Dispersant for lithium iron phosphate

Abstract

A composition suitable for use in a composition for preparing an electrode for a rechargeable battery is provided. The present invention relates to a composition comprising (a) a lithium iron phosphate-based positive electrode active material and (b) an essentially linear polymer or oligomer having at least one acidic phosphate ester group.

Description

[Technical Field]

[0001] The present invention relates to a composition comprising a lithium iron phosphate-based active cathode material and an essentially linear polymer or oligomer, a cathode for a battery comprising the composition, a battery comprising the cathode, the use of the essentially linear polymer or oligomer to reduce the viscosity of a slurry comprising particles of the lithium iron phosphate-based active cathode material, and a process for preparing an electrode slurry for a battery. [Background technology]

[0002] US2020 / 0028174A describes a lithium iron phosphate electrode material having hydrogenated nitrile butadiene rubber as a dispersant.

[0003] CN103545527A describes a battery slurry dispersant for Li lithium-ion batteries. The dispersant is a copolymer of acrylic acid, maleic anhydride, (hydroxyethyl) methacrylate phosphate, and an allyl-functional polyethylene oxide macromonomer. The dispersant has a comb-type polymer structure. It is prepared in an aqueous environment and contains lithium carboxylate groups.

[0004] CN102237521A describes tartaric acid esters as dispersants for Li lithium-ion battery slurries. Preferably, tartrates are used in combination with citrate esters.

[0005] JP2014-149968A describes an aqueous slurry for battery electrodes that contains lithium iron phosphate, a water-soluble polymer, and a dispersant. The dispersant is a salt of a linear polymer or oligomer having a phosphate ester, such as a lithium salt, a sodium salt, a potassium salt, an ammonium salt, or an organic amine salt. Summary of the Invention [Problem to be solved by the invention]

[0006] There is a continuing need to further improve compositions comprising lithium iron phosphate-based positive electrode active materials suitable for preparing electrodes for rechargeable batteries, particularly in terms of compositions having desirable low viscosity, good dispersion stability, and also in terms of providing desirable electrochemical stability of the rechargeable batteries and low volume resistivity of the resulting electrodes. [Means for solving the problem]

[0007] The present invention provides a composition comprising: (a) a lithium iron phosphate-based positive electrode active material, and (b) An essentially linear polymer or oligomer having at least one acidic phosphate ester group. DETAILED DESCRIPTION OF THE INVENTION

[0008] The compositions of the present invention are highly suitable for use in compositions for preparing electrodes for rechargeable batteries. The compositions have desirable low viscosity, good dispersion stability, and further provide desirable electrochemical properties for rechargeable batteries and low volume resistivity for the resulting electrodes. One important advantage over other lithium ion chemistries is their thermal and chemical stability, which improves battery safety.

[0009] Lithium iron phosphate based positive electrode active materials are known in the art.

[0010] The lithium iron phosphate-based positive electrode active material can be represented by the following chemical formula I: Li 1+a Fe 1-x M x PO 4-b A b

[0011] In the formula, M represents at least one selected from the group consisting of manganese (Mn), nickel (Ni), cobalt (Co), copper (Cu), scandium (Sc), titanium (Ti), chromium (Cr), vanadium (V), and zinc (Zn); A represents at least one selected from the group consisting of sulfur (S), selenium (Se), fluorine (F), chlorine (Cl), and iodine (I); a is in the range of −0.5 to 0.5; x is in the range of 0.0 to 0.5; and b is in the range of 0.0 to 0.1.

[0012] In some embodiments, the lithium iron phosphate-based active cathode material is represented by the formula LiFePO4, which is a naturally occurring mineral of the olivine (triphylite) series. LiFePO4 has been identified as a polyanion class cathode material for use in batteries. It has gained significant market acceptance due to its low cost, non-toxicity, natural abundance of iron, its excellent thermal stability, safety characteristics, electrochemical performance, and specific capacity.

[0013] Commercial lithium iron phosphate-based cathode active materials are usually synthetic materials. The synthesis methods for lithium iron phosphate materials mainly include solid-state and liquid-state methods. Solid-state methods include high-temperature solid-state reaction, carbothermal reduction, microwave synthesis, and mechanical alloying. Solid-state synthesis is the most commonly used method for preparing electrode materials due to its simple process and easy industrialization. Carbothermal reduction is the most commonly used solid-state method. In this method, inexpensive ferric iron is reduced to ferrous iron using an organic carbon precursor compound such as citric acid, and pyrolytic carbon is simultaneously coated on the lithium iron phosphate to enhance electrical conductivity.

[0014] Liquid-phase methods include liquid-phase precipitation, sol-gel synthesis, and hydrothermal synthesis. For example, in the hydrothermal synthesis, raw materials undergo a chemical reaction under high temperature and pressure conditions using water as a solvent in a sealed pressure vessel. After filtering, washing, and drying, nanoprecursors are obtained, which can then be calcined at high temperatures to obtain lithium iron phosphate. Liquid-phase preparation methods generally result in lithium iron phosphate-based materials with narrower particle size distributions.

[0015] Although lithium iron phosphate-based positive electrode active materials are structurally very stable, they have drawbacks such as low electrical conductivity and low ionic conductivity. Therefore, it is preferable to use lithium iron phosphate-based positive electrode active materials in such a way that the electrical conductivity is improved by coating the surface of the lithium iron phosphate-based positive electrode active material with carbon and the particle size of the lithium iron phosphate-based positive electrode active material is reduced to improve the ionic conductivity.

[0016] In view of the above, in the composition according to the present invention, the surface of the lithium iron phosphate-based material is at least partially coated with a conductive carbon-based material. In a more preferred embodiment, the carbon content of the lithium iron phosphate-based material is in the range of 0.4 to 2.0 wt %, preferably 0.5 to 1.7 wt %, calculated based on the weight of the lithium iron phosphate-based material.

[0017] In a more preferred embodiment, the lithium iron phosphate-based material is present in the form of particles having an average particle size D50 in the range of 100 to 5000 nm, more preferably 200 to 4000 nm. Particle size can be suitably determined using laser diffraction using the Mie theory of light scattering. Particle size is reported as volume equivalent spherical diameter.

[0018] The compositions of the present invention further include an essentially linear polymer or oligomer having at least one acid phosphate ester group. The polymer or oligomer is essentially linear. Essentially linear means the essential absence or complete absence of polymer branches covalently attached to the polymer or oligomer backbone. Generally, a polymer or oligomer is considered essentially linear if the linear backbone constitutes 90-100% by weight of the polymer. The polymer or oligomer comprises at least two, preferably at least three, repeat units of polymerized monomers. Generally, the polymer or oligomer comprises 3-500 repeat units of polymerized monomers. The polymer or oligomer can be based on one or more types of monomers.

[0019] In a preferred embodiment, the essentially linear polymer or oligomer comprises an ether repeating unit. The oligomer or polymer may be a polyether, for example, a polyether prepared by ring-opening polymerization of a cyclic ether group such as an epoxide, an oxetane, or an oxolane. Examples of suitable epoxides include ethylene oxide, propylene oxide, glycidyl ether, glycidyl ester, and mixtures thereof. Suitable oxetanes include unsubstituted or substituted oxetanes, such as trimethylolpropane oxetane.

[0020] In a further preferred embodiment, the essentially linear polymer or oligomer comprises ester repeat units. The oligomer or polymer may be a polyester, for example, a polyester based on a dicarboxylic acid, a diol, and optionally a monoalcohol, a monocarboxylic acid, or a combination thereof. Alternatively, a polymer containing ester groups can be prepared by ring-opening polymerization of a lactone. Examples of suitable lactones include epsilon-caprolactone and delta-valerolactone.

[0021] In a further embodiment, the polymer or oligomer comprises ester and ether groups. In one embodiment, the polymer may be a block copolymer comprising at least one polyether block and at least one polyester block. Alternatively, the ester and ether groups may be randomly distributed.

[0022] The essentially linear polymer or oligomer (b) preferably has a number average molecular weight in the range of 250 to 5000 g / mol, more preferably in the range of 250 to 4000 g / mol, even more preferably in the range of 250 to 3500 g / mol.

[0023] The number-average molecular weight Mn and the weight-average molecular weight Mw are suitably determined by gel permeation chromatography using tetrahydrofuran as eluent and polystyrene as calibration standard in accordance with DIN 55672-1:2007-08.

[0024] The essentially linear polymer or oligomer contains at least one acid phosphate ester group, which exists as a monoester and a diester of phosphoric acid.

[0025] The number of acidic phosphate groups may vary in individual polymer or oligomer molecules. Some individual molecules may have multiple acidic phosphate groups. It is also possible for a polymer or oligomer to include individual molecules that have no acidic phosphate groups.

[0026] In an exemplary embodiment, the essentially linear polymer or oligomer has an average number of acid phosphate ester groups per molecule in the range of 0.8 to 4.0, preferably 0.8 to 2.5, and most preferably 0.8 to 2.1.

[0027] In exemplary embodiments, the acidic phosphate ester group is the terminal group of an essentially linear polymer or oligomer. In some embodiments, the essentially linear polymer or oligomer has one terminal acidic phosphate ester group. In these embodiments, the other terminal group can be a hydroxyl group, or an alkyl ester or alkyl ether group. In further embodiments, both terminal groups of the essentially linear polymer or oligomer are acidic phosphate groups. In still further embodiments, the essentially linear polymer or oligomer has two acidic phosphate ester groups at one end and zero or one acidic phosphate ester groups at the other end. In some embodiments, the acidic phosphate ester groups can be located along the polymer chain or can interrupt the polymer chain.

[0028] It is generally preferred that the essentially linear polymer or oligomer have a low content of carboxylic acid groups or salts thereof. In a particularly preferred embodiment, the essentially linear polymer or oligomer is free of, or essentially free of, carboxylic acid groups or salts thereof. Thus, the essentially linear polymer or oligomer preferably has an average number of carboxylate and carboxylic acid groups per molecule ranging from 0.0 to 2.0, preferably from 0.0 to 0.5.

[0029] Essentially linear polymers or oligomers having at least one acidic phosphate ester group are suitably prepared by reacting a hydroxyl-functional polymer or oligomer precursor with an ester-forming phosphorus compound. An ester-forming phosphorus compound is understood to be a compound capable of forming a phosphate ester by reaction with a compound containing a hydroxyl group. Examples of ester-forming phosphorus compounds include polyphosphoric acid, phosphorus pentoxide, phosphorus chloride, and acetyl phosphate (acetyl phosphate). Special substitution patterns can occur when using special phosphorylating agents, particularly phosphoryl chloride. Polyphosphoric acid and phosphorus pentoxide are preferred, with polyphosphoric acid being particularly preferred. Primarily monoesters are formed with polyphosphoric acid, while monoester / diester mixtures are formed with phosphorus pentoxide. Monoesters are preferred. It is also possible to use a mixture of various components to be phosphorylated in the phosphorylation reaction. The reaction of the ester-forming phosphorus compound with the hydroxyl compound is preferably carried out in the absence of a solvent at temperatures up to 150°C, preferably below 100°C. However, the reaction can also be carried out in the presence of a suitable inert solvent, such as methoxypropyl acetate.

[0030] The weight ratio of the lithium iron phosphate-based positive electrode active material to the essentially linear polymer or oligomer having at least one acidic phosphate ester group can vary widely. In a typical embodiment, the amount of polymer or oligomer (b) is in the range of 0.01 to 5.00 wt. %, preferably 0.05 to 3.00 wt. %, calculated based on the total weight of components (a) and (b).

[0031] In exemplary embodiments, the compositions of the present invention comprise a single type of essentially linear polymer or oligomer having at least one acidic phosphate ester group. However, in some embodiments, it has been found that using a combination of two or more essentially linear polymers or oligomers having at least one acidic phosphate ester group is advantageous in terms of viscosity reduction. The different types of oligomers or polymers may differ in terms of the type of polymer backbone, molecular weight, or average number of acidic phosphate groups.

[0032] In some embodiments, it may be advantageous to include an additional polymeric dispersant in the composition, which is different from the essentially linear polymer or oligomer having at least one acidic phosphate ester group, and which can facilitate the dispersion of other particles present in the composition, such as the lithium iron phosphate-based active cathode material or the conductive carbon-based material.

[0033] In a preferred embodiment, the composition of the present invention is liquid or in the form of a paste at a temperature of 20°C. To make the composition liquid or pasty, the composition preferably contains one or more solvents. The solvent may be an organic solvent or water. In a preferred embodiment, the composition is a non-aqueous composition. A non-aqueous composition is a composition in which water is not the primary liquid diluent. A non-aqueous composition generally has a low water content or does not contain any intentionally added water. Suitably, the water content of a non-aqueous composition is in the range of 0 to 10% by weight, preferably 0 to 5% by weight, calculated based on the weight of the composition. Generally, an organic solvent is selected that can dissolve the polymeric or oligomeric components of the composition. The organic solvent may also contain two or more organic solvents, for example, a mixture of two or more solvents. Examples of suitable solvents include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene, toluene, and fluorobenzene; or carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R—CN (wherein R is a linear, branched, or cyclic C to C hydrocarbon group, which may contain a double-bonded aromatic ring or an ether bond); amide compounds such as dimethylformamide compounds; dioxolanes such as 1,3-dioxolane; or sulfolane. Examples of further suitable solvents include aprotic dipolar solvents such as dimethyl sulfoxide, dimethylformamide, or N-methylpyrrolidone, or other solvents containing an amide group. When water is used as the solvent, it may be preferable to further include a thickener. The amount of solvent is adjusted to obtain a viscosity that allows the paste to be easily applied to a collector.

[0034] Generally, the organic solvent is present in the composition of the present invention in an amount of from 10 to 90% by weight, calculated based on the total weight of the composition.

[0035] In a further embodiment, the organic solvent is present in an amount of 15.0 to 60.0% by weight, calculated based on the combined weight of components (a) and (b).

[0036] In another embodiment, the composition further includes an organic polymer binder different from component (b). The binder improves adhesion between particles of the positive electrode active material and between the positive electrode active material and the current collector. Examples of binders include fluoropolymers such as polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, and polytetrafluoroethylene; rubber-based binders such as styrene-butadiene rubber (SBR), ethylene-propylene-diene monomer rubber (EPDM), sulfonated EPDM, and fluororubber; polyethylene; polypropylene; polyvinyl alcohol; polyvinylpyrrolidone; polyacrylonitrile; carboxymethyl cellulose (CMC); starch; hydroxypropyl cellulose; regenerated cellulose; and polyacrylate-based binders. If desired, a binder can be used in forming the aqueous dispersion.

[0037] The amount of binder used is preferably 1.0 to 50.0 parts by mass, more preferably about 1.0 to 20.0 parts by mass, and even more preferably 1.0 to 10.0 parts by mass, per 100 parts by mass of the nonvolatile material of the composition.

[0038] To enhance the electrical conductivity of the electrode material, the composition may further comprise an electrically conductive carbon material. A carbon-based material is a material consisting of 90 to 100% by weight of carbon. A conductive carbon-based material is selected for use in the field of battery electrode manufacturing. Examples of suitable conductive carbon-based materials include carbon black, carbon nanotubes, graphite, carbon fiber, graphene, fullerene, and mixtures thereof. Preferred carbon-based materials are carbon black, graphene, and carbon nanotubes. Specific types of suitable carbon black are furnace black and acetylene black.

[0039] In a further embodiment, the present invention also relates to a positive electrode for a battery comprising the composition of the present invention.

[0040] The term battery encompasses a single electrochemical cell containing a positive electrode and a negative electrode, a separator disposed between the positive and negative electrodes, and an electrolyte. The term battery also encompasses a collection of multiple electrochemical cells or cell assemblies. The term positive electrode or cathode refers to the electrode where reduction occurs during a discharge cycle.

[0041] The electrolyte is preferably a compound capable of providing lithium ions within the battery. Lithium salts are commonly used.

[0042] Specific examples of suitable lithium salts include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiBr, LiI, or LiB(C2O4)2. Lithium salts are generally used in a concentration range of 0.1M to 2.0M.

[0043] The composition is preferably used in the form of a paste. The electrode paste can be obtained by kneading the components of the composition. For kneading, known devices such as a ribbon mixer, a screw kneader, a Spartan granulator, a Loedige mixer, a planetary mixer, or a universal mixer can be used. The electrode paste can be formed into a sheet shape, a pellet shape, or the like.

[0044] The electrode may be formed by molding the electrode paste described above, for example, by applying the electrode paste to a current collector, drying it, and then pressing it.

[0045] Examples of current collectors include foils and meshes of aluminum, nickel, copper, stainless steel, etc. The paste coating thickness is generally 40 to 200 μm. There are no particular limitations on the paste application method, and examples of application methods include applying the paste with a doctor blade or bar coater and then forming it with a roll press or the like.

[0046] Examples of pressure molding include roll pressure molding and compression molding. The pressure for pressure molding is about 1 to 3 t / cm. 2 As the electrode density increases, the battery capacity per volume generally increases. However, if the electrode density is too high, the cycle characteristics generally decrease. When the electrode paste according to a preferred embodiment of the present invention is used, the deterioration of the cycle characteristics is small even if the electrode density is increased. Generally, the electrode density is 1.0 to 4.0 g / cm. 3 In some embodiments, the electrode density of the cathode is in the range of 2.0 to 3.5 g / cm 3 and the anode density is in the range of 1.2 to 2.0 g / cm 3 The range is.

[0047] As described above, it has been discovered that the presence of an essentially linear polymer or oligomer having at least one acidic phosphate ester group in an electrode slurry containing a lithium iron phosphate-based active cathode material effectively reduces the viscosity of the slurry, making the slurry easier to handle without the need to add large amounts of viscosity-reducing solvents.

[0048] Thus, in a further aspect, the present invention relates to the use of an essentially linear polymer or oligomer having at least one acidic phosphate ester group for reducing the viscosity of a slurry containing particles of a lithium iron phosphate-based active positive electrode material. The present invention also relates to a method for reducing the viscosity of a slurry containing particles of a lithium iron phosphate-based active positive electrode material, the method comprising the step of incorporating into the slurry an essentially linear polymer or oligomer having at least one acidic phosphate ester group.

[0049] In a further embodiment, the present invention provides a method for producing a pharmaceutical composition comprising the steps of: (i) providing a lithium iron phosphate-based positive electrode active material; (ii) providing a solvent; (iii) providing an essentially linear polymer or oligomer having at least one acidic phosphate ester group; (iv) providing an organic polymer binder other than an essentially linear polymer or oligomer having terminal phosphate ester groups; (v) mixing the components provided in steps (i) through (iv) in any suitable order; The present invention relates to a method for preparing an electrode slurry for a battery, comprising: [Example]

[0050] raw material All raw materials were purchased from Sigma-Aldrich (Merck) unless otherwise stated.

[0051] Methoxypoly(ethylene glycol) Mw 350 (MPEG 350) Methoxypoly(ethylene glycol) Mw 500 (MPEG 500) ε-caprolactone γ-valerolactone 4-Dodecylbenzenesulfonic acid (DBSA) Isodecanol Polyphosphoric acid (PPA) Phosphorus pentoxide (P2O5) Dibutyltin dilaurate (DBTL) 2-Ethylhexyl glycidyl ether (EHGE) Trifluoromethanesulfonic acid (TFMSA) N-methyl-2-pyrrolidone (NMP)

[0052] K-Kat XK-633 (Zinc Catalyst) - King Ind. Emulsogen TS100 (Tristyrylphenol Ethoxylate) - Clariant Makon-TD 8 (Tridecyl Alcohol Ethoxylate)-Stepan Lutensol AT50 (C16-C18-Fatty Alcohol Ethoxylate) - BASF Pluronic® RPE 1740 (EO-PO block polyether) - BASF

[0053] DY-3 Lithium Iron Phosphate (LFP) - Dynanonic YN-5 Lithium Iron Phosphate Material (LFP) - Yuneng

[0054] Super P (Carbon Black) - Imerys Kynar HSV 900 (PVDF) - Arkema Sokalan K30 (PVP)-BASF HNBR (Arlanxeo)

[0055] Method for producing intermediate products Method for preparing intermediate I-1 (MPEG-initiated polyester) A clean, dry four-neck flask (250 mL) equipped with a condenser, stirrer, temperature sensor, and nitrogen line was charged with MPEG 350 (50.06 g), ε-caprolactone (32.43 g), γ-valerolactone (18.39 g), and DBSA (0.11 g), heated to 80°C, and stirred at this temperature for 3 h.

[0056] Method for producing intermediate I-2 (alcohol-initiated polyester) Isodecanol (14.35 g), ε-caprolactone (85.55 g), and K-Kat XK-633 (0.10 g) were placed in a clean, dry four-neck flask (250 mL) equipped with a condenser, stirrer, temperature sensor, and nitrogen line, and heated to 170 °C and stirred at this temperature for 3 h.

[0057] Method for producing intermediate I-3 (tristyrylphenol ethoxylate-initiated polyester) A clean, dry four-neck flask (250 mL) equipped with a condenser, stirrer, temperature sensor, and nitrogen line was charged with Emulsogen TS 100 (55.76 g), ε-caprolactone (7.52 g), γ-valerolactone (6.60 g), and DBTL (0.02 g), heated to 170 °C, and stirred at this temperature for 3 h.

[0058] Method for preparing intermediate I-4 (MPEG-initiated statistical polyester / ether) MPEG 500 (54.55 g), ε-caprolactone (24.91 g), 2-ethylhexyl glycidyl ether (20.51 g), and TFMSA (0.03 g) were placed in a clean, dry four-neck flask (250 mL) equipped with a condenser, stirrer, temperature sensor, and nitrogen line, heated to 80 °C, and stirred at this temperature for 3 h.

[0059] General Method for Preparing Linear Phosphate Ester Functionalized Dispersants (P) A clean, dry four-neck flask (250 mL) equipped with a condenser, stirrer, temperature sensor, and nitrogen line was charged with component A (see Table 1) and heated to 50°C. Then, phosphorylated component B was slowly added to the mixture. After complete addition, the mixture was heated to 80°C and stirred at this temperature for 4 h.

[0060] [Table 1]

[0061] General preparation method for LFP cathode standard slurry (S1) YN-5 (24.0 g), carbon black (0.15 g), and PVDF (0.5 g) were charged into a 250 mL plastic container and mixed for 10 minutes at 2000 rpm in a Hauschild SpeedMixer®. Dispersant (0.05 g) diluted with NMP (13.27 g) was then added to the dry mixture, and the slurry was further mixed at 2000 rpm for 20 minutes.

[0062] General preparation method for LFP cathode standard slurry (S2) DY-3 (24.0 g), carbon black (0.15 g), and PVDF (0.5 g) were charged into a 250 mL plastic container and mixed for 10 minutes at 2000 rpm in a Hauschild SpeedMixer®. Dispersant (0.05 g) diluted with NMP (16.43 g) was then added to the dry mixture, and the slurry was further mixed at 2000 rpm for 20 minutes.

[0063] Preparation method of dispersant-free LFP cathode standard slurry (S2-0) DY-3 (24.0 g), carbon black (0.15 g), and PVDF (0.55 g) were charged into a 250 mL plastic container and mixed for 10 minutes at 2000 rpm in a Hauschild SpeedMixer®. NMP (16.43 g) was then added to the dry mixture, and the slurry was further mixed for 20 minutes at 2000 rpm.

[0064] General preparation method for conductive slurry (S3) Carbon black (1.05 g), PVDF (0.73 g), Dispersant P (0.73 g), and NMP (30.83 g) were charged to a 250 mL plastic container and mixed in a Hauschild SpeedMixer® at 2000 rpm for 20 minutes.

[0065] Manufacturing method of dispersant-free conductive slurry (S3-0) Carbon black (1.48 g), PVDF (1.02 g) and NMP (30.83 g) were charged into a 250 mL plastic container and mixed in a Hauschild SpeedMixer® at 2000 rpm for 20 minutes.

[0066] Viscosity measurement The LFP cathode slurries (S1 / S2) were first stored at room temperature for 1 hour. The rheology of the slurries was evaluated using an Anton Paar MCR rheometer and cone-plate CP-50 at a measurement temperature of 25°C according to the following protocol:

[0067] [Table 2]

[0068] [Table 3]

[0069] Table 3 shows that all of the LFP slurries according to the invention have lower viscosities than the comparative LFP slurries, which allows for the formulation of slurries according to the invention with a given target viscosity using less solvent.

[0070] The LFP slurry exhibits thixotropic behavior. The viscosity of the slurry decreases when exposed to shear forces. This is indicated by the viscosity value V2 in Table 3 above. During the process of fabricating electrodes from the slurry, it is advantageous for the viscosity of the slurry to increase when the slurry is applied and the shear forces are removed. Therefore, viscosity recovery after exposure to shear forces has ended is highly desirable. The recovered viscosity is indicated by the viscosity value V3 in Table 3 above. Viscosity recovery is expressed as the viscosity quotient V3 / V1. The LFP slurries of the present invention exhibit high viscosity recovery. In particular, the LFP slurries of the present invention exhibit an improved balance of low initial viscosity and good recovery.

[0071] Volume resistivity measurement The LFP slurry was coated onto a PET sheet by a doctor blade method. After drying, the sheet was cut into pieces with a side length of 3 cm, and the volume resistivity of the formed electrode layer was measured at 25°C using a four-point probe and a low resistivity meter (Loresta-AX).

[0072] [Table 4]

[0073] Evaluation of electrochemical stability The conductive slurry (S3) was coated onto copper foil and aluminum foil, respectively. After drying, the conductive layer was cut into circular electrodes with a diameter of 18 mm, and a model cell was assembled using a separator made from glass fiber (EL-CELL Products, Model No. ECC1-01-0012-C / L). Lithium metal was used as the anode material. A solution of 1 mol LiPF6 dissolved in ethylene carbonate and propylene carbonate (1:1 volume ratio) was prepared as the electrolyte used in the test cells. Cyclic voltammetry (CV) of these test cells was performed using the electrode layer on aluminum foil versus Li / Li. + Measured at 2.5V to 4.8V, and using an electrode layer on copper foil, vs. Li / Li +The potential was measured from 2.5 V to 0.1 V at 1000 kJ / s. The scan rate was 0.05 mV / s. Three series of cycles were measured. The electrochemical stability of the dispersant was determined by comparing the CV curves of the electrodes with and without the dispersant, and no inherent hysteresis was observed.

[0074] [Table 5]

[0075] All CV curves show no hysteresis in the applied voltage range, indicating good electrochemical stability of the dispersant.

Claims

1. (a) a lithium iron phosphate-based positive electrode active material; (b) an essentially linear polymer or oligomer having at least one acidic phosphate ester group; A composition comprising:

2. The composition of claim 1 , wherein the essentially linear polymer or oligomer comprises ether repeat units.

3. 3. The composition of claim 1 or 2, wherein the essentially linear polymer or oligomer comprises ester repeat units.

4. 4. The composition according to claim 1, wherein the essentially linear polymer or oligomer (b) has a number average molecular weight in the range of 250 to 5000 g / mol, preferably in the range of 250 to 4000 g / mol, determined by gel permeation chromatography in accordance with DIN 55672-1:2007-08.

5. 5. A composition according to any one of claims 1 to 4, wherein the essentially linear polymer or oligomer has an average number of acid phosphate ester groups per molecule in the range of from 0.8 to 4.0, preferably from 0.8 to 2.

5.

6. 6. The composition of any one of claims 1 to 5, wherein the essentially linear polymer or oligomer has an average number of carboxylate and carboxylic acid groups per molecule in the range of 0.0 to 2.

0.

7. 7. The composition of claim 1, wherein the lithium iron phosphate-based material is present in the form of particles having an average particle size D50 in the range of 100 to 5000 nm as measured by laser diffraction.

8. 8. The composition of claim 1, wherein the amount of polymer or oligomer (b) is in the range of 0.01 to 5.00% by weight, calculated based on the total weight of components (a) and (b).

9. The composition of any one of claims 1 to 8, wherein the composition further comprises one or more solvents.

10. 10. The composition of claim 9, wherein the one or more solvents are present in an amount of 15.0 to 60.0% by weight, calculated based on the total weight of components (a) and (b).

11. 11. The composition of claim 9 or 10, wherein the one or more solvents are organic solvents.

12. The composition of any one of claims 1 to 11, wherein the composition further comprises an organic polymer binder different from component (b).

13. The composition according to any one of claims 1 to 12, wherein the surface of the lithium iron phosphate-based material is at least partially coated with a conductive carbon-based material.

14. The composition of any one of claims 1 to 13, wherein the composition further comprises a conductive carbon material.

15. 15. The composition of any one of claims 1 to 14, wherein the composition further comprises a polymeric dispersant, the polymeric dispersant being different from the essentially linear polymer or oligomer having at least one acidic phosphate ester group.

16. A positive electrode for a battery, the electrode comprising the composition of any one of claims 1 to 15.

17. A battery comprising the positive electrode according to claim 16, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte.

18. Use of an essentially linear polymer or oligomer having at least one acidic phosphate ester group to reduce the viscosity of a slurry containing particles of a lithium iron phosphate-based positive electrode active material.

19. 1. A method for preparing an electrode slurry for a battery, comprising the steps of: (i) providing a lithium iron phosphate-based positive electrode active material; (ii) providing a solvent; (iii) providing an essentially linear polymer or oligomer having at least one acidic phosphate ester group; (iv) providing an organic polymer binder different from said essentially linear polymer or oligomer having terminal phosphate ester groups; (v) mixing the ingredients provided in steps (i)-(iv) in any suitable order; A method comprising:

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