MANUFACTURING PROCESSES FOR ELECTROCHEMICAL CAPERSUSCENTS

Description

Technical field of the invention

[0001] The invention relates to the field of electrical capacitors, and more particularly to that of double-layer electrochemical capacitors. More specifically, it relates to a method for manufacturing an electrochemical capacitor that facilitates the impregnation of the electrodes and the separator by a viscous electrolyte. State of the art

[0002] Double-layer electrochemical (super)capacitors have been known for a long time. They are based on a capacitive mechanism: charges adsorb onto an electrode, creating an electrochemical double layer. More precisely, they comprise a negative electrode and a positive electrode, separated by a separator and immersed in a liquid electrolyte. These various components are housed in a container that must be sealed due to the presence of the liquid electrolyte. If the electrodes and separator are all flexible sheets, they can be wound; other geometric shapes exist. These devices are also called "ultracapacitors"; a basic overview is given, for example, in the brochure " Product Guide Maxwell Technologies@ BOOSTCAP ®< Ultracapacitors » published by the Maxwell company in 2009.

[0003] Typically, the fabrication of such an electrochemical capacitor begins by cutting the electrodes to appropriate dimensions. The electrodes and their separator are then arranged in the desired geometric configuration. The resulting stack is then placed in a container, which is filled with liquid electrolyte and sealed to create a leak-proof enclosure. Such a process and device are described, for example, in US 2009 / 169989 A1.

[0004] The separator electrically separates the electrodes of opposite polarity, but it must be porous to allow the passage of ions moving within the electrolyte. To achieve high power density, the electrodes are also porous, increasing their surface area for electrochemical reactions. This raises the issue of electrolyte impregnation of both the separator and the electrodes. Ideally, the liquid electrolyte should completely saturate both the separator and the electrodes to ensure optimal cell performance. In particular, incomplete impregnation can lead to a decrease in electrical performance. Under these conditions, the known manufacturing process described above does, however, present certain drawbacks, primarily related to impregnation requirements.

[0005] In particular, the capacitor's geometric possibilities are limited. In other words, such a capacitor cannot adopt certain shapes without exhibiting degraded performance. Furthermore, this manufacturing process is relatively time-consuming, or even impossible, when the chosen electrolyte has high viscosity or when the electrodes have poor wettability. Indeed, in these cases, the impregnation of the separator and electrodes by the liquid electrolyte can take a long time to complete, or may even remain incomplete.

[0006] This problem arises particularly when the electrolyte is an ionic liquid; such devices are described, for example, in the publication "Supercapacitors utilizing ionic liquids" by A. Eftekhari, published in 2017 in the journal Energy Storage Materials, vol. 9, p. 46-69. The document WO 2014 / 001212 (Evonik Litarion GmbH) proposes a process in which the electrodes and the separator are installed in the container, then an excess of electrolyte is added, the process is allowed to complete the impregnation, and the electrolyte is subjected to a force capable of removing the excess.

[0007] The problem is also known in the field of lithium-ion batteries, and several solutions have been proposed. US patents 8,047,241 (Hibar Systems, Ltd), 2015 / 0364746 (CMWTEC Technologie GmbH), 2017 / 0005360 (Nissan Motor Co, Ltd), and 2012 / 069100 (Li-Tec Battery GmbH) describe highly complex battery filling machines capable of creating a vacuum around the battery casing. In a different approach, W. Pfleging and J. Pröll proposed structuring the electrode surfaces by forming parallel channels through laser beam irradiation (J. Materials Chemistry A 2014, pp. 14918–14926); this adds an extra manufacturing step to the process.

[0008] Furthermore, while it is desirable in the interest of device performance that the capacitor volume be completely filled with electrolyte, it is also desirable, given the cost of the electrolyte, to minimize the electrolyte volume.

[0009] In view of the above, the invention aims to remedy at least some of the drawbacks of the prior art presented above.

[0010] In particular, it aims to propose a process that makes it possible to manufacture an electrochemical capacitor capable of adopting a wide variety of geometries.

[0011] It also aims to propose such a process, which is faster to implement than in the previous art.

[0012] It also aims to propose such a process, which can be implemented with high viscosity liquid electrolytes.

[0013] Its ultimate aim is to propose such a process, which can be implemented with electrodes exhibiting low wettability. Objects of the invention

[0014] According to the invention, at least one of the above objectives is achieved by means of a method for manufacturing an electrochemical capacitor, said electrochemical capacitor comprising • a sealed enclosure, • at least one pair of electrodes, each pair comprising a positive electrode and a negative electrode, • at least one separator, each separator separating said positive electrode and said negative electrode of one pair of electrodes, and • a liquid electrolyte, received in said enclosure, in which process the electrodes and the respective separators are introduced into said envelope, and then the walls of said envelope are sealed, said process being characterized in that at least one so-called dry electrode of at least one pair of electrodes is first impregnated with said electrolyte, outside said envelope, so as to obtain at least one so-called impregnated electrode, then, during a so-called evacuation step, ∘ said impregnated electrode is brought into contact with one of the two faces of a dry separator, and optionally the other of the two faces of said dry separator is brought into contact with the other electrode of said pair of electrodes, and ∘ a certain quantity of the electrolyte is evacuated from said impregnated electrode, so as to obtain a so-called final electrode and to impregnate with at least a part of said quantity of electrolyte the separator and, possibly, the other electrode of said pair.

[0015] According to other features of the invention: The impregnated electrodes are introduced into the casing, particularly a flexible casing, and then at least part of the electrolyte is removed. The electrolyte is removed by vacuuming the casing. The electrolyte is removed by means of a complementary mechanical action, particularly compression. Dry electrodes are cut to their required dimensions, and then impregnation is carried out. A blank, particularly a roll, intended to form several electrodes is impregnated, and then the impregnated blank is cut to obtain a plurality of impregnated electrodes. The electrolyte is removed from the impregnated electrode, and then the final electrodes are introduced into the casing, particularly a rigid casing. The electrolyte is removed by rolling the impregnated electrode(s) upon itself. The dry electrode(s) have a compressibility of between 20% and 80%. where each dry electrode has a porosity between 40% and 90%.The dry electrode is impregnated such that the ratio between the mass of the impregnated electrode and the mass of the dry electrode is between 1.1 and 5. At least one electrode of each pair of electrodes is impregnated. All the electrodes are impregnated.

[0016] According to the invention, the step of impregnating the electrodes and their separator is carried out outside the casing, before the latter is sealed and made watertight. To this end, the invention advantageously takes advantage of the high porosity and compressibility characteristics of certain electrode materials that can be used. Typically, an appropriate quantity of electrolyte is selected to impregnate the electrodes. Preferably, this quantity should saturate the electrodes with electrolyte while preventing any electrolyte from being expelled from the electrode pores. In other words, during this preliminary wetting step, it is preferable that the separator not be moistened by the electrolyte in contact with the electrodes.Once this wetting has been carried out, the different constituent elements are introduced inside the bag, then the electrodes are compressed, so that the electrolyte is partially driven out of these electrodes and wets the separators.

[0017] The method according to the invention is applicable to electrodes of various types. By way of non-limiting example, we will first mention the "pouch cell" assembly, in which the electrodes and the separator are housed in a flexible pouch; such a device is described in WO 2018 / 185419 (NawaTechnologies). Within this pouch, the electrodes and the separator are arranged substantially flat. In this case, the electrodes can be cut, if necessary, after or before the impregnation step with the electrolyte. A stack is then formed between the moistened electrodes and their separator, advantageously taking care that the separator is not moistened. This stack is then sealed inside the pouch under a controlled atmosphere. Compression is then applied to the capacitor, which moistens the separator.This compression can be achieved mechanically, for example using a compression box, and / or by creating a vacuum inside the bag.

[0018] The invention also finds application in a jelly roll cell assembly, in which the electrodes and the separator are housed in a substantially rigid container. These electrodes and the intermediate separator are then coiled upon themselves, in a spiral fashion. In this case, the electrodes can be split after or before the impregnation step with the electrolyte. The separator is then inserted between the two impregnated electrodes, taking advantageous care, as in the previous example, to ensure that the separator itself is not moistened. The electrodes and the intermediate separator are then subjected to a winding operation, during which a compressive force is applied. This expels some of the electrolyte from the electrodes towards the separator. The resulting coil is then sealed inside the pouch, which is closed to form the airtight envelope.

[0019] It should be noted that the plaintiff deserves credit for identifying the source of the drawbacks related to the prior art manufacturing process. In particular, the plaintiff observed that these drawbacks stem primarily from the fact that the prior art involves impregnation, which is carried out after the electrodes and separator have been placed inside the bag. More specifically, in the prior art process, the components (electrodes and separators) are impregnated from one side of the cell (typically from the top); the electrolyte must therefore penetrate a considerable thickness of material to fully impregnate these components.

[0020] On the contrary, according to the invention, this impregnation is carried out beforehand, and the electrolyte only has to pass through the thickness of a sheet representing the element. Consequently, this makes it possible to give the final capacitor specific geometries that are not industrially viable with the prior art manufacturing process. Furthermore, the process according to the invention is perfectly suited to a high-viscosity electrolyte, as well as to electrodes with low wettability. By way of example (not limiting), ionic liquids have certain advantages as electrolytes for supercapacitors (non-flammability, non-volatility, electrochemical stability), but have the disadvantage of exhibiting high viscosity at room temperature (20°C). Their use in a prior art manufacturing process results in a prolonged impregnation time. The invention overcomes this limitation.The advantage of the process according to the invention is all the greater as the viscosity of the electrolyte is high.

[0021] In the process according to the invention, the two electrodes of the electrode pair may be identical or different. If they are different, their compressibility and / or thickness may be identical or different, and therefore they may have different absorption capacities for the electrolyte. In one embodiment of the invention, one of the electrodes is compressible and thick, and the other is thin and less compressible. In this case, the thick, compressible electrode is impregnated outside the casing so that it subsequently wets the separator and the other electrode during compression within the casing.

[0022] Advantageously, the thickness of the compressible parts [cm], i.e., the electrodes and the separator, multiplied by the effective compression ratio [%], is at least equal to the average porosity of the incompressible parts [%] multiplied by the thickness of the incompressible parts. Thus, the volume of electrolyte [cm³] discharged during the discharge step is at most equal to the product of the thickness [cm] of the impregnated electrode, the compressibility [%] of the electrode, and its surface area [cm²]. In practice, this volume [cm³] corresponds to the product of the thickness [cm] of the impregnated electrode, the effective compression ratio of the impregnated electrode [%], and its surface area [cm²]. The volume [cm³] required to impregnate the separator is equal to the product of the porosity [%] of the separator, its thickness [cm], and its surface area [cm²].The volume [cm³] required to impregnate the second electrode of the electrode pair is equal to the product of the porosity [%] of said second electrode, its thickness [cm³], and its surface area [cm³]. During the evacuation step, the volume to be evacuated from the impregnated electrode must be at least equal to the volume required to impregnate the separator, plus, if applicable, the volume required to impregnate the second electrode. Thus, a person skilled in the art can select and size the electrodes and the separator. Description of the figures

[0023] The invention will be described below, with reference to the accompanying drawings given solely by way of non-limiting examples, in which: [ Fig. 1 [ ] is a schematic view, illustrating a first step in the realization of a capacitor according to a first embodiment of the invention. ] Fig. 2[ ] is a schematic view, illustrating a second stage in the realization of the capacitor according to the first embodiment of the invention. Fig. 3 [ ] is a schematic view, illustrating a third step in the realization of the capacitor according to the first embodiment of the invention. ] Fig. 4 [ ] is a schematic view, illustrating a variant of this first embodiment. ] Fig. 5 [ ] is a schematic view, illustrating a first step in the realization of a capacitor according to a second embodiment of the invention. ] Fig. 6 [ ] is a schematic view, illustrating a second stage in the realization of the capacitor according to the second embodiment of the invention. ] Fig. 7 [ ] is a front view, illustrating a further embodiment of the capacitor according to the invention. Fig. 8 [ ] is a front view, illustrating another additional embodiment of the capacitor according to the invention. Fig. 9 ] is a front view, illustrating yet another additional embodiment of the capacitor according to the invention.

[0024] The following numerical reference symbols are used in the figures and in the description below: Description Description 1 Capacitor 10 Dry electrode (positive) 11 Electrode 10 saturated with electrolyte 12 Final (positive) electrode 20 Dry electrode (negative) 21 Electrode 20 saturated with electrolyte 22 Final electrode (negative) 30 Separator 60 Collector 40 Envelope (pocket) 50 Electrolyte bath 60 Collector 70 Electrode material roll 71 Electrolyte-impregnated roller 70

[0025] Three-digit numeric references have the same meaning as two-digit ones, respectively, the latter having been increased by one or more hundreds. Detailed description

[0026] There figure 3 illustrates the various components that form an electrochemical capacitor according to the invention. Two electrodes are shown. 12 And 22, respectively positive and negative, a separator 30, collectors 60 as well as a pocket40 defining an open volume V40 The capacitor also includes other constituent elements, of a type known per se, which are not shown in this figure. These include various metal strips intended to form solder rings.

[0027] The electrodes, separator, and pouch, for example, are of a type known per se. The electrode 22 The negative electrode can be made of activated carbon, the positive electrode 12 in vertically aligned carbon nanotubes (abbreviated VACNT), the pocket 40 made of plastic, and the separator 30 made of polypropylene. The nature of these different components is not an essential feature of the invention. Therefore, their constituent material is not described in further detail at this stage.

[0028] According to the invention, it is planned to impregnate at least one of the electrodes 10 Or 20,by means of a liquid electrolyte. The following will describe the impregnation of the electrode. 10, it being understood that the impregnation of the other electrode is similar. For this purpose, a bath is prepared 50 of this electrolyte, which is of any suitable type. For example, this electrolyte can be a ternary liquid mixture comprising a monomer, an ionic liquid and a solvent.

[0029] The electrode 10 is soaked in the bath 50, for a duration typically between 1 and 10 seconds. At the end of this soaking step, a so-called impregnated electrode is obtained, bearing the reference 11 on the figure 1 . Advantageously, this electrode 11is saturated, meaning that substantially all of its pores are filled with the electrolyte. It is preferable that the electrolyte be trapped by this electrode. In the context of the present invention, this term "trapping" means that another element, such as the separator, in contact with the impregnated electrode 11, will not be moistened by the electrolyte.

[0030] To achieve saturation, as defined above, a person skilled in the art can adjust several parameters. First, they can consider the electrode's compressibility. This parameter can be determined, for example, by measuring the decrease in thickness of the electrode when a predetermined pressure is applied; this determination can be made, for instance, by analogy with ISO 11752, which, however, is intended to apply to typically thicker materials. A person skilled in the art can also consider the electrode's porosity. Finally, a person skilled in the art can adjust the impregnation time according to the viscosity of the bath's electrolyte. 50.

[0031] By way of non-exhaustive examples: the compressibility of the electrode is between 10% and 80%; the porosity of the electrode is between 40% and 90%; the viscosity of the electrolyte is between 0.34 cp and 30 cp (measured at the temperature of the electrolyte during impregnation).

[0032] At the end of the impregnation process, the electrode 11 has trapped a certain mass of electrolyte. We note M11 / M10 the ratio between the respective masses of the impregnated electrode 11 and the so-called dry electrode 10. This ratio is typically between 1.1 and 5.

[0033] The impregnated positive electrode 11 is then positioned on the separator 30, in a manner known per se. Then, the negative electrode is placed on the separator, also in the usual way; this is illustrated in the figure 2 .This negative electrode can, if necessary, be impregnated in a step analogous to that described above for the positive electrode. 10. The electrodes are then wrapped with the separators, and the collectors are welded to the metal strips of the electrodes. Finally, the collectors are sealed. 60 to the pouch, and the pouch is then sealed. Once sealed, this pouch forms an envelope for the final electrolytic capacitor, designated as a whole by the reference 1 on the figure 2 .

[0034] According to the invention, the pouch is advantageously placed under vacuum. This creates a pressure difference between the inside and outside of the pouch, which generates a compressive force on the impregnated electrode, represented by arrow V on the figure 2Therefore, this compression expels the initially present electrolyte from the pores of the impregnated electrode, as indicated by arrow E on the figure 2 . This expelled electrolyte fills the internal volume of the envelope, wetting in particular the separator.

[0035] In addition to the force created by the pressure difference mentioned above, a complementary force can be applied, for example of a mechanical type, represented by arrow C on the figure 3 This therefore allows for precise adjustment of the total force exerted, which is equal to the sum of the force due to the vacuum and the additional force mentioned above. On the figures 1 to 3 Reference 10 designates the so-called dry electrode, reference 11 refers to the so-called impregnated electrode, while the reference 12 designates the so-called final electrode.

[0036] It should be noted that, advantageously, no additional volume of electrolyte is added, apart from that used to impregnate the electrode(s). Under these conditions, with reference to the figure 1 If a single electrode is impregnated, it is made to trap the predetermined amount of electrolyte, intended to fill the final capacitor.

[0037] In the case where both electrodes are impregnated, the amount of electrolyte trapped by these two electrodes is ensured to correspond to the total amount of electrolyte intended to fill the final capacitor. It can be assumed that each electrode traps the same amount of electrolyte. Alternatively, it can be assumed that the amounts of electrolyte trapped by the two electrodes are different. This is particularly feasible if these two electrodes have at least one different parameter, such as their compressibility, porosity, thickness, or composition. In the illustrated example, both electrodes are impregnated. Similar to the references 10 has 12 The references above 20,21 And 22 designate the other electrode respectively in the dry, impregnated and final state.

[0038] The invention includes two main embodiments. In the first embodiment, as described above, each electrode is cut to the required size before the impregnation operation. To verify that the correct amount of electrolyte is trapped, each electrode can, for example, be weighed immediately after the impregnation operation.

[0039] In the second embodiment, each electrode is cut to the required size after the impregnation operation. In this respect, as shown in the figure 4 , For example, a roll-shaped strip of material is used. 70, intended to form a plurality of electrodes. This roll is then unrolled and, advantageously continuously, is subjected to impregnation in the bath 50. Finally, this impregnated roller 71is cut to form electrodes that have absorbed a certain amount of electrolyte. To verify that the desired amount of electrolyte is impregnated on the roll, tests can be carried out on specific samples of the roll.

[0040] THE figures 5 and 6 describe a second variant embodiment, namely of the "jelly roll" type. In these figures, the mechanical elements analogous to those of the figures of the first embodiment are assigned the same reference numbers, increased by the number 100.

[0041] In a way that is well known in itself, the capacitor 101 death figures 5 and 6 includes two electrodes 112 And 122, respectively positive and negative, a separator 130, as well as a container 140. This capacitor differs from that of the first embodiment, primarily in that the container 140 is noticeably rigid, while the pocket40 is flexible. Moreover, in this second embodiment, the electrodes and the separator are wound around themselves.

[0042] In the prior art, the electrodes and separator are first wound, then inserted into the rigid container, and finally filled with the electrolyte. According to the invention, at least one of the two dry electrodes is first impregnated with the electrolyte, and then these impregnated electrodes are placed 111 And 121 on either side of the separator, flat, as shown in the figure 5

[0043] These electrodes and separators are then folded back on themselves, by any appropriate means, as shown in the figure 6 .This winding operation creates a compressive force C' which expels the electrolyte from the electrode along the arrows E', thus moistening the separator. These various constituent elements, namely the electrodes 112,122 and the separator 130 Now impregnated, they are then introduced into the interior volume of the rigid container. In a manner known per se, this container is sealed, a step which is not shown in the diagram. figure 6 and we add the collectors 160.

[0044] There figure 7 illustrates a further embodiment of the invention. On this figure 7 mechanical elements similar to those of the first embodiment are assigned the same reference numbers, increased by the number 200.

[0045] On this figure 7We find a capacitor formed by a plurality of electrode pairs, each comprising a positive and a negative electrode, with a separator interposed between these two electrodes. The implementation of each pair is analogous to that described with reference to the first embodiment.

[0046] Next, each pair of electrodes, equipped with its separator, is arranged one below the other. A current collector is inserted between adjacent electrodes belonging to two facing pairs. This stack is placed in a bag, similar to those in the first embodiment. Then, in a manner similar to that described above, this bag is evacuated and, optionally, an additional compression force is applied to expel the electrolyte from each impregnated electrode.

[0047] THE figures 8 and 9illustrate additional embodiments, highlighting the specific advantages of the invention. On these figures 8 and 9 mechanical elements similar to those of the first embodiment are assigned the same reference numbers, increased respectively by 300 and 400.

[0048] The capacitor of the figure 8 is obtained in a manner analogous to that described with reference to the first embodiment. This capacitor is remarkable in that it has a very large form factor. In other words, its longitudinal dimension, or length, is much greater than its transverse dimension, or height. Typically, the ratio between this length and this height can be greater than 10.

[0049] Such a form factor is not reliably achievable in the prior art. Indeed, in the known technique, the electrode must be impregnated with the electrolyte by capillary action. The time required for this impregnation is particularly long. Moreover, such impregnation often proves unsatisfactory. In contrast, thanks to the invention, pre-impregnating the electrodes eliminates these technical problems.

[0050] The capacitor of the figure 9is obtained in a manner analogous to that described with reference to the first embodiment. This capacitor is integrated into a rigid curved part, meaning that, at certain points, the electrodes and their separator are subjected to significant mechanical deflections. For example, the radius of curvature of the electrodes and the separator is less than 1 cm. These electrodes and the separator can each comprise several sections with opposite concavities, meaning that the concavity of one section is oriented in one direction, while the concavity of another section is oriented in the opposite direction.

[0051] Such a capacitor cannot be reliably obtained in the prior art because, due to the presence of these significant curvatures, the electrode cannot properly wet the entire active surface of the separator. In contrast, thanks to the invention, the pre-impregnation of the electrodes makes it possible to achieve such curvatures while ensuring satisfactory impregnation of the separator. The radius of curvature of the electrodes and the separator can, in particular, be less than 7 mm. EXAMPLES Example 1

[0052] In this first example, a capacitor manufactured according to the prior art is compared with a capacitor manufactured according to the invention. The following constituent elements were used: Two VACNT-type electrodes, synthesized by NAWA (as described, for example, in US 2016 / 0289826). Each electrode is 70 µm thick, with lengths of 3 cm and widths of 2 cm. These electrodes have a porosity of 80% and a compressibility of approximately 30%. An EMITFSI (ethylmethylimidazolium trifluoromethanesulfonylimide) electrolyte manufactured by the company Solvionic. A cellulose separator, manufactured by Dreamweaver. This separator is 30 µm thick, while its length and width are similar to those of the electrodes described above. It is covered by a flexible, laminated aluminum-polyethylene pouch.

[0053] A first capacitor is formed from the above components, according to a process known in the prior art. In essence, the electrodes and the separator, placed between them, are introduced into the flexible pouch. The pouch is then filled with a volume of electrolyte equal to 0.15 mL. The walls of the pouch are then welded together under a pressure of 100 mbar, so that the pouch forms a sealed envelope.

[0054] A second capacitor is formed from the above components, according to a process in accordance with the invention, as described with reference to figures 1 to 3To this end, each electrode is impregnated with a volume of electrolyte equal to 0.03 mL. The separator is placed between these impregnated electrodes, and then the assembly is introduced into the bag. The bag is then sealed and pressurized to 100 mbar, which forces the electrolyte out of the electrodes, thus impregnating the separator.

[0055] These two capacitors have similar, standard shapes. Thus, the two walls of the pocket, the two electrodes, and the separator are arranged flat, one below the other, as on the figure 3 .

[0056] For each of these capacitors, the impedance is measured on a potentiostat sold by BLOLOGIC, at 0 V with a 10 mV amplitude, from 100 kHz to 0.1 Hz. The equivalent series resistance (ESR) is defined as the real part of the complex impedance, and the capacitance is defined by the relation: − 1 2 ∗ π ∗ f ∗ Im Z with f the frequency, and Im(Z) the imaginary part of the complex impedance, are determined at a frequency of 1 Hz.

[0057] It can be seen that the ESR values ​​are similar for the two electrodes, since the electrode manufactured according to the invention has a value of 0.50 Ohm while the electrode according to the prior art has a value of 0.48 Ohm. Furthermore, these two electrodes have the same capacitance value of 0.13 F

[0058] In addition, each of the capacitors was disassembled after manufacturing. This allowed verification that, in both cases, the separator had been correctly impregnated.

[0059] This comparative example shows that a capacitor, made according to the invention, has properties close to those of a capacitor of the prior art, insofar as the electrodes used have a sufficient compressibility value.

[0060] Therefore, this highlights that the invention guarantees high reliability in capacitor performance. It is possible to produce capacitors with a very high form factor, such as that of the figure 8 , or whose envelope has substantially curved shapes, like that of the figure 9 .

[0061] It is noted that in VACNT-type electrodes, the electrolyte is retained by capillary action, much like a sponge. This electrolyte retention is achieved similarly in porous electrodes other than VACNT-type electrodes. Since the impregnation occurs on the outside of the carbon nanotubes, which are not substantially compressible, internal impregnation of the tubes is unnecessary and may even have a negative effect. Example 2

[0062] In this second example, a capacitor manufactured according to the prior art is compared with a capacitor manufactured according to the invention. The following components were used: Two activated carbon electrodes, synthesized by Samwha; each electrode is 120 µm thick, with lengths of 2 cm and widths of 3 cm. These electrodes have a porosity of 70% and a compressibility of approximately 8%. An EMITFSI (ethylmethylimidazolium trifluoromethanesulfonylimide) electrolyte manufactured by Solvionic. A cellulose separator, manufactured by Dreamweaver. This separator is 30 µm thick, with lengths and widths similar to those of the electrodes described above. A flexible, laminated aluminum-polyethylene pouch.

[0063] A first capacitor is formed from the above components, according to a process known in the prior art. In essence, the electrodes and the separator, placed between them, are introduced into the flexible pouch. The pouch is then filled with a volume of electrolyte equal to 0.2 mL. The walls of the pouch are then welded together under a pressure of 100 mbar, so that the pouch forms a sealed envelope.

[0064] A second capacitor is formed from the above components, according to a process in accordance with the invention, as described with reference to figures 1 to 4To this end, each electrode is impregnated with a volume of electrolyte equal to 0.05 mL. The separator is placed between these impregnated electrodes, and then the assembly is introduced into the bag. The bag is then sealed and pressurized to 100 mbar, which forces the electrolyte out of the electrodes, thus impregnating the separator.

[0065] For each of these capacitors, the impedance is measured on a potentiostat sold by BIOLOGIC, at 0 V with a 10 mV amplitude, from 100 kHz to 0.1 Hz. The equivalent series resistance (ESR) is defined as the real part of the complex impedance, and the capacitance is defined by the relation: − 1 2 ∗ π ∗ f ∗ Im Z with f the frequency, and lm(Z) the imaginary part of the complex impedance, are determined at a frequency of 1 Hz.

[0066] It is observed that the ESR values ​​are significantly different for the two electrodes, since the electrode according to the invention has a value of 9.10 while the electrode according to the prior art has a value of 0.94. Furthermore, these two electrodes have significantly different capacitance values. Indeed, the electrode according to the invention has a value of 0.09, while the electrode made according to the prior art has a value of 0.39.

[0067] Furthermore, each of the capacitors was disassembled after manufacturing. This allowed verification that, in the case of the capacitor according to the prior art, the separator was correctly impregnated. In contrast, in the case of the capacitor according to the invention, the impregnation of the separator could not be carried out correctly.

[0068] This comparative example shows that a capacitor, made according to the invention, does not have satisfactory properties if the electrodes have low compressibility. Example 3

[0069] In this third example, a capacitor with an elongated form factor manufactured according to the prior art is compared to a capacitor manufactured according to the invention. The following constituent elements were used: Two VACNT-type electrodes, synthesized by NAWA (see example 1). Each electrode is 70 µm thick, with lengths of 9 cm and widths of 2 cm. These electrodes have a porosity of 80% and a compressibility of approximately 30%. An EMITFSI (ethylmethylimidazolium trifluoromethanesulfonylimide) electrolyte, manufactured by the company Solvionic.A cellulose separator, manufactured by Dreamweaver. This separator is 30 µm thick, while its length and width are similar to those of the electrodes described above. It is covered by a flexible, laminated aluminum-polyethylene pouch.

[0070] A first capacitor is formed from the above components, according to a process known in the prior art. In essence, the electrodes and the separator, placed between them, are introduced into the flexible pouch. The pouch is then filled with a volume of electrolyte equal to 1 mL. The walls of the pouch are then welded together under a pressure of 100 mbar, so that the pouch forms a sealed envelope.

[0071] A second capacitor is formed from the above components, according to a process in accordance with the invention, as described with reference to figures 1 to 4To this end, each electrode is impregnated with a volume of electrolyte equal to 0.15 mL. The separator is placed between these impregnated electrodes, and then the assembly is introduced into the bag. The bag is then sealed and pressurized to 100 mbar, which forces the electrolyte out of the electrodes, thus impregnating the separator.

[0072] For each of these capacitors, the impedance is measured on a potentiostat sold by BIOLOGIC Biologic, at 0 V with a 10 mV amplitude, from 100 kHz to 0.1 Hz. The equivalent series resistance (ESR) is defined as the real part of the complex impedance, and the capacitance is defined by the relation: − 1 2 ∗ π ∗ f ∗ Im Z with f the frequency, and Im(Z) the imaginary part of the complex impedance, are determined at a frequency of 1 Hz.

[0073] It can be seen that the ESR values ​​are significantly different for the two electrodes, since the electrode according to the invention has a value of 0.18 Ohm while the electrode according to the prior art has a value of 5 Ohm. Furthermore, these two electrodes have significantly different capacitance values. Indeed, the electrode according to the invention has a value of 0.31 F, while the electrode made according to the prior art has a value of 0.08 F.

[0074] Furthermore, each of the capacitors was disassembled after manufacturing. This allowed verification that, in the case of the capacitor according to the prior art, the separator was not properly impregnated. In contrast, in the case of the capacitor according to the invention, the impregnation of the separator was successfully achieved.

[0075] This comparative example shows that the present invention makes it possible to produce capacitors with elongated form factors more efficiently than the prior art.

Claims

1. A method for manufacturing an electrochemical capacitor (1), said electrochemical capacitor comprising - a waterproof envelope (40), - at least one pair of electrodes, each pair comprising a positive electrode and a negative electrode, - at least one separator (30), each separator separating said positive electrode and said negative electrode of a pair of electrodes, and - a liquid electrolyte, received in said envelope, in which method the electrodes and the respective separators are introduced into said envelope, then the walls of said envelope are sealed, said method comprising the following steps : - during a step called impregnation which precedes the introduction of the electrodes and the separator in said envelope, at least one electrode (10;20), called dry, of at least one electrode pair is first impregnated with said electrolyte, outside of said envelope, so as to obtain at least one electrode (11;21) called impregnated, then, during a stage called evacuation, - said impregnated electrode (11; 21) is brought into contact with one of the two faces of a dry separator (30), and optionally the other of the two faces of said dry separator is brought into contact with the other electrode of said electrode pair, and - a certain quantity of the electrolyte is evacuated from said impregnated electrode, so as to obtain a so-called final electrode (12;22) and to impregnate with at least a part of said quantity of electrolyte the separator and, possibly, the other electrode of said couple, and said method being characterized in that : - a blank, in particular a roll, intended to form several electrodes is impregnated, and then the impregnated blank is cut so as to obtain a plurality of impregnated electrodes ; - the impregnated electrodes and the separator(s) are introduced into the envelope, in particular into a flexible envelope, and then at least part of the electrolyte is removed, preferably by vacuuming the envelope.

2. Method according to claim 1, wherein the electrolyte is removed by means of a complementary mechanical action, in particular a compression action.

3. Method according to any one of claims 1 to 2, in which dry electrodes are cut to their required dimensions, and then impregnation is carried out.

4. Method according to claim 1, wherein the electrolyte is removed from the impregnated electrode, and then the final electrodes are introduced into the envelope, in particular into a rigid envelope.

5. Method according to the preceding claim, wherein the electrolyte is removed by winding the impregnated electrode or each impregnated electrode around themselves.

6. Method according to any one of the preceding claims, wherein the dry electrode or each electrode has a compressibility of between 20% and 80%.

7. Method according to any one of the preceding claims, wherein the dry electrode or each dry electrode has a porosity of between 40% and 90%.

8. Method according to any one of the preceding claims, wherein the dry electrode is impregnated such that the ratio between the mass of the impregnated electrode and the mass of the dry electrode is between 1.1 and 5.

9. Method according to any one of the preceding claims, wherein at least one electrode of each pair of electrodes is impregnated.

10. Method according to any one of the preceding claims, characterized in that all the electrodes are impregnated.