Spheroidized phosphate positive electrode material and preparation method thereof

Abstract

The invention relates to the technical field of positive electrode materials, and discloses a spheroidized phosphate positive electrode material and a preparation method thereof. The preparation method comprises the following steps: atomizing phosphate precursor slurry into liquid drops, enabling the liquid drops to do free-fall-like motion under a specific vacuum degree, enabling the liquid drops to shrink under the action of surface tension in the falling process, and heating and drying through thermal radiation to obtain spherical phosphate precursor particles, and sintering to obtain the spheroidized phosphate positive electrode material. According to the method, a suspension microgravity field is simulated by constructing a free-fall-like stroke in a high-vacuum environment, the shear interference of a traditional current-carrying gas field on the morphology of liquid drops and segregation deformation caused by gravity settling are eliminated, the shrinkage effect of surface tension of the liquid drops is brought into full play, extreme close packing is achieved, and the liquid drops can be fully deposited. And the prepared spheroidized phosphate positive electrode material has better comprehensive performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of positive electrode materials, in particular to a spherical phosphate-based positive electrode material and a preparation method thereof. BACKGROUND

[0002] Phosphate-based positive electrode materials (such as LiMPO4, 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, such materials generally have low electronic conductivity and limited ion diffusion path, and their morphology characteristics have a decisive influence on the processing performance of the electrode and the volumetric energy density of the battery. In order to improve the performance of phosphate-based materials, achieving the spheroidization of particles is an effective means recognized by the field.

[0003] At present, there is a method for preparing spherical positive electrode materials by atomization in the prior art (such as CN105336929B). This technology atomizes a solution containing lithium salt, metal salt and phosphate salt into small droplets, and drives the droplets into a horizontally or obliquely arranged tubular furnace (such as a quartz tube or a corundum tube) for drying and solidification by using a vacuum pumping system. However, this prior art still has obvious limitations in preparing high-performance spherical phosphate materials:

[0004] 1. Interference and damage to the regularity of the morphology by the carrier flow field: In this scheme, the moving height of the droplets depends on the carrier flow generated by the vacuum pumping system, and the droplets move at a forward speed in the narrow cavity of the tubular furnace. In this carrier gas field, the droplets are easily deformed by uneven shear force, and are prone to collide with the tube wall, causing particle breakage or out-of-roundness, making it difficult to obtain spherical particles with high roundness.

[0005] 2. Component segregation and deformation induced by gravity: The tubular furnace of the prior art is usually horizontally arranged, and the droplets are always subjected to constant vertical downward gravity during horizontal movement. During the process of dehydrating and solidifying the droplets, gravity will cause the internal components of the droplets to segregate and settle, resulting in uneven internal structure of the generated secondary particles, and even forming non-spherical particles due to collapse, which seriously affects the bulk density of the material (usually less than 1.6 g / cm³).

[0006] 3. Non-ideal drying kinetic environment: Although the prior art mentions a vacuum pumping system, its essence is to act as a carrier medium, and the inside of the tubular furnace is not in a high-vacuum static environment, and the droplets are still affected by air resistance during falling / moving.

[0007] Therefore, how to overcome the current technology of current-carrying interference and gravity influence, provide a preparation method capable of realizing high sphericity, super high bulk density and excellent conductive network synergistic improvement of phosphate-based positive electrode material, is the current positive electrode material field to be solved. SUMMARY

[0008] One of the purposes of the present application is to solve the problem of low sphericity and low bulk density of lithium iron phosphate material in the prior art.

[0009] The second purpose of the present application is to provide a preparation method of spheroidized phosphate-based positive electrode material, and the prepared spheroidized phosphate-based positive electrode material has high sphericity, high bulk density, high compaction and excellent electrochemical performance.

[0010] In order to achieve the above-mentioned purpose, the first aspect of the present application provides a preparation method of spheroidized phosphate-based positive electrode material, comprising the following steps:

[0011] S1: providing a phosphate-based precursor slurry;

[0012] S2: atomizing the phosphate-based precursor slurry into droplets, and making the droplets perform a quasi-free fall motion, the droplets shrink into a ball and dry in the falling process under the action of surface tension, to obtain spheroidized phosphate-based precursor particles;

[0013] S3: sintering the spheroidized phosphate-based precursor particles to obtain a phosphate-based positive electrode material;

[0014] In step S2, the quasi-free fall motion at least meets the following conditions: the initial speed of the droplets is not more than 5 cm / s, the vacuum degree is negative 0.095 MPa-negative 0.098 MPa, and the falling process is heated by a thermal radiation method.

[0015] The second aspect of the present application provides a microgravity granulation device for implementing the above-mentioned preparation method, comprising: a tower body, the inside of the tower body is provided with a channel falling along the gravity direction, for the quasi-free fall motion of the droplets;

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

[0017] A thermal radiation heating device is arranged on the side wall of the tower body, for heating the droplets performing quasi-free fall motion in the tower body;

[0018] And a vacuum system connected with the tower body, for maintaining the vacuum degree inside the tower body.

[0019] The third aspect of the present application provides a spherical phosphate-based positive electrode material prepared by the above method, wherein the spherical phosphate-based positive electrode material has a shape of a quasi-spherical body.

[0020] Advantages:

[0021] The preparation method provided by the first aspect of the present application fundamentally changes the drying dynamics process of the liquid droplets by constructing a quasi-free-fall environment under a specific vacuum degree to simulate a suspended microgravity field, eliminates external deformation interference, and simultaneously realizes the densification of the structure, so that the prepared phosphate-based positive electrode material is highly spherical, the bulk density is greater than or equal to 1.7 g / cm3, which is 12%-15% higher than that of the traditional method, 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 less than or equal to 10 Ω·cm, the 0.1C discharge capacity is greater than or equal to 156 mAh / g, the 10C high-rate discharge capacity is greater than or equal to 105%, and the capacity attenuation rate is less than or equal to 5% after 500 cycles.

[0022] The microgravity granulation device for implementing the above preparation method provided by the second aspect of the present application constructs an ideal physical field by the cooperation of the structure of the tower space, the vacuum system and the heat radiation device, not only provides the necessary free-fall travel, but also eliminates the problem of liquid droplet wall hanging and collision commonly found in traditional tubular devices, ensures the consistency of the particle morphology, the heat radiation heating device arranged on the side wall avoids the turbulent interference caused by traditional hot air drying, realizes the overall and rapid drying of the liquid droplets through the radiation penetration effect, effectively prevents the internal pressure burst caused by the premature crust on the surface of the particles, ensures the roundness of the secondary particles, and provides a hardware guarantee for the large-scale production of high-quality positive electrode materials.

[0023] The third aspect of the present application provides that the spherical phosphate-based positive electrode material has a quasi-spherical morphology, the particle surface is smooth and uniformly distributed, the bulk density is significantly improved, the compaction density can reach 2.6 g / cm3-2.8 g / cm3, and the volume energy density of the battery is enhanced; at the same time, an efficient intrinsic conductive network is constructed in the material, and the contact resistance in the particle is greatly reduced. Experimental data shows that the material has extremely high discharge specific capacity (0.1C≥159 mAh / g) and excellent rate performance (500-week capacity retention rate≥95%), which significantly improves the performance of the phosphate-based material under large-current charging and discharging. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 FIG. 1 is an SEM image of the spherical lithium iron phosphate positive electrode material prepared in Example 1, magnified 1000 times;

[0025] Figure 2 FIG. 2 is an SEM image of the spherical lithium manganese iron phosphate positive electrode material prepared in Example 2, magnified 1000 times;

[0026] Figure 3 is a SEM image of the spheroidized lithium iron phosphate positive electrode material prepared in Comparative Example 1, magnified by 1000 times;

[0027] Figure 4 is a structural schematic diagram of the micro-gravity granulation equipment provided by some embodiments of the present application;

[0028] Figure 5 is a structural schematic diagram of the atomizing nozzle provided by some embodiments of the present application;

[0029] Figure 6 is a structural schematic diagram of the micro-gravity granulation equipment provided by some embodiments of the present application. DETAILED DESCRIPTION

[0030] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The endpoints of the ranges and any values are understood to be approximate values. The exact numerical values of the endpoints of the ranges and any values are approximations that allow for a little variation either ways without resulting in a change in the basic function of the compositions or methods, or methods described herein. The exact numerical values of the endpoints of the ranges and any values are not to be construed in a manner against the applicant, but rather the preferred scope of equivalents based on reasonable expectation.

[0031] In the present application, unless otherwise specified, the room temperature or normal temperature all represent 25±2℃.

[0032] In the present application, Dv50 all represents the particle size value corresponding to the cumulative particle size distribution number of 50% of the granulation material, and Dv100 has a similar definition to Dv50, which will not be repeated here in the present application, and those skilled in the art should not understand it as a limitation on the present application.

[0033] As described above, the first aspect of the present application provides a preparation method of a spheroidized phosphate-based positive electrode material, comprising the following steps:

[0034] S1: providing a phosphate-based precursor slurry;

[0035] S2: atomizing the phosphate-based precursor slurry into droplets, and making the droplets perform a quasi-free-fall motion, the droplets shrink into spheres under the action of surface tension during falling and dry to obtain spheroidized phosphate-based precursor particles;

[0036] S3: sintering the spheroidized phosphate-based precursor particles to obtain a spheroidized phosphate-based positive electrode material;

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

[0038] The preparation method provided in the first aspect of the application simulates a suspended microgravity field by constructing a quasi-free-fall environment at a specific vacuum degree, fundamentally changes the drying dynamics process of the droplet, and reduces the air resistance and airflow shear force on the droplet to a very low level in a high-vacuum environment, so that the droplet can realize perfect centripetal contraction under the driving of only the surface tension, and the "hollow ball" or "apple-shaped" distortion caused by airflow interference in traditional spray drying is avoided. Meanwhile, the quasi-free-fall process provides sufficient self-assembly time for the phosphate active material particles in the droplet, and the solvent is uniformly removed from the inside to the outside under the uniform induction of the thermal radiation, so as to promote the close packing of the spheroidized phosphate precursor particles and improve the compactness of the precursor from the source.

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

[0040] According to a preferred embodiment of the application, the phosphate precursor slurry is a lithium iron phosphate precursor slurry, and step S1 is performed in the following manner but is not limited thereto: iron source, phosphorus source and lithium source are dissolved in a solvent, the pH value is adjusted to 3.5-4.5, and grinding treatment is performed to obtain the phosphate precursor slurry.

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

[0042] Further, the solvent is water, and it should be noted that the application does not have special requirements for the addition amount of the solvent, and the iron source, the phosphorus source and the lithium source can be dissolved. Further, a dispersant is further added in step S1, and the addition amount of the dispersant accounts for 0.5wt%-2wt% of the solvent. The dispersant is at least one of polyethylene glycol and citric acid.

[0043] According to some preferred embodiments of the application, in step S1, the solid content of the phosphate precursor slurry is 35wt%-45wt%. Under this preferred condition, the spheroidized phosphate positive electrode material has more excellent performance.

[0044] According to some preferred embodiments of the present application, in step S1, the particle size distribution of the particles in the phosphate precursor slurry satisfies: Dv50 is 0.5-1 µm, and Dv100 is 2-5.5 µm. Under this preferred condition, the spheroidized phosphate-based positive electrode material prepared has more excellent performance.

[0045] In step S2, the falling height of the free-fall-like motion is 1.5-3 m. Under this preferred condition, the spheroidized phosphate-based positive electrode material prepared has better performance.

[0046] In step S2, the particle size of the droplets is 10-100 µm. Further preferably, the particle sizes of the droplets are not uniform, and can be adjusted according to the need for particle grading in actual production. Under this preferred condition, the spheroidized phosphate-based positive electrode material prepared has better performance.

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

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

[0049] The second aspect of the present application provides a microgravity granulation device for implementing the above preparation method, as shown in Figure 4 The device includes a tower body 1, which is internally provided with a channel for falling in the direction of gravity, for the free-fall-like motion of the droplets.

[0050] An atomizing nozzle 2 is arranged at the top of the tower body 1, for atomizing the phosphate precursor slurry into droplets.

[0051] A heat radiation heating device 3 is arranged on the side wall of the tower body 1, for heating the droplets in the free-fall-like motion in the tower body 1.

[0052] A vacuum system 4 is connected to the tower body 1, for maintaining the vacuum degree 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 application, the top of the tower body 1 is further provided with a pressure sensor, which is electrically connected with the controller of the vacuum system 4, for monitoring and adjusting the vacuum degree in the tower in real time.

[0062] According to some preferred embodiments of the present application, as shown in Figure 6 Further preferably, the slurry delivery system comprises a slurry storage tank and a delivery pump connected in sequence, the slurry storage tank is used for storing the positive material precursor slurry, and the delivery pump is used for delivering the positive material precursor slurry to the atomizing nozzle 2.

[0063] According to some preferred embodiments of the present application, as shown in Figure 6 Further preferably, the material of the observation window 7 is high-temperature-resistant quartz glass, and the observation window 7 is sealingly connected with the observation hole of the tower body 1 through a flange fastener.

[0064] The third aspect of the present application provides a spheroidized phosphate-based positive material prepared by the above preparation method, wherein the spheroidized phosphate-based positive material has a shape of quasi-spherical body. Further, the spheroidized phosphate-based positive material has a bulk density of ≥1.7 g / cm3.

[0065] The third aspect of the present application provides that the spheroidized phosphate-based positive material has a quasi-spherical body morphology, a smooth and uniform particle surface, a significantly improved bulk density, and an electrode compaction density of 2.6 g / cm3-2.8 g / cm3, thereby enhancing the volume energy density of the battery. At the same time, a high-efficiency intrinsic conductive network is constructed inside the material, thereby greatly reducing the contact resistance inside the particles. Experimental data show that the material has a very high discharge specific capacity (0.1C≥159 mAh / g) and excellent rate performance (10C retention rate≥95%), thereby significantly improving the performance of the phosphate-based material under large-current charging and discharging.

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

[0067] Example 1

[0068] A spheroidized phosphate-based positive material A1 was prepared, and the specific steps were as follows:

[0069] S1: providing a lithium iron phosphate precursor slurry, which is prepared in the following manner: dissolving an iron source, a phosphorus source and a lithium source in a solvent, adjusting the pH value to 4, adding a dispersing agent, 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 the phosphorus source are both iron phosphate, the lithium source is lithium carbonate, the addition amount of the iron source, the phosphorus source and the lithium source is such that the molar ratio of Fe element, P element and Li element in the lithium iron phosphate precursor slurry is 1:1:1, and the amount of the iron phosphate is 3 kg, the solvent is water, the amount of water is 6 kg, the dispersing agent is citric acid, and the amount is 1 wt% of water.

[0071] S2: atomizing the lithium iron phosphate precursor slurry into droplets, and making the droplets perform a quasi-free fall motion, the droplets shrink into spheres and dry in the falling process under the action of surface tension, to obtain spherical lithium iron phosphate precursor particles.

[0072] This step is carried out in a microgravity granulation device as shown in Figure 4 The microgravity granulation device comprises:

[0073] A tower body 1, which is internally provided with a channel falling in the direction of gravity, and the effective falling height of the channel is 2 m;

[0074] An atomizing nozzle 2, which is arranged at the top of the tower body 1, and the nozzle aperture of the atomizing nozzle 2 is 10 µm-100 µm, and the number of the atomizing nozzles 2 is 100, and the number of atomizing nozzles 2 with different apertures is normally distributed;

[0075] A heat radiation heating device 3, which is an infrared heater, and is arranged around the side wall of the tower body 1, and is used for heating the precursor slurry droplets falling in the direction of gravity in the channel, and the temperature adjustment range of the infrared heater is 100-500 ℃;

[0076] And a vacuum system 4, which is connected with the tower body 1, and the vacuum system 4 comprises a vacuum pump group 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 with a size of 10 µm-100 µm by the atomizing nozzle 2, the droplets fall in the direction of gravity along the channel in the tower body 1, the channel is cylindrical, the inner diameter is 1.5 m, and the height is 2 m (i.e., the effective falling height of the droplets is 2 m), the initial speed of the droplets is 3 cm / s, the droplets are heated by the heat radiation heating device 3, the temperature is 200 ℃, and the vacuum degree inside the tower body 1 is maintained at -0.095 MPa by the vacuum system.

[0078] S3: sintering treatment is performed on the spheroidized lithium iron phosphate precursor particles to obtain a spheroidized lithium iron phosphate positive electrode material, denoted as A1;

[0079] Specifically, the sintering treatment is performed in a nitrogen atmosphere, including a temperature rising treatment and a constant temperature treatment, the temperature rising treatment has a rate of 5℃ / min, and the constant temperature treatment has a temperature of 800℃ and a constant temperature time of 10h.

[0080] Example 2

[0081] A spheroidized phosphate-based positive electrode material A2 is prepared, and the specific steps are as follows:

[0082] S1: A lithium manganese iron phosphate precursor slurry is provided, and is prepared in the following manner: iron source, manganese source, phosphorus source and lithium source are dissolved in a solvent, the pH value is adjusted to 4, a dispersing agent is added, and a sand mill is used for grinding treatment 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 satisfies: Dv50 is 0.67µm, and Dv100 is 5.2µm;

[0083] The iron source and the phosphorus source are both iron phosphate, the manganese source is manganese carbonate, the lithium source is lithium carbonate, and the addition amount of the iron source, the manganese source, the phosphorus source and the lithium source makes the molar ratio of Fe element, Mn element, P element and Li element in the lithium manganese iron phosphate precursor slurry be 0.6:0.4:1:1, and the amount of the iron phosphate is 3kg, the solvent is water, the amount of water is 6kg, the dispersing agent is polyethylene glycol, and the amount is 1wt% of water.

[0084] S2: The lithium manganese iron phosphate precursor slurry is atomized into droplets, and the droplets are subjected to a free-fall-like motion, the droplets are shrunk into balls under the action of surface tension during falling and dried to obtain spheroidized lithium manganese iron phosphate precursor particles.

[0085] This step is carried out in a microgravity granulation equipment as shown in the figure. Figure 4 The microgravity granulation equipment includes:

[0086] A tower body 1, which is internally provided with a channel falling along the direction of gravity, and the effective falling height of the channel is 2m;

[0087] An atomizing nozzle 2 is arranged at the top of the tower body 1, the nozzle aperture of the atomizing nozzle 2 is 10µm-100µm, the number of the atomizing nozzles 2 is 100, and the number of atomizing nozzles 2 with different apertures is normally distributed;

[0088] The heat radiation heating device 3 is an infrared heater, which is arranged around the side wall of the tower body 1, and is used to heat the precursor slurry droplets falling along the gravity direction in the channel. The temperature adjustment range of the infrared heater is 200-800℃.

[0089] The vacuum system 4 is connected with the tower body 1, and comprises a vacuum pump group 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 with a size of 10-100μm by the atomizing nozzle 2, and the droplets fall along the gravity direction in the channel inside the tower body 1. The channel is cylindrical, with an inner diameter of 1.5m and a height of 2m (i.e., the effective falling height of the droplets is 2m). The initial speed of the droplets is 5cm / s. The droplets are heated by the heat radiation heating device 3, and the temperature is 200℃. The vacuum degree inside the tower body 1 is maintained at -0.095MPa by the vacuum system.

[0091] S3: The spheroidized lithium iron phosphate precursor particles are subjected to a sintering treatment to obtain a spheroidized lithium manganese iron phosphate positive electrode material, which is denoted as A2.

[0092] Specifically, the sintering treatment is carried out in a nitrogen atmosphere, and comprises a temperature rising treatment and a constant temperature treatment. The temperature rising treatment is carried out at a rate of 5℃ / min, and the constant temperature treatment is carried out at a temperature of 800℃ for 10h.

[0093] Example 3

[0094] The spheroidized lithium iron phosphate positive electrode material A3 is prepared as follows:

[0095] The difference is that the vacuum degree inside the tower body 1 is maintained at -0.098MPa by the vacuum system, and the height of the channel inside the tower body 1 in the micro-gravity granulation equipment is adjusted so that the effective falling height of the droplets is 1.5m. The rest of the preparation process and the specific parameters are the same as those in Example 1, and the spheroidized lithium iron phosphate positive electrode material A3 is obtained.

[0096] Example 4

[0097] The spheroidized lithium iron phosphate positive electrode material A4 is prepared as follows:

[0098] The difference is that the height of the channel inside the tower body 1 in the micro-gravity granulation equipment is adjusted so that the effective falling height of the droplets is 1.2m. The rest of the preparation process and the specific parameters are the same as those in Example 1, and the spheroidized lithium iron phosphate positive electrode material A4 is obtained.

[0099] Example 5

[0100] The spheroidized lithium iron phosphate positive electrode material A5 is prepared as follows:

[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 Example 1, and a spherical phosphate-based positive electrode material is prepared, which is denoted as A5.

[0102] Comparative Example 1

[0103] Preparation of a spherical phosphate-based positive electrode material B1:

[0104] The difference is that the initial speed of the liquid droplets is 10 cm / s, the vacuum system 1 is closed, and the quasi-free fall is carried out at normal pressure. The rest of the preparation process and specific parameters are the same as Example 1, and a spherical lithium iron phosphate positive electrode material is prepared, which is denoted as B1.

[0105] Test Example

[0106] The spherical phosphate-based positive electrode materials prepared in the above examples and comparative examples are tested for performance, and the test method is as follows. The specific test results are shown in Table 1 below.

[0107] 1. The test method for the bulk density is as follows: the spherical phosphate-based positive electrode material sample prepared in the above examples and comparative examples is weighed as m1 (20 g), and is carefully poured into a graduated cylinder with a volume of V0 (25 mL) through a funnel. The initial loose volume of the sample is observed and recorded. The graduated cylinder is fixed on a tap density tester, the amplitude is set to 3 mm, the vibration frequency is 250 times / min, and continuous vibration is carried out until the volume no longer changes. The volume of the sample after vibration V1 is read and recorded. The bulk density of the sample is calculated according to the formula p1 = m1 / V1.

[0108] 2. The test method for the tap density is as follows: 5 g of the spherical phosphate-based positive electrode material prepared in the above examples and comparative examples is poured into a steel mold with a diameter (Φ) of 10 mm, and is uniformly pressed to 100 MPa at a pressure of 10 MPa. The pressure is maintained for 30 s, and the thickness h and mass m of the compact are measured after the pressure is released. The tap density p2 = 4m / (pΦ²h) is calculated. -1

[0109] 3. The test method for the powder resistivity is as follows: 2 g of the lithium iron phosphate positive electrode material prepared in the above examples and comparative examples is placed in a four-probe mold with a diameter of 16 mm, and is leveled by tapping. The voltage is kept at 10 MPa for 30 s, and the resistance value R of the four-probe resistance meter is directly read. The powder resistivity is calculated according to the built-in formula of the instrument.

[0110] 4. Electrochemical performance test: the spherical phosphate-based positive electrode materials prepared in the above examples and comparative examples are assembled into lithium ion batteries according to the following methods, and are tested for 0.1C, 10C discharge capacity and 500 cycle capacity retention rate: ​

[0111] Positive electrode: the spheroidized phosphate-based positive electrode material is mixed into a uniform slurry according to a mass ratio of spheroidized phosphate-based positive electrode material: carbon black: PVDF = 80: 10: 10, with N-methylpyrrolidone as a solvent, the positive electrode slurry is coated on the surface of an aluminum foil, vacuum dried at 110 DEG C overnight, and roll-pressed to obtain a positive electrode sheet, wherein the roll-pressing process parameters are: roll-pressing temperature 45 DEG C, linear pressure 200 N / mm, roll gap 80 mu m, and roll-pressing speed 1 m / min;

[0112] Negative electrode: a lithium metal sheet;

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

[0114] Separator: a polypropylene microporous separator;

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

[0116] Table 1

[0117] As can be seen from the above table, the present application simulates a suspended microgravity field by constructing a free-fall-like environment at a specific vacuum degree, fundamentally changes the drying dynamics process of the liquid droplets, eliminates external deformation interference, and simultaneously realizes the densification of the structure, so that the prepared phosphate-based positive electrode material is highly spheroidized, has a higher compaction density, a lower powder resistivity, and more excellent electrochemical performance.

[0118] The present application exemplarily provides an SEM image of the spheroidized lithium iron phosphate positive electrode material prepared in Example 1 (see Figure 1 ), an SEM image of the lithium iron manganese phosphate positive electrode material prepared in Example 2 (see Figure 2 ), and an SEM image of the spheroidized lithium iron phosphate positive electrode material prepared in Comparative Example 1 (see Figure 3 ). Figure 1 , Figure 2 and Figure 3 It can be obviously seen from the comparison that the spheroidized phosphate-based positive electrode material prepared by the method provided by the present application has a higher spheroidization degree and is a quasi-spherical body.

[0119] The preferred embodiments of the present application are described in detail above, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including that each technical feature is combined in any other suitable manner. These simple modifications and combinations should also be considered as disclosed by the present application and fall within the protection scope of the present application.

Claims

1. A method for preparing a spherical phosphate-based cathode material, characterized in that, The method comprises the following steps: S1: providing a phosphate-based precursor slurry; S2: atomizing the phosphate-based precursor slurry into droplets, and making the droplets undergo a quasi-free-fall motion, the droplets being shrunk into spheres and dried under the action of surface tension during falling, to obtain spheroidized phosphate-based precursor particles; S3: sintering the spheroidized phosphate-based precursor particles to obtain spheroidized phosphate-based positive electrode materials; In step S2, the quasi-free-fall motion at least meets the following conditions: the initial speed of the droplets is not more than 5 cm / s, the vacuum degree is -0.095 MPa to -0.098 MPa, and the falling process is heated by a heat radiation method.

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

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

4. The method of claim 1, wherein, In step S2, the temperature of the heating treatment is 180°C to 220°C. And / or, in step S2, the heat radiation method is an infrared heating method.

5. The production method according to any one of claims 1 to 4, characterized by, In step S1, the solid content of the phosphate-based precursor slurry is 35wt%-45wt%; And / or, in step S1, the particle size distribution of the particles in the phosphate-based precursor slurry meets: Dv50 is 0.5 µm to 1 µm, and Dv100 is 2 µm to 5.5 µm.

6. The method of any one of claims 1-4, wherein, In step S1, the phosphate-based precursor slurry comprises 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 method of any one of claims 1-4, wherein the method further comprises, In step S3, the sintering treatment is carried out in a protective gas, comprising a temperature rising treatment and a constant temperature treatment, the rate of the temperature rising treatment is 3-8°C / min, the temperature of the constant temperature treatment is 750°C-850°C, and the constant temperature time is 8h-12h.

8. A spherical phosphate-based cathode material prepared by the method of any one of claims 1 to 7, characterized in that, The spheroidized phosphate-based positive electrode material is a quasi-spherical shape.

9. The spheronized phosphate-based cathode material according to claim 8, characterized in that, The spheroidized phosphate-based positive electrode material has a bulk density ≥1.7g / cm³.

Images