Electrode formulation for LI-ION BATTERY and electrode manufacturing process by low residence time extrusion

Abstract

The invention relates to an electrode formulation for a Li-ion battery. The invention also relates to a method for preparing electrodes using said formulation, by short residence time compounding / extrusion. The invention finally relates to an electrode obtained by this method as well as to Li-ion secondary batteries comprising at least one such electrode.

Description

Title of the invention: Electrode formulation for LI-ION BATTERY and method for manufacturing electrode by low residence time extrusion FIELD OF THE INVENTION

[0001] The present invention relates generally to the field of electrical energy storage in rechargeable secondary batteries of the Li-ion type. More specifically, the invention relates to an electrode formulation for a Li-ion battery. The invention also relates to a method for preparing electrodes using said formulation, by short residence time compounding / extrusion. The invention finally relates to an electrode obtained by this method as well as to Li-ion secondary batteries comprising at least one such electrode. TECHNICAL BACKGROUND

[0002] A Li-ion battery comprises at least one negative electrode or anode coupled to a copper current collector, one positive electrode or cathode coupled to an aluminum current collector, a separator, and an electrolyte. The electrolyte consists of a lithium salt, generally lithium hexafluorophosphate, mixed with a solvent which is a mixture of organic carbonates, chosen to optimize the transport and dissociation of ions. A high dielectric constant promotes the dissociation of ions, and therefore, the number of ions available in a given volume, while a low viscosity is favorable to ionic diffusion which plays an essential role, among other parameters, in the charging and discharging rates of the electrochemical system.

[0003] For their part, the electrodes generally comprise at least one current collector on which is deposited a composite material which is constituted by: a material called active because it has electrochemical activity with respect to lithium, a polymer which acts as a binder, plus one or more electronically conductive additives which are generally carbon black or acetylene black, and possibly a surfactant.

[0004] During charging, lithium is inserted into the active material of the negative electrode and its concentration is kept constant in the solvent by the deintercalation of an equivalent quantity of the active material of the positive electrode. Insertion into the negative electrode results in a reduction of the lithium and it is therefore necessary to supply, via an external circuit, the electrons to this electrode, coming from the positive electrode. During discharge, the reverse reactions take place.

[0005] It is known that substituting carbon black or acetylene black with carbon nanotubes (CNTs), or adding CNTs to such conductive additives, has many advantages: increased electrical conductivity, better integration around the particles of active material, good intrinsic mechanical properties, ability to form a better connected electrical network in the mass of the electrode and between the metal collector and the active material, good maintenance of the capacity during cycling in the composite electrode material, etc.

[0006] The introduction of CNTs into the formulations of the materials constituting the electrodes presents difficulties. Thus, when the dispersion of CNTs is carried out directly in liquid formulations (especially in organic solvent bases), there is a high viscosification of the dispersion and a low stability of such a dispersion when the mixture does not contain polymers or stabilizing agents. To overcome this drawback, ball mixers, grinders and high shear mixers are used.

[0007] To overcome these problems, the Applicant has proposed in document WO 2011 / 117530 a masterbatch in agglomerated solid form comprising from 15 to 40% by weight of CNTs, at least one solvent and from 1 to 40% by weight of at least one polymer binder. Furthermore, document EP 2 081 244 describes a liquid dispersion based on CNTs, a solvent and a binder, which is intended to be sprayed onto a layer of active electrode material.

[0008] These solutions are still imperfect, because they do not always make it possible to avoid the persistence of CNT aggregates in these compositions, so that a fraction of the CNTs is not used optimally to improve the electrical conductivity of the electrode obtained from these compositions.

[0009] Furthermore, document US 2011 / 171364 describes a paste based on CNT agglomerates mixed with a dispersant such as poly(vinyl pyrrolidone) or PVP, with an aqueous or organic solvent, and optionally with a binder. The method for manufacturing this paste comprises a step of grinding (or ultrasonication) of entangled clusters of CNTs, having an average diameter of approximately 100 μm. This step makes it possible to obtain CNT agglomerates having a size of less than 10 μm in at least one dimension, i.e. a degree of dispersion, on the Hegman scale, greater than 7. The grinding can be carried out before or after mixing the CNTs with the dispersant, the solvent, and the optional binder.

[0010] The solution proposed in this document has the disadvantage of using a manufacturing process comprising a grinding step, preferably by pulverization, which is likely to present risks of environmental pollution, or even health risks. In addition, the resulting paste has a viscosity of at least 5,000 cPs, which can lead to dispersion difficulties in some cases.

[0011] Document US 2011 / 0171371 describes the preparation of a Li-ion battery electrode, comprising a composition based on carbon nanotubes. In order to facilitate the dispersion of the carbon nanotubes in the low binder composition, the size of the CNT agglomerates is reduced in particular using a jet mill.

[0012] Another solution has been proposed by the applicant in document EP 2780401 which describes the use of a mixing device for preparing the composition containing carbonaceous conductive fillers, a solvent and a binder, and by the use of a dispersant, such as PVP, in this composition. This process makes it possible to make the carbonaceous conductive fillers easily handleable for liquid phase applications, by dispersing them efficiently in a medium containing a solvent and a binder, suitable in particular for the manufacture of an electrode, without resorting to a step comprising grinding (in particular in a ball mill or by pulverization), passage through ultrasound or passage through a rotor-stator system of the carbonaceous conductive fillers, and without using a surfactant.

[0013] This process, however, has the disadvantage of requiring several steps for the preparation of a battery electrode. Indeed, each ingredient must be prepared beforehand using mixers or planetary mixers, which implies the use of up to 24 mixer lines for an 8 GWh production line. However, the optimization of electrode manufacturing processes remains a priority for Li-ion battery manufacturers.

[0014] There is therefore a need to provide Li-ion battery electrode formulations which are suitable for simplified implementation, without requiring prior transformation steps.

[0015] The invention therefore aims to remedy at least one of the drawbacks of the prior art, namely to propose a complete electrode formulation which is introduced directly into the dosers of an extruder.

[0016] The invention also aims to provide a method for manufacturing a Li-ion battery electrode which comprises a single extrusion step from a complete electrode formulation, with a very low residence time.

[0017] The invention also relates to the electrodes prepared by means of this method. Finally, the invention aims to provide rechargeable Li-ion secondary batteries comprising at least one such electrode. Summary of the invention

[0018] The invention relates firstly to a method for continuously manufacturing a Li-ion battery electrode, said method comprising the following steps: - introduce all the constituents of the electrode in the solid state, as well as a solvent, into an extruder doser, - mix by compounding to obtain a complete electrode formulation, - extruding said formulation for a period of less than 5 minutes, preferably between 30 seconds and 3 minutes, to obtain an electrode material, - applying said electrode material to a metal support to obtain a Li-ion battery electrode, and - drying said electrode material and calendering it.

[0019] According to one embodiment, said electrode formulation comprises from 65 to 95% of solid mixture and from 5 to 35% of solvent, and preferably from 70 to 90% of solid mixture for 10 to 30% of solvent.

[0020] According to one embodiment, said solid mixture comprises: - from 90 to 98%, and preferably from 92 to 97% of an active electrode material, - from 0.5 to 3%, and preferably from 1 to 2% of a fluorinated polymer binder, - from 0.05 to 3%, and preferably from 0.15 to 2% of carbon nanotubes, - from 0.25 to 3%, and preferably from 1 to 3% of at least one conductive filler carbonaceous distinct from carbon nanotubes, and - from 0.25 to 1% of a dispersant,

[0021] the sum of all these ingredients being 100%.

[0022] According to one embodiment, the solvent is water.

[0023] According to one embodiment, said solvent is an organic solvent chosen from: N-methyl pyrrolidone (NMP), dimethyl sulfoxide (DMSO), dimethylformamide (DMF), ketones, acetates, furans, alkyl carbonates, alcohols and their mixtures.

[0024] According to one embodiment, said active electrode material is in particular a metal oxide containing lithium.

[0025] According to one embodiment, said fluorinated polymer binder is in particular chosen from polyvinylidene fluoride (PVDF) homopolymers and copolymers or terpolymers based on vinylidene fluoride.

[0026] The carbon nanotubes may be single-walled, double-walled, or multi-walled, and are preferably multi-walled carbon nanotubes obtained by a chemical vapor deposition process.

[0027] According to one embodiment, said carbon conductive filler distinct from the carbon nanotubes is chosen from carbon nanofibers, carbon black and graphene.

[0028] According to one embodiment, the polymeric dispersant, which is distinct from said binder, is chosen from poly(vinyl pyrrolidone), poly(phenyl acetylene), poly(meta-phenylene vinylidene), polypyrrole, poly(para-phenylene benzobisoxazole, poly(vinyl alcohol), and mixtures thereof.

[0029] According to one embodiment, said metal support of the electrodes is generally made of aluminum for the cathode and copper for the anode.

[0030] The method according to the invention makes it possible to obtain an electrode from a paste applied to said metal support.

[0031] The invention also relates to a Li-ion battery electrode obtained by the method described above.

[0032] According to one embodiment, said electrode is a cathode.

[0033] According to one embodiment, said electrode is an anode.

[0034] Another object of the invention is a Li-ion secondary battery comprising a negative electrode, a positive electrode and an electrolyte, in which at least one of the electrodes is obtained by the method described above.

[0035] Another object of the invention is a complete electrode formulation comprising from 65 to 95% of solid mixture and from 5 to 35% of solvent, and preferably from 70 to 90% of solid mixture for 10 to 30% of solvent.

[0036] According to one embodiment, said solid mixture comprises: - from 90 to 98%, and preferably from 92 to 97% of an active electrode material, - from 0.5 to 3%, and preferably from 1 to 2% of a fluorinated polymer binder, - from 0.05 to 3%, and preferably from 0.15 to 2% of carbon nanotubes, - from 0.25 to 3%, and preferably from 1 to 3% of at least one conductive filler carbonaceous distinct from carbon nanotubes, and - from 0.25 to 1% of a dispersant, the sum of all these ingredients being 100%.

[0037] The present invention overcomes the drawbacks of the prior art. More particularly, it provides a complete electrode formulation intended to be introduced directly into the dosers of an extruder. The invention also provides a simplified Li-ion battery electrode manufacturing method; - there is no prior transformation of the different raw materials used for the manufacture of an electrode; - the process comprises a single extrusion step from said complete electrode formulation, with a very short residence time, less than 5 minutes. This has a major impact on the quality of the formulation and on the performance of the electrode, as well as on the production cost which decreases significantly. Indeed, an extrusion unit implementing the process according to the invention can replace up to 8 mixing units intended to supply 8 extrusion lines in current electrode manufacturing processes. BRIEF DESCRIPTION OF THE FIGURES

[0038] [Fig. 1] is a graph illustrating a Ragone diagram showing the variation of the discharge capacity of an electrode formulation, measured in mAh / g, as a function of the discharge rate (C-rate). Description of the embodiments

[0039] The invention is now described in more detail and in a non-limiting manner in the following description.

[0040] According to a first aspect, the invention relates to a method for the continuous manufacture of a Li-ion battery electrode, said method comprising the following steps: - introducing all the constituents of the electrode in the solid state, as well as a solvent, into an extruder doser, - mix by compounding to obtain a complete electrode formulation, - extruding said formulation for a period of less than 5 minutes, preferably between 30 seconds and 2 minutes, to obtain an electrode material, - applying said electrode material to a metal support to obtain a Li-ion battery electrode, and - calendering said electrode material.

[0041] Typically, this method implements a complete electrode formulation obtained by compounding a solid mixture comprising all the ingredients of the electrode, and a solvent.

[0042] According to various embodiments, said method comprises the following characteristics, where appropriate combined. The contents indicated are expressed by weight, unless otherwise indicated.

[0043] According to one embodiment, said electrode formulation comprises from 65 to 95% of solid mixture and from 5 to 35% of solvent, and preferably from 70 to 90% of solid mixture for 10 to 30% of solvent.

[0044] Advantageously, said solid mixture comprises: - from 90 to 98%, and preferably from 92 to 97% of an active electrode material, - from 0.5 to 3%, and preferably from 1 to 2% of a fluorinated polymer binder, - from 0.05 to 3%, and preferably from 0.15 to 2% of carbon nanotubes, - from 0.25 to 3%, and preferably from 1 to 3% of at least one conductive filler carbonaceous distinct from carbon nanotubes, and - from 0.25 to 1% of a dispersant,

[0045] the sum of all ingredients being 100%. Solvent

[0046] The solvent used in the electrode formulation is water or an organic solvent. According to one embodiment, the solvent is water.

[0047] According to one embodiment, said solvent is an organic solvent chosen from: N-methyl pyrrolidone (NMP), dimethyl sulfoxide (DMSO), dimethylformamide (DMF), ketones, acetates, furans, alkyl carbonates, alcohols and mixtures thereof. Active electrode material

[0048] The active electrode material is chosen from the group consisting of:

[0049] i) transition metal oxides with spinel structure of LiM2O4 type, where M represents a metal atom containing at least one of the metal atoms selected from the group formed by Mn, Fe, Co and Ni, said oxides preferably containing at least one atom of Mn and / or Ni;

[0050] ii) transition metal oxides with a lamellar structure of the LiM02 type where M represents a metal atom containing at least one of the metal atoms selected from the group formed by Mn, Fe, Co and Ni;

[0051] iii) oxides with polyanionic frameworks of the LiMy(XOz)n type where: - M represents a metal atom containing at least one of the metal atoms selected from the group consisting of Mn, Fe and Co, and - X represents one of the atoms selected from the group formed by P, Si, Ge, S and As.

[0052] An example of this type of oxide is LiFePO4.

[0053] iv) vanadium-based oxides,

[0054] v) graphite,

[0055] vi) graphene,

[0056] vii) carbon nanotubes,

[0057] viii) silicon or its composites with carbon, and

[0058] ix) titanates.

[0059] Electrode active materials i) to iii) are more suitable for the preparation of cathodes, while electrode active materials iv) and ix) are more suitable for the preparation of anodes. Fluoropolymer binder

[0060] The polymeric binder is chosen from the group consisting of fluorinated polymers defined in particular as follows:

[0061] (i) those comprising at least 50 mol% of at least one monomer of formula (I):

[0062] CFX^CXoX, (I)

[0063] where X1, X2 and X3 independently denote a hydrogen or halogen atom (in particular fluorine or chlorine), such as poly(vinylidene fluoride) (PVDF), preferably in α-form, poly(trifluoroethylene) (PVF3), polytetrafluoroethylene (PTFE), copolymers of vinylidene fluoride with either hexafluoropropylene (HFP), trifluoroethylene (VF3), tetrafluoroethylene (TFE), or chlorotrifluoroethylene (CTFE), fluoroethylene / propylene copolymers (FEP), copolymers of ethylene with either fluoroethylene / propylene (FEP), tetrafluoroethylene (TFE), or chlorotrifluoroethylene (CTFE);

[0064] (ii) those comprising at least 50 mol% of at least one monomer of formula (II):

[0065] R-O-CH-CH2 (II)

[0066] where R denotes a perhalogenated (in particular perfluorinated) alkyl radical, such as perfluoropropyl vinyl ether (PPVE), perfluoroethyl vinyl ether (PEVE) and copolymers of ethylene with perfluoromethylvinyl ether (PMVE), said binder preferably being PVDF.

[0067] The term "PVDF" as used herein includes homopolymers of vinylidene fluoride (VDF) or copolymers of VDF and at least one other comonomer in which VDF represents at least 50 mol%. The comonomers polymerizable with VDF are selected from vinyl fluoride, trifluoroethylene, chlorotrifluoroethylene (CTFE), 1,2-difluoroethylene, tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoro(alkyl vinyl) ethers such as perfluoro(methylvinyl)ether (PMVE), perfluoro(ethylvinyl)ether (PEVE), perfluoro(propylvinyl)ether (PPVE), perfluoro(1,3-dioxozole); perfluoro(2,2dimethyl-1,3dioxozole) (PDD), the product of formula CF2=CFOCF2CF(CF3)OCF2CF2X in which X is SO2F, CO2H, CH2OH; CH2OCN or CH2OPO3H, the product of formula CF2=CFOCF2CF2SO2F; the product of formula F(CF2)nCH2OCF=CF2 in which n is 1,2,3,4 or 5, the product of formula R1CH2OCF=CF2 in which RI is hydrogen or F(CF2)z and z is 1, 2, 3, or 4;the product of formula R3OCF=CH2 in which R3 is F(CF2)z and z is 1, 2, 3, or 4 or perfluorobutylethylene (PFBE), fluoroethylenepropylene (FEP), 3,3,3-trifluoropropene, 2 trifluoromethyl-3,3,3-trifluoro-l-propene, 2,3,3,3-tetrafluoropropene or HFO-1234yf, El,3,3,3-tetrafluoropropene or HFO-1234zeE, Zl,3,3,3-tetrafluoropropene or HFO-1234zeZ, 1,1,2,3-tetrafluoropropene or HFO-1234yc, lel,2,3,3-tetrafluoropropene or HFO-1234ye, 1,1,3,3-tetrafluoropropene or HFO-1234zc and chlorotetrafluoropropene or HCFO-1224. ;

[0068] According to one embodiment, the copolymer is a terpolymer.

[0069] According to another embodiment, said binder is a fluoropolymer carrying function(s) capable of developing adhesion to a metal substrate and good cohesion of the material making up the electrode. It may be a VDF-based polymer (containing at least 50 mol% of VDF) further comprising units carrying at least one of the following functions: carboxylic acid, carboxylic acid anhydride, carboxylic acid esters, epoxy groups (such as glycidyl), amide groups, alcohol groups, carbonyl groups, mercapto groups, sulfide, oxazoline groups and phenolic groups. The function is introduced onto the fluoropolymer by a chemical reaction which may be grafting or copolymerization of the fluoropolymer with a compound carrying at least one of said functional groups, according to techniques well known to those skilled in the art.

[0070] According to one embodiment, the carboxylic acid function is a hydrophilic group of (meth)acrylic acid type chosen from acrylic acid, methacrylic acid, hydroxyethyl(meth)acrylate, hydroxypropyl(meth)acrylate and hydroxyethylhexyl(meth)acrylate.

[0071] According to one embodiment, the units carrying the carboxylic acid function further comprise a heteroatom chosen from oxygen, sulfur, nitrogen and phosphorus.

[0072] When the fluoropolymer is functionalized, the content of functional groups ensuring the adhesion of the binder to a metal is at least 0.05 mol%, preferably at least 0.15 mol%. Carbon nanotubes (CNTs)

[0073] The carbon nanotubes used in the formulation according to the invention may be of the single-walled, double-walled or multi-walled type. The double-walled nanotubes may in particular be prepared as described by FLAHAUT et al. in Chem. Com. (2003), 1442. The multi-walled nanotubes may for their part be prepared as described in document WO 03 / 02456. Preferred according to the invention are multi-walled carbon nanotubes obtained using a chemical vapor deposition (or CVD) process, by catalytic decomposition of a carbon source (preferably of plant origin), as described in particular in the Applicant's application EP 1 980 530.

[0074] The nanotubes usually have an average diameter ranging from 0.1 to 100 nm, preferably from 0.4 to 50 nm and, better still, from 1 to 30 nm, or even from 10 to 15 nm, and advantageously a length of 0.1 to 10 μm. Their length / diameter ratio is preferably greater than 10 and most often greater than 100. Their specific surface area is for example between 100 and 300 m2 / g, advantageously between 200 and 300 m2 / g, and their apparent density may in particular be between 0.05 and 0.5 g / cm3 and more preferably between 0.1 and 0.2 g / cm3. Multi-walled nanotubes may for example example include 5 to 15 sheets (or walls) and more preferably 7 to 10 sheets. These nanotubes may or may not be treated.

[0075] An example of raw carbon nanotubes is notably commercially available from the company ARKEMA under the trade name Graphistrength® C100.

[0076] These nanotubes can be purified and / or treated (for example oxidized) and / or functionalized, before their use in the process according to the invention.

[0077] The purification of the nanotubes can be carried out by washing with a sulfuric acid solution, so as to remove any residual mineral and metallic impurities, such as iron, originating from their preparation process. The weight ratio of the nanotubes to the sulfuric acid can in particular be between 1:2 and 1:3. The purification operation can also be carried out at a temperature ranging from 90 to 120°C, for example for a period of 5 to 10 hours. This operation can advantageously be followed by steps of rinsing with water and drying the purified nanotubes. The nanotubes can alternatively be purified by heat treatment at high temperature, typically above 1000°C.

[0078] The oxidation of the nanotubes is advantageously carried out by bringing them into contact with a sodium hypochlorite solution containing from 0.5 to 15% by weight of NaOCl and preferably from 1 to 10% by weight of NaOCl, for example in a weight ratio of nanotubes to sodium hypochlorite ranging from 1:0.1 to 1:1. The oxidation is advantageously carried out at a temperature below 60°C and preferably at room temperature, for a period ranging from a few minutes to 24 hours. This oxidation operation can advantageously be followed by steps of filtration and / or centrifugation, washing and drying of the oxidized nanotubes.

[0079] The functionalization of the nanotubes can be carried out by grafting reactive units such as vinyl monomers to the surface of the nanotubes. The material constituting the nanotubes is used as a radical polymerization initiator after having been subjected to a heat treatment at more than 900°C, in an anhydrous and oxygen-free medium, which is intended to eliminate the oxygenated groups from its surface. It is thus possible to polymerize methyl methacrylate or hydroxyethyl methacrylate on the surface of carbon nanotubes in order to facilitate in particular their dispersion in the fluorinated binder.

[0080] Raw nanotubes, i.e. nanotubes which are neither oxidized nor purified nor functionalized and have not undergone any other chemical and / or thermal treatment, may be used in the present invention. Alternatively, purified nanotubes, in particular by high-temperature heat treatment, may be used.

[0081] Preferably, carbon nanotubes are used in the present invention in the form of solid aggregates of size between 1 μm and 5 mm, preferably between 200 μm and 3 mm.

[0082] Carbon conductive filler other than carbon nanotubes

[0083] These fillers comprise at least one filler chosen from carbon nanofibers, graphenes and carbon black.

[0084] Carbon black is used in powder form or in compacted form.

[0085] Carbon nanofibers are, like carbon nanotubes, nanofilaments produced by chemical vapor deposition (or CVD) from a carbon source which is decomposed on a catalyst containing a transition metal (Fe, Ni, Co, Cu), in the presence of hydrogen, at temperatures of 500 to 1200°C. However, these two carbon charges differ in their structure (I. MARTIN-GULLON et al., Carbon 44 (2006) 1572-1580). Indeed, carbon nanotubes consist of one or more graphene sheets wrapped concentrically around the axis of the fiber to form a cylinder with a diameter of 10 to 100 nm. In contrast, carbon nanofibers consist of more or less organized graphitic zones (or turbostratic stacks) whose planes are inclined at variable angles relative to the axis of the fiber. These stacks can take the form of platelets, fishbones or stacked cups to form structures with a diameter generally ranging from 100 nm to 500 nm or more.Furthermore, carbon black is a colloidal carbonaceous material manufactured industrially by incomplete combustion of heavy petroleum products, which is in the form of carbon spheres and aggregates of these spheres and whose dimensions are generally between 10 and 1000 nm.

[0086] It is preferred to use carbon nanofibers having a diameter of 100 to 200 nm, for example approximately 150 nm (VGCF® from SHOWA DENKO), and advantageously a length of 100 to 200 pm.

[0087] Graphene refers to a flat, isolated and individualized graphite sheet, but also, by extension, an assembly comprising between one and a few dozen sheets and having a flat or more or less wavy structure. This definition therefore includes FLG (Few Layer Graphene or weakly stacked graphene), NGP (Nanosized Graphene Plates or nanometric-sized graphene plates), CNS (Carbon NanoSheets or graphene nanosheets), GNR (Graphene NanoRibbons or graphene nanoribbons). However, it excludes carbon nanotubes and nanofibers, which are respectively made up of the winding of one or more graphene sheets in a coaxial manner and the turbostratic stacking of these sheets.

[0088] It is further preferred that the graphene used according to the invention is not subjected to an additional step of chemical oxidation or functionalization.

[0089] The graphene used according to the invention is advantageously obtained by chemical vapor deposition or CVD, preferably according to a process using a powder catalyst based on a mixed oxide. It is characteristically in the form of particles with a thickness of less than 50 nm, preferably less than 15 nm, more preferably less than 5 nm and with lateral dimensions of less than one micron, preferably from 10 nm to less than 1000 nm, more preferably from 50 to 600 nm, or even from 100 to 400 nm. Each of these particles generally contains from 1 to 50 sheets, preferably from 1 to 20 sheets and more preferably from 1 to 10 sheets, or even from 1 to 5 sheets which are capable of being separated from each other in the form of independent sheets, for example during ultrasonic treatment. Dispersing

[0090] The polymeric dispersant is distinct from said fluorinated binder. It is advantageously chosen from poly(vinyl pyrrolidone), poly(phenyl acetylene), poly(meta-phenylene vinylidene), polypyrrole, poly(para-phenylene benzobisoxazole, poly(vinyl alcohol), and mixtures thereof. Process flow

[0091] According to one embodiment, the electrode manufacturing method according to the invention uses as a compounding device a micro-extruder marketed by the company DSM at laboratory level. Industrially, BUSS co-kneaders or twin-screw extruders are used.

[0092] The micro-extruder comprises: feeding means, in particular at least one hopper for powdered materials and / or at least one injection pump for liquid materials; high shear mixing means, for example a co-rotating or counter-rotating twin-screw extruder; an outlet head which gives its shape to the outgoing material; and means for cooling, in air or using a water circuit, the material.

[0093] In the first step of the process according to the invention, the solvent and the components of the solid mixture are introduced into the extruder, namely: the active electrode material, the fluorinated polymer binder, the carbon nanotubes, the other carbon conductive fillers, and the polymer dispersant, which have been pre-mixed beforehand. The solid mixture is introduced gradually, while monitoring the increase in torque.

[0094] During the extrusion step, the temperature in the extruder is maintained between 50 and 200°C.

[0095] According to one embodiment, the CNTs and / or the carbonaceous conductive filler distinct from the carbon nanotubes are mixed with solvent in the pre-doser of the extrusion line. Indeed, the CNTs have the capacity to adsorb liquids without losing the solid form. For example, 100 g of the Graphistrength® C100 CNTs can absorb 800 g of the NMP solvent without losing the fluidity of the powder. Similarly, carbon black has a significant solvent adsorption capacity. The mixtures of CNTs and / or other conductive fillers with the solvent, carried out in the pre-doser of the extrusion line, can be carried out with the gravimetric doser directly in the main hopper of the extruder at the same time as the other constituents of the solid mixture. This avoids the injection of liquid into the compounding zone and considerably improves the mixing quality.

[0096] This pre-dispersion step is particularly suitable for high electrode weights (greater than or equal to 25 mg / cm2).

[0097] According to one embodiment, which can be combined with that described above, all or part of the solvent present in the electrode formulation comes from a latex comprising the fluorinated polymer binder particles and said solvent.

[0098] The solvent and the solid mixture are then mixed by compounding to obtain a complete electrode formulation.

[0099] The extrusion of said formulation is carried out in a single step lasting less than 5 minutes, preferably between 30 seconds and 3 minutes, to obtain an electrode material in the form of a paste with a Brookfield viscosity of between 1500 and 20,000 cP.

[0100] These extrusion conditions are very favorable for co-dispersing the active charge and the CNTs.

[0101] The extrusion line can be equipped with a vacuum pump after the compounding zone to evacuate part of the solvent. This is intended to recover the electrode material in the form of powder usable for coating deposition by dry process or powder, followed by calendering. Said material suitable for the dry process can contain small quantities of organic solvent or water, because this does not change the physical state of the formulation, the material remains manipulable in the solid state.

[0102] The electrode material thus obtained is applied to a metal collector to obtain a Li-ion battery electrode, for example by means of a scraper blade device for coating. The metal supports of the electrodes are generally made of aluminum for the cathode and copper for the anode.

[0103] The electrode material is then dried, and is then subjected to calendering. According to one embodiment, the calendering is carried out in several hot stages. (between 120 and 160°C depending on the quantity of residual solvent) during which the powder is transformed into a film having a thickness of 50 to 150 qm and a porosity of 10 to 40 mg / cm2.

[0104] Another object of the invention is the electrode obtained by the method described above. According to one embodiment, said electrode is a cathode. According to one embodiment, said electrode is an anode.

[0105] Another object of the invention is a Li-ion secondary battery comprising a negative electrode, a positive electrode and an electrolyte, in which at least one of the electrodes is obtained by the method described above. The quality of the complete electrode formulation and its rapid transformation thanks to the method according to the invention have a beneficial impact on the performance of the electrode.

[0106] Another subject of the invention is the complete electrode formulation described above, comprising from 65 to 95% of solid mixture and from 5 to 35% of solvent, and preferably from 70 to 90% of solid mixture for 10 to 30% of solvent. This formulation is particularly suitable for being implemented in the dry process according to the invention. EXAMPLES

[0107] The following examples illustrate in a non-limiting manner the scope of the invention. Example 1 according to the invention

[0108] A complete cathode formulation is prepared, the solid mixture of which having the following mass composition is prepared by dry pre-mixing beforehand: - 93.9% NMC 622 powder (LiNio>6Mnoj2Cooj202) marketed by the UMICORE company 1.5% PVDF homopolymer KYNAR® HSV 900 - 2% purified Graphistrength®C100 NTCs - 2% LI100 carbon black marketed by DENKA 0.6% PVP.

[0109] A micro-extruder marketed by the company DSM is used. NMP is introduced, followed by the said solid mixture. The quantity of NMP added to the said solid mixture is adjusted so as to obtain viscosities between 6000 and 8000 cP.

[0110] We follow the following steps: - Introduction of 9.35 ml of NMP into the extruder, preheated to 50°C; once the NMP is introduced, the screw speed is increased to 240 rpm; - 42.6 g of the aforementioned solid mixture are gradually introduced during 30-60 seconds; the torque is continuously monitored, it is adjusted with NMP so as to remain in the range 1000 - 1400 Nm; - Once the torque has stabilized, 4.9 g of NMP are gradually introduced over 30-60 seconds; the torque gradually decreases to 100 Nm; - The product (cathode material) is recovered in the form of a paste, the NMP content and fineness (North gauge from 0 to 100 qm) of which are tested; the dry mass is 78%; - The paste thus obtained is used to coat an aluminum sheet using a scraper blade coating device; the electrode is then dried in a ventilated oven at 130°C for 30 minutes; - The coating thickness is adjusted according to the desired surface load, at 18 mg / cm2; - Calendering is then carried out at 70°C and the density of the electrode is checked to obtain a porosity of 40%; - The calendered electrodes are then used to evaluate the adhesion between the paste and the metal support, by means of a peel test at 180°C.

[0111] The cathodes thus prepared are used to prepare a button cell with a Li anode, a Celgard PP2500 separator and an electrolyte formulation (1 M LiFSI in EC / DEC (3 / 7 v / v) + 2%FEC).

[0112] The battery thus obtained is tested according to the Ragone protocol indicated in table 1:

[0113] [Tables 1]

[0114] The results obtained for a battery according to the invention as well as those obtained with a battery whose cathode is prepared by means of a conventional mixer (see comparative example 2 below) are represented in the diagram of [Fig.l], which shows the variation of the discharge capacity of an electrode formulation, measured in mAh / g, as a function of the discharge rate (C-rate).

[0115] These results show that the behavior of a battery comprising a cathode prepared by the method according to the invention is similar to that of a battery comprising a cathode prepared by conventional methods. Example 2 (comparative)

[0116] The same electrode formulation as in Example 1 was prepared using a conventional mixer. Preparation of an NTC / PVDF / NMP masterbatch

[0117] A 5% by weight solution of PVDF (Kynar® HSV 900 from ARKEMA) was previously prepared by dissolving the polymer powder in N-methyl pyrrolidone (NMP); the solution was stirred at 50°C for 60 min.

[0118] The CNTs (ARKEMA's Graphistrength® C100) were introduced into the first feed hopper of a BUSS® MDK 46 co-kneader (L / D = 11), equipped with a re-extrusion screw and a granulation device. The 5% PVDF (Kynar® HSV 900) solution in N-methyl pyrrolidone (NMP) was injected in liquid form at 80°C into the first zone of the co-kneader. The temperature settings and flow rate within the co-kneader were as follows: Zone 1: 80°C, Zone 2: 80°C, Screw: 60°C, flow rate: 15 kg / h.

[0119] At the outlet of the die, the cutting of the masterbatch granules was carried out dry. The granules were packaged in a hermetic container to avoid the loss of NMP during storage. The composition of the final masterbatch was as follows: 30% by weight of carbon nanotubes, 3.5% by weight of PVDF resin and 66.5% by weight of NMP.

[0120] Use of NTC / PVDF / NMP masterbatch for the manufacture of an electrode

[0121] Step a) 20 g of masterbatch granules were wetted with 160 g of NMP solvent. After 2 hours of static impregnation at room temperature, the masterbatch granules were dispersed in the solvent using a Silverson® L4RT mixer at 6000 rpm for 15 minutes. Significant heating during the dispersion operation was observed: the mixture containing the CNTs reached a temperature of 67°C. The solution obtained was designated “NTC Premix”.

[0122] Step b) 14.3 g of Kynar® HSV 900 and 5.72 g of PVP were dissolved in 276 g of NMP solvent using a disc mixer type stirrer for 4 hours.

[0123] Step c) 279g of NMC 622 powder (LiNio,6Mno,2Coo,202) marketed by the company UMICORE were dispersed in the Kynar solution; during this step, the powder was added gradually with stirring (600 rpm). The suspension obtained was designated “Premix NMC”.

[0124] Step d) In order to obtain a good dispersion of the CNTs around the NMC active material, the 2 CNT and NMC Premixes obtained respectively during steps a) and c) were mixed for 10 minutes using a flocculating stirrer at 600 rpm and then using a Silverson® L4RT mixer for 15 minutes at 3000 rpm. The composition of the ink in dry matter was as follows: 2% CNTs; 5% Kynar® HSV 900 and 93% NMC 622 with a dry matter content of 40% in the NMP solvent.

[0125] Step e) The pasty formulation thus obtained is used to coat an aluminum sheet using a scraper blade device for coating; the electrode is then dried in a ventilated oven at 130°C for 30 minutes.

[0126] Step D Calendering is then carried out at 70°C and the density of the electrode is checked so as to obtain a porosity of 40%.

[0127] Example 3 - Preparation of a cathode formulation according to the invention

[0128] The cathode formulation contains: - 93.9% NMC 622 powder (LiNio^Mno^Coo^CL) marketed by the UMICORE company 1.5% PVDF homopolymer KYNAR® HSV 900 - 2% purified Graphistrength®C100 CNTs - 2% carbon black (NdC) LI100 marketed by the company DENKA 0.6% PVP.

[0129] Step a) 200 g of NTC Graphistrength® Cl00 HP and 200 g of carbon black are pre-mixed with 1000 g of NMP in a 5 liter drum placed on the rotating rollers for 15 min. The NMP solvent is adsorbed by the NTC and NdC without changing the powder appearance.

[0130] Step b) The Mixture from step a) was introduced into a 10 Liter drum containing 9390 g of NMC622, 150 g of PVDF and 60 g of PVP. The drum was placed on the rotating rollers for 15 min.

[0131] Step c) extrusion. The mixture from step b) was introduced into the gravimetric feeder, including the main feeder of the Clextral BC21 extruder. The extruder is equipped with a feed hopper. The screw profile has two mixing zones and an atmospheric degassing well upstream of the 2nd mixing zone. The mixture was fed with a flow rate of 10 kg / h into the feed hopper. The screw speed is 300 rpm. The material was recovered directly from the screw outlet (without die) in the form of a homogeneous powder with a “wet” appearance in a drum. The set temperature of all extruder zones is 60°C. The mass % of NMP in the extruded formulation is 8.5%.

[0132] Step d) The extruded formulation was applied to a 25 pm aluminum (Al) sheet, using a coating scraper blade device, the carrier-squeegee gap being 400 pm. Then, the Al carrier with the powder coating was placed in a ventilated oven at 160°C for 3 min to consolidate the particles before calendering.

[0133] Step e) Calendering. The Al-supported coating is then calendered at 160°C in 3 steps, reducing the gap between the calender rollers: 1st pass at 300 pm, 2nd at 250 pm and 3rd at 150 pm. Then, the coating was dried at 130°C for 30 min to remove the residual NMP. The gap for the final calendering was adjusted to respect the final porosity of 40% as in examples 1 and 2.

Claims

Claims

1. A method for continuously manufacturing a Li-ion battery electrode, said method comprising the following steps: - introducing all the constituents of the electrode in the solid state, namely: from 90 to 98% of an electrode active material, from 0.5 to 3% of a fluorinated polymer binder, from 0.05 to 3% of carbon nanotubes, from 0.25 to 3% of at least one carbonaceous conductive filler distinct from the carbon nanotubes, and from 0.25 to 1% of a dispersant, the sum of all the ingredients being 100%, as well as a solvent, into an extruder doser, - mixing by compounding to obtain an electrode formulation comprising from 65 to 95% of solid mixture and from 5 to 35% of solvent, - extruding said formulation for a period of less than 5 minutes, preferably between 30 seconds and 3 minutes, to obtain an electrode material in the form of Brookfield viscosity paste between 1500 and 20.000 cP, - applying said electrode material to a metal support to obtain a Li-ion battery electrode, and - calendering said electrode material.

2. The method of claim 1, wherein the electrode formulation comprises 70 to 90% solid mixture to 10 to 30% solvent.

3. A method according to either of claims 1 or 2, wherein said solid mixture comprises: - from 92 to 97% of an active electrode material, - from 1 to 2% of a fluoropolymer binder, - from 0.15 to 2% of carbon nanotubes, - from 1 to 3% of at least one carbon conductive filler distinct from the carbon nanotubes, and - from 0.25 to 1% of a dispersant, the sum of all ingredients being 100%.

4. Method according to one of claims 1 to 3, in which the solvent is water or an organic solvent chosen from: N-methyl pyrrolidone, dimethyl sulfoxide, dimethylformamide, ketones, acetates, furans, alkyl carbonates, alcohols and their mixtures.

5. Method according to one of claims 1 to 4, in which the active electrode material is chosen from the group consisting of: i. transition metal oxides with spinel structure of the LiM2O4 type, where M represents a metal atom containing at least one of the metal atoms selected from the group formed by Mn, Fe, Co and Ni, said oxides preferably containing at least one atom of Mn and / or Ni; ii. transition metal oxides with a lamellar structure of the LiM02 type where M represents a metal atom containing at least one of the metal atoms selected from the group consisting of Mn, Fe, Co and Ni; iii. polyanionic framework oxides of the LiMy(X0z)n type where M represents a metal atom containing at least one of the metal atoms selected from the group consisting of Mn, Fe and Co, and X represents one of the atoms selected from the group consisting of P, Si, Ge, S and As; iv. vanadium-based oxides; v. graphite; vi. graphene; vii. carbon nanotubes; viii. silicon or its composites with carbon, and ix. titanates.

6. Method according to one of claims 1 to 5, in which the fluorinated polymeric binder is chosen from the group consisting of fluorinated polymers defined as follows: - those comprising at least 50 mol% of at least one monomer of formula (I): CFX1=CX2X3 (I) where XI, X2 and X3 independently denote a hydrogen or halogen atom (in particular fluorine or chlorine), such as poly(vinylidene fluoride) (PVDF), preferably in α-form, poly(trifluoroethylene) (PVF3), polytetrafluoroethylene (PTFE), copolymers of vinylidene fluoride with either

7. hexafluoropropylene (HFP), either trifluoroethylene (VF3), or tetrafluoroethylene (TFE), or chlorotrifluoroethylene (CTFE), fluoroethylene / propylene copolymers (FEP), copolymers of ethylene with either fluoroethylene / propylene (FEP), or tetrafluoroethylene (TFE), or chlorotrifluoroethylene (CTFE); and - (ii) those comprising at least 50 mol% of at least one monomer of formula (II): RO-CH-CH2 (II) where R denotes a perhalogenated (in particular perfluorinated) alkyl radical, such as perfluoropropyl vinyl ether (PPVE), perfluoroethyl vinyl ether (PEVE) and copolymers of ethylene with perfluoromethylvinyl ether (PMVE), said binder preferably being PVDF. Method according to one of claims 1 to 6, wherein said binder is a polyvinylidene fluoride chosen from homopolymers of vinylidene fluoride (VDF) and copolymers of VDF and at least one other comonomer in which the VDF represents at least 50% by moles, the comonomers polymerizable with the VDF being chosen from: vinyl fluoride, trifluoroethylene, chlorotrifluoroethylene (CTFE), 1,2-difluoroethylene, tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoro(alkyl vinyl) ethers such as perfluoro(methylvinyl)ether (PMVE), perfluoro(ethylvinyl)ether (PEVE), perfluoro(propylvinyl)ether (PPVE), perfluoro(1,3-dioxozole); perfluoro(2,2dimethyl-1,3dioxozole) (PDD), the product of formula CF2=CFOCF2CF(CF3)OCF2CF2X in which X is SO2F, CO2H, CH2OH; CH2OCN or CH2OPO3H, the product of formula CF2=CFOCF2CF2SO2F;the product of formula F(CF2)nCH2OCF=CF2 in which n is 1, 2, 3, 4 or 5, the product of formula R1CH2OCF=CF2 in which RI is hydrogen or F(CF2)z and z is 1, 2, 3, or 4; the product of formula R3OCF=CH2 in which R3 is F(CF2)z and z is 1, 2, 3, or 4 or perfluorobutylethylene (PFBE), fluoroethylenepropylene (FEP), 3,3,3-trifluoropropene, 2 trifluoromethyl-3,3,3-trifluoro-l-propene, 2,3,3,3-tetrafluoropropene or HFO-1234yf, E-1,3,3,3-tetrafluoropropene or HFO-1234zeE, Zl,3,3,3-tetrafluoropropene or HFO-1234zeZ, 1,1,2,3-tetrafluoropropene or HFO-1234yc, lel,2,3,3-tetrafluoropropene or HFO-1234ye, 1,1,3,3-; tetrafluoropropene or HFO-1234zc and chlorotetrafluoropropene or HCFO-1224.

8. Method according to one of claims 1 to 7, in which the carbon nanotubes are in the form of solid aggregates of size between 1 pm and 5 mm, preferably between 200 pm and 3 mm, and are chosen from nanotubes of the single-walled, double-walled or multi-walled type.

9. Method according to one of claims 1 to 8, in which the carbon conductive filler other than carbon nanotubes comprises at least one filler chosen from carbon nanofibers, graphenes and carbon black.

10. A method according to one of claims 1 to 9, wherein said polymeric dispersant is selected from poly(vinyl pyrrolidone), poly(phenyl acetylene), poly(meta-phenylene vinylidene), polypyrrole, poly(para-phenylene benzobisoxazole, poly(vinyl alcohol), and mixtures thereof.

11. A complete Li-ion battery electrode formulation comprising from 65 to 95% of solid mixture and from 5 to 35% of solvent, and preferably from 70 to 90% of solid mixture for 10 to 30% of solvent, said solid mixture comprising: - from 92 to 97% of an electrode active material, - from 1 to 2% of a fluorinated polymer binder, - from 0.15 to 2% of carbon nanotubes, - from 1 to 3% of at least one carbonaceous conductive filler distinct from the carbon nanotubes, and - from 0.25 to 1% of a dispersant, the sum of all ingredients being 100%, said solvent being water or an organic solvent selected from: N-methyl pyrrolidone, dimethyl sulfoxide, dimethylformamide, ketones, acetates, furans, alkyl carbonates, alcohols and their mixtures.

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