Viscosity reduction type lithium iron phosphate precursor slurry dispersing agent as well as preparation method and application thereof

Abstract

The invention discloses a viscosity reduction type lithium iron phosphate precursor slurry dispersing agent as well as a preparation method and application thereof, and belongs to the technical field of battery materials. The dispersing agent is prepared by taking isopentenol polyoxyethylene ether, unsaturated carboxylic acid or salt thereof, unsaturated substituted benzene ring or salt thereof and substituted acrylamide as reaction monomers through free radical polymerization under the action of an initiator and a chain transfer agent. On the premise that the solid content of the lithium iron phosphate precursor slurry is not reduced or improved, the viscosity of the slurry is reduced, the dispersity and the aging stability of the slurry are improved, the slurry is prevented from settling and flocculating before spray drying or in the spray drying process, the production efficiency is improved, the energy consumption in the production process is reduced, and the production cost is further reduced.

Description

Technical Field

[0001] This application belongs to the technical field of battery materials, and particularly relates to a viscosity-reducing dispersant for lithium iron phosphate precursor slurry, its preparation method and application. Background Art

[0002] In recent years, with the rapid development of the downstream consumer markets of lithium batteries such as consumer electronics, new energy vehicles and energy storage in China, the market demand for lithium batteries and their upstream materials has also increased rapidly, thus promoting the rapid development of the cathode material industry in China. According to data, the shipment volume of lithium battery cathode materials in China in 2022 was about 1.9 million tons, a year-on-year increase of 68.1%. Among them, the shipment volume of lithium iron phosphate cathode materials accounted for the highest proportion, at 58.5%. At present, the market concentration of the lithium iron phosphate industry in China is relatively high, and leading enterprises such as Hunan Yueneng, Deli Fang Nano, Changzhou Lithium Source, and Hubei Wanrun occupy most of the market share. Some ternary material manufacturers and manufacturers in other fields have also entered the lithium iron phosphate field. In the long run, there will be overcapacity in lithium iron phosphate, and cost will become one of the core competitive factors.

[0003] The main production methods of lithium iron phosphate at home and abroad are mainly solid-phase method and liquid-phase method. Among them, the solid-phase method includes high-temperature solid-phase method, carbothermal reduction method, microwave synthesis method, pulsed laser precipitation method; the liquid-phase method includes sol-gel synthesis method, solvent synthesis method, etc. And the iron phosphate process in the carbothermal reduction method will be the mainstream production route of lithium iron phosphate in the future. Its production process is as follows: mixing and grinding a certain proportion of precursor powder materials (iron phosphate, lithium carbonate) and carbon source in water or organic solvents; after the particle size is within a certain range, stop grinding and discharge to form lithium iron phosphate precursor slurry; then carry out spray drying to obtain lithium iron phosphate precursor; finally, obtain lithium iron phosphate material through high-temperature sintering. Among them, the mixing and dispersion process is an important link for lithium iron phosphate and also for lithium battery production. The dispersion and uniformity directly affect the material properties after sintering and synthesis.

[0004] The main problems existing in the current lithium iron phosphate precursor pulping process are as follows: 1) As the particle size of the lithium iron phosphate precursor develops towards the nanoscale and becomes smaller and smaller, it is very easy to form secondary aggregates during the mixing and dispersion process of the slurry, thus causing serious agglomeration of the lithium iron phosphate precursor slurry and affecting the subsequent sintering quality; 2) The solid content of the lithium iron phosphate precursor slurry in the production process is about 28-40%. If the solid content of the lithium iron phosphate precursor slurry is further increased, the slurry viscosity will rise sharply, which is not conducive to the discharging, conveying and spray drying of the slurry. Moreover, as the viscosity increases, the frictional force during the grinding, conveying and spray drying processes also increases, increasing the energy consumption of the whole process.

[0005] At present, there are few literature reports on dispersants for lithium iron phosphate precursors. For example, the Chinese invention patent with the publication number CN115072694A discloses a lithium iron phosphate cathode material, its preparation method, and a lithium-ion battery. During the dispersion process of the precursor, small molecule compounds such as cetyltrimethylammonium bromide, PEG, N-methylpyrrolidone, salicylic acid, CTAB, ascorbic acid, dimethyl succinate, Tween 20, and citric acid are added to promote the uniformity of the slurry dispersion, providing favorable conditions for obtaining a high powder compaction density in the subsequent process; another example is the Chinese invention patent with the publication number CN104300119A, which discloses a preparation method of a lithium iron phosphate cathode material. Using triammonium citrate, ammonium polymethacrylate, or a combination thereof as a dispersant, and ammonium carboxymethyl cellulose, polyethylene oxide, polyvinyl alcohol, gum arabic powder, or a combination thereof as a binder, by adding the dispersant and the binder simultaneously, the solid content and viscosity of the slurry are adjusted, taking into account both the processing performance of the slurry and the chemical performance of the product. When the solid content of the slurry is increased from 20% to 65%, the viscosity increases from 800 mPa·s to within 2000 mPa·s, and the change in viscosity is much smaller than that of the slurry without adding a dispersant and a binder. The addition of the dispersant enables the slurry viscosity to remain unchanged or only increase slightly when the solid content of the slurry is significantly increased; yet another example is the Chinese invention with the publication number CN102504127A, which discloses a polycarboxylic acid-based super dispersant for dispersing lithium iron phosphate precursors. By means of free radical polymerization, isopentenyl polyoxyethylene ether and acrylic acid-based small molecule monomers are copolymerized to prepare a polymer polycarboxylate dispersant, which can effectively prevent the formation of secondary aggregates of the electrode active material in the slurry and does not introduce impurity ions not contained in the precursor, thereby ensuring the uniform mixing of the precursor and further producing a lithium iron phosphate product with excellent performance.

[0006] Although the dispersants in the above-mentioned schemes have a certain ability to disperse and reduce viscosity, there are still the following problems: 1) The adsorption ability of small molecule dispersants to precursor particles is weak, resulting in poor slurry stability, which is not conducive to storage and transfer; 2) The addition amounts of the dispersant and the binder are too large, and the actual increase in the content of the precursor is limited, without cost advantages, and it is not conducive to industrialized large-scale production; 3) The problem of uniform dispersion of the precursor slurry is partially solved, but the viscosity of the slurry is not reduced, and there is still a risk of blockage during the subsequent spray drying process.

[0007] Therefore, the current problem is that when using a conventional spray dryer for treatment, if the solid content of the slurry is increased, the viscosity of the slurry will increase sharply, resulting in blockage of the pipeline and nozzle. How to maintain a low viscosity of the slurry while increasing the solid content of the slurry, that is, improving the treatment efficiency, is an urgent problem to be solved. Summary of the Invention

[0008] 1. Object of the Invention

[0009] In view of the contradiction between the viscosity and solid content of lithium iron phosphate precursor slurry in the prior art, the present application provides a viscosity-reducing dispersant for lithium iron phosphate precursor slurry, its preparation method and application. Using this dispersant can reduce the viscosity of lithium iron phosphate precursor slurry without reducing or increasing the solid content of the lithium iron phosphate precursor slurry, and can also improve the dispersibility and stability over time of the lithium iron phosphate precursor slurry, preventing sedimentation and flocculation phenomena from occurring before or during spray drying of the lithium iron phosphate precursor slurry, thereby improving production efficiency, reducing energy consumption during the production process, and further reducing production costs.

[0010] 2. Technical Solution

[0011] To solve the above problems, the technical solutions adopted in the present application are as follows:

[0012] The present application provides a viscosity-reducing dispersant for lithium iron phosphate precursor slurry, and the general structural formula of this dispersant is as follows:

[0013]

[0014] In the formula:

[0015] R1 is H or COOM;

[0016] R2 is CH3 or H;

[0017] R3 is H, OH, NH2, CH3, Cl, Br, I, OCH3, SO3M, B(OH)2, CN, NO2, PO3HM or COOM;

[0018] R4 is H, a straight-chain or branched C1 to C10 alkyl group, hydroxymethyl, hydroxyethyl, hydroxypropyl, and hydroxybutyl;

[0019] R5 is H, a straight-chain or branched C1 to C10 alkyl group, hydroxymethyl, hydroxyethyl, hydroxypropyl, and hydroxybutyl;

[0020] M is H, Li, Na, K or ammonium group;

[0021] a, b, c, d, and n are all integers, where a, b, c, d are taken from 1 to 100; n is taken from 2 to 80.

[0022] Furthermore, the above-mentioned viscosity-reducing dispersant for lithium iron phosphate precursor slurry has the following structure:

[0023]

[0024] In the formula:

[0025] R1 is H;

[0026] R2 is H;

[0027] R3 is H;

[0028] R4 is CH3;

[0029] R5 is CH3;

[0030] M is ammonium group;

[0031] a, b, c, d, and n are all integers, where a:b:c:d = 100:24:21:6 and n = 25. Further, the dispersant for a viscosity-reducing lithium iron phosphate precursor slurry is structured as follows:

[0032]

[0033] In the formula:

[0034] R1 is COOM;

[0035] R2 is H;

[0036] R3 is NH2;

[0037] R4 is H;

[0038] R5 is H;

[0039] M is ammonium group;

[0040] a, b, c, d, and n are all integers, where a:b:c:d = 100:38:52:9 and n = 30. Further, the dispersant for a viscosity-reducing lithium iron phosphate precursor slurry is structured as follows:

[0041]

[0042] In the formula:

[0043] R1 is H;

[0044] R2 is CH3;

[0045] R3 is CH3;

[0046] R4 is H;

[0047] R5 is n-butyl;

[0048] M is ammonium group;

[0049] a, b, c, d, and n are all integers, where a:b:c:d = 100:23:17:6; n = 30. Further, the dispersant for a viscosity-reducing lithium iron phosphate precursor slurry is structured as follows:

[0050]

[0051] In the formula:

[0052] R1 is H;

[0053] R2 is CH3;

[0054] R3 is H;

[0055] R4 is H;

[0056] R5 is hydroxymethyl;

[0057] M is ammonium group;

[0058] a, b, c, d, and n are all integers, where a:b:c:d = 100:24:19:3 and n = 53.

[0059] Furthermore, the above-mentioned viscosity-reducing lithium iron phosphate precursor slurry dispersant has the following structure:

[0060]

[0061] In the formula:

[0062] R1 is H;

[0063] R2 is H;

[0064] R3 is SO3M;

[0065] R4 is H;

[0066] R5 is hydroxymethyl;

[0067] M is Li;

[0068] a, b, c, d, and n are all integers, where a:b:c:d = 100:15:21:3 and n = 60.

[0069] This application also provides a preparation method of the above-mentioned viscosity-reducing lithium iron phosphate precursor slurry dispersant. This method uses isopentenyl alcohol polyoxyethylene ether, unsaturated carboxylic acid or its salt, unsaturated substituted benzene ring or its salt, and substituted acrylamide as reaction monomers, and through free radical polymerization under the action of an initiator and a chain transfer agent.

[0070] Furthermore, the preparation method of the above-mentioned viscosity-reducing lithium iron phosphate precursor slurry dispersant includes the following steps:

[0071] a. Weigh the reaction monomers of unsaturated carboxylic acid or its salt, unsaturated substituted benzene ring or its salt, isopentenyl alcohol polyoxyethylene ether, and substituted acrylamide, initiator, and chain transfer agent according to the ratio;

[0072] b. Dissolve isopentenyl alcohol polyoxyethylene ether in water and keep the temperature at 40 - 80 °C to obtain solution A;

[0073] c. Dissolve the unsaturated carboxylic acid or its salt, unsaturated substituted benzene ring or its salt, substituted acrylamide and chain transfer agent in water, and mix evenly to obtain mixed solution B;

[0074] d. Dissolve the initiator in water to obtain solution C;

[0075] e. Slowly dropwise add mixed solution B and solution C to solution A at a constant speed. The dropping time is 2 - 3 hours. After the dropping is completed, keep the temperature at 40 - 80 °C and react for 2 - 4 hours, then cool down and add an alkaline regulator to neutralize to a pH value of 7 - 8 to obtain a viscosity-reducing type lithium iron phosphate precursor slurry dispersant.

[0076] Further, the above-mentioned chain transfer agent includes one or any combination of mercaptoacetic acid, 2-mercaptopropionic acid, 3-mercaptopropionic acid, mercaptoethanol, 2-hydroxypropyl mercaptan, isopropanol, terpinolene, 2-amino-methyl-1-propanol, vinyl acetate, hypophosphite.

[0077] Further, the above-mentioned initiator includes one or any combination of ammonium persulfate, potassium persulfate, hydrogen peroxide, tert-butyl hydroperoxide.

[0078] Further, the above-mentioned alkaline regulator includes one or any combination of ammonia water, sodium hydroxide, potassium hydroxide or lithium hydroxide, and the addition amount is such that the solvent is neutralized to a pH value of 7 - 8.

[0079] Further, the above-mentioned unsaturated carboxylic acid or its salt, unsaturated substituted benzene ring or its salt, isopentenol polyoxyethylene ether and substituted acrylamide are in the following mass percentages: unsaturated carboxylic acid or its salt 15 - 40%, unsaturated substituted benzene ring or its salt 1 - 15%, isopentenol polyoxyethylene ether 10 - 40%, substituted acrylamide monomer 1 - 15%, and the sum of the mass percentages is 100%.

[0080] Further, the dosage of the above-mentioned chain transfer agent is 0.1% - 1% of the total mass of the reaction monomers.

[0081] Further, the dosage of the above-mentioned initiator is 3.0% - 6.0% of the total mass of the reaction monomers.

[0082] Further, the above-mentioned water is deionized water.

[0083] This application also provides the use of the above-mentioned viscosity-reducing type lithium iron phosphate precursor slurry dispersant in the preparation of lithium iron phosphate precursor slurry.

[0084] Further, the use of the above-mentioned viscosity-reducing type lithium iron phosphate precursor slurry dispersant in the preparation of lithium iron phosphate precursor slurry includes adding the viscosity-reducing type lithium iron phosphate precursor slurry dispersant to the lithium iron phosphate precursor slurry, and the addition amount is 1% - 5% of the solid content.

[0085] The present application also provides a method for preparing a viscosity-reducing lithium iron phosphate precursor slurry, which includes blending a carbon source, an iron source, a phosphorus source, and the above-mentioned viscosity-reducing lithium iron phosphate precursor slurry dispersant.

[0086] Further, the above-mentioned carbon source includes sucrose.

[0087] Further, the above-mentioned iron source includes iron phosphate.

[0088] Further, the above-mentioned phosphorus source includes lithium carbonate.

[0089] The present application also provides a method for preparing lithium iron phosphate, which includes preparing the above-mentioned viscosity-reducing lithium iron phosphate precursor slurry, and then spray-drying and sintering.

[0090] 3. Beneficial effects

[0091] Compared with the prior art, the beneficial effects of the present application are as follows:

[0092] (1) The viscosity-reducing lithium iron phosphate precursor slurry dispersant provided by the present application, its preparation method and application. The advantage of this viscosity-reducing lithium iron phosphate precursor slurry dispersant is that the substituted benzene ring is a conjugated structure, which can form an electron cloud conjugation effect with the precursor particles; by introducing an amide group, hydrogen bond interaction is generated with the surface of the precursor particles, so that the dispersant can be more firmly adsorbed on the surface of the lithium iron phosphate precursor particles, reducing the surface tension of the particles; at the same time, a long-chain polyether side chain is introduced, making the structure of the dispersant more stretched on the surface of the lithium iron phosphate precursor, with a thinner hydration film, making the slurry more uniformly dispersed. Without reducing or increasing the solid content of the lithium iron phosphate precursor slurry, the viscosity of the slurry is reduced, the dispersibility and time-dependent stability of the slurry are improved, preventing sedimentation and flocculation phenomena from occurring before or during spray drying of the slurry, improving production efficiency, reducing energy consumption during the production process, and further reducing production costs.

[0093] (2) The viscosity-reducing lithium iron phosphate precursor slurry dispersant provided by the present application, its preparation method and application. The viscosity-reducing lithium iron phosphate precursor slurry dispersant has an ideal degree of polymerization and carboxyl, amino, aromatic ring and polyether functional groups, and makes the dispersed substances dispersed and stable through steric hindrance effect and electrostatic repulsion.

[0094] (3) The viscosity-reducing lithium iron phosphate precursor slurry dispersant provided by the present application, its preparation method and application. Its preparation method has simple process, easy operation, short production cycle, low cost, no environmental pollution, and is suitable for industrial scale production. Specific embodiments

[0095] The following further describes the present application in combination with specific embodiments.

[0096] It should be noted that the terms such as "upper", "lower", "left", "right", "middle", etc. cited in this specification are only for the sake of clarity in narration and are not used to limit the scope of implementation. The change or adjustment of their relative relationship, without substantial change in the technical content, should also be regarded as the scope within which this application can be implemented.

[0097] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs; the term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0098] For those not specified in the examples, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments without indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0099] As used herein, the term "about" is used to provide flexibility and imprecision associated with a given term, measurement, or value. Those skilled in the art can easily determine the degree of flexibility of a specific variable.

[0100] As used herein, the term "at least one of..." is intended to be synonymous with "one or more of...". For example, "at least one of A, B, and C" clearly includes only A, only B, only C, and their respective combinations.

[0101] Concentrations, amounts, and other numerical data may be presented herein in a range format. It should be understood that such a range format is used only for convenience and brevity and should be interpreted flexibly as including not only the numerical values explicitly recited as the range limits but also all individual numerical values or sub-ranges subsumed within the stated range as if each numerical value and sub-range were explicitly recited. For example, a numerical range of about 1 to about 4.5 should be interpreted as including not only the explicitly recited limit values of 1 to about 4.5 but also the individual numbers (such as 2, 3, 4) and sub-ranges (such as 1 to 3, 2 to 4, etc.). The same principle applies to ranges that recite only one numerical value, such as "less than about 4.5", which should be interpreted as including all of the above values and ranges. In addition, this interpretation should apply regardless of the breadth of the range or feature being described.

[0102] Example 1

[0103] This example provides a viscosity-reducing lithium iron phosphate precursor slurry dispersant and its preparation method.

[0104] Weigh 27.5 g (36.0%) of isopentenyl alcohol polyoxyethylene ether monomer (molecular weight 1200) and dissolve it in 40 g of deionized water. Heat it to 70 °C and keep it warm to obtain solution A;

[0105] Weigh 30.0 g (39.3%) of acrylic acid, 10.3 g (13.5%) of styrene, 8.6 g (11.3%) of N,N-dimethylacrylamide, and 0.78 g of mercaptoethanol in 20 g of deionized water to obtain a mixed solution B;

[0106] Dissolve 4.58 g of ammonium persulfate in 20 g of water to obtain a solution C;

[0107] Dropwise add the mixed solution B and the solution C to the solution A at a constant speed for 3.0 hours. After the addition is completed, keep it warm at 70 °C for 4 hours, then cool it down and neutralize it with ammonia water to a pH value of 7 - 8 to obtain a viscosity-reducing type lithium iron phosphate precursor slurry dispersant.

[0108] The molecular structural formula of the viscosity-reducing type lithium iron phosphate precursor slurry dispersant obtained in this example is as follows, where a:b:c:d = 100:24:21:6.

[0109]

[0110] Example 2

[0111] This example provides a viscosity-reducing type lithium iron phosphate precursor slurry dispersant and its preparation method.

[0112] Weigh 30.3 g (37.3%) of isopentenol polyoxyethylene ether monomer (molecular weight 1400) and dissolve it in 40 g of deionized water, heat it up to 70 °C and keep it warm to obtain a solution A;

[0113] Weigh 30.0 g (36.9%) of maleic acid, 11.5 g (14.1%) of 4-aminostyrene, 9.5 g (11.7%) of acrylamide, and 0.08 g of mercaptoethanol in 20 g of deionized water to obtain a mixed solution B;

[0114] Dissolve 4.87 g of ammonium persulfate in 20 g of water to obtain a solution C;

[0115] Dropwise add the mixed solution B and the solution C to the solution A at a constant speed for 3.0 hours. After the addition is completed, keep it warm at 70 °C for 4 hours, then cool it down and neutralize it with ammonia water to a pH value of 7 - 8 to obtain a viscosity-reducing type lithium iron phosphate precursor slurry dispersant.

[0116] The molecular structural formula of the viscosity-reducing type lithium iron phosphate precursor slurry dispersant obtained in this example is as follows, where: a:b:c:d = 100:38:52:9.

[0117]

[0118] Example 3

[0119] This embodiment provides a viscosity-reducing dispersant for lithium iron phosphate precursor slurry and a preparation method thereof.

[0120] Weigh 32.4 g (38.7%) of isopentenol polyoxyethylene ether monomer (molecular weight 1400) and dissolve it in 40 g of deionized water. Heat it to 75 °C and keep it warm to obtain solution A.

[0121] Weigh 30.0 g (35.8%) of methacrylic acid, 11.5 g (13.7%) of 4-methylstyrene, 9.8 g (11.7%) of N-butyl methacrylamide, and 0.42 g of mercaptoethanol in 20 g of deionized water to obtain a mixed solution B.

[0122] Dissolve 2.49 g of ammonium persulfate in 20 g of water to obtain solution C.

[0123] Dropwise add the mixed solution B and solution C to solution A at a constant speed for 3.5 hours. After the addition is completed, keep it warm at 75 °C for 4 hours, and then cool it down and neutralize it with ammonia water to a pH value of 7 - 8 to obtain a dispersant for the viscosity-reducing lithium iron phosphate precursor slurry.

[0124] The molecular structural formula of the viscosity-reducing dispersant for lithium iron phosphate precursor slurry obtained in this embodiment is as follows, where a:b:c:d = 100:23:17:6.

[0125]

[0126] Example 4

[0127] This embodiment provides a viscosity-reducing dispersant for lithium iron phosphate precursor slurry and a preparation method thereof.

[0128] Weigh 46.7 g (38.7%) of isopentenol polyoxyethylene ether monomer (molecular weight 2400) and dissolve it in 60 g of deionized water. Heat it to 75 °C and keep it warm to obtain solution A.

[0129] Weigh 45.0 g (37.3%) of methacrylic acid, 15.4 g (12.8%) of styrene, 13.5 g (11.2%) of N-hydroxymethyl methacrylamide, and 1.19 g of 2-amino-methyl-1-propanol in 30 g of deionized water to obtain a mixed solution B.

[0130] Dissolve 4.74 g of ammonium persulfate in 30 g of water to obtain solution C.

[0131] Dropwise add the mixed solution B and solution C to solution A at a constant speed for 3.5 hours. After the addition is completed, keep it warm at 75 °C for 4 hours, and then cool it down and neutralize it with ammonia water to a pH value of 7 - 8 to obtain a dispersant for the viscosity-reducing lithium iron phosphate precursor slurry.

[0132] The molecular structural formula of the viscosity-reducing lithium iron phosphate precursor slurry dispersant obtained in this embodiment is as follows, where: a:b:c:d = 100:24:19:3.

[0133]

[0134] Example 5

[0135] This example provides a viscosity-reducing lithium iron phosphate precursor slurry dispersant and its preparation method.

[0136] Weigh 39.8 g (36.7%) of isopentenyl alcohol polyoxyethylene ether monomer (molecular weight 2700) and dissolve it in 50 g of deionized water. Heat it to 70 °C and keep it warm to obtain solution A;

[0137] Weigh 40.0 g (36.9%) of acrylic acid, 15.2 g (14.0%) of 4-styrenesulfonic acid, 13.5 g (12.4%) of N-methylolacrylamide, and 1.09 g of mercaptoacetic acid in 40 g of deionized water to obtain a mixed solution B;

[0138] Dissolve 6.56 g of ammonium persulfate in 40 g of water to obtain solution C;

[0139] Dropwise add the mixed solution B and solution C to solution A at a constant speed. The dropping time is 3.5 hours. After the dropping is completed, keep it warm at 75 °C for 4 hours, and then cool it down and neutralize it with lithium hydroxide to a pH value of 7 - 8 to obtain a dispersant for the viscosity-reducing lithium iron phosphate precursor slurry.

[0140] The molecular structural formula of the viscosity-reducing lithium iron phosphate precursor slurry dispersant obtained in this embodiment is as follows, where a:b:c:d = 100:15:21:3.

[0141]

[0142] Example 6

[0143] This example provides an application evaluation of the viscosity-reducing lithium iron phosphate precursor slurry dispersant prepared in Examples 1 - 5.

[0144] Use the viscosity-reducing lithium iron phosphate precursor slurry dispersant prepared in Examples 1 - 5, commercially available lithium iron phosphate precursor slurry dispersant 1, commercially available lithium iron phosphate precursor slurry dispersant 2, and a blank control (without dispersant) to grind and disperse the lithium iron phosphate precursor slurry. The dispersion method is as follows:

[0145] Prepare the slurry:

[0146] Pour the weighed zirconium beads into the nano grinder and record the number of zirconium beads (generally 180 g, filling 75% of the grinding cavity); use a stainless steel spoon to slowly add the weighed sucrose, iron phosphate, and lithium carbonate into a small plastic cup in turn, and record the weights of sucrose, iron phosphate, and lithium carbonate (the ratio is 9:18:73); finally, add deionized water and record the weight (according to the experimental requirements, the total amount of the slurry is 250 g, which can make the slurry circulate and grind normally in the nano grinder, and the solid content of the slurry is controlled at 40% ± 1);

[0147] Mix and stir the slurry with the dispersant:

[0148] Add the prepared slurry to the dispersant (generally add 1% of the solid content). After adding the dispersant, use a stirrer to conduct the initial mixing and stirring of the slurry and the dispersant at a rotation speed of 1200 rpm / min for 10 min;

[0149] Grind the slurry:

[0150] Slowly pour the dispersed slurry into the nano grinder. First, slowly start the rotation speed of the grinder and increase the speed to 2000 rpm / min, then slowly start the circulation pump (to avoid congestion caused by too large particles in the early stage of the slurry). After seeing the slurry at the discharge port circulate and grind in the grinder, quickly increase the grinding speed to 4000 rmp / min and start timing for grinding for 60 min.

[0151] After grinding, use a Mastersizer 3000 ultra-high-speed intelligent particle size analyzer and an Anton Paar MCR102e rheometer to test the particle size and viscosity of the dispersed slurry respectively. The evaluation results are shown in Table 1:

[0152] Table 1 Evaluation results of the lithium iron phosphate precursor dispersed slurry

[0153] Slurry particle size / nm Slurry viscosity / mPa·S Particle size after standing for 4 h / nm State after standing for 4 h Example 1 318 138 331 Uniform dispersion Example 2 325 150 340 Uniform dispersion Example 3 297 83 310 Uniform dispersion Example 4 308 103 322 Uniform dispersion Example 5 340 175 353 Uniform dispersion Example 6 332 143 345 Uniform dispersion Commercially available 1 310 272 345 Uniform dispersion Commercially available 2 326 305 368 The slurry is stratified and there is a little sediment at the bottom Blank control 432 298 520 There is a large amount of sediment at the bottom

[0154] It can be seen from the data in Table 1 that the particle size and viscosity of the lithium iron phosphate precursor slurry are lower than those of the blank control. After standing for 4 hours, each example is a homogeneous solution, and there are a large number of sedimentations at the bottom of the blank control; compared with two commercially available competitors, the dispersant prepared in this application also has certain advantages. It shows that the dispersant prepared in this application has a good dispersing effect on the lithium iron phosphate precursor slurry, can stabilize the slurry and inhibit sedimentation, and has excellent performance.

Claims

1. A viscosity-reducing dispersant for lithium iron phosphate precursor slurry, characterized in that, The general formula of the dispersant structure is as follows: In the formula: R1 is H or COOM; R2 is CH3 or H; R3 is H, OH, NH2, CH3, Cl, Br, I, OCH3, SO3M, B(OH)2, CN, NO2, PO3HM or COOM; R4 is H, a straight-chain or branched C1-C10 alkyl group, hydroxymethyl, hydroxyethyl, hydroxypropyl or hydroxybutyl; R5 is H, a straight-chain or branched C1-C10 alkyl group, hydroxymethyl, hydroxyethyl, hydroxypropyl or hydroxybutyl; M is H, Li, Na, K or ammonium group; a, b, c, d, and n are all integers, where a, b, c, d are taken from 1 to 100; n is taken from 2 to 80.

2. The dispersant for the viscosity-reducing type lithium iron phosphate precursor slurry according to claim 1, wherein, In the formula: R1 is H, R2 is H, R3 is H, R4 is CH3, R5 is CH3, M is ammonium group, a:b:c:d = 100:24:21:6, n = 25; or R1 is COOM, R2 is H, R3 is NH2, R4 is H, R5 is H, M is ammonium group, a:b:c:d = 100:38:52:9, n = 30; or R1 is H, R2 is CH3, R3 is CH3, R4 is H, R5 is n-butyl, M is ammonium group, a:b:c:d = 100:23:17:6, n = 30; or R1 is H, R2 is CH3, R3 is H, R4 is H, R5 is hydroxymethyl, M is ammonium group, a:b:c:d = 100:24:19:3, n = 53; or R1 is H, R2 is H, R3 is SO3M, R4 is H, R5 is hydroxymethyl, M is Li, a:b:c:d = 100:15:21:3, n = 60.

3. The preparation method of a viscosity-reducing type lithium iron phosphate precursor slurry dispersant according to claim 1 or 2, characterized in that The method uses isopentenyl alcohol polyoxyethylene ether, unsaturated carboxylic acid or its salt, unsaturated substituted benzene ring or its salt, and substituted acrylamide as reaction monomers, and is formed by free radical polymerization under the action of an initiator and a chain transfer agent.

4. The preparation method according to claim 3, characterized in that, The unsaturated carboxylic acid or its salt, unsaturated substituted benzene ring or its salt, isopentenyl alcohol polyoxyethylene ether, and substituted acrylamide monomers are as follows by mass percentage: Unsaturated carboxylic acid or its salt 15-40%; Unsaturated substituted benzene ring or its salt 1-15%; Isopentenyl alcohol polyoxyethylene ether 10-40%; Substituted acrylamide 1-15%; The sum of the mass percentages is 100%.

5. The preparation method according to claim 4, characterized in that The method includes the following steps: a. Weigh the unsaturated carboxylic acid or its salt, unsaturated substituted benzene ring or its salt, isopentenyl alcohol polyoxyethylene ether, substituted acrylamide, reaction initiator, and chain transfer agent according to the ratio; b. Dissolve isopentenyl alcohol polyoxyethylene ether in water and keep the temperature at 40-80°C to obtain solution A; c. Dissolve the unsaturated carboxylic acid or its salt, unsaturated substituted benzene ring or its salt, substituted acrylamide, and chain transfer agent in water, and mix evenly to obtain mixed solution B; d. Dissolve the initiator in water to obtain solution C; e. Slowly drip mixed solution B and solution C into solution A at a constant speed. The dripping time is 2-3 hours. After the dripping is completed, keep the temperature at 40-80°C and react for 2-4 hours, and then cool down and add an alkaline regulator to neutralize to a pH value of 7-8 to obtain a viscosity-reducing type lithium iron phosphate precursor slurry dispersant.

6. According to the preparation method described in claim 5, characterized in that The chain transfer agent includes one or any combination of mercaptoacetic acid, 2-mercaptopropionic acid, 3-mercaptopropionic acid, mercaptoethanol, 2-hydroxypropyl mercaptan, isopropanol, terpinolene, 2-amino-methyl-1-propanol, vinyl acetate, and hypophosphite; and / or The initiator includes one or any combination of ammonium persulfate, potassium persulfate, hydrogen peroxide, and tert-butyl hydroperoxide; and / or The basic regulator includes one or any two of ammonia water, sodium hydroxide, potassium hydroxide, and lithium hydroxide.

7. The preparation method according to claim 6, characterized in that, The dosage of the chain transfer agent is 0.1% - 1% of the total mass of the reaction monomers; and / or the dosage of the initiator is 3.0% - 6.0% of the total mass of the reaction monomers.

8. Use of a dispersant for a viscosity-reducing lithium iron phosphate precursor slurry according to claim 1 or 2, and / or a preparation method of a dispersant for a viscosity-reducing lithium iron phosphate precursor slurry according to any one of claims 3-7 in the preparation of a lithium iron phosphate precursor slurry.

9. A preparation method of a viscosity-reducing lithium iron phosphate precursor slurry, characterized in that, It includes blending a carbon source, an iron source, a phosphorus source, and a dispersant for a viscosity-reducing lithium iron phosphate precursor slurry according to claim 1 or 2.

10. A method for preparing lithium iron phosphate, characterized in that, It includes preparing a viscosity-reducing lithium iron phosphate precursor slurry according to claim 9, and grinding, spray drying, and sintering.

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