Preparation method of phosphate-based positive electrode material and phosphate-based positive electrode material

Abstract

The invention relates to the field of battery materials, in particular to a preparation method of a phosphate positive electrode material and the phosphate positive electrode material. The phosphate-based positive electrode material comprises a phosphate-based active material and a carbon layer coating the phosphate-based active material, the graphitization degree of the carbon layer is high, the material powder resistance is low, and lithium ions can be easily removed and embedded. According to the preparation method provided by the invention, the size-adjustable phosphate positive electrode material is obtained through a one-time sintering process by virtue of the structural design of the block copolymer, the compaction density of the material powder is 2.0 g / cc to 2.7 g / cc, and the uniformity and consistency of the material are good. And the prepared secondary lithium ion battery has excellent rate capability and is suitable for the fields of high-end power, energy storage and subdivision.

Description

Technical Field

[0001] This invention relates to the field of battery materials, specifically to a method for preparing a phosphate-based cathode material and the phosphate-based cathode material itself. Background Technology

[0002] Phosphate-based cathode materials, due to the high covalent bond energy of the phosphate tetrahedra in their crystal structure, possess advantages such as high thermal stability, long cycle life, and low raw material cost, and have become the mainstream materials for power batteries and energy storage batteries. Among them, lithium iron phosphate (LFP) has become one of the most promising cathode materials due to its excellent thermal stability, good cycle performance, and environmental friendliness. However, traditional lithium iron phosphate materials still face several technical bottlenecks in practical applications, which restrict their further promotion and industrialization.

[0003] First, the current high-end lithium iron phosphate materials are prepared using a two-stage sintering process, which generally suffers from high energy consumption, complex processes, and low raw material utilization, resulting in high production costs. Second, due to defects in the carbon coating on the material surface, lithium batteries experience rapid capacity decay and poor cycle life during long-term use, especially under high temperature or high-rate charge / discharge conditions, where their cycle life decreases significantly.

[0004] Therefore, there is an urgent need to develop a new type of phosphate-based cathode material and its preparation method, which can effectively improve the structural stability and electrochemical performance of the material while reducing the process cost, thereby slowing down the battery aging rate and extending its service life to meet the growing demand for high-performance energy storage systems.

[0005] CN119240644 A discloses a method for preparing a composite carbon source coated lithium iron phosphate material, comprising: firstly mixing and grinding iron phosphate, lithium source, first carbon source and solvent to obtain a slurry, and then spray drying to obtain a powder material; secondly mixing the powder material and a second carbon source, and then sintering under an inert atmosphere to obtain the composite carbon source coated lithium iron phosphate material; wherein the first carbon source includes a small molecule carbon source with a pyrolysis temperature not higher than 500℃, and the second carbon source includes a high thermally stable carbon source with a pyrolysis temperature not lower than 600℃. This method introduces a second carbon source with a high boiling point and high pyrolysis temperature. Relying on its high boiling point, the second carbon source can continuously coat lithium iron phosphate particles with carbon through its own fluidity during the fusion-growth process after the first carbon source has pyrolyzed, achieving uniform coating. Furthermore, its high decomposition temperature ensures that even after the lithium iron phosphate particles have fused and grown, they can still be uniformly coated through pyrolysis, guaranteeing a carbon layer on the surface of the fused and grown particles. This solves the shortcomings of existing technologies regarding poor coating of fused and grown lithium iron phosphate particles, leading to low reactivity and short cycle life.

[0006] However, its preparation process is complex, requiring multiple sintering processes, resulting in high energy consumption, high cost, and lost production capacity; moreover, the particle size of the obtained lithium iron phosphate cathode material is uncontrollable, with poor sphericity and poor product consistency. Summary of the Invention

[0007] One of the objectives of this invention is to provide a method for preparing phosphate-based cathode materials. This method is simple, requires only one sintering process, and has low energy consumption.

[0008] The second objective of this invention is to provide a phosphate-based cathode material that combines controllable particle size, high sphericity, high compaction density, and low powder resistivity.

[0009] To achieve the above objectives, a first aspect of the present invention provides a method for preparing a phosphate-based cathode material, comprising the following steps:

[0010] S1: A phosphate-based raw material composition and a block copolymer are added sequentially to a solvent in a specific mass ratio. The phosphate-based raw material composition contains a lithium source, a phosphorus source, an M source, and a carbon source. After mixing and grinding, a slurry is obtained. The slurry is then spray-dried to obtain a dry powder containing the block copolymer. The M source contains at least one of an iron source, a manganese source, and a sodium source. The solvent contains at least one of water, methanol, ethanol, acetone, N,N-dimethylacetamide, and dimethylformamide.

[0011] S2: Under a protective gas atmosphere, the dry powder is subjected to a sintering process to obtain a phosphate-based cathode material sinter.

[0012] S3: The phosphate-based cathode material sinter is pulverized to obtain the phosphate-based cathode material; the volumetric particle size distribution of the phosphate-based cathode material satisfies the following conditions: Dv10 is 0.2µm~0.4µm, Dv50 is 0.7µm~1.5µm, Dv90 is 2µm~4µm, and Dv100 is 5µm~15µm; the phosphate-based cathode material comprises a phosphate-based active material and a carbon layer coated on the phosphate-based active material, the thickness of the carbon layer is 2nm-10nm, and the content of the carbon layer is 1wt%-4wt%.

[0013] The present invention provides a method for preparing phosphate-based cathode materials. By designing the molecular structure of block copolymers, "inclusions" are formed in the slurry system. Utilizing the structural differences of these "inclusions," lithium iron phosphate cathode materials with different particle sizes and quantities can be prepared, meaning the compaction density can be controlled between 2.0 g / cc and 2.70 g / cc, achieving customization of the phosphate cathode material. The primary particles prepared by this method have high sphericity, uniform carbon layer coating on the cathode material surface, and a powder resistivity not exceeding 60 Ω·cm. The process of this invention is simple, the raw materials are inexpensive and readily available, and the one-step sintering process significantly reduces production energy consumption.

[0014] A second aspect of this invention provides a phosphate-based cathode material, comprising a phosphate-based active material and a carbon layer coating the phosphate-based active material. The carbon layer is formed by in-situ sintering of a block copolymer and a carbon source. The block copolymer includes AB-type diblock copolymers, ABA-type triblock copolymers, ABC-type triblock copolymers, etc.; the block copolymer is also a multiblock copolymer structure of An1-Bn2, (An1-Bn2)n3, An1-Bn2-An3, (An1-Bn2-An3)n4, where n1, n2, n3, and n4 represent the number of repeating units. The molecular weight of segment A in the block copolymer is 1000-200000, the molecular weight of segment B is 1000-200000, and the molecular weight of the optionally present segment C is 1000-200000. Through molecular structure design, the length, composition ratio, and arrangement of different segments of the block copolymer can be controlled to achieve different structural morphologies and aggregation behaviors. The monomers of the block copolymer are at least two of the following: polyethylene glycol, polypropylene, polyamide amine, polyethyleneimine, polyoxyethylene, polyoxypropylene, polyvinylpyrrolidone, polylactic acid, polylactic-co-hydroxyacetic acid, polyhydroxyacetic acid, polycaprolactone, aminopolymethyl methacrylate, and polycaprolactone.

[0015] The phosphate-based cathode material provided by this invention has a volumetric particle size distribution that satisfies at least the following conditions: Dv10 is 0.2µm-0.4µm, Dv50 is 0.7µm-1.5µm, Dv90 is 2µm-4µm, and Dv100 is 5µm-15µm. Furthermore, the phosphate-based cathode material exhibits controllable particle size and high sphericity, achieving a powder resistivity not exceeding 60Ω·cm. Simultaneously, the material's powder compaction density is adjustable between 2.0g / cc and 2.70g / cc. This method allows for the customization of cathode materials, greatly expanding their application areas. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the carbon coating of the phosphate-based cathode material provided by the present invention, wherein, Figure 1 (a) is a schematic diagram of a phosphate-based cathode material with uneven carbon coating. Figure 1 (b) is a schematic diagram of a phosphate-based cathode material with a uniform carbon layer coating;

[0017] Figure 2 This is a schematic diagram of the structure of particles in the slurry provided by the present invention;

[0018] Figure 3 This is a SEM image of the lithium iron phosphate cathode material A1 prepared in Example 1 of the present invention, with a scale bar of 1 μm;

[0019] Figure 4This is a SEM image of the lithium iron phosphate cathode material A2 prepared in Example 2 of the present invention, with a scale bar of 1 μm;

[0020] Figure 5 This is a SEM image of the lithium iron phosphate cathode material prepared in Example 3 of the present invention, with a scale bar of 1 μm (A3).

[0021] Figure 6 This is an SEM image of the lithium iron manganese phosphate cathode material prepared in Example 5 of the present invention, with a scale bar of 1 μm (A5).

[0022] Figure 7 This is a SEM image of the lithium iron phosphate cathode material B1 prepared by comparative example B1 of the present invention, with a scale bar of 1 μm.

[0023] Figure 8 This is a SEM image of lithium iron manganese phosphate cathode material B2 prepared by comparative example B2 of the present invention, with a scale bar of 1 μm.

[0024] Figure 9 This is the A1 Raman image of the lithium iron phosphate cathode material prepared in Example 1 of this invention;

[0025] Figure 10 This is the Raman diagram of lithium iron phosphate cathode material B1 prepared in Comparative Example 1 of this invention;

[0026] Figure 11 This is a comparison chart of the electrical properties of lithium iron phosphate cathode material A1 prepared in Example 1 of the present invention and lithium iron phosphate cathode material B1 prepared in Comparative Example 1. Detailed Implementation

[0027] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0028] In this invention, "optional existence" means two cases: existence and non-existence, that is, it means two cases: containing and not containing.

[0029] In this invention, unless otherwise stated, room temperature or normal temperature refers to 25±2℃.

[0030] In this invention, unless otherwise stated, all pressures are gauge pressures.

[0031] In this invention, the molar ratio represents the ratio of the amounts of substances.

[0032] In this invention, Dv10 represents the particle size value corresponding to the cumulative volumetric particle size distribution number of the phosphate-based cathode material reaching 10%; Dv50, Dv90 and Dv100 have similar definitions to Dv10, and will not be described in detail here. Those skilled in the art should not understand this as a limitation of the invention.

[0033] As mentioned above, a first aspect of the present invention provides a method for preparing a phosphate-based cathode material, comprising the following steps:

[0034] S1: A phosphate-based raw material composition and a block copolymer are added sequentially to a solvent in a specific mass ratio. The phosphate-based raw material composition contains a lithium source, a phosphorus source, an M source, and a carbon source. After mixing and grinding, a slurry is obtained. The slurry is then spray-dried to obtain a dry powder containing the block copolymer. The M source contains at least one of an iron source, a manganese source, and a sodium source. The solvent contains at least one of water, methanol, ethanol, acetone, N,N-dimethylacetamide, and dimethylformamide.

[0035] S2: Under a protective gas atmosphere, the dry powder is subjected to a sintering process to obtain a phosphate-based cathode material sinter.

[0036] S3: The phosphate-based cathode material sinter is pulverized to obtain the phosphate-based cathode material; the volumetric particle size distribution of the phosphate-based cathode material satisfies the following conditions: Dv10 is 0.2µm~0.4µm, Dv50 is 0.7µm~1.5µm, Dv90 is 2µm~4µm, and Dv100 is 5µm~15µm; the phosphate-based cathode material comprises a phosphate-based active material and a carbon layer coated on the phosphate-based active material, the thickness of the carbon layer is 2nm-10nm, and the content of the carbon layer is 1wt%-4wt%.

[0037] Research has shown that adding the block copolymer in step S1, followed by mixing and grinding, yields a stable slurry. After spray drying in step S2, the slurry undergoes sintering in step S3. During this process, the lithium source, phosphorus source, and M source in the phosphate-based raw material composition form a phosphate-based active material. The carbon source and block copolymer uniformly coat the phosphate-based active material, generating a highly graphitized carbon layer in situ, thus obtaining the phosphate-based cathode material.

[0038] like Figure 1 The image shows a schematic diagram of carbon coating on phosphate-based cathode materials. Traditional phosphate-based cathode materials include... Figure 1 As shown in (a), the carbon layer coating is uneven, and the lack of carbon layer coating results in severe interfacial side reactions, which will significantly reduce the rate performance and cycle performance of the battery when applied to it. The carbon coating of the phosphate-based cathode material prepared by the method provided in this invention is as follows. Figure 1As shown in (b), the carbon layer is uniformly coated and there are no critical surface side reactions. Moreover, the carbon layer on the surface of the phosphate-based cathode material is an in-situ generated highly graphitized carbon layer, which can improve the conductivity of the "particle-to-particle" contact network of the phosphate-based cathode material and greatly reduce the powder resistivity of the phosphate-based cathode material.

[0039] like Figure 2 As shown, the method for preparing phosphate-based cathode materials provided by this invention involves designing the molecular structure of block copolymers to form "inclusions" in the slurry system. By utilizing the structural differences of these "inclusions," lithium iron phosphate cathode materials with different particle sizes can be prepared, meaning the compaction density can be controlled between 2.0 g / cc and 2.70 g / cc, achieving customization of the phosphate cathode material. The primary particles prepared by this method have high sphericity, uniform carbon layer coating on the cathode material surface, and a powder resistivity not exceeding 60 Ω·cm, resulting in excellent rate performance in battery characterization. This technology greatly expands the high-end and niche application areas of the product and features long service life and superior cycle performance.

[0040] Furthermore, the method for preparing phosphate-based cathode materials provided by this invention uses inexpensive and readily available raw materials, has a simple process flow, and requires only one sintering treatment to obtain the phosphate-based cathode material described in this invention, which greatly reduces the production cost of industrialization and has strong practicality.

[0041] According to some preferred embodiments of the present invention, the carbon layer is formed by in-situ sintering of the block copolymer and the carbon source. The block copolymer includes at least one of AB-type diblock copolymer, ABA-type triblock copolymer, and ABC-type triblock copolymer. The block copolymer is also a multiblock copolymer structure of An1-Bn2, (An1-Bn2)n3, An1-Bn2-An3, or (An1-Bn2-An3)n4, where n1, n2, n3, and n4 represent the number of repeating units. The molecular weight of segment A in the block copolymer is 1,000 to 200,000, the molecular weight of segment B is 1,000 to 200,000, and the molecular weight of the optionally present segment C is 1,000 to 200,000. By designing the molecular structure, the length, composition ratio, and arrangement of different segments of the block copolymer can be controlled to give it different structural morphologies and aggregation behaviors, thereby allowing precise control of the morphology and performance of the phosphate-based cathode material.

[0042] More preferably, the block copolymer comprises C, H, O, optionally present N, optionally present P, and optionally present S elements, and comprises at least one of hydroxyl, amino, carboxyl, phosphate, ether, ester, and phospholipid groups. More preferably, the monomers of the block copolymer comprise at least two combinations of polyethylene glycol, polypropylene, polyamide amine, polyethyleneimine, polyoxyethylene, polyoxypropylene, polyvinylpyrrolidone, polylactic acid, polylactic-co-glycolic acid, polyglycolic acid, polycaprolactone, aminopolymethyl methacrylate, and polycaprolactone. For example, the block copolymer is: polypropylene oxide-ethylene oxide-polypropylene oxide block copolymer, polylactic acid-polyethylene glycol-maleimide block copolymer, polystyrene-polyoxyethylene-polystyrene block copolymer, polyethylene glycol-polypropionic acid block copolymer, polylactic acid-glycolic acid-polyethylene glycol-polylactic acid-glycolic acid block copolymer, polypropionic acid-polylactic acid-polyglycolic acid triblock copolymer, polylactic acid-glycolic acid-polyethylene glycol block copolymer, and polylactic acid-polyethylene glycol block copolymer.

[0043] According to some preferred embodiments of the present invention, in step S1, the ratio of the total amount of the carbon source and the block copolymer added to the mass ratio of the M source in the phosphate-based raw material composition is (5~20):100. Under this preferred condition, the obtained phosphate-based cathode material has better sphericity, higher compaction density, and lower powder resistivity. It should be noted that the ratio of the amount of the carbon source and the copolymer additive added can be adjusted according to the actual situation, as long as the total amount of both added is within the mass ratio of the M source in the phosphate-based raw material composition (5~20):100.

[0044] More preferably, in step S1, the ratio of the amount of the block copolymer added to the mass of the M source is (1-10):100. Under this preferred condition, the resulting phosphate-based cathode material has better sphericity, higher compaction density, lower powder resistivity, and better electrochemical performance.

[0045] According to some preferred embodiments of the present invention, the phosphate-based active material comprises at least one of lithium iron phosphate, lithium manganese iron phosphate, and sodium iron phosphate. The carbon source comprises, but is not limited to, at least one of glucose, fructose, sucrose, maltose, polyethylene glycol, polyglycerol, and citric acid.

[0046] According to some preferred embodiments of the present invention, the carbon layer comprises at least one of amorphous carbon, graphite carbon layer, and carbon nanotubes.

[0047] According to some preferred embodiments of the present invention, in step S1, the phosphate-based raw material composition includes a phosphorus source, a lithium source, and an M source, wherein the M source includes at least one of an iron source, a manganese source, and a sodium source.

[0048] According to some preferred embodiments of the present invention, in step S1, the amount of M source, phosphorus source and lithium source added is such that the molar ratio of M element, phosphorus element and lithium element in the phosphate-based raw material composition is (0.9~1.0):1.0:(1.0~1.1).

[0049] Furthermore, the phosphorus source is a phosphorus-containing compound. Preferably, the phosphorus source comprises at least one of phosphoric acid, iron phosphate, lithium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, lithium dihydrogen phosphate, and lithium phosphate.

[0050] Furthermore, the lithium source is a lithium-containing compound. Preferably, the lithium source comprises at least one of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, lithium phosphate, lithium acetate, lithium oxalate, and lithium nitrate.

[0051] Furthermore, the iron source is an iron-containing compound. Preferably, the iron source comprises one of ferric phosphate, ferrous nitrate, ferric oxide, ferrous oxalate, and magnetite.

[0052] Furthermore, the manganese source is a compound containing manganese. Preferably, the manganese source comprises at least one of manganese nitrate, manganese carbonate, manganese oxalate, manganese dioxide, and manganese tetroxide.

[0053] Further, the sodium source is a sodium-containing compound. Preferably, the sodium source comprises at least one selected from sodium carbonate, sodium hydroxide, sodium phosphate, and sodium oxalate.

[0054] It should be noted that the present invention does not have any special requirements on the order of mixing and grinding processes; the order can be selected according to the actual situation.

[0055] More preferably, the grinding is carried out in a ball mill and / or a sand mill, wherein the zirconium balls used in the sand mill have a particle size of 0.1µm to 1.0µm.

[0056] More preferably, in step S1, the volumetric particle size distribution of the solid particles in the slurry satisfies at least the following conditions: 0.2µm≤Dv50≤0.5µm, 0.5µm<Dv90<2.0µm; under these preferred conditions, the obtained phosphate-based cathode material has better sphericity, higher compaction density, lower powder resistivity, and better electrochemical performance.

[0057] More preferably, the amount of solvent used is such that the solid content of the slurry obtained in step S1 is 20wt%-50wt%, and the viscosity at 25°C is 50mPa·s~800mPa·s. Under these preferred conditions, the phosphate-based cathode material obtained has better sphericity, higher compaction density, lower powder resistivity, and better electrochemical performance.

[0058] According to some preferred embodiments of the present invention, in step S2, the inlet temperature of the spray drying process is 80℃-250℃, the outlet temperature is 50℃~95℃, and the processing time is 0.5h~4h.

[0059] According to some preferred embodiments of the present invention, in step S3, the protective gas is at least one of nitrogen, helium, neon, and argon.

[0060] According to some preferred embodiments of the present invention, in step S3, the primary sintering process includes a heating stage and a isothermal stage. The heating rate of the heating stage is 2℃ / min to 10℃ / min, the temperature of the isothermal stage is 700℃ to 850℃, and the isothermal time is 5h to 15h.

[0061] It should be noted that in step S4, the present invention does not have special requirements for the crushing process; conventional methods used in the art are sufficient, as long as the phosphate-based sintered body can be crushed to a size distribution that meets the requirements. For example, the crushing process includes sequential air jet milling and mechanical milling.

[0062] A second aspect of this invention provides a phosphate-based cathode material prepared by the aforementioned method. The phosphate-based cathode material comprises a phosphate-based active material and a carbon layer coating the phosphate-based active material. The carbon layer is formed by in-situ sintering of a block copolymer and a carbon source. The block copolymer includes AB-type diblock copolymers, ABA-type triblock copolymers, ABC-type triblock copolymers, etc.; the block copolymer is also a multiblock copolymer structure of An1-Bn2, (An1-Bn2)n3, An1-Bn2-An3, (An1-Bn2-An3)n4, where n1, n2, n3, and n4 represent the number of repeating units. The molecular weight of segment A in the block copolymer is 1000~200000, the molecular weight of segment B is 1000~200000, and the molecular weight of the optional segment C is 1000~200000. Through molecular structure design, the length, composition ratio, and arrangement of different segments of the block copolymer can be controlled to achieve different structural morphologies and aggregation behaviors. The monomers of the block copolymer are at least two of the following: polyethylene glycol, polypropylene, polyamide amine, polyethyleneimine, polyoxyethylene, polyoxypropylene, polyvinylpyrrolidone, polylactic acid, polylactic-co-hydroxyacetic acid, polyhydroxyacetic acid, polycaprolactone, aminopolymethyl methacrylate, and polycaprolactone.

[0063] The phosphate-based cathode material provided by this invention has a volumetric particle size distribution that satisfies at least the following conditions: Dv10 is 0.2µm-0.4µm, Dv50 is 0.7µm-1.5µm, Dv90 is 2µm-4µm, and Dv100 is 5µm-15µm. Furthermore, the particle size of the phosphate-based cathode material is controllable, exhibiting high sphericity. While achieving a powder resistivity not exceeding 60Ω·cm, the material's powder compaction density can be adjusted between 2.0g / cc and 2.70g / cc. This method allows for the customization of cathode materials, greatly expanding their application areas.

[0064] The present invention will be described in detail below through examples. Unless otherwise specified, the experimental instruments and raw materials involved in the following embodiments are commercially available. The specific compositions of the block copolymers in each embodiment are shown in Table 1 below.

[0065] Example 1

[0066] Preparation of lithium iron phosphate cathode material A1:

[0067] S1: Accurately weigh the phosphate-based raw material composition and the block copolymer, and add them to the solvent in sequence according to the mass ratio. The phosphate-based raw material composition contains lithium source, phosphorus source, iron source and carbon source. After mixing and grinding, a slurry is obtained. The slurry is spray-dried to obtain dry powder containing block copolymer.

[0068] Specifically:

[0069] The iron and phosphorus sources are both iron phosphate, the lithium source is lithium carbonate, the carbon source is glucose, and the block copolymer is a polypropylene oxide-ethylene oxide-polypropylene oxide block copolymer with a molecular weight of 15,000.

[0070] The molar ratio of iron to phosphorus to lithium in the phosphate-based raw material composition is 1:1.03:1.04. The mass of iron phosphate is 1000g, the mass of lithium carbonate is 251.9g, the amount of glucose added is 90g (9wt% of the mass of iron phosphate), the amount of block copolymer added is 30g (3wt% of the mass of iron phosphate), and the solvent is deionized water (2547g).

[0071] Deionized water was added to a grinding jar, followed by the sequential addition of ferric phosphate, lithium carbonate, glucose, and a polypropylene oxide-ethylene oxide-polypropylene oxide block copolymer. After mixing and grinding, a slurry was obtained. The grinding was performed in a sand mill using zirconium balls with a particle size of 0.32 µm. The slurry had a solid content of 35 wt% and a viscosity of 150 mPa·s at 25°C. The particle size distribution of the solid particles was as follows: Dv50 = 0.362 µm, Dv90 = 0.571 µm, and Dv100 = 0.870 µm.

[0072] The slurry was subjected to spray drying, with the inlet air temperature at 230°C and the outlet air temperature at 95°C, for a duration of 2 hours, to obtain a dry powder containing block copolymers.

[0073] S2: Under a protective gas atmosphere, the dry powder is subjected to a sintering process to obtain a phosphate-based cathode material sinter.

[0074] Specifically:

[0075] The protective gas is nitrogen. The first sintering process includes a heating stage and a isothermal stage. The heating rate of the heating stage is 3℃ / min, and the temperature of the isothermal stage is 790℃, with an isothermal time of 8h.

[0076] S3: The phosphate-based cathode material sinter is crushed, and the crushing process includes sequential air jet milling and mechanical milling to obtain the lithium iron phosphate cathode material A1.

[0077] The volumetric particle size distribution and performance parameters of the prepared lithium iron phosphate cathode material A1 are shown in Table 2 below.

[0078] Example 2

[0079] Preparation of lithium iron phosphate cathode material A2:

[0080] S1: Accurately weigh the phosphate-based raw material composition and the block copolymer, and add them to the solvent in sequence according to the mass ratio. The phosphate-based raw material composition contains lithium source, phosphorus source, iron source and carbon source. After mixing and grinding, a slurry is obtained. The slurry is spray-dried to obtain dry powder containing block copolymer.

[0081] Specifically:

[0082] The iron and phosphorus sources are both iron phosphate, the lithium source is lithium carbonate, the carbon source is glucose, and the block copolymer is polylactic acid-polyethylene glycol-maleimide block copolymer with a molecular weight of 25,000.

[0083] The molar ratio of iron to phosphorus to lithium in the phosphate-based raw material composition is 1:1.035:1.035. The mass of iron phosphate is 1000g, the mass of lithium carbonate is 250.60g, the amount of glucose added is 60g, which accounts for 6wt% of the mass of iron phosphate; the amount of block copolymer added is 50g, which accounts for 5wt% of the mass of iron phosphate; and the solvent is deionized water, which is added in an amount of 2450g.

[0084] Deionized water was added to a grinding jar, followed by the sequential addition of ferric phosphate, lithium carbonate, glucose, and polylactic acid-polyethylene glycol-maleimide block copolymer. After mixing and grinding, a slurry was obtained. The grinding was performed in a sand mill using zirconium balls with a particle size of 0.25 µm. The slurry had a solid content of 35 wt% and a viscosity of 230 mPa·s at 25°C. The particle size distribution of the solid particles was as follows: Dv50 = 0.375 µm, Dv90 = 0.575 µm, and Dv100 = 0.871 µm.

[0085] The slurry was subjected to spray drying, with the inlet air temperature at 230°C and the outlet air temperature at 95°C, for a duration of 2 hours, to obtain a dry powder containing block copolymers.

[0086] S2: Under a protective gas atmosphere, the dry powder is subjected to a sintering process to obtain a phosphate-based cathode material sinter.

[0087] Specifically:

[0088] The protective gas is nitrogen. The first sintering process includes a heating stage and a isothermal stage. The heating rate of the heating stage is 3℃ / min, and the temperature of the isothermal stage is 800℃, with an isothermal time of 6h.

[0089] S3: The phosphate-based cathode material sinter is crushed, and the crushing process includes sequential air jet milling and mechanical milling to obtain the lithium iron phosphate cathode material A2.

[0090] The volumetric particle size distribution and performance parameters of the prepared lithium iron phosphate cathode material A2 are shown in Table 2 below.

[0091] Example 3

[0092] Preparation of lithium iron phosphate cathode material A3:

[0093] S1: Accurately weigh the phosphate-based raw material composition and the block copolymer, and add them to the solvent in sequence according to the mass ratio. The phosphate-based raw material composition contains lithium source, phosphorus source, iron source and carbon source. After mixing and grinding, a slurry is obtained. The slurry is spray-dried to obtain dry powder containing block copolymer.

[0094] Specifically:

[0095] The iron and phosphorus sources are both iron phosphate, the lithium source is lithium carbonate, the carbon source is glucose, and the block copolymer is a polystyrene-polyoxyethylene-polystyrene block copolymer with a molecular weight of 15,000.

[0096] The molar ratio of iron:phosphorus:lithium in the raw material composition is 1:1.03:1.05. The mass of iron phosphate is 1000g, the mass of lithium carbonate is 254.60g, the amount of glucose added is 5wt% of the mass of iron phosphate, and the amount added is 60g; the block copolymer accounts for 6wt% of the mass of iron phosphate, and the amount added is 60g; the solvent is anhydrous methanol, and the amount added is 3080g.

[0097] Deionized water was added to a grinding jar, followed by the sequential addition of ferric phosphate, lithium carbonate, glucose, and polystyrene-polyoxyethylene-polystyrene block copolymer. After mixing and grinding, a slurry was obtained. The grinding was carried out in a sand mill using zirconium balls with a particle size of 0.25 µm. The slurry had a solid content of 30 wt% and a viscosity of 180 mPa·s at 25°C. The particle size distribution of the solid particles was as follows: Dv50 = 0.333 µm, Dv90 = 0.517 µm, and Dv100 = 0.767 µm.

[0098] The slurry was subjected to spray drying, with the inlet air temperature at 80°C and the outlet air temperature at 40°C, for a duration of 2 hours, to obtain a dry powder containing block copolymers.

[0099] S2: Under a protective gas atmosphere, the dry powder is subjected to a sintering process to obtain a phosphate-based cathode material sinter.

[0100] Specifically:

[0101] The protective gas is nitrogen. The first sintering process includes a heating stage and a isothermal stage. The heating rate of the heating stage is 3℃ / min, and the temperature of the isothermal stage is 760℃, with an isothermal time of 10h.

[0102] S3: The phosphate-based cathode material sinter is crushed, and the crushing process includes sequential air jet milling and mechanical milling to obtain the lithium iron phosphate cathode material A3.

[0103] The volumetric particle size distribution and performance parameters of the prepared lithium iron phosphate cathode material A3 are shown in Table 2 below.

[0104] Example 4

[0105] Preparation of lithium iron phosphate cathode material A4:

[0106] S1: Accurately weigh the phosphate-based raw material composition and the block copolymer, and add them to the solvent in sequence according to the mass ratio. The phosphate-based raw material composition contains lithium source, phosphorus source, iron source and carbon source. After mixing and grinding, a slurry is obtained. The slurry is spray-dried to obtain dry powder containing block copolymer.

[0107] Specifically:

[0108] The iron and phosphorus sources are iron phosphate, the lithium source is lithium carbonate, the carbon source is glucose, and the block copolymer is polyethylene glycol-polypropionic acid block copolymer with a molecular weight of 20,000.

[0109] The molar ratio of iron to phosphorus to lithium in the phosphate-based raw material composition is 1:1.033:1.054. The mass of iron phosphate is 1000g, the mass of lithium carbonate is 255.63g, the amount of glucose added is 80g, which accounts for 8wt% of the mass of iron phosphate; the amount of block copolymer added is 60g, which accounts for 6wt% of the mass of iron phosphate; and the amount of deionized water added is 3660g.

[0110] Deionized water was added to a grinding jar, followed by the sequential addition of ferric phosphate, lithium carbonate, glucose, and polylactic acid-polyethylene glycol block copolymer. After mixing and grinding, a slurry was obtained. The grinding was carried out in a sand mill using zirconium balls with a particle size of 0.25 µm. The slurry had a solid content of 28 wt% and a viscosity of 60 mPa·s at 25°C. The particle size distribution of the solid particles was as follows: Dv50 = 0.351 µm, Dv90 = 0.542 µm, and Dv100 = 0.871 µm.

[0111] The slurry was subjected to spray drying, with the inlet air temperature at 230°C and the outlet air temperature at 95°C, for a duration of 2 hours, to obtain a dry powder containing block copolymers.

[0112] S2: Under a protective gas atmosphere, the dry powder is subjected to a sintering process to obtain a phosphate-based cathode material sinter.

[0113] Specifically:

[0114] The protective gas is nitrogen. The first sintering process includes a heating stage and a isothermal stage. The heating rate of the heating stage is 3℃ / min, and the temperature of the isothermal stage is 750℃, with an isothermal time of 8h.

[0115] S3: The phosphate-based cathode material sinter is crushed, and the crushing process includes sequential air jet milling and mechanical milling to obtain the lithium iron phosphate cathode material A4.

[0116] The volumetric particle size distribution and performance parameters of the prepared lithium iron phosphate cathode material A4 are shown in Table 2 below.

[0117] Example 5

[0118] Preparation of lithium manganese iron phosphate cathode material A5:

[0119] S1: Accurately weigh the phosphate-based raw material composition and the block copolymer, and add them to the solvent in sequence according to the mass ratio. The phosphate-based raw material composition contains lithium source, phosphorus source, M source and carbon source. After mixing and grinding, a slurry is obtained. The slurry is spray-dried to obtain dry powder containing block copolymer.

[0120] Specifically:

[0121] The phosphorus source is iron phosphate and ammonium dihydrogen phosphate. The M source includes iron and manganese sources. The iron source is iron phosphate, the manganese source is manganese carbonate, the lithium source is lithium carbonate, and the carbon source is sucrose. The block copolymer is polylactic acid-glycolic acid-polyethylene glycol-polylactic acid-glycolic acid block copolymer with a molecular weight of 35,000.

[0122] The molar ratio of iron:manganese:phosphorus:lithium in the phosphate-based raw material composition is 0.4:0.6:1.033:1.049; the mass of iron phosphate is 400g, the mass of manganese carbonate is 451.72g, the mass of ammonium dihydrogen phosphate is 452.03g, the mass of lithium carbonate is 254.38g, the amount of sucrose added accounts for 4.7wt% of the total mass of iron phosphate and manganese carbonate, and the amount added is 40g; the block copolymer accounts for 5.8wt% of the total mass of iron phosphate and manganese carbonate, and the amount added is 50g; the solvent is deionized water, and the amount added is 3845g.

[0123] Deionized water was added to a ball mill jar, followed by the sequential addition of ferric phosphate, lithium carbonate, manganese carbonate, ammonium dihydrogen phosphate, sucrose, and polylactic acid-glycolic acid-polyethylene glycol-polylactic acid-glycolic acid block copolymer for coarse grinding. The zirconium balls in the ball mill had a particle size of 0.6 µm. Once the particle size of the solid particles in the slurry from ball milling met the requirements of Dv50 < 0.8 µm and Dv100 < 4 µm, the slurry was transferred to a sand mill for fine grinding. The zirconium balls in the sand mill had a particle size of 0.25 µm. The particle size distribution of the solid particles in the slurry after sand milling was: Dv50 0.314 µm, Dv90 0.499 µm, and Dv100 0.767 µm; the solid content of the slurry was 30 wt%, and the viscosity at 25 °C was 300 mPa·s.

[0124] The slurry was subjected to spray drying, with the inlet air temperature at 230°C and the outlet air temperature at 95°C, for a duration of 2 hours, to obtain a dry powder containing block copolymers.

[0125] S2: Under a protective gas atmosphere, the dry powder is subjected to a sintering process to obtain a phosphate-based cathode material sinter.

[0126] Specifically:

[0127] The protective gas is nitrogen. The first sintering process includes a heating stage and a isothermal stage. The heating rate of the heating stage is 3℃ / min, and the temperature of the isothermal stage is 740℃, with an isothermal time of 8h.

[0128] S3: The phosphate-based cathode material sinter is crushed by air jet milling to obtain the lithium iron phosphate cathode material A5.

[0129] The volumetric particle size distribution and performance parameters of the prepared lithium iron phosphate cathode material A5 are shown in Table 2 below.

[0130] Comparative Example 1

[0131] Preparation of lithium iron phosphate cathode material B1:

[0132] S1: Accurately weigh the phosphate-based raw material composition and add it to the solvent in sequence according to the mass ratio. The phosphate-based raw material composition contains lithium source, phosphorus source, iron source and carbon source. After mixing and grinding, a slurry is obtained. The slurry is then spray-dried to obtain dry powder.

[0133] The iron and phosphorus sources are both iron phosphate, the lithium source is lithium carbonate, and the carbon source is glucose.

[0134] The molar ratio of iron:phosphorus:lithium in the phosphate-based raw material composition is 1:1.03:1.04. The mass of iron phosphate is 1000g, the mass of lithium carbonate is 251.88g, the amount of glucose added is 13wt% of the mass of iron phosphate, the amount added is 130g, the solvent is deionized water, and the amount added is 2566g.

[0135] Deionized water was added to a grinding jar, followed by the sequential addition of ferric phosphate, lithium carbonate, and glucose. After mixing and grinding, a slurry was obtained. The grinding was carried out in a sand mill, using zirconium balls with a particle size of 0.32 µm. The slurry had a solid content of 35 wt% and a viscosity of 280 mPa·s at 25°C. The particle size distribution of the solid particles was as follows: Dv50 = 0.368 µm, Dv90 = 0.569 µm, and Dv100 = 0.871 µm.

[0136] The slurry was subjected to spray drying, with the inlet air temperature at 230°C and the outlet air temperature at 95°C, for a duration of 2 hours, to obtain dry powder.

[0137] S2: Under a protective gas atmosphere, the dry powder is subjected to a sintering process to obtain a phosphate-based cathode material sinter.

[0138] Specifically:

[0139] The protective gas is nitrogen. The first sintering process includes a heating stage and a isothermal stage. The heating rate of the heating stage is 3℃ / min, and the temperature of the isothermal stage is 790℃, with an isothermal time of 8h.

[0140] S3: The lithium iron phosphate material is crushed, and the crushing process includes sequential air jet milling and mechanical milling to obtain the lithium iron phosphate cathode material B1.

[0141] The volumetric particle size distribution and performance parameters of the prepared lithium iron phosphate cathode material B1 are shown in Table 1 below.

[0142] Comparative Example 2

[0143] Preparation of lithium manganese iron phosphate cathode material B2:

[0144] S1: Accurately weigh the phosphate-based raw material composition and add it to the solvent in sequence according to the mass ratio. The phosphate-based raw material composition contains lithium source, phosphorus source, M source and carbon source. After mixing and grinding, a slurry is obtained. The slurry is spray-dried to obtain a dry powder containing block copolymer.

[0145] Specifically:

[0146] The phosphorus source includes iron phosphate and ammonium dihydrogen phosphate, the M source includes iron source and manganese source, the iron source is iron phosphate, the manganese source is manganese carbonate, the lithium source is lithium carbonate, and the carbon source is sucrose.

[0147] The molar ratio of iron:manganese:phosphorus:lithium in the phosphate-based raw material composition is 0.4:0.6:1.033:1.049; the mass of iron phosphate is 400g, the mass of manganese carbonate is 451.72g, the mass of ammonium dihydrogen phosphate is 452.03g, the mass of lithium carbonate is 254.38g, the amount of sucrose added accounts for 7.63wt% of the total mass of iron phosphate and manganese carbonate, and the amount added is 65g; the solvent is deionized water, and the amount added is 3790g.

[0148] Deionized water was added to a ball mill jar, followed by ferric phosphate, lithium carbonate, manganese carbonate, ammonium dihydrogen phosphate, and sucrose, which were then added sequentially for coarse grinding. The zirconium balls in the ball mill had a particle size of 0.6 µm. Once the particle size of the solid particles in the slurry met the requirements of Dv50 < 0.8 µm and Dv100 < 4 µm, the slurry was transferred to a sand mill for fine grinding. The zirconium balls in the sand mill had a particle size of 0.25 µm. The particle size distribution of the solid particles in the slurry after sand milling was: Dv50 0.316 µm, Dv90 0.497 µm, and Dv100 0.766 µm. At this point, the solid content of the slurry was 30 wt%, and the viscosity at 25 °C was 620 mPa·s.

[0149] The slurry was subjected to spray drying, with the inlet air temperature at 230°C and the outlet air temperature at 95°C, for a duration of 2 hours, to obtain dry powder.

[0150] S2: Under a protective gas atmosphere, the dry powder is subjected to a sintering process to obtain a phosphate-based cathode material sinter.

[0151] Specifically:

[0152] The protective gas is nitrogen. The first sintering process includes a heating stage and a isothermal stage. The heating rate of the heating stage is 3℃ / min, and the temperature of the isothermal stage is 740℃, with an isothermal time of 8h.

[0153] S3: The phosphate-based cathode material sinter is crushed by air jet milling to obtain the lithium iron phosphate cathode material B2.

[0154] The volumetric particle size distribution and performance parameters of the prepared lithium iron phosphate cathode material B2 are shown in Table 2 below.

[0155] Test case

[0156] The phosphate-based cathode materials prepared in the examples and comparative examples were subjected to performance tests. The test methods were carried out in accordance with industry standard test methods. The specific test results are shown in Table 2.

[0157]

[0158]

[0159] As can be seen from Tables 1 and 2, compared with the phosphate-based cathode materials prepared in the comparative example, the phosphate-based cathode materials prepared in this embodiment have higher compaction density, lower powder resistivity, and better electrical performance.

[0160] from Figure 3 and Figure 4 It can be seen that the lithium iron phosphate cathode materials prepared in Examples 1 and 2 of this invention have rounded particles with high sphericity after airflow pulverization, exhibiting significant particle size variations. Figure 7 It can be seen that after air jet milling, the lithium iron phosphate cathode material prepared in Comparative Example 1 has a large number of large fragments and particles, which are irregularly shaped and have obvious edges and corners. Figure 5 It can be seen that in Example 3 of the present invention, by designing the structure of the block copolymer and controlling its proportion and "encapsulation" morphology in the slurry, a lithium iron phosphate cathode material with relatively uniform particle size can be obtained; from Figure 6 It can be seen that the carbon layer coating of the lithium manganese iron phosphate cathode material prepared in Example 5 of the present invention is uniform and the material has good monodispersity. Figure 8It can be seen that the lithium manganese iron phosphate cathode material prepared in Comparative Example 2 suffers from severe grain refinement due to the disordered carbon coating inhibiting the growth of material particles; combined with Figure 9 The image shows the Raman diagram of the lithium iron phosphate cathode material prepared in Example 1 of this invention. It can be seen that the carbon layer of the lithium iron phosphate cathode material has a high degree of graphitization after the addition of the block copolymer. Figure 10 The image shows the Raman spectrum of the lithium iron phosphate cathode material prepared in Comparative Example 1. It can be seen that the carbon layer of the lithium iron phosphate cathode material has many defects and a low degree of graphitization in the carbon layer structure; furthermore, from... Figure 11 It can be seen that the rate performance of the lithium iron phosphate cathode material in Example 1 of this invention is significantly better than that of the lithium iron phosphate cathode material in Comparative Example 1. In summary, the carbon coating layer of the phosphate-based cathode material obtained by controlling the block copolymer structure of this invention is more continuous and uniform, which is beneficial to the performance of electrical properties; and controlling the block copolymer structure can effectively control the particle morphology of the phosphate-based cathode material, making its energy density higher.

[0161] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing a phosphate-based cathode material, characterized in that, Includes the following steps: S1: A phosphate-based raw material composition and a block copolymer are added sequentially to a solvent in a specific mass ratio. The phosphate-based raw material composition contains a lithium source, a phosphorus source, an M source, and a carbon source. After mixing and grinding, a slurry is obtained. The slurry is then spray-dried to obtain a dry powder containing the block copolymer. The M source contains at least one of an iron source, a manganese source, and a sodium source. The solvent contains at least one of water, methanol, ethanol, acetone, N,N-dimethylacetamide, and dimethylformamide. S2: Under a protective gas atmosphere, the dry powder is subjected to a sintering process to obtain a phosphate-based cathode material sinter. S3: The phosphate-based cathode material sinter is pulverized to obtain the phosphate-based cathode material; the volumetric particle size distribution of the phosphate-based cathode material satisfies the following conditions: Dv10 is 0.2µm~0.4µm, Dv50 is 0.7µm~1.5µm, Dv90 is 2µm~4µm, and Dv100 is 5µm~15µm; the phosphate-based cathode material comprises a phosphate-based active material and a carbon layer coated on the phosphate-based active material, the thickness of the carbon layer is 2nm-10nm, and the content of the carbon layer is 1wt%-4wt%.

2. The preparation method according to claim 1, characterized in that, The carbon layer is formed by in-situ sintering of the block copolymer and the carbon source. The block copolymer includes at least one of AB-type diblock copolymer, ABA-type triblock copolymer, and ABC-type triblock copolymer. The molecular weight of segment A in the block copolymer is 1,000 to 200,000, the molecular weight of segment B is 1,000 to 200,000, and the molecular weight of the optionally present segment C is 1,000 to 200,000.

3. The preparation method according to claim 1, characterized in that, The block copolymer contains C, H, O, optional N, optional P, and optional S elements, and includes at least one of hydroxyl, amino, carboxyl, phosphate, ether, ester, and phospholipid groups.

4. The preparation method according to any one of claims 1 to 3, characterized in that, The phosphate-based active material includes at least one of lithium iron phosphate, lithium manganese iron phosphate, and sodium iron phosphate. And / or, the carbon source comprises at least one of glucose, fructose, sucrose, maltose, polyethylene glycol, polyglycerol, and citric acid; And / or, the monomers of the block copolymer comprise at least two combinations of polyethylene glycol, polypropylene, polyamide amine, polyethyleneimine, polyoxyethylene, polyoxypropylene, polyvinylpyrrolidone, polylactic acid, polylactic-co-hydroxyacetic acid, polyhydroxyacetic acid, polycaprolactone, aminopolymethyl methacrylate, and polycaprolactone.

5. The preparation method according to any one of claims 1 to 3, characterized in that, The ratio of the total amount of the carbon source and the block copolymer added to the mass of the M source is (5-20):100; And / or, the ratio of the amount of the block copolymer added to the mass of the M source is (1-10):

100.

6. The preparation method according to any one of claims 1 to 3, characterized in that, The amount of M source, phosphorus source and lithium source added is such that the molar ratio of M element, phosphorus element and lithium element in the phosphate-based raw material composition is (0.9~1.0):1.0:(1.0~1.1).

7. The preparation method according to any one of claims 1 to 3, characterized in that, The grinding is carried out in a ball mill and / or a sand mill, wherein the zirconium balls used in the sand mill have a particle size of 0.10µm-1µm; And / or, the volumetric particle size distribution of the solid particles in the slurry at least satisfies the following condition: 0.2µm ≤ Dv50 ≤ 0.5µm, 0.5µm <Dv90≤2.0µm; And / or, the solid content of the slurry is 20wt%~50wt%; And / or, the viscosity of the slurry at 25°C is 50 mPa·s to 800 mPa·s.

8. The preparation method according to any one of claims 1 to 3, characterized in that, The spray drying process has an inlet temperature of 80℃~250℃, an outlet temperature of 50℃~95℃, and a processing time of 0.5h~4h.

9. The preparation method according to any one of claims 1 to 3, characterized in that, The primary sintering process includes a heating stage and a isothermal stage. The heating rate of the heating stage is 2℃ / min to 10℃ / min, and the temperature of the isothermal stage is 700℃ to 850℃, with an isothermal time of 5h to 15h; and / or, the protective gas is at least one of nitrogen, helium, neon, and argon.

10. A phosphate-based cathode material prepared by any one of claims 1 to 9.

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