Spherical phosphate-based cathode materials and their preparation methods

Abstract

This invention relates to the field of cathode material technology, and discloses a spherical phosphate-based cathode material and its preparation method. The preparation method includes: atomizing a phosphate-based precursor slurry into droplets, and subjecting the droplets to a near-free fall motion under a specific vacuum level. During the fall, the droplets contract under surface tension and are dried by thermal radiation to obtain spherical phosphate-based precursor particles, which are then sintered to obtain the spherical phosphate-based cathode material. This invention simulates a suspended microgravity field by constructing a near-free fall path under high vacuum, eliminating the shear interference of the traditional carrier gas field on the droplet morphology and the segregation deformation caused by gravity settling. It fully utilizes the contraction effect of droplet surface tension, achieving extremely close packing, and the resulting spherical phosphate-based cathode material exhibits superior overall performance.

Description

Technical Field

[0001] This invention relates to the field of cathode material technology, specifically to a spherical phosphate-based cathode material and its preparation method. Background Technology

[0002] Phosphate-based cathode materials (such as LiMPO4, where M is one or more of Fe, Mn, V, Co, Ni, etc.) have become an important research direction in the fields of power batteries and large-capacity energy storage due to their stable crystal structure, high safety, and long cycle life. However, these materials generally suffer from low electronic conductivity and limited ion diffusion paths, and their morphology has a decisive influence on the electrode processing performance and the volumetric energy density of the battery. To improve the performance of phosphate-based materials, achieving particle spheroidization is a recognized effective method in this field.

[0003] Currently, there is a method for preparing spherical cathode materials using atomization (e.g., CN105336929B). This technique involves atomizing a solution containing lithium salt, metal salt, and phosphate into small droplets, and then using a vacuum system to drive the droplets into a horizontally or inclined tube furnace (such as a quartz tube or corundum tube) for drying and curing. However, this existing technology still has significant limitations in preparing high-performance spherical phosphate materials:

[0004] 1. Disruption of morphological regularity due to interference from the current-carrying field: In this scheme, the movement of droplets is highly dependent on the current-carrying force generated by the vacuum system, and the droplets move at a forward velocity within the narrow cavity of the tube furnace. In this current-carrying gas field, the droplets are easily deformed by uneven shear forces and are prone to collisions with the tube wall, leading to particle breakage or loss of roundness, making it difficult to obtain perfectly spherical particles with high roundness.

[0005] 2. Gravity-induced component segregation and deformation: Existing tubular furnaces are typically horizontally arranged, and the droplets are constantly subjected to a constant downward vertical gravitational force during their horizontal movement. Before the droplets are fully dehydrated and solidified, gravity causes sedimentation and segregation of the internal components, resulting in uneven internal structures of the secondary particles and even collapse to form non-spherical particles, severely affecting the material's bulk density (typically below 1.6 g / cm³).

[0006] 3. The drying dynamics environment is not ideal: Although the existing technology mentions a vacuum system, it is essentially a flow-carrying medium. The inside of the tube furnace is not a high vacuum static environment, and the droplet falling / moving process is still affected by airflow resistance.

[0007] Therefore, how to overcome the current-carrying interference and gravity effects in the existing technology, and provide a preparation method that can achieve a synergistic improvement in high sphericity, ultra-high packing density and excellent conductive network of phosphate-based cathode materials, is an urgent issue to be solved in the field of cathode materials. Summary of the Invention

[0008] One of the objectives of this invention is to solve the problems of low sphericity and low packing density of lithium iron phosphate materials in the prior art.

[0009] The second objective of this invention is to provide a method for preparing spherical phosphate-based cathode materials, which results in spherical phosphate-based cathode materials that possess high sphericity, high packing density, high compaction, and excellent electrochemical performance.

[0010] To achieve the above objectives, a first aspect of the present invention provides a method for preparing a spherical phosphate-based cathode material, comprising the following steps:

[0011] S1: Provides phosphate-based precursor slurry;

[0012] S2: The phosphate precursor slurry is atomized into droplets, and the droplets are subjected to a near-free fall motion. During the fall, the droplets shrink into spheres under the action of surface tension and are dried to obtain spherical phosphate precursor particles.

[0013] S3: The spherical phosphate precursor particles are sintered to obtain a phosphate cathode material.

[0014] In step S2, the free-fall motion must meet at least the following conditions: the initial velocity of the droplet does not exceed 5 cm / s, the vacuum degree is -0.095 MPa to -0.098 MPa, and the falling process is heated by thermal radiation.

[0015] A second aspect of the present invention provides a microgravity granulation device for implementing the aforementioned preparation method, comprising: a tower body, wherein the tower body is provided with a channel for the droplets to fall along the direction of gravity, for the droplets to undergo a quasi-free fall motion;

[0016] An atomizing nozzle is disposed at the top of the tower body for atomizing the phosphate precursor slurry into droplets;

[0017] A thermal radiation heating device is installed on the side wall of the tower body to heat droplets that are undergoing free-fall motion inside the tower body.

[0018] A vacuum system, connected to the tower body, is used to maintain the vacuum level inside the tower body.

[0019] A third aspect of the present invention provides a spherical phosphate-based cathode material prepared by the aforementioned method, wherein the spherical phosphate-based cathode material is shaped like a sphere.

[0020] Beneficial effects:

[0021] The preparation method provided by the first aspect of this invention constructs a free-fall-like environment under a specific vacuum degree, simulating a suspended microgravity field. This fundamentally changes the drying dynamics of the droplets, eliminates external deformation interference, and simultaneously achieves structural densification. This results in a highly spherical phosphate-based cathode material with a bulk density ≥1.7 g / cm³, which is 12%-15% higher than traditional methods. The intrinsic conductivity of the material is increased by more than 20%, the electrode compaction density can reach 2.6 g / cm³-2.8 g / cm³, the powder resistivity is ≤10 Ω·cm, the 0.1C discharge capacity is ≥156 mAh / g, the 10C high-rate discharge capacity is ≥105%, and the capacity decay rate after 500 cycles is ≤5%.

[0022] The microgravity granulation equipment provided by the second aspect of the present invention for implementing the aforementioned preparation method constructs an ideal physical field through the structural synergy of the tower space, vacuum system and thermal radiation device. This not only provides the necessary free fall path but also eliminates the droplet adhesion and collision problems common in traditional tubular equipment, ensuring the consistency of particle morphology. The thermal radiation heating device set on the side wall avoids the turbulence interference caused by traditional hot air drying and achieves the overall and rapid drying of droplets through the radiation penetration effect. This effectively prevents premature shelling on the particle surface, which could lead to internal pressure bursting and ensure the roundness of the secondary particles, providing hardware support for the large-scale production of high-quality cathode materials.

[0023] The third aspect of this invention provides a spherical phosphate-based cathode material exhibiting a near-spherical morphology, with smooth and uniformly distributed particle surfaces, significantly improved packing density (compacted density reaching 2.6 g / cm³-2.8 g / cm³), enhancing the volumetric energy density of the battery. Simultaneously, a highly efficient intrinsic conductive network is constructed within the material, significantly reducing the contact resistance within the particles. Experimental data show that this material possesses extremely high discharge specific capacity (0.1C ≥ 159 mAh / g) and excellent rate performance (500-cycle capacity retention ≥ 95%), significantly improving the performance of phosphate-based materials under high-current charge-discharge conditions. Attached Figure Description

[0024] Figure 1 This is a 1000x magnified SEM image of the spherical lithium iron phosphate cathode material prepared in Example 1;

[0025] Figure 2 This is a 1000x magnified SEM image of the spherical lithium manganese iron phosphate cathode material prepared in Example 2;

[0026] Figure 3 This is a 1000x magnified SEM image of the spherical lithium iron phosphate cathode material prepared in Comparative Example 1.

[0027] Figure 4 This is a schematic diagram of the microgravity granulation equipment provided in some embodiments of the present invention;

[0028] Figure 5 This is a schematic diagram of the structure of an atomizing nozzle provided in some embodiments of the present invention;

[0029] Figure 6 This is a structural schematic diagram of a microgravity granulation device provided in other embodiments of the present invention. Detailed Implementation

[0030] 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.

[0031] In this invention, unless otherwise stated, room temperature or normal temperature refers to 25±2℃.

[0032] In this invention, Dv50 represents the particle size value corresponding to the cumulative particle size distribution number of the granulated material reaching 50%. Dv100 has a similar definition to Dv50. These will not be described in detail here, and those skilled in the art should not understand them as limitations on this invention.

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

[0034] S1: Provides phosphate-based precursor slurry;

[0035] S2: The phosphate precursor slurry is atomized into droplets, and the droplets are subjected to a near-free fall motion. During the fall, the droplets shrink into spheres under the action of surface tension and are dried to obtain spherical phosphate precursor particles.

[0036] S3: The spherical phosphate precursor particles are sintered to obtain a spherical phosphate cathode material;

[0037] In step S2, the free-fall motion must meet at least the following conditions: the initial velocity of the droplet does not exceed 5 cm / s, the vacuum degree is -0.095 MPa to -0.098 MPa, and the falling process is heated by thermal radiation.

[0038] The preparation method provided by the first aspect of the present invention simulates a suspended microgravity field by constructing a quasi-free fall environment under a specific vacuum degree, fundamentally changing the drying dynamics of droplets. Under high vacuum, the air resistance and airflow shear force experienced by the droplets during fall are reduced to extremely low levels, enabling the droplets to achieve perfect centripetal contraction driven only by surface tension, avoiding the "hollow sphere" or "apple-shaped" distortion caused by airflow interference in traditional spray drying. At the same time, the quasi-free fall process provides sufficient self-assembly time for the phosphate active material particles inside the droplets. Under the uniform induction of thermal radiation, the solvent is uniformly removed from the inside out, promoting the compaction of spherical phosphate precursor particles, thereby improving the density of the precursor from the source.

[0039] In step S1, the phosphate-based precursor slurry includes, but is not limited to, at least one of lithium iron phosphate precursor slurry, lithium manganese phosphate precursor slurry, lithium manganese iron phosphate precursor slurry, and lithium sodium iron phosphate precursor slurry.

[0040] According to a preferred embodiment of the present invention, the phosphate-based precursor slurry is a lithium iron phosphate precursor slurry, and step S1 is performed in the following manner, but not limited to: dissolving an iron source, a phosphorus source and a lithium source in a solvent, adjusting the pH value to 3.5-4.5, and grinding to obtain the phosphate-based precursor slurry.

[0041] Furthermore, the amount of iron source, phosphorus source and lithium source added is such that the molar ratio of Fe, P and Li elements in the phosphate precursor slurry is 1:0.9-1.1:1.02-1.05.

[0042] Furthermore, the solvent is water. It should be noted that the present invention does not have special requirements on the amount of solvent added, as long as it is sufficient to dissolve the iron source, phosphorus source, and lithium source. Even further, a dispersant is added in step S1, the amount of which is 0.5wt%-2wt% of the solvent, and the dispersant is at least one of polyethylene glycol and citric acid.

[0043] According to some preferred embodiments of the present invention, in step S1, the solid content of the phosphate-based precursor slurry is 35wt%-45wt%. Under these preferred conditions, the resulting spherical phosphate-based cathode material exhibits superior performance.

[0044] According to some preferred embodiments of the present invention, in step S1, the particle size distribution of the particles in the phosphate-based precursor slurry satisfies: Dv50 is 0.5µm-1µm, and Dv100 is 2µm-5.5µm. Under these preferred conditions, the resulting spherical phosphate-based cathode material exhibits superior performance.

[0045] In step S2, the free-fall motion occurs at a height of 1.5m-3m. Under these preferred conditions, the resulting spherical phosphate-based cathode material exhibits superior performance.

[0046] In step S2, the droplet size is 10µm-100µm. More preferably, the droplet size varies, which can be adjusted according to the particle size distribution requirements in actual production. Under this preferred condition, the resulting spherical phosphate-based cathode material exhibits superior performance.

[0047] In step S2, the temperature of the heating treatment is 180℃-220℃, and the thermal radiation method is infrared heating.

[0048] In step S3, the sintering process is carried out in a protective gas, which is at least one of nitrogen and an inert gas. The sintering process includes a heating process and a isothermal process. The heating rate is 3-8℃ / min, the isothermal temperature is 750℃-850℃, and the isothermal time is 8h-12h.

[0049] A second aspect of the present invention provides a microgravity granulation apparatus for carrying out the aforementioned preparation method, such as... Figure 4 As shown, it includes: a tower body 1, the tower body 1 having a channel inside that falls along the direction of gravity, for the droplets to undergo a free-fall motion;

[0050] Atomizing nozzle 2 is disposed at the top of the tower body 1 and is used to atomize the phosphate precursor slurry into droplets;

[0051] A thermal radiation heating device 3 is installed on the side wall of the tower body 1 and is used to heat the droplets that are in a free-fall motion inside the tower body 1.

[0052] And a vacuum system 4, connected to the tower body 1, for maintaining the vacuum level inside the tower body 1.

[0053] The microgravity granulation equipment provided in the second aspect of this invention, through the structural synergy of the tower space, vacuum system, and thermal radiation device, provides hardware support for the large-scale production of high-quality cathode materials. An ideal physical field is constructed: the vertical tower, combined with the vacuum system, not only provides the necessary free-fall path but also eliminates the droplet adhesion and collision problems common in traditional tubular equipment, ensuring the consistency of particle morphology. Heating is precise and uniform: the thermal radiation heating device located on the side wall avoids the turbulence interference caused by traditional hot air drying, achieving integral and rapid drying of droplets through the radiation penetration effect. This effectively prevents premature crusting on the particle surface, which could lead to internal pressure bursting and ensure the sphericity of the secondary particles.

[0054] Preferably, the effective drop height of the channel is 1.5m-3m.

[0055] Preferably, the nozzle orifice diameter of the atomizing nozzle 2 is 10μm-100μm. More preferably, such as... Figure 5 As shown, there are multiple atomizing nozzles 2, and the specific number is determined according to actual production needs. For example, the number of atomizing nozzles 2 is 10, 100, or 1000.

[0056] According to some preferred embodiments of the present invention, the plurality of atomizing nozzles 2 have the same aperture size and are used to synthesize and produce cathode materials with the same particle size.

[0057] According to other preferred embodiments of the present invention, the aperture sizes of the plurality of atomizing nozzles 2 are different to meet the requirements of particle size distribution of positive electrode materials in actual production, and to synthesize positive electrode materials with different particle sizes.

[0058] According to some preferred embodiments of the present invention, the thermal radiation heating device 3 is an infrared heater, which is arranged around the side wall of the tower body 1. More preferably, the infrared heater is arranged in segments along the height direction of the tower body 1.

[0059] According to some preferred embodiments of the present invention, the vacuum system 4 includes a vacuum pump assembly and a vacuum interface connected to the side wall of the tower body 1.

[0060] According to some preferred embodiments of the present invention, such as Figure 6 As shown, the bottom of the tower body 1 is provided with a particle collection bin 5, which is used to receive secondary particles that have fallen freely and been dried. More preferably, the particle collection bin 5 is a conical receiving bin, and the bottom of the conical receiving bin is connected to an airlock discharge valve. When it is necessary to discharge the secondary particles, the air supply pressure is reduced, causing the secondary particles to flow through the valve outlet.

[0061] According to some preferred embodiments of the present invention, a pressure sensor is also provided at the top of the tower body 1. The pressure sensor is electrically connected to the controller of the vacuum system 4 and is used to monitor and adjust the vacuum level inside the tower in real time.

[0062] According to some preferred embodiments of the present invention, such as Figure 6 As shown, the front end of the atomizing nozzle 2 is also connected to a slurry delivery system 6. More preferably, the slurry delivery system includes a slurry storage tank and a delivery pump connected in sequence. The slurry storage tank is used to store the cathode material precursor slurry, and the delivery pump is used to deliver the cathode material precursor slurry to the atomizing nozzle 2.

[0063] According to some preferred embodiments of the present invention, such as Figure 6 As shown, the side wall of the tower body 1 is also provided with an observation window 7, which is used to monitor the free fall and spherical contraction state of the droplets after atomization by the atomizing nozzle 2 in the tower body 1. More preferably, the observation window 7 is made of high-temperature resistant quartz glass and is sealed to the observation hole of the tower body 1 by flange fasteners.

[0064] A third aspect of the present invention provides a spherical phosphate-based cathode material prepared by the aforementioned preparation method, wherein the spherical phosphate-based cathode material has a near-spherical shape. Further, the bulk density of the spherical phosphate-based cathode material is ≥1.7 g / cm³.

[0065] The third aspect of this invention provides a spherical phosphate-based cathode material exhibiting a near-spherical morphology, with smooth and uniformly distributed particle surfaces, significantly improved packing density, and an electrode compaction density reaching 2.6 g / cm³-2.8 g / cm³, thereby enhancing the volumetric energy density of the battery. Simultaneously, a highly efficient intrinsic conductive network is constructed within the material, significantly reducing the contact resistance within the particles. Experimental data show that this material possesses extremely high discharge specific capacity (0.1C ≥ 159 mAh / g) and excellent rate performance (10C retention ≥ 95%), significantly improving the performance of phosphate-based materials under high-current charge and discharge conditions.

[0066] The present invention will be described in detail below through examples. In the following examples, unless otherwise specified, the experimental instruments and raw materials involved are all commercially available products.

[0067] Example 1

[0068] The specific steps for preparing spherical phosphate-based cathode material A1 are as follows:

[0069] S1: A lithium iron phosphate precursor slurry is provided, which is prepared by dissolving an iron source, a phosphorus source, and a lithium source in a solvent, adjusting the pH value to 4, adding a dispersant, and grinding the mixture using a sand mill to obtain the lithium iron phosphate precursor slurry; wherein the solid content of the lithium iron phosphate precursor slurry is 40 wt%, and the particle size distribution of the particles in the lithium iron phosphate precursor slurry satisfies: Dv50 is 0.7 µm, and Dv100 is 3.1 µm;

[0070] The iron source and phosphorus source are both iron phosphate, and the lithium source is lithium carbonate. The amount of iron source, phosphorus source and lithium source added is such that the molar ratio of Fe, P and Li elements in the lithium iron phosphate precursor slurry is 1:1:1, and the amount of iron phosphate is 3 kg, the solvent is water, the amount of water is 6 kg, and the dispersant is citric acid, the amount of which is 1 wt% of water.

[0071] S2: The lithium iron phosphate precursor slurry is atomized into droplets, and the droplets are subjected to a near-free fall motion. During the fall, the droplets shrink into spheres under the action of surface tension and are dried to obtain spherical lithium iron phosphate precursor particles.

[0072] This step is as follows: Figure 4 The microgravity granulation process is carried out in the microgravity granulation apparatus shown, which includes:

[0073] Tower body 1, the tower body 1 has an internal channel for falling along the direction of gravity, the effective falling height of the channel is 2m;

[0074] Atomizing nozzle 2 is disposed at the top of the tower body 1. The nozzle orifice diameter of the atomizing nozzle 2 is 10µm-100µm, and the number of atomizing nozzles 2 is 100. The number of atomizing nozzles 2 with different orifice diameters follows a normal distribution.

[0075] The thermal radiation heating device 3 is an infrared heater, which is arranged around the side wall of the tower body 1 to heat the precursor slurry droplets falling along the direction of gravity in the channel. The temperature adjustment range of the infrared heater is:

[0076] And a vacuum system 4, which is connected to the tower body 1, the vacuum system 4 including a vacuum pump set and a vacuum interface connected to the side wall of the tower body 1.

[0077] Specifically, the lithium iron phosphate precursor slurry is atomized into droplets of 10μm-100μm through atomizing nozzle 2. The droplets fall along the direction of gravity through a channel inside the tower body 1. The channel is cylindrical with an inner diameter of 1.5m and a height of 2m (that is, the effective falling height of the droplets is 2m). The initial velocity of the droplets is 3cm / s. The droplets are heated to 200℃ by a thermal radiation heating device 3. The vacuum degree inside the tower body 1 is maintained at -0.095MPa by a vacuum system.

[0078] S3: The spherical lithium iron phosphate precursor particles are sintered to obtain spherical lithium iron phosphate cathode material, denoted as A1;

[0079] Specifically, the sintering process is carried out in a nitrogen atmosphere and includes a heating process and a isothermal process. The heating rate is 5°C / min, the isothermal temperature is 800°C, and the isothermal time is 10h.

[0080] Example 2

[0081] The specific steps for preparing spherical phosphate-based cathode material A2 are as follows:

[0082] S1: A lithium manganese iron phosphate precursor slurry is provided, which is prepared by dissolving an iron source, a manganese source, a phosphorus source and a lithium source in a solvent, adjusting the pH value to 4, adding a dispersant, and grinding the mixture using a sand mill to obtain the lithium manganese iron phosphate precursor slurry; wherein, the solid content of the lithium manganese iron phosphate precursor slurry is 40wt%, and the volume average particle size of the particles in the lithium manganese iron phosphate precursor slurry meets the following requirements: Dv50 is 0.67µm, and Dv100 is 5.2µm;

[0083] The iron and phosphorus sources are both iron phosphate, the manganese source is manganese carbonate, and the lithium source is lithium carbonate. The amount of iron, manganese, phosphorus, and lithium sources added is such that the molar ratio of Fe, Mn, P, and Li elements in the lithium manganese iron phosphate precursor slurry is 0.6:0.4:1:1. The amount of iron phosphate used is 3 kg, the solvent is water, the amount of water used is 6 kg, and the dispersant is polyethylene glycol, the amount of which is 1 wt% of water.

[0084] S2: The lithium manganese iron phosphate precursor slurry is atomized into droplets, and the droplets are subjected to a near-free fall motion. During the fall, the droplets shrink into spheres under the action of surface tension and are dried to obtain spherical lithium manganese iron phosphate precursor particles.

[0085] This step is as follows: Figure 4 The microgravity granulation process is carried out in the microgravity granulation apparatus shown, which includes:

[0086] Tower body 1, the tower body 1 has an internal channel for falling along the direction of gravity, the effective falling height of the channel is 2m;

[0087] Atomizing nozzle 2 is disposed at the top of the tower body 1. The nozzle orifice diameter of the atomizing nozzle 2 is 10µm-100µm, and the number of atomizing nozzles 2 is 100. The number of atomizing nozzles 2 with different orifice diameters follows a normal distribution.

[0088] The thermal radiation heating device 3 is an infrared heater, which is arranged around the side wall of the tower body 1 to heat the precursor slurry droplets falling along the direction of gravity in the channel. The temperature adjustment range of the infrared heater is:

[0089] And a vacuum system 4, which is connected to the tower body 1, the vacuum system 4 including a vacuum pump set and a vacuum interface connected to the side wall of the tower body 1.

[0090] Specifically, the lithium manganese iron phosphate precursor slurry is atomized into droplets of 10μm-100μm through atomizing nozzle 2. The droplets fall along the direction of gravity through a channel inside the tower body 1. The channel is cylindrical with an inner diameter of 1.5m and a height of 2m (that is, the effective falling height of the droplets is 2m). The initial velocity of the droplets is 5cm / s. The droplets are heated to 200℃ by a thermal radiation heating device 3. The vacuum degree inside the tower body 1 is maintained at -0.095MPa by a vacuum system.

[0091] S3: The spherical lithium iron phosphate precursor particles are sintered to obtain spherical lithium manganese iron phosphate cathode material, denoted as A2;

[0092] Specifically, the sintering process is carried out in a nitrogen atmosphere and includes a heating process and a isothermal process. The heating rate is 5°C / min, the isothermal temperature is 800°C, and the isothermal time is 10h.

[0093] Example 3

[0094] Preparation of spherical phosphate-based cathode material A3:

[0095] The difference lies in the vacuum level maintained inside the tower 1 at -0.098 MPa using a vacuum system, and the height of the channel inside the tower 1 in the microgravity granulation equipment is adjusted to ensure an effective drop height of 1.5 m for the droplets. The remaining preparation process and specific parameters are the same as in Example 1, resulting in spherical lithium iron phosphate cathode material, denoted as A3.

[0096] Example 4

[0097] Preparation of spherical phosphate-based cathode material A4:

[0098] The difference lies in adjusting the height of the channel inside tower 1 of the microgravity granulation equipment so that the effective droplet falling height is 1.2m. The remaining preparation process and specific parameters are the same as in Example 1, resulting in spherical lithium iron phosphate cathode material, denoted as A4.

[0099] Example 5

[0100] Preparation of spherical phosphate-based cathode material A5:

[0101] The difference is that the solid content of the phosphate precursor slurry is adjusted to 30 wt%. The rest of the preparation process and specific parameters are the same as in Example 1, and spherical lithium iron phosphate cathode material is obtained, denoted as A5.

[0102] Comparative Example 1

[0103] Preparation of spherical phosphate-based cathode material B1:

[0104] The difference is that the initial velocity of the droplet is 10 cm / s, and the vacuum system 1 is closed, so the near-free fall motion takes place under normal pressure. The rest of the preparation process and specific parameters are the same as in Example 1, and a spherical lithium iron phosphate cathode material is obtained, denoted as B1.

[0105] Test case

[0106] The spherical phosphate-based cathode materials prepared in the above examples and comparative examples were subjected to performance tests. The test methods are as follows, and the specific test results are shown in Table 1 below.

[0107] 1. Bulk Density Test Method: Weigh out spherical phosphate-based cathode material samples prepared in the above examples and comparative examples, denoted as m1 (20g), and carefully pour them into a graduated cylinder with a volume of V0 (25mL) through a funnel. Observe and record the initial loose volume of the sample. Fix the graduated cylinder on a tapped density tester, set the amplitude to 3mm, and the vibration frequency to 250 times / min, and vibrate continuously until the volume no longer changes. Read and record the volume V1 of the sample after tapping. Calculate the bulk density of the sample according to the formula ρ1=m1 / V1.

[0108] 2. The method for testing compaction density is as follows: Take 5g of the spherical phosphate-based cathode material sample prepared in the above examples and comparative examples, pour it into a steel mold with a diameter (Φ) of 10mm, and press it at 10MPa. -1 The pressure was uniformly increased to 100 MPa and held for 30 seconds. After depressurization, the thickness h and mass m of the compacted blank were measured, and the compaction density ρ2 = 4m / (πΦ²h) was calculated.

[0109] 3. The method for testing the resistivity of powder is as follows: Take 2g of lithium iron phosphate cathode material samples with a diameter of 16mm prepared in the above examples and comparative examples respectively, tap them gently to flatten them, apply a constant pressure of 10 MPa for 30s, directly read the resistance value R of the four-probe resistance meter, and calculate the resistivity of the powder according to the built-in formula of the instrument.

[0110] 4. Electrochemical performance testing: The spherical phosphate-based cathode materials prepared in the above examples and comparative examples were assembled into lithium-ion batteries according to the following methods, and 0.1C and 10C discharge capacity tests and 500-cycle capacity retention tests were performed:

[0111] Positive electrode: Spherical phosphate-based positive electrode material was prepared into a uniform slurry with a mass ratio of spherical phosphate-based positive electrode material: carbon black: PVDF = 80:10:10, using N-methylpyrrolidone as a solvent. The positive electrode slurry was coated on the surface of aluminum foil, vacuum dried overnight at 110°C, and then rolled to obtain the positive electrode sheet. The rolling process parameters were: rolling temperature 45 °C, linear pressure 200 N / mm, roll gap 80µm, and rolling speed 1m / min.

[0112] Negative electrode: Lithium metal sheet;

[0113] Electrolyte: solute is LiPF6, solvent is ethylene carbonate (EC) and diethyl carbonate (DEC), concentration is 1.0 mol / L, EC:DEC volume ratio = 1:1;

[0114] Diaphragm: Polypropylene microporous diaphragm;

[0115] Lithium-ion battery assembly: Assemble button-type lithium-ion full cells in an inert atmosphere glove box according to the assembly sequence of lithium metal sheet-separator-electrolyte-positive electrode sheet.

[0116] Table 1

[0117]

[0118] As can be seen from the results in the table above, this invention simulates a suspended microgravity field by constructing a near-free fall environment under a specific vacuum level, fundamentally changing the drying dynamics of droplets, eliminating external deformation interference, and simultaneously achieving structural densification. This results in highly spherical phosphate-based cathode materials with higher compaction density, lower powder resistivity, and superior electrochemical performance.

[0119] This invention provides, by way of example, SEM images of the spherical lithium iron phosphate cathode material prepared in Example 1 of this invention (see [link]). Figure 1 SEM image of the lithium manganese iron phosphate cathode material prepared in Example 2 (see below). Figure 2 SEM image of the spherical lithium iron phosphate cathode material prepared in Comparative Example 1 (see below). Figure 3 ),from Figure 1 , Figure 2 and Figure 3 The comparison clearly shows that the spherical phosphate-based cathode material prepared by the method provided in this invention has a higher sphericity and is nearly spherical.

[0120] 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 spherical phosphate-based cathode material, characterized in that, Includes the following steps: S1: Provides phosphate-based precursor slurry; S2: The phosphate precursor slurry is atomized into droplets, and the droplets are subjected to a near-free fall motion. During the fall, the droplets are contracted into spheres by surface tension and dried to obtain spherical phosphate precursor particles. S3: The spherical phosphate precursor particles are sintered to obtain a spherical phosphate cathode material; In step S2, the free-fall motion must meet at least the following conditions: the initial velocity of the droplet does not exceed 5 cm / s, the vacuum degree is -0.095 MPa to -0.098 MPa, and the falling process is heated by thermal radiation, with the temperature of the heating treatment being 180℃ to 220℃.

2. The production method according to claim 1, characterized by, In step S2, the falling height of the free-fall motion is 1.5m-3m.

3. The preparation method according to claim 1, characterized in that, In step S2, the droplet size is 10µm-100µm.

4. The method of claim 1, wherein, In step S2, the thermal radiation method is an infrared heating method.

5. The method of any one of claims 1-4, wherein, In step S1, the solid content of the phosphate-based precursor slurry is 35wt%-45wt%. Alternatively, in step S1, the particle size distribution of the particles in the phosphate precursor slurry satisfies: Dv50 is 0.5µm-1µm, and Dv100 is 2µm-5.5µm.

6. The preparation method according to any one of claims 1-4, characterized in that, In step S1, the phosphate-based precursor slurry includes at least one of lithium iron phosphate precursor slurry, lithium manganese phosphate precursor slurry, lithium manganese iron phosphate precursor slurry, and lithium sodium iron phosphate precursor slurry.

7. The preparation method according to any one of claims 1-4, characterized in that, In step S3, the sintering process is carried out in a protective gas and includes a heating process and a isothermal process. The heating rate is 3-8℃ / min, the isothermal temperature is 750℃-850℃, and the isothermal time is 8h-12h.

8. A spherical phosphate-based cathode material prepared by the method according to any one of claims 1-7, characterized in that, The spherical phosphate-based cathode material is spherically shaped.

9. The spherical phosphate-based cathode material according to claim 8, characterized in that, The bulk density of the spherical phosphate-based cathode material is ≥1.7 g / cm³.

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