Binder for dry coated electrodes

Abstract

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

Description

[Technical field]

[0001] The present invention relates generally to the field of electrical energy storage in lithium accumulators of the Li-ion type. More specifically, the present invention relates to a non-fibrillizable binder for dry-coated electrodes for Li-ion batteries. Another subject of the invention is a method for producing electrodes using said binder. The present invention also relates to a lithium-ion battery produced by incorporating said electrode. [Background technology]

[0002] The basic cell of a Li-ion accumulator or lithium battery consists of an anode (when discharging), usually made of a lithium insertion compound of the metal oxide type such as LiMn2O4, LiCoO2 or LiNiO2, and a cathode (also when discharging), between which an electrolyte that conducts lithium ions is inserted.

[0003] Rechargeable or secondary batteries have an advantage over primary (non-rechargeable) batteries because the relevant chemical reactions occurring at the positive and negative electrodes of the battery are reversible. The electrodes of secondary batteries can be regenerated several times by applying an electric charge. Many advanced electrode systems have been developed to store the electric charge. At the same time, much effort has been put into the development of electrolytes that can improve the capacity of electrochemical cells.

[0004] For their part, the electrodes generally comprise at least one current collector, on which is deposited in the form of a film a composite material consisting of a so-called active material, electrochemically active towards lithium, a polymer acting as a binder, one or more electronically conductive additives, generally carbon black or acetylene black, and optionally a surfactant.

[0005] Binders are counted among the so-called inactive components, since they do not directly contribute to the battery capacity. However, their important role in electrode processing and their considerable impact on the electrochemical performance of the electrode 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 purpose of using binders is to form a stable network of the solid components of the electrode, i.e., active materials and conductive agents (cohesion). The binder must also ensure the adhesion (adhesion) between the composite electrode and the current collector.

[0006] Polyvinylidene fluoride (PVDF) is used as a binder in lithium-ion batteries due to its excellent electrochemical stability, good binding ability, and high adhesion to electrode materials and current collectors. PVDF can only be dissolved in certain organic solvents, such as N-methylpyrrolidone (NMP), which is volatile, flammable, explosive, and highly toxic, leading to serious environmental problems. In fact, in the wet slurry method, the active material and binder are dispersed in a liquid solution. The liquid used is usually an organic solvent or water. The dispersion is cast onto a current collector and then dried in a high-temperature oven to produce the electrode. In this method, a large amount of energy is required to dry the liquid components of the slurry, and the organic solvent further generates harmful vapors that require special equipment to prevent their free release into the environment.

[0007] Compared to traditional wet suspension electrode manufacturing methods, dry (solvent-free) manufacturing methods are simpler. These methods eliminate the emission of volatile organic compounds and offer the possibility to manufacture electrodes of higher thickness (>120 μm) with higher energy density of the final energy storage device. The change in manufacturing technology has little effect on the active material of the electrode, but the polymer additives responsible for the mechanical integrity of the electrode must be adapted to the new manufacturing conditions.

[0008] US2019 / 0305316 discloses dry process electrode films comprising particulate non-fibrillating binders with specific particle sizes, and a method for obtaining a film flexible enough to be handled in a roll-to-roll process by using a fibrillating binder. However, fibrillating binders require either extra shear in addition to dispersing the components, which is highly energy consuming and destructive to the active material. US2020 / 0313193 also discloses dry process electrode films comprising elastic polymer binders, where the dry electrode film is self-supporting and contains at most a negligible amount of polytetrafluoroethylene. US2020 / 0313193 mainly discloses polyethylene as an elastic polymer binder, which is not electrochemically stable enough to be used in both the cathode and anode of lithium-ion secondary batteries. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] US Patent Application Publication No. 2019 / 0305316 [Patent Document 2] US Patent Application Publication No. 2020 / 0313193 Summary of the Invention [Problem to be solved by the invention]

[0010] Therefore, there remains a need to develop new binder and electrode compositions for Li-ion batteries that are suitable for processing without the use of organic solvents. [Means for solving the problem]

[0011] According to a first aspect, the present invention provides a cellulose ester having a melting point between 145° C. and 200° C. as measured according to ASTM D3418 and a melting point of 100 s as measured according to ASTM D3835. -1and a melt viscosity of less than 50 kP measured at 230° C. at a shear rate of 1000 nm.

[0012] In particular, the melting point is defined as the temperature at the peak of the melting endotherm measured according to ASTM D3418.

[0013] The present invention provides binders with specific properties that allow the preparation of flexible free-standing films. By using the fluoropolymer binders of the present invention, ductile electrode films can be obtained in just one step of mixing and applying the electrode by a dry process.

[0014] The present invention also provides a binder that does not contain fibrillizable material to avoid an additional shear step, therefore the total energy consumption of the process is less compared to when a fibrillizable binder is used.

[0015] Furthermore, the fluoropolymer binders according to the present invention are more electrochemically stable than polyethylene, allowing for higher capacity and cycling characteristics in electrochemical cells employing such electrodes.

[0016] According to a preferred embodiment, said fluoropolymer has a flexural modulus, measured according to ASTM D790, of more than 1000 MPa.

[0017] According to a preferred embodiment, the 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-1-propene, 2,3,3,3-tetrafluoropropene, fluorinated vinyl ethers, fluorinated allyl ethers and fluorinated dioxoles.

[0018] According to a preferred embodiment, the fluoropolymer is selected from the group consisting of homopolymers and copolymers of vinylidene fluoride containing at least 50% by weight of vinylidene fluoride repeat units, the comonomer being selected from the group consisting of chlorotrifluoroethylene, hexafluoropropene and trifluoroethylene.

[0019] According to a preferred embodiment, the fluoropolymer is a polyvinylidene fluoride (PVDF) homopolymer or a copolymer of vinylidene fluoride and hexafluoropropene.

[0020] According to a preferred embodiment, said fluoropolymer is a polyvinylidene fluoride homopolymer having head-to-tail defects in the chain of vinylidene fluoride units, the degree of head-to-tail defects not exceeding 10%.

[0021] According to a preferred embodiment, the fluoropolymer comprises a functionalized monomer in an amount of 0.01 to 15 weight percent based on total monomers, preferably in an amount of 0.05 to 5 weight percent based on total monomers, and even more preferably in an amount of 0.05 to 1.5 weight percent based on total monomers.

[0022] According to a preferred embodiment, the functionalized monomer having at least one functional group is selected from acrylic acid, methacrylic acid, vinylsulfonic acid, vinylphosphonic acid, itaconic acid, maleic acid and the salts of such compounds, allyl glycidyl ether, methallyl glycidyl ether, crotonic acid glycidyl ether and acetic acid glycidyl ether, ethylene carbonate, hydroxylethyl acrylate and hydroxylpropyl acrylate.

[0023] According to a preferred embodiment, said fluoropolymer is prepared by either emulsion or suspension polymerization, preferably emulsion polymerization.

[0024] According to a preferred embodiment, said fluoropolymer is a powder having a particle size distribution with a Dv50 of less than 20 μm, preferably less than 15 μm, in particular less than 10 μm.

[0025] Dv50 is the particle size at the 50th percentile (by volume) of the cumulative size distribution of particles. This parameter can be determined by laser granulometry. It applies to all Dv50s listed in this specification. Measurements are performed by dry path by laser diffraction on powders using a Malvern INSITEC System particle size analyzer at a focus of 100 mm.

[0026] According to a second aspect, the present invention provides a dry coated electrode comprising the non-fibrillating binder of the present invention, a conductive agent and a dry active material.

[0027] According to a preferred embodiment, the dry coated electrode according to claim 8 has the following mass composition: a. 50% to 99.9%, preferably 50% to 99%, of an active material; b. 25% to 0%, preferably 25% to 0.5%, of a conductive agent; c. 25% to 0.05%, preferably 25% to 0.5%, of a non-fibrillating binder; d. having 0-5% of at least one additive selected from the group consisting of plasticizers, ionic liquids, dispersants for conductive additives, and flow aids; All these percentages add up to 100%.

[0028] According to a preferred embodiment, the conductive agent is composed of one or more materials selected from the group consisting of carbon black such as acetylene black and Ketjen black, carbon nanotubes, carbon nanofibers, and carbon fibers such as vapor-grown carbon fibers, and metal powders such as SUS powder and aluminum powder.

[0029] According to a preferred embodiment, the active material for the positive electrode is LiCoO2, Li(Ni,Co,Al)O2, Li (1+x) , Ni a Mnb Co c (x is a real number equal to or greater than 0; 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, Li 1+x Mn 2-x-y M y LiMn spinel substituted with different elements having a composition represented by the formula O4 (wherein M represents at least one metal selected from Al, Mg, Co, Fe, Ni and Zn, and x and y each independently represent a real number between 0 and 2), lithium titanate Li x TiO y (x and y each independently represent a real number between 0 and 2), and lithium metal phosphate having a composition represented by LiMPO4 (M represents Fe, Mn, Co, or Ni).

[0030] According to a preferred embodiment, the active material for the negative electrode is a lithium alloy, a metal oxide, a carbon material such as graphite or hard carbon, silicon, a silicon alloy, Li4TiO 12 is selected from the group consisting of:

[0031] According to a third aspect, the present invention provides a method for preparing a dry coated electrode according to the invention, said method comprising a thermomechanical treatment step carried out at a temperature ranging from 20° C. below the melting point of the non-fibrillizable binder to 50° C. above the melting point of the non-fibrillizable binder.

[0032] 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.

[0033] The invention makes it possible to ensure the cohesion and mechanical integrity of the electrode, ensures good filming or compaction of the formulation, which may be difficult to achieve with solventless processes, produces adhesion on the metal substrate, ensures homogeneity of the electrode composition across the thickness and width of the electrode, ensures homogeneity in the thickness and width of the electrode, and reduces the overall binder content in the electrode, which is still higher for known dry processes than for standard slurry processes. The advantage of this technology is that it improves the following properties of the electrode: homogeneity of the composition in the thickness, cohesion, and adhesion on the metal substrate. It also allows a reduction in the proportion of binder required 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 PREFERRED EMBODIMENTS

[0034] According to a first aspect of the present invention, there is provided a non-fibrillizable binder for a dry-coated electrode.

[0035] The term "fluoropolymer" means a polymer formed by polymerization of at least one fluoromonomer, and includes homopolymers, copolymers, terpolymers and higher polymers that are thermoplastic. In certain embodiments of the present invention, the fluoropolymer contains at least 50 mole percent of one or more fluoromonomers in polymerized form.

[0036] "Thermoplastic" is understood herein to mean a non-elastic polymer. An elastic polymer is defined as a polymer that can be stretched to twice its original length at ambient temperature and rapidly recovers to within about 10% of its original length after the stress is released, as indicated by ASTM Special Technical Publication No. 184.

[0037] In a preferred embodiment, the binder comprises a fluoropolymer having a melting point, measured according to ASTM D3418, 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, in particular between 150°C and 175°C, more particularly between 150°C and 170°C, most particularly between 150°C and 165°C, especially between 150°C and 160°C.

[0038] In a preferred embodiment, the binder has a viscosity of 230° C. and 100 s measured according to ASTM D3835. -1 Advantageously, the fluoropolymer comprises a fluoropolymer having a melt viscosity of less than 50 kP measured at a shear rate of 230° C. and 100 s. -1 of less than 48 kP, preferably less than 46 kP, more preferably less than 44 kP, specifically less than 42 kP, and more specifically less than 40 kP, measured at a shear rate of 100 .mu.m.

[0039] Preferably, the fluoropolymer has a viscosity of 230° C. and 100 s measured according to ASTM D3835. -1 of greater than 1 kP, more preferably greater than 2 kP, especially greater than 3 kP, and particularly greater than 3.5 kP, measured at a shear rate of 100 .mu.m.

[0040] In a preferred embodiment, the binder comprises 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, particularly between 150°C and 175°C, more particularly between 150°C and 170°C, most particularly between 150°C and 165°C, especially between 150°C and 160°C, measured according to ASTM D3418, and the fluoropolymer has a melting point between 230°C and 100s measured according to ASTM D3835. -1of less than 50 kP, advantageously less than 48 kP, preferably less than 46 kP, more preferably less than 44 kP, particularly less than 42 kP, and more particularly less than 40 kP, measured at a shear rate of 100 .mu.m.

[0041] Thus, the binder comprises 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, particularly between 150°C and 175°C, more particularly between 150°C and 170°C, most particularly between 150°C and 165°C, especially between 150°C and 160°C, measured according to ASTM D3418, and the fluoropolymer has a melting point between 230°C and 100s measured according to ASTM D3835. -1 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, and more specifically less than 40 kP, measured at a shear rate of 230° C. and 100 s, measured according to ASTM D3835. -1 of greater than 1 kP, preferably greater than 2 kP, more preferably greater than 3 kP, specifically greater than 3.5 kP, measured at a shear rate of 100 .mu.m.

[0042] In a preferred embodiment, said fluoropolymer has a flexural modulus measured according to ASTM D790 of more than 1000 MPa. Advantageously, said fluoropolymer has a flexural modulus measured according to ASTM D790 of less than 3000 MPa, preferably less than 2900 MPa, more preferably less than 2800 MPa, in particular less than 2700 MPa, particularly less than 2600 MPa, more particularly less than 2500 MPa.

[0043] Thus, the binder comprises 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, particularly between 150°C and 175°C, more particularly between 150°C and 170°C, most particularly between 150°C and 165°C, especially between 150°C and 160°C, measured according to ASTM D3418, and the fluoropolymer has a melting point between 230°C and 100s measured according to ASTM D3835. -1 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, particularly less than 42 kP, and more particularly less than 40 kP, measured at a shear rate of 1000 MPa or more, and said fluoropolymer has a flexural modulus of greater than 1000 MPa, measured according to ASTM D790.

[0044] Preferably, the binder comprises 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, particularly between 150°C and 175°C, more particularly between 150°C and 170°C, most particularly between 150°C and 165°C, especially between 150°C and 160°C, as measured according to ASTM D3418, and the fluoropolymer has a melting point between 230°C and 100°C, as measured according to ASTM D3835. -1 and said fluoropolymer has a flexural modulus, measured according to ASTM D790, of more than 1000 MPa and less than 3000 MPa, preferably less than 2900 MPa, more preferably less than 2800 MPa, particularly less than 2700 MPa, particularly less than 2600 MPa, more particularly less than 2500 MPa.

[0045] In a more preferred embodiment, the fluoropolymer has a melting point, measured according to ASTM D3418, between 145° C. and 160° C., preferably between 150° C. and 160° C. Alternatively, the fluoropolymer has a melting point, measured according to ASTM D3418, between 160° C. and 180° C.

[0046] In a more preferred embodiment, the fluoropolymer has a viscosity of 230° C. and 100 s measured according to ASTM D3835. -1 Alternatively, the fluoropolymer has a melt viscosity of between 1 and 10 kP, preferably between 2 and 10 kP, and more preferably between 3 and 9 kP, measured at a shear rate of 230° C. and 100 s according to ASTM D3835. -1 The melt viscosity measured at a shear rate of 10 to 50 kP, preferably 15 to 40 kP, and more preferably 20 to 40 kP.

[0047] In a more preferred embodiment, the fluoropolymer has a flexural modulus measured according to ASTM D790 between 1000 MPa and 1500 MPa, preferably between 1000 MPa and 1400 MPa, more preferably between 1000 MPa and 1300 MPa. Alternatively, the fluoropolymer has a flexural modulus measured according to ASTM D790 between 1300 and 3000 MPa, preferably between 1300 and 2750 MPa, more preferably between 1300 and 2500 MPa.

[0048] In a most preferred embodiment, the fluoropolymer has: - melting point between 145°C and 160°C, preferably between 150°C and 160°C, measured according to ASTM D3418 - 230℃ and 100s measured according to ASTM D3835 -1 A melt viscosity measured at a shear rate of between 10 and 50 kP, preferably between 15 and 40 kP, and more preferably between 20 and 40 kP.

[0049] In another most preferred embodiment, the fluoropolymer, preferably a polyvinylidene fluoride (PVDF) homopolymer, has: - Melting point between 160°C and 180°C measured according to ASTM D3418 - 230℃ and 100s measured according to ASTM D3835 -1 A melt viscosity measured at a shear rate of between 1 and 10 kP, preferably between 2 and 10 kP, more preferably between 3 and 9 kP.

[0050] In another most preferred embodiment, the fluoropolymer, preferably a polyvinylidene fluoride (PVDF) homopolymer, has: - Melting point between 160°C and 180°C measured according to ASTM D3418 - 230℃ and 100s measured according to ASTM D3835 -1 A melt viscosity measured at a shear rate of between 10 and 50 kP, preferably between 15 and 40 kP, and more preferably between 20 and 40 kP.

[0051] In a particularly preferred embodiment, the fluoropolymer has: - melting point between 145°C and 160°C, preferably between 150°C and 160°C, measured according to ASTM D3418 - 230℃ and 100s measured according to ASTM D3835 -1 A melt viscosity measured at a shear rate of between 10 and 50 kP, preferably between 15 and 40 kP, and more preferably between 20 and 40 kP. - a flexural modulus measured according to ASTM D790 between 1000 MPa and 1500 MPa, preferably between 1000 MPa and 1400 MPa, more preferably between 1000 MPa and 1300 MPa

[0052] In another particularly preferred embodiment, the fluoropolymer, preferably a polyvinylidene fluoride (PVDF) homopolymer, has: - Melting point between 160°C and 180°C measured according to ASTM D3418 - 230℃ and 100s measured according to ASTM D3835 -1 A melt viscosity measured at a shear rate of between 1 and 10 kP, preferably between 2 and 10 kP, more preferably between 3 and 9 kP. a flexural modulus measured according to ASTM D790 between 1300 and 3000 MPa, preferably between 1300 and 2750 MPa, more preferably between 1300 and 2500 MPa, in particular between 1500 and 2500 MPa

[0053] In another particularly preferred embodiment, the fluoropolymer, preferably a polyvinylidene fluoride (PVDF) homopolymer, has: - Melting point between 160°C and 180°C measured according to ASTM D3418 - 230℃ and 100s measured according to ASTM D3835 -1 A melt viscosity measured at a shear rate of between 10 and 50 kP, preferably between 15 and 40 kP, and more preferably between 20 and 40 kP. a flexural modulus measured according to ASTM D790 between 1300 and 3000 MPa, preferably between 1300 and 2750 MPa, more preferably between 1300 and 2500 MPa, in particular between 1500 and 2000 MPa

[0054] In a preferred embodiment, the 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-1-propene, 2,3,3,3-tetrafluoropropene, fluorinated vinyl ethers, fluorinated allyl ethers and fluorinated dioxoles.

[0055] Preferably, the fluoropolymer comprises at least one fluoromonomer selected from the group consisting of vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, hexafluoropropene and fluorinated vinyl ethers. In particular, the fluoropolymer comprises at least vinylidene fluoride repeat units.

[0056] In a particular embodiment, the fluoropolymer is selected from the group consisting of homopolymers and copolymers of vinylidene fluoride containing at least 50% by weight of vinylidene fluoride repeat units, the comonomer being selected from the group consisting of chlorotrifluoroethylene, hexafluoropropene and trifluoroethylene. Particularly preferred copolymers are copolymers of vinylidene fluoride with hexafluoropropene, hexafluoropropene or chlorotrifluoroethylene, containing from about 50 to about 99 weight percent vinylidene fluoride, more preferably from about 70 to about 99 weight percent vinylidene fluoride.

[0057] The term "PVDF" as used herein includes vinylidene fluoride (VDF) homopolymer or copolymers of VDF and at least one other comonomer, where the vinylidene fluoride represents at least 50% by weight.

[0058] In a preferred embodiment, the fluoropolymer is a polyvinylidene fluoride (PVDF) homopolymer or a copolymer of vinylidene fluoride and hexafluoropropene.Preferably, the fluoropolymer is a polyvinylidene fluoride (PVDF) homopolymer, a copolymer of vinylidene fluoride and hexafluoropropene, and the level of HFP is 50% by weight or less, advantageously 40% by weight or less, preferably 30% by weight or less, more preferably 20% by weight or less, particularly less than 10% by weight, more particularly less than 8% by weight.Accordingly, the copolymer of vinylidene fluoride and hexafluoropropene comprises vinylidene fluoride repeat units and hexafluoropropene repeat units.

[0059] Preferably, when the fluoropolymer is a copolymer of vinylidene fluoride and hexafluoropropene and the level of HFP is 50% by weight or less, advantageously 40% by weight or less, preferably 30% by weight or less, more preferably 20% by weight or less and especially less than 10% by weight, the fluoropolymer has: - melting point between 145°C and 160°C, preferably between 150°C and 160°C, measured according to ASTM D3418 - 230℃ and 100s measured according to ASTM D3835 -1 A melt viscosity measured at a shear rate of between 10 and 50 kP, preferably between 15 and 40 kP, and more preferably between 20 and 40 kP.

[0060] More preferably, when the fluoropolymer is a copolymer of vinylidene fluoride and hexafluoropropene and the level of HFP is 50% by weight or less, advantageously 40% by weight or less, preferably 30% by weight or less, more preferably 20% by weight or less and especially less than 10% by weight, the fluoropolymer has: - melting point between 145°C and 160°C, preferably between 150°C and 160°C, measured according to ASTM D3418 - 230℃ and 100s measured according to ASTM D3835 -1 A melt viscosity measured at a shear rate of between 10 and 50 kP, preferably between 15 and 40 kP, and more preferably between 20 and 40 kP. - a flexural modulus measured according to ASTM D790 between 1000 MPa and 1500 MPa, preferably between 1000 MPa and 1400 MPa, more preferably between 1000 MPa and 1300 MPa

[0061] In a particular embodiment, the fluoropolymer is a polyvinylidene fluoride homopolymer or a copolymer of vinylidene fluoride and hexafluoropropene having head-to-tail defects in the chain of vinylidene fluoride units. The term "head-to-tail defects" refers to an inversion of the chain of vinylidene fluoride units. Preferably, the degree of head-to-tail defects does not exceed 10%. The degree of head-to-tail defects can be determined by: 19Advantageously, 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%, particularly does not exceed 5% and more particularly does not exceed 4%.

[0062] In another particular embodiment, the fluoropolymer is a copolymer of vinylidene fluoride and hexafluoropropene, with a level of HFP of 15% by weight or less, advantageously 14% by weight or less, preferably 13% by weight or less, more preferably 12% by weight or less, in particular less than 11% by weight, more particularly less than 10% by weight, and most particularly less than 8% by weight. The hexafluoropropene repeat units are randomly distributed along the polyvinylidene fluoride backbone.

[0063] The fluoropolymer may further comprise a monomer having at least one functional group selected from carboxyl, epoxy, carbonyl or hydroxyl. Examples of monomers capable of introducing carboxyl functionality are unsaturated monobasic or dibasic acid monomers in free acid, salt form or anhydride form selected from the group consisting of sulfonic acid, phosphonic acid and carboxylic acid groups and their salts or anhydrides. Such monomers are acrylic acid, methacrylic acid, vinyl sulfonic acid, vinyl phosphonic acid, itaconic acid, maleic acid and salts of such compounds. Examples of monomers capable of introducing epoxy functionality are allyl glycidyl ether, methallyl glycidyl ether, crotonic acid glycidyl ether and acetic acid glycidyl ether. An example of a monomer capable of introducing carbonyl functionality is ethylene carbonate. Examples of monomers capable of introducing hydroxyl functionality are hydroxyl ethyl acrylate and hydroxyl propyl acrylate.

[0064] The functionalizing monomers may be used in an amount of 0.01 to 15 weight percent based on total monomers. Preferably, they are used in an amount of 0.05 to 5 weight percent based on total monomers, and even more preferably, in an amount of 0.05 to 1.5 weight percent based on total monomers.

[0065] Functionalized fluoropolymers are mainly produced by heterogeneous polymerization reactions, including suspension, emulsion and microemulsion systems.Generally, each of these reactions requires at least one acid-functionalized monomer or its salt, at least one fluoromonomer and a radical initiator in a suitable reaction medium.In addition, the emulsion polymerization of halogen-containing monomers generally requires a surfactant that can emulsify both reactants and reaction products during the polymerization reaction.

[0066] According to one embodiment, the fluoropolymers used in the present invention are prepared by an emulsion polymerization process in the absence of fluorinated surfactants.

[0067] In some variants, the functionalized fluoropolymers used in the present invention can be prepared using methods similar to those disclosed in document WO2012 / 030784. 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.

[0068] A pressurized polymerization reactor equipped with an agitator and heat control means is charged with water, preferably deionized water, one or more functionalized monomers and at least one fluoromonomer. The mixture may optionally contain one or more of surfactants, buffers, antifouling agents or chain transfer agents for molecular weight control of the polymer product. Before introducing the monomer or monomers, air is preferably removed from the reactor to obtain an oxygen-free environment for the polymerization reaction. The order of collecting the polymerization ingredients may vary, but generally it is preferred that at least a portion of the functionalized monomer is present in the aqueous reaction medium before the start of polymerization of the fluoromonomer. An additional amount of functionalized monomer may be fed to the reactor during the reaction.

[0069] In one embodiment, water, initiator, functionalized monomer, and optionally surfactant, antifoulant, chain transfer agent, and / or buffer are charged to the reactor, and the reactor is heated to the desired reaction temperature. Fluoromonomer is then fed to the reactor, preferably at a rate that provides an essentially constant pressure. Alternatively, fluoromonomer, functionalized monomer, and initiator can be fed to the reactor along with one or more optional ingredients. The monomer feed is terminated when the desired weight of monomer is fed to the reactor. Additional radical initiator is optionally added, and the reaction is carried out for an appropriate period of time. The reactor pressure decreases as the monomer in the reactor is consumed.

[0070] Upon completion of the polymerization reaction, the reactor is brought to ambient temperature and residual unreacted monomer is vented to atmospheric pressure. The aqueous reaction medium containing the fluoropolymer is then recovered from the reactor as a latex. The latex consists of a stable mixture of the reaction components, i.e., water, surfactant, initiator (and / or initiator decomposition products) and functionalized fluoropolymer solids. The latex may contain from about 10 to about 50 weight percent, preferably 20 to 40 weight percent, of polymer solids. The polymer in the latex is in the form of small particles having a size range of about 30 nm to about 800 nm.

[0071] After polymerization, the fluoropolymer is stirred, thickened and dried.

[0072] The fluoropolymer thus obtained is processed to form a powder. The fluoropolymer powder can be obtained by various methods. The powder can be obtained directly by emulsion or suspension synthesis methods, by drying by spray drying or by freeze drying. The powder can also be obtained by comminution techniques such as freeze-grinding, in which the fluoropolymer is brought to a temperature below room temperature before grinding, for example using liquid nitrogen.

[0073] In a preferred embodiment, the fluoropolymer is a powder with a particle size distribution with Dv50 less than 20 μm, preferably less than 15 μm, more preferably less than 10 μm. At the end of the powder production process, i.e. after polymerization and drying steps, the particle size can be adjusted and optimized by selection or screening methods and / or by grinding if Dv50 is greater than 10 μm. The particle size distributions mentioned herein are usually obtained when the fluoropolymer is prepared by emulsion method.

[0074] In another preferred embodiment, the fluoropolymer is prepared by a suspension method.

[0075] In a second aspect of the present invention, there is provided a dry coated electrode comprising a non-fibrillizable binder according to the present invention, a conductive agent, and a dry active material.

[0076] In a preferred embodiment, the dry coated electrode has the following mass composition: a. 50% to 99.9%, preferably 50% to 99%, of an active material; b. 25% to 0%, preferably 25% to 0.5%, of a conductive agent; c. 25% to 0.05%, preferably 25% to 0.5%, of a non-fibrillizable binder; d. having 0-5% of at least one additive selected from the group consisting of plasticizers, ionic liquids, dispersants for conductive additives, and flow aids; All these percentages add up to 100%.

[0077] The conductive agent in the dry-coated electrode includes one or more materials that can improve electrical conductivity. Some examples include carbon black such as acetylene black and ketjen black; carbon fibers such as carbon nanotubes, carbon nanofibers, and vapor-grown carbon fibers; and metal powders such as SUS powder and aluminum powder.

[0078] The active material is a material that can store and release lithium ions.

[0079] In a preferred embodiment, the electrode is a negative electrode. In particular, for a negative electrode, the active material is selected from the group consisting of lithium alloys, metal oxides, carbon materials such as graphite or hard carbon, silicon, silicon alloys, and Li4TiO 12 The shape of the negative electrode active material is not particularly limited, but is preferably particulate.

[0080] In another preferred embodiment, the electrode is a positive electrode. Preferably, for a positive electrode, the active material is LiCoO2, Li(Ni,Co,Al)O2, Li (1+x) , Ni a Mn b Co c (x is a real number equal to or greater than 0; 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, Li 1+x Mn 2-x-y M y LiMn spinel substituted with different elements having a composition represented by the formula: O4, in which M represents at least one metal selected from Al, Mg, Co, Fe, Ni, and Zn, and x and y each independently represent a real number between 0 and 2; x TiO y wherein x and y each independently represent a real number between 0 and 2, and lithium metal phosphate having a composition represented by LiMPO4 (M represents Fe, Mn, Co, or Ni).

[0081] The surface of each of the above materials may be coated. The coating material is not particularly limited as long as it has lithium ion conductivity and contains a material that can be held in the form of a coating layer on the surface of the active material. Examples of coating materials include LiNbO3, Li4Ti5O 12 and Li3PO4.

[0082] The shape of the positive electrode active material is not particularly limited, but it is preferably in the form of particles.

[0083] The present invention also relates to a method for preparing a dry coated electrode, comprising a thermomechanical treatment step carried out at a temperature ranging from 20° C. below the melting point of the non-fibrillizable binder to 50° C. above the melting point of the non-fibrillizable binder.

[0084] The method for preparing a dry coated electrode includes the following steps. - mixing an active material in the form of a non-fibrillizable binder of the present invention and a conductive agent to prepare an electrode formulation; - depositing the electrode formulation on a substrate by a solvent-free method to obtain a Li-ion battery electrode; - consolidating said electrode by a thermomechanical treatment carried out at a temperature ranging from 20°C below the melting point of the non-fibrillizable binder to 50°C above the melting point of the non-fibrillizable binder.

[0085] The components (the active material, the binder, the conductive agent, and optional additives) are mixed in powder form to prepare an electrode formulation.

[0086] The method for preparing a dry coated electrode includes the following steps. - mixing an active material, a non-fibrillizable binder of the present invention in powder form as described above, and a conductive agent using a method that provides an electrode formulation that can be applied to a metal substrate by a "solvent-free" method; - depositing the electrode formulation on a substrate by a solvent-free method to obtain a Li-ion battery electrode; - consolidating said electrode by a thermomechanical treatment carried out at a temperature ranging from 20°C below the melting point of the non-fibrillizable binder to 50°C above the melting point of the non-fibrillizable binder.

[0087] A "solvent-free" method is one that does not require a residual solvent evaporation step after the deposition step.

[0088] Thermomechanical treatment refers to the application of temperatures from 20° C. below the melting temperature of the polymer to 50° C. above the melting temperature of the polymer using mechanical pressure. The pressure applied during thermomechanical treatment is generally less than 1 kN / mm, preferably less than 0.75 kN / mm, more preferably less than 0.5 kN / mm. Such thermomechanical treatment can be carried out, for example, by a calender with heatable rolls or a plate-plate press that can also be heated.

[0089] According to one embodiment, after the powder mixing step, the electrodes are manufactured by a solventless spray method, by depositing the formulation on a metal substrate, by a pneumatic spray method, by electrostatic spraying, by immersion in a fluidized powder bed, by sprinkling, by electrostatic screen printing, by deposition with a rotating brush, by deposition with a dosing rotating roll, by calendaring.

[0090] According to one embodiment, after the powder mixing step, the electrode is manufactured in two steps by a solvent-free method. The first step consists in producing a free-standing film from the premixed formulation using a thermomechanical method such as extrusion, calendaring or thermocompression. In the second step, the free-standing film is laminated onto a metal substrate by a method combining temperature and pressure such as calendaring or thermocompression.

[0091] The mass ratio of the conductive agent to the active material is preferably 0 to 10%, and more preferably 0 to 7%.

[0092] The mass ratio of the binder to the active material is preferably 0.1 to 10%, and more preferably 0.5 to 7%.

[0093] According to one embodiment, all of the electrode components are mixed at once according to conventional methods to provide the electrode formulation.

[0094] In one embodiment, the electrode formulation is applied to a substrate by electrostatic screen printing. Some examples of substrates are current collectors such as metal foils and metal meshes, polymer films, or solid electrolyte layers of solid-state batteries.

[0095] The preferred thickness of the electrode is 0.1 μm to 1000 μm, and more preferably 0.1 μm to 300 μm.

[0096] 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, and at least one electrode is a dry-coated electrode according to the present invention. EXAMPLES

[0097] The following examples illustrate the invention without limiting it.

[0098] <Material> PVDF 1: A homopolymer of vinylidene fluoride having a melting temperature of 165-172°C, a melt viscosity of 4-8 kP, and a flexural modulus of 1655-2310 MPa.

[0099] PVDF 2: A homopolymer of vinylidene fluoride having head-to-tail defects (5.5% defects) and having a melting temperature of 161°C, a melt viscosity of 23.5-29.5 kP, and a flexural modulus of 1380-1790 MPa.

[0100] PVDF 3: A copolymer of vinylidene fluoride and hexafluoropropylene (about 5% by weight HFP) with acrylic acid moieties having a functionality of about 1% by weight, characterized by a melt temperature of 151-157°C, a melt viscosity of 34-38 kP, and a flexural modulus of 1030 MPa.

[0101] PVDF 4: A copolymer of vinylidene fluoride and hexafluoropropylene (about 5% by weight HFP - random distribution), characterized by a melting temperature of 155-160°C, a melt viscosity of 23-27 kP and a flexural modulus of 1034-1241 MPa.

[0102] PVDF 5: A copolymer of vinylidene fluoride and hexafluoropropylene (about 12% by weight HFP) characterized by a melting temperature of 140-143°C, a melt viscosity of 12-20 kP, and a flexural modulus of 620-827 MPa.

[0103] PVDF 6: A copolymer of vinylidene fluoride and hexafluoropropylene (about 18% by weight HFP) characterized by a melting temperature of 117-125°C, a melt viscosity of 5-16 kP, and a flexural modulus of 192-276 MPa.

[0104] <Electrode formulation> A negative electrode was prepared using each of the above PVDFs. 158-C (graphite, BTR) and binder 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 for 30 seconds at 2000 rpm by ARE-310 (Thinky). The mixed powder was sandwiched between two sheets of copper foil. The copper foil and powder were compressed in a roll press (SA-602, Tester Sangyo) at 160°C, 10 kN load, and 0.5 m / min speed. The prepared electrode was bent into a U-shape, and if there was no crack or breakage, it was OK, and if there was any crack or breakage, it was not OK (NOK). The properties and results of each binder tested are shown in Table 1.

[0105] [Table 1]

Claims

1. A non-fibrillable binder for dry-coated electrodes, comprising a fluoropolymer having a melting point between 145°C and 200°C as measured according to ASTM D3418, and a melt viscosity of less than 50 kP as measured at 230°C and a shear rate of 100 s⁻¹ according to ASTM D3835.

2. The binder according to claim 1, wherein the fluoropolymer has a flexural modulus greater than 1000 MPa as measured according to ASTM D790.

3. The binder according to claim 1, wherein the 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-1-propene, 2,3,3,3-tetrafluoropropene, fluorinated vinyl ether, fluorinated allyl ether, and fluorinated dioxol.

4. The binder according to claim 1, wherein the fluoropolymer is selected from the group consisting of homopolymers and copolymers of vinylidene fluoride containing at least 50% by weight of vinylidene fluoride repeating units, and the comonomer is selected from the group consisting of chlorotrifluoroethylene, hexafluoropropene, and trifluoroethylene.

5. The binder according to claim 1, wherein the fluoropolymer is a polyvinylidene fluoride (PVDF) homopolymer or a copolymer of vinylidene fluoride and hexafluoropropene.

6. The binder according to claim 1, wherein the fluoropolymer is a polyvinylidene fluoride homopolymer having head-tail defects in the chain of vinylidene fluoride units, and the degree of head-tail defects does not exceed 10%.

7. The binder according to claim 1, wherein the fluoropolymer contains a functionalized monomer in an amount of 0.01 to 15 weight percent based on the total monomer.

8. The binder according to claim 6, wherein the functionalized monomer having at least one functional group is selected from acrylic acid, methacrylic acid, vinyl sulfonic acid, vinyl phosphonic acid, itaconic acid, maleic acid, and salts of such compounds; allyl glycidyl ether, metharyl glycidyl ether, glycidyl ether of crotonic acid, and glycidyl ether of acetate; ethylene carbonate; hydroxylethyl acrylate and hydroxyl propyl acrylate.

9. The binder according to claim 1, wherein the fluoropolymer is produced by either emulsion polymerization or suspension polymerization.

10. The binder according to claim 1, wherein the fluoropolymer is a powder having a particle size distribution with a Dv50 of less than 20 μm as measured by laser particle size measurement.

11. A dry coated electrode comprising a non-fibrillable binder, a dry active material, and optionally a conductive agent, according to any one of claims 1 to 10.

12. The following mass composition, namely, a. 50% to 99.9% active material, b. Conductive agent in a concentration of 25% to 0% c. A non-fibrillable binder containing 25% to 0.05% d. Having at least one additive selected from the group consisting of plasticizers, ionic liquids, dispersants for conductive additives, and flow aids, in an amount of 0 to 5%. The dry coated electrode according to claim 11, wherein the sum of all these percentages is 100%.

13. The dry coated electrode according to claim 11, wherein the conductive agent is composed of one or more materials from carbon black; carbon fibers; and metal powder.

14. The active material is a different element-substituted LiM having a composition represented by LiCoO2, Li(Ni,Co,Al)O2, Li(1+x), NiaMnbCoc (where x is a real number greater than or equal to 0, 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, Li1+xMn2-x-yMyO4 A dry coated electrode for a positive electrode according to claim 11, comprising n spinel, where M represents at least one metal selected from Al, Mg, Co, Fe, Ni, and Zn, and x and y each independently represent a real number between 0 and 2; lithium titanate LixTiOy, where x and y each independently represent a real number between 0 and 2; and a lithium metal phosphate having a composition represented by LiMPO4, where M represents Fe, Mn, Co, or Ni, selected from the group.

15. A dry coated electrode for a negative electrode according to claim 11, wherein the active material is selected from the group consisting of lithium alloy, metal oxide, carbon material, silicon, silicon alloy, and Li4TiO12.

16. A process for manufacturing a dry coated electrode according to claim 11, comprising a thermomechanical treatment step carried out at a temperature in the range from 20°C below the melting point of the non-fibrillable binder to 50°C above the melting point of the non-fibrillable binder.

17. A lithium-ion battery comprising a positive electrode, a negative electrode, and a separator, wherein at least one electrode is a dry-coated electrode as described in claim 11.