FR3007205A1 - METHOD FOR MANUFACTURING A CURRENT COLLECTOR FOR SECONDARY BATTERY - Google Patents

Abstract

This method of manufacturing a secondary battery current collector comprises the following steps: activation of a polymeric substrate by cold plasma treatment; - Formation of a current collector by depositing an aqueous suspension of carbon nanotubes on the surface of the substrate treated with the cold plasma.

Description

FIELD OF THE INVENTION The invention relates to a method for manufacturing a carbon nanotube current collector for a secondary battery. The fields of use of the present invention relate in particular to applications requiring a flexible battery, such as, for example, textiles. STATE OF THE PRIOR ART A secondary battery is a rechargeable battery which comprises a battery core consisting of two electrodes between which an electrolyte is inserted. This electrolyte is generally supported by an electrode separator. These elements can be protected and electrically isolated from the outside of the battery by a flexible or rigid housing.

By way of example, FIG. 1 illustrates a lithium-ion secondary battery (1) whose stack core comprises: a positive electrode (3) consisting of at least one lithium cation insertion material; an electrode separator (4); a negative electrode (5). The two positive (3) and negative (5) electrodes are respectively associated with the current collectors (2) and (6).

The battery core is completely covered by the package, or case (7). On the other hand, a part of the current collectors (2) and (6) remains visible, outside the packaging (7) so as to be able to electrically connect the battery. The methods of the prior art make it possible in particular to prepare metal current collectors (aluminum, copper, steel, nickel, etc.) whose electronic conductivity is compatible with the circulation of electrons in the operation of a secondary battery. However, the properties of these collectors, particularly those of aluminum, can be altered by corrosion. The Applicant has developed a method of manufacturing current collectors not only to eliminate corrosion problems, but also to improve the resistance of the collector resistance properties to the substrate on which the secondary battery rests. SUMMARY OF THE INVENTION The present invention relates to a method of manufacturing a carbon current collector, in particular for depositing said collector on flexible substrates. This current collector is resistant to corrosion phenomena which can generally alter the properties of metal collectors of the prior art. This current collector can be used in a secondary battery, and in particular a lithium-ion battery or an alkaline battery (zinc-nickel for example). More specifically, the present invention relates to a method of manufacturing a secondary battery current collector, comprising the following steps: activation of a polymeric substrate by cold plasma treatment; forming a current collector by depositing an aqueous suspension of carbon nanotubes (CNTs) on the surface of the substrate treated with the cold plasma; optionally, drying the deposit of carbon nanotubes.

The cold plasma treatment is advantageously a corona treatment, that is to say the application of an electric discharge to the polymeric substrate at high frequency. It is advantageously carried out under ambient atmosphere, that is to say under air.

The power of the cold plasma treatment is advantageously between 10 and 600 watts / min / m 2, more advantageously still between 60 and 100 watts / min / m 2.

This plasma treatment notably makes it possible to improve the surface energy of the substrate and therefore its wettability. This treatment thus improves the adhesion / adhesion of the current collector to the substrate.

The cold plasma surface treatment is generally located on the part of the substrate to be covered by the current collector. It improves the bond between the treated surface and the deposited current collector. Indeed, the aqueous suspension of CNT adheres less strongly to an untreated surface.

In order to better define the parts of the substrate treated by cold plasma, a particular embodiment of the invention consists in placing a mask on the substrate, before the plasma treatment. This mask thus makes it possible to create a particular pattern for the current collector.

The masking of at least a portion of the surface of the substrate can in particular be carried out using adhesives so as to obtain a good definition of the edges. The substrate is of polymeric type. It has a thickness advantageously less than 150 micrometers, and more advantageously between 20 and 100 micrometers. It may especially be at least one material selected from the group consisting of the following compounds: polyacrylates (AA); acrylonitrile-butadiene-styrene (ABS); ethylene vinyl alcohol (E / VAL); fluoroplastics (PTFE), (FEP, PFA, CTFE); impact polystyrene (HIPS: high impact polystyrene); melamine formaldehyde (MF); liquid crystal polymers (LCP); polyacetal (POM); acrylo nitrile (PAN); phenol-formaldehyde plastic (PF); polyamide (PA); polyamide-imide (PAI); polyaryl ether ketone (PAEK) polyether ether ketone (PEEK); cis 1,4-polybutadiene (PBD); trans 1,4-polybutadiene (PBD); poly 1-butene (PB); polybutylene terephthalate (PBT); polycaprolactam; polycarbonate (PC); polycarbonate / acrylonitrile butadiene styrene (PC / ABS); poly 2,6-dimethyl-1,4-phenylene ether (PPE); polydicyclopentadiene (PDCP); polyester (PL); polyether ether ketone (PEEK); polyetherimide (PEI); polyethylene (PE, LDPE, MDPE, HDPE, UHDPE); polyethylenechlorinates (PEC); poly (ethylene glycol) (PEG); polyethylene hexamethylene dicarbamate (HDPE); polyethylene oxide (PEO); polyethersulfone (PES); polyethylene sulphide (PES); polyethylene terephthalate (PET); phenolics (PF); poly hexamethylene adipamide (PHMA); poly hexamethylene sebacamide (PHMS); polyhydroxyethyl methacrylate (HEMA); polyimide (PI such as KAPTON); polyisobutylene (PM); polyketone (PK); polylactic acid (PLA); poly methyl methacrylate (PMMA); poly methyl pentene (PMP); poly m-methyl styrene (PMMS); poly p-methyl styrene (PPMS); polyoxymethylene (POM); poly pentamethylene hexamethylene dicarbamate (PPHD); poly-methylenylene; isophthalamide (PMIA); polyphenylene oxide (PPO); poly p-phenylene sulphide (PPS); poly p-phenylene terephthalamide (PPTA); polyphthalamide (PTA); polypropylene (PP); poly propylene oxide (PPDX); poly styrene (PS); polysulfone (PSU); poly tetrafluoroethylene (PTFE); poly (trimethylene terephthalate) (PTT); polyurethane (PU); polyvinyl butyral (PVB); polyvinyl chloride (PVC); polyvinylidene chloride (PVDC); polyvinylidene fluoride (PVDF); poly vinyl methyl ether (PVME); poly (vinyl pyrrolidone) (PVP) silicone (SI); styrene-acrylonitrile resin (SAN); thermoplastic elastomers (TPE); thermoplastic polymers (TP); and urea-formaldehyde (UF). It is advantageously a flexible substrate. The current collector thus obtained advantageously has flexibility properties. According to a particular embodiment, all the constituents of the secondary battery containing this current collector in CNT have mechanical flexibility properties.

By flexible means a material having the property to resume, partially or preferably completely, its shape after being compressed, twisted or stretched. The thickness of the layer of carbon nanotubes (CNT) deposited is advantageously between 1 and 50 microns, more advantageously between 10 and 20. Preferably, the aqueous suspension of carbon nanotubes comprises between 1 and 30% by weight of nanotubes of carbon.

It is advantageously deposited on the substrate by spraying or printing (screen printing or inkjet). For example, the deposition of the CNT suspension can be achieved by means of a spraying equipment, the fineness of the ejection cone is controllable.

The spraying conditions are typically as follows: pressure: 1 to 3 bars; - size of the nozzle: 500 to 1200 micrometers.

The aqueous suspension of CNT may comprise at least one additive that may especially be chosen from the group comprising dispersants and nanoscale electronic conductors, such as carbon black. Among the dispersants, a conductive polymer, for example of the PEDOT-PSS or polyaniline type, may be added in proportions of less than 10% by weight. In addition to its conductive appearance, the polymer also allows good dispersion of CNTs. The aqueous suspension of NTC may in particular be GRAPHISTRENGTH® C Ml-20 marketed by Arkema, and comprising 20% by weight of MWNT (multi-walled carbon nanotubes). The CNTs used are electrical conductors or semiconductors. They generally have a conductivity of between 1 and 100 S / cm.

As already indicated, after the deposition of the aqueous suspension of CNTs, the process may also comprise a step of drying the carbon nanotubes deposited on the substrate. This drying is advantageously carried out at a temperature of between 60 and 120 ° C.

The drying time is advantageously between 10 and 60 minutes. According to a particular embodiment, the steps of depositing the CNT suspension and optionally drying it are repeated to adjust the thickness of the current collector.

The present invention also relates to the current collector obtained according to the method described above, but also to its use in a secondary battery, in particular a lithium-ion battery.

This current collector comprises a substrate associated with a layer of carbon nanotubes. It is advantageously flexible. On the other hand, the present invention also relates to a secondary battery, advantageously a lithium-ion battery, comprising the current collector described above, as well as its manufacturing method. This secondary battery comprises at least one battery core.

Its manufacturing process comprises the following steps: activation of a polymeric substrate by cold plasma treatment; forming a first current collector by depositing an aqueous suspension of carbon nanotubes on the surface of the polymeric substrate treated with the cold plasma; optionally, drying the aqueous suspension of deposited carbon nanotubes; forming a first electrode on the first current collector, advantageously by depositing an electrode ink, in particular by printing; forming an electrode separator on the first electrode; forming a second electrode of opposite sign to the first electrode, on the electrode separator, advantageously by deposition of an electrode ink, in particular by printing; forming a second current collector on the second electrode, preferably carbon nanotubes. According to a particular embodiment, a mask may be positioned on the substrate, prior to the cold plasma treatment. This mask thus makes it possible to create a particular pattern for the current collector, that is to say, to define the zone 20 of attachment for the deposition of NTC. According to another particular embodiment, a mask may be positioned on the current collector, consisting of NTC, prior to the deposition of the first electrode. Advantageously, this mask covers a part of the current collector, so that the first electrode is not deposited on the entire current collector in NTC. A mask may be used for the deposition of each element of the secondary battery, so as to obtain a device in which part of the current collectors 30 remains apparent to form the electrical connections. When the battery is lithium-ion type, the positive-sign electrode is a lithiated electrode. On the other hand, in a zinc-nickel alkaline secondary battery, the positive electrode is based on zinc whereas the negative electrode is based on nickel. The first and / or second electrodes are advantageously deposited by printing an ink containing an electrode material.

The materials used to prepare this secondary battery are those commonly used by those skilled in the art. According to the embodiment used, the electrode materials can be deposited on the current collectors by coating, screen printing, inkjet, or spraying. The current collector in NTC deposited according to the method - object of the invention has surface properties compatible with the subsequent printing of a positive or negative electrode ink. In the secondary battery according to the invention, the at least one stack core is advantageously a stack of a first electrode, an electrode separator, and a second electrode of opposite sign to the first.

When it comprises a plurality of stack cores, they are advantageously deposited so as to form a stack ("stack"). In addition, and advantageously, each of the electrodes of the cell or cores is associated with a current collector. The current collector is in contact with the face of the electrode opposite to the electrode separator. It can thus make it possible to ensure the electrical contact with the outside of the battery. The deposition of the electrochemical core can be achieved by successive deposition of the different layers according to methods forming part of the knowledge of those skilled in the art. Thus, according to a particular embodiment, in the process according to the invention, the cell core can be produced according to the following steps: depositing a first current collector in NTC; depositing a first electrode, advantageously a negative electrode; depositing an electrode separator; depositing a second electrode of opposite sign to the first electrode; depositing a second current collector, advantageously by spraying a suspension of CNTs.

Advantageously, the current separator covers the entirety of the first electrode and partially the first current collector. Preferably, it also covers part of the substrate.

The negative electrode may be printed from an ink of negative electrode material. It is advantageously printed by screen printing through a screen (stencil) in a specific pattern. The thickness of the layer thus printed depends on the rheology of the ink, the thickness of the stencil and the pressure applied to the screen-printing doctor. The deposit is then dried, preferably between 60 and 120 ° C, for a time depending on the dry extract of the ink, as well as the thickness of the layer.

The dried ink can then be densified by calendering to reduce the contact resistances of the electronic conduction network and to adjust the final porosity. For example, in the case of a lithium-ion battery, the negative electrode may in particular be made from graphite or titanate material Li4Ti5O12 in the case of power electrodes. As regards the electrode separator, it may be composed of a microporous polymer or composite separator impregnated with organic electrolyte allowing the displacement of the lithium ion (case of a lithium-ion battery) of the positive electrode. to the negative electrode and vice versa (case of charging or discharging) thus generating the current. For example, a separator based on PVdF-HFP (polyvinylidene fluoride - cohexafluoropropene) can be printed from an ink according to the technique described above, directly on the first electrode. After deposition, the separator ink is advantageously dried at 60 to 120 ° C. The separator thus obtained may be porous or dense depending on the formulation used. It can then be soaked with electrolyte.

The electrolyte is generally a mixture of organic solvents, such as carbonates, in which an alkali metal salt is added. In a lithium-ion battery, this salt may especially be a lithium salt, for example LiPF6 or LiTFSI (lithium bis (trifluoromethanesulfonyl) imide). As far as possible, this mixture is free of traces of water or oxygen. The lithiated positive electrode of a lithium-ion battery consists of at least one lithium cation insertion material, for example LiFePO4 (lithium iron phosphate), or transition metal oxides (lamellar materials: oxide lithiated cobalt, LiCoO2 LiNiO 33Mno 33C00 3302 ...). The insertion material constituting the positive electrode can be deposited on the electrode separator, or on a current collector, by various deposition techniques such as coating, screen printing, inkjet or sputtering.

For example, an ink, in particular based on lithium iron phosphate (lithium-ion battery), can be printed directly on the electrode separator. In addition, advantageously, the positive electrode ink is based on a solvent that does not make it possible to solubilize the electrode separator, and does not require further densification. The positive electrode inks are preferably aqueous inks comprising a polymeric binder of polyacrylic acid type. The second current collector may result from sputtering, on the second electrode, a suspension of carbon nanotubes or metal particles. The secondary battery thus formed can then be encapsulated. This secondary battery advantageously has flexibility properties. The method - object of the invention, can also be implemented so as to manufacture several current collectors, and therefore several secondary batteries, in parallel on the same substrate. These batteries can then be connected together or disconnected by cutting the substrate. Advantageously, the secondary battery can have the following advantages: interconnection of systems to be fed via a common substrate; - versatility of the materials used (substrate, coating) in terms of properties; - flexibility and fineness of the finished product; - low cost process.

The invention and the advantages thereof will appear more clearly from the following figures and examples given to illustrate the invention and not in a limiting manner. DESCRIPTION OF THE FIGURES FIG. 1 illustrates a conventional secondary battery. EXAMPLES OF THE INVENTION A current collector was prepared according to the following method: A PET substrate (polyethylene terephthalate) of 140 micrometers in thickness and having an initial surface energy of 40mN / m, is treated by a process Corona type cold plasma / 10-50 kV) to increase its surface energy to 80mN / m.

A suspension of NTC (GRAPHISTRENGTH® C M1-20 sold by Arkema, and comprising 20% by weight of multi-walled carbon nanotubes) is then deposited by spraying on the substrate, and then dried at 80 ° C. These deposition and drying steps are repeated in order to obtain a layer whose thickness is of the order of 10 microns. Increasing the surface energy of the PET substrate allows the aqueous NTC slurry to spread properly over and adhere to the polymer. The resulting nanotube layer is flexible. It adheres to the substrate and has an electronic conductivity of the order of 105 S / m, which is compatible with the current collection application for a lithium-ion battery electrode.

By way of comparison, Table 1 presents the electronic conductivities of aluminum, copper and nanotubes. Materials Electrical Conductivity in S / m Copper 59.6x106 Aluminum 37.7x106 NTC (MWNT) 105 Table 1: Electrical Conductivity of Materials for Current Collection (MWNT = Multilayered Carbon Nanotubes)

Claims (13)

REVENDICATIONS1. A method of manufacturing a current collector for a secondary battery, comprising the following steps: activation of a polymeric substrate by cold plasma treatment; - Formation of a current collector by depositing an aqueous suspension of carbon nanotubes on the surface of the substrate treated with the cold plasma. 2. A method of manufacturing a current collector for secondary battery according to claim 1, characterized in that the cold plasma treatment is a corona treatment. 3. A method of manufacturing a secondary battery current collector according to claim 1 or 2, characterized in that the power of the cold plasma treatment is between 10 and 600 watts / min / m2. 4. A method of manufacturing a current collector for secondary battery according to one of the preceding claims, characterized in that the substrate is in the form of a sheet of at least one material selected from the group consisting of the following compounds : polyacrylates; acrylonitrile-butadiene-styrene; ethylene vinyl alcohol; fluoroplastics; polystyrene impact; melamine formaldehyde; liquid crystal polymers; polyacetal; acrylo nitrile; phenol-formaldehyde plastic; polyamide; polyamide-imide; polyaryl ether ketone polyether ether ketone; cis 1,4-polybutadiene; trans 1,4-polybutadiene; poly 1-butene; polybutylene terephthalate; polycaprolactam; polycarbonate; polycarbonate / acrylonitrile butadiene styrene; poly 2,6-dimethyl-1,4-phenylene ether; polydicyclopentadiene; polyester; polyether ether ketone; polyetherimide; polyethylene; polyethylenechlorinates; poly (ethylene glycol); polyethylene hexamethylene dicarbamate; polyethylene oxide; polyethersulfone; polyethylene sulphide; polyethylene terephthalate; phenolics; poly hexamethylene adipamide; poly hexamethylene sebacamide; polyhydroxyethyl methacrylate; poly imide; polyisobutylene; polyketone; polylactic acid; poly methyl methacrylate; poly methyl pentene; poly m-methyl styrene; poly p-methyl styrene; polyoxymethylene; poly pentamethylene hexamethylene dicarbamate; poly m-phenylene; isophthalamide; polyphenylene oxide; poly p-phenylene sulphide; poly p-phenylene terephthalamide; polyphthalamide; polypropylene; poly propylene oxide; poly styrene; polysulfone; polytetrafluoroethylene; poly (trimethylene terephthalate); polyurethane; polyvinyl butyral; polyvinyl chloride; polyvinylidene chloride; polyvinylidene fluoride; poly vinyl methyl ether; poly (vinyl pyrrolidone) silicone; styrene-acrylonitrile resin; thermoplastic elastomers; thermoplastic polymers; and urea-formaldehyde. 5. A method of manufacturing a secondary battery current collector according to one of the preceding claims, characterized in that the aqueous suspension of carbon nanotubes comprises between 1 and 30% by weight of carbon nanotubes. 6. A method of manufacturing a current collector for secondary battery according to one of the preceding claims, characterized in that the aqueous suspension of carbon nanotubes is deposited by spraying or printing. 7. A method of manufacturing a current collector for secondary battery according to one of the preceding claims, characterized in that it further comprises a step of positioning a mask on the substrate before the cold plasma treatment. 8. current collector obtained by the process - object of one of claims 1 to 7, said current collector comprising a substrate associated with a layer of carbon nanotubes. Flexible current collector according to claim 8. 10. Use of the current collector according to claim 8 or 9 in a secondary battery, preferably lithium-ion type. 11. A method of manufacturing a secondary battery, according to the following steps: activation of a polymeric substrate by cold plasma treatment; forming a first current collector by depositing an aqueous suspension of carbon nanotubes on the polymeric substrate; optionally, drying the aqueous suspension of deposited carbon nanotubes; - forming a first electrode on the first current collector, preferably by printing; depositing an electrode separator on the first electrode; depositing a second electrode of sign opposite the first electrode, by depositing on the electrode separator, advantageously by printing; depositing a second current collector on the second electrode, advantageously made of carbon nanotubes. 12. A method of manufacturing a secondary battery according to claim 11, characterized in that it further comprises a step of positioning a mask on the substrate prior to the cold plasma treatment. 13. A method of manufacturing a secondary battery according to one of claims 11 to 12, characterized in that it further comprises a step of positioning a mask on the current collector, consisting of the deposit of carbon nanotubes, prior to depositing the first electrode.