BONDING IN ELECTROCHEMICAL CELLS, AND STACKING OF ELECTROCHEMICAL CELLS

Abstract

Disclosed is an electrochemical cell or a stack of at least two electrochemical cells, wherein at least two components of the electrochemical cell or of the stack of electrochemical cells are bonded together by means of a strip of adhesive which can be removed again, in particular without residue or destruction, by stretching substantially in the bonding plane, wherein the strip of adhesive comprises one or more adhesive material layers and optionally one or more carrier layers, and wherein the outer upper surface and the outer lower surface of the strip of adhesive are formed by the one or more adhesive material layers. Also disclosed is the use of a strip of adhesive of this kind for bonding together components in an electrochemical cell or in a stack of at least two electrochemical cells.

Claims

1. An electrochemical cell or stack of at least two electrochemical cells, comprising at least two components of the electrochemical cell or of the stack of electrochemical cells bonded to one another by means of an adhesive strip which is redetachable by extensive stretching substantially in the bond plane, the adhesive strip comprising one or more layers of pressure sensitive adhesive and optionally one or more carrier layers, and one outer upper and one outer lower face of the adhesive strip being formed by the layer or layers of pressure sensitive adhesive.

2. The electrochemical cell or stack of electrochemical cells as claimed in claim 1, wherein the adhesive strip is redetachable without residue or destruction by extensive stretching substantially in the bond plane.

3. The electrochemical cell or stack of electrochemical cells as claimed in claim 1, wherein the adhesive strip consists of a single layer of pressure sensitive adhesive.

4. The electrochemical cell or stack of electrochemical cells as claimed in claim 1, wherein the adhesive strip comprises a carrier layer and two layers of pressure sensitive adhesive, the two layers of pressure sensitive adhesive being disposed on the opposite surfaces of the carrier layer and forming one outer upper and one outer lower face of the adhesive strip.

5. The electrochemical cell or stack of electrochemical cells as claimed in claim 1, wherein the adhesive strip comprises at least one layer of pressure sensitive adhesive based on vinylaromatic block copolymer.

6. The electrochemical cell or stack of electrochemical cells as claimed in claim 5, wherein the vinylaromatic block copolymers comprise polymer blocks (i) predominantly formed of vinylaromatics (A blocks) and at the same time (ii) blocks predominantly formed by polymerization of 1,3-dienes (B blocks) or of butylenes (B blocks).

7. The electrochemical cell or stack of electrochemical cells as claimed in claim 5, wherein the at least one layer of pressure sensitive adhesive is constructed on the basis of vinylaromatic block copolymer and tackifier resin, a tackifier resin having a DACP of greater than 30 C., having an MMAP of greater than 50 C., and/or having a softening temperature of greater than 95 C.

8. The electrochemical cell or stack of electrochemical cells as claimed in claim 1, wherein the adhesive strip comprises at least one layer of pressure sensitive adhesive based on at least one block copolymer which is constructed at least partially of (meth)acrylic derivatives, the block copolymer comprising at least the unit P(A)-P(B)-P(A) composed of at least one polymer block P(B) and at least two polymer blocks P(A), and P(A) independently of one another representing homopolymer or copolymer blocks of monomers A, the polymer blocks P(A) each having a softening temperature in the range from +20 C. to +175 C., P(B) representing a homopolymer or copolymer block of monomers B, the polymer block P(B) having a softening temperature in the range from 100 C. to +10 C., and the polymer blocks P(A) and P(B) being not homogeneously miscible with one another.

9. The electrochemical cell or stack of electrochemical cells as claimed in claim 1, wherein the adhesive strip comprises at least one layer of pressure sensitive adhesive based on polyisobutylene homopolymer and/or polyisobutylene copolymer.

10. The electrochemical cell or stack of electrochemical cells as claimed in claim 1, wherein the adhesive strip comprises at least one layer of pressure sensitive adhesive based on solid acrylonitrile-butadiene rubber and further comprising tackifier resin, the fraction of tackifier resin being in total 30 to 130 phr.

11. The electrochemical cell or stack of electrochemical cells as claimed in claim 1, wherein the adhesive strip comprises at least one layer of pressure sensitive adhesive which is crosslinked.

12. The electrochemical cell or stack of electrochemical cells as claimed in claim 1, wherein the adhesive strip comprises at least one layer of pressure sensitive adhesive in which there is modified silica.

13. The electrochemical cell or stack of electrochemical cells as claimed in claim 1, wherein the adhesive strip comprises at least one layer of pressure sensitive adhesive which comprises endblock reinforcer resin.

14. The electrochemical cell or stack of electrochemical cells as claimed in claim 1, wherein the carrier layer of the adhesive strip, if present, has an elongation at break in the longitudinal direction and/or the transverse direction of at least 100%.

15. The electrochemical cell or stack of electrochemical cells as claimed in claim 1, wherein the carrier layer of the adhesive strip, if present, is made of polyethylene having a density of 0.94 g/cm.sup.3 or less.

16. The electrochemical cell or stack of electrochemical cells as claimed in claim 1, wherein the one or more layers of pressure sensitive adhesive and, if present, the one or more carrier layers are substantially free from platinum poisons.

17. The electrochemical cell or stack of electrochemical cells as claimed in claim 1, wherein the adhesive strip is embodied such that the at least two components of the electrochemical cell or of the stack of electrochemical cells are bonded to one another over the full area by means of the adhesive strip.

18. The electrochemical cell or stack of electrochemical cells as claimed in claim 1, wherein the adhesive strip is embodied such that the at least two components of the electrochemical cell or of the stack of electrochemical cells are bonded to one another over part of the area by means of the adhesive strip.

19. The electrochemical cell or stack of electrochemical cells as claimed in claim 1, wherein the adhesive strip is embodied such that it has at least one nonadhesive pull tab region, starting from which the detachment operation can be implemented by extensive stretching, said region projecting beyond those surfaces of the at least two components that are to be bonded.

20. The electrochemical cell or stack of electrochemical cells as claimed in claim 19, wherein the pull tab region of the adhesive strip is not adhesive.

21. The electrochemical cell or stack of electrochemical cells as claimed in claim 1, wherein the electrochemical cell is a fuel cell or the stack of electrochemical cells is a stack of fuel cells.

22. The electrochemical cell or stack of electrochemical cells as claimed in claim 1, wherein in the electrochemical cell or in the stack of electrochemical cells, the following components are bonded to one another by means of the adhesive strip: (a) bipolar half-plates, (b) (i) membrane-electrode assemblies and (ii) bipolar plates or bipolar half-plates, (c) (i) current collector plates and (ii) bipolar plates or bipolar half-plates, and/or (d) (i) current collector plates and (ii) insulating plates or media distributor plates.

23. A method for bonding with the adhesive strip as claimed in claim 1 components in an electrochemical cell or in a stack of at least two electrochemical cells to one another, wherein the electrochemical cell is a fuel cell or wherein the stack of electrochemical cells is a stack of fuel cells.

24. The method as claimed in claim 23, wherein the electrochemical cell or the stack of electrochemical cells is operated after bonding and subsequently the adhesive strip is redetached by extensive stretching substantially in the bond plane.

25. The method of an adhesive strip as claimed in claim 1 for bonding components in an electrochemical cell or in a stack of at least two electrochemical cells to one another in order to obtain more particularly residue-free and destruction-free redetachability of the adhesive strip by extensive stretching of the adhesive strip substantially in the bond plane, wherein the electrochemical cell is a fuel cell or wherein the stack of electrochemical cells is a stack of fuel cells.

26. The method as claimed in any of claim 23, wherein in the electrochemical cell or in the stack of electrochemical cells, the following components are bonded to one another by means of the adhesive strip: (a) bipolar half-plates, (b) (i) membrane-electrode assemblies and (ii) bipolar plates or bipolar half-plates, (c) (i) current collector plates and (ii) bipolar plates or bipolar half-plates, and/or (d) (i) current collector plates and (ii) insulating plates or media distributor plates.

27. The method as claimed in claim 23, wherein the adhesive strip is embodied such that the components of the electrochemical cell or of the stack of electrochemical cells are bonded to one another over the full area or bonded to one another over part of the area, by means of the adhesive strip.

28. The method as claimed in claim 23, wherein the adhesive strip is embodied such that it has at least one nonadhesive pull tab region, starting from which the detachment operation can be implemented by extensive stretching, said region projecting beyond those surfaces of the components that are to be bonded, wherein the pull tab region.

Description

FIGURES

[0165] FIG. 1 shows an inventively employable three-layer adhesive strip in the form of a frame-shaped diecut (three-dimensional drawing).

[0166] FIG. 2 shows an inventively employable single-layer adhesive strip in the form of a frame-shaped diecut (three-dimensional drawing).

[0167] FIG. 3 shows a membrane-electrode assembly bonded inventively on either side to a respective bipolar half-plate (three-dimensional drawing).

[0168] FIG. 1 shows the inventively employable adhesive strip 1, made up of three layers 2, 3, 4, which is redetachable without residue or destruction by extensive stretching substantially in the bond plane. The carrier layer 2 is of single-layer embodiment. Disposed on the carrier layer 2 on either side are layers 3, 4 of pressure sensitive adhesive (PSA), forming an outer upper and an outer lower face of the adhesive strip 1. The adhesive strip 1 is cut into a frame-shaped adhesive tape section (diecut). The adhesive strip 1, furthermore, has one projecting nonadhesive pull tab region 5 per side, starting from which the detachment operation can be performed by extensive stretching substantially in the bond zone. The pull tab regions 5 each comprise an extension of the layer sequence of the adhesive strip 1, there being disposed in the pull tab regions 5, on one outer upper and one outer lower face of the adhesive strip 1, a respective antiadhesive layer 6 and 7, preferably in the form of a double-sidedly siliconized release film 6 and 7, in order to render the pull tab regions 5 nonadhesive.

[0169] FIG. 2 shows the inventively employable adhesive strip 1, made of a single layer 3 of pressure sensitive adhesive (PSA), which is redetachable without residue or destruction by extensive stretching substantially in the bond plane. The adhesive strip 1 is cut into a frame-shaped adhesive tape section (diecut). The adhesive strip 1, furthermore, has one projecting nonadhesive pull tab region 5 per side, starting from which the detachment operation can be performed by extensive stretching substantially in the bond zone. The pull tab regions 5 each comprise an extension of the adhesive strip 1 made of a single PSA layer 3, there being disposed in the pull tab regions 5, on one outer upper and one outer lower face of the adhesive strip 1, a respective antiadhesive layer 6 and 7, preferably in the form of a double-sidedly siliconized release film 6 and 7, in order to render the pull tab regions 5 nonadhesive.

[0170] FIG. 3 shows an assembly made up of a rectangular membrane-electrode assembly 8 and two rectangular bipolar half-plates 9 and 10, where the membrane-electrode assembly 8 is bonded on its marginal reinforcement on both sides to respectively one of the bipolar half-plates 9 and 10, by means of the inventively employable single-layer adhesive strip (diecut) 1 with pull tab regions 5, as described in FIG. 2.

EXAMPLES

[0171] An adhesive strip redetachable without residue or destruction by extensive stretching substantially in the bond plane, and consisting of a single layer of pressure sensitive adhesive based on unhydrogenated styrene block copolymer, was cut by a laser into two frame-shaped adhesive tape sections (diecuts). These diecuts were used to bond a rectangular membrane-electrode assembly on its marginal reinforcement on both sides to a respective rectangular bipolar half-plate. The design of the diecuts was such that they had a plurality of pull tab regions projecting over the ultimately bonded surfaces of the components, specifically in each case one pull tab region per bonded side, starting from which it was possible to perform the detachment operation by extensive stretching substantially in the bond zone. The pull tab regions each constituted an extension of the adhesive strip composed of a single PSA layer; disposed in the pull tab regions on one outer upper and one outer lower face of the adhesive strip was (i) in each case no antiadhesive layer (example 1 with adhesive pull tab regions) or (ii) in each case one antiadhesive layer in the form of a double-sidedly siliconized release film (example 2 with nonadhesive pull tab regions).

[0172] The component assemblies from examples 1 and 2 were subsequently each tested as follows. Testing was carried out successfully for imperviousness of the bonds, by subjecting them to 1.5 bar water pressure in the interior of the bonded plates. No water emerged. Additionally, the two bonds were readily separable by extensive stretching of the adhesive strips (in each case starting from one of the pull tab regions) substantially in the bond plane, thus allowing the membrane-electrode assembly to be conveniently replaced. In this procedure, the bipolar half-plates and the membrane-electrode assembly remained undamaged. Furthermore, there were no residues of adhesive visible on the formerly bonded surfaces of the stated components. The stated components, could therefore be bonded easily again, as before, to a respective diecut of the strippable adhesive strip, and the resultant component assembly also passed the test for imperviousness of the bonds as described above.

Test Methods

[0173] Unless stated otherwise, all measurements were conducted at 23 C. and 50% rel. air humidity.

[0174] The mechanical and adhesive data were ascertained as follows:

Elongation at Break, Tear Strength and Stress at 50% Elongation

[0175] Elongation at break, tear strength (tear force), and stress at 50% elongation were measured in accordance with DIN 53504 using S3-size dumbbell specimens, at a separation rate of 300 mm per minute. The test conditions were 23 C. and 50% rel. air humidity.

Detachment Force

[0176] Detachment force (stripping force or stripping stress) was ascertained using an adhesive strip having the dimensions of length 50 mmwidth 20 mm with a pull tab region which is nonadhesive at the upper end. The adhesive strip was bonded between two steel plates in a mutually congruent arrangement and having dimensions of 50 mm30 mm with a contact pressure of 50 newtons in each case. The steel plates each have a hole to accommodate an S-shaped steel hook at their lower end. The lower end of the steel hook bears a further steel plate, by means of which the test arrangement can be fixed for measurement in the lower clamping jaw of a tensile tester. The bonds were stored at +40 C. for a period of 24 hours. After reconditioning to room temperature, the adhesive strip was detached at a strain rate of 1000 mm per minute parallel to the plane of the bond and in a contact-free manner with respect to the edge regions of the two steel plates. At the same time, the requisite detachment force in newtons (N) was measured. What is reported is the average of the stripping stress values (in N per mm.sup.2), measured in the region in which the adhesive strip has detached from the steel substrates over a bond length of between 10 mm and 40 mm.

Peel Adhesion

[0177] The determination of peel adhesion (according to AFERA 5001) was conducted as follows. The defined substrate used was galvanized steel sheet having a thickness of 2 mm (sourced from Rocholl GmbH). The adhesive strip to be examined was cut to a width of 20 mm and a length of about 25 cm, provided with a handling section and, immediately thereafter, pressed onto the chosen substrate five times with a 4 kg steel roller at an advance rate of 10 m/min. Immediately thereafter, the adhesive strip was pulled away from the substrate at an angle of 180 with a tensile tester (from Zwick) at a velocity v=300 mm/min, and the force required for the purpose at room temperature was measured. The measured value (in N/cm) is obtained as the average value from three individual measurements.

DACP

[0178] 5.0 g of test substance (the tackifier resin sample to be examined) are weighed into a dry test tube, and 5.0 g of xylene (isomer mixture, CAS [1330-20-7], 98.5%, Sigma-Aldrich #320579 or comparable) are added. The test substance is dissolved at 130 C. and then cooled down to 80 C. Any xylene that escapes is made up for with fresh xylene, such that 5.0 g of xylene are present again. Subsequently, 5.0 g of diacetone alcohol (4-hydroxy-4-methyl-2-pentanone, CAS [123-42-2], 99%, Aldrich # H41544 or comparable) are added. The test tube is shaken until the test substance has dissolved completely. For this purpose, the solution is heated to 100 C. The test tube containing the resin solution is then introduced into a Novomatics Chemotronic Cool cloud point measuring instrument and heated therein to 110 C. It is cooled down at a cooling rate of 1.0 K/min. The cloud point is detected optically. For this purpose, that temperature at which the turbidity of the solution is 70% is registered. The result is reported in C. The lower the DACP, the higher the polarity of the test substance.

MMAP

[0179] 5.0 g of test substance (the tackifier resin sample under investigation) are weighed into a dry test tube and 10 ml of dry aniline (CAS [62-53-3], 99.5%, Sigma-Aldrich #51788 or comparable) and 5 ml of dry methylcyclohexane (CAS [108-87-2], 99%, Sigma-Aldrich #300306 or comparable) are added. The test tube is shaken until the test substance has dissolved completely. For this purpose, the solution is heated to 100 C. The test tube containing the resin solution is then introduced into a Novomatics Chemotronic Cool cloud point measuring instrument and heated therein to 110 C. It is cooled down at a cooling rate of 1.0 K/min. The cloud point is detected visually. For this purpose, that temperature at which the turbidity of the solution is 70% is registered. The result is reported in C. The lower the MMAP, the higher the aromaticity of the test substance.

Softening Temperature

[0180] The softening temperature, especially resin softening temperature, is carried out in accordance with the relevant methodology, which is known as ring & ball and is standardized according to ASTM E28.

[0181] The determination uses an HRB 754 automated ring & ball tester from Herzog. Specimens, especially resin specimens, are first finely mortared. The resulting powder is introduced into a brass cylinder with a base aperture (internal diameter at the top part of the cylinder 20 mm, diameter of the base aperture in the cylinder 16 mm, cylinder height 6 mm) and melted on a hotplate. The amount introduced is chosen such that the specimen under test, after melting, fully fills the cylinder without protruding.

[0182] The resulting sample body, complete with cylinder, is inserted into the sample mount of the HRB 754. Glycerol or water is typically used to fill the heating bath. The test balls have a diameter of 9.5 mm and weigh 3.5 g. In line with the HRB 754 procedure, the ball is arranged above the sample body in the heating bath and is placed down on the sample body. Located 25 mm below the base of the cylinder is a catch plate, with a light barrier 2 mm above it. During the measuring procedure, the temperature is raised at 5 C./min. Within the temperature range of the softening temperature, the ball begins to move through the base aperture in the cylinder until eventually it comes to rest on the catch plate. In this position, it is detected by the light barrier, and the temperature of the heating bath at this point in time is registered. A duplicate determination takes place. The softening temperature is the average value from the two individual measurements.

Glass Transition Temperature (T.SUB.g.)

[0183] Glass transition pointsreferred to synonymously as glass transition temperaturesare reported as the result of measurements by means of differential scanning calorimetry (DSC) according to DIN 53 765, especially sections 7.1 and 8.1, but with uniform heating and cooling rates of 10 K/min in all heating and cooling steps (cf. DIN 53 765; section 7.1; note 1). The sample weight is 20 mg.

Thickness

[0184] The thickness of a PSA layer or an adhesive strip can be determined by determining the thickness of a section, defined in terms of its length and width, of such a layer or strip applied to a carrier, minus the (known or separately determinable) thickness of a section of the same dimensions of the carrier used. The thickness of the PSA layer or the adhesive strip can be determined using commercial thickness measuring instruments (caliper test instruments) with accuracies of less than 1 m deviation. If variations in thickness are found, the average of measurements at at least three representative sites is reported, i.e., more particularly not measured at creases, folds, specks, and the like.

[0185] As already in the case of the thickness of a PSA layer or of an adhesive strip, the thickness of a carrier can also be determined using commercial thickness measuring instruments (caliper test instruments) with accuracies of less than 1 m deviation. If variations in thickness are found, the average of measurements at at least three representative sites is reported, i.e., more particularly not measured at creases, folds, specks, and the like.

Density

[0186] The density of a carrier is ascertained by forming the quotient of mass and thickness of the carrier. For this purpose, the mass of a section, defined in terms of its length and width, of the carrier is determined. Furthermore, the thickness of the carrier having the same dimensions is ascertained by means of a commercial thickness measuring instrument (caliper test instrument) with an accuracy of less than 1 m deviation. If variations in thickness are found, the average of measurements at at least three representative sites is reported, i.e., more particularly not measured at creases, folds, specks, and the like.