of the second component are materials less resistant to sustained stress, such as heavily loaded classes of materials from which the first component can be made, and non-crystalline polymers, such as polystyrene, poly (methyl methacrylate), and polycarbonate. Furthermore, it is also contemplated that the second component may be a metallic electrode or a carbon, titanium ioxide or ceramic component.

In a preferred embodiment of the present invention, the substantially continuous opening provided in the first component has sides that are perpendicular or substantially perpendicular to the plane of the first component, while the substantially continuous erect portion provided in the second component has sides that are perpendicular or substantially perpendicular to the plane of the second component. It will be understood that the sealing system of the present invention will operate in any orientation, depending on the orientation of the components to be joined. Although perpendicular or substantially perpendicular seals are preferred, the seal can be angled up to about 45 °, if desired.

It will be understood that while the seal of the present invention preferably has a substantially constant cross-sectional profile, the cross-section may vary along the length of the seal, if desired.

It will be understood that a plurality of components of an electrochemical galvanic cell are bonded together in this manner. Consequently, when the first and second components are formed from polymeric materials, the second component will not generally be provided only with at least one substantially continuous erect portion projecting from a first of its surfaces, but would generally be provided also of at least one substantially continuous female opening in the second of their surfaces, in order to allow it to be attached to a further component. It will be appreciated that any component that is provided with a female opening, even if it is also provided with an erect part, must be made from a deformable material. When the second component is made from a non-deformable material, such as metal, a different arrangement is required in order to allow a plurality of components to be joined. The second component would then generally be provided with upright parts on both the first and second surfaces, allowing the upright part on the second surface to join an additional component made from a deformable material that has a complementary groove formed in it. .

By bringing the first and second components together, the interference between the sides of the opening and the sides of the erect part is such as to develop a degree of stress on their contact, typically 10 to 100 MN / m.², enough to deform them into tight conformity with one another. The shape of the erect part and the opening, in conjunction with the tight conformity already obtained, is such as to sustain this stress at a level, typically 1 to 10 MN / m², sufficient to maintain a seal against pressures used in electrochemical cells typically ranging from 10 to 1,000 kN / m². The degree of interference and the exact shapes of the upright and opening are determined by the mechanical properties of the materials from which they are made, the tolerances and surface finish with which they can be manufactured, and the ease of manufacture. desired assembly and disassembly. It will be understood that end plates and tie bars can also be used,

ES 2 175 165 T3 as long as necessary to maintain the integrity of the cell, if it is internally under pressure.

The misalignment-induced deformation should be sufficient to reshape the mating surfaces for irregularities. Generally, the degree of mismatch between the width of the opening w of the first component and the width of the erect part of the second component is such as to generate a stress strain of 0.1 to 20%, more preferably 3 to 5%. , of the material on the sealing surfaces.

Although the width of the erect part in the second component is greater than the width w of the female opening in the first component, in order to force them into contact along their sides, the reverse situation persists, in relation to the others. adjacent parts of these components. It is important that these other adjacent parts are relieved, in order to confine the forced contact between the components to their sides. The depth of the root of the opening is thus greater than the height of the erect part, and the width of the mouth of the opening is greater than the width of the base of the erect part. The widening of the opening mouth and the relief radius of the erect part also serve to protect the sealing surfaces from damage during assembly, and to facilitate the assembly process. The sealing of the present invention is thus provided by the application of the sides of the erect part to the sides of the opening and does not require tightening of the stack, either to form or to maintain the seal. The sealing forces of the present invention are thus perpendicular to the compression forces in the stack of electrochemical components.

The shape of the opening root must, however, closely complement the shape of the erect part, in order to preserve the shape of the opening and sustain the forces arising from contact between the two components. Similarly, the volume of material in the first component around the opening should be sufficient for this purpose, typically providing solid material around the opening at a distance of no less than the depth of the opening.

It will be understood that the first component can comprise a plurality of openings and that the second component can comprise the same number of complementary upright parts, such that the two components seal and bond in more than one place. Alternatively, the first component can be sealed to more than one second component, so that the number of openings in the first component equals the number of upright parts in the second components.

A plurality of electrochemical components can be bonded together to form a partial module stack, for example, a partial module stack containing 10 or more complete cells. In such an arrangement, the membranes and other cell components are not unduly stressed. Such stacks of partial modules are relatively robust when formed and can be handled as a unit. Several stacks of partial modules can then be joined using known techniques or using the method of the invention, in order to provide the desired final module. For example, 10 stacks of partial modules could be joined together to provide a final module comprising up to 100 complete cells, or even more stacks of partial modules could be joined together to provide a final module comprising up to 100 different complete cells.

The method of the present invention allows an electrochemical or galvanic cell to be manufactured relatively easily to the required tolerances with the minimum of equipment, process steps, and cost. Additionally and importantly, since the seal between the first and second components is generated by mechanical means, it can be used in order to join together components that are made from different polymeric materials, including those that are incompatible with the technical welding that have been used previously in the technique. An additional advantage of the method of the invention is that the components can be disassembled in order to locate and repair faults, which do not necessarily have to be related to the sealing mechanisms but which can be, for example, membrane or membrane faults. electrode.

In particular, the method of the present invention can be used to attach the frame component of an electrochemical cell to the electrodes, even when the materials from which the frame and the electrodes are made are unsuitable to be welded together.

The present invention will be further described with reference to the accompanying drawings, in which:

Figure 1A shows a diagrammatic section through sections of a first component and a second component before being pressed against each other;

Figure 1B shows a diagrammatic section through the first and second components of Figure 1A when pressed against each other;

Figure 2 shows a diagrammatic section through an electrochemical cell formed by the method of the invention; and Figures 3A and 3B show diagrammatic sections through sections of a first alternative component and a second alternative complementary component before being pressed against each other.

Referring to Figures 1A and 1B of the drawings, a first component 1 formed from a deformable thermoplastic material, such as high-density polyethylene, has a groove 2 of width w and height h formed in ael. The second component 3 has an erect part 4 formed in it. It will be seen from the relative dimensions of the erect part 4 and of the opening 2 that the erect part has a width greater than w and a height less than h.

Components 1 and 3 are press fit with each other, the upright part 4 being pressed into the opening 2, the opening deforming sufficiently to receive the upright part.

A seal between the two parts is planned

ES 2 175 165 T3 between the vertical sides of the opening 2 and the erect part 4, as shown at S and S 'on Figure 1B of the drawings.

Referring to Figure 2, a redox flow battery 5 is shown in schematic cross section. The battery comprises a stack of twelve bipolar electrodes 6 that are provided, at each end of the stack, with electrical connections 7 and 8. The bipolar electrodes are separated from each other by cation exchange membranes 9 and are each attached to a insulating flow frame 10. Each insulating flow frame 10 is attached to the next frame in the stack by a seal between the parts being formed, as described with reference to Figures 1A and 1B. The upright portions on the flow frames 10, which extend continuously or substantially continuously around the frames, are shown at 4. The upright portions 4 are pressed into corresponding continuous or substantially continuous grooves formed in the adjacent flow frame. Electrodes 6 are sealed to insulating flow frames 10 by suitable means, not specifically shown.

Two electrolytes A and B fill the cavities formed between the alternate sides of the bipolar electrode 6 and the membranes 9. The flow distribution means for electrolytes A and B are not shown.

The redox flow coil has end plates 11 and 12 that are profiled such that they can be sealed to the upper flow frame shown in the stack and the lower flow frame shown in the stack, respectively.

It will be understood that tie bars and end plates (not shown) may also be required to maintain cell integrity, if internally pressurized.

Referring to Figures 3A and 3B, a first component 20 (shown at 10X magnification in Figure 3A) was formed from a deformable thermoplastic material, such as high density polyethylene. This component has an opening 21 having a height corresponding to h. The walls of the opening have a minor inward slope beginning at point X on the wall. At point X, where the inner wall begins to slope, the opening has a width w of 2.614 mm and a width w ', where the slope of the inner wall ends, of 2.358 mm.

A second component 23 (shown at 10X magnification in Figure 3B) was formed from polyethylene. The second component has an erect part 24 formed in an ileum. The erect part has a height H that is less than the height h of the opening 21 in Figure 3A. At its widest point, the erect part has a width W of 2.512mm which is greater than the width w 'of opening 21.

Components 20 and 23 are press fit with one another, upright portion 24 being pressed into opening 21, which deforms sufficiently to accommodate it. With the design as illustrated in Figures 3A and 3B, the sealing area between components 20 and 23 is as small as practicable, which facilitates assembly of the components and also maintenance of the assembly, while the Forces generated are less than those encountered with designs with a larger seal area.