Porous current collector with junction obtained by thermal sealing of a hot-melt polymer to a dense electrical connection tab for a sealed electrochemical system.

Abstract

Porous current collector with a junction obtained by thermal sealing of a hot-melt polymer to a dense electrical connection tab for a sealed electrochemical system. The invention relates to a sealed electrochemical system, comprising: - a package (6); - an electrically conductive and porous substrate (2S, 3S), forming a current collector and supporting, on at least one of its principal faces, at least one continuous pattern of active material of an electrode (2I, 3I); the porous substrate preferably being carbon fiber-based; - at least one electrically conductive and dense tab (4, 5), bonded to the substrate by at least one electrically conductive junction (J) obtained by thermal sealing of an electrically conductive hot-melt polymer (7), the tab supporting on each of its principal faces at least one sealing tape sealed to the package to ensure its airtight closure. Figure for the abstract: Fig. 12

Description

Title of the invention: Porous current collector with junction obtained by thermal sealing of a hot-melt polymer to a dense electrical connection tab for a sealed electrochemical system. technical field

[0001] The present invention relates to the field of electrochemical systems comprising a package to ensure the sealing of the core against the outside.

[0002] More particularly, it may be metal-ion electrochemical generators, which operate according to the principle of insertion or disinsertion, or in other words intercalation-disintercalation, of metal ions in at least one electrode.

[0003] It relates more particularly to an electrochemical lithium or lithium-ion battery.

[0004] The invention relates in particular to the realization of the junction between a porous current collector, in particular based on carbon fibers, with a metallic output tab for a metal-ion electrochemical accumulator.

[0005] Although described with reference to a Lithium-ion battery, the invention applies to any metal-ion electrochemical battery, i.e. also sodium-ion, Magnesium-ion, Aluminium-ion batteries...or more generally to any electrochemical battery such as lithium-sulfur or lithium-air. Previous technique

[0006] As schematically illustrated in figures 1 and 2, a lithium-ion battery or accumulator usually comprises at least one electrochemical cell consisting of an electrolyte constituent 1 between a positive electrode or cathode 2 and a negative electrode or anode 3, a current collector 4 connected to the cathode 2, a current collector 5 connected to the anode 3 and finally, a package 6 arranged to contain the electrochemical cell with sealing while being traversed by a part of the current collectors 4, 5.

[0007] The architecture of conventional lithium-ion batteries comprises an anode, a cathode, and an electrolyte. Several types of conventional architectural geometry are known:

[0008] - a cylindrical geometry as disclosed in the US patent application 2006 / 0121348,

[0009] - a prismatic geometry as disclosed in US patents 7348098, US 7338733;

[0010] - a stacked geometry as disclosed in the US patent applications 2008 / 060189, US 2008 / 0057392, and US patent 7335448.

[0011] The electrolyte component 1 may be in solid, liquid, or gel form. In the latter form, the component may comprise a polymer, ceramic, or microporous composite separator impregnated with organic or ionic liquid electrolyte(s) that allows the movement of lithium ions from the cathode to the anode for charging and vice versa for discharging, thereby generating the current. The electrolyte is generally a mixture of organic solvents, for example, carbonates, to which a lithium salt, typically LiPF6, is added.

[0012] The positive electrode or cathode 2 is made of lithium cation insertion materials which are generally composite, such as lithium iron phosphate LiFePO4, lithium cobalt oxide LiCoO2, lithium manganese oxide, possibly substituted, LiMn2O4, or transition metal oxides, such as lamellar materials, for example, a material based on LiN1xMn1xCoO2 with x+y+z = 1, such as LiN1xMn1xCo0.33O2 more commonly called NMC111, LiN1xMn1xCo0.2O2 more commonly called NMC622, or LiN1xMn1xCo0.1O2 more commonly called NMC811, or a nickel-cobalt-aluminum oxide-type material LiN1xCoO2 with x+y+z = 1, such as LiNi0.8Co0.15Al0.05O3 more commonly known as NCA.

[0013] The negative electrode or anode is very often made of carbon, graphite or Li4TiO5Oi2 (titanate material), possibly also silicon-based or lithium-based, or tin-based and their alloys or silicon-based composite.

[0014] The negative electrode, as well as the positive electrode, may also contain electronic conductive additives and polymer additives which give it mechanical properties and electrochemical performance suitable for the lithium-ion battery application or its implementation process.

[0015] The positive and negative electrodes are conventionally manufactured by coating, by continuously depositing an ink containing the active material, a solvent, a binder, and possibly an electrically conductive additive, onto the current collectors. The most commonly used technique is the slot die coating technique. In practice, a metal strip intended to form the current collector passes between a drive roller and a die in the form of a distribution slot, connected to a reservoir containing the ink. A layer of ink is thus formed on the metal strip in its central portion, the lateral strips (or edges) of the strip remaining bare. The solvent is then evaporated during in-line drying to form the electrode. A drying step is then carried out to evaporate the solvent residues. Finally, a calendering step is performed to decrease the porosity and increase the conductivity of the electrode.

[0016] The current collector 4 connected to the positive electrode is generally made of aluminum.

[0017] The current collector 5 connected to the negative electrode is generally made of copper, nickel-plated copper or aluminum.

[0018] More specifically, aluminum is used for the common current collectors of positive and negative Li4Ti50i2 titanate electrodes. Copper is used for the negative electrodes of graphite (Cgr), silicon (Si) or silicon composite (Si-C).

[0019] A lithium-ion battery or accumulator can obviously comprise a plurality of electrochemical cells which are stacked one on top of the other.

[0020] Traditionally, a Li-ion battery or accumulator uses a pair of materials at the anode and cathode enabling it to operate at a high voltage level, typically equal to 3.6 Volts.

[0021] Depending on the type of application targeted, the aim is to produce either a thin and flexible lithium-ion battery or a rigid battery: the packaging is then either flexible or rigid and in the latter case constitutes a kind of casing.

[0022] Rigid packaging (cases) is usually made from a metallic material, typically an aluminum alloy or stainless steel or from a rigid polymer such as acrylonitrile butadiene styrene (ABS).

[0023] Flexible packaging is usually made from a multilayer composite material consisting of an aluminum foil covered by one or more polymer films laminated by bonding. In most of these flexible packages, the polymer covering the aluminum is chosen from polyethylene (PE), polypropylene (PP), polyamide (PA), or may be in the form of an adhesive layer made of polyester-polyurethane. Showa Denko markets this type of composite material for use as battery packaging under the references NADR-0N25 / AL40 / CPP40 or ADR-0N25 / AL40 / CPP80.

[0024] Figure 3 illustrates this type of flexible packaging 6, which is arranged to insulate and seal the electrochemical cell C while being traversed by two strips or tabs 4, 5, commonly called "tabs," forming the poles and extending in the plane of the electrochemical cell. As shown in Figure 3, reinforcements of polyolefin-based polymer 60 can be provided to improve the heat sealing of the packaging 6 around the strips 4, 5.

[0025] The main advantage of flexible packaging is its lightness. Li-ion batteries with the highest energy densities therefore use flexible packaging. The major disadvantage of this flexible packaging is that its seal can deteriorate significantly over time due to the lack of chemical resistance of the seal. accomplished.

[0026] Rigid packaging is used when the applications are demanding where a long service life is required, for example with much higher pressures to withstand and a stricter level of sealing required, typically less than 108 mbar.l / s, or in highly demanding environments such as the aeronautical or space sector.

[0027] The main advantage of rigid packaging is therefore its high and sustained sealing over time due to the fact that the closure of the cases is achieved by welding, generally by laser welding.

[0028] To achieve optimal performance of Li-ion batteries, the electrochemical cell(s) must be sealed against atmospheric humidity. To guarantee this sealing at the external connections of the battery, manufacturers use rivets or, in the case of rigid packaging, laser welding.

[0029] In the case of flexible packaging, a sealing tape is used. It is generally based on a heat-fusible polymer around a metal outlet tab.

[0030] The tab can be sold as such and is sized according to the current flow, which is related to the total battery capacity. For cells with a capacity of less than 2 Ah, or more precisely when the current flow is less than 5 A, the tab has a width of 5 mm and a thickness of 0.5 mm. The sealing tape is laminated and bonded to the tab and is generally 10 mm long, 5 mm wide, and 0.3 mm thick. An example of such an aluminum tab is shown in [Fig. 4].

[0031] Thus, as shown in [Fig.3], reinforcements in polyolefin-based polymer 60 are provided to improve the heat sealing of the packaging 6 around the tabs 4, 5, and thus guarantee the sealing of the accumulator from the outside in (water, oxygen, nitrogen...) and vice versa (electrolyte, gases due to electrochemical reactions...).

[0032] Generally, the attached tabs 4, 5 are fixed to the substrates forming the current collectors of the electrodes by ultrasonic welding. The tabs are generally made of nickel when fixed to a copper collector and of aluminum when fixed to an aluminum collector.

[0033] An example of an aluminum tab 4 fixed to an aluminum collector is shown in [Fig. 4]. A hot-melt polymer tape 60 is laminated and bonded to each main face of the tab 4.

[0034] The tabs with ribbon being initially supplied in the form of a continuous rolled strip, the length is cut according to the need for the metal tab 4. In the case where the accumulator comprises a single electrochemical cell, the external connection can also be ensured directly by the current-collecting substrates of the electrodes which are cut in a tab shape.

[0035] In this case, a sealing tape, sold separately from the tab, is added to each main face of the current-collecting substrate, as shown in [Fig. 5]. This hot-melt polymer tape is generally 5 mm wide and 0.1 mm thick. Since the tape is initially supplied as a continuous rolled strip, the length is cut to the required length for the current-collecting substrate.

[0036] As can be seen in figures 4 and 5, the metal tab 4, typically made of aluminum, is either welded to the current collector 40 by weld points S, or is an integral part of the current collector 40.

[0037] In the literature, there are various attempts to substitute the metallic substrates of the current collectors with carbon substrates as well as solutions for bonding these substrates with metallic output tabs.

[0038] One can thus cite patent US8465871 B2 which discloses the implementation of a carbon felt substrate and a method for connecting a metal outlet tab to the substrate by riveting.

[0039] Patent EP2619832B1 in the name of the applicant discloses an electrode current collector for lithium battery, which is porous and is made of woven or non-woven carbon fibers.

[0040] Patent application WO2017 / 055705 in the name of the applicant also describes a method of fixing between a metal collector and a carbon felt which consists of impregnating the carbon felt with a mixture of a metal powder and making a weld between the metal collector and the impregnated carbon felt

[0041] The proposed solutions are not entirely satisfactory. Indeed, on the one hand, the resulting seal is not guaranteed, and on the other hand, these solutions do not actually allow for a sufficiently flexible accumulator assembly to allow a battery resulting from this assembly to conform to any object.

[0042] This is why the applicant proposed in patent EP3486971B1 a sewing attachment of a metal tab to the current collector based on a porous substrate preferably based on carbon fibers, using a carbon wire and / or a metal wire, and adding a hot-melt polymer tape on either side of the tab to ensure sealing, or welding a tab comprising a bonded laminated sealing tape.

[0043] Other solutions have already been proposed.

[0044] Patent applications CN202088602 and CN202308101 disclose the use of a thermofusible polymer based on polypropylene (PP) to ensure sealing at the point of an exiting tab of a current collector based on carbon fibers.

[0045] Patent application CN107910486 describes a method for stapling a carbon substrate to a metal tab.

[0046] Patent application CN109216703 describes a porous and flexible current collector for a Li-ion battery on which a thin layer of metal is deposited by vacuum technique. The current collector is based on a polyolefin PP or PE loaded with carbon black (CB) and carbon nanotubes (CNT) which is stretched to create porosity.

[0047] Patent application CN107591554 refers to a current collector in the form of a porous substrate which may be carbon fiber based for the all-solid battery, the solid electrolyte being polymerized in situ in the porous substrate.

[0048] Patent application EP3089241 describes a Zn / NiO-OH battery whose electrodes contain a carbon fibre-based current collector whose interconnection with an output tab is ensured by an adhesive paste based on Ni or carbon.

[0049] Patent CN 106113484 refers to the realization of welding by induced current between a metal and a composite material made of a thermoplastic with carbon fibers: the heat released by the induced current which heats the metal also melts the thermoplastic.

[0050] Patent EP2975681B1 describes a method for producing a current collector for a battery with a three-dimensional structure, composed of several layers of a non-woven substrate incorporating conductive fibers (metal filaments, carbon fibers, fibers of a conductive polymer or metallized polymer fibers), substrate to which conductive strips, generally metallic, are welded or fused by coating, electric welding, ultrasonic welding or thermal welding.

[0051] Not all of these solutions are completely satisfactory in terms of electrical contact performance.

[0052] There is therefore a need to improve lithium battery electrodes which are made from carbon-based current collector substrates, in particular to improve the electrical contact between a metal tab and a carbon-based current collector substrate, ensuring the sealing of the batteries while giving them flexible characteristics to ensure conformability to a battery which may result from an assembly of several of these batteries to be able to conform to any object.

[0053] The object of the invention is to meet at least part of this need(s). Description of the invention

[0054] To this end, the invention relates, in one of its aspects, to a sealed electrochemical system, comprising:

[0055] - a package;

[0056] - an electrically conductive and porous substrate, forming a current collector and supporting, on at least one of its main faces, at least one continuous pattern of active material of an electrode; the porous substrate preferably being carbon fiber based;

[0057] - at least one electrically conductive and dense strip, bonded to the substrate according at least one electrically conductive junction obtained by thermal sealing of an electrically conductive thermofusible polymer, the tab supporting on each of its main faces at least one sealing tape sealed to the packaging to guarantee the airtight closure of the latter.

[0058] By "porous" we mean here and within the framework of the invention, not airtight or impermeable to an electrolyte in particular through the edge of the substrate.

[0059] Conversely, by "dense" we mean here and within the scope of the invention, airtight or impermeable to an electrolyte of the electrochemical system. The mass density of the tab is then equal to the theoretical density of the bulk material constituting it.

[0060] By "electrically conductive", we mean here and within the framework of the invention, a conductivity greater than or equal to IS / cm.

[0061] The packaging of a system according to the invention can be rigid or flexible.

[0062] Preferably, the tab is metallic, more preferably made of aluminum, copper, or nickel. It preferably has a thickness between 6µm and 500µm. However, any other dense and sufficiently conductive material, such as certain sintered ceramics, can also be considered.

[0063] Preferably, the electrically conductive hot melt polymer is a compound comprising a polymer which on the one hand has the ability to soften under the effect of heat and to harden again upon cooling, and on the other hand comprises at least one electrically conductive charge, preferably carbon-based, so that it is electrically conductive.

[0064] Advantageously, the electrically conductive carbon-based filler is selected from carbon black, carbon fibers, carbon nanotubes, graphite, graphene and their derivatives, or a mixture of these carbon compounds. The filler may also be metal-based, preferably in the form of metal wires made of aluminum, copper, or nickel.

[0065] The electrically conductive charge loading rate of the hot-melt polymer is advantageously between 5 and 95% of the total mass of the compound, advantageously still between 15 and 55% by mass and even more advantageously between 25 and 45% of the total mass of the compound.

[0066] Preferably, the hot-melt polymer is a polypropylene (PP) type elastomer and its derivatives or polyethylene (PE) and its derivatives. It may also be a thermoplastic of the polyamide (PA) type or poly(ethylene terephthalate) (PET) or polyether ether ketone (PEEK) type and its derivatives or polysulfone (PS) and its derivatives or any other type of polymer that softens under the effect of heat and hardens again upon cooling.

[0067] An advantageous electrically conductive hot melt polymer is already commercially available in the form of granules (or "masterbatch" in English), for example under the reference "PP Black Masterbatch-MBB1231" in the name of the company CHUANGDA PLASTIC INDUSTRY CO., LIMITED, of polymer composition in PP loaded with carbon black at a mass percentage of 35% + / - 3%, or under the reference "CC00024002BG - 46-BK-80 BK PP MASTERBATCH" in the name of the company POLYONE, of polymer composition in PP loaded with carbon black at a mass percentage of 40%.

[0068] To fix the electrically conductive tab to the current collector based on a carbon substrate, granules of the hot-melt polymer can be used directly. Alternatively, a film can advantageously be applied prior to thermal sealing, for example using a heated press or by extrusion.

[0069] An electrically conductive hot-melt polymer film produced by hot pressing or extrusion advantageously has a thickness between 20 and 500 pm, and more advantageously between 50 and 200 pm.

[0070] The width of a sealing tape is preferably between 0.5 and 1 cm. The thickness of a sealing tape is preferably between 0.05 and 0.2 mm.

[0071] Preferably, the sealing tape is based on a hot-melt polymer. However, any other sealing material, such as an adhesive or glass, can also be considered, provided that it is compatible with the electrolyte of the electrochemical system.

[0072] According to an advantageous embodiment, the porous substrate is a carbon fiber-based substrate. Advantageously, it may be a non-woven substrate. A metallic foam, such as a nickel or copper foam, may also be considered as a porous substrate.

[0073] According to this advantageous embodiment, the carbon fiber-based substrate is a nonwoven made from carbon fibers with a diameter preferably between 2 and 20 pm, preferably with a diameter-to-length aspect ratio greater than 10, and preferably with a density between 1.8 and 2.2.

[0074] The carbon non-woven substrate preferably has a thickness between 100 and 250 pm, preferably a density between 30 and 1100 mg / cm3, preferably a porosity between 50 and 98%.

[0075] The inventors' choice to use a porous current collector based on carbon fibers provides the following numerous advantages:

[0076] - increased flexibility compared to conventional metal collectors in Li-ion batteries,

[0077] - similar flexibility for the positive and negative electrodes since one can use the same carbon fiber-based substrate, i.e., with the same thickness and mechanical properties,

[0078] - increased tear resistance compared to a current collector classic tallique

[0079] - an increase in mass energy density compared to a collector of conventional metallic current, the density of carbon being lower than that of copper or aluminum,

[0080] - very good electrochemical compatibility of carbon with most of the electrode insertion materials.

[0081] On the other hand, since the carbon fiber-based substrate is porous, by retaining external connections also in carbon fiber-based substrate in the form of a bare strip / tongue emerging from the current collector, the inventors were able to observe that the sealing of a Li-ion battery was not guaranteed.

[0082] Also, to improve this, the inventors considered using external metallic connections in the form of dense conductive tabs which are fixed to the carbon substrate by thermal sealing using an electrically conductive hot melt polymer, preferably in the form of at least one film, which is intercalated between the conductive tabs and the carbon substrate.

[0083] The links between metal tabs and carbon substrates proposed according to the state of the art, as described in patent application WO2017 / 055705 and patents US8465871B2, EP2619832B1, EP3486971B1 had shortcomings in terms of mechanical strength, electrical conductivity and flexibility at the junctions.

[0084] According to the invention, the electrical contact between the metal tab and the carbon fiber-based substrate is made over an entire surface or section by an electrically conductive hot-melt polymer and not only by points, as described in patent EP3486971B1, the contact resistance is reduced.

[0085] This is governed by the following equation 1:

[0086] [Equation 1]

[0087] i S' = 0 M — 5'

[0088] with R being the resistance (Q), q being the resistivity of the material (Q.cm), l the length current passage (cm) and S the current passage cross-section (cm2).

[0089] The current passage cross-section is all the more important when the currents are high, in particular when the applications in question require power (high charging or discharging currents).

[0090] The mechanical properties of the carbon-metal junction are also improved because, by softening under the effect of heat, the electrically conductive hot melt polymer will stick and therefore adhere to the metal tab and the carbon fiber-based substrate, and may even become impregnated in the carbon fibers, thus promoting mechanical adhesion.

[0091] As regards the actual manufacture of the electrode, the following procedure can be followed.

[0092] The preparation of the electrode ink (active insertion material) is carried out by mixing the constituents, namely the active material, the polymer binder, and the electronic conductor. The polymer binder, PVdF or a water-soluble polymer in the case of conventional Li-ion batteries, provides the mechanical properties of the electrodes while ensuring good contact between the electrolyte and the material grains. The electronic conductor, often carbon black, improves the electronic conductivity of the electrodes.

[0093] The electrode ink is then deposited on the carbon fiber current collector by a coating process which consists of pouring the ink onto the collector, thus forming a continuous electrode strip.

[0094] There are also other deposition techniques such as printing, spraying, dispensing, or others that consist of depositing the ink in the form of patterns on the collector. This forms continuous electrode patterns instead of a continuous strip.

[0095] The continuous electrode patterns are preferably produced by printing technique from prepared ink, more preferably by screen printing on current-collecting substrates based on carbon fibers.

[0096] Other printing techniques can be used such as flexography, gravure, inkjet, aerosol jet printing... An important advantage of printing techniques is the ability to produce patterns of various cross-sections (square, rectangular, round or more complex) and therefore allows for a certain degree of freedom in the design of the accumulator according to the invention.

[0097] Among printing techniques, screen printing has the advantage of being able to deposit a larger quantity of ink in a single pass, which makes it possible to obtain heavy paper weights and therefore high capacities. Similarly, production rates are high compared to coating, which is the conventional process used by battery manufacturers; typically, a printing speed of 20 to 30 m / min for rotary screen printing compared to a speed of 15 at 20 m / min for coating.

[0098] Once the continuous electrode pattern has been deposited, it is dried. To do this, the solvent is evaporated by passing the electrode through a continuous oven or statically through a ventilated oven. The electrodes are then calendered and cut according to the pattern required for the application.

[0099] The invention also relates to an electrochemical accumulator (A), in particular a metal-ion accumulator, made from a sealed electrochemical system described above, comprising a stack of the following elements:

[0100] - at least one negative electrode;

[0101] - at least one positive electrode;

[0102] - at least one electrically insulating separator film incorporating an electrolyte, arranged in contact with the negative electrode pattern and the positive electrode pattern;

[0103] - a package arranged to contain the negative and positive electrodes, and the film of separator, with sealing while being traversed by a first and a second pole of the accumulator each consisting of the conductive tab thermally sealed by an electrically conductive polymer to the porous substrate of the negative and positive electrodes, the sealing tapes of the negative and positive electrodes being thermally sealed to the packaging.

[0104] Regarding the implementation of the external connection, for each negative or positive electrode, a metal tab is attached to form the external connection or terminal of a battery. The attachment is achieved by thermal sealing using an electrically conductive, heat-fusible polymer, preferably in the form of a film.

[0105] As mentioned above, to ensure the battery is sealed, regardless of the pole configuration, a sealing tape is used. This tape can be either laminated and glued to the metal tab (the tab is sold with the sealing tape) or applied separately and fixed between the packaging and the tabs around them. In the case of an applied sealing tape, it is preferably made of polyethylene (PE) or polypropylene (PP).

[0106] The packaging for a battery according to the invention preferably consists of a single flexible pouch. It can be made from a multi-layer composite material consisting of an aluminum foil covered by one or more polymer films laminated by bonding. The polymer covering the aluminum can be chosen from polyethylene (PE), polypropylene (PP), polyamide (PA), or can be in the form of an adhesive layer made of polyester-polyurethane. Showa Denko markets this type of composite material for use as battery packaging under the references NADR-0N25 / AL40 / CPP40 or ADR-0N25 / AL40 / CPP80. Thus, the flexible pouch according to the invention is advantageously made from a multi-layered, aluminized, airtight film.

[0107] To seal the flexible pouch by heat sealing, three sides of the pouch can first be heat-sealed while leaving the fourth side open for activating the battery by filling it with electrolyte. Once this filling is complete, the fourth side is heat-sealed, with the metal tabs passing through the seal. The challenge of ensuring the packaging is airtight, given that carbon fiber-based electrical connections must protrude from it, then becomes clear.

[0108] The accumulator according to the invention can be a Li-ion accumulator, the electrode patterns being made of lithium insertion material.

[0109] The term “lithium-based insert material electrode” refers, in this context and within the scope of the invention, to an electrode pattern comprising at least one lithium insert material and at least one polymer binder. Optionally, the electrode pattern may also include an electronic conductor, for example, carbon nanofibers, carbon nanotubes, or carbon black.

[0110] By "lithium insertion material", in particular for positive electrode patterns, is meant here and within the scope of the invention, a material selected from the lithia oxides comprising manganese of spinel structure, the lithia oxides of lamellar structure and mixtures thereof, the lithia oxides with poly-anionic frameworks of formula LiMy(XOz)n with M representing an element selected from Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Si, B and Mo, X representing an element selected from P, Si, Ge, S and As, y, z and n being positive integers.

[0111] By "lithium insertion material", particularly for the negative electrode patterns, is also meant a material selected from: lithium or non-lithiumized titanium oxide, for example Li4Ti50i2 or TiO2, graphite, silicon, or silicon composite. More particularly, the material of the negative electrode patterns may be selected from carbon materials, non-lithiumized titanium oxides and their derivatives, and lithium-lithiumized titanium oxides such as Li4Ti50i2 and their derivatives, and a mixture thereof.

[0112] By "lithium derivative", we mean here and within the framework of the invention, compounds of formula Li(4.xi)MxiTi50i2 and Li4Ti(5 yi)NyiOi2, where xl and yl are respectively between 0 and 0.2 and M and N are respectively chemical elements chosen from Na, K, Mg, Nb, Al, Ni, Co, Zr, Cr, Mn, Fe, Cu, Zn, Si and Mo.

[0113] By "non-lithia derivative", we mean here and within the framework of the invention, Ti(5 yi)NyiOi2, with yl between 0 and 0.2 and N is a chemical element selected from Na, K, Mg, Nb, Al, Ni, Co, Zr, Cr, Mn, Fe, Cu, Zn, Si and Mo.

[0114] Preferably, the anodes are made of graphite and the cathodes of LiNixCoyMn(i_xy)O2 (NCM).

[0115] By "separator", we mean here and within the scope of the invention, an electrical insulator, An ionic conductor formed from at least one polymer material. The separator is preferably a single-layer or multi-layer microporous polymer film based on polyolefin (PP) and / or PE. Each separator film is cut according to the desired pattern by a mechanical or laser process.

[0116] The separator can be applied directly to the electrode patterns (positive or negative) by printing, preferably screen printing, from a polymer solution. According to this embodiment, the separator can be selected from the following polymers:

[0117] - polyvinylidene fluoride (PVdF) or derivatives, polyvinyl acetate (PVA), the polymethyl methacrylate (PMMA), polyoxyethylene (POE) or derivatives, polyethylene terephthalate (PET), polyacrylics or derivatives, polyolefins such as polypropylene, polyethylene, cellulose;

[0118] - copolymers of the PVdF-HFP (hexafluoropropylene), PVdF-POE, etc. type;

[0119] - conducting ionomers of conducting cations or crystalline polymers of cations;

[0120] - thermally or photosensitive polymers that crosslink under the action of heat or UV radiation,

[0121] - UV- or thermally polymerizable monomers, carrier or not of an ionic charge based on a lithium salt, such as PolyHIPE.

[0122] The polymer is dissolved in a solvent, or in a solvent / non-solvent mixture in the case of a phase inversion process.

[0123] The polymer solution is deposited onto the electrode patterns as a thin layer, and then the solvent is evaporated by passing the electrode through a continuous or static oven. Depending on the polymer and the processing method used, the thin layer of the electrolytic component can be porous, dense, or gelled in the presence of the electrolyte. The thickness of the polymer layer is preferably between 5 and 40 µm.

[0124] Other separators can be considered, such as composites made of a very thin polymer layer, on the order of 15 µm. The polymer used can be PET, or polyethylene terephthalate. This very thin polymer sheet can then be coated with alumina (Al₂O₃) and silica (SiO₂) ceramic grains. The separator marketed under the name SEPARION by EVONIK is a good example.

[0125] Separators based on polymers reinforced with glass fibers for mechanical properties can also be considered. These separators are nonwovens because the glass fibers are only randomly mixed together.

[0126] Finally, ceramic separators containing alumina can be considered, which has the advantage of having a retarding effect on runaway reaction. thermal.

[0127] The electrolyte according to the invention may be a liquid formed by a mixture of carbonate and at least one lithium salt. By "lithium salt," we preferably mean a salt selected from LiPF6, LiCl4, LiBF4, and LiAsF6.

[0128] Alternatively, the electrolyte may comprise one or more ionic liquids based on lithium ions, namely a salt consisting of lithium cations complexed with inorganic or organic anions, which has the property of being in a liquid state at room temperature. An ionic liquid, depending on the nature of the anion, may be hydrophilic or hydrophobic. Examples of ionic liquids include ionic liquids based on hydrophobic anions such as trifluoromethanesulfonate (CF3SO3), bis(trifluoromethanesulfonate imide [(CF3SO2)2N] and tris(trifluoromethanesulfonate) methide [(CF3SO2)3C].

[0129] Preferably, the surface area of ​​each negative electrode motif is greater than the surface area of ​​each positive electrode motif. This ensures that all metal ions from the positive insertion material, such as Li+ ions in a lithium battery, can migrate to the negative electrode and thus become intercalated into the structure. In addition to aligning the positive electrode motifs with those of the negative electrode, the surface area of ​​the negative electrode motifs can also be increased relative to that of the positive electrode motifs. This can be achieved by adding a strip of active material to each side of each negative electrode motif. Such an added strip typically has a width of 1 mm.

[0130] The invention also relates to a method for making a sealed electrochemical system comprising the following steps:

[0131] a / obtaining a continuous pattern of active electrode material on an electrically conductive and porous substrate forming a current collector;

[0132] b / making at least one electrically conductive junction between at least one electrically conductive and dense strip and the substrate, by thermal sealing using an electrically conductive hot-melt polymer,

[0133] c / production on each of the main faces of the tab, of at least one sealing tape intended for the airtight closure of the packaging,

[0134] d / sealing between sealing tape and packaging.

[0135] The advantages of the architecture of an accumulator or battery according to the invention compared to electrode architectures with a carbon current-collecting substrate according to the prior art are numerous, among which we can mention:

[0136] - improved sealing because the closure of the flexible packaging is made on a dense material of the battery electrodes, namely the implementation of carbon-metal junctions containing a sealing tape,

[0137] - a lower electrical contact resistance at the junction due to a higher contact area due to the bonding by an electrically conductive polymer between the metal tab and the carbon fiber-based substrate,

[0138] - a larger current passage cross-section to allow the battery to to support higher currents, for applications requiring power (high charge and discharge currents),

[0139] - the absence of a compromise to be found between mechanical resistance and contact surface because no holes are created as with riveting according to the state of the art.

[0140] Other advantages and features of the invention will become more apparent from the detailed description of examples of implementation of the invention given by way of illustration and not limitation with reference to the following figures. Brief description of the drawings

[0141] [Fig-1] [Fig.1] is a schematic exploded perspective view showing the different components of a lithium-ion battery.

[0142] [Fig.2] [Fig.2] is a front view showing a lithium-ion battery with its flexible packaging according to the state of the art.

[0143] [Fig.3] [Fig.3] is a perspective view of a lithium-ion battery with its flexible packaging according to the state of the art.

[0144] [Fig.4] [Fig.4] is a reproduction of a photographic view of an example of metal tab, as intended to be welded to a current collector of an electrode in order to form a lithium-ion battery pole according to the state of the art.

[0145] [Fig.5] [Fig.5] is a reproduction of a photographic view of the connection external current collection substrate of the positive electrode which is cut into a tab shape to form a lithium-ion battery pole according to the state of the art.

[0146] [Fig.6] [Fig.6] is a reproduction of a photographic view of a part positive electrode according to the invention comprising a carbon fiber-based substrate supporting on one of its main faces a pattern of positive lithium insertion material.

[0147] [Fig.7] [Fig.7] is a reproduction of a photographic view of a part negative electrode according to the invention comprising a carbon fiber-based substrate supporting on one of its main faces a pattern of negative lithium insertion material.

[0148] [Fig.8] Fig.8 illustrates in perspective view an example of implementation by a screen printing technique for electrode patterns on carbon fiber-based substrates.

[0149] [Fig.9] [Fig.9] is a schematic view showing a connection obtained by thermal sealing of a hot melt polymer between an electrical connection tab and a carbon-based electrode collector substrate.

[0150] [Fig. 10] [Fig. 10] is a photographic view of a connection like that of [Fig. 9],

[0151] [Fig. 11] [Fig. 11] reproduces [Fig.9] by also showing the integration of a sealing tape around the connecting tab.

[0152] [Fig. 12] [Fig. 12] is a reproduction of a photographic view of a part of a positive electrode according to the invention comprising a carbon fiber-based substrate supporting on one of its main faces a pattern of positive lithium insertion material and a metallic electrical connection tab linked to the substrate by a junction obtained by thermal sealing of a hot-melt polymer.

[0153] [Fig. 13] [Fig. 13] is a reproduction of a photographic view of a portion of a negative electrode according to the invention comprising a carbon fiber-based substrate supporting on one of its main faces a pattern of positive lithium insertion material and a metallic electrical connection tab linked to the substrate by a junction obtained by thermal sealing of a hot-melt polymer.

[0154] [Fig. 14] [Fig. 14] is a perspective view showing a step in the realization of a Li-ion battery according to the invention comprising a positive electrode according to [Fig.12] and a negative electrode according to [Fig.13].

[0155] [Fig. 15] [Fig. 15] is a perspective view showing the Li-ion accumulator according to [Fig. 14] once finalized. Detailed description

[0156] For the sake of clarity, the same references designating the same elements of a battery according to the prior art and of a battery according to the invention are used for all figures 1 to 15.

[0157] It is specified that the different elements according to the invention are represented solely for the sake of clarity and that they are not to scale.

[0158] Figures 1 to 5 have already been discussed in the preamble. They will therefore not be detailed below.

[0159] The invention is described below with reference to an example of an embodiment of a positive electrode 2 according to the invention and of a negative electrode 3 according to the invention.

[0160] The positive electrode 2 first includes a carbon fiber-based substrate 2S forming a current collector and supporting, on one of its main faces, a continuous pattern of positive metal ion insertion active material 21 ([Fig.6]).

[0161] The negative electrode 3 also includes a carbon fiber-based substrate 3S forming a current collector and supporting, on one of its main faces, a continuous pattern of negative metal ion insertion active material 31 ([Fig.7]).

[0162] By way of example, the carbon fibers from which a 2S or 3S substrate is made may have a diameter of about 7 pm and a density of 2. A 2S substrate or 3S based on these carbon fibers can thus have a thickness of 150 pm, a density of 628 mg / cm3 and a porosity of 69%.

[0163] For each of these electrodes 2, 3 the electrode pattern is obtained by carrying out the following four main steps 1 / to 4 / .

[0164] Step 1: Preparation of the electrode ink by mixing the constituents, namely the active material, the polymer binder, and the electronic conductor. The polymer binder, PVdF or a water-soluble polymer, provides the mechanical properties of the electrodes while ensuring good contact between the electrolyte and the material grains. The electronic conductor, often carbon black, improves the electronic conductivity of the electrodes.

[0165] Step 2 / : The electrode is implemented using a screen printing technique.

[0166] Figure 8 illustrates a screen-printing deposit. A bead of ink 30 obtained according to step 1 / is deposited directly onto the silkscreen mask 31 resting itself on a frame 32. The ink cord 30 is then pushed by a squeegee 33 at an adjustable speed 34.

[0167] The pressure applied, also adjustable, on the squeegee 33 allows the ink to pass through the mask 31 and to deposit the ink on the carbon fiber-based current collector substrate 2S, 3S, thus forming electrode patterns 35.

[0168] The pressure on the doctor blade 33 allows adjustment of the surface capacity setting when the patterns 35 are stencils, and allows the ink 30 to pass through the mesh of the grid when the patterns 35 need to be separated. A pattern 35 can be a simple geometric shape such as a square, rectangle, or circle, but can also be more complex (calligraphy, etc.). In screen printing, the surface capacity is set by the thickness of the mask 31 and by the size and shape of the mesh if the printing patterns 35 are obtained using a grid. This printing technique is not a "roll-to-roll" but a "reel-to-reel" printing technique, i.e., semi-continuous. It is carried out on a 2S or 3S printing substrate, in this case, the carbon non-woven substrate.

[0169] Step 3: Once the ink has been deposited on the carbon fiber, 2S, or 3S substrate, it is dried. The solvent is then evaporated by passing the electrode through a continuous oven or statically in a ventilated oven.

[0170] Step 4 / : The electrodes are then calendered and cut according to the pattern intended by the application.

[0171] In the illustrated example, the positive electrode 2 comprises as active material LiNi0.6Co0.2Mn0.2O2, designated by NCM622 and the negative electrode 3 is graphite-based.

[0172] Next, joints are made of a metal tab 4, 5 with the carbon fiber-based substrate 2S, 3S respectively of the positive electrode 2 and the negative electrode 3.

[0173] An example of a junction is shown in Figures 9 and 10: the electrically conductive hot-melt polymer 7 is intercalated between the porous carbon fiber-based current collector 2S and the metal tab 4.

[0174] In addition, a sealing tape 60 is used to ensure the airtight closure of the packaging on these dense tabs, rather than on porous carbon fiber tabs. The sealing tape 60 can either be laminated and bonded to the metal tab (tab sold with the sealing tape), or applied and fixed between the packaging and the tabs around them.

[0175] Fig. 11 represents the electrically conductive hot melt polymer 7 intercalated between the porous carbon fiber-based current collector 2S and the metal tab 4 with sealing tape 60.

[0176] In the illustrated example, to make these carbon-metal junctions, an aluminium strip with laminated-bonded sealing tape 60, 5 mm wide and 0.5 mm thick, is used for the positive electrode NCM 2 and a nickel strip with laminated-bonded sealing tape 5, 5 mm wide and 0.5 mm thick, is used for the negative graphite electrode 3.

[0177] These metal tabs 4, 5 are fixed to the carbon fiber 2S, 3S collecting substrate by means of an electrically conductive hot-melt polymer film 7 intercalated between each metal tab 4, 5 and the associated carbon fiber 2S, 3S collecting substrate.

[0178] The electrically conductive hot melt polymer film 7 chosen is of composition PP loaded with carbon black at a mass percentage of 40%, marketed under the reference "CC00024002BG - 46-BK-80 BK PP MASTERBATCH" of the company POLYONE.

[0179] The electrically conductive hot-melt polymer film is first produced from granules by hot pressing at 200°C under 0.5 MPa for 30 seconds. The resulting film thickness is 500 µm.

[0180] The heat seal is performed using a heat sealer, marketed under the reference "TP-701-B Heat Seal Tester" by Tester Sangyo Co. The temperature of the lower and upper jaws is set at 200°C. The heat seal is performed at a pressure of 0.5 MPa for 6 seconds.

[0181] The carbon-metal junctions J obtained by thermal sealing of the electrically conductive thermofusible polymer film 7 are shown respectively in [Fig. 12], for the positive electrode NCM 2 with its aluminum tab 4 and in [Fig. 13], for the negative graphite electrode 3 with its nickel tab 5.

[0182] Once the positive NCM 2 and negative graphite 3 electrodes according to the invention finished with their junctions J with metal tabs 4, 5 the accumulator A is made as usual by stacking the positive electrode 2, the negative electrode 3 and an electrically insulating separator of microporous polymer type 1 intercalated between the positive electrode 2 and the negative electrode 3 ([Fig. 14]).

[0183] A flexible packaging 6, sealed against electrolyte and air, of type NADR-0N25 / AL40 / CPP40 from the manufacturer Showa Denko, is arranged to contain the positive electrode 2 and negative electrode 3 and the microporous separator film while being traversed by the tabs 4, 5 forming the poles of the accumulator.

[0184] Finally, the flexible packaging 6 is closed. Three sides of the packaging are thus thermally sealed, and the fourth side is kept open to allow activation of the accumulator, which consists of filling the inside of the packaging container thus formed with electrolyte. After activation of the accumulator, this fourth side is also thermally sealed ([Fig. 15]).

[0185] The invention is not limited to the examples just described; in particular, features of the illustrated examples can be combined in unillustrated variants.

[0186] Other variants and improvements may be envisaged without departing from the scope of the invention.

Claims

Demands

1. A sealed electrochemical system comprising: - a package (6); - an electrically conductive and porous substrate (2S, 3S) forming a current collector and supporting, on at least one of its principal faces, at least one continuous pattern of active material of an electrode (21, 31); the porous substrate preferably being carbon fiber-based; - at least one electrically conductive and dense tab (4, 5) linked to the substrate by at least one electrically conductive junction (J) obtained by thermal sealing of an electrically conductive thermofusible polymer (7), the tab supporting on each of its principal faces at least one sealing tape sealed to the package to ensure the hermetic closure of the latter.

2. System according to any one of the preceding claims, the thickness of the tongue being between 6 and 500pm.

3. System according to any one of the preceding claims, the tab being metallic, preferably made of aluminium, copper or nickel.

4. System according to any one of the preceding claims, the electrically conductive hot melt polymer being a compound comprising a hot melt polymer comprising at least one electrically conductive charge preferably carbon-based.

5. System according to claim 4, the electrically conductive carbon-based charge being selected from carbon black, carbon fibers, carbon nanotubes, graphite, graphene and their derivatives, or a mixture of these carbon compounds, or being metal-based, preferably in the form of metal wires of aluminum, copper or nickel.

6. System according to claim 4 or 5, the rate of electrically conductive charge loading of the hot melt polymer being between 5 and 95% of the total mass of the compound, advantageously also between 15 and 55% by mass and even more advantageously between 25 and 45% of the total mass of the compound.

7. System according to any one of claims 4 to 6, the hot-melt polymer is a polypropylene (PP) and its derivatives or polyethylene (PE) and its derivatives type elastomer. It may also be a polyamide (PA) or polyethylene terephthalate (PET) type thermoplastic or polyether ether ketone (PEEK) and its derivatives or polysulfone (PS) and its derivatives

8. System according to any one of the preceding claims, the electrically conductive hot melt polymer being in the form of granules or a film advantageously implemented prior to thermal sealing.

9. System according to claim 8, the electrically conductive hot melt polymer film having a thickness of between 20 and 500 pm, advantageously between 50 and 200 pm.

10. System according to any one of the preceding claims, the porous substrate being a non-woven substrate based on carbon fibers.

11. System according to claim 10, the non-woven substrate being made from carbon fibers of diameter between 2 and 20 pm, preferably with a diameter-to-length aspect ratio greater than 10, and preferably with a density between 1.8 and 2.

2.

12. System according to claim 10 or 11, the non-woven substrate having a thickness between 100 and 250 pm, preferably a density between 30 and 1100 mg / cm3, preferably a porosity between 50 and 98%.

13. System according to any one of the preceding claims, the width of a sealing tape being between 0.5 and 1 cm, the thickness of a sealing tape preferably being between 0.05 and 0.2 mm.

14. An electrochemical accumulator (A), in particular a metal-ion accumulator, constituted from a sealed electrochemical system according to any one of the preceding claims, comprising a stack of the following elements: - at least one negative electrode; - at least one positive electrode; - at least one electrically insulating separator film incorporating an electrolyte, arranged in contact with the negative electrode pattern and the positive electrode pattern; - a package (6) arranged to contain the negative and positive electrodes, and the separator film, sealed while being traversed by a first and a second pole of the accumulator, each consisting of the conductive strip thermally sealed by an electrically conductive polymer to the porous substrate of the negative and positive electrodes, the sealing strips (60) of the negative and positive electrodes being thermally sealed to the packaging (6).

15. Method of making a sealed electrochemical system comprising the following steps: a / obtaining a continuous pattern of active electrode material on an electrically conductive and porous substrate forming a current collector; b / making at least one electrically conductive junction between at least one electrically conductive and dense strip and the substrate, by thermal sealing using an electrically conductive hot melt polymer; c / making at least one sealing tape on each of the main faces of the strip for the airtight closure of the packaging; d / sealing between the sealing tape and the packaging.

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