Dispersant for lithium iron phosphate

Abstract

The invention relates to a composition comprising a) a positive electrode active material based on lithium iron phosphate, and b) a substantially linear polymer or oligomer having at least one acidic phosphate group.

Description

[0001] The present invention relates to a composition comprising a positive electrode active material based on lithium iron phosphate and a substantially linear polymer or oligomer, a positive electrode for a battery comprising the composition, a battery comprising the positive electrode, use of the substantially linear polymer or oligomer for reducing the viscosity of a slurry comprising particles of a positive electrode active material based on lithium iron phosphate, and a method for preparing an electrode slurry for a battery.

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

[0003] CN 103545527 A describes a battery slurry dispersant for lithium-ion batteries. The dispersant is a copolymer of acrylic acid, maleic anhydride, (hydroxyethyl) methacrylate phosphate and allyl-functional polyethylene oxide macromonomer. The dispersant has a comb-like polymer structure. It is prepared in an aqueous environment and contains lithium carboxylate groups.

[0004] CN 102237521 A describes tartrate as a dispersant for lithium-ion battery slurries. Preferably, the tartrate is used in combination with a citrate.

[0005] JP 2014 149968A describes an aqueous slurry for battery electrodes, which includes lithium iron phosphate, a water-soluble polymer and a dispersant. The dispersant is a salt of a linear polymer or oligomer with a phosphate ester, such as a lithium salt, a sodium salt, a potassium salt, an ammonium salt and an organic amine salt.

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

[0007] The present invention provides a composition comprising

[0008] a) a positive electrode active material based on lithium iron phosphate, and

[0009] b) Substantially linear polymers or oligomers having at least one acidic phosphate group.

[0010] The composition of the present invention is very suitable for preparing a composition for an electrode of a rechargeable battery. The composition has an ideal low viscosity, good dispersion stability, and also provides ideal electrochemical performance of a rechargeable battery, as well as a low volume resistivity of the resulting electrode. An important advantage over other lithium ion chemistries is thermal and chemical stability, which improves the safety of the battery.

[0011] Positive electrode active materials based on lithium iron phosphate are known in the art.

[0012] The lithium iron phosphate-based positive electrode active material can be represented by the following formula I:

[0013] Li 1+a Fe 1-x M x PO 4-b A b

[0014] In the formula, M represents at least one 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 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.

[0015] In some embodiments, the lithium iron phosphate-based positive electrode active material is of the formula LiFePO 4 It is a natural mineral of the olivine family (trilobite). LiFePO 4 It is identified as a multi-anion cathode material for batteries. It has gained considerable market acceptance due to its low cost, non-toxicity, abundant natural iron content, thermal stability, safety, excellent electrochemical performance and specific capacity.

[0016] Commercial lithium iron phosphate-based cathode active materials are usually synthetic materials. The synthesis methods of lithium iron phosphate materials mainly include solid-phase method and liquid-phase method. The solid-phase method includes high-temperature solid-phase reaction method, carbon thermal reduction method, microwave synthesis method and mechanical alloying method. The solid-phase synthesis method is simple in process and easy to industrialize. It is currently the most commonly used method for preparing electrode materials. The carbon thermal reduction method is the most common solid-phase method. The carbon thermal reduction method uses organic carbon precursor compounds, such as citric acid, to reduce cheap trivalent iron to divalent iron, and at the same time, pyrolyzed carbon is coated on the lithium iron phosphate to improve the conductivity.

[0017] Liquid phase methods include liquid phase precipitation method, sol-gel method and hydrothermal synthesis method. Taking the hydrothermal method as an example, water is used as a solvent in a closed pressure vessel, and the raw materials undergo a chemical reaction under high temperature and high pressure conditions. After filtering, washing and drying, a nano precursor is obtained, and finally lithium iron phosphate is obtained by high temperature calcination. The particle size distribution of lithium iron phosphate-based materials obtained by the liquid phase preparation method is generally narrow.

[0018] The positive electrode active material based on lithium iron phosphate is a positive electrode active material with a very stable structure, but has the disadvantage of low electrical conductivity and ion conductivity. Therefore, the positive electrode active material based on lithium iron phosphate is preferably used in a manner of coating carbon on the surface of the positive electrode active material based on lithium iron phosphate to improve electrical conductivity and reducing the particle size of the positive electrode active material based on lithium iron phosphate to improve ion conductivity.

[0019] 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 further preferred embodiment, the carbon content of the lithium iron phosphate-based material is in the range of 0.4 to 2.0 wt %, preferably in the range of 0.5 to 1.7 wt %, calculated based on the weight of the lithium iron phosphate-based material.

[0020] In a further 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 in the range of 200 to 4000 nm. The particle size may be suitably determined using laser diffraction, Mie theory using light scattering. The particle size is reported in the form of volume equivalent spherical diameter.

[0021] The composition of the present invention also comprises a substantially linear polymer or oligomer having at least one acidic phosphate group. The polymer or oligomer is substantially linear. Substantially linear refers to the substantial or complete absence of polymer branches covalently attached to the polymer or oligomer backbone. Typically, a polymer or oligomer is considered substantially linear when the linear backbone accounts for 90 to 100% of the polymer weight. The polymer or oligomer comprises at least two, preferably at least three repeating units of polymerized monomers. Typically, the polymer or oligomer comprises 3 to 500 repeating units of polymerized monomers. The polymer or oligomer can be based on one or more types of monomers.

[0022] In a preferred embodiment, the substantially linear polymer or oligomer comprises ether repeating units. The oligomer or polymer can be a polyether, for example a polyether prepared by the ring-opening polymerization of a cyclic ether group (for example epoxide, oxetane and oxolane). The example of a suitable epoxide comprises ethylene oxide, propylene oxide, glycidyl ether, glycidyl ester and mixtures thereof. Suitable oxetanes comprise unsubstituted oxetanes or substituted oxetanes, for example trimethylolpropane oxetanes.

[0023] In a further preferred embodiment, the substantially linear polymer or oligomer comprises ester repeating units. The oligomer or polymer may be a polyester, for example a polyester based on a dicarboxylic acid, a diol and optionally a monohydric alcohol, a monocarboxylic acid and a combination thereof. Alternatively, the polymer containing the ester group may be prepared by ring-opening polymerization of a lactone. Examples of suitable lactones include ε-caprolactone and δ-valerolactone.

[0024] In another embodiment, the polymer or oligomer contains ester groups and ether groups. In one embodiment, the polymer can be a block copolymer comprising at least one polyether block and at least one polyester block. Alternatively, the ester groups and ether groups can be randomly distributed.

[0025] The substantially linear polymer or oligomer b) preferably has a number average molecular weight in the range from 250 to 5000 g / mol, more preferably in the range from 250 to 4000 g / mol, and even more preferably in the range from 250 to 3500 g / mol.

[0026] The number average molecular weight Mn and the weight average molecular weight Mw are determined appropriately by gel permeation chromatography in accordance with DIN 55672-1:2007-08 using tetrahydrofuran as the eluent and polystyrene as the calibration standard.

[0027] The substantially linear polymer or oligomer contains at least one acidic phosphate group. Acidic phosphate groups are present in the mono- and diesters of phosphoric acid.

[0028] The number of acidic phosphate groups can vary in individual polymer or oligomer molecules. Some individual molecules may have multiple acidic phosphate groups. The polymer or oligomer may also include individual molecules that do not have acidic phosphate groups.

[0029] In an exemplary embodiment, the substantially linear polymer or oligomer has an average number of acidic phosphate groups per molecule in the range from 0.8 to 4.0, preferably from 0.8 to 2.5, and most preferably from 0.8 to 2.1.

[0030] In an exemplary embodiment, the acidic phosphate group is a terminal group of the substantially linear polymer or oligomer. In some embodiments, the substantially linear polymer or oligomer has one terminal acidic phosphate group. In these embodiments, the other terminal group can be a hydroxyl group, or an alkyl ester or alkyl ether group. In a further embodiment, both terminal groups of the substantially linear polymer or oligomer are acidic phosphate groups. In yet another embodiment, the substantially linear polymer or oligomer has two acidic phosphate groups at one end and no or one acidic phosphate group at the other end. In some embodiments, the acidic phosphate group can be located on the polymer chain or can interrupt the polymer chain.

[0031] It is generally preferred that the substantially linear polymer or oligomer has a low content of carboxylic acid groups or salts thereof. In particularly preferred embodiments, the substantially linear polymer or oligomer contains no or substantially no carboxylic acid groups or salts thereof. Thus, the substantially linear polymer or oligomer preferably has an average number of carboxylate and carboxylic acid groups per molecule of 0.0 to 2.0, preferably 0.0 to 0.5.

[0032] The substantially linear polymer or oligomer having at least one acidic phosphate group is suitably prepared by reaction of a hydroxyl-functional polymer or oligomer precursor with an ester-forming phosphorus compound. An ester-forming phosphorus compound is understood to be a compound that is capable of forming a phosphoric acid ester by reaction with a compound containing a hydroxyl group. Examples of ester-forming phosphorus compounds include polyphosphoric acid, phosphorus pentoxide, phosphorus oxychloride and acetylphosphoric acid. When special phosphorylating agents, in particular phosphorus oxychloride, are used, special substitution patterns may occur. Polyphosphoric acid and phosphorus pentoxide are preferred, but polyphosphoric acid is particularly preferred. Polyphosphoric acid mainly forms monoesters, phosphorus pentoxide forms monoester / diester mixtures. Monoesters are preferred. It is also possible to use mixtures of various components to be phosphorylated in the phosphorylation reaction.

[0033] The reaction of the ester-forming phosphorus compound with the hydroxy compound is preferably carried out without solvent at a temperature of 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.

[0034] The weight ratio of the positive active material based on lithium iron phosphate to the substantially linear polymer or oligomer having at least one acidic phosphate group can vary within a wide range. In a typical embodiment, the amount of polymer or oligomer b) is in the range of 0.01 to 5.00%, preferably in the range of 0.05 to 3.00%, calculated on the weight sum of components a) and b).

[0035] In an exemplary embodiment, the composition of the present invention comprises a single type of substantially linear polymer or oligomer with at least one acidic phosphate group. However, in some embodiments, it is found that the combination of using two or more types of substantially linear polymer or oligomer with at least one acidic phosphate group is advantageous in reducing viscosity. Different types of oligomers or polymers can differ in the type, molecular weight or average number of acidic phosphate groups of the polymer backbone.

[0036] In some embodiments, it may be advantageous to include another polymer dispersant in the composition that is different from the substantially linear polymer or oligomer having at least one acidic phosphate group. This other polymer dispersant can facilitate the dispersion of the lithium iron phosphate-based positive active material or other particles present in the composition (e.g., conductive carbon-based materials).

[0037] In a preferred embodiment, the composition of the present invention is a liquid or paste at a temperature of 20°C. In order to make the composition liquid or paste-like, the composition preferably comprises 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 main liquid diluent. Non-aqueous compositions generally have a low content of water or do not contain any intentionally added water at all. Suitably, the water content of the non-aqueous composition is in the range of 0 to 10% by weight, preferably 0 to 5% by weight, calculated on the weight of the composition. Typically, an organic solvent is selected that is capable of dissolving the polymer or oligomer component of the composition. The organic solvent may also comprise more than one organic solvent, such as 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), ethyl methyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC) and propylene carbonate (PC); alcohol solvents such as ethanol and isopropanol; nitriles such as R-CN (wherein R is a linear, branched or cyclic C2-C20 hydrocarbon group, and may include a double bond aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolane may be used as an organic solvent. Other examples of suitable solvents include aprotic dipolar solvents such as dimethyl sulfoxide, dimethylformamide or N-methylpyrrolidone, or other solvents containing amide groups. In the case of using water as a solvent, a thickener may be preferably used. The amount of the solvent is adjusted to obtain a viscosity that enables easy application of the paste onto a current collector.

[0038] Typically, the organic solvent is present in the composition of the present invention in an amount of 10 to 90 weight percent, based on the total weight of the composition.

[0039] In another embodiment, the organic solvent is present in an amount of 15.0 to 60.0 weight percent, calculated as the sum of the weights of components a) and b).

[0040] In another embodiment, the composition further comprises an organic polymer binder different from component b). The binder improves the adhesion between the positive active material particles and the adhesion between the positive active material and the current collector. Examples of binders include known binders, such as: fluorine-based polymers, such as polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymers 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; polyvinyl pyrrolidone, polyacrylonitrile; carboxymethyl cellulose (CMC); starch; hydroxypropyl cellulose; regenerated cellulose; and polyacrylate-based binders. If desired, the binder can be used in the form of an aqueous dispersion.

[0041] The binder is suitably used in an amount of 1.0 to 50.0 parts by mass, particularly about 1.0 to 20.0 parts by mass, more preferably 1.0 to 10.0 parts by mass, relative to 100 parts by mass of the nonvolatile matter of the composition.

[0042] In order to improve the electrical conductivity of the electrode material, the composition may also include a conductive carbon material. Carbon-based materials refer to materials having a carbon content of 90% to 100% by weight. When used in the manufacturing field of battery electrodes, conductive carbon-based materials should be selected. 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. The specific types of suitable carbon black are furnace black and acetylene black.

[0043] In another embodiment, the present invention also relates to a positive electrode for a battery, wherein the electrode comprises the composition of the present invention.

[0044] The term "battery" includes a single electrochemical cell comprising a positive electrode and a negative electrode, a separator between the positive electrode and the negative electrode, and an electrolyte. The term "battery" also includes a collection of multiple electrochemical cells or battery components.

[0045] The term positive electrode or cathode refers to the electrode at which reduction occurs during the discharge cycle.

[0046] The electrolyte is preferably a compound capable of providing lithium ions in the battery. Lithium salts are generally used. Specific examples of suitable lithium salts include LiPF 6 、LiClO 4 、LiAsF 6 , LiBF 4 、LiSbF 6 、LiAlO 4 、LiAlCl 4 、LiCF 3 SO 3 ,LiC4 F 9 SO 3 、LiN(C 2 F 5 SO 3 ) 2 、LiN(C 2 F 5 SO 2 ) 2 、LiN(CF 3 SO 2 ) 2 , LiCl, LiBr, Lil or LiB(C 2 O 4 ) 2 The concentration of the lithium salt is typically in the range of 0.1M to 2.0M.

[0047] The composition is suitable for use in a paste. A paste for an electrode can be obtained by kneading the components of the composition. Kneading can be performed using known equipment, such as a ribbon mixer, a screw kneader, a Spartan granulator, a Loedige mixer, a planetary mixer or a universal mixer. The paste for an electrode can be formed into a sheet, a granular form, etc.

[0048] The electrode can be formed by molding the above-mentioned paste for the electrode. For example, the electrode is obtained by applying the paste for the electrode to a current collector, and then drying and press-molding.

[0049] Examples of current collectors include foils and meshes of aluminum, nickel, copper, stainless steel, etc. The coating thickness of the paste is generally 40 to 200 μm. The paste coating method is not particularly limited, and examples of the coating method include a method of coating using a doctor blade or a rod coater, followed by molding using a roll press, etc.

[0050] Examples of press molding include roll molding, compression molding, etc. The pressure of press molding is preferably about 1 to 3 t / cm 2 As the electrode density increases, the battery capacity per unit volume generally increases. However, if the electrode density increases too much, the cycle characteristics generally decrease. If the paste for electrode in the preferred embodiment of the present invention is used, the cycle characteristics decrease little even if the electrode density increases. Generally, the electrode density is between 1.0 and 4.0 g / cm 3 In some embodiments, the electrode density of the cathode is between 2.0 and 3.5 g / cm 3 The density of the anode is in the range of 1.2 to 2.0 g / cm 3 within the range.

[0051] As described above, it has been found that the presence of a substantially linear polymer or oligomer having at least one acidic phosphate group in an electrode slurry comprising a positive active material based on lithium iron phosphate effectively reduces the viscosity of the slurry. This facilitates the handling of the slurry without the need to add large amounts of viscosity-reducing solvents.

[0052] Therefore, in another aspect, the present invention also relates to the use of a substantially linear polymer or oligomer having at least one acidic phosphate group for reducing the viscosity of a slurry containing positive active material particles based on lithium iron phosphate. The present invention also relates to a method for reducing the viscosity of a slurry containing positive active material particles based on lithium iron phosphate, the method comprising the step of adding a substantially linear polymer or oligomer having at least one acidic phosphate group to the slurry.

[0053] In yet another embodiment, the present invention is directed to a method for preparing an electrode slurry for a battery, comprising the steps of:

[0054] i) providing a positive electrode active material based on lithium iron phosphate,

[0055] ii) providing a solvent,

[0056] iii) providing a substantially linear polymer or oligomer having at least one acidic phosphate group,

[0057] iv) providing an organic polymer binder other than a substantially linear polymer or oligomer having terminal phosphate groups,

[0058] v) mixing the components provided in steps i) to iv) in any suitable order. Example

[0059] raw materials

[0060] Unless otherwise stated, all raw materials were purchased from Sigma-Aldrich (Merck).

[0061] Methoxypolyethylene glycol Mw 350 (MPEG 350)

[0062] Methoxypolyethylene glycol Mw 500 (MPEG 500)

[0063] ε-Caprolactone

[0064] γ-Valerolactone

[0065] 4-Dodecylbenzenesulfonic acid (DBSA)

[0066] Isodecyl alcohol

[0067] Polyphosphoric acid (PPA)

[0068] Phosphorus pentoxide (P 2 O 5 )

[0069] Dibutyltin dilaurate (DBTL)

[0070] 2-Ethylhexyl glycidyl ether (EHGE)

[0071] Trifluoromethanesulfonic acid (TFMSA)

[0072] N-Methyl-2-pyrrolidone (NMP)

[0073] K-Kat XK-633(Zinc Catalyst)-King Ind.

[0074] Emulsogen TS100 (Tristyrylphenol ethoxylate) - Clariant

[0075] Makon-TD 8 (Tridecyl alcohol ethoxylate) - Stepan

[0076] Lutensol AT50 (C16-C18-fatty alcohol ethoxylate) - BASF

[0077] Pluronic RPE 1740 (EO-PO block polyether)-BASF

[0078] DY-3 Lithium Iron Phosphate Based Materials (LFP) - Dynanonic

[0079] YN-5 Lithium Iron Phosphate Based Materials (LFP) - Yuneng

[0080] Super P(Carbon Black)-Imerys

[0081] Kynar HSV 900(PVDF)-Arkema

[0082] Sokalan K30(PVP)-BASF

[0083] HNBR(Arlanxeo)

[0084] Preparation method of intermediate product

[0085] Preparation method of intermediate I-1 (MPEG starting polyester)

[0086] In a clean, dry four-necked flask (250 mL) equipped with a condenser, a stirrer, a temperature sensor and a nitrogen pipeline, MPEG 350 (50.06 g), ε-caprolactone (32.43 g), γ-valerolactone (18.39 g) and DBSA (0.11 g) were placed, heated to 80°C and stirred at this temperature for 3 h.

[0087] Preparation method of intermediate I-2 (alcohol-initiated polyester)

[0088] In a clean, dry four-necked flask (250 mL) equipped with a condenser, a stirrer, a temperature sensor and a nitrogen pipeline, isodecyl alcohol (14.35 g), ε-caprolactone (85.55 g) and K-Kat XK-633 (0.10 g) were placed, heated to 170° C., and stirred at this temperature for 3 h.

[0089] Preparation method of intermediate I-3 (tristyrylphenol ethoxylate starting polyester)

[0090] In a clean, dry four-necked flask (250 mL) equipped with a condenser, a stirrer, a temperature sensor and a nitrogen pipeline, Emulsogen TS100 (55.76 g), ε-caprolactone (7.52 g), γ-valerolactone (6.60 g) and DBTL (0.02 g) were placed, heated to 170° C., and stirred at this temperature for 3 hours.

[0091] Preparation of Intermediate I-4 (MPEG-Initiated Statistical Polyester / Ether)

[0092] In a clean, dry four-necked flask (250 mL) equipped with a condenser, stirrer, temperature sensor and nitrogen line, MPEG 500 (54.55 g), ε-caprolactone (24.91 g), 2-ethylhexyl glycidyl ether (20.51 g) and TFMSA (0.03 g) were placed, heated to 80°C and stirred at this temperature for 3 h.

[0093] General preparation method of linear phosphate functionalized dispersants (P)

[0094] Component A (see Table 1) was added to a clean, dry four-necked flask (250 mL) equipped with a condenser, a stirrer, a temperature sensor and a nitrogen pipeline, heated to 50°C, and then the phosphorylated component B was slowly added to the mixture. After the addition, the mixture was heated to 80°C and stirred at this temperature for 4 hours.

[0095] Table 1: Formulations of dispersants P-1 to P-7

[0096]

[0097] General preparation method of LFP cathode standard slurry (S1)

[0098] YN-5 (24.0 g), carbon black (0.15 g) and PVDF (0.5 g) were placed in a 250 mL plastic container and heated in a Hauschild The mixture was mixed at 2000 rpm for 10 minutes. Dispersant (0.05 g) diluted in NMP (13.27 g) was then added to the dry mixture and the slurry was mixed at 2000 rpm for 20 minutes.

[0099] General preparation method of LFP cathode standard slurry (S2)

[0100] DY-3 (24.0 g), carbon black (0.15 g) and PVDF (0.5 g) were placed in a 250 mL plastic container and heated in a Hauschild The slurry was mixed at 2000 rpm for 10 minutes. Dispersant (0.05 g) diluted in NMP (16.43 g) was then added to the dry mixture and the slurry was mixed at 2000 rpm for 20 minutes.

[0101] Preparation method of dispersant-free LFP cathode standard slurry (S2-0)

[0102] DY-3 (24.0 g), carbon black (0.15 g) and PVDF (0.55 g) were placed in a 250 mL plastic container and heated in a Hauschild The mixture was mixed at 2000 rpm for 10 minutes. NMP (16.43 g) was then added to the dry mixture and the slurry was mixed at 2000 rpm for 20 minutes.

[0103] General preparation method of conductive paste (S3)

[0104] Carbon black (1.05 g), PVDF (0.73 g), dispersant P (0.73 g) and NMP (30.83 g) were placed in a 250 mL plastic container and heated in a Hauschild Mix at 2000 rpm for 20 minutes.

[0105] Preparation method of conductive paste without dispersant (S3-0)

[0106] Carbon black (1.48 g), PVDF (1.02 g) and NMP (30.83 g) were placed in a 250 mL plastic container and heated in a Hauschild Mix at 2000 rpm for 20 minutes.

[0107] Viscosity measurement

[0108] The LFP cathode slurries (S1 / S2) were initially stored at room temperature for one hour. The rheological properties of the slurries were evaluated using an Anton Paar MCR rheometer at a measurement temperature of 25°C and a cone-plate CP-50 according to the following protocol:

[0109] Table 2: Viscosity Measurement Scheme

[0110]

[0111] Table 3: Viscosity and Recovery Rate V3 / V1 of LFP Slurry

[0112]

[0113] The comparative examples are marked with *

[0114] It can be inferred from Table 3 that the viscosities of all LFP slurries of the present invention are lower than those of the comparative LFP slurries. This allows the slurries of the present invention to be formulated with a smaller amount of solvent to have a given target viscosity.

[0115] The LFP slurry exhibits thixotropy. The viscosity of the slurry decreases when subjected to shear force. This is represented by the viscosity value V2 in Table 3 above. During the process of manufacturing an electrode from the slurry, it is advantageous for the viscosity of the slurry to increase when the slurry is applied and there is no shear force. Therefore, it is highly desirable to recover the viscosity after the shear force ends. The recovered viscosity is represented by the viscosity value V3 in Table 3 above. The recovery of viscosity is expressed as the quotient of viscosity V3 / V1. The LFP slurries of the present invention exhibit high viscosity recovery. Specifically, the LFP slurries of the present invention exhibit an improved balance of low initial viscosity and good recovery.

[0116] Measurement of Volume Resistivity

[0117] The LFP slurry was coated onto a PET plate by a doctor blade. 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).

[0118] Table 4: Volume Resistivity of Electrode Layers of Different LFP Slurries

[0119]

[0120] Electrochemical Stability Evaluation

[0121] The conductive slurry (S3) was respectively coated on copper foil and aluminum foil. After drying, the conductive layer was cut into circular electrodes with a diameter of 18 mm and assembled into a model battery (EL-CELL product, model ECC1-01-0012-C / L) with a glass fiber separator. Lithium metal was used as the anode material. Prepare 1 mole of LiPF 6A solution dissolved in ethylene carbonate and propylene carbonate (1:1 volume percent ratio) was used as the electrolyte for the test cells. The cyclic voltammetry (CV) of these test cells was measured at 2.5 V to 4.8 V vs Li / Li+ when the electrode layer was on aluminum foil and at 2.5 V to 0.1 V vs Li / Li+ when the electrode layer was on copper foil. The scan rate was 0.05 mV / s. Three consecutive cycles were measured. The electrochemical stability of the dispersant was determined by comparing the CV curves of the electrodes with and without the dispersant showing the absence of intrinsic hysteresis.

[0122] Table 5: CV of conductive paste

[0123]

[0124] All CV curves showed no hysteresis within the applied voltage range, indicating that the dispersants had good electrochemical stability.

Claims

1. A composition comprising a) a positive electrode active material based on lithium iron phosphate, and b) Substantially linear polymers or oligomers having at least one acidic phosphate group.

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

3. A composition according to any one of the preceding claims, wherein the substantially linear polymer or oligomer comprises ester repeating units.

4. The composition according to any one of the preceding claims, wherein the substantially 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 according to DIN 55672-1:2007-08.

5. A composition according to any one of the preceding claims, wherein the substantially linear polymer or oligomer has an average of 0.8 to 4.0 acidic phosphate groups per molecule, preferably 0.8 to 2.

5.

6. The composition of any preceding claim, wherein the substantially linear polymer or oligomer has an average of 0.0 to 2.0 carboxylate and carboxylic acid groups per molecule.

7. A composition according to any one of the preceding claims, 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 determined using laser diffraction.

8. The composition according to any one of the preceding claims, wherein the amount of polymer or oligomer b) is in the range of 0.01 to 5.00 wt. %, calculated on the sum of the weights of components a) and b).

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

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

11. A composition according to claim 9 or 10, wherein the one or more solvents are organic solvents.

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

13. The composition according to any one of the preceding claims, 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 preceding claim, wherein the composition further comprises a conductive carbon material.

15. The composition of any preceding claim, wherein the composition further comprises a polymeric dispersant other than a substantially linear polymer or oligomer having at least one acidic phosphate group.

16. A positive electrode for a battery, wherein the positive electrode comprises a composition according to any one of the preceding claims. 17 . A battery comprising the positive electrode according to claim 16 and a negative electrode, a separator and an electrolyte located between the positive electrode and the negative electrode.

18. Use of a substantially linear polymer or oligomer having at least one acidic phosphate group for reducing the viscosity of a slurry comprising positive active material particles based on lithium iron phosphate.

19. A method for preparing a battery electrode slurry, wherein The following steps are involved: i) providing a positive electrode active material based on lithium iron phosphate, ii) providing a solvent, iii) providing a substantially linear polymer or oligomer having at least one acidic phosphate group, iv) providing an organic polymer binder other than a substantially linear polymer or oligomer having terminal phosphate groups, v) mixing the components provided in steps i) to iv) in any suitable order.

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