FR3138447A1 - Current collector for electrochemical device for storing or generating electrical energy - Google Patents

Abstract

Current collector (1) for an electrical energy storage system or electrical generation system comprising an electronically conductive substrate (2), an electrically non-conductive polymer matrix (4), and carbon nanotubes (3). These nanotubes comprise a first end (31) fixed on the surface of the electronic conductive substrate (2) and electrically connected to the latter, as well as a second end (32), opposite the first end, capable of collecting the current from a electrode, so as to create on the surface of the electronically conductive substrate (2), a layer comprising a plurality of collection regions, which are electrically isolated from each other by interposed zones of the electrically non-conductive polymer matrix. Each collection region includes a plurality of said carbon nanotubes, and all of the second ends of the carbon nanotubes of each collection region protrude beyond the surface of the electrically non-conductive polymer matrix. Figure for abstract: Fig. 3.

Description

Current collector for electrochemical device for storing or generating electrical energy Technical field of the invention

The present invention relates to the field of electrochemical devices, and more precisely to the field of electrochemical devices for the storage and generation of electrical energy. It concerns more precisely current collectors usable in electrochemical systems and devices for generating electrical energy, such as fuel cells, and in electrochemical systems and devices for storing electrical energy, such as batteries (and more). particularly lithium ion batteries and lithium–air batteries) and supercapacitors. These current collectors have a particular geometry which allows, when used in energy storage devices, to optimize the adhesion of the active material of the electrode to the current collector while limiting the resistance of the electrode. interface. The invention also relates to a method of manufacturing such a current collector, having a new architecture, which gives it excellent electrical conductivity.

State of the art

The electrodes of energy storage devices, particularly electrochemical systems, are usually made by depositing an active material on thin electrically conductive films called current collectors. Current collectors allow electric current to flow to and/or from the active material, while providing mechanically robust support for the active material. The main current collectors used in these energy storage devices are sheets of aluminum, copper, stainless steel or nickel, with a thickness of less than 40 µm.

The electrodes of these energy storage devices are generally made up of active material particles, binders ensuring the mechanical cohesion of the electrode and conductive particles ensuring electrical conductivity within the electrode.

Sufficient adhesion of the active material to the current collector is desirable in order to ensure the processability of the electrode during the assembly stages of the electrochemical system, for example during cutting or winding stages. This adhesion is also desirable in order to optimize the lifespan of the energy storage device comprising it. The materials used to make the current collector being different from those present in the electrode, the binders must ensure both the cohesion of the active material but also the good adhesion of the latter to the current collector, this which can constrain the choice. In addition, the proportion of binder in the active material must be adjusted to ensure sufficient adhesion to the current collector. In order to optimize the operation of the system, the electronic transfer between the current collector and the active material must be as efficient as possible. The contact between the current collector and the active material made up of particles leads to the formation of an electrical interface resistance. This electrical resistance is all the more important as the quantity of binder in the active material is significant. There is therefore a compromise between the need to ensure adhesion of the active material to the current collector and the need to limit the interface resistance.

Increasing the proportion of binders and electrically conductive particles in the active material ensures both good adhesion and limits interface resistance. However, these elements do not contribute to the active material's ability to store electrical energy, which is its primary purpose. It is desirable to maintain the highest possible level of active particles in the active material in order to obtain the most efficient energy storage system possible, while reducing production and raw material costs.

Different types of current collector giving better performance to the electrical energy storage devices containing them have been developed. It is known from EP 2 500 969 A1 to use as a current collector, an aluminum sheet comprising between 0.01 to 3.0% by mass of dispersed and supported carbonaceous particles in order to reduce the electrical interface resistance. From US 8,785,053 B2, it is known to use a current collector comprising a support and a layer of uniformly distributed carbon nanotubes, placed on this support, in order to give it high resistance to corrosion.

In order to limit corrosion or prevent oxidation of the current collector even when the operating potential of the electrical energy storage device is greater than or equal to the oxidation potential of the material forming the current collector, it is known of EP 3 716 378 A1 to coat the current collector of an electrical energy storage device with an interface layer. This interface layer comprises a binder and a conductive material such as carbon particles, particularly in the form of carbon black, graphite, graphene or even carbon nanotube. It is also known from US 2012/0121974 to protect the current collector of the cathode by a porous protective conductive coating comprising carbon or conductive graphite.

However, this interface layer still generates an electrical contact resistance both between the interface layer and the substrate, and between this interface layer and the active material. Furthermore, the contact surface between the active material and the current collector being small, it is necessary to use a significant quantity of carbon particles in this interface layer.

An objective of the present invention is to remedy at least partly the disadvantages of the prior art mentioned above.

It aims in particular to propose a current collector usable in any electrochemical energy storage system making it possible to effectively ensure the adhesion of the active material while limiting the interface resistance.

It aims in particular to propose a process which makes it possible to manufacture in a simple, reliable and rapid manner a current collector having a very long lifespan.

It also aims to provide an energy storage device, preferably an electrochemical energy storage system such as a battery, a supercapacitor, or even a fuel cell, having a very long lifespan.

Objects of the invention

At least one of the above objectives is achieved via at least one of the objects according to the invention, as presented below. The present invention proposes as respective objects a current collector, its manufacturing method as well as an energy storage device such as a battery, these objects being worded in the appended claims.

The present invention proposes as a first object a current collector for an electrochemical energy storage system or electrochemical generation system comprising:

has. an electronic conductive substrate,

b. a non-electrically conductive polymer matrix, and

vs. carbon nanotubes comprising

- a first so-called transfer end, making it possible to transfer the current to the substrate, this first end being electrically connected to the surface of said electronically conductive substrate,

- as well as a second end, opposite said first end, called collection end, capable of collecting the current from an external active material, in particular from an electrode.

so as to create on the surface of said electronically conductive substrate, a layer comprising a plurality of collection regions, which are electrically isolated from each other by interposed zones of said electrically non-conductive polymer matrix, and where

- each collection region comprises a plurality of said carbon nanotubes, and

- all of the second ends of said carbon nanotubes of each collection region protrude beyond the surface of the electrically non-conductive polymer matrix.

According to other characteristics of the current collector according to the invention, which can be taken in isolation or according to any technically compatible characteristic:

• the carbon nanotubes of the collection regions have, in top view, an average intertube spacing of less than 100 nm,
• said collection regions have, when viewed from above, a circular shape, and the smallest distance between the outer edges of said collection regions is, when viewed from above, greater than or equal to 1 µm, preferably greater than 10 µm,
• said electronic conductive substrate is chosen from copper, aluminum, nickel, stainless steel, heavily doped silicon, carbon and composite materials comprising carbon and, preferably, from composite materials comprising carbon and a resin chosen from polyester, vinyl ester, epoxy, phenolic, polyimide, polyamide, polypropylene, polyetheretherketone resins or a mixture of one or more of these,
• said electronic conductive substrate is chosen from planar substrates, substrates in the form of a grid, substrates in the form of fibers and substrates in the form of felt,
• said carbon nanotubes, electrically connected to the surface of said electronically conductive substrate, have
  • a thickness less than 10 µm, preferably less than 1 µm and/or
  • a developed surface area greater than 100 m²/g, preferably greater than 250 m²/g,
• the volume ratio of non-electrically conductive polymer matrix/carbon nanotubes is less than 300%, preferably less than 200%, and even more preferably less than 70%.

The invention also relates to a device for storing or generating electrical energy such as a battery, a supercapacitor or a fuel cell comprising a current collector according to the invention.

The invention also relates to an electrochemical system for storing or generating electrical energy comprising a current collector according to the invention.

Finally, the subject of the invention is a method of manufacturing a current collector comprising an electronically conductive substrate, carbon nanotubes having one end fixed to the surface of said electronically conductive substrate, and a non-electrically conductive polymer matrix, said method comprising the following successive steps:

has. synthesizing, on the electronically conductive substrate, vertically aligned carbon nanotubes so as to form a mat, preferably by the chemical vapor deposition technique, or transferring aligned nanotubes synthesized on another substrate onto said electronically conductive substrate;

b. deposit, by any appropriate means, preferably by a liquid phase deposition process, said non-electrically conductive polymer matrix, on said carbon nanotubes,

so as to create on the surface of said electronically conductive substrate, a layer comprising a plurality of collection regions, which are electrically isolated from each other by interposed zones of said electrically non-conductive polymer matrix, and where

- each collection region comprises a plurality of said carbon nanotubes, and

- all of the second ends of said aligned carbon nanotubes of each collection region protrude beyond the surface of the electrically non-conductive polymer matrix.

Advantageously, the deposition of said non-electrically conductive polymer matrix, during step b) is carried out by a method chosen from coating, spraying, soaking-withdrawal, extrusion, infiltration in one or more stages, and infusion in one or more stages.

Figures

The invention will be described below, with reference to the appended drawings, given solely by way of non-limiting examples. Figures 1 to 10 illustrate certain aspects of the invention. Figures 1 to 3 show, schematically, a current collector according to the invention.

is a longitudinal sectional view, illustrating a current collector (1) according to the invention comprising an electronic conductive substrate (2), vertically aligned carbon nanotubes (3) forming collection regions (33) and a polymer matrix non-electrically conductive (4) forming interlayer zones (41) of non-electrically conductive polymer matrix.

is a top view, analogous to the , illustrating a current collector (1) according to the invention, and more particularly, the circular shapes of the collection regions (33) each comprising a plurality of vertically aligned carbon nanotubes (3) as well as the smallest distance (d ) between the outer edges of said collection regions.

is a longitudinal sectional view, illustrating an electrode (10) of an energy storage system comprising a current collector (1) according to the invention and active material (5) placed on this current collector.

schematically represents a three-dimensional exploded perspective view of a standardized Swagelok™ type cell, making it possible to evaluate the supercapacitor components in the wet process, and showing a central separator, electrodes arranged at both ends of the central separator and current collectors arranged on the ends of the electrodes, on the side opposite the separator.

schematically represents a three-dimensional exploded perspective view of a standardized Swagelok™ type cell, allowing the supercapacitor components to be evaluated in the dry process, and showing a central separator, self-supporting electrodes arranged at both ends of the central separator and current collectors arranged on the ends of the self-supporting electrodes, on the side opposite the separator.

represents schematically, an exploded three-dimensional view of a standardized “coin cell 2032” type battery half-cell, allowing the components of a battery to be evaluated, and revealing a central separator (Celgard 3501 impregnated with a solution electrolytic 1M LiPF ₆ in a mixture of ethyl carbonate (EC) and diethyl carbonate (DEC) with an EC/DEC ratio (1:1)), electrodes arranged at both ends of the central separator and current collectors arranged on the ends of the electrodes, on the side opposite the separator.

schematically represents an exploded three-dimensional view of an open cell device comprising a substrate such as a current collector according to the invention assembled with a separator (Celgard 3501) impregnated with an EMITFSI 99.5% ionic liquid ( Solvionic), so as to form a substrate/separator/substrate structure after pressing under 1 N by tightening the screws of the pressing plates with a torque screwdriver.

represents Nyquist diagrams obtained with current collectors according to the invention comprising different volume ratios SBR/C (%), in particular current collectors having a volume ratio SBR/C of 153% (×), 191% (points marked by triangles), 298% (points marked by diamonds), 687% (points marked by squares), and a commercial current collector of type NPC-055D Korea JCC supplied by the company Samwha (--) , as well as details of these same diagrams.

represents the Equivalent Series Resistance (ESR) evaluated from the Nyquist diagrams presented in , for different SBR/C volume ratios of different current collectors, in particular a commercial current collector of the NPC-055D Korea JCC type supplied by the company Samwha (--), current collectors according to the invention comprising between 0.15 mg of SBR per cm² and 0.43 mg of SBR per cm² as produced in Example 3 (points marked by black discs), layers of VACNT as produced in Example 1 without polymeric coating (points marked by triangles), and current collectors according to the invention comprising more than 1 mg of SBR per cm² as developed in Example 3 (points marked by squares).

shows the results of visual evaluation tests of the mechanical resistance of a commercial current collector of type NPC-055D Korea JCC supplied by the company Samwha, of a supported VACNT layer as developed in example 1 without polymer coating, and that of current collectors according to the invention, for different volume ratios SBR/C.

Description of the invention

We describe here a current collector according to the invention, with reference to Figures 1, 2 and 3. The present invention describes a current collector (1) for an electrochemical system or device for storing or generating electrical energy comprising:

1. an electronic conductive substrate (2),
2. a non-electrically conductive polymer matrix (4), and
3. carbon nanotubes which are advantageously vertically aligned nanotubes (3), hereinafter VACNT from the English “Vertically Aligned Carbon NanoTubes”, said nanotubes comprising
   • a first so-called transfer end (31), making it possible to transfer the current to the substrate, this first end being fixed on the surface of said electronically conductive substrate, and electrically connected to the surface of said electronically conductive substrate,
   • as well as a second end (32), opposite said first end, called collection end, capable of collecting the current from an external active material (5), in particular from an electrode.

so as to create on the surface of said electronically conductive substrate (2), a layer comprising a plurality of collection regions, which are electrically isolated from each other by intermediate zones of said non-electrically conductive polymer matrix, and where

• each collection region comprises a plurality of said carbon nanotubes, and
• all of the second ends of said carbon nanotubes of each collection region protrude beyond the surface of the electrically non-conductive polymer matrix.

The invention will be explained below mainly in relation to vertically aligned carbon nanotubes, which represent a particularly advantageous embodiment of the invention. This does not, however, limit the scope of the invention to vertically aligned nanotubes: for example, the nanotubes can be aligned other than vertically, while remaining parallel to each other (for example they can be tilted), or they may be unaligned with each other. Furthermore, the nanotubes may have been synthesized (i.e. deposited by a chemical process, typically in the vapor phase) on this electronically conductive substrate, or they may have been mechanically transferred to said electronically conductive substrate, after having been synthesized on another substrate. A transfer of vertically aligned nanotubes from one substrate to another can be done using techniques known to those skilled in the art; an example will be given below.

The presence of vertically aligned carbon nanotubes (3) on the electronic conductive substrate (2), hereinafter referred to as a layer of vertically aligned carbon nanotubes or VACNT mats, provides numerous electrical contact points for the active material. (5), thanks to their large specific surface area and their vertical orientation. The synthesis of VACNTs on the electronic conductive substrate (2) ensures direct electrical contact between the electronic conductive substrate (2) and the active material (5) through the unit tubes of the VACNTs. This makes it possible to limit the quantity of conductive particles in the active material but also to significantly reduce the interface resistance between the active material (5) and the electronic conductive substrate (2).

The presence of a non-electrically conductive polymer matrix (4) makes it possible to improve the adhesion of the VACNTs to the substrate. It offers purely polymeric attachment zones to the active material (5) of the electrode, freeing up the choice of binders ensuring the mechanical cohesion of the electrode. The fact of using such a non-electrically conductive polymer matrix (4) makes it possible to significantly reduce the quantity of binder within the electrode. The electrically non-conductive polymer matrix (4) is preferably an electronically non-conductive material, and advantageously has good ionic conductivity.

The inventors noticed that the coating of VACNTs directly synthesized on an electronically conductive substrate (2), with an electrically non-conductive polymer matrix (4) made it possible to generate a bimodal porosity particularly suited to the intended application. Indeed, the synthesized VACNT mat advantageously has a regular inter-tube spacing of less than 100 nm, preferably of the order of 5 to 50 nm depending on the synthesis conditions. The electrically non-conductive polymer matrix (4) is advantageously produced from any suitable electrically non-conductive polymer or mixture of suitable electrically non-conductive polymers, such as poly(styrene/butadiene) known as the acronym SBR (from the English Styrene-Butadiene Rubber), carboxymethylcellulose known by the acronym CMC or even poly(acrylic acid) known by the acronym PAA.

The non-electrically conductive polymer matrix, in particular the polymer(s) constituting this polymer matrix will be chosen according to the final use of the current collector according to the invention, of the energy storage device comprising it, in particular of the temperature resistance in operation targeted by the device, of the different materials constituting said device, such as the active material of the electrodes. We will particularly use poly(styrene/butadiene) as a polymer matrix because it has good temperature resistance, good chemical and electrochemical compatibility with the active materials and binders used in battery electrodes, and it is inexpensive.

The deposition of the electrically non-conductive polymer matrix (4) on the electronically conductive substrate (2) previously coated with vertically aligned carbon nanotubes (3) creates, in a surprising manner, whatever its deposition process. , on the surface of said electronically conductive substrate (2), a layer comprising a plurality of collection regions (33), which are electrically isolated from each other by intermediate zones (41) of said non-electrically conductive polymer matrix , and where each collection region (33) comprises a plurality of said vertically aligned carbon nanotubes (3).

Advantageously, the vertically aligned carbon nanotubes of the collection regions (33) have an average inter-tube spacing of less than 100 nm in order to ensure sufficient direct electrical contact between the electronically conductive substrate (2) and the active material (5). , in particular an electrode. Said collection regions (33) advantageously have a circular shape and the smallest distance (d) between the outer edges of said collection regions is greater than or equal to 1 µm, preferably greater than 10 µm, preferably between 1 and 50 µm . This distance is of the order of the size of the active material particles usually used in the electrodes of electrochemical energy storage systems. This particular structure of the current collector according to the invention has both zones very suitable for the adhesion of the active material (i.e. intermediate zones of the polymer matrix non-conductive of electricity) and zones very suitable for conduction electrical (i.e. collection regions). The collection regions (33) and the interlayer zones (41) of the non-electrically conductive polymer matrix are distributed homogeneously on the surface of the current collector, not generating inhomogeneities in adhesion or conduction electrical, which could be detrimental to the operation of the energy storage device comprising such a current collector according to the invention.

The current collector according to the invention makes it possible, in an optimal manner, to effectively ensure adhesion of the active material while limiting the interface resistance when:

• the vertically aligned carbon nanotubes of the collection regions (33) have an average inter-tube spacing of less than 100 nm, and
• said collection regions (33) have a circular shape, and where the smallest distance (d) between the outer edges of said collection regions is greater than or equal to 1 µm, preferably greater than 10 µm, preferably between 1 and 50 µm.

The vertically aligned carbon nanotubes (3), electrically connected to the surface of said electronic conductive substrate (2), advantageously have a thickness of less than 10 µm, preferably less than 1 µm in order to minimize the additional mass linked to the use of these vertically aligned carbon nanotubes (3) ie minimize the final weight of the current collector according to the invention, and ultimately optimize the electrochemical energy storage system comprising such a current collector according to the invention.

The vertically aligned carbon nanotubes (3), electrically connected to the surface of said electronically conductive substrate (2), advantageously have a developed surface area greater than 100 m²/g, preferably greater than 250 m²/g in order to maximize contact between the external active material (5), in particular an electrode and carbon nanotubes, preferably the so-called collection ends (32) of the carbon nanotubes.

The volume ratio of non-electrically conductive polymer matrix/carbon nanotubes of the current collector according to the invention, hereinafter also called volume ratio of polymer matrix/C, is advantageously less than 300%, preferably less than 200%, and even more preferably less than 70%. This volume ratio is determined as a function of the quantity of carbon nanotubes and that of the polymer(s) constituting the electrically non-conductive polymer matrix present within the current collector according to the invention, and their respective theoretical densities. A polymer matrix/C volume ratio of less than 300%, preferably less than 200%, and even more preferably less than 70%, advantageously makes it possible to effectively ensure adhesion of the active material while limiting the existing interface resistance. between the electronically conductive substrate and the active material of the electrode, regardless of the chemical nature of the electrically non-conductive polymer matrix. The polymer matrix/C volume ratio is advantageously chosen as a function of the final application of the energy storage device comprising a current collector according to the invention.

The shape of the electronic conductive substrate is advantageously adapted to the architecture of the energy storage device comprising it. The electronic conductive substrate can thus be chosen from planar substrates, substrates in the form of a grid, substrates in the form of fibers and substrates in the form of felt. The chemical nature of the electronic conductive substrate is chosen in particular according to the operating methods of the energy storage device comprising it and the processes used during the manufacture of this energy storage device. The electronic conductive substrate can be a metal, an alloy of metals or even composite materials comprising carbon called hereinafter carbon materials. It is preferably chosen from copper, aluminum, nickel, stainless steel, heavily doped silicon, carbon and composite materials comprising carbon and, preferably, composite materials comprising carbon and a resin chosen from polyester, vinyl ester, epoxy, phenolic, polyimide, polyamide, polypropylene, polyetheretherketone resins or a mixture of one or more of these.

We now describe the production of vertically aligned carbon nanotubes in the form of mats.

Vertically aligned carbon nanotubes, in the form of mats, almost free of by-products and having controlled physicochemical characteristics (length, diameter, density of the carbon nanotubes), can be produced on an electronically conductive substrate, by any means. , and are advantageously synthesized by the chemical vapor deposition process (Chemical Vapor Deposition in English, better known by the acronym CVD).

Vertically aligned carbon nanotube mats or layers can be made by this one- or two-step process on the surface of the electronically conductive substrate. The carbon nanotubes, obtained by one or other of these processes, advantageously have a diameter of between 5 nm and 50 nm, which ensures a good compromise in the developed surface (which must be large to improve electrical contact ) and the intrinsic electrical conductivity of the nanotubes.

The one-step chemical vapor deposition process from aerosols, preferably from a solution of ferrocene in toluene, makes it possible to synthesize, on substrates of different natures, vertically aligned carbon nanotubes having physicochemical characteristics that can be modulated depending on the intended application, in particular by controlling the diameter, length and density of the carbon nanotubes, over a wide range. In this one-step process, carbonaceous and catalytic precursors are injected simultaneously into the reactor, at a temperature between 550°C and 850°C, so as to induce the nucleation and growth of carbon nanotubes. The synthesis temperature is advantageously around 800°C. This is a low-cost and easily industrializable process. This process makes it possible to obtain carbon nanotubes having a diameter advantageously between 20 and 40 nm for a density of 10 ⁹ carbon nanotubes/cm² and more generally a diameter between 5 and 50 nm for a density between 10 ⁸ and 10 ¹² nanotubes/cm².

The two-step chemical vapor deposition process comprises the deposition of a layer of a catalyst material carried out prior to the step of nucleation and growth of carbon nanotubes from a gaseous carbon source, such as 'acetylene. The use of acetylene makes it possible to lower the synthesis temperature to a temperature below 650°C. This offers the possibility of growing carbon nanotubes on substrates with a lower melting temperature such as aluminum. This process advantageously makes it possible to obtain carbon nanotubes having a diameter less than 5 nm, denser than those obtained by the one-step process (density greater than or equal to 10 ¹¹ carbon nanotubes/nm²).

Furthermore, the growth rate and film thickness of carbon nanotubes can be adjusted by controlling the reaction temperature, or by adjusting the concentration of acetylene in the reactor. Adjustment of the size of the catalyst particles, the catalyst material used, the reagents and/or the additive species, the temperature, the pressure and other parameters, by methods known to those skilled in the art, allows to control, appropriately, the morphology and density of the vertically aligned carbon nanotubes in these VACNT layers or mats.

The electronic conductive substrate, as indicated previously, can be heavily doped silicon, a metal or an alloy of metals, carbon materials. For growth on metals or on carbonaceous substrates, the deposition of a barrier sublayer, preferably SiO _x , prior to the growth of carbon nanotubes by chemical vapor deposition is sometimes necessary to avoid the diffusion of carbon in the substrate, or to promote the reactivity of the catalyst. For one-step processes, this deposition precedes feeding the reactor with catalyst and carbon precursors necessary for the growth of carbon nanotubes. For two-step processes this deposition precedes the deposition of the catalyst. Deposition on an aluminum substrate does not require depositing a barrier undercoat because the native oxide already acts as a barrier undercoat.

We now describe the production of a current collector according to the invention.

On the supported mats or layers of vertically aligned carbon nanotubes, a non-electrically conductive polymer matrix is deposited by any appropriate means, preferably by a liquid phase deposition process, so as to obtain a collector current according to the invention. The deposition of this polymeric matrix makes it possible to create on the surface of the electronically conductive substrate, a layer comprising a plurality of collection regions, which are electrically isolated from each other by interposed zones of said non-electrically conductive polymeric matrix, and or

• each collection region comprises a plurality of said vertically aligned carbon nanotubes, and
• all of the second ends of said vertically aligned carbon nanotubes of each collection region protrude beyond the surface of the electrically non-conductive polymer matrix.

Advantageously, the deposition of said non-electrically conductive polymer matrix is carried out by any appropriate means, preferably by a method chosen from coating, spraying, soaking-removal of a liquid phase in which the polymer(s) are dissolved in a suitable solvent. This solvent is then extracted, in particular by evaporation. The deposition of the polymeric matrix can also be carried out by extrusion, infiltration in one or more stages or even by infusion in one or more stages. After deposition of the polymer matrix, the current collector according to the invention can also undergo a hot pressing or lamination step, in order to consolidate its mechanical structure.

These deposit methods are simple and quick to implement. The method used to deposit said polymer matrix will be chosen in particular depending on the chemical nature of the polymer matrix used.

Examples

The invention is illustrated below by examples which, however, do not limit the invention. These examples relate to the preparation of a current collector according to the invention and their evaluation with regard to a commercial current collector. The commercial current collector, used for comparison, is a sheet referenced NPC-055D Korea JCC supplied by the Samwha company. The commercial current collector is made of an aluminum sheet 50 µm thick, coated on these two opposite faces with a carbon coating with a thickness between 1 and 2 µm, and comprising carbon black particles having an average diameter of 160 µm integrated in a polymeric binder.

Example 1 : Production of VACNT mats in a single step by chemical vapor deposition process

Vertically aligned carbon nanotubes were synthesized on an aluminum substrate by chemical vapor deposition (CVD), from ferrocene dissolved in toluene, hydrogen and acetylene.

To do this, a 20µm thick aluminum substrate is fed continuously into a roll-to-roll reactor. The reaction chamber is supplied with argon, acetylene, hydrogen, ferrocene and toluene vapors. The temperature of the substrate in the reaction chamber is 615°C. The pressure in the reaction chamber is atmospheric pressure (plus or minus 15 Pa). The speed of movement of the aluminum substrate is adjusted so that the passage time of the substrate in the reaction chamber is equal to 2 min. At the outlet of the roll-to-roll reactor, the substrate is covered with a layer of VACNT with a thickness equal to 2 µm.

Example 2 : Production of VACNT mats in two stages by chemical vapor deposition process

A 6-inch silicon wafer (p-type, 1-10 Ω.cm, Silicon Quest International) was supplied and then cleaned using a standard “piranha” solution comprising one part hydrogen peroxide to three parts of sulfuric acid. A 1/10 nm patterned Fe/Al ₂ O ₃ catalyst film was then deposited onto this cleaned silicon wafer, via electron beam evaporation in a single pump cycle using a Temescal VES -2550 coupled with an FDC-8000 film deposition controller. The catalyst pattern was fabricated by peeling off a 1-μm-thick image-inversion photoresist layer (AZ-5214E), which itself was patterned by photolithography. The catalyst was deposited over the entire surface of the silicon wafer. The areas where the catalyst was deposited on the photoresist were then removed by soaking in an acetone bath for 5 min, with gentle sonication. The catalyst film thickness was measured during deposition using a quartz crystal monitor and was subsequently confirmed by Rutherford backscatter spectrometry (RBS).

The silicon wafer coated with the Fe/Al ₂ O ₃ patterned film was introduced into a single-zone atmospheric pressure quartz tubular furnace (Lindberg), having an inner diameter of 22 mm on the 30 cm long heating plate. The oven was then brought to the set temperature of 700°C in 30 minutes and then maintained for an additional 15 minutes under 400 standard cm ³ / minute of Argon. A mixture of argon (Ar, 99.999%, Airgas), ethylene (C ₂ H ₄ , 99.5%, Airgas) and hydrogen (H ₂ , 99.999%, BOC) under a flow of 100/500 /200 cm ³ standard / minute of C ₂ H ₄ /H ₂ /Ar was then introduced into the tubular furnace, in order to induce the development of carbon nanotubes. This flow was maintained for 1 minute to allow the growth of the carbon nanotubes.

The H ₂ and C ₂ H ₄ flows were then interrupted and a flow of 400 standard cm ³ /min of Argon was maintained for a further 10 minutes in order to displace the gaseous reactants from the tube furnace, before being reduced to a slight flow while the oven cools to a temperature below 100°C.

A layer of carbon nanotubes mainly oriented perpendicular to the substrate, i.e. a layer of VACNT, approximately 5 µm thick was obtained.

Example 3 : Preparation of a current collector according to the invention

The supported VACNT layers previously obtained and as developed in Example 1 and in Example 2, were coated with a copolymer of butadiene and styrene (known under the acronym SBR, from English Styrene-Butadiene Rubber ) by dip coating. To do this, a toluene solution comprising 20 mg of SBR per mL was prepared. The VACNT layers, previously obtained, were dipped in this solution with a dipping speed of 10 mm/s, then remained immersed in this solution for 10 seconds before being removed at a speed of 10 mm/s .

In order to evaluate the influence of the polymer matrix/C volume ratio, abbreviated below in the examples, SBR/C volume ratio, current collectors according to the invention were developed by carrying out several cycles, of soaking-immersion- removal, as indicated previously, in the toluene solution comprising 20 mg of SBR per mL.

In order to develop a current collector according to the invention comprising 4.5 mg of SBR per cm², a toluene solution comprising 100 mg of SBR per mL was prepared, then was pipetted onto a layer of VACNT supported such that 'elaborated in example 1.

Current collectors according to the invention produced from supported VACNT layers as synthesized in Example 1 and comprising between 0.15 mg of SBR per cm² and 4.5 mg of SBR per cm² were thus obtained. The properties of these current collectors were compared in particular by impedance spectroscopy, to those of supported VACNT layers as developed in Example 1 without polymeric coating, to those of the aluminum substrate and to those of the current collector. commercial NPC-055D Korea JCC supplied by the Samwha company.

Example 4 : Evaluation of current collectors according to the invention

4.1: in Swagelok™ type supercapacitor cells comprising wet electrodes based on activated carbon

In a mortar, 85% by weight of activated carbon (ie activated carbon (hereinafter CA) serving as active material), 10% by weight of polyvinylidene fluoride used as a binder (Kynar 3103) and 5% by weight of carbon black (Timcal ™) were mixed in N-Methyl-2-pyrrolidone abbreviated hereinafter NMP. The viscous solution obtained was then deposited by doctor blade coating at a thickness of 200 μm, on a current collector according to the invention as developed in Example 3 comprising on average 0, 23 mg SBR / cm², and for comparison, on an aluminum substrate, and on the commercial current collector. After drying in an oven, current collector + electrode discs were cut and assembled, in a glove box, with a separator (Celgard EPP 1208) impregnated with an ACN NEt4BF4 1M electrolyte (ABCR) as indicated in , so as to form a Swagelok™ type supercapacitor cell.

The impedance spectroscopy measurements were carried out in potentiostatic mode, with a constant voltage fixed at 0.02V and a frequency sweep between 400 kHz and 100 mHz. The Equivalent Series Resistance (commonly abbreviated ESR) was evaluated from measurements carried out using impedance spectroscopy and presented below in Table 1.

Current collector used Equivalent Series Resistance [Ω.cm²] Aluminum substrate 0.37 Current collector according to the invention comprising on average 0.23 mg of SBR per cm² 0.80 Commercial Current Collector NPC-055D Korea JCC (Samwha) 1.29

4.2: in Swagelok™ type supercapacitor cells comprising self-supporting electrodes

95% by weight of reference CA YP80F (Kuraray), 5% by weight of an aqueous solution comprising 60% polytetrafluoroethylene (PTFE) (Sigma Aldrich) were mixed in ethanol, under magnetic stirring and heating. The paste obtained was then flattened until reaching a thickness of approximately 150 μm, then discs were cut from the films obtained and dried in an oven. The self-supported electrodes, also called “dry” electrodes in English, thus obtained were then assembled, in a glove box, with a substrate serving as a current collector, a separator (Celgard EPP 1208) impregnated with an electrolyte ACN NEt4BF4 1M (ABCR) as indicated in , so as to form a Swagelok™ type supercapacitor cell.

For comparison, the Swagelok™ type supercapacitor cell was produced with different substrates, serving as current collectors, namely, an aluminum substrate, a current collector according to the invention as developed in the example 3 comprising on average 0.23 mg SBR / cm², and the aforementioned commercial current collector. The Equivalent Series Resistance (ESR) was evaluated from measurements carried out by impedance spectroscopy and presented below in table 2.

Current collector used Equivalent Series Resistance [Ω.cm²] Aluminum substrate 0.61 Current collector according to the invention comprising on average 0.23 mg of SBR per cm² 0.85 Commercial Current Collector NPC-055D Korea JCC (Samwha) 1.35

4.3: in a half-cell battery cell of the “coin cells 2032” type

- production of a cathode layer in LiFePO ₄ on a substrate which can serve as a current collector

In a mortar, 75% by weight of LiFePO ₄ hereinafter LFP (Sigma Aldrich), 5% by weight of polyvinylidene fluoride (PVdF) used as a binder (Kynar 1810) and 20% by weight of carbon black (Norit) were mixed in N-Methyl-2-pyrrolidone, known under the acronym NMP. The viscous solution obtained was then deposited by doctor blade coating at a thickness of 100 μm, on a current collector according to the invention as developed in Example 3 comprising on average 0, 23 mg SBR / cm², and for comparison, on an aluminum substrate in order to obtain a cathode layer. After drying in an oven, current collector + electrode discs were cut then assembled, in a glove box, with a separator (Celgard 3501) impregnated with an electrolytic solution of LiPF ₆ at 1M in a mixture of carbon dioxide. ethyl (hereinafter EC) and diethyl carbonate (hereinafter DEC) of EC/DEC ratio (1:1) (Sigma Aldrich), and a lithium metal disk, as indicated in , so as to form half a battery cell.

The impedance spectroscopy measurements were carried out in potentiostatic mode, with a constant voltage fixed at 0V and a frequency sweep between 10 kHz and 100 mHz. The Equivalent Series Resistance (ESR) was evaluated from measurements carried out by impedance spectroscopy and presented below in table 3.

Current collector used Series Equivalent Resistance (Ω.cm²) Aluminum substrate 110 Current collector according to the invention comprising on average 0.23 mg of SBR per cm² 23

- production of a cathode layer in LiNi _0.8 Mn _0.1 Co _0.1 O ₂ on a substrate which can be used as a current collector

A coating of LiNi _0.8 Mn _0.1 Co _0.1 O ₂ hereinafter NMC811 was produced on a substrate which can be used as a current collector. In a mortar, 222.5 g of NMC811, 3.18 g of polyvinylidene fluoride (PVdF) used as a binder and 1.36 g of carbon black were mixed in 74.1 g of N-Methyl-2-pyrrolidone (NMP). The solution obtained has a solid fraction of 75.1% and a viscosity of 2910 mPa at 25 °C. This viscous solution was then deposited by doctor blade coating at a thickness of 100 μm, on a current collector according to the invention as developed in Example 3 comprising on average 0.23 mg SBR / cm², and for comparison, on an aluminum substrate in order to obtain a cathode layer. After drying in an oven, making it possible to eliminate the NMP, current collector + electrode discs were cut then assembled, in a glove box, with a separator (Celgard 3501) impregnated with 40 µL of an electrolytic solution of LiPF ₆ at 1M in a mixture of ethyl carbonate (hereinafter EC) and diethyl carbonate (hereinafter DEC) of EC/DEC ratio (1:1) (Sigma Aldrich), and a metallic lithium disk , as indicated in , so as to form half a battery cell.

The electrodes produced include 98% by weight of NMC811 as active material, 0.6% by weight of conductive carbon and 1.4% by weight of PVdF.

The electrodes produced were characterized by power pulse test and ohmic drop measurement under the same operating conditions.

4.4: Evaluation of the current collector according to the invention by impedance spectroscopy

Current collectors according to the invention comprising between 0.15 mg of SBR per cm² and 4.5 mg of SBR per cm² as developed in Example 3, layers of VACNT as developed in Example 1 without polymeric coating, an aluminum substrate and the commercial current collector NPC-055D Korea JCC (Samwha), were evaluated by impedance spectroscopy.

To do this, each of these substrates was introduced into an “open” cell device as presented in and assembled with a separator (Celgard 3501) impregnated with an EMITFSI 99.5% ionic liquid (Solvionic) as electrolyte, so as to form a substrate/separator/substrate structure.

The impedance spectroscopy measurements were carried out in potentiostatic mode, with a constant voltage fixed at 0.02V and a frequency sweep between 400 kHz and 100 mHz.

The Nyquist diagrams obtained with these different substrates are presented in ; they make it possible to evaluate the Equivalent Series Resistance (ESR) as well as the additional parallel resistance linked to the diffusion of ions as indicated in the publication by D. Larcher et al., “Energy storage in the world of transport” , Chemistry and transport, EDP Science (2014) Chapter 13. The Equivalent Series Resistance (ESR) was evaluated from measurements carried out in impedance spectroscopy and presented below in table 4 and represented below in as a function of the volume ratio SBR/C of the current collectors according to the invention, with regard to the commercial current collector NPC-055D Korea JCC (Samwha).

Substrate evaluated Commercial Current Collector NPC-055D Korea JCC (Samwha) Current collectors according to the invention comprising a VACNT layer supported and coated with SBR Mass of SBR [mg/cm²] - 0 0.15 0.32 0.43 1 1.25 1.95 4.5 SBR/carbon volume ratio [%] - 0 23 49 66 153 191 298 687 Equivalent Series Resistance [Ω.cm²] 4.4 2.5 2.7 3.9 4.3 5.7 5.9 6.7 81.0

The mechanical resistance of the different current collectors according to the invention was evaluated visually, as illustrated in , by finger scraping (to the left of the samples) and scratching with pliers (to the right of the samples). The current collectors according to the invention, in particular comprising an SBR/C volume ratio of 49% and 687%, have better mechanical resistance than a supported VACNT layer as developed in Example 1 or that a commercial current collector NPC-055D Korea JCC (Samwha).

The properties of the current collectors according to the invention are summarized in Table 5 below.

Substrate evaluated Equivalent Resistance Series ESR [Ω.cm²] VACNT layers as developed in Example 1 without polymeric coating 2.5 Current collectors according to the invention comprising between 0.15 mg of SBR per cm² and 0.43 mg of SBR per cm² as developed in Example 3 2.7 < ESR < 4.3 Commercial Current Collector NPC-055D Korea JCC (Samwha) 4.4 Current collectors according to the invention comprising more than 1 mg of SBR per cm² as developed in Example 3 > 5.7

Example 5 : Transfer of vertically aligned nanotubes from their growth substrate to another substrate

A sample of vertically aligned nanotubes (in the form of a mat with a thickness of approximately 30 μm) was produced in accordance with Example 1, on a stainless steel substrate instead of an aluminum substrate. The sample was then mechanically compressed against a copper current collector (12 µm thick) without surface coating, using a laboratory, stainless steel roller calender (TOB-JS-300), with a gap of 30 µm and a maximum pressure of 500 N/mm. At the calender outlet, the carbon nanotubes were transferred to the copper current collector: they were in the form of a VACNT mat on a copper substrate.

Claims (10)

Current collector (1) for an electrical energy storage system or electrical generation system comprising:

1. an electronic conductive substrate (2),
2. a non-electrically conductive polymer matrix (4), and
3. carbon nanotubes (3), said nanotubes comprising
   • a first so-called transfer end (31), making it possible to transfer the current to the substrate, this first end being fixed on the surface of said electronic conductive substrate (2) and electrically connected to the latter,
   • as well as a second end (32), opposite said first end, called collection end, capable of collecting the current from an external active material, in particular from an electrode.

so as to create on the surface of said electronically conductive substrate (2), a layer comprising a plurality of collection regions, which are electrically isolated from each other by intermediate zones of said non-electrically conductive polymer matrix, and where

• each collection region comprises a plurality of said carbon nanotubes, and
• all of the second ends of said carbon nanotubes of each collection region protrude beyond the surface of the electrically non-conductive polymer matrix.

Current collector according to claim 1, characterized in that said carbon nanotubes are aligned, and preferably substantially perpendicularly aligned with respect to the substrate, these nanotubes substantially perpendicularly aligned with respect to the substrate being called here "vertically aligned carbon nanotubes". Current collector according to claim 2 characterized, in top view, in that

1. the vertically aligned carbon nanotubes of the collection regions have an average intertube spacing of less than 100 nm, and/or
2. said collection regions have a circular shape and in that the smallest distance between the outer edges of said collection regions is greater than or equal to 1 µm, preferably greater than 10 µm.

Current collector, according to any one of the preceding claims, characterized in that said electronic conductive substrate is chosen from copper, aluminum, nickel, stainless steel, heavily doped silicon, carbon and composite materials comprising carbon and, preferably, from composite materials comprising carbon and a resin chosen from polyester, vinyl ester, epoxy, phenolic, polyimide, polyamide, polypropylene, polyetheretherketone resins or a mixture of one or more of these . Current collector, according to any one of the preceding claims, characterized in that said electronic conductive substrate is chosen from planar substrates, substrates in the form of a grid, substrates in the form of fibers and substrates in the form of felt. Current collector, according to any one of the preceding claims, characterized in that said vertically aligned carbon nanotubes, electrically connected to the surface of said electronically conductive substrate, have

1. a thickness less than 10 µm, preferably less than 1 µm and/or
2. a developed surface area greater than 100 m²/g, preferably greater than 250 m²/g.

Current collector, according to any one of the preceding claims, characterized in that the volume ratio of non-electrically conductive polymer matrix/carbon nanotubes is less than 300%, preferably less than 200%, and even more preferably less at 70%. Device for storing or generating electrical energy such as a battery, a supercapacitor or a fuel cell, characterized in that it comprises a current collector according to any one of claims 1 to 7. Method for manufacturing a current collector comprising an electronically conductive substrate, carbon nanotubes having one end fixed on the surface of said electronically conductive substrate, and a non-electrically conductive polymer matrix, said method comprising the following successive steps:

1. synthesizing, on the electronically conductive substrate, vertically aligned carbon nanotubes so as to form a mat, preferably by the chemical vapor deposition technique, or transferring aligned nanotubes synthesized on another substrate to said electronically conductive substrate;
2. deposit, by any appropriate means, preferably by a liquid phase deposition process, said non-electrically conductive polymer matrix, on said carbon nanotubes,

so as to create on the surface of said electronically conductive substrate, a layer comprising a plurality of collection regions, which are electrically isolated from each other by interposed zones of said electrically non-conductive polymer matrix, and where

• each collection region comprises a plurality of said carbon nanotubes, and
• all of the second ends of said carbon nanotubes of each collection region protrude beyond the surface of the electrically non-conductive polymer matrix.

Method of manufacturing a current collector comprising an electronically conductive substrate, carbon nanotubes having one end fixed on the surface of said electronically conductive substrate, and an electrically non-conductive polymer matrix, according to claim 9, characterized in that that the deposition of said non-electrically conductive polymer matrix, during step b) is carried out by a method chosen from coating, spraying, soaking-withdrawal, extrusion, infiltration in one or several stages, and infusion in one or more stages.