Anode-like slurry as well as preparation method and application thereof

Abstract

The invention provides anode-like slurry as well as a preparation method and application thereof. The anode-like slurry is composed of lithium iron phosphate and a solvent; the specific area of the lithium iron phosphate is 5-30m < 2 > / g; the carbon content of the lithium iron phosphate is 1.3-1.9%, and the percentage is the mass percentage of the carbon in the lithium iron phosphate; the pH (Potential of Hydrogen) of the lithium iron phosphate is 9.00 to 9.60; the ratio of iron to phosphorus of the lithium iron phosphate is 0.96 to 1.00; the lithium-phosphorus ratio of the lithium iron phosphate is 1-1.05; the compaction density of the lithium iron phosphate powder is 2-3g / cm < 3 >; the primary particles of the lithium iron phosphate are spherical; and the lithium iron phosphate accounts for 10%-50% of the mass of the similar positive electrode slurry. When the viscosity of the anode slurry does not exceed 20000 mPa.s, the viscosity of the similar anode slurry and the viscosity of the anode slurry are in positive correlation, and the viscosity of the anode slurry can be judged according to the positive correlation.

Description

Technical Field

[0001] The present invention relates to a method for evaluating the processing performance of cathode materials in the new energy field, and in particular to a cathode slurry and a preparation method and application thereof. Background Art

[0002] When preparing positive electrode slurry for existing lithium-ion batteries, the positive electrode material, conductive agent, binder, and solvent are mixed in a certain proportion. The slurry is then prepared using mechanical homogenization equipment according to a specific process procedure. The slurry's performance is then evaluated. Conventional evaluation indicators include the slurry's viscosity, solid content, fineness, and stability. The viscosity and stability of the slurry are among the most important indicators. If the viscosity of the slurry is too high, it will be difficult to apply and the dispersion effect will be poor. If the viscosity of the slurry is too low, the application will be uneven. Stability mainly refers to whether stratification occurs after the slurry is placed. Stratification during the slurry placement process will affect the slurry's uniformity. How to quickly and accurately measure the viscosity and stability of positive electrode slurries is an urgent problem in this field.

[0003] Conventional cathode slurry evaluation involves both oil-based and water-based formulations. The oil-based formulation is the most common and versatile method. In the oil-based formulation, the cathode material, conductive agent, and binder (oil-based binder) are thoroughly dispersed and mixed with NMP solvent in a specific ratio to create a stable slurry. In the water-based formulation, the oil-based binder is replaced with an aqueous binder, such as CMC or acrylic binder, and the solvent is replaced with water instead of NMP. Because carbon-coated lithium iron phosphate (LiFePO4) tends to aggregate and stratify in water, a dispersant and defoaming agent are added to prepare the slurry.

[0004] The existing positive electrode slurry evaluation method has complex processes, many types of slurry raw materials, and long slurry dispersion time. It is impossible to quickly realize the testing and feedback of the positive electrode slurry in a short period of time. In the industrial production process, it is impossible to monitor the viscosity of the positive electrode slurry. Summary of the Invention

[0005] In order to overcome the defects of the prior art in the evaluation method of positive electrode slurry, such as complex process, many types of slurry raw materials, long slurry dispersion time, and inability to quickly realize the testing and feedback of positive electrode slurry, the present invention provides a type of positive electrode slurry and its preparation method and application.

[0006] The present invention prepares lithium iron phosphates with varying specific surface areas, then uses these to prepare a cathode-like slurry. By evaluating the performance of the cathode-like slurry, the method can be applied to evaluate the performance of cathode slurries. This method allows for rapid testing and feedback of cathode slurries, enabling monitoring of cathode slurry viscosity during industrial production. The present method for evaluating cathode-like slurries is simple, requires fewer homogenizing raw materials, and requires a shorter homogenization and dispersion time.

[0007] The present invention solves the aforementioned technical problems through the following technical solutions.

[0008] The present invention provides a cathode slurry consisting of lithium iron phosphate and a solvent;

[0009] Wherein, the specific area of ​​the lithium iron phosphate is 5-30m 2 / g;

[0010] Wherein, the carbon content of the lithium iron phosphate is 1.3-1.9%, and the percentage is the mass percentage of the carbon in the lithium iron phosphate;

[0011] Wherein, the pH of the lithium iron phosphate is 9.00-9.60;

[0012] Wherein, the iron-phosphorus ratio of the lithium iron phosphate is 0.96-1.00;

[0013] Wherein, the lithium-phosphorus ratio of the lithium iron phosphate is 1-1.05;

[0014] The powder compaction density of the lithium iron phosphate is 2-3 g / cm 3 ;

[0015] Wherein, the primary particle morphology of the lithium iron phosphate is spherical;

[0016] The mass percentage of the lithium iron phosphate in the positive electrode slurry is 10%-50%.

[0017] In the present invention, the “spherical” in “the primary particles of the lithium iron phosphate are spherical” generally refers to a structure similar in appearance to a sphere.

[0018] In the present invention, preferably, the specific area of ​​the lithium iron phosphate is 7.4-27.84m 2 / g, for example 13.25m 2 / g or 17.41m 2 / g. The larger the specific surface area of ​​lithium iron phosphate, the greater the viscosity of the corresponding positive electrode slurry, the worse the stability of the prepared positive electrode slurry will be, and agglomeration and stratification will occur easily.

[0019] In the present invention, preferably, the carbon content of the lithium iron phosphate is 1.36-1.86%, such as 1.43% or 1.51%, where the percentage is the mass percentage of the carbon in the lithium iron phosphate.

[0020] In the present invention, preferably, the pH of the lithium iron phosphate is 9.35-9.42, such as 9.37 or 9.38. In the present invention, The pH test method of lithium iron phosphate is as follows: take 10g lithium iron phosphate and 90g The mixture is mixed with water except carbon dioxide, and then the supernatant is taken to test the pH value of the product. The model of the testing equipment is SD-05, and the manufacturer is Mettler.

[0021] In the present invention, preferably, the iron-to-phosphorus ratio of the lithium iron phosphate is 0.97-0.985, such as 0.975 or 0.98.

[0022] In the present invention, preferably, the lithium-phosphorus ratio of the lithium iron phosphate is 1.03-1.035.

[0023] In the present invention, preferably, the resistivity of the lithium iron phosphate is 15-35Ω·cm, more preferably 18.7-32.6Ω·cm, such as 19.5Ω·cm or 23.4Ω·cm.

[0024] In the present invention, preferably, the powder compaction density of the lithium iron phosphate is 2.34-2.5g / cm 3 , for example 2.43 g / cm 3 or 2.48g / cm 3 .

[0025] In the present invention, preferably, the solvent is one or more of NMP, anhydrous ethanol, a 95% ethanol aqueous solution, isopropyl alcohol, toluene, and acetonitrile, where % represents the volume percentage of the ethanol in the ethanol aqueous solution. The solvent can effectively disperse the lithium iron phosphate, preventing the lithium iron phosphate from agglomerating and stratifying during dispersion.

[0026] In the present invention, preferably, the mass percentage of the lithium iron phosphate in the cathode-like slurry is 10%, 20%, or 40%. When the mass percentage of lithium iron phosphate is too low, the viscosity of the cathode-like slurry will be too low, making it impossible to perform differentiated evaluation. When the mass percentage of lithium iron phosphate is too high, the viscosity of the cathode-like slurry will be too high, resulting in agglomeration and stratification problems.

[0027] In the present invention, preferably, the method for preparing the cathode slurry comprises mixing and dispersing the lithium iron phosphate and the solvent.

[0028] The dispersion method may be one or more of mechanical stirring, ball milling, and magnetic stirring, and the dispersion method may be such that the positive electrode slurry can be effectively sheared.

[0029] The time and speed of the dispersion vary according to different dispersion methods.

[0030] When the dispersion method is mechanical stirring, preferably, the speed of the mechanical stirring is 800-3000 rpm, for example, 800 rpm, 2000 rpm or 3000 rpm; preferably, the mechanical stirring time is 5-20 minutes. If the time is too short, the dispersion effect is poor, and if the time is too long, the efficiency becomes low.

[0031] In the present invention, the method for preparing lithium iron phosphate may include the following steps:

[0032] S1. reacting the mixture A to obtain a ferric phosphate precursor, and treating the ferric phosphate precursor to obtain a ferric phosphate precursor;

[0033] Wherein, the mixture A comprises an iron source and an acid solution; the acid solution comprises an organic acid solution and a phosphoric acid solution;

[0034] S2. Sand-milling the mixture B to obtain a lithium iron phosphate precursor solution; the lithium iron phosphate precursor solution is treated to obtain lithium iron phosphate; wherein the mixture B comprises the iron phosphate precursor obtained in S1, a lithium source, a carbon source and deionized water.

[0035] In the present invention, in order to prepare lithium iron phosphate samples with different specific surface areas, it is first necessary to prepare iron phosphate precursors with different particle sizes and uniform size.

[0036] In S1, the reaction process is generally accompanied by stirring.

[0037] In S1, preferably, the viscosity of the ferric phosphate precursor is 8000-20000 cps, more preferably 10000-20000 cps, for example 15000 cps.

[0038] In S1, preferably, the processing operations performed on the ferric phosphate precursor include grinding, spray drying, sintering and air flow crushing in sequence.

[0039] Preferably, the average particle size of the ground ferric phosphate precursor is 10 μm-30 μm, for example, 12 μm, 16 μm, 21 μm or 26 μm.

[0040] The grinding operation and conditions may be conventional grinding operations and conditions in the art; the grinding may be, for example, sand milling or ball milling.

[0041] The grinding is generally performed using a sand mill.

[0042] The sand mill is, for example, a vertical sand mill, a horizontal sand mill, a basket sand mill or a double-cone rod sand mill. The horizontal sand mill is, for example, a nano-scale horizontal sand mill.

[0043] The grinding beads used in the sand mill are, for example, zirconium oxide beads.

[0044] The particle size of the grinding beads used in the sand mill is preferably 0.1-3.0 mm, for example 0.3 mm or 0.4 mm.

[0045] Wherein, during the spray drying, the air inlet temperature may be 250-280°C, for example 220°C.

[0046] Wherein, during the spray drying, the outlet temperature may be 105-130°C, for example 110°C.

[0047] The sintering is generally carried out in an inert gas atmosphere, wherein the inert gas is generally nitrogen, and preferably, the purity of the nitrogen is 99.999%.

[0048] The sintering is generally performed by heating the material from room temperature to the sintering temperature, preferably at a heating rate of 2-5°C / min.

[0049] The sintering temperature may be 400°C-550°C, such as 500°C, 510°C, 520°C or 530°C.

[0050] The sintering time may be 5-10 hours, for example 8 hours.

[0051] The iron phosphate in the iron phosphate precursor contains a small amount of carbon source, which does not affect the subsequent preparation of lithium iron phosphate material using the iron phosphate precursor. If the carbon source on the surface of the iron phosphate in the iron phosphate precursor needs to be removed, it can be kept in an air atmosphere of 400℃-550℃ for 1-2 hours and then cooled to obtain an iron phosphate product with the surface carbon source removed.

[0052] The pneumatic crushing generally produces an iron phosphate precursor. The iron phosphate precursor generally includes iron phosphate primary particles and agglomerates of the iron phosphate primary particles. The iron phosphate primary particles are generally the smallest particles in the iron phosphate product after pneumatic crushing. The iron phosphate primary particles are generally spherical particles. Preferably, the average particle size of the iron phosphate primary particles is 50 nm to 1800 nm.

[0053] In S1, preferably, the particle size of the iron phosphate precursor satisfies D10>0.3 μm, for example, D10 is 0.41 μm, 0.43 μm, 0.44 μm or 0.45 μm.

[0054] In S1, preferably, the particle size of the iron phosphate precursor satisfies D50=0.5-3 μm, for example, D50 is 1.1 μm, 1.2 μm, 1.27 μm or 1.31 μm.

[0055] In S1, preferably, the particle size of the iron phosphate precursor satisfies D99<20 μm, for example, D99 is 4.71 μm, 5.01 μm, 5.12 μm, 5.17 μm or 5.21 μm.

[0056] In S1, preferably, the organic acid in the organic acid solution is a carboxylic acid compound.

[0057] Among them, preferably, the carboxylic acid compound is one or more of formic acid, acetic acid, oxalic acid, citric acid, tartaric acid and malic acid, and the carboxylic acid compound is, for example, citric acid and oxalic acid, or malic acid and tartaric acid.

[0058] In S1, preferably, the organic acid is a high molecular weight polymer obtained by copolymerizing an unsaturated olefin containing a carboxylic acid through free radical polymerization, such as poly(meth)acrylic acid.

[0059] In S1, preferably, the purity of the organic acid is 99.5%.

[0060] In S1, the organic acid solution generally refers to an aqueous solution of an organic acid.

[0061] In S1, preferably, the molar number of carboxyl groups in the organic acid is twice the molar number of iron atoms in the iron source.

[0062] In S1, the phosphoric acid solution generally refers to an aqueous solution of phosphoric acid. The concentration of phosphoric acid in the phosphoric acid solution is preferably 20-85%, for example, 49%, 59% or 62%, where % is the mass percentage of the phosphoric acid in the phosphoric acid solution.

[0063] In S1, the phosphoric acid in the phosphoric acid solution can be conventional phosphoric acid in the art, such as industrial-grade phosphoric acid, food-grade phosphoric acid, electrical-grade phosphoric acid, or electronic-grade phosphoric acid. The electrical-grade phosphoric acid can be purchased from Guangxi Qinzhou Chengxing Chemical Technology Co., Ltd.

[0064] In S1, preferably, the iron content in the iron source is 95 wt% or more, more preferably 99 wt% or more, and even more preferably 99.5 wt% or more, for example 97% or 99.7 wt%.

[0065] In S1, the iron source is a conventional iron source in the art; preferably, the iron source is iron powder and / or a compound containing iron and oxygen elements.

[0066] Preferably, the iron powder includes one or more of primary reduced iron powder, secondary reduced iron powder, carbonyl reduced iron powder and electrolytic iron powder.

[0067] Preferably, the iron content in the iron powder is 95 wt % or more, more preferably 99 wt % or more, and even more preferably 99.5 wt % or more, for example 97 wt % or 99.7 wt %.

[0068] Preferably, the compound containing iron and oxygen elements includes ferric oxide and / or ferrosoferric oxide.

[0069] Preferably, the purity of the ferric oxide is 95 wt % or more, more preferably 99 wt % or more, and even more preferably 99.5 wt % or more.

[0070] Preferably, the purity of the ferrosoferric oxide is 95 wt % or more, more preferably 99 wt % or more, and even more preferably 99.5 wt % or more.

[0071] In S1, preferably, the mesh size of the iron source is 100-1000 mesh, more preferably 200-500 mesh, for example, 250 mesh or 300 mesh.

[0072] In S1, preferably, the reaction temperature of the iron source and the acid solution is 20-95°C, more preferably 30-90°C, further more preferably 80-95°C, for example 35°C, 45°C or 55°C.

[0073] In S1, the reaction of the iron source with the acid solution preferably includes adding the iron source to the acid solution in a stirring state.

[0074] In S1, preferably, the molar ratio of the iron element in the iron source to the phosphorus element in the phosphoric acid solution is 0.96-1.00, for example, 0.96, 0.97, 0.975, 0.98, 0.985, 0.99 or 0.995.

[0075] In S1, preferably, the mixture A further includes a dopant.

[0076] Preferably, the dopant is a titanium-based catalyst, such as titanium dioxide.

[0077] Preferably, the dopant comprises one or more of magnesium, aluminum, vanadium, titanium and combinations thereof. The doping element in the dopant is to improve the conductivity of the lithium iron phosphate cathode material.

[0078] Preferably, the amount of the dopant added is 0.005 atom%-0.015 atom% of the amount of the phosphoric acid added.

[0079] Preferably, the dopant is added by first mixing the dopant with the acid solution, and then mixing it with the iron source to obtain the mixture A.

[0080] In S2, preferably, the lithium source is one or more of lithium hydroxide monohydrate, lithium carbonate, lithium dihydrogen phosphate, lithium phosphate and lithium acetate.

[0081] Preferably, the lithium carbonate is industrial grade lithium carbonate or battery grade lithium carbonate.

[0082] In S2, preferably, the molar ratio of the lithium element in the lithium source to the phosphorus element in the iron phosphate precursor obtained in S1 is 1-1.05, for example, 1.02, 1.025, 1.03 or 1.035.

[0083] In S2, the carbon source is a conventional carbon source in the art, and can be one or more of sucrose, polyethylene glycol and glucose.

[0084] In S2, preferably, the residual carbon of the carbon source is 1.0%-2.0%, for example, 1.30%, 1.35%, 1.40%, 1.45% or 1.50%.

[0085] In S2, preferably, the average particle size of the lithium iron phosphate precursor solution is 200 nm-1200 nm, for example, 400 nm, 600 nm or 800 nm.

[0086] In S2, preferably, the solid content of the lithium iron phosphate precursor solution is 30%-80%, for example, 45%.

[0087] In S2, preferably, the processing steps include spray drying, sintering and air flow crushing.

[0088] Wherein, during the spray drying, the air inlet temperature may be 250-280°C, for example, 220°C.

[0089] Wherein, during the spray drying, the outlet temperature may be 105-130°C, for example, 110°C.

[0090] The sintering is generally carried out in an inert gas atmosphere, wherein the inert gas is generally nitrogen, and preferably, the purity of the nitrogen is 99.999%.

[0091] The sintering is generally performed by heating the material from room temperature to the sintering temperature, preferably at a heating rate of 2-5°C / min.

[0092] The sintering temperature may be 680°C-780°C, for example, 720°C, 730°C, 740°C, 750°C or 760°C.

[0093] The sintering time may be 8-15 hours, for example 10 hours.

[0094] Among them, lithium iron phosphate is generally obtained after the air flow is broken.

[0095] In S2, preferably, the particle size of the lithium iron phosphate satisfies D10=0.3-0.7 μm, for example, D10 is 0.43 μm, 0.44 μm, 0.45 μm or 0.46 μm.

[0096] In S2, preferably, the particle size of the lithium iron phosphate satisfies D50=1.0-2.0 μm, for example, D50 is 1.24 μm, 1.34 μm, 1.35 μm, 1.45 μm or 1.47 μm.

[0097] In S2, preferably, the particle size of the lithium iron phosphate satisfies D99=4.0-10.0 μm, for example, D99 is 4.67 μm, 5.43 μm, 5.64 μm, 6.12 μm or 6.72 μm.

[0098] The present invention provides a method for preparing the aforementioned cathode slurry, which comprises mixing and dispersing the lithium iron phosphate and the solvent;

[0099] The mass percentage of the lithium iron phosphate in the positive electrode slurry is 10%-50%.

[0100] In the present invention, the dispersion method can be one or more of mechanical stirring, ball milling, and magnetic stirring, as long as the dispersion method can effectively shear the positive electrode slurry.

[0101] In the present invention, the time and speed of the dispersion vary according to different dispersion methods.

[0102] In some preferred embodiments of the present invention, the dispersion method is mechanical stirring, the speed of the mechanical stirring is 800-3000 rpm, for example, 800 rpm, 2000 rpm or 3000 rpm, and the mechanical stirring time is 5-20 minutes. If the time is too short, the dispersion effect is poor, and if the time is too long, the efficiency is reduced.

[0103] The present invention also provides a use of the aforementioned similar positive electrode slurry in evaluating the viscosity of positive electrode slurry.

[0104] In the present invention, the positive electrode slurry generally refers to an oil-based positive electrode slurry, wherein preferably, the oil-based slurry comprises lithium iron phosphate, a conductive agent, a binder, and a solvent.

[0105] In the present invention, the viscosity of the positive electrode slurry is generally evaluated by testing the viscosity of the positive electrode slurry.

[0106] The viscosity of the positive electrode slurry may be tested using conventional testing methods in the art.

[0107] Wherein, when the viscosity of the positive electrode slurry does not exceed 20000 mPa.s, the viscosity of the positive electrode slurry-like material is positively correlated with the viscosity of the positive electrode slurry.

[0108] In one embodiment of the present invention, the mass ratio of the lithium iron phosphate to the NMP is 1:4. The formula for predicting the viscosity of the positive electrode slurry from the viscosity of the positive electrode slurry is as follows:

[0109] Y=-4925+8.03X-0.000693*X 2 +500 (b-8.5) +50(c-0.5 )

[0110] X=142+54a+5.58*a*a

[0111] Where a represents the value of specific surface area (5m 2 / g<am 2 / g<30m 2 / g), b represents the pH value (0<b<9.6), c represents the carbon content (0%<c%<2.5%), X is the viscosity of the positive electrode slurry, and Y is the fitting value of the viscosity of the oil system positive electrode slurry;

[0112] Preferably, the preparation method of the oil-based positive electrode slurry comprises uniformly mixing the positive electrode material lithium iron phosphate, the conductive agent conductive carbon black, and the binder polyvinylidene fluoride in a mass ratio of 93.5:3.5:3, then adding NMP and continuing to mix until the slurry solid content is 48%, and dispersing the mixture by mechanical stirring, controlling the mechanical stirring linear speed to 15 m / s, and mechanically mixing for 2.5 hours.

[0113] On the basis of conforming to the common sense in this field, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0114] The reagents and raw materials used in the present invention are commercially available.

[0115] The positive progress effect of the present invention is:

[0116] The present invention provides a quasi-positive electrode slurry, which is prepared from lithium iron phosphate and a solvent with specific parameters. Compared with the positive electrode slurry, the quasi-positive electrode slurry simplifies the formulation system and optimizes the homogenization process. The viscosity of the quasi-positive electrode slurry can be tested quickly and efficiently. When the viscosity of the positive electrode slurry does not exceed 20,000 mPa.s, the viscosity of the quasi-positive electrode slurry is positively correlated with the viscosity of the positive electrode slurry, and the viscosity of the positive electrode slurry can be judged based on this.

[0117] In the present invention, the application of cathode-like slurry in evaluating the viscosity of cathode slurry is compared with the traditional method. ① The process is simple and the equipment is simple; ② The types of slurry raw materials are few and the cost is low; ③ The slurry dispersion time is short and the evaluation efficiency is high, which can improve the R&D efficiency, quickly realize the testing and feedback of cathode-like slurry, and then realize the monitoring of cathode slurry viscosity in the industrial production process, which has obvious economic value. BRIEF DESCRIPTION OF THE DRAWINGS

[0118] Figure 1 This is a primary particle size morphology diagram of the lithium iron phosphate obtained in Example 1. DETAILED DESCRIPTION

[0119] The present invention is further illustrated by way of examples below, but the present invention is not limited to the scope of the examples. Experimental methods in the following examples where specific conditions are not specified were performed according to conventional methods and conditions, or selected according to the product specifications.

[0120] The particle sizes involved in the present invention are all obtained by testing with a laser particle size analyzer, the manufacturer of the laser particle size analyzer is OMEC, and the model is Topsizer laser particle size analyzer.

[0121] The lithium iron phosphate involved in the examples and comparative examples of the present invention is prepared according to the preparation method of the lithium iron phosphate of the present invention.

[0122] Example 1

[0123] This embodiment provides a lithium iron phosphate, and the preparation method thereof is as follows:

[0124] 1. According to the molar ratio of iron to phosphorus of 0.985:1, 11.035 kg of 85% food-grade phosphoric acid was added to 12 L of deionized water and stirred for dilution. Under stirring, 5.292 kg of 200-mesh electrolytic iron powder with a purity of 99.5% was slowly added. The reaction was carried out at 80-94°C. When no gas was generated during the reaction, the material was put into a ball mill for ball milling to obtain Product A.

[0125] 2. Prepare a solution of 5 kg malic acid and 5 kg deionized water at a lithium to phosphorus molar ratio of 1.03:1. Gradually add 0.73 kg sucrose and 3.66 kg industrial-grade lithium carbonate to the solution while stirring. Add 115 g titanium dioxide. Reaction at 45°C to obtain Product B.

[0126] 3. Add product B to product A, mix and stir until the viscosity of the system decreases rapidly, and continue sand grinding. When the material particle size D50 is about 1200nm, add deionized water and adjust the solid content of the slurry to 40%.

[0127] 4. The reaction product slurry is spray-dried, sintered, and crushed to obtain lithium iron phosphate positive electrode material.

[0128] The spray drying conditions are: the air inlet temperature is 280°C and the outlet temperature is 120°C. The calcination conditions are: in a 99.999% pure nitrogen atmosphere, gradually heating from room temperature to 750°C at a heating rate of 3°C / min, keeping the temperature at 750°C for 10 hours, and then cooling to obtain a sintered product. The crushing conditions are: the sintered product is processed by air flow crushing equipment to obtain the target finished positive electrode lithium iron phosphate material. The primary particle size morphology of the obtained lithium iron phosphate is as follows Figure 1 shown.

[0129] Example 2

[0130] This embodiment provides a lithium iron phosphate, and the preparation method thereof is as follows:

[0131] 1. According to the molar ratio of iron to phosphorus of 0.980:1, 11.035 kg of 85% food-grade phosphoric acid was added to 12 L of deionized water and stirred for dilution. Under stirring, 5.26 kg of 200-mesh electrolytic iron powder with a purity of 99.5% was slowly added. The reaction was carried out at 80-94°C. When no gas was generated during the reaction, the material was put into a ball mill for ball milling to obtain Product A.

[0132] 2. Prepare a solution of 5 kg malic acid and 5 kg deionized water at a lithium to phosphorus molar ratio of 1.035:1. Gradually add 0.78 kg sucrose and 3.68 kg industrial-grade lithium carbonate to the solution while stirring. Add 115 g titanium dioxide. Reaction at 45°C to obtain Product B.

[0133] 3. Add product B to product A, mix and stir until the viscosity of the system decreases rapidly, and continue sand grinding. When the material particle size D50 is about 800nm, add deionized water and adjust the solid content of the slurry to 40%.

[0134] 4. The reaction product slurry is spray-dried, sintered, and crushed to obtain lithium iron phosphate positive electrode material.

[0135] The spray drying conditions are: an air inlet temperature of 280°C and an outlet temperature of 120°C. The calcination conditions are: in a 99.999% pure nitrogen atmosphere, gradually heating from room temperature to 730°C at a rate of 3°C / min, maintaining the temperature at 730°C for 10 hours, and then cooling to obtain a sintered product. The crushing conditions are: the sintered product is processed through a pneumatic crushing device to obtain the target finished positive electrode lithium iron phosphate material.

[0136] Example 3

[0137] This embodiment provides a lithium iron phosphate, and the preparation method thereof is as follows:

[0138] 1. According to the molar ratio of iron to phosphorus of 0.975:1, 11.035 kg of 85% food-grade phosphoric acid was added to 12 L of deionized water and stirred for dilution. Under stirring, 5.26 kg of 200-mesh electrolytic iron powder with a purity of 99.5% was slowly added. The reaction was carried out at 80-94°C. When no gas was generated during the reaction, the material was put into a ball mill for ball milling to obtain Product A.

[0139] 2. Prepare a solution of 5 kg malic acid and 5 kg deionized water at a lithium to phosphorus molar ratio of 1.035:1. Gradually add 0.85 kg sucrose and 3.68 kg industrial-grade lithium carbonate to the solution while stirring. Add 115 g titanium dioxide. Reaction at 45°C to obtain Product B.

[0140] 3. Add product B to product A, mix and stir until the viscosity of the system decreases rapidly, and continue sand grinding. When the material particle size D50 is about 500nm, add deionized water and adjust the solid content of the slurry to 40%.

[0141] 4. The reaction product slurry is spray-dried, sintered, and crushed to obtain lithium iron phosphate positive electrode material.

[0142] The spray drying conditions are: an air inlet temperature of 280°C and an outlet temperature of 120°C. The calcination conditions are: in a 99.999% pure nitrogen atmosphere, gradually heating from room temperature to 720°C at a rate of 5°C / min, maintaining the temperature at 720°C for 10 hours, and then cooling to obtain a sintered product. The crushing conditions are: the sintered product is processed through a pneumatic crushing device to obtain the target finished positive electrode lithium iron phosphate material.

[0143] Example 4

[0144] This embodiment provides a lithium iron phosphate, and the preparation method thereof is as follows:

[0145] 1. According to the molar ratio of iron to phosphorus of 0.975:1, 11.035 kg of 85% food-grade phosphoric acid was added to 12 L of deionized water and stirred for dilution. Under stirring, 5.21 kg of 200-mesh electrolytic iron powder with a purity of 99.5% was slowly added. The reaction was carried out at 80-94°C. When no gas was generated during the reaction, the material was put into a ball mill for ball milling to obtain Product A.

[0146] 2. Prepare a solution of 5 kg malic acid and 5 kg deionized water at a lithium to phosphorus molar ratio of 1.035:1. Gradually add 1.26 kg sucrose and 3.68 kg industrial-grade lithium carbonate to the solution while stirring. Add 115 g titanium dioxide. Reaction at 45°C to obtain Product B.

[0147] 3. Add product B to product A, mix and stir until the viscosity of the system decreases rapidly, and continue sand grinding. When the material particle size D50 is about 200nm, add deionized water and adjust the solid content of the slurry to 40%.

[0148] 4. The reaction product slurry is spray-dried, sintered, and crushed to obtain lithium iron phosphate positive electrode material.

[0149] The spray drying conditions are: an air inlet temperature of 280°C and an outlet temperature of 120°C. The calcination conditions are: in a 99.999% pure nitrogen atmosphere, gradually increasing the temperature from room temperature to 700°C at a rate of 5°C / min, maintaining the temperature at 700°C for 12.5 hours, and then cooling to obtain a sintered product. The crushing conditions are: the sintered product is processed through a pneumatic crushing device to obtain the target finished positive electrode lithium iron phosphate material.

[0150] Example 5

[0151] This embodiment provides a method for homogenizing a positive electrode slurry, and the specific steps are as follows:

[0152] 20 g of the lithium iron phosphate obtained in Example 1 and 80 g of NMP were mixed and dispersed by mechanical stirring. The mechanical stirring speed was controlled to 15 m / s and the mechanical mixing was performed for 2.5 h.

[0153] Example 6

[0154] This embodiment provides a method for homogenizing a positive electrode slurry, and the specific steps are as follows:

[0155] 20 g of the lithium iron phosphate obtained in Example 2 was mixed with 80 g of NMP, and dispersed by mechanical stirring. The mechanical stirring speed was controlled to 15 m / s, and the mechanical mixing was performed for 2.5 h.

[0156] Example 7

[0157] 20 g of the lithium iron phosphate obtained in Example 3 and 80 g of NMP were mixed and dispersed by mechanical stirring. The mechanical stirring speed was controlled to 15 m / s and the mechanical mixing was performed for 2.5 h.

[0158] Example 8

[0159] 20 g of the lithium iron phosphate obtained in Example 4 was mixed with 80 g of NMP, and dispersed by mechanical stirring. The mechanical stirring speed was controlled to 15 m / s, and the mechanical mixing was performed for 2.5 hours.

[0160] Comparative Example 1

[0161] This comparative example provides a method for homogenizing an oil-based positive electrode slurry, and the specific steps are as follows:

[0162] Prepare a positive electrode slurry using the lithium iron phosphate (LiFePO4) obtained in Example 1, conductive carbon black (SuperP), and binder polyvinylidene fluoride (PVDF) in a ratio of 93.5:3.5:3. First, mix the LiFePO4, SuperP, and PVDF evenly according to the above ratios. Then, add NMP and continue mixing until the slurry has a solids content of approximately 48%. Disperse the mixture using mechanical stirring at a speed of 15 m / s for 2.5 hours.

[0163] Comparative Example 2

[0164] This comparative example provides a method for homogenizing an oil-based positive electrode slurry. The only difference between this method and comparative example 1 is that the lithium iron phosphate obtained in Example 2 is used, and the other steps and conditions are the same as those in comparative example 1.

[0165] Comparative Example 3

[0166] This comparative example provides a method for homogenizing an oil-based positive electrode slurry. The only difference between this method and comparative example 1 is that the lithium iron phosphate obtained in Example 3 is used, and the other steps and conditions are the same as those in comparative example 1.

[0167] Comparative Example 4

[0168] This comparative example provides a method for homogenizing an oil-based positive electrode slurry. The only difference between this method and comparative example 1 is that the lithium iron phosphate obtained in Example 4 is used, and the other steps and conditions are the same as those in comparative example 1.

[0169] Effect Example 1

[0170] The test methods for specific surface area, carbon content, pH, iron-phosphorus ratio, lithium-phosphorus ratio, resistivity, and powder compaction density of lithium iron phosphate can be found in the national standard: GBT 33822-2017 Nanolithium Iron Phosphate.

[0171] The primary particle size morphology of lithium iron phosphate was obtained by scanning electron microscopy.

[0172] The parameters of the lithium iron phosphate prepared in Example 1-4 are shown in Table 1:

[0173] Table 1

[0174]

[0175] Effect Example 2

[0176] (1) Solid content test method

[0177] Equipment name: Halogen moisture meter; Equipment manufacturer: Shanghai Yixin.

[0178] Place the sample in a sample tray and peel it, add about 2.7-3.3g of sample, record the mass as m1, spread the sample evenly on the sample tray, set the temperature to 130℃ for drying, and when the solid content is stable, record the mass m2, and the test is completed.

[0179] Solid content = m1 / m2*100%.

[0180] (2) Rotational viscosity test method

[0181] Instrument name: optional viscometer; equipment model: NDJ-8S; equipment manufacturer: Shanghai Qiuzuo Scientific Instrument Co., Ltd.

[0182] (3) Fineness test method

[0183] Instrument name: Fineness scraper; Equipment model: QXD0-50; Equipment manufacturer: Foshan Nanbeichao E-Commerce Co., Ltd.

[0184] Take out a few drops of the obtained positive electrode slurry and drop them into the deepest part of the groove, that is, the part with the largest scale value.

[0185] Hold the scraper with both hands and place it horizontally at the maximum scale value (at the edge of the sample) so that the scraper is in vertical contact with the scraper surface. Within 3 seconds, pull the scraper from the maximum scale value to the minimum scale value.

[0186] Immediately adjust your sight to an angle of 15° to 30° with the groove plane, observe the evenly exposed areas of the particles in the groove against the light, and note the corresponding scale value, which is the fineness value.

[0187] (4) Slurry stability evaluation method

[0188] Pour the slurry into a transparent graduated cylinder, seal it tightly, and place it at room temperature to observe the changes in the slurry filling volume over time. The shorter the storage time, the less stable the slurry will be. The more stable the slurry will be if it does not separate after 7 days of storage.

[0189] (5) The mass of lithium iron phosphate is 20g, and the mass of NMP is 80g, which are dispersed to prepare a cathode slurry. The formula for predicting the viscosity of the cathode slurry from the viscosity of the cathode slurry is as follows:

[0190] Y=-4925+8.03X-0.000693*X 2 +500 (b-8.5) +50 (c-0.5 )

[0191] X=142+54a+5.58*a*a

[0192] Where a represents the value of specific surface area (5m 2 / g<am 2 / g<30m 2 / g), b represents the pH value (0<b<10), and c represents the carbon content (0%<c%<2.5%).

[0193] Wherein, X is the viscosity of the cathode slurry.

[0194] Wherein, Y is the viscosity fitting value of the oil system positive electrode slurry, i.e., the viscosity of the positive electrode slurry using a conventional oil system obtained by fitting the viscosity of the similar positive electrode slurry. The positive electrode material lithium iron phosphate is Conductive carbon black (SuperP) for electrical agent, polyvinylidene fluoride (PVDF) for binder ) were mixed uniformly in a mass ratio of 93.5:3.5:3, and then NMP was added and continued to mix until the solid content of the slurry was 48%. Mechanical stirring was used for dispersion, and the mechanical stirring line speed was controlled to be 15 m / s, and the mechanical mixing was performed for 2.5 h.

[0195] The performance parameters of the positive electrode slurries prepared in Examples 5-8 and the performance parameters of the positive electrode slurries prepared in Comparative Examples 1-4 are shown in Table 2:

[0196] Table 2

[0197]

[0198] As can be seen from Table 2, the fitted viscosity value of the oil-based positive electrode slurry obtained from the viscosity of the positive electrode slurry of the present invention is basically consistent with the viscosity of the positive electrode slurry. This shows that the application of the positive electrode slurry of the present invention in evaluating the viscosity of the positive electrode slurry is accurate. Moreover, compared with the homogenization method of the oil-based positive electrode slurry, the positive electrode slurry of the present invention has fewer types of homogenization raw materials and lower costs; simple process and equipment; short homogenization dispersion time, high evaluation efficiency, can quickly measure viscosity, and accurately evaluate the viscosity of the positive electrode slurry.

Claims

1. A positive electrode slurry, characterized in that: It consists of lithium iron phosphate and solvent; Wherein, the specific area of ​​the lithium iron phosphate is 5-30m 2 / g; Wherein, the carbon content of the lithium iron phosphate is 1.3-1.9%, and the percentage is the mass percentage of the carbon in the lithium iron phosphate; Wherein, the pH of the lithium iron phosphate is 9.00-9.60; Wherein, the iron-phosphorus ratio of the lithium iron phosphate is 0.96-1.00; Wherein, the lithium-phosphorus ratio of the lithium iron phosphate is 1-1.05; The powder compaction density of the lithium iron phosphate is 2-3 g / cm 3 ; Wherein, the primary particle morphology of the lithium iron phosphate is spherical; The mass percentage of the lithium iron phosphate in the positive electrode slurry is 10%-50%.

2. The cathode slurry according to claim 1, characterized in that The lithium iron phosphate meets one or more of the following conditions: (1) The specific area of ​​the lithium iron phosphate is 7.4-27.84m 2 / g, for example 13.25m 2 / g or 17.41m 2 / g; (2) The carbon content of the lithium iron phosphate is 1.36-1.86%, for example, 1.43% or 1.51%, where the percentage is the mass percentage of the carbon in the lithium iron phosphate; (3) The pH of the lithium iron phosphate is 9.35-9.42, for example, 9.37 or 9.38; (4) The iron-to-phosphorus ratio of the lithium iron phosphate is 0.97-0.985, for example 0.975 or 0.98; (5) The lithium iron phosphate has a lithium-phosphorus ratio of 1.03-1.035; (6) The resistivity of the lithium iron phosphate is 15-35 Ω·cm, preferably 18.7-32.6 Ω·cm, for example 19.5 Ω·cm or 23.4 Ω·cm; (7) The powder compaction density of the lithium iron phosphate is 2.34-2.5 g / cm 3 , for example 2.43 g / cm 3 or 2.48g / cm 3 .

3. The cathode slurry according to claim 1, characterized in that It meets one or more of the following conditions: (1) The solvent is one or more of NMP, anhydrous ethanol, 95% ethanol aqueous solution, isopropanol, toluene, and acetonitrile; % is the volume percentage of the ethanol in the ethanol aqueous solution; (2) The mass percentage of the lithium iron phosphate in the cathode slurry is 10%, 20% or 40%; (3) The method for preparing the cathode slurry includes mixing and dispersing the lithium iron phosphate and the solvent.

4. The cathode slurry according to claim 3, characterized in that The dispersion method is one or more of mechanical stirring, ball milling, and magnetic stirring; Wherein, when the dispersion method is mechanical stirring, preferably, the rotation speed of the mechanical stirring is 800-3000 rpm, such as 800 rpm, 2000 rpm or 3000 rpm; preferably, the time of the mechanical stirring is 5-20 minutes.

5. The cathode slurry according to claim 1, wherein: The preparation method of lithium iron phosphate comprises the following steps: S1. reacting the mixture A to obtain a ferric phosphate precursor, and treating the ferric phosphate precursor to obtain a ferric phosphate precursor; Wherein, the mixture A comprises an iron source and an acid solution; the acid solution comprises an organic acid solution and a phosphoric acid solution; S2. Sand-milling the mixture B to obtain a lithium iron phosphate precursor solution; the lithium iron phosphate precursor solution is treated to obtain lithium iron phosphate; wherein the mixture B comprises the iron phosphate precursor obtained in S1, a lithium source, a carbon source and deionized water.

6. The cathode slurry according to claim 1, characterized in that The preparation method of the lithium iron phosphate meets one or more of the following conditions: (1) In S1, the viscosity of the ferric phosphate precursor is 8000-20000 cps, preferably 10000-20000 cps, for example 15000 cps; (2) In S1, the processing operations of the ferric phosphate precursor include grinding, spray drying, sintering and air flow crushing in sequence; (3) In S1, the particle size of the iron phosphate precursor satisfies D10>0.3 μm, for example, D10 is 0.41 μm, 0.43 μm, 0.44 μm or 0.45 μm; (4) In S1, the particle size of the iron phosphate precursor satisfies D50=0.5-3 μm, for example, D50 is 1.1 μm, 1.2 μm, 1.27 μm or 1.31 μm; (5) In S1, the particle size of the iron phosphate precursor satisfies D99<20 μm, for example, D99 is 4.71 μm, 5.01 μm, 5.12 μm, 5.17 μm or 5.21 μm; (6) In S1, the organic acid in the organic acid solution is a carboxylic acid compound; Preferably, the carboxylic acid compound is one or more of formic acid, acetic acid, oxalic acid, citric acid, tartaric acid and malic acid, and the carboxylic acid compound is, for example, citric acid and oxalic acid, or malic acid and tartaric acid; (7) In S1, the purity of the organic acid is 99.5%; (8) In S1, the molar number of carboxyl groups in the organic acid is twice the molar number of iron atoms in the iron source; (9) In S1, the phosphoric acid solution refers to an aqueous solution of phosphoric acid. The concentration of phosphoric acid in the phosphoric acid solution is preferably 20-85%, for example, 49%, 59% or 62%, where % is the mass percentage of the phosphoric acid in the phosphoric acid solution; (10) In S1, the iron content in the iron source is 95 wt% or more, preferably 99 wt% or more, more preferably 99.5 wt% or more, for example 97% or 99.7 wt%; (11) In S1, the mesh size of the iron source is 100-1000 mesh, more preferably 200-500 mesh, for example 250 mesh or 300 mesh; (12) In S1, the reaction temperature of the iron source and the acid solution is 20-95°C, more preferably 30-90°C, and even more preferably 80-95°C, for example, 35°C, 45°C or 55°C. (13) In S1, the molar ratio of the iron element in the iron source to the phosphorus element in the phosphoric acid solution is 0.96-1.00; (14) In S1, the mixture A further includes a dopant; Preferably, the dopant is a titanium-based catalyst, such as titanium dioxide; (15) In S2, the lithium source is one or more of lithium hydroxide monohydrate, lithium carbonate, lithium dihydrogen phosphate, lithium phosphate and lithium acetate; (16) In S2, the molar ratio of the lithium element in the lithium source to the phosphorus element in the iron phosphate precursor obtained in S1 is 1-1.05, for example, 1.02, 1.025, 1.03 or 1.035; (17) In S2, the carbon source is one or more of sucrose, polyethylene glycol and glucose; (18) In S2, the residual carbon content of the carbon source is 1.0% to 2.0%, such as 1.30%, 1.35%, 1.40%, 1.45% or 1.50%; (19) In S2, the average particle size of the lithium iron phosphate precursor solution is 200 nm to 1200 nm, for example, 400 nm, 600 nm or 800 nm; (20) In S2, the solid content of the lithium iron phosphate precursor solution is 30%-80%, for example, 45%; (21) In S2, the processing steps include spray drying, sintering and air flow crushing; (22) In S2, the particle size of the lithium iron phosphate satisfies D10=0.3-0.7 μm, for example, D10 is 0.43 μm, 0.44 μm, 0.45 μm or 0.46 μm; (23) In S2, the particle size of the lithium iron phosphate satisfies D50=1.0-2.0 μm, for example, D50 is 1.24 μm, 1.34 μm, 1.35 μm, 1.45 μm or 1.47 μm; (24) In S2, the particle size of the lithium iron phosphate satisfies D99=4.0-10.0 μm; for example, D99 is 4.67 μm, 5.43 μm, 5.64 μm, 6.12 μm or 6.72 μm.

7. A method for preparing a cathode-like slurry according to any one of claims 1 to 6, characterized in that: mixing and dispersing the lithium iron phosphate and the solvent; The mass percentage of the lithium iron phosphate in the positive electrode slurry is 10%-50%.

8. The method for preparing a cathode-like slurry according to claim 7, wherein: The dispersion method is one or more of mechanical stirring, ball milling, and magnetic stirring; Wherein, when the dispersion method is mechanical stirring, preferably, the rotation speed of the mechanical stirring is 800-3000 rpm, such as 800 rpm, 2000 rpm or 3000 rpm; preferably, the time of the mechanical stirring is 5-20 minutes.

9. Use of the positive electrode slurry according to any one of claims 1 to 6 in evaluating the viscosity of positive electrode slurry.

10. Use of the positive electrode slurry according to claim 9 in evaluating the viscosity of a positive electrode slurry, which satisfies one or more of the following conditions: (1) The positive electrode slurry is an oil-based positive electrode slurry; wherein, Preferably, the oil system slurry comprises lithium iron phosphate, a conductive agent, a binder and a solvent; (2) evaluating the viscosity of the positive electrode slurry by testing the viscosity of the positive electrode slurry, wherein when the viscosity of the positive electrode slurry does not exceed 20,000 mPa.s, the viscosity of the positive electrode slurry is positively correlated with the viscosity of the positive electrode slurry; (3) When the mass ratio of the lithium iron phosphate to the NMP is 1:4, the formula for predicting the viscosity of the positive electrode slurry from the viscosity of the positive electrode slurry is as follows: Y=-4925+8.03X-0.000693*X 2 +500 (b-8.5) +50 (c-0.5 ) X=142+54a+5.58*a*a Where a represents the value of specific surface area (5m 2 / g<am 2 / g<30m 2 / g), b represents the pH value (0<b<9.6), c represents the carbon content (0%<c%<2.5%), X is the viscosity of the positive electrode slurry, and Y is the fitting value of the viscosity of the oil system positive electrode slurry; Preferably, the preparation method of the oil-based positive electrode slurry comprises uniformly mixing the positive electrode material lithium iron phosphate, the conductive agent conductive carbon black, and the binder polyvinylidene fluoride in a mass ratio of 93.5:3.5:3, then adding NMP and continuing to mix until the slurry solid content is 48%, and dispersing the mixture by mechanical stirring, controlling the mechanical stirring linear speed to 15 m / s, and mechanically mixing for 2.5 hours.

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