Lithium battery electrode binder

Abstract

The present invention relates to a binder composition comprising a vinylidene fluoride polymer and its use in the manufacture of electrodes for secondary batteries.

Description

[Technical Field]

[0001] The present invention relates to a binder composition comprising a vinylidene fluoride polymer and its use in the manufacture of electrodes for secondary batteries. [Background technology]

[0002] Electrochemical devices such as secondary batteries typically include a positive electrode, a negative electrode, and an electrolyte.

[0003] The most important component of a lithium-ion secondary battery is the positive electrode (cathode), whose performance affects the overall performance of the battery. Various attempts have been made to obtain cathode materials that are low in manufacturing cost and have high energy capacity while maintaining high-temperature stability.

[0004] Conventional positive electrode active materials are generally of the LiMO2 type, LiMPO4 type, Li2MPO3F type, Li2MSiO4 type (wherein M is Co, Ni, Mn, Fe, or a combination thereof), LiMn2O4 type, or S8 type.

[0005] Among these materials, lithium iron phosphate (LiFePO4 or LFP) with an olivine structure has a high theoretical capacity (170 mAhg -1 ), which has attracted attention as a promising cathode material for lithium-ion batteries due to its high safety and economic advantages.

[0006] However, olivine-type phosphate materials have low electrical conductivity and low lithium ion diffusion coefficients. To address these issues, several approaches have been proposed, including morphology control, surface coating with additional layers, and the use of conductive additives.

[0007] Nanosizing is a known method to improve the rate performance of LFP cathodes by shortening the lithium ion migration length. However, nanosized LFPs have a very large surface area, so a binder with higher binding strength is required to maintain a level of bonding to the aluminum foil of the cathode. Furthermore, the slurry viscosity of nanosized LFPs is very high, and they can easily physically gel or increase in viscosity during storage.

[0008] Electrodes for lithium batteries are typically manufactured by mixing a binder with powdered electrode active material.

[0009] Fluoropolymers, such as vinylidene fluoride-based polymers, have been used as binders for forming positive electrodes. In particular, polyvinylidene fluoride (PVDF) provides good electrochemical stability and high adhesion to electrode materials and current collectors. Therefore, PVDF is a preferred binder material for electrode slurries.

[0010] US Patent Application Publication No. 2015 / 0280238 discloses a stable electrode binder dispersion for use in the manufacture of LFP cathodes for lithium-ion batteries, the dispersion comprising PVDF dispersed in an organic diluent and a (meth)acrylic polymer dispersant.

[0011] Chinese Patent No. 101752546 discloses a method for manufacturing LFP electrodes by using a binder composition containing HSV900 polyvinylidene fluoride, a commercially available PVDF homopolymer obtained by emulsion polymerization.

[0012] However, certain PVDF polymers have a significant drawback in that when used to prepare slurries for forming positive electrodes with LFP active materials, the viscosity of the slurry increases rapidly and they often form gels, thereby preventing their use as binders in LPF cathodes.

[0013] The present invention provides a positive electrode-forming composition containing an olivine-type active material that can prevent gelation while enabling the production of an electrode with improved adhesion and electrochemical stability. Summary of the Invention

[0014] It has been discovered that certain vinylidene fluoride polymers have very good adhesion to metal substrates and can be used to prepare electrode-forming compositions with improved slurry viscosity over time.

[0015] Accordingly, an object of the present invention is to provide a positive electrode-forming composition (C) for use in the manufacture of an electrode for an electrochemical device, comprising: a) at least one cathode active material (AM) that is a phospho-olivine material having an average particle size of 100 nm to 20 μm; b) 1,000,000 g.mol as determined by GPC using conventional calibration with polystyrene -1 Greater than 2,000,000 g.mol -1 a VDF-based polymer [polymer (F)] having a molecular weight of less than 1000 ppm, characterized in that it is obtained by a process comprising a radical polymerization step using a non-water-soluble organic radical initiator system; c) at least one solvent (S); d) optionally at least one conductivity-imparting additive; The positive electrode forming composition (C) comprises:

[0016] In another aspect, the present invention provides a method for producing an electrode (electrode (E)), comprising the use of an electrode-forming composition (C), (I) providing a metal substrate having at least one surface; (II) providing an electrode-forming composition (C) as defined above; (III) applying the composition (C) prepared in step (II) onto at least one surface of the metal substrate prepared in step (I), thereby obtaining an assembly comprising a metal substrate coated with the composition (C) on at least one surface; (IV) drying the assembly obtained in step (III); (V) subjecting the dried assembly obtained in step (IV) to a compression step to obtain the electrode (E) of the present invention. Regarding use, including

[0017] In a further object, the present invention relates to an electrode (E) obtainable by the method of the present invention.

[0018] In a still further object, the present invention relates to an electrochemical device comprising at least one electrode (E) of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] The term "VDF-based polymer" is intended to mean VDF homopolymers (PVDF) and VDF-based copolymers comprising repeating units derived from VDF and repeating units derived from at least one fluorinated comonomer (CF) different from VDF.

[0020] The VDF-based polymer (F) of the present invention does not contain hydrogenated monomers with polar groups.

[0021] The term "repeating unit derived from vinylidene fluoride" (commonly also designated vinylidene difluoride, 1,1-difluoroethylene, VDF) is intended to mean a repeating unit of formula CF2=CH2.

[0022] Non-limiting examples of suitable fluorinated comonomers (CF) include, among others: (a) C2-C8 fluoro and / or perfluoroolefins such as tetrafluoroethylene (TFE), hexafluoropropylene (HFP), pentafluoropropylene and hexafluoroisobutylene; (b) C2-C8 hydrogen-containing monofluoroolefins such as vinyl fluoride, 1,2-difluoroethylene, and trifluoroethylene; (c)Formula CH2=CH-R f0 (In the formula, R f0 is a C1-C6 perfluoroalkyl group), (d) Chloro-, and / or bromo-, and / or iodo-C2-C6 fluoroolefins such as chlorotrifluoroethylene (CTFE). (e) perfluoro(alkyl) vinyl ethers such as perfluoro(methyl) vinyl ether (PMVE), perfluoro(ethyl) vinyl ether (PEVE), and perfluoro(propyl) vinyl ether (PPVE); (f) Perfluoro(1,3-dioxole); perfluoro(2,2-dimethyl-1,3-dioxole) (PDD).

[0023] In a preferred embodiment, the polymer (F) is semi-crystalline and contains 0.1 to 20.0 mol %, preferably 0.3 to 10.0 mol %, more preferably 0.5 to 5.0 mol % of repeating units derived from said fluorinated comonomer (CF).

[0024] The polymer (F) can be an elastomeric or semi-crystalline polymer, preferably a semi-crystalline polymer.

[0025] As used herein, the term "semi-crystalline" means a fluoropolymer that has at least one crystalline melting point in addition to a glass transition temperature Tg by DSC analysis. For the purposes of the present invention, semi-crystalline fluoropolymer is intended herein to mean a fluoropolymer that has a heat of fusion of 10 to 90 J / g, preferably 30 to 80 J / g, more preferably 35 to 75 J / g, measured according to ASTM D4591.

[0026] For purposes of the present invention, the term "elastomer" is intended to denote a true elastomer or a polymer resin that serves as a building block to obtain a true elastomer.

[0027] True elastomers are defined by ASTM, Special Technical Bulletin, Standard No. 184, as materials that can be stretched to twice their inherent length at room temperature and that, when released after being held under tension for 5 minutes, simultaneously return to within 10% of their original length.

[0028] The polymer (F) of the present invention usually has a melting temperature (Tm) within the range of 150 to 200°C.

[0029] The melting temperature can be determined from a DSC curve obtained by differential scanning calorimetry (hereinafter also referred to as DSC). When a DSC curve shows multiple melting peaks (endothermic peaks), the melting temperature (Tm) is determined based on the peak with the largest peak area.

[0030] It is understood that defects or other impurity type sites may be contained in the polymer (F), but these do not detract from its properties.

[0031] The polymer (F) preferably has a molecular weight greater than 1,200,000 g.mol −1 and less than 1,800,000 g.mol −1 as determined by GPC using conventional calibration with polystyrene, as detailed below.

[0032] The polymer (F) is characterized in that it is obtained by a polymerization process in the presence of a water-insoluble organic radical initiator system.

[0033] Specifically, the polymer (F) is - polymerizing vinylidene fluoride (VDF) and optional comonomers (CF) in an aqueous medium in the presence of a water-insoluble organic radical initiator system and at least one suspending agent; - maintaining a pressure in the reaction vessel above the critical pressure of vinylidene fluoride; - maintaining the temperature in the reaction vessel at a temperature greater than 31°C and up to a maximum of 70°C; It can be obtained by a method comprising:

[0034] The term "initiator system" includes a single initiator or a mixture of initiators, each of which is typically dissolved or suspended in a solvent (e.g., a hydrocarbon solvent) that is added to the polymerization process.

[0035] The term "water-insoluble" is intended to mean that the organic radical initiator system has a solubility in water of less than 1 g / l.

[0036] Preferred water-insoluble initiators are water-insoluble peroxide initiators and water-insoluble peroxydicarbonates.

[0037] Examples of organic radical initiator systems for use in preparing polymer (F) include organic dialkyl peroxides such as di-t-butyl peroxide (DTBP); dialkyl peroxydicarbonates such as diisopropyl peroxydicarbonate (IPP), di-N-propyl peroxydicarbonate (NPP), diethyl peroxydicarbonate, di-sec-butyl peroxydicarbonate (DBP); and t-alkyl peroxybenzoates such as tert-butyl- or tert-amyl-peroxypivalate.

[0038] In a preferred embodiment of the present invention, the polymer (F) used in the composition (C) is obtained by a polymerization process in the presence of a tert-alkylperoxybenzoate initiator, more preferably the initiator used is tert-amylperoxypivalate.

[0039] The amount of radical initiator required for polymerization depends on its activity and the temperature used for polymerization. The total amount of radical initiator used is usually 100 to 30,000 ppm, preferably 400 to 1,000 ppm, based on the total weight of the monomers used.

[0040] The organic radical initiator may be added to the reaction mixture in pure form, as a solution, suspension, or emulsion, depending on the initiator selected.

[0041] The organic radical initiator system may include a chain transfer agent (CTA).

[0042] CTAs suitable for the polymerization process to prepare polymer (F) for use in the present invention are known in the art and are typically selected from the group consisting of short hydrocarbon chains such as ethane and propane, alcohols such as ethanol, tert-butanol and isopropanol, esters such as ethyl acetate and diethyl maleate, and diethyl carbonate.

[0043] When an organic peroxide is used as an initiator, it could also serve as an effective CTA during the course of the free radical polymerization.

[0044] When used, the CTA may be added all at once at the beginning of the reaction, or in portions, or continuously throughout the course of the reaction. The amount of CTA and its mode of addition depend on the desired properties of the resulting polymer (F).

[0045] A preferred CTA for use in the method of the present invention is diethyl carbonate.

[0046] In the process for preparing polymer (F), the pressure is maintained above the critical pressure of vinylidene fluoride. Generally, the pressure is maintained at a value greater than 50 bar, preferably greater than 75 bar, and even more preferably greater than 100 bar.

[0047] Polymer (F) is typically supplied in powder form according to the process described above.

[0048] Polymer (F) typically has a particle size in the range of 10 μm to 500 μm.

[0049] Polymer (F) is typically characterized in that the gel fraction determined in a 0.25 wt% / volume solution of Polymer (F) in an N,N-dimethylacetamide (DMA) solution containing 0.01 N lithium bromide is less than 3%.

[0050] For the purposes of the present invention, the term "positive electrode active material (AM)" is intended to denote a compound that can incorporate or insert into its structure and substantially release alkali or alkaline earth metal ions therefrom during the charge and discharge phases of an electrochemical device. Compound (AM) can preferably incorporate or insert and release lithium ions.

[0051] The term "phospho-olivine material" includes compounds having the following formula: Li x A y D z PO4 (where A is selected from the group consisting of Mn, Fe, Co, Ni and Cu, D is selected from the group consisting of Mg, Ca, Sr, Ba, and x, y and z are numbers satisfying the following relationships: 0.9 < x < 1.2, 0 < y < 1.5, 0 ≦ z < 1.5).

[0052] Component A is preferably Fe, Mn and Ni, particularly preferably Fe.

[0053] Component D is preferably Mg or Ca.

[0054] Examples of compounds having an olivine structure include lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), and lithium manganese phosphate.

[0055] Furthermore, it is also possible to use, as the positive electrode active material (AM), a material whose surface is partially or entirely coated with carbon to supplement electrical conductivity.

[0056] The amount of coated carbon is preferably 20 parts by weight or less, more preferably 10 parts by weight or less, and even more preferably 5 parts by weight or less, based on 100 parts by weight of the positive electrode active material.

[0057] The compound having an olivine structure is present in the composition (C) in an amount of 70% by mass or more relative to 100% by mass of the entire positive electrode active material (AM).

[0058] According to one embodiment, the phospho-olivine material comprises lithium iron phosphate (LFP).

[0059] According to one embodiment, the phospho-olivine material comprises lithium manganese iron phosphate (LMFP).

[0060] According to one embodiment, the phospho-olivine material consists of a blend of LFP and LMFP, with the blend ratio varying from 0% to 100% by weight of each component.

[0061] More preferably, this is 90% by mass or more, and most preferably, the positive electrode active material (AM) consists solely of phospho-olivine material.

[0062] Most preferably, the positive electrode active material (AM) consists solely of lithium iron phosphate (LFP) or lithium iron manganese phosphate (LMFP).

[0063] Phospho-olivine active materials suitable for use in the electrodes of the present invention can have a nanometer particle size, meaning a size of less than 2 μm, or a micrometer particle size, meaning particles average between 2 μm and 1 mm in size.

[0064] In a preferred embodiment of the present invention, the cathode composition of the present invention is a nanosized phospho-olivine material characterized by an average particle size of 2 μm or less, in particular a nanometer particle size in the range of 100 nm to 2 μm.

[0065] The applicant has surprisingly found that the known problem of increased slurry viscosity of nano-sized LFP cathode slurry compositions can be avoided by using a polymer (F) having a molecular weight greater than 1,000,000 g.mol-1 and less than 2,000,000 g.mol-1, which is obtained by a polymerization process in the presence of a non-aqueous organic radical initiator system.

[0066] The solvent (S) may preferably be an organic polar solvent, examples of which include N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, hexamethylphosphamide, dioxane, tetrahydrofuran, tetramethylurea, triethyl phosphate, and trimethyl phosphate. These solvents may be used alone or in a mixture of two or more species.

[0067] The electrode-forming composition (C) of the present invention may optionally further comprise at least one conductive agent.

[0068] Examples may include carbon black, graphite fine powder, carbon nanotubes, graphene or fibers, or carbonaceous materials, such as fine powders or fibers of metals, such as nickel or aluminum. The optional conductive agent is preferably carbon black. Carbon black is available, for example, under the brand names Super P® or Ketjenblack®.

[0069] In another aspect, the present invention provides a method for producing a positive electrode (E) using the electrode-forming composition (C), (I) providing a metal substrate having at least one surface; (II) providing an electrode-forming composition (C) as defined above; (III) applying the composition (C) prepared in step (II) onto at least one surface of the metal substrate prepared in step (I), thereby obtaining an assembly comprising a metal substrate coated with the composition (C) on at least one surface; (IV) drying the assembly obtained in step (III); (V) subjecting the dried assembly obtained in step (IV) to a compression step to obtain the electrode (E) of the present invention. Regarding use, including

[0070] In a further object, the present invention relates to an electrode (E) obtainable by the method of the present invention.

[0071] The applicant has surprisingly found that the electrode (E) of the present invention exhibits outstanding adhesion of the binder to the current collector.

[0072] Therefore, the electrode (E) of the present invention is particularly suitable for use in electrochemical devices, in particular in secondary batteries.

[0073] For the purposes of the present invention, the term "secondary battery" is intended to mean a rechargeable battery.

[0074] The secondary battery of the present invention is preferably an alkali metal secondary battery or an alkaline earth metal secondary battery.

[0075] The secondary battery of the present invention is more preferably a lithium ion secondary battery.

[0076] In a still further object, the present invention relates to an electrochemical device comprising at least one electrode (E) of the present invention.

[0077] Preferably, the electrochemical device according to the present invention is a secondary battery. - Positive and negative electrodes Including, The positive electrode here is the electrode (E) of the present invention.

[0078] Electrochemical devices according to the present invention can be fabricated by standard methods known to those skilled in the art.

[0079] The present invention will now be described with reference to the following examples, the purposes of which are merely illustrative and are not intended to limit the scope of the invention.

[0080] Experimental section raw materials HSV900: PVDF homopolymer obtained by emulsion polymerization, commercially available from Arkema. Nano-LFP: LFP DY-3, D50 0.6~1.8μm, commercially available from Dynamic. Carbon nanotubes (CNTs): Multi-walled carbon nanotubes (MWCNTs) in N-methyl-2-pyrrolidone (NMP) solvent.

[0081] Determination of the intrinsic viscosity of the polymer (F) The intrinsic viscosity (η) [dl / g] was calculated based on the fall time at 25°C of a solution obtained by dissolving the polymer (F) in N,N-dimethylformamide at a concentration of about 0.2 g / dl using an Ubbelhode viscometer, according to the following formula:

number

[0082] DSC analysis DSC analysis was performed according to the ASTM D4591 standard and the melting point (T f2 ) was determined at a heating rate of 10 °C / min.

[0083] GPC analysis For GPC analysis, a 0.25 wt % / volume solution was prepared by dissolving polymer (F) in N,N-dimethylacetamide containing 0.01 N lithium bromide at 45° C. for at least 2 hours.

[0084] The latter solution was then poured into a steel centrifuge tube and stirred at 20,000 rpm at 25°C for at least 1 hour.

[0085] The supernatant was then subjected to GPC analysis at 45 °C using a degassed eluent consisting of N,N-dimethylacetamide containing 0.01 N lithium bromide. A refractive index detector coupled with a set of four columns with different pore sizes was used to separate the different molecular weights. Conventional 15-point calibration was used to determine the relative molecular weights of VDF-based polymers using polystyrene standards up to >3,000,000 g / mol.

[0086] Determination of the gel content of polymer (F) To determine the gel content, a 0.25 wt % / volume solution was prepared by dissolving polymer (F) in N,N-dimethylacetamide containing 0.01 N lithium bromide at 45°C.

[0087] The latter solution was then poured into a steel centrifuge tube and stirred at 20,000 rpm at 25°C.

[0088] The supernatant was then removed and the bottom of the steel tube containing the gel was placed in an oven at 150°C for 48 hours.

[0089] After drying, the gel content was quantified as the percentage difference in weight of the steel tube before and after centrifugation.

[0090] Example 1: Preparation of polymer L-1 In a 4 L reactor equipped with an impeller rotating at a speed of 650 rpm, 2425 g of demineralized water and 0.27 g of PEO (Alkox®-E45 manufactured by Alkorox) per kg of total monomers and 0.33 g of hydroxypropyl methylcellulose (Methocel®-K100 manufactured by DuPont Nutrition Biosciences SAS) per kg of total monomers were successively introduced. The oxygen present in the reactor was removed by a vacuum and nitrogen purge sequence at a fixed temperature of 14° C. This sequence was repeated three times.

[0091] Then, 1.46 g of a solution (75%) of the initiator t-amyl perpivalate (from United Initiators) in isododecane, 7.94 g of diethyl carbonate were introduced into the reactor.

[0092] The stirring speed was then increased to 880 rpm, and 1062 g of VDF was added to the reactor. The reactor was then gradually heated until a set point temperature of 46°C was reached. The pressure was kept constant at 120 bar by VDF throughout the polymerization run. A total of 529 g of VDF was added, and no further VDF was added. The reaction was then stopped by degassing the suspension until atmospheric pressure was reached.

[0093] The polymer was then collected by filtration and suspended in clean water in a stirred tank. After washing, the polymer was dried overnight in an oven at 65° C. 1184 g of dry powder was recovered.

[0094] Intrinsic viscosity of 0.41 l / g, T of 169.8°C f2 , 1700000g.mol -1 Polymer L-1 was obtained having a weight average molecular weight (Mw) of 1000 ppm and a gel content of less than 3%.

[0095] Comparative Example 2: Preparation of Polymer A Into an 80 liter reactor equipped with an impeller rotating at a speed of 250 rpm, 52.4 kg of demineralized water and 0.4 g of hydroxypropyl methylcellulose (Methocel®-K100 from Dow) per kg of VDF were successively introduced. The oxygen present in the reactor was removed by a sequence of vacuum and nitrogen purges at a fixed temperature of 20° C. This sequence was repeated three times.

[0096] Then, 41.38 g of a solution (75%) of the initiator t-amyl perpivalate (from United Initiators) in isododecane and 250.02 g of diethyl carbonate were introduced into the reactor. Immediately after, the stirring speed was increased to 300 rpm, and 22.99 kg of VDF were added to the reactor. The reactor was then gradually heated until a set-point temperature of 52 °C was reached. The pressure was kept constant at 120 bar by VDF throughout the entire polymerization run. A total of 11.49 kg of VDF was added, and no further VDF was added. The temperature was then increased to 65 °C, and the reaction was then stopped after a total of 169 minutes by degassing the suspension until atmospheric pressure was reached.

[0097] The polymer was then collected by filtration and suspended in clean water in a stirred tank. After washing, the polymer was dried overnight in an oven at 65° C. 29.94 kg of dry powder was recovered.

[0098] Polymer A: Intrinsic viscosity of 0.27 l / g, T of 169.3°C f2 A polymer with a weight average molecular weight (Mw) of 871000 g.mol-1 and a gel content of less than 3% was obtained.

[0099] Comparative Example 3: Polymer B HSV900, available from ARKEMA, manufactured by emulsion process, with an intrinsic viscosity of 0.168 l / g and a T of 162°C. f2 , a product with a weight average molecular weight (Mw) of 613000 g.mol-1, and a gel content of 54%, all data measured by the procedures detailed above.

[0100] General preparation of electrodes using LFP active material A positive electrode with a final composition of 95.75 wt % LFP, 3.5 wt % polymer L-1, A or B, 0.75 wt % conductive additive was prepared as follows.

[0101] An initial dispersion was prepared by premixing 34.3 g of an 8 wt % solution of polymer L-1, A, or B in NMP, 75.07 g of LFP, 14.7 g of CNTs predispersed in NMP at 4 wt %, and 15.93 g of NMP in a centrifugal mixer for 10 min.

[0102] The mixture was then mixed for 50 minutes at 1500 rpm using a high-speed butterfly impeller. An additional 5.2 g of NMP was then added to the dispersion, which was then further mixed for 5 minutes using a centrifugal mixer. The resulting composition was cast onto a 15 μm-thick Al foil using a doctor blade, and the coated layer was dried in a vacuum oven at 90°C for approximately 50 minutes to obtain a cathode. The dried coating layer had a thickness of approximately 100 μm.

[0103] Measurement of slurry viscosity Slurry viscosity was measured on an AntonPaar Rheolab QC using a concentric cylinder setup (measuring cup: C-CC27 / QC-LTD Bob: CC27 / P6) with peltier temperature control at 25° C. Steady-state viscosity was measured from shear rates of 0.1 to 1000 1 / s.

[0104] Adhesion strength measurement Adhesion peel strength between aluminum foil and electrode: To evaluate the adhesion of the dried coating layer to the Al foil, a 90° peel test was carried out according to the setup described in standard ASTM D6862 at 20°C and a speed of 300 mm / min.

[0105] Adhesion and Slurry Viscosity Using the polymers of Examples 1 to 3 as binders, electrode compositions were prepared according to the procedures set forth above. The slurry viscosity and adhesion values ​​are shown in Table 1.

[0106] [Table 1]

[0107] The results show that the polymers of the present invention have improved adhesion to the current collector compared to Polymer A, and therefore perform better.

[0108] Slurry gelation measurement The viscosity of the slurry over time was measured using an AntonPaar MCR92 with a 50 mm diameter smooth parallel plate configuration (measurement plate: PP50) and Peltier temperature control at 25 °C. To reveal the trend of the viscosity over time, frequency sweep tests were performed at a constant strain (0.5%) in the range of 0.1–100 rad / s for different times.

[0109] The polymers of Examples 1-3 were used as binders and the relative increase in slurry viscosity was measured according to the procedure set forth above. The values ​​of the relative increase in slurry viscosity over time are shown in Table 2.

[0110] [Table 2]

[0111] The results show that the polymers of the present invention exhibit excellent slurry stability over time, ie, comparable to Polymer A and significantly superior to Polymer B.

Claims

1. A positive electrode-forming composition (C) for use in manufacturing an electrode for an electrochemical device, comprising: a) at least one cathode active material (AM) that is a phospho-olivine material having a D50 average particle size of 100 nm to 20 μm; b) 1,000,000 g.mol measured as described herein －１ Greater than 2,000,000 g.mol －１ a VDF-based polymer [polymer (F)] having a molecular weight of less than 1000 ppm, which is obtained by a process comprising a radical polymerization step using a water-insoluble organic radical initiator system; c) at least one solvent (S); d) optionally at least one conductivity-imparting additive; A positive electrode-forming composition (C) comprising:

2. 2. The composition (C) of claim 1, wherein the polymer (F) is a VDF homopolymer.

3. 2. The composition (C) of claim 1, wherein the polymer (F) is a VDF-based copolymer comprising repeating units derived from VDF and repeating units derived from at least one fluorinated comonomer (CF) different from VDF.

4. The fluorinated comonomer (CF) (a) C fluoroethylenes such as tetrafluoroethylene (TFE), hexafluoropropylene (HFP), pentafluoropropylene, and hexafluoroisobutylene ２ ~C ８ Fluoro- and / or perfluoroolefins, (b) C such as vinyl fluoride, 1,2-difluoroethylene, and trifluoroethylene ２ ~C ８ hydrogen-containing monofluoroolefins, (c) Formula CH ２ =CH-R ｆ０ (In the formula, R ｆ０ is C １ ~C ６ perfluoroalkyl ethylenes, (d) chloro-, and / or bromo-, and / or iodo-C, such as chlorotrifluoroethylene (CTFE) ２ ~C ６ fluoroolefins, (e) perfluoro(alkyl) vinyl ethers such as perfluoro(methyl) vinyl ether (PMVE), perfluoro(ethyl) vinyl ether (PEVE), and perfluoro(propyl) vinyl ether (PPVE); (f) Perfluoro(1,3-dioxole); Perfluoro(2,2-dimethyl-1,3-dioxole) (PDD) The composition (C) according to claim 3, selected from the group consisting of:

5. Composition (C) according to any one of claims 1 to 4, wherein the polymer (F) preferably has a molecular weight greater than 1,200,000 g mol-1 and less than 1,800,000 g mol-1, determined by GPC using conventional calibration with polystyrene.

6. The composition (C) according to any one of claims 1 to 5, wherein the polymer (F) is obtainable by a process comprising radical polymerization using an organic radical initiator system selected from the group consisting of organic dialkyl peroxides, such as di-t-butyl peroxide (DTBP); dialkyl peroxydicarbonates, such as diisopropyl peroxydicarbonate (IPP), di-N-propyl peroxydicarbonate (NPP), diethyl peroxydicarbonate, di-sec-butyl peroxydicarbonate (DBP); and t-alkyl peroxybenzoates, such as tert-butyl- or tert-amyl-peroxypivalate.

7. The active material (AM) has the following formula: Li ｘ A ｙ D ｚ PO ４ 7. Composition (C) according to any one of claims 1 to 6, which is a phospho-olivine material of the formula: (wherein A is selected from the group consisting of Mn, Fe, Co, Ni and Cu; D is selected from the group consisting of Mg, Ca, Sr and Ba; and x, y and z are numbers satisfying the following relationships: 0.9<x<1.2, 0<y<1.5, 0≦z<1.5).

8. 8. The composition (C) of claim 7, wherein the active material (AM) is selected from the group consisting of lithium iron phosphate (LFP), lithium iron manganese phosphate (LMFP), and lithium manganese phosphate.

9. Composition (C) according to claim 7 or 8, wherein said active material (AM) has a D50 average particle size less than or equal to 2 μm, preferably in the range comprised between 100 nm and 2 μm.

10. A method for producing an electrode [electrode (E)], comprising the steps of: (I) providing a metal substrate having at least one surface; (II) preparing the electrode-forming composition (C) according to any one of claims 1 to 9; (III) applying the composition (C) prepared in step (II) onto at least one surface of the metal substrate prepared in step (I), thereby obtaining an assembly including a metal substrate coated with the composition (C) on at least one surface; (IV) drying the assembly obtained in step (III); (V) subjecting the dried assembly obtained in step (IV) to a compression step to obtain the electrode (E) of the present invention. A method comprising:

11. 11. An electrode (E) obtainable by the method according to claim 10.

12. Electrochemical device comprising at least one electrode (E) according to claim 11.

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