Lithium iron phosphate precursor slurry additive and carbon-coated lithium iron phosphate

Abstract

The invention belongs to the technical field of lithium iron phosphate batteries, and particularly relates to a lithium iron phosphate precursor slurry additive and carbon-coated lithium iron phosphate. The main component polycondensate A is rich in amino groups, hydroxyl groups, benzene rings and other functional groups capable of forming strong intermolecular force with lithium iron phosphate, and can be adsorbed on the surfaces of lithium iron phosphate particles during slurry grinding, at the moment, polyether side chains rich in the polycondensate A form a hydrated protective layer, flocculent precipitation between two lithium iron phosphate particles is prevented, and the lithium iron phosphate particles are prevented from being separated from each other. Therefore, uniform particle size distribution of the lithium iron phosphate is ensured, and the viscosity of the slurry is greatly reduced; the compound component ether amine polymer B can also be strongly adsorbed on the surface of the lithium iron phosphate to assist the main component polycondensate A in reducing the viscosity of the slurry; meanwhile, the compound C is an organic salt, so that the electrostatic repulsion on the surface of the lithium iron phosphate can be enhanced, and outstanding effects on reducing the viscosity of the slurry and shortening the grinding time are achieved.

Description

Technical Field

[0001] This invention belongs to the field of lithium iron phosphate battery technology, specifically relating to a lithium iron phosphate precursor slurry additive and carbon-coated lithium iron phosphate. Background Technology

[0002] With the global energy structure transitioning towards low-carbonization, the demand for high-performance lithium batteries in electric vehicles, energy storage systems, and consumer electronics is surging. Lithium iron phosphate (LFP) materials, with their high safety, long cycle life (theoretical cycle count > 2000 cycles), and cost advantages, have become the preferred cathode material in the lithium battery field. In 2023, the installed capacity of LFP batteries in China reached 67.5%, far exceeding that of ternary lithium batteries. Their energy density has increased from 90-120 Wh / kg in the early days to over 160 Wh / kg, and technological advancements have significantly reduced the cost of lithium batteries. The research and development of lithium iron phosphate (LFP) cathode materials can be traced back to the 1990s, but early industrialization was slow due to limitations in low conductivity and tap density. After 2000, through carbon coating technology and nanotechnology, the material performance was significantly improved. The production methods for LFP cathode materials mainly fall into two categories: solid-state and liquid-state methods. The solid-state method, due to its mature technology and low cost, dominates, accounting for over 70% of production. The core of the process involves mechanically grinding lithium, iron, phosphorus, and carbon sources, followed by calcination at high temperatures to crystallize the material and form a carbon coating layer to improve conductivity. Its advantages include simple process, low cost, and suitability for large-scale production. However, solid-state production also has its own intractable technical challenges. First, with the development of radial nano-sized lithium iron phosphate particles, secondary agglomeration is prone to occur during slurry mixing, resulting in high viscosity of the precursor slurry, which affects the quality of subsequent spray drying and high-temperature calcination, increases production energy consumption, and reduces production efficiency. Second, the requirements for fast charging performance of current power batteries are becoming increasingly stringent, and there is an urgent need to continue to improve the conductivity and ion diffusion rate of lithium iron phosphate materials. However, the carbon coating technology currently used is limited by problems such as uneven lithium iron phosphate particle size and uneven coating layer thickness, making it difficult to meet the high-rate fast charging requirements.

[0003] Therefore, there is currently no good low-cost solution that can simultaneously improve the dispersion of lithium iron phosphate and the uniformity of the carbon coating layer. Based on this, the present invention makes a useful attempt.

[0004] It should be noted that the information disclosed in this background section is only for understanding the background technology of the present application concept, and therefore, the above description is not considered to constitute prior art information. Summary of the Invention

[0005] This disclosure provides at least one lithium iron phosphate precursor slurry additive and a carbon-coated lithium iron phosphate.

[0006] In a first aspect, embodiments of this disclosure provide a lithium iron phosphate precursor slurry additive, comprising: condensate A, etheramine polymer B, and compound C; the molecular structural formula of condensate A is: ; Where x, y, z, m, and n are the number of repeating units in the structural unit, with values ​​ranging from x=5 to 80, y=5 to 100, z=3 to 30, m=5 to 50, and n=0 to 10; R1 represents -H or C1-C4 alkyl, R2 represents -H or -CH3, R3 represents -H, -COOH, -SO3H, or C1-C4 alkyl, R4 represents -H or -CH3, R5 represents -H, -COOH, -SO3H, or C1-C4 alkyl, R6 and R7 independently represent -H, C1-C3 alkyl, or -CH2CH2OH, G represents oligosaccharide molecules, including glucose, sucrose, and fructose; the substituents on the benzene ring of the condensation polymer A are all located in the ortho or para position of the oxygen atom; the structural formula of the etheramine polymer B is: ; Where a and b are the number of repeating units of the structural unit, with values ​​ranging from a=1 to 5 and b=2 to 10; R8 represents -H or -CH3; the compound C is a combination of one or more of sodium formate, potassium formate, ammonium formate, sodium acetate, potassium acetate, ammonium acetate, sodium oxalate, potassium oxalate, ammonium oxalate, sodium tripolyphosphate, and sodium hexametaphosphate in any proportion.

[0007] In one optional embodiment, the mass ratio of the condensation polymer A, the ether amine polymer B, and the compound C is 60–90: 5–15: 1–3.

[0008] In one optional embodiment, the lithium iron phosphate precursor slurry additive exists in the form of an aqueous solution with a solid content of 30-60 wt%, wherein the solid content is the percentage of the sum of the masses of the condensation polymer A, the ether amine polymer B, and the compound C to the total mass of the lithium iron phosphate precursor slurry additive.

[0009] In one optional embodiment, the preparation method of the condensation polymer A includes: mixing saccharified phenoxy polyether A1, phenoxy compound A2, aniline compound A3, and acidic catalyst A4 evenly, heating to 80-120°C, then slowly adding formaldehyde dropwise, and maintaining the temperature after the addition is completed to obtain condensation polymer A; wherein, the molar ratio of saccharified phenoxy polyether A1, phenoxy compound A2, aniline compound A3, and acidic catalyst A4 is 5-80:5-100:3-30:3-10; and the amount of formaldehyde used is 1-1.5 times the total molar amount of saccharified phenoxy polyether A1, phenoxy compound A2, and aniline compound A3.

[0010] In one optional embodiment, the saccharified phenoxy polyether A1 is a product of the dehydration condensation of phenoxy polyether and oligosaccharide, and its molecular structural formula is: ; Where m is the number of repeating units of the structural unit, and the value ranges from m=5 to 50; R1 represents -H or C1-C4 alkyl group, and R1 is located at the ortho or para position on the benzene ring; G represents oligosaccharide molecules, including glucose, sucrose, and fructose.

[0011] In one optional embodiment, the molecular structural formula of the phenoxy compound A2 is: ; Where n is the number of repeating units of the structural unit, and the value range is n=0~10; R3 represents -H, -COOH, -SO3H, C1-C4 alkyl, R3 is located at the ortho or para position on the benzene ring, and R4 represents -H or -CH3.

[0012] In one optional embodiment, the molecular structural formula of the aniline compound A3 is: ; R5 represents -H, -COOH, -SO3H, C1-C4 alkyl groups, while R6 and R7 independently represent -H, C1-C3 alkyl groups or -CH2CH2OH.

[0013] In one alternative embodiment, the acidic catalyst A4 comprises any one of sulfuric acid, hydrochloric acid, methanesulfonic acid, phosphoric acid, and p-toluenesulfonic acid.

[0014] Secondly, this disclosure also provides a method for preparing carbon-coated lithium iron phosphate, comprising the following steps: S1, adding a phosphorus source, an iron source, a lithium source, a carbon source, water, and the lithium iron phosphate precursor slurry additives as described above into a mill for grinding to obtain a precursor slurry; S2, spray drying the precursor slurry to remove moisture to obtain a precursor; S3, calcining the dried precursor in an inert gas atmosphere to obtain carbon-coated lithium iron phosphate crude material; S4, pulverizing and sieving the carbon-coated lithium iron phosphate crude material to obtain carbon-coated lithium iron phosphate.

[0015] Thirdly, this disclosure also provides a lithium iron phosphate battery, which is prepared using carbon-coated lithium iron phosphate prepared by the method described above.

[0016] The beneficial effects of this invention are as follows: the main component of this lithium iron phosphate precursor slurry additive, condensate A, is rich in functional groups such as amino, hydroxyl, and benzene rings, which can form strong intermolecular forces with lithium iron phosphate. These functional groups can be adsorbed onto the surface of lithium iron phosphate particles during slurry grinding. At this time, the polyether side chains in condensate A form a hydration protective layer, preventing flocculation and precipitation between two lithium iron phosphate particles, thereby ensuring uniform lithium iron phosphate particle size distribution and significantly reducing slurry viscosity. Secondly, the main component condensate A is rich in oligosaccharide molecules, which not only increase the hydration protective layer... The steric hindrance also allows it to synergize with oligosaccharide molecules in the carbon source, inducing oligosaccharide molecules to deposit uniformly on the surface of lithium iron phosphate. After calcination, the degree of graphitization is high, and the thickness of the carbon coating layer is more uniform, which inhibits excessive growth of lithium iron phosphate and is beneficial to improving battery cycle performance. Finally, the compound component etheramine polymer B can also be strongly adsorbed on the surface of lithium iron phosphate, assisting the main component condensate A in reducing the viscosity of the slurry. At the same time, compound C is an organic salt that can enhance the electrostatic repulsion on the surface of lithium iron phosphate, which has a significant effect on reducing slurry viscosity and shortening grinding time.

[0017] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention are realized and obtained through the structures particularly pointed out in the description.

[0018] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described in detail below. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] As used herein, the phrases “in one embodiment,” “according to one embodiment,” “in some embodiments,” etc., generally refer to the fact that a particular feature, structure, or characteristic following the phrase can be included in at least one embodiment of this disclosure. Therefore, a particular feature, structure, or characteristic can be included in more than one embodiment of this disclosure, such that these phrases do not necessarily refer to the same embodiment. As used herein, the terms “example,” “exemplary,” etc., are used to “serve as an example, instance, or illustration.” Any implementation, aspect, or design described herein as “example” or “exemplary” is not necessarily to be construed as preferred or superior to other implementations, aspects, or designs. Rather, the use of the terms “example,” “exemplary,” etc., is intended to present concepts in a specific manner.

[0021] In this document, as used herein, expressions such as “at least one of…” modify the entire list of elements when following a list of elements, rather than individual elements in the list. For example, the expression “at least one of a, b, and c” should be understood to include only a, only b, only c, both a and b, both a and c, both b and c, or all of a, b, and c.

[0022] The terminology used herein is for the purpose of describing specific exemplary configurations only and is not intended to be limiting. As used herein, the singular articles “a,” “an,” and “the” may also be intended to include plural forms unless otherwise clearly stated herein. The terms “comprising,” “including,” and “having” are inclusive and thus specify the presence of features, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or combinations thereof. The method steps, processes, and operations described herein should not be construed as requiring them to be performed in the specific order discussed or shown, unless specifically identified as such. Additional or alternative steps may be employed.

[0023] To address the issues of secondary agglomeration of slurry and uneven lithium iron phosphate coating, some researchers have reported solutions. For the first problem, the main approach is to add chemical dispersants during slurry grinding. For the second problem, the main approach is to use techniques such as doping the carbon coating with metals or polymers.

[0024] For example, patent CN120309829A reports a viscosity-reducing dispersant for lithium iron phosphate precursor slurry, its preparation method, and its application. This dispersant has a polycarboxylic acid comb structure. Without reducing or increasing the solid content of the lithium iron phosphate precursor slurry, it reduces the slurry viscosity, improves the slurry's dispersibility and long-term stability, prevents sedimentation and flocculation before or during spray drying, improves production efficiency, and reduces energy consumption and costs. Patent CN120511296A discloses a lithium iron phosphate precursor additive and its preparation method. Its dispersing components contain long-chain fluorinated esters and organic acids, achieving the dual goals of particle dispersion and solid content improvement at extremely low addition levels, while also suppressing foam generation. Patent CN119833634A discloses a method for preparing a dispersant, comprising boron-containing compounds, polyethylene glycol, acrylate monomers, initiators, and inorganic solvents. This method effectively reduces slurry viscosity and improves the graphitization degree of the product while ensuring solid content. Patent CN119430117A discloses a method for preparing carbon-coated lithium iron phosphate. Compared with conventional methods, it adds styrene monomer, cationic monomer, initiator, etc. to the precursor slurry, polymerizes it in situ to form a polymer, and then carbonizes the polymer by calcination to obtain carbon-coated lithium iron phosphate. This method controls the lithium iron phosphate to a nanoscale size while coating it with a porous carbon layer, which helps to reduce the electrochemical anodic reaction of lithium iron phosphate materials and improve their rate performance. Patent CN1190595088 discloses a method for preparing modified carbon-coated lithium iron phosphate cathode materials. It adopts a two-stage sintering method. Before the second sintering, boron / nitrogen co-doped single-walled carbon nanotubes are introduced as an inorganic carbon source. At the same time, polyacrylate-polyacrylamide-polystyrene triblock copolymer is introduced as a dispersant. The nitrogen atoms and boron atoms can synergistically enhance the conductivity of the carbon coating layer. The steric barrier formed by the copolymer dispersant can effectively prevent the aggregation of boron / nitrogen co-doped single-walled carbon nanotubes, further improving the electrochemical performance of lithium iron phosphate. Patent CN118772342A provides a method for preparing a compound dispersant for lithium iron phosphate precursor slurry. This dispersant comprises a main dispersant (polycarboxylic acid / polyether copolymer), an alcohol-based auxiliary dispersant, and an acidity regulator. It not only possesses excellent dispersing properties, preventing the slurry viscosity from rapidly increasing during grinding, thus effectively improving the solid content of the obtained lithium iron phosphate precursor slurry, but also serves as a carbon source, synergistically enhancing the uniformity of the carbon coating layer on the surface of the final carbon-coated lithium iron phosphate material. This, in turn, effectively improves the energy density of lithium-ion batteries.

[0025] Some of the above technical solutions only propose a dispersant that can improve the viscosity of the precursor slurry, but cannot solve the defects of lithium iron phosphate morphology or coating layer to improve energy density. Furthermore, the synthesis of these dispersants is relatively complex, and their cost is slightly higher than that of traditional polyethylene glycol dispersants, which is not conducive to widespread adoption. Some solutions propose adding new organic or inorganic carbon sources to the carbon coating layer to replace traditional sucrose, glucose, etc. However, given the significant proportion of carbon sources in lithium battery slurries, such a large addition would increase costs exponentially, which is impractical and unlikely to be applied in practice.

[0026] The shortcomings of the above solutions are the result of the inventor's practical experience and careful research. Therefore, the discovery process of the above problems and the solutions proposed in this disclosure below should be considered as the inventor's contribution to this disclosure.

[0027] The following describes some embodiments of the present invention in detail. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0028] This disclosure provides a lithium iron phosphate precursor slurry additive, comprising: condensate A, ether amine polymer B, and compound C; the molecular structural formula of condensate A is: ; Where x, y, z, m, and n are the number of repeating units in the structural unit, with values ​​ranging from x=5 to 80, y=5 to 100, z=3 to 30, m=5 to 50, and n=0 to 10; R1 represents -H or C1-C4 alkyl, R2 represents -H or -CH3, R3 represents -H, -COOH, -SO3H, or C1-C4 alkyl, R4 represents -H or -CH3, R5 represents -H, -COOH, -SO3H, or C1-C4 alkyl, R6 and R7 independently represent -H, C1-C3 alkyl, or -CH2CH2OH, G represents oligosaccharide molecules, including glucose, sucrose, and fructose; the substituents on the benzene ring of the condensation polymer A are all located in the ortho or para position of the oxygen atom; the structural formula of the etheramine polymer B is: ; Where a and b are the number of repeating units of the structural unit, with values ​​ranging from a=1 to 5 and b=2 to 10; R8 represents -H or -CH3; the compound C is a combination of one or more of sodium formate, potassium formate, ammonium formate, sodium acetate, potassium acetate, ammonium acetate, sodium oxalate, potassium oxalate, ammonium oxalate, sodium tripolyphosphate, and sodium hexametaphosphate in any proportion.

[0029] In one optional embodiment, the mass ratio of the condensation polymer A, the ether amine polymer B, and the compound C is 60–90: 5–15: 1–3.

[0030] In one optional embodiment, the lithium iron phosphate precursor slurry additive exists in the form of an aqueous solution with a solid content of 30-60 wt%, wherein the solid content is the percentage of the sum of the masses of the condensation polymer A, the ether amine polymer B, and the compound C to the total mass of the lithium iron phosphate precursor slurry additive.

[0031] In one optional embodiment, the preparation method of the condensation polymer A includes: mixing saccharified phenoxy polyether A1, phenoxy compound A2, aniline compound A3, and acidic catalyst A4 evenly, heating to 80-120°C, then slowly adding formaldehyde dropwise, and maintaining the temperature after the addition is completed to obtain condensation polymer A; wherein, the molar ratio of saccharified phenoxy polyether A1, phenoxy compound A2, aniline compound A3, and acidic catalyst A4 is 5-80:5-100:3-30:3-10; and the amount of formaldehyde used is 1-1.5 times the total molar amount of saccharified phenoxy polyether A1, phenoxy compound A2, and aniline compound A3.

[0032] In one optional embodiment, the saccharified phenoxy polyether A1 is a product of the dehydration condensation of phenoxy polyether and oligosaccharide, and its molecular structural formula is: ; Where m is the number of repeating units of the structural unit, and the value ranges from m=5 to 50; R1 represents -H or C1-C4 alkyl group, and R1 is located at the ortho or para position on the benzene ring; G represents oligosaccharide molecules, including glucose, sucrose, and fructose.

[0033] In one optional embodiment, the molecular structural formula of the phenoxy compound A2 is: ; Where n is the number of repeating units of the structural unit, and the value range is n=0~10; R3 represents -H, -COOH, -SO3H, C1-C4 alkyl, R3 is located at the ortho or para position on the benzene ring, and R4 represents -H or -CH3.

[0034] In one optional embodiment, the molecular structural formula of the aniline compound A3 is: ; R5 represents -H, -COOH, -SO3H, C1-C4 alkyl groups, while R6 and R7 independently represent -H, C1-C3 alkyl groups or -CH2CH2OH.

[0035] In one alternative embodiment, the acidic catalyst A4 comprises any one of sulfuric acid, hydrochloric acid, methanesulfonic acid, phosphoric acid, and p-toluenesulfonic acid.

[0036] This disclosure also provides a method for preparing carbon-coated lithium iron phosphate, comprising the following steps: S1, adding a phosphorus source, an iron source, a lithium source, a carbon source, water, and the lithium iron phosphate precursor slurry additives as described above into a mill for grinding to obtain a precursor slurry; S2, spray drying the precursor slurry to remove moisture to obtain a precursor; S3, calcining the dried precursor in an inert gas atmosphere to obtain carbon-coated lithium iron phosphate crude material; S4, pulverizing and sieving the carbon-coated lithium iron phosphate crude material to obtain carbon-coated lithium iron phosphate.

[0037] This disclosure also provides a lithium iron phosphate battery, which is prepared using carbon-coated lithium iron phosphate prepared by the method described above.

[0038] Specifically, the addition of the lithium iron phosphate precursor slurry additive described in this invention to prepare carbon-coated lithium iron phosphate has the following beneficial effects: (1) It can increase the solid content by about 10-20% under the premise that the viscosity of the lithium iron phosphate precursor slurry remains unchanged, and the slurry is not easy to settle. After standing for a period of time, the viscosity increase is not significant, which greatly reduces the difficulty of the slurry spray drying process, while promoting the improvement of grinding efficiency and shortening the grinding time; (2) It can make the lithium iron phosphate particle size distribution more uniform and improve the compaction density; (3) The carbon coating layer on the surface of lithium iron phosphate is more uniform, which promotes the conduction of electrons and lithium ions, and the degree of graphitization is also higher, effectively improving the rate performance.

[0039] In this embodiment of the invention, the molecular weight of the polymer was determined using a Waters 1515 gel permeation chromatography system. (Gel column: Agilent PLgel 5 μm MIXED-C; eluent: DMF; mobile phase rate: 1.0 mL / min; detector: Waters 2414 differential refractive index detector; molecular weight standard: polystyrene GPC standard).

[0040] First, we introduce the preparation method of saccharified phenoxy polyether A1, the raw material required for the synthesis of condensation polymer A.

[0041] Synthesis Example A1-1: 125g of phenoxyethanol polyoxyethylene ether (weight average molecular weight 1250) was added to a reaction vessel and heated to 70°C to dissolve. Then, 14.4g of glucose and 2g of p-toluenesulfonic acid catalyst were added and stirred to dissolve. The system was then evacuated and heated to 125°C while maintaining the vacuum condition. The reaction was then kept at this temperature for 8 hours and cooled to obtain saccharified phenoxypolyether A1-1.

[0042] The preparation methods of saccharified phenoxy polyethers A1-2 to A1-5 are the same as those of A1-1, and the raw materials and reaction conditions are shown in the table below.

[0043] Table 1. Raw materials used in synthesis examples A1-1 to A1-5

[0044] Note: EO stands for ethylene oxide unit, and PO stands for propylene oxide unit.

[0045] The synthesis method of condensation polymer A will be introduced next.

[0046] Synthesis Example A-1: ​​Saccharified phenoxy polyether A1-1 (0.1 mol, 141.2 g), p-hydroxybenzoic acid (0.1 mol, 13.8 g), p-aminobenzenesulfonic acid (0.06 mol, 10.4 g), and sulfuric acid catalyst (0.01 mol, 0.98 g) were added to a reactor and mixed thoroughly. The mixture was then heated to 105 °C. Subsequently, a 37% formaldehyde solution (0.28 mol, 22.7 g) was slowly added dropwise over 1 hour. After the addition was complete, the reaction continued for 8 hours. The reaction temperature was then maintained at 105 °C, and a vacuum was applied using an oil pump for 4 hours to obtain condensation polymer A-1. The weight-average molecular weight of A-1 was measured to be 12650, and the PDI was 1.77.

[0047] Synthesis Example A-2: Saccharified phenoxy polyether A1-2 (0.1 mol, 208 g), o-hydroxybenzenesulfonic acid (0.05 mol, 8.7 g), p-methylaniline (0.025 mol, 2.68 g), and 85% phosphoric acid solution (0.0125 mol, 1.44 g) were added to a reactor and mixed thoroughly. The mixture was then heated to 120°C, and subsequently, 37% formaldehyde solution (0.18 mol, 14.6 g) was slowly added dropwise over 1 hour. After the addition was complete, the reaction continued for 6 hours. The reaction temperature was then maintained at 120°C, and a vacuum was applied using an oil pump for 6 hours to obtain condensation polymer A-2. The weight-average molecular weight of A-2 was measured to be 22650, and the PDI was 1.96.

[0048] Synthesis Example A-3: Saccharified phenoxy polyether A1-3 (0.2 mol, 164 g), the propylene oxide adduct of p-methylphenoxyethanol (PO adduct number 10, 0.22 mol, 161 g), N,N-dimethyl-p-methylaniline (0.075 mol, 10.1 g), and sulfuric acid catalyst (0.0125 mol, 1.23 g) were added to a reactor and mixed thoroughly. The mixture was then heated to 120 °C, and subsequently, a 37% formaldehyde solution (0.6 mol, 48.6 g) was slowly added dropwise over 1 hour. After the addition was complete, the reaction continued for 10 hours. The reaction temperature was then maintained at 120 °C, and a vacuum was applied using an oil pump for 2 hours to obtain condensation polymer A-3. The weight-average molecular weight of A-3 was measured to be 25890, and the PDI was 2.11.

[0049] Synthesis Example A-4: Saccharified phenoxy polyether A1-4 (0.1 mol, 190 g), salicylic acid (0.1 mol, 13.8 g), N,N-dimethylaniline (0.04 mol, 4.84 g), and sulfuric acid catalyst (0.02 mol, 1.96 g) were added to a reactor and mixed thoroughly. The mixture was then heated to 110 °C, and subsequently, a 37% formaldehyde solution (0.36 mol, 29.2 g) was slowly added dropwise over 1 hour. After the addition was complete, the reaction continued for 3 hours. The reaction temperature was then maintained at 110 °C, and a vacuum was applied using an oil pump for 9 hours to obtain condensation polymer A-4. The weight-average molecular weight of A-4 was measured to be 29970, and the PDI was 1.58.

[0050] Synthesis Example A-5: Saccharified phenoxy polyether A1-5 (0.1 mol, 236 g), the ethylene oxide adduct of phenoxyethanol (EO adduct number 4, 0.1 mol, 31.4 g), p-aminobenzenesulfonic acid (0.1 mol, 17.3 g), and sulfuric acid catalyst (0.033 mol, 3.23 g) were added to a reactor and mixed thoroughly. The mixture was then heated to 115 °C, and subsequently, a 37% formaldehyde solution (0.36 mol, 29.2 g) was slowly added dropwise over 1 hour. After the addition was complete, the reaction was continued for 12 hours to obtain condensation polymer A-5. The weight-average molecular weight of A-5 was measured to be 7730, and the PDI was 1.66.

[0051] The following examples illustrate the method for preparing lithium iron phosphate additives according to the present invention. The etheramine polymers used in the following examples are ring-opening adducts of organic amines and ethylene oxide / propylene oxide, respectively: Etheramine polymer B-1: A ring-opening adduct of ethylenediamine and ethylene oxide in 20 molar amounts.

[0052] Etheramine polymer B-2: A ring-opening adduct of ethylenediamine with 10 molar amounts of ethylene oxide and 26 molar amounts of propylene oxide, in the form of random copolymerization.

[0053] Etheramine polymer B-3: Diethylenetriamine undergoes ring-opening addition with 30 moles of ethylene oxide, followed by addition with 10 moles of propylene oxide, resulting in a block structure.

[0054] Etheramine polymer B-4: a ring-opening adduct of triethylenetetramine and ethylene oxide in 30 molar amounts.

[0055] In Example 1, 600g of water was added to the reactor, followed by 600g of condensation polymer A-1, 50g of ether amine polymer B-1, and 12g of sodium formate. After stirring and dissolving, the lithium iron phosphate additive of the present invention was obtained, and the solid content was measured to be 51.2%.

[0056] In Example 2, 1200g of water was added to the reactor, followed by 600g of condensation polymer A-2, 150g of ether amine polymer B-2, and 22g of sodium acetate. After stirring and dissolving, the lithium iron phosphate additive of the present invention was obtained, and the solid content was measured to be 38.6%.

[0057] In Example 3, 1800g of water was added to the reactor, followed by 800g of condensation polymer A-3, 100g of ether amine polymer B-3, and 30g of potassium oxalate. After stirring and dissolving, the lithium iron phosphate additive of the present invention was obtained, and the solid content was determined to be 33.1%.

[0058] In Example 4, 2000g of water was added to the reactor, followed by 750g of condensation polymer A-4, 150g of ether amine polymer B-4, and 25g of sodium hexametaphosphate. After stirring and dissolving, the lithium iron phosphate additive of the present invention was obtained, and the solid content was determined to be 31.3%.

[0059] In Example 5, 1000g of water was added to the reactor, followed by 800g of condensation polymer A-5, 25g each of ether amine polymers B-1 and B-4, and 10g of sodium tripolyphosphate. After stirring and dissolving, the lithium iron phosphate additive of the present invention was obtained, and the solid content was measured to be 45.0%.

[0060] To more clearly demonstrate the performance advantages of the lithium iron phosphate additive described in this invention, five comparative examples are given below.

[0061] Comparative Example 1, Example 1, did not include etheramine polymer B-1.

[0062] Comparative Example 2, Example 1, did not include sodium formate.

[0063] Comparative Example 3, Example 1, did not include etheramine polymer B-1 and sodium formate.

[0064] Comparative Example 4: Polyethylene glycol with a molecular weight of 5000. This is a commonly used dispersant in the production of lithium iron phosphate precursors in the industry, which can improve the solid content of the slurry and shorten the production time.

[0065] Comparative Example 5 was prepared by referring to the dispersant preparation method used in Example 7 of Patent CN118772342A.

[0066] The following describes in more detail the effect of the lithium iron phosphate additive of the present invention on the performance of lithium iron phosphate precursor materials through application examples.

[0067] The experimental and characterization methods used in the application examples are described.

[0068] 1. Preparation of precursors Lithium carbonate, iron phosphate, oligosaccharides, and water were added to a sand mill in a specific ratio. Then, corresponding examples and comparative samples (blank samples without additives) were added at a ratio of 0.25%. The sand mill was turned on and the mixture was ground for a period of time to obtain a lithium iron phosphate precursor slurry. The slurry was then dried using a spray dryer to remove the moisture, yielding a crude product. Finally, the lithium iron phosphate material was obtained through high-temperature sintering and pulverization.

[0069] 2. Slurry viscosity test Using a Jingtian NDJ-8S viscometer with rotor No. 2 at a speed of 30 RPM, the viscosity of lithium iron phosphate precursor slurry after grinding in a sand mill for a certain period of time was tested. Under the same grinding time, a lower viscosity indicates a better viscosity-reducing effect of the additive.

[0070] 3. Slurry particle size test The particle size of the lithium iron phosphate precursor slurry after grinding for a certain period of time was tested using a Malvern Mastersizer 3000 laser particle size analyzer.

[0071] 4. Raman spectroscopy test The lithium iron phosphate powder obtained after high-temperature sintering and pulverization was tested using a Thermo Fischer LabRam HR Evolution spectrometer. The test conditions were: excitation wavelength 532 nm, spectral range 100-2600 cm⁻¹. -1 The ID / IG value, which characterizes the degree of graphitization, can be obtained. Within a certain range, the smaller this value, the higher the degree of graphitization.

[0072] 5. Electrode compaction density and internal resistance test Lithium iron phosphate powder obtained by high-temperature sintering and pulverization was mixed with conductive carbon black, PVDF, NMP solvent, etc., and dispersed in a vacuum degassing machine for 4 hours. The slurry was then coated onto electrodes, and after drying the electrodes, the compaction density and resistance were tested.

[0073] 6. Button test The electrodes obtained above were assembled into 2032 coin cells for electrochemical performance testing. A Li electrode was used as the negative electrode, a PE film as the battery separator, and a LiPF6 EC / DEC solution as the electrolyte. The discharge specific capacity (mAh / g) of the lithium battery at different rates (0.1C, 1C, and 3C) was tested at 25°C.

[0074] Application Example 1 tested the viscosity of the slurry after grinding and standing for 4 hours after adding the lithium iron phosphate additive described in this invention, as well as the time required to grind the particle size to 400 nm. As shown in Table 2, it can be seen that after adding Examples 1-5, the initial viscosity of the slurry was 140-210 cp, and the standing viscosity was 150-260 cp, with a viscosity increase rate of less than 36%. In contrast, the initial viscosity of the slurry in Comparative Examples 4-5 was around 450 cp, and the viscosity increased by more than 60% after standing for 4 hours. This indicates that the performance of the lithium iron phosphate additive described in this invention in reducing and stabilizing slurry viscosity is significantly better than some conventional lithium iron phosphate precursor dispersants. The slurry viscosity of Comparative Examples 1-3 was greater than that of Examples 1-5, but better than that of Comparative Examples 4-5, indicating that using condensation polymer A alone has a good dispersion effect, but the effect is even better after combining ether amine polymer B and compound C. In addition, during the grinding process, samples were taken and the particle size of the slurry was tested using a particle size analyzer. The grinding stop time was defined as when the average particle size reached 400 nm. The table shows that the grinding time for Examples 1-5 and Comparative Example 1 was approximately 3.3 hours, while that for Comparative Examples 4-5 was approximately 6 hours. This indicates that the lithium iron phosphate additive described in this invention can effectively reduce production time and improve production efficiency. Furthermore, the grinding times for Comparative Examples 2 and 3 were longer than those of the examples, indicating that compound C can effectively shorten the grinding time.

[0075] Table 2 Slurry viscosity

[0076] In Application Example 2, the Raman spectra of the lithium iron phosphate cathode material formed after slurry drying and calcination were tested, as shown in Table 3. From I... D / I G The data shows that the values ​​for Examples 1-5 and Comparative Examples 1-3 are between 0.87 and 0.89, while those for Comparative Examples 4-5 are between 0.93 and 0.95. This indicates that the addition of the lithium iron phosphate additive described in this invention (the main active ingredient being condensate A) results in a higher degree of graphitization in the material. This conclusion is also confirmed in the resistivity tests of the electrodes. The resistivity of Examples 1-5 is significantly lower than that of Comparative Examples 4-5, indicating that the carbon coating of the materials in these examples is more uniform, and the conductivity is greatly improved. Furthermore, the resistivity of Examples 1-5 is also lower than that of Comparative Examples 1-3. This may be because the ether amine product B and compound C play a role in particle size control, resulting in better material uniformity and thus reducing resistance. Table 2 shows that the compaction density of Examples 1-5 > Comparative Examples 1-3 > Comparative Examples 4-5, which corresponds to the resistivity test data, further demonstrating that the particle size control of Examples 1-5 is more uniform.

[0077] Table 3. Raman spectra, electrode compaction density, and resistivity of lithium iron phosphate materials.

[0078] Application Example 3, Table 4 shows the electrochemical performance test results of the electrode. It is easy to see from the table that the rate discharge specific capacity of Examples 1-5 is better than that of Comparative Examples 1-3, and even better than that of Comparative Examples 4-5. The capacity retention rate of Examples 1-5 after 500 3C cycles is greater than 98%, while that of Comparative Examples 4-5 is only around 94%. The electrochemical test results indicate that the lithium iron phosphate additive described in this invention can effectively improve the rate performance and capacity retention rate of the battery.

[0079] Table 4 Electrochemical performance test results

[0080] In summary, the main component of this lithium iron phosphate precursor slurry additive, condensation polymer A, is rich in functional groups such as amino, hydroxyl, and benzene rings, which can form strong intermolecular forces with lithium iron phosphate. These functional groups can be adsorbed onto the surface of lithium iron phosphate particles during slurry grinding. At this time, the polyether side chains in condensation polymer A form a hydration protective layer, preventing flocculation and precipitation between lithium iron phosphate particles, thus ensuring uniform lithium iron phosphate particle size distribution and significantly reducing slurry viscosity. Secondly, the main component, condensation polymer A, is rich in oligosaccharide molecules, which not only increase the steric hindrance of the hydration protective layer, but also... It can also form a synergistic effect with oligosaccharide molecules in the carbon source, inducing oligosaccharide molecules to be uniformly deposited on the surface of lithium iron phosphate. After calcination, the degree of graphitization is high and the thickness of the carbon coating layer is more uniform, which inhibits the excessive growth of lithium iron phosphate and is conducive to improving the battery cycle performance. Finally, the compound component etheramine polymer B can also be strongly adsorbed on the surface of lithium iron phosphate, assisting the main component condensation polymer A to reduce the viscosity of the slurry. At the same time, compound C is an organic salt that can enhance the electrostatic repulsion of the lithium iron phosphate surface, which has an outstanding effect on reducing the viscosity of the slurry and shortening the grinding time.

[0081] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A lithium iron phosphate precursor slurry additive, characterized in that, include: Condensation polymer A, etheramine polymer B, and compound C; The molecular structural formula of the condensation polymer A is: ; Where x, y, z, m, and n are the number of repeating units in the structural unit, and their values ​​range from x=5 to 80, y=5 to 100, z=3 to 30, m=5 to 50, and n=0 to 10; R1 represents -H or C1-C4 alkyl, R2 represents -H or -CH3, R3 represents -H, -COOH, -SO3H, C1-C4 alkyl, R4 represents -H or -CH3, R5 represents -H, -COOH, -SO3H, C1-C4 alkyl, R6 and R7 independently represent -H, C1-C3 alkyl or -CH2CH2OH, G represents oligosaccharide molecules, including glucose, sucrose, and fructose; The substituents on the benzene ring of the condensation polymer A are all located in the ortho or para position of the oxygen atom. The structural formula of the etheramine polymer B is: ; Where a and b are the number of repeating units in the structural unit, and their values ​​range from a=1 to 5 and b=2 to 10; R8 indicates -H or -CH3; The compound C is a composition of one or more of sodium formate, potassium formate, ammonium formate, sodium acetate, potassium acetate, ammonium acetate, sodium oxalate, potassium oxalate, ammonium oxalate, sodium tripolyphosphate, and sodium hexametaphosphate, mixed in any proportion.

2. The lithium iron phosphate precursor slurry additive as described in claim 1, characterized in that, The mass ratio of the condensation polymer A, the ether amine polymer B, and the compound C is 60–90: 5–15: 1–3.

3. The lithium iron phosphate precursor slurry additive as described in claim 1, characterized in that, The lithium iron phosphate precursor slurry additive exists in the form of an aqueous solution with a solid content of 30-60 wt%. The solid content is the percentage of the sum of the masses of the condensation polymer A, the ether amine polymer B, and the compound C to the total mass of the lithium iron phosphate precursor slurry additive.

4. The lithium iron phosphate precursor slurry additive as described in claim 1, characterized in that, The preparation method of the condensation polymer A includes: After mixing saccharified phenoxy polyether A1, phenoxy compound A2, aniline compound A3, and acidic catalyst A4 evenly, the mixture is heated to 80-120°C, and then formaldehyde is slowly added dropwise. After the addition is completed, the mixture is kept at the temperature to obtain condensate A. The molar ratio of the saccharified phenoxy polyether A1, phenoxy compound A2, aniline compound A3, and acidic catalyst A4 is 5-80:5-100:3-30:3-10. The amount of formaldehyde used is 1 to 1.5 times the total molar amount of saccharified phenoxy polyether A1, phenoxy compound A2, and aniline compound A3.

5. The lithium iron phosphate precursor slurry additive as described in claim 4, characterized in that, The saccharified phenoxy polyether A1 is a product of the dehydration condensation of phenoxy polyether and oligosaccharide, and its molecular structure is as follows: ; Where m is the number of repeating units in the structural unit, and the value range is m = 5 to 50; R1 represents an alkyl group of -H or C1-C4, located at the ortho or para position on the benzene ring, and G represents an oligosaccharide molecule, including glucose, sucrose, and fructose.

6. The lithium iron phosphate precursor slurry additive as described in claim 4, characterized in that, The molecular structural formula of the phenoxy compound A2 is: ; Where n is the number of repeating units in the structural unit, and the value range is n=0 to 10; R3 represents -H, -COOH, -SO3H, or C1-C4 alkyl groups. R3 is located at the ortho or para position on the benzene ring. R4 represents -H or -CH3.

7. The lithium iron phosphate precursor slurry additive as described in claim 4, characterized in that, The molecular structural formula of the aniline compound A3 is: ; R5 represents -H, -COOH, -SO3H, C1-C4 alkyl groups, while R6 and R7 independently represent -H, C1-C3 alkyl groups or -CH2CH2OH.

8. The lithium iron phosphate precursor slurry additive as described in claim 4, characterized in that, The acidic catalyst A4 includes any one of sulfuric acid, hydrochloric acid, methanesulfonic acid, phosphoric acid, and p-toluenesulfonic acid.

9. A method for preparing carbon-coated lithium iron phosphate, characterized in that, Includes the following steps: S1, add phosphorus source, iron source, lithium source, carbon source, water and lithium iron phosphate precursor slurry additive as described in any one of claims 1-8 into a mill for grinding to obtain precursor slurry; S2, the precursor slurry is spray-dried to remove moisture, and the precursor is obtained; S3, the dried precursor is calcined in an inert gas atmosphere to obtain carbon-coated lithium iron phosphate crude material. S4, the carbon-coated lithium iron phosphate coarse material is crushed and sieved to obtain carbon-coated lithium iron phosphate.

10. A lithium iron phosphate battery, characterized in that, Carbon-coated lithium iron phosphate prepared by the method described in claim 9.

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