Dry coated electrode binder

Abstract

The present invention relates to a non-fibrillable binder for a dry-coated electrode, said binder being a fluoropolymer having a melting point between 145 °C and 200 °C measured according to ASTM D3418 and a melt viscosity of less than 50 kP measured at 230 °C and a shear rate of 100 s⁻¹ measured according to ASTM D3835. More specifically, the invention relates to a dry-coated electrode for a Li-ion battery. The invention also relates to lithium-ion batteries manufactured by incorporating said electrode.

Description

Title of the invention: Binder for dry coated electrode Scope of the invention

[0001] The present invention relates generally to the field of electrical energy storage in lithium-ion batteries. More specifically, the invention relates to a non-fibrillable solvent for a dry-coated electrode for a Li-ion battery. Another subject of the invention is a method for preparing an electrode using said binder. The invention also relates to lithium-ion batteries manufactured by incorporating said electrode. Background of the invention

[0002] An elementary cell of a Li-ion storage battery or lithium battery comprises an anode (at discharge), and a cathode (also at discharge) generally composed of a metal oxide type lithium insertion compound, such as LiMn2O4, LiCoO2 or LiNiO2, between which is inserted an electrolyte which conducts lithium ions.

[0003] Rechargeable or secondary cells are more advantageous than primary (non-rechargeable) cells because the associated chemical reactions that take place at the positive and negative electrodes of the battery are reversible. The electrodes of secondary cells can be regenerated several times by applying an electrical charge. Many advanced electrode systems have been developed to store an electrical charge. In parallel, considerable effort has been devoted to the development of electrolytes capable of improving the capabilities of electrochemical cells.

[0004] For their part, the electrodes generally include at least one current collector on which is deposited, in the form of a film, a composite material consisting of a material called active material 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.

[0005] Binders are classified among the components called inactive components since they do not directly contribute to the cell's capacity. However, their key role in electrode processing and their considerable influence on the electrochemical performance of electrodes have been widely described. The main relevant physical and chemical properties of binders are thermal stability, chemical and electrochemical stability, tensile strength (strong adhesion and cohesion), and flexibility. The main objective of using a binder is to form stable networks of the solid components of the electrodes, i.e., the active materials and conductive agents (cohesion). In addition, the binder must ensure close contact of the composite electrode to the current collector (adhesion).

[0006] Polyvinylidene fluoride (PVDF) is used in lithium-ion batteries because of its excellent electrochemical stability, good bonding capacity, and strong adhesion to electrode materials and current collectors. PVDF can only be dissolved in certain organic solvents such as N-methylpyrrolidinone (NMP), which is volatile, flammable, explosive, and highly toxic, leading to serious environmental concerns. In the wet mud process, active materials and binders are dispersed in a liquid solution. The liquids used are usually organic solvents or water. The dispersion is poured onto a current collector and then dried in a high-temperature oven to produce an electrode.In this process, a large amount of energy is required to dry the liquid components of the sludge, and the organic solvents also produce harmful vapors that require special equipment to prevent free emissions into the environment.

[0007] Compared to the conventional wet suspension electrode manufacturing process, dry (solvent-free) manufacturing processes are simpler; these processes eliminate emissions of volatile organic compounds and offer the possibility of manufacturing electrodes with greater thicknesses (> 120 µm), resulting in a higher energy density of the final energy storage device. The change in production technology will have little impact on the active material of the electrodes; however, the polymer additives responsible for the mechanical integrity of the electrodes must be adapted to the new manufacturing conditions.

[0008] US patent 2019 / 0305316 discloses dry-process electrode films comprising a microparticulate, non-fibrillable binder having certain particle sizes and a method for obtaining a film flexible enough to be handled for roll-to-roll processing using fibrillable binders. However, fibrillable binders require additional shearing beyond component dispersion. This consumes a significant amount of energy and is destructive to the active materials. US patent 2020 / 0313193 also discloses dry-process electrode films comprising an elastic polymeric binder in which the dry electrode film is self-supporting and comprises at most a non-substantial amount of polytetrafluoroethylene.US document 2020 / 0313193 primarily discloses polyethylene, as an elastic polymeric binder, which is not electrochemically stable enough for use in both a cathode and anode of secondary lithium-ion batteries.

[0009] Therefore, there is still a need to develop new binders and new electrode compositions for Li-ion batteries that are suitable for processing without the use of organic solvents. Summary of the invention

[0010] According to a first aspect, the present invention provides a non-fibrillable binder for a dry-coated electrode, said binder being made of a fluoropolymer having a melting point between 145 °C and 200 °C measured according to ASTM D3418 and a molten viscosity of less than 50 kP measured at 230 °C and a shear rate of 100 s-1 measured according to ASTM D3835.

[0011] In particular, the melting point is defined as the temperature at the maximum of the endotherm of melting measured according to ASTM D3418.

[0012] The present invention provides a binder with specific properties enabling the preparation of a flexible, self-supporting film. Using the fluoropolymer binder of the present invention, a ductile electrode film can be obtained through a single mixing and electrode application step by dry processing.

[0013] The present invention also provides binders free of fibrillable materials to avoid an additional shearing step. Thus, the total energy consumption of the process is lower compared to a process where fibrillable binders are used.

[0014] In addition, the fluoropolymer binders according to the present invention are more electrochemically stable than polyethylene, which allows for superior capacity and cycling properties in electrochemical cells using such electrodes.

[0015] According to a preferred embodiment, said fluoropolymer has a flexural modulus greater than 1000 MPa measured according to ASTM D790.

[0016] According to a preferred embodiment, said fluoropolymer comprises at least one fluoromonomer selected from the group consisting of vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, hexafluoropropene, vinyl fluoride, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropene, 3,3,3-trifluoro-l-propene, 2,3,3,3-tetrafluoropropene, fluorinated vinyl ethers, fluorinated allyl ethers and fluorinated dioxoles.

[0017] According to a preferred embodiment, said fluoropolymer is chosen from the group consisting of vinylidene fluoride homopolymers and copolymers containing at least 50% by weight of vinylidene fluoride repeating motifs, the comonomer being chosen from the group consisting of chlorotrifluoroethylene, hexafluoropropene and trifluoroethylene.

[0018] According to a preferred embodiment, the fluoropolymer is a poly(vinylidene fluoride) (PVDF) type homopolymer or a vinylidene fluoride copolymer with hexafluoropropene.

[0019] According to a preferred embodiment, said fluoropolymer is a poly(vinylidene fluoride) homopolymer having head-to-tail defects in the chain of vinylidene fluoride motifs, and the degree of head-to-tail defects not exceeding 10%.

[0020] According to a preferred embodiment, said fluoropolymer comprises functionalized monomers in an amount from 0.01 to 15 percent by weight on the basis of the total monomers, preferably from 0.05 to 5 percent by weight on the basis of the total amount of monomers, and even more preferably in an amount from 0.05 to 1.5 percent by weight on the basis of the total monomers.

[0021] According to a preferred embodiment, said functionalized monomers comprising at least one functionality are selected from: acrylic acid, methacrylic acid, vinylsulfonic acid, vinylphosphonic acid, itaconic acid, maleic acid and salts of such compounds; allyl and glycidyl ethers, methyl glycidyl ether, crotonic acid glycidyl ether and acetic acid glycidyl ether; ethylene carbonate; hydroxyethyl acrylate and hydroxypropyl acrylate.

[0022] According to a preferred embodiment, said fluoropolymer is produced either by emulsion polymerization or by suspension polymerization, preferably by emulsion polymerization.

[0023] According to a preferred embodiment, said fluoropolymer is a powder having a particle size distribution having a Dv50 of less than 20 pm, preferably less than 15 pm, in particular less than 10 pm.

[0024] Dv50 is the particle size at the 50th percentile (by volume) of the cumulative particle size distribution. This parameter can be determined by laser granulometry. This applies to all Dv50 values ​​described in this description.

[0025] According to a second aspect, the present invention provides a dry coated electrode comprising the non-fibrillable binder of the present invention, a conductive agent and a dry active material.

[0026] According to a preferred embodiment, the dry-coated electrode according to the present invention has the following mass composition:

[0027] a. 50% to 99.9% active material, preferably 50% to 99%

[0028] b. 25% to 0% of conducting agent, preferably 25% to 0.5%,

[0029] c. 25% to 0.05% non-fibrillable binder, preferably 25% to 0.5%,

[0030] d. 0% to 5% of at least one additive chosen from the group consisting of a plasticizer, an ionic liquid, a dispersing agent for conductive additive, and an auxiliary flow agent;

[0031] the sum of all these percentages being 100%.

[0032] According to a preferred embodiment, said conducting agents are composed of one or more materials from among carbon blacks, such as acetylene black, Ketjen black; carbon fibers, such as a carbon nanotube, a carbon nanofiber, a carbon fiber by vapor phase growth; metal powders such as a SUS powder, and an aluminum powder.

[0033] According to a preferred embodiment, for a positive electrode, said active material is chosen from the group consisting of: LiCoO2, Li(Ni, Co, Al)O2, Li(l+ x), NiaMnbCoc (x represents a real number of 0 or more, a = 0.8, 0.6, 0.5, or 1 / 3, b = 0.1, 0.2, 0.3, or 1 / 3, c = 0.1, 0.2, or 1 / 3), LiNiO2, LiMn2O4, LiCoMnO4, Li3NiMn3O3, Li3Fe2(PO4)3, Li3V2(PO4)3, a LiMn spinel substituted by a different element having a composition represented by Ll+xMn2-x-yMyO4, M representing at least one metal chosen from Al, Mg, Co, Fe, Ni, and Zn, x and y independently representing a number real number between 0 and 2, lithium titanate LixTiOy - x and y independently representing a real number between 0 and 2, and a metal and lithium phosphate having a composition represented by LiMPO4, M representing Fe, Mn, Co, or Ni.

[0034] According to a preferred embodiment, for a negative electrode, said active material is chosen from the group consisting of: a lithium alloy, a metal oxide, a carbon material such as graphite or hard carbon, silicon, a silicon alloy and Li4TiO12.

[0035] According to a third aspect, the present invention provides a method for preparing the dry-coated electrode according to the present invention, said method comprising a thermomechanical treatment step carried out at a temperature in the range of 20 °C below the melting point of the non-fibrillable binder up to 50 °C above the melting point of the non-fibrillable binder.

[0036] According to a fourth aspect, the present invention provides a Li-ion battery comprising a positive electrode, a negative electrode and a separator, at least one electrode being a dry-coated electrode according to the present invention.

[0037] The present invention makes it possible to ensure the cohesion and mechanical integrity of the electrode, guaranteeing good film formation or consolidation of formulations, which can be difficult to achieve with solvent-free processes; to generate adhesion to the metallic substrate; to ensure the homogeneity of the electrode composition throughout its thickness and width; to reduce the overall binder content in the electrode, which, in the case of known dry processes, is even higher than in a standard slurry process. The advantage of these technologies is to improve the following properties of the electrode: the homogeneity of the composition in thickness, cohesion, and adhesion to the metallic substrate. It also allows for a reduction in the binder content in the electrode, as well as a reduction in the temperature and duration of the heat treatment required to improve adhesion. Detailed description of the invention

[0038] According to a first aspect of the present invention, a non-fibrillable binder for a dry-coated electrode is provided.

[0039] The term "fluoropolymer" means a polymer formed by the polymerization of at least one fluoromonomer, and includes homopolymers, copolymers, terpolymers, and higher polymers that are thermoplastic. The fluoropolymer in certain embodiments of the invention contains at least 50 percent by mole of one or more fluoromonomers in polymerized form.

[0040] By "thermoplastic" is meant a non-elastomeric polymer. An elastomeric polymer is defined as a polymer which can be stretched, at room temperature, up to twice its original length and which, after stress relief, rapidly recovers its original length, up to about 10%, as indicated by ASTM in Special Technical Publication No. 184.

[0041] In a preferred embodiment, said binder is made of a fluoropolymer having a melting point between 145 °C and 200 °C measured according to ASTM D3418, preferably between 150 °C and 195 °C, more preferably between 150 °C and 190 °C, specifically between 150 °C and 185 °C, more specifically between 150 °C and 180 °C.

[0042] In a preferred embodiment, said binder is made of a fluoropolymer having a melt viscosity of less than 50 kP measured at 230 °C and at a shear rate of 100 s-1 measured according to ASTM D3835. Advantageously, said fluoropolymer has a melt viscosity of less than 48 kP, preferably less than 46 kP, more preferably less than 44 kP, specifically less than 42 kP, more specifically less than 40 kP measured at 230 °C and at a shear rate of 100 s-1 measured according to ASTM D3835.

[0043] Preferably, said fluoropolymer has a melt viscosity greater than 1 kP, more preferably greater than 2 kP, in particular greater than 3 kP, specifically greater than 3.5 kP measured at 230 °C and at a shear rate of 100 s-1 measured according to ASTM D3835.

[0044] In a preferred embodiment, said binder is made of a fluoropolymer having a melting point between 145 °C and 200 °C, preferably between 150 °C and 195 °C, more preferably between 150 °C and 190 °C, specifically between 150 °C and 185 °C, more specifically between 150 °C and 180 °C measured according to ASTM D3418; and said fluoropolymer has a melt viscosity of less than 50 kP, advantageously less than 48 kP, preferably less than 46 kP, more preferably less than 44 kP, specifically less than 42 kP, more specifically less than 40 kP measured at 230 °C and at a shear rate of 100 s-1 measured according to ASTM D3835.

[0045] Thus, said binder is made of a fluoropolymer having a melting point between 145 °C and 200 °C, preferably between 150 °C and 195 °C, more preferably between 150 °C and 190 °C, specifically between 150 °C and 185 °C, more specifically between 150 °C and 180 °C measured according to ASTM D3418; and said fluoropolymer has a molten viscosity of less than 50 kP, advantageously less than 48 kP, preferably less than 46 kP, more preferably less than 44 kP, specifically less than 42 kP, more specifically less than 40 kP measured at 230 °C and at a shear rate of 100 s-1 measured according to ASTM D3835; and said fluoropolymer has a melt viscosity greater than 1 kP, preferably greater than 2 kP, more preferably greater than 3 kP, specifically greater than 3.5 kP measured at 230 °C and at a shear rate of 100 s-1 measured according to ASTM D3835.

[0046] In a preferred embodiment, said fluoropolymer has a flexural modulus greater than 1000 MPa measured according to ASTM D790. Advantageously, said fluoropolymer has a flexural modulus less than 3000 MPa, preferably less than 2900 MPa, more preferably less than 2800 MPa, in particular less than 2700 MPa, specifically less than 2600 MPa, more specifically less than 2500 MPa measured according to ASTM D790.

[0047] Thus, said binder is made of a fluoropolymer having a melting point between 145 °C and 200 °C, preferably between 150 °C and 195 °C, more preferably between 150 °C and 190 °C, specifically between 150 °C and 185 °C, more specifically between 150 °C and 180 °C measured according to ASTM D3418; and said fluoropolymer has a molten viscosity of less than 50 kP, advantageously less than 48 kP, preferably less than 46 kP, more preferably less than 44 kP, specifically less than 42 kP, more specifically less than 40 kP measured at 230 °C and at a shear rate of 100 s-1 measured according to ASTM D3835; and said fluoropolymer has a flexural modulus greater than 1000 MPa measured according to ASTM D790.

[0048] Preferably, said binder is made of a fluoropolymer having a melting point between 145 °C and 200 °C, preferably between 150 °C and 195 °C, more preferably between 150 °C and 190 °C, specifically between 150 °C and 185 °C, more specifically between 150 °C and 180 °C measured according to ASTM standards D3418; and said fluoropolymer has a melt viscosity of less than 50kP, advantageously less than 48kP, preferably less than 46kP, more preferably less than 44kP, specifically less than 42kP, more specifically less than 40kP measured at 230 °C and at a shear rate of 100 s-1 measured in accordance with ASTM D3835; and said fluoropolymer has a flexural modulus greater than 1000 MPa measured in accordance with ASTM D790 and less than 3000 MPa, preferably less than 2900 MPa, more preferably less than 2800 MPa, particularly less than 2700 MPa, specifically less than 2600 MPa, more specifically less than 2500 MPa measured in accordance with ASTM D790.

[0049] In a preferred embodiment, said fluoropolymer has a melting point between 145 °C and 160 °C, preferably between 150 °C and 160 °C, measured according to ASTM D3418. Alternatively, said fluoropolymer has a melting point between 160 °C and 180 °C measured according to ASTM D3418.

[0050] In a more preferred embodiment, said fluoropolymer has a melt viscosity of between 1 and 10 kP, preferably between 2 and 10 kP, more preferably between 3 and 9 kP, measured at 230 °C and at a shear rate of 100 s⁻¹ measured according to ASTM D3835. Alternatively, said fluoropolymer has a melt viscosity of between 10 and 50 kP, more preferably between 20 and 40 kP, measured at 230 °C and at a shear rate of 100 s⁻¹ measured according to ASTM D3835.

[0051] In a more preferred embodiment, said fluoropolymer has a flexural modulus of between 1,000 and 1,500 MPa, preferably between 1,000 and 1,400 MPa, more preferably between 1,000 MPa and 1,300 MPa measured according to ASTM D790. Alternatively, said fluoropolymer has a flexural modulus of between 1,300 and 3,000 MPa, preferably between 1,300 and 2,750 MPa, more preferably between 1,300 and 2,500 MPa measured according to ASTM D790.

[0052] In a particularly preferred embodiment, said fluoropolymer has

[0053] - a melting point between 145 °C and 160 °C, preferably between 150 °C and 160 °C, measured according to ASTM D3418,

[0054] - a molten viscosity between 10 and 50 kP, preferably between 15 and 40 kP, more preferably between 20 and 40 kP measured at 230 °C and a shear rate of 100 s⁻¹ measured according to ASTM D3835, and

[0055] - a flexural modulus between 1,000 MPa and 1,500 MPa, preferably between 1000 and 1400 MPa, more preferably between 1000 MPa and 1300 MPa measured according to ASTM D790.

[0056] In another particularly preferred embodiment, said fluoropolymer has

[0057] - a melting point between 160 °C and 180 °C measured according to ASTM standard D3418,

[0058] - a molten viscosity between 1 and 10 kP, preferably between 2 and 10 kP, more preferably between 3 and 9 kP measured at 230 °C and a shear rate of 100 s⁻¹ measured according to ASTM D3835, and

[0059] - a flexural modulus between 1,300 and 3,000 MPa, preferably between 1,300 and 2,750 MPa, more preferably between 1,300 and 2,500 MPa, in particular between 1,500 and 2,500 MPa measured according to ASTM D790.

[0060] In another particularly preferred embodiment, said fluoropolymer has

[0061] - a melting point between 160 °C and 180 °C measured according to ASTM standard D3418,

[0062] - a molten viscosity between 10 and 50 kP, preferably between 15 and 40 kP, more preferably between 20 and 40 kP measured at 230 °C and a shear rate of 100 s⁻¹ measured according to ASTM D3835, and

[0063] - a flexural modulus between 1,300 and 3,000 MPa, preferably between 1,300 and 2,750 MPa, more preferably between 1,300 and 2,500 MPa, in particular between 1,300 and 2,000 MPa measured according to ASTM D790.

[0064] In a preferred embodiment, said fluoropolymer comprises at least one fluoromonomer selected from the group consisting of vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, hexafluoropropene, vinyl fluoride, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropene, 3,3,3-trifluoro-l-propene, 2,3,3,3-tetrafluoropropene, fluorinated vinyl ethers, fluorinated allyl ethers and fluorinated dioxoles.

[0065] Preferably, said fluoropolymer comprises at least one fluoromonomer selected from the group consisting of vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, hexafluoropropene, and fluorinated vinyl ethers. In particular, said fluoropolymer comprises at least repeating vinylidene fluoride units.

[0066] In a particular embodiment, said fluoropolymer is selected from the group consisting of vinylidene fluoride homopolymers and copolymers containing at least 50% by weight of vinylidene fluoride repeating units, the comonomer being selected from the group consisting of chlorotrifluoroethylene, hexafluoropropene, and trifluoroethylene. In particular, preferred copolymers are vinylidene fluoride copolymers with hexafluoropropene, hexafluoropropene, or chlorotrifluoroethylene, comprising from about 50 to about 99% by weight of vinylidene fluoride, more preferably from about 70 to about 99% by weight of vinylidene fluoride.

[0067] The term "PVDF" used here includes vinylidene fluoride (VDF) homopolymers or copolymers of VDF and at least one other comonomer in which vinylidene fluoride represents at least 50% by weight.

[0068] In a preferred embodiment, the fluoropolymer is a poly(vinylidene fluoride) (PVDF) homopolymer or a vinylidene fluoride copolymer with hexafluoropropene. Preferably, the fluoropolymer is a poly(vinylidene fluoride) (PVDF) homopolymer or a vinylidene fluoride copolymer with hexafluoropropene in which the HFP content is less than or equal to 50% by weight, advantageously less than or equal to 40% by weight, preferably less than or equal to 30% by weight, more preferably less than or equal to 20% by weight, and in particular less than 10% by weight. Thus, the vinylidene fluoride copolymer with hexafluoropropene comprises repeating units of vinylidene fluoride and repeating units of hexafluoropropene.

[0069] In a particular embodiment, the fluoropolymer is a poly(vinylidene fluoride) homopolymer having head-to-tail defects in the chain of vinylidene fluoride motifs. The term "head-to-tail defects" refers to the inversion in the chain of vinylidene fluoride motifs. Preferably, the degree of head-to-tail defects does not exceed 10%. The degree of head-to-tail defects is measured by 19F NMR. Advantageously, the degree of head-to-tail defects does not exceed 9%, preferably does not exceed 8%, more preferably does not exceed 7%, in particular does not exceed 6%, specifically does not exceed 5%, more specifically does not exceed 4%.

[0070] In another particular embodiment, the fluoropolymer is a copolymer of vinylidene fluoride with hexafluoropropene in which the HFP content is less than or equal to 15% by weight, advantageously less than or equal to 14% by weight, preferably less than or equal to 13% by weight, more preferably less than or equal to 12% by weight, particularly less than 11% by weight, more particularly less than 10% by weight, and the repeating motifs of hexafluoropropene are randomly distributed along the poly(vinylidene fluoride) backbone.

[0071] The fluoropolymer may further comprise monomers having at least one functionality selected from carboxyl, epoxy, carbonyl, and hydroxyl. Examples of monomers capable of introducing carboxyl functionalities are monomers of the unsaturated monobasic acid or unsaturated dibasic acid type in the form of free acid, salt, or anhydride, selected from the group consisting of sulfonic acid groups, phosphonic acid groups, and carboxylic acid groups and their corresponding salts or anhydrides. Such monomers are acrylic acid, methacrylic acid, a vinylsulfonic acid, Examples of monomers capable of introducing epoxy functionalities include vinylphosphonic acid, itaconic acid, maleic acid, and salts of such compounds. Examples of monomers capable of introducing epoxy functionalities include allyl glycidyl ether, methyl glycidyl ether, crotonic acid glycidyl ether, and acetic acid glycidyl ether. Examples of monomers capable of introducing carbonyl functionalities include ethylene carbonate. Examples of monomers capable of introducing hydroxyl functionalities include hydroxyethyl acrylate and hydroxypropyl acrylate.

[0072] The functionalized monomers can be used in an amount ranging from 0.01 to 15 percent by weight based on the total monomers. Preferably, they are used in an amount ranging from 0.05 to 5 percent by weight based on the total monomers, and even more preferably in an amount ranging from 0.05 to 1.5 percent by weight based on the total monomers.

[0073] The functionalized fluoropolymer is mainly produced via heterogeneous polymerization reactions, including suspension, emulsion, and microemulsion systems. Generally, each of these reactions requires at least one acid-functionalized monomer or a corresponding salt, at least one fluoromonomer, and a radical initiator in a suitable reaction medium. Furthermore, emulsion polymerizations of halogen-containing monomers generally require a surfactant capable of emulsifying both reactants and reaction products for the duration of the polymerization reaction.

[0074] According to one embodiment, the fluoropolymers used in the present invention are prepared by an emulsion polymerization process in the absence of a fluorinated surfactant.

[0075] In certain embodiments, a process similar to that disclosed in document WO 2012 / 030784 can be used to prepare the functionalized fluoropolymers used in the present invention. The temperature used for polymerization can vary from 20 to 130 °C. The pressure used for polymerization can vary from 280 to 20,000 kPa.

[0076] A pressurized polymerization reactor equipped with a stirrer and a thermal control device is loaded with water, preferably demineralized water, one or more functionalized monomers, and at least one fluoromonomer. The mixture may optionally contain one or more of a surfactant, a buffering agent, an antifouling agent, or a chain transfer agent for regulating the molecular weight of the polymer product. Before the introduction of the monomer or monomers, air is preferably removed from the reactor to obtain an oxygen-free environment for the polymerization reaction. The order in which the polymerization components are assembled can be modified, although it is generally preferred that at least a portion of the functionalized monomer be present in the aqueous reaction medium before the initiation of fluoromonomer polymerization. An additional amount of functionalized monomer can be fed into the reactor during the reaction.

[0077] In one embodiment, water, an initiator, a functionalized monomer, and optionally a surfactant, an antifouling agent, a chain transfer agent, and / or a buffer are loaded into the reactor, and the reactor is heated to the desired reaction temperature. The fluoromonomer(s) is / are then fed into the reactor, preferably at a rate that produces a practically constant pressure. Alternatively, the fluoromonomer, the functionalized monomer, and the initiator may be fed into the reactor, along with one or more of the optional ingredients. Monomer feeding is complete when the desired weight of monomer has been fed into the reactor. Additional radical initiator is optionally added, and the reaction is allowed to proceed for a suitable duration. The reactor pressure decreases as the monomer in the reactor is consumed.

[0078] Once the polymerization reaction is complete, the reactor is brought to room temperature and the unreacted residual monomer is aerated at atmospheric pressure. The aqueous reaction medium containing the fluoropolymer is then recovered from the reactor in the form of a latex. The latex consists of a stable mixture of the reaction components, namely water, surfactant, initiator (and / or initiator decomposition products), and solids of functionalized fluoropolymer. The latex may contain approximately 10 to approximately 50 percent polymer solids, preferably 20 to 40 percent by weight. The polymer in the latex is in the form of small particles with a size range of approximately 30 nm to approximately 800 nm.

[0079] Following polymerization, the fluoropolymer is stirred, thickened and dried.

[0080] The fluoropolymer thus obtained is processed to form a powder. The powder of Fluoropolymer can be obtained by various processes. Powder can be obtained directly by an emulsion or suspension synthesis process, followed by spray drying or freeze-drying. Powder can also be obtained by grinding techniques, such as cryo-milling, where the fluoropolymer is cooled below ambient temperature, for example using liquid nitrogen, before grinding.

[0081] In a preferred embodiment, said fluoropolymer is a powder having a particle size distribution with a Dv50 of less than 20 pm, preferably less than 15 pm, more preferably less than 10 pm. At the end of the powder manufacturing step, namely after polymerization and drying steps, the particle size can be adjusted and optimized by processes of selection or screening and / or grinding in cases where the Dv50 is above 10 µm. The particle size distribution mentioned here is usually obtained when the fluoropolymer is prepared by an emulsion process.

[0082] In another preferred embodiment, said fluoropolymer is prepared by means of a suspension process.

[0083] In a second aspect of the present invention, a dry-coated electrode is provided. The dry-coated electrode comprises the non-fibrillable binder of the present invention, a conductive agent, and a dry active material.

[0084] In a preferred embodiment, the dry-coated electrode has the following mass composition:

[0085] a. 50% to 99.9% active material, preferably 50% to 99%

[0086] b. 25% to 0% of conducting agent, preferably 25% to 0.5%,

[0087] c. 25% to 0.05% non-fibrillable binder, preferably 25% to 0.5%,

[0088] d. 0% to 5% of at least one additive chosen from the group consisting of a plasticizer, an ionic liquid, a dispersing agent for conductive additive, and an auxiliary flow agent;

[0089] the sum of all these percentages being 100%.

[0090] The conductive agents in the dry-coated electrode are composed of one or more materials that can improve conductivity. Some examples include carbon blacks such as acetylene black, Ketjen black; carbon fibers, such as a carbon nanotube, a carbon nanofiber, a carbon fiber by vapor-phase growth; metal powders such as SUS powder, and aluminum powder.

[0091] Active materials are materials that are capable of storing and releasing lithium ions.

[0092] In a preferred embodiment, said electrode is a negative electrode. In particular, for a negative electrode, said active material is selected from the group consisting of a lithium alloy, a metal oxide, a carbon material such as graphite or hard carbon, silicon, a silicon alloy, and Li4Ti50i2. The shape of the active material of the negative electrode is not particularly limited but is preferably particulate.

[0093] In another preferred embodiment, said electrode is a positive electrode. Preferably, for a positive electrode, said active material is chosen from the group consisting of LiCoO2, Li(Ni,Co,Al)O2, Li(l+x)NiaMnbCoc (x represents a real number of 0 or more, a = 0.8, 0.6, 0.5, or 1 / 3, b = 0.1, 0.2, 0.3, or 1 / 3, c = 0.1, 0.2, or 1 / 3), LiNiO2, LiMn2O4, LiCoMnO4, Li3NiMn3O3, Li3Fe2(PO4)3, Li3V2(PO4)3, a LiMn spinel substituted by a different element having a composition represented by Ll+xMn2-x-yMyO4, M representing at least one metal chosen from Al, Mg, Co, Fe, Ni, and Zn, x and y independently representing a real number between 0 and 2, lithium titanate LixTiOy - x and y independently representing a real number between 0 and 2, and a metal and lithium phosphate having a composition represented by LiMP04, M representing Fe, Mn, Co, or Ni.

[0094] Furthermore, the surface of each of the materials described above can be coated. The coating material is not particularly limited as long as it has lithium ion conductivity and contains a material capable of being maintained as a coating layer on the surface of the active material. Examples of coating materials include LiNbO3, Li4Ti5O12, and Li3PO4.

[0095] The shape of the active material of the positive electrode is not particularly limited but is preferably particulate.

[0096] The invention also relates to a method for preparing the dry-coated electrode, said method comprising a thermomechanical treatment step carried out at a temperature in the range of 20 °C below the melting point of the non-fibrillable binder up to 50 °C above the melting point of the non-fibrillable binder.

[0097] Said method for preparing the dry-coated electrode comprises the following steps:

[0098] - mixture of the active material, the non-fibrillable binder of the present invention under powder form as described above, and of the conductive agent using a process that provides an electrode formulation applicable to a metallic substrate by a "solvent-free" process;

[0099] - deposition of said electrode formulation onto a substrate by a solvent-free process to obtain a Li-ion battery electrode, and

[0100] - consolidation of said electrode by a thermomechanical treatment carried out at a temperature in the range of 20 °C below the melting point of the non-fibrillable binder up to 50 °C above the melting point of the non-fibrillable binder.

[0101] A “solvent-free” process is a process that does not require a residual solvent evaporation step after the deposition step.

[0102] A thermomechanical treatment refers to the application of a temperature from 20 °C below the polymer's melting point to 50 °C above the polymer's melting point, under mechanical pressure. The pressure applied during the thermomechanical treatment is generally less than 1 kN / mm², preferably less than 0.75 kN / mm², and more preferably less than 0.5 kN / mm². Such a thermomechanical treatment can be carried out, for example, by a calendering machine with heated rollers or a plate press that can also be heated.

[0103] According to one embodiment, after the powder mixing step, the electrode is manufactured by a solvent-free spraying process, by depositing the formulation onto the metallic substrate, by a pneumatic spraying process, by electrostatic spraying, by dipping in a fluidized powder bed, by sprinkling, by electrostatic screen printing, by deposition with rotary brushes, by deposition with rotary adding rollers, by calendering.

[0104] According to one embodiment, after the powder mixing step, the electrode is manufactured by a solvent-free, two-step process. The first step consists of manufacturing a self-supporting film from the premixed formulation using a thermomechanical process such as extrusion, calendering, or thermocompression. In the second step, the self-supporting film is laminated onto the metallic substrate by a process combining temperature and pressure, such as calendering or thermocompression.

[0105] The mass ratio of conducting agents to active material is preferably 0 to 10%, more preferably 0 to 7%.

[0106] The mass ratio of binder to active material is preferably from 0.1 to 10%, more preferably from 0.5 to 7%.

[0107] According to one embodiment, the electrode components are all mixed at once according to conventional processes, leading to an electrode formulation.

[0108] In one embodiment, said electrode formulation is applied to a substrate by electrostatic screen printing. Some examples of substrates are current collectors such as a metal foil and metal mesh, polymer films, or a solid electrolyte layer of a solid-state battery.

[0109] The preferred thickness of an electrode is from 0.1 pm to 1000 pm, preferably from 0.1 pm to 300 pm.

[0110] In a third aspect of the present invention, a Li-ion battery is provided. Preferably, the Li-ion battery comprises a positive electrode, a negative electrode and a separator, at least one electrode being a dry-coated electrode according to the present invention. Examples

[0111] The following examples illustrate the present invention without limiting it. Materials:

[0112] PVDF 1: Vinylidene fluoride homopolymer having a melting point of 165 °C, a melt viscosity of 4 kP and a flexural modulus of 1655 MPa.

[0113] PVDF 2: Vinylidene fluoride homopolymer having head-to-tail defects (5.5% defects) and a melting temperature of 161 °C, a melt viscosity of 23.5 kP and a flexural modulus of 1380 MPa.

[0114] PVDF 3: Copolymer of vinylidene fluoride and hexafluoropropylene (approximately 5 wt% of HFP) comprising an acrylic acid group having a functionality of approximately 1 wt% characterized by a melting temperature of 151 °C, a melt viscosity of 34 kP and a flexural modulus of 1030 MPa.

[0115] PVDF 4: Copolymer of vinylidene fluoride and hexafluoropropylene (approximately 5 wt% HFP - randomly distributed) characterized by a melting temperature of 155 °C, a melt viscosity of 23 kP and a flexural modulus of 1034 MPa.

[0116] PVDF 5: Copolymer of vinylidene fluoride and hexafluoropropylene (approximately 12 wt% HFP) characterized by a melting temperature of 140 °C, a melt viscosity of 12 kP and a flexural modulus of 620 MPa.

[0117] PVDF 6: Copolymer of vinylidene fluoride and hexafluoropropylene (approximately 18 wt% HFP) characterized by a melting temperature of 117 °C, a melt viscosity of 5 kP and a flexural modulus of 192 MPa. Electrode Formulation

[0118] A negative electrode is prepared using each PVDF described above. 158-C (graphite, BTR) and binders were added to a 125 mL plastic bottle with a lid. The ratio of 158-C to binder was 98.5 / 1.5 by weight. Zirconia beads were added to the container. The powder was mixed by an ARE-310 (Thinky) at 2000 rpm for 30 s. The mixed powder was sandwiched between two copper sheets. The copper sheet and powder were compressed in a roller press (SA-602, TESTER SANGYO CO., LTD.) at 160 °C, load of 10 kN, speed of 0.5 m / min. The prepared electrodes were bent into a U-shape and considered OK if no cracks or breaks occurred, and not OK (abbreviated "NOK") if cracks or breaks were observed. The properties of each tested binder and the results are presented in Table 1.

[0119] [Tables 1] Binder Name Melting Point Melt Viscosity Flexural Modulus Bending Result PVDF 1 168 °C 6 kP 1982 MPa OK PVDF 2 161 °C 26.5 kP 1585 MPa OK PVDF 3 154 °C 36 kP 1030 MPa OK PVDF 4 157 °C 25 kP 1137 MPa OK PVDF 5 142 °C 16 kP 723 MPa NOK PVDF 6 121 °C 10 kP 234 MPa NOK

[0120] Melting point measured according to ASTM D3418 / Viscosity in the molten state measured at 230 °C and a shear rate of 100 s-1 according to ASTM D3835 / Bending modulus measured according to ASTM D790

Claims

Demands

1. A non-fibrillable binder for a dry-coated electrode, said binder being a fluoropolymer being a homopolymer of vinylidene fluoride and having a melting point between 160°C and 180°C measured according to ASTM D3418, a melt viscosity between 1 and 10 kP or between 15 and 50 kP measured at 230°C and a shear rate of 100 s⁻¹ measured according to ASTM D3835; and a flexural modulus between 1300 and 3000 MPa measured according to ASTM D790

2. Binder according to the preceding claim, said fluoropolymer being a vinylidene fluoride homopolymer having head-to-tail defects in the chain of vinylidene fluoride motifs, and the degree of head-to-tail defects not exceeding 10%.

3. Binder according to any one of claims 1 to 2, said fluoropolymer comprising functionalized monomers in an amount from 0.01 to 15 percent by weight on the basis of the total monomers, preferably from 0.05 to 5 percent by weight on the basis of the total monomers, and even more preferably in an amount from 0.05 to 1.5 percent by weight on the basis of the total monomers.

4. Binder according to claim 3, said functionalized monomers having at least one functionality being selected from: acrylic acid, methacrylic acid, vinylsulfonic acid, vinylphosphonic acid, itaconic acid, maleic acid and salts of such compounds; allyl glycidyl ether, methyl glycidyl ether, crotonic acid glycidyl ether and acetic acid glycidyl ether; ethylene carbonate; hydroxyethyl acrylate and hydroxypropyl acrylate.

5. Binder according to any one of claims 1 to 4, said fluoropolymer being a powder having a particle size distribution having a Dv50 of less than 20 pm, preferably less than 15 pm, in particular less than 10 pm.

6. Dry coated electrode comprises a non-fibrillable binder according to any one of the preceding claims, a dry active material and optionally a conductive agent.

7. A dry-coated electrode according to the preceding claim, having the following mass composition: a. 50% to 99.9% active material, preferably 50% to 99%, b. 25% to 0% conducting agent, preferably 25% to 0.5%, c. 25% to 0.05% non-fibrillable binder, preferably 25% to 0.5%, d. 0% to 5% of at least one additive selected from the group consisting of a plasticizer, an ionic liquid, a dispersing agent for a conducting additive, and a flow aid; the sum of all these percentages being 100%.

8. Dry coated electrode according to any one of claims 6 or 7, said conductive agents, if present, being composed of one or more materials from among carbon blacks, such as acetylene black, Ketjen black; carbon fibers, such as a carbon nanotube, a carbon nanofiber, a carbon fiber by vapor phase growth; metal powders such as a SUS powder, and an aluminum powder.

9. A dry-coated electrode according to any one of claims 6 to 8, wherein, for a positive electrode, said active material is selected from the group consisting of: LiCoO2, Li(Ni,Co,Al)O2, Li(l+x), NiaMnbCoc (x represents a real number of 0 or more, a = 0.8, 0.6, 0.5, or 1 / 3, b = 0.1, 0.2, 0.3, or 1 / 3, c = 0.1, 0.2, or 1 / 3), LiNiO2, LiMn2O4, LiCoMnO4, Li3NiMn3O3, Li3Fe2(PO4)3, Li3V2(PO4)3, a LiMn spinel substituted by a different element having a composition represented by Ll+xMn2-x-yMyO4, M representing at least one metal selected from Al, Mg, Co, Fe, Ni, and Zn, x and y independently representing a real number between 0 and 2, lithium titanate LixTiOy - x and y independently representing a real number between 0 and 2, and a metal and lithium phosphate having a composition represented by LiMPO4, M representing Fe, Mn, Co, or Ni.

10. Dry coated electrode according to any one of claims 6 to 8, wherein, for a negative electrode, said active material is selected from the group consisting of: a lithium alloy, a metal oxide, a carbon material such as graphite or hard carbon, silicon, a silicon alloy and Li4TiO12.

11. A method for preparing the dry-coated electrode according to any one of claims 6 to 10, comprising the following steps: - mixing of the active material, the non-fibrillable binder of the present invention in powder form, and optionally the conductive agent using a process that provides an electrode formulation applicable to a metallic substrate by a "solvent-free" process; - deposition of said electrode formulation onto a substrate by a solvent-free process to obtain a Li-ion battery electrode, and - consolidation of said electrode by a thermomechanical treatment carried out at a temperature in the range of 20 °C below the melting point of the non-fibrillable binder up to 50 °C above the melting point of the non-fibrillable binder.

12. Li-ion battery comprising a positive electrode, a negative electrode and a separator, at least one electrode being a dry-coated electrode according to any one of claims 6 to 10.