Jet mill system for preparing low-magnetism positive electrode material and application of jet mill system

Abstract

The invention belongs to the technical field of battery preparation, and particularly relates to a jet mill system for preparing a low-magnetism positive electrode material and application. The invention provides a jet mill system for preparing a low-magnetism positive electrode material. The jet mill system comprises a stock bin and a jet mill, the stock bin is used for storing a positive electrode material; the jet mill is communicated with the stock bin, and the positive electrode material is conveyed into the jet mill to be crushed and then magnetic impurities are removed; the jet mill comprises a cavity, the cavity comprises a smashing area and a grading area from bottom to top, a blind plate is arranged at the bottom of the cavity, and a permanent magnet is arranged above the blind plate and used for removing magnetic impurities. The permanent magnet is arranged at the bottom of the cavity, so that the positive electrode material can be crushed and magnetic impurities can be separated at the same time, the iron removal efficiency is improved, a sieving iron removal process is not needed, the production cost is reduced, and the production efficiency is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of battery preparation, and in particular relates to a jet mill system for preparing low-magnetic positive electrode materials and an application thereof. Background Art

[0002] Magnetic impurities usually refer to metal fragments or objects with magnetic properties that are accidentally found in products or materials. When magnetic impurities (metallic single substances or alloys or oxides such as Fe, Ni, Zn, Cr, etc.) appear in the positive electrode material, it will cause an internal short circuit in the battery. After the positive electrode material is prepared into a battery, when charging, the voltage reaches the redox potential of these impurities, and they will be oxidized at the positive electrode and then reduced at the negative electrode, thereby precipitating metal. When the metal single substance at the negative electrode accumulates to a certain extent, the sharp metal edges will pierce the diaphragm, causing a micro short circuit and self-discharge. In this process, the electrolyte gradually releases HF, oxidizing the single metal to form a stable MF (M is a metal element), and even forming MF·3H2O. Due to the poor electronic conductivity of MF, a convex structure will be formed to directly contact the SEI film of the positive and negative electrodes. Eventually, it causes undesirable phenomena such as battery combustion and explosion, resulting in safety accidents. Such abnormal batteries need to undergo multiple cycles of charge and discharge before they can be discovered. At this time, it is too late to remedy, so it is necessary to solve it from the source.

[0003] During the preparation of positive electrode materials, raw materials, wear of processing equipment, etc. will introduce magnetic impurities; in the prior art, electromagnetic iron removers are generally used to remove magnetic substances. Under the action of gravity, the material passes through a well-shaped grid with a certain magnetic field strength. Under the action of the magnetic field, the magnetic substances are adsorbed on the grid and collected, thus being separated from the positive electrode materials. However, relying on its own gravity, the material passes through the well-shaped grid in the form of agglomerates, and some magnetic impurities are entrained by the positive electrode materials and hidden inside the agglomerates, resulting in poor separation effect. Summary of the invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defect of poor separation effect of positive electrode materials and magnetic impurities in the prior art, thereby providing a jet mill system and application for preparing low-magnetic positive electrode materials.

[0005] In the prior art for preparing positive electrode materials, for example, in the preparation of positive electrode materials for lithium-ion batteries, some magnetic substances will be introduced during the preparation of precursors, the addition of lithium sources and additives. After the sintering process, the magnetic substances enter the crystal structure of the positive electrode materials, resulting in excessive magnetic substances in the prepared positive electrode materials. In addition, metal machines are also required for mixing, sintering, and conveying in the preparation of positive electrode materials. The abrasive metal foreign matter generated during use will be crushed to the target particle size together with the positive electrode materials in the airflow crushing process and enter the battery preparation link.

[0006] The positive electrode material is pulverized into a suitable particle size in the air flow milling stage. Under the action of strong airflow, the magnetic material repeatedly rubs and collides in the pulverizing chamber, turning into small particles. The particles are mixed into the positive electrode material particles with similar particle sizes and cannot be separated. They enter the subsequent battery preparation stage and produce abnormal batteries.

[0007] To this end, the present invention provides the following technical solutions.

[0008] The present invention provides a jet mill system for preparing low-magnetic positive electrode materials, comprising a silo and a jet mill;

[0009] The silo is used to store positive electrode materials;

[0010] The air flow mill is connected to the silo, and conveys the positive electrode material to the inside of the air flow mill for crushing and then removing magnetic impurities; the air flow mill includes a cavity, and the cavity includes a crushing area and a grading area from bottom to top, a blind plate is provided at the bottom of the cavity, and a permanent magnet is provided above the blind plate, and the permanent magnet is used to remove magnetic impurities; the side wall of the cavity is provided with a gas input port at the bottom of the crushing area, and gas is input into the crushing area, and the gas is used to crush the positive electrode material; the grading area is provided with a grading wheel, which is used to grade the crushed positive electrode material, and the side wall of the cavity is provided with a material discharge port near the top of the grading area, which is used to output the graded positive electrode material.

[0011] The working principle of the airflow mill for preparing low-magnetic positive electrode materials is as follows: coarsely crushed positive electrode materials mixed with magnetic impurities enter the airflow mill, and under the action of the airflow, the coarsely crushed positive electrode materials collide rapidly with each other, and the crushed fine particles pass through the grading wheel under the action of the induced draft fan; and the magnetic impurities mixed therein are directly adsorbed by the permanent magnet, thereby preventing the subsequent magnetic impurities from continuing to be crushed and mixed into the positive electrode materials, greatly improving the purity of the positive electrode materials in the subsequent preparation of batteries.

[0012] In an optional embodiment, the magnetic field strength of the permanent magnet is 8000-15000 GS.

[0013] In an optional implementation, the permanent magnet is adapted to the size of the blind plate.

[0014] In an optional embodiment, the upper surface of the permanent magnet is an arc-shaped surface. Figure 1 ;

[0015] In an optional embodiment, the permanent magnet includes at least one of neodymium iron boron and ferrite.

[0016] The present invention also provides a method for preparing a low-magnetic positive electrode material, wherein the low-magnetic positive electrode material is prepared by using the above-mentioned jet mill system for preparing a low-magnetic positive electrode material, comprising the following steps:

[0017] Gas is introduced into the crushing zone; the positive electrode material is transported to the crushing zone for crushing; part of the crushed positive electrode material settles to the surface of the permanent magnet for demagnetization, and part enters the classification zone for classification; after classification, coarse powder and fine powder are obtained, the fine powder is discharged, and the coarse powder settles to the crushing zone for crushing again.

[0018] In an optional embodiment, the gas introduction rate is 10.0-40.0 Nm 3 / min;

[0019] In an optional embodiment, the delivery rate of the positive electrode material is 300-700 Kg / h.

[0020] In an optional embodiment, the particle size of the fine powder is 2.0-8.0 μm;

[0021] In an optional embodiment, the positive electrode material includes LiCoO2, LiNi x Co y Mn 1-x-y At least one of O2 and LiFePO4; the x satisfies: 0.1≤x≤1, and the y satisfies: 0.1≤y≤1.

[0022] In an optional implementation, after the positive electrode material is crushed, the permanent magnet is removed, the magnetic material on the permanent magnet is cleaned, and the permanent magnet is installed back on the blind plate to crush the positive electrode material next time.

[0023] The present invention also provides a low-magnetic positive electrode material prepared by the above preparation method.

[0024] In an optional embodiment, the content of magnetic substance in the low-magnetic positive electrode material is 1-20 ppb.

[0025] The technical solution of the present invention has the following advantages:

[0026] 1. The present invention provides a jet mill system for preparing low-magnetic positive electrode materials, comprising a silo and a jet mill; the silo is used to store positive electrode materials; the jet mill is connected to the silo, and transports the positive electrode materials to the inside of the jet mill for crushing and removing magnetic impurities; the jet mill comprises a cavity, and the cavity comprises a crushing area and a grading area from bottom to top, a blind plate is provided at the bottom of the cavity, a permanent magnet is provided above the blind plate, and the permanent magnet is used to remove magnetic impurities; a gas input port is provided on the side wall of the cavity at the bottom of the crushing area, and gas is input into the crushing area, and the gas is used to crush the positive electrode materials; a grading wheel is provided in the grading area, which is used to grade the crushed positive electrode materials, and a material discharge port is provided on the side wall of the cavity near the top of the grading area, which is used to output the graded positive electrode materials.

[0027] The present invention creatively proposes that a permanent magnet is provided on the blind plate at the bottom of the airflow mill chamber, which can simultaneously crush the positive electrode material and separate the magnetic impurities, thereby improving the iron removal efficiency, eliminating the need for a screening iron removal process, reducing production costs, and not affecting the progress of the positive electrode material crushing, thereby increasing production efficiency, overcoming the technical bias of the prior art of adding an extra step to remove iron, simplifying the process, and being easier to implement in practical applications. The permanent magnet has a slow magnetic decay, making it easy to assemble with the airflow mill and also easy to disassemble and remove the magnetic impurities adsorbed on the permanent magnet.

[0028] 2. The present invention provides a jet mill system for preparing low-magnetic positive electrode materials, wherein the magnetic field strength of the permanent magnet is 8000-15000GS; the magnetic impurities in the crushed positive electrode materials can be better absorbed in the preferred magnetic field strength of the permanent magnet, and the positive electrode materials will not be adsorbed. The permanent magnet is preferably consistent in size with the blind plate, so that the permanent magnet and the blind plate are more firmly assembled. The upper surface of the permanent magnet is preferably an arc surface, which further increases the contact area between the permanent magnet and the magnetic impurities and increases the enrichment of adsorbed magnetic substances.

[0029] 3. The preparation method of the low-magnetic positive electrode material provided by the present invention, the present invention regulates the gas introduction rate and the delivery rate of the positive electrode material, and cooperates with a specific permanent magnet, which can further improve the iron removal effect of the positive electrode material and reduce the residual amount of magnetic substances. In the stage of crushing the positive electrode material, the gas introduction rate and the positive electrode material delivery rate are regulated to ensure that the positive electrode material is repeatedly rubbed and crushed under the action of the airflow, so that the gas action and the delivery amount of the positive electrode material are matched, the crushing effect is better, and it also helps the permanent magnet on the blind plate to adsorb magnetic substances and improve the removal rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0031] Figure 1 It is a schematic structural diagram of the permanent magnet of the present invention in which the upper surface is an arc-shaped surface;

[0032] Figure 2 is a structural diagram of a jet mill for preparing a low-magnetic positive electrode material according to Example 1 of the present invention;

[0033] Reference numerals:

[0034] 1-silo; 2-first motor; 3-input pipeline; 4-second motor; 5-output pipeline; 6-chamber; 7-classifying wheel; 8-gas input port; 9-permanent magnet; 10-blind plate; 11-support member. DETAILED DESCRIPTION

[0035] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the guidance of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0036] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be purchased commercially.

[0037] Example 1

[0038] This embodiment provides a jet mill system for preparing a low-magnetic positive electrode material, comprising:

[0039] Silo 1, used for storing positive electrode materials;

[0040] The air flow mill is connected to the silo through the input pipe 3. The first motor 2 provides conveying power for the silo to convey the positive electrode material in the silo to the air flow mill. The air flow mill includes a cavity 6, which includes a crushing zone and a grading zone from bottom to top. A blind plate 10 is provided at the bottom of the cavity, and a permanent magnet 9 is provided above the blind plate. The magnetic field strength of the permanent magnet is 10000GS. A gas input port 8 is provided at the bottom of the crushing zone on the side wall of the cavity, and high-pressure gas is input into the crushing zone, and the high-pressure gas crushes the positive electrode material. A material input port is also provided on the side wall of the cavity, and the material input port is located above the gas input port, which is used to send the positive electrode material into the crushing zone for crushing. The grading zone is provided with a grading wheel 7, which is used to grade the crushed positive electrode material. The crushed positive electrode material is crushed by the grading wheel to obtain fine powder and coarse powder. The coarse powder settles to the crushing zone for crushing again, and the fine powder is discharged into the output pipe 5 through the material discharge port for collection; the material discharge port is provided on the side wall of the cavity near the top area of ​​the grading zone.

[0041] The jet mill also includes a second motor 4 and a support 11. The second motor provides power for the classifying wheel; the support is used to support the cavity; the structural diagram is shown in FIG. Figure 2 .

[0042] The working principle of the air flow mill system of the present invention is as follows: the positive electrode material is repeatedly collided and crushed in the crushing chamber under the action of high-pressure gas, and the magnetic substance therein is exposed and adsorbed on the permanent magnet to be separated from the positive electrode material. After crushing, the fine powder that meets the requirements can pass through the classification wheel and is output through the output pipeline for subsequent processing; the coarse powder that does not pass through the classification wheel settles to the crushing area and is crushed again under the action of high-pressure gas, wherein the magnetic substance contained in the coarse powder is exposed and adsorbed by the permanent magnet until the crushing is completed.

[0043] It should be noted that the positive electrode materials of the present invention are LiCoO2, LiNixCoyMn1-x-yO2 (1.0≥x≥0.1, 1.0≥y≥0.1), and LiFePO4; the gas can be at least one of air, nitrogen, argon, and oxygen.

[0044] This embodiment also provides a method for preparing a low-magnetic positive electrode material, comprising the following steps:

[0045] Gas is introduced into the crushing zone at a rate of 30 Nm 3 / min; the positive electrode material is transported to the pulverizing area for pulverization, and the transport rate of the positive electrode material is 400Kg / h; the pulverized positive electrode material is partially settled to the surface of the permanent magnet for demagnetization, and partially enters the grading area for grading; after grading, coarse powder and fine powder are obtained, the fine powder is discharged, and the coarse powder is settled to the pulverizing area for pulverization again; the particle size of the fine powder is 4.0μm.

[0046] Example 2

[0047] This embodiment provides a method for preparing a low-magnetic positive electrode material, using the air flow mill system of Embodiment 1. Compared with Embodiment 1, the only difference is that the magnetic field strength of the permanent magnet is 8000 GS instead of the magnetic field strength of the permanent magnet of Embodiment 1 being 10000 GS.

[0048] Example 3

[0049] This embodiment provides a method for preparing a low-magnetic positive electrode material, using the air flow mill system of Embodiment 1. The only difference from Embodiment 1 is that the magnetic field strength of the permanent magnet is 12000 GS instead of the magnetic field strength of the permanent magnet of Embodiment 1 being 10000 GS.

[0050] Example 4

[0051] This embodiment provides a method for preparing a low-magnetic positive electrode material, using the air flow mill system of Embodiment 1. Compared with Embodiment 1, the only difference is that the magnetic field strength of the permanent magnet is 6000 GS instead of the magnetic field strength of the permanent magnet of Embodiment 1 being 10000 GS.

[0052] Example 5

[0053] This embodiment provides a method for preparing a low-magnetic positive electrode material, using the air flow mill system of Embodiment 1. Compared with Embodiment 1, the only difference is that the magnetic field strength of the permanent magnet is 15000 GS instead of the magnetic field strength of the permanent magnet of Embodiment 1 being 10000 GS.

[0054] Comparative Example 1

[0055] This comparative example provides a jet mill, which is different from Example 1 in that no permanent magnet is provided above the blind plate at the bottom of the jet mill cavity.

[0056] This comparative example also provides a method for preparing an iron-removing positive electrode material, comprising the following steps:

[0057] After sintering, the LiNi 0.5 Co 0.2 Mn 0.3 The coarse positive electrode material after O2 rolling is passed into the air flow mill for crushing. 0.5 Co 0.2 Mn 0.3 O2 is transported to an electromagnetic iron remover through an output pipeline, and the magnetic field strength of the iron remover is 9000GS; the iron removal positive electrode material is obtained.

[0058] Comparative Example 2

[0059] This comparative example provides a jet mill, which is different from Example 1 in that no permanent magnet is provided above the blind plate at the bottom of the jet mill cavity.

[0060] This comparative example also provides a method for preparing a positive electrode material, comprising the following steps:

[0061] After sintering, the LiNi 0.5 Co 0.2 Mn 0.3 The coarse-grained positive electrode material after O2 rolling is passed into a jet mill for pulverization to obtain a positive electrode material.

[0062] Comparative Example 3

[0063] This comparative example provides an air flow mill, which is different from Example 1 in that a soft magnetic material (manganese-zinc ferrite) is arranged above the blind plate at the bottom of the air flow mill cavity instead of a permanent magnet.

[0064] This comparative example also provides a method for preparing an iron-removing positive electrode material, comprising the following steps:

[0065] After sintering, the LiNi 0.5 Co 0.2 Mn 0.3 The coarse-grained positive electrode material after the O2 rolling is passed into the air flow mill for crushing to obtain the iron-free positive electrode material.

[0066] Test Case

[0067] The performance tests of the positive electrode materials prepared in each embodiment and comparative example are as follows:

[0068] (1) Magnetic material detection method: 300 g of crushed positive electrode material was placed in 500 mL of pure water, a permanent magnet with a rubber sleeve was added, and the mixture was sealed in a plastic barrel, and the drum was continuously rolled for 1 h; the permanent magnet was taken out, and the magnetic material adsorbed on the surface of the permanent rubber sleeve was rinsed with pure water, and the magnetic material was transferred to 6 mol / L hydrochloric acid, heated to boiling, and the boiling was continued for 10 min. After the solution was cooled, the volume was fixed, and the content of Fe, Cr, and Zn elements in the solution was detected by inductively coupled plasma mass spectrometry (ICP), and the results were calculated by the standard curve method. The results are shown in Table 1;

[0069] (2) Preparation of button cells: positive electrode materials (from various embodiments and comparative examples), carbon black, polyvinylidene fluoride and N-methylpyrrolidone were mixed in a mass ratio of 8:1:1:4, stirred, and the resulting slurry was coated on one side of an aluminum foil, and vacuum dried at 105° C. for 2 h. The edges of the dried electrode sheets were trimmed and placed in a tablet press to compact the electrode sheets at a pressure of 25 MPa. The compacted electrode sheets were cut into small discs in the cut sheets to obtain positive electrode sheets;

[0070] The button battery is assembled in a glove box filled with dry nitrogen, wherein the moisture and oxygen content in the glove box is less than 0.1 ppm, and the assembly steps specifically include placing the positive electrode plate prepared as above on the positive electrode side of the button battery housing with a gasket, with the coated surface of the positive electrode plate facing away from the positive electrode side of the button battery housing, wherein the content of the positive electrode material coated on the positive electrode plate is 10 mg, and then adding 50 μL of electrolyte to the positive electrode plate, placing a diaphragm, and then adding 50 μL of electrolyte, placing a lithium sheet as a negative electrode plate, and then placing a gasket, a shrapnel, and the negative electrode side housing of the button battery in sequence, and encapsulating to obtain a CR2032 button battery.

[0071] (3) Voltage drop detection method: At room temperature, the CR2032 button cell prepared above was charged and discharged once at a rate of 0.1C, charged to 4.400V at 0.01C, and left to stand for 0.5h to reach an electrochemical equilibrium state.

[0072] Use a high-precision digital multimeter (DMM) to measure the voltage between the positive and negative electrodes every hour and record the voltage drop per hour. The results are shown in Table 2.

[0073] (4) Cyclic performance test method: At room temperature, the CR2032 button cell prepared above was charged and discharged once at a rate of 0.1C and 100 times at a rate of 1C. The results are shown in Table 2.

[0074] Table 1

[0075]

[0076]

[0077] Table 2

[0078] Voltage drop (V / d) Cycle performance (%) Example 1 0.010 95.2 Example 2 0.025 93.1 Example 3 0.012 94.2 Example 4 0.025 92.5 Example 5 0.010 95.1 Comparative Example 1 0.050 90.3 Comparative Example 2 0.095 85.3 Comparative Example 3 0.088 86.7

[0079] It can be seen from Tables 1-2 that the low magnetic positive electrode material prepared by the air flow mill system provided by the present invention has a significantly reduced magnetic content, and after the battery is made, the voltage drop decreases while the cycle performance increases, indicating that the low magnetic positive electrode material prepared by the present invention has a good separation effect from magnetic impurities, thereby improving the electrical performance of the positive electrode material after it is made into a battery.

[0080] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the scope of protection of the invention.

Claims

1. A jet mill system for preparing low magnetic positive electrode materials, characterized in that: Including silo and jet mill; The silo is used to store positive electrode materials; The air flow mill is connected to the silo, and conveys the positive electrode material to the inside of the air flow mill for crushing and then removing magnetic impurities; the air flow mill includes a cavity, and the cavity includes a crushing area and a grading area from bottom to top, a blind plate is provided at the bottom of the cavity, and a permanent magnet is provided above the blind plate, and the permanent magnet is used to remove magnetic impurities; the side wall of the cavity is provided with a gas input port at the bottom of the crushing area, and gas is input into the crushing area, and the gas is used to crush the positive electrode material; the grading area is provided with a grading wheel, which is used to grade the crushed positive electrode material, and the side wall of the cavity is provided with a material discharge port near the top of the grading area, which is used to output the graded positive electrode material.

2. The jet mill system according to claim 1, characterized in that: The magnetic field strength of the permanent magnet is 8000-15000 GS.

3. The jet mill system according to claim 1 or 2, characterized in that: The size of the permanent magnet is matched with that of the blind plate.

4. The jet mill system according to any one of claims 1 to 3, characterized in that: The upper surface of the permanent magnet is an arc-shaped surface; and / or, The permanent magnet includes at least one of neodymium iron boron and ferrite.

5. A method for preparing a low magnetic positive electrode material, characterized in that: The method of preparing a low magnetic positive electrode material using the jet mill system for preparing a low magnetic positive electrode material according to any one of claims 1 to 4 comprises the following steps: Gas is introduced into the crushing zone; the positive electrode material is transported to the crushing zone for crushing; part of the crushed positive electrode material settles to the surface of the permanent magnet for demagnetization, and part enters the classification zone for classification; after classification, coarse powder and fine powder are obtained, the fine powder is discharged, and the coarse powder settles to the crushing zone for crushing again.

6. The preparation method according to claim 5, characterized in that: The gas introduction rate is 10.0-40.0Nm 3 / min; and / or, The delivery rate of the positive electrode material is 300-700 Kg / h.

7. The preparation method according to claim 5 or 6, characterized in that: The particle size of the fine powder is 2.0-8.0 μm; and / or, The positive electrode material includes LiCoO2, LiNi x Co y Mn 1-x-y At least one of O2 and LiFePO4; the x satisfies: 0.1≤x≤1, and the y satisfies: 0.1≤y≤1.

8. The preparation method according to any one of claims 5 to 7, characterized in that: After the positive electrode material is crushed, the permanent magnet is removed, the magnetic material on the permanent magnet is cleaned, and the permanent magnet is installed back on the blind plate to crush the positive electrode material next time.

9. A low magnetic positive electrode material, characterized in that: The method is prepared by any one of claims 5 to 8.

10. The low magnetic positive electrode material according to claim 9, characterized in that: The content of magnetic substance in the low-magnetic positive electrode material is 1-20 ppb.

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