Method for preparing high-performance ternary cathode materials using rapid expansion of supercritical fluid

Abstract

The present invention discloses a method for preparing high-performance ternary cathode materials by utilizing the rapid expansion of supercritical fluids, which relates to the field of secondary battery technology and comprises the following steps: placing a coating material in a reactor, pumping in a solvent, and adjusting the temperature and pressure in the reactor so that the solvent reaches a supercritical state; maintaining the temperature and pressure in the reactor so that the coating material reaches a saturated state in the supercritical solvent to obtain a supercritical solution; heating the supercritical solution and rapidly spraying it into a reaction chamber through a first nozzle, while simultaneously rapidly spraying the ternary cathode material into the reaction chamber through a second nozzle under the influence of an airflow, and causing a collision reaction to obtain a high-performance ternary cathode material. In the present invention, the supercritical solution rapidly expands and decompresses in a very short time, thereby generating a pressure drop that rapidly reduces the solubility of the supercritical solvent, causing the coating material to precipitate out of supersaturation and collide with the ternary material carried by the airflow, thereby obtaining a uniformly coated high-performance ternary cathode material; the method is simple to operate, has a good coating effect, and improves the electrochemical performance of the material.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary batteries, and in particular to a method for preparing a high-performance ternary positive electrode material by utilizing the rapid expansion of a supercritical fluid. Background Art

[0002] With the development of new energy, lithium-ion batteries have developed rapidly. Among lithium-ion battery materials, cathode materials, as one of the important key materials, are of great significance in determining the performance of batteries.

[0003] Ternary cathode materials have high energy density, but suffer from short cycle life and poor safety. The short cycle life is due to the side reaction between the high-valent Ni and the electrolyte during charging, which causes material failure. The poor safety is due to the uncontrollable reaction, which triggers thermal runaway, leading to battery combustion, explosion, and other accidents.

[0004] In order to improve the comprehensive performance of ternary cathode materials, researchers have done a lot of research on doping and coating, such as Al 3+ Doping, Zr 2+ Coating methods such as doping, oxide coating, and phosphate coating generally involve dry mixing the raw materials and then sintering them to adhere the coating agent to the ternary material. However, research has found that the coating agent cannot evenly and firmly adhere to the ternary material using these methods. The reasons may be: the coating agent does not easily form a strong chemical bond with the ternary material; the coating agent itself is difficult to disperse; and the coating agent particles are too large to easily adhere to the ternary material. As a result, the performance of the ternary cathode material after coating, such as cycle stability, has limited improvement. Summary of the Invention

[0005] Based on the technical problems existing in the background technology, the present invention proposes a method for preparing high-performance ternary positive electrode materials by using the rapid expansion of supercritical fluid, coating the surface of the ternary positive electrode material with a modified material to improve its electrochemical performance. The method is simple to operate, has a good coating effect, and is highly feasible.

[0006] The present invention proposes a method for preparing a high-performance ternary cathode material by utilizing rapid expansion of a supercritical fluid, comprising the following steps:

[0007] S1. Placing the coating material in a reactor, pumping in a solvent, and adjusting the temperature and pressure in the reactor to make the solvent reach a supercritical state; maintaining the temperature and pressure in the reactor until the coating material reaches a saturated state in the supercritical solvent to obtain a supercritical solution;

[0008] S2. The supercritical solution is further heated and rapidly sprayed into the reaction chamber through the first nozzle. At the same time, the ternary cathode material to be coated is rapidly sprayed into the reaction chamber through the second nozzle under the airflow. The two materials collide and react, and the product in the reaction chamber is collected, which is a uniformly coated high-performance ternary cathode material; wherein the first nozzle and the second nozzle are located on the same horizontal line and the materials are sprayed horizontally so that the flow paths of the materials intersect.

[0009] In the above S2, the flow path refers to the path along which the material is ejected from the nozzle.

[0010] Preferably, the chemical formula of the ternary cathode material is LiNi 1-x-y Co x Mn y O2, where 0<x≤0.5, 0<y≤0.35.

[0011] Preferably, in S1, the coating material is a conductive material; preferably one or more of a conductive polymer and a carbon material; wherein the conductive polymer includes one or more of polyacetylene, polyaniline, polypyrrole, polythiophene, and polyphenylene vinylene; and the carbon material includes one or more of carbon black, carbon nanotubes, and graphene.

[0012] Preferably, in S1, the solvent is one or a mixture of carbon dioxide, ethane, ethylene, and propane.

[0013] Preferably, in S1, the mass percentage of the coating material to the solvent is 0.1-5:95-99.9.

[0014] Preferably, in S1, the temperature in the reactor is adjusted to 20-60° C. and the pressure is adjusted to 5-20 MPa to make the solvent reach a supercritical state; the temperature and pressure in the reactor are maintained for 10-45 minutes until the coating material reaches a saturated state in the supercritical solvent.

[0015] Preferably, in S2, the supercritical solution is further heated to 70-130°C and rapidly sprayed into the reaction chamber through the first nozzle.

[0016] Preferably, in S2, the mass ratio of the ternary positive electrode material to the coating material is 20-200:1.

[0017] Preferably, in S2, the supercritical solution is rapidly sprayed into the reaction chamber through the first nozzle at a flow rate of v1, v1 = 50-85 m / s; the ternary positive electrode material is rapidly sprayed into the reaction chamber through the second nozzle at a flow rate of v2 carried by the air flow, v2 = 50-75 m / s; v1 ≥ v2.

[0018] Preferably, in S2, the two materials collide and react for 1-10 minutes.

[0019] Beneficial effect: The present invention discloses a method for preparing high-performance ternary cathode materials by utilizing the rapid expansion of supercritical fluids. The method comprises placing a coating material in a reactor, compressing a solvent into the reactor with a pump, and maintaining a certain temperature and pressure to make it reach a supercritical state. After the coating material in the reactor reaches a saturated state in the supercritical solvent, it is rapidly ejected through a nozzle. Due to the rapid expansion and decompression in a very short time (10 -8 ~10 -5 ), resulting in a pressure drop that rapidly reduces the solubility of the supercritical solvent, causing the coating material to precipitate due to supersaturation. Since uniform conditions are instantly achieved in the expanded solution, a powder with a very small particle size and uniform distribution is precipitated. Furthermore, the supercritical solution is further heated before passing through the nozzle. Because the nozzle temperature is higher than the holding temperature in the reactor, the solubility of the solute there is lower than that in the reactor, resulting in supersaturation and the precipitation of micronuclei. At this time, the ternary cathode material to be coated, carried by the airflow at a certain flow rate, violently collides with the coating material. The coating material can be uniformly and stably coated on the surface of the ternary cathode material. After a certain period of time, a uniformly coated, high-performance ternary cathode material is obtained.

[0020] The coating process of this invention is achieved solely by changing the system pressure, without the need for adding other substances, thus avoiding the introduction of other impurities that could contaminate the product. Furthermore, the supercritical fluid used is typically a gas under normal conditions, resulting in minimal residual solvent in the resulting product. Compared to conventional coating methods, the supercritical fluid rapid expansion process does not involve the use of large amounts of fluid solvent, reducing wastewater discharge and energy consumption during solvent recovery. The supercritical fluid used can generally be recycled simply by compression, significantly simplifying the process.

[0021] The present invention is simple to operate, has a good coating effect, and is highly feasible. The coating material can be uniformly and stably coated on the surface of the ternary cathode material. By coating the conductive material on the surface of the ternary cathode material using this method, the stability and conductivity of the ternary cathode material can be improved, effectively enhancing the rate performance and cycle stability of lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a SEM image of the high-performance ternary cathode material prepared in Example 1 of the present invention;

[0023] Figure 2 This is an SEM image of the uncoated ternary cathode material in Comparative Example 1 of the present invention;

[0024] Figure 3 This is a comparison chart of the high-temperature cycle performance of batteries made from the ternary positive electrode materials prepared in Example 1 of the present invention and Comparative Examples 1-2. DETAILED DESCRIPTION

[0025] To facilitate understanding of the present invention, the present invention will be described more fully below in conjunction with specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to provide a more thorough and comprehensive understanding of the disclosure of the present invention.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0027] The technical solution of the present invention will be described more clearly and completely below with reference to specific embodiments.

[0028] The structural formula of the ternary cathode material used in the following embodiments is LiNi 0.7 Co 0.1 Mn 0.2 O2.

[0029] Example 1

[0030] A high-performance ternary cathode material is prepared as follows:

[0031] First, weigh 5g of polypyrrole and place it in the reactor. Then, pump a certain amount of carbon dioxide into the reactor to mix it thoroughly to achieve a polypyrrole mass percentage of 2.5%. Adjust the temperature in the reactor to 65°C and the pressure to 15Mpa to make the solvent reach a supercritical state. Maintain the temperature and pressure of the reactor for 30 minutes, and the coating material in the reactor reaches a saturated state in the supercritical solvent. The supercritical solution containing the coating material is heated to 120°C and quickly ejected in the reaction chamber through a throttling device (first nozzle), and the 100g ternary positive electrode material to be coated is also carried by an air flow of 65m / s and quickly sprayed into the reaction chamber through the second nozzle. After 5 minutes of reaction, the product can be collected in the container in the reaction chamber. This product is a uniformly coated high-performance ternary positive electrode material.

[0032] Example 2

[0033] A high-performance ternary cathode material is prepared as follows:

[0034] First, weigh 0.5g of polypyrrole and place it in a reactor. Then, pump a certain amount of carbon dioxide into the reactor to mix it thoroughly to achieve a polypyrrole mass percentage of 2.5%. Adjust the temperature in the reactor to 65°C and the pressure to 15Mpa to make the solvent reach a supercritical state. Maintain the temperature and pressure of the reactor for 30 minutes, and the coating material in the reactor reaches a saturated state in the supercritical solvent. The supercritical solution containing the coating material is heated to 120°C and quickly ejected in the reaction chamber through a throttling device (nozzle), and the 100g ternary positive electrode material to be coated is also quickly sprayed into the reaction chamber by an air flow of 65m / s. After reacting for 5 minutes, the product can be collected in the container in the reaction chamber. This product is a uniformly coated high-performance ternary positive electrode material.

[0035] Example 3

[0036] A high-performance ternary cathode material is prepared as follows:

[0037] First weigh 2.5g of polypyrrole and place it in a reactor, then pump a certain amount of carbon dioxide into the reactor to mix it thoroughly to achieve a mass percentage of polypyrrole of 2.5%, adjust the temperature in the reactor to 65°C and the pressure to 15Mpa, so that the solvent reaches a supercritical state. Maintain the temperature and pressure of the reactor for 30 minutes, and the coating material in the reactor reaches a saturated state in the supercritical solvent. The supercritical solution containing the coating material is heated to 120°C and quickly ejected in the reaction chamber through a throttling device (first nozzle), and the 100g ternary positive electrode material to be coated is also carried by an air flow of 65m / s and quickly sprayed into the reaction chamber through the second nozzle. After reacting for 5 minutes, the product can be collected in the container of the reaction chamber. This product is a uniformly coated high-performance ternary positive electrode material.

[0038] Example 4

[0039] A high-performance ternary cathode material is prepared as follows:

[0040] First weigh 5g of polypyrrole and place it in a reactor, then pump a certain amount of carbon dioxide into the reactor to mix it thoroughly to achieve a mass percentage of polypyrrole of 2.5%, adjust the temperature in the reactor to 50°C and the pressure to 10Mpa, so that the solvent reaches a supercritical state. Maintain the temperature and pressure of the reactor for 30 minutes, and the coating material in the reactor reaches a saturated state in the supercritical solvent. The supercritical solution containing the coating material is heated to 120°C and quickly ejected in the reaction chamber through a throttling device (first nozzle), and 100g of the ternary positive electrode material to be coated is also carried by an air flow of 50m / s and quickly sprayed into the reaction chamber through the second nozzle. After reacting for 5 minutes, the product can be collected in the container of the reaction chamber. This product is a uniformly coated high-performance ternary positive electrode material.

[0041] Example 5

[0042] A high-performance ternary cathode material is prepared as follows:

[0043] First weigh 5g of polypyrrole and place it in a reactor, then pump a certain amount of carbon dioxide into the reactor to mix it thoroughly to achieve a mass percentage of polypyrrole of 2.5%, adjust the temperature in the reactor to 65°C and the pressure to 20Mpa, so that the solvent reaches a supercritical state. Maintain the temperature and pressure of the reactor for 30 minutes, and the coating material in the reactor reaches a saturated state in the supercritical solvent. The supercritical solution containing the coating material is heated to 120°C and quickly ejected in the reaction chamber through a throttling device (first nozzle), and the 100g ternary positive electrode material to be coated is also carried by an air flow of 75m / s and quickly sprayed into the reaction chamber through the second nozzle. After reacting for 5 minutes, the product can be collected in the container in the reaction chamber. This product is a uniformly coated high-performance ternary positive electrode material.

[0044] Comparative Example 1

[0045] A ternary positive electrode material, compared with Example 1, this comparative example is a ternary positive electrode material LiNi without coating treatment 0.7 Co 0.1 Mn 0.2 O2.

[0046] Comparative Example 2

[0047] A high-performance ternary positive electrode material. Compared with Example 1, in this comparative example, polypyrrole is coated on the surface of the ternary positive electrode material by a conventional mechanical mixing method; specifically, polypyrrole and the ternary positive electrode material are ball-milled in a mass ratio of 5:100, and then the mixture is subjected to a high-temperature sintering treatment in a roller kiln with an oxygen atmosphere at 890°C for 12 hours to obtain a polypyrrole-coated ternary positive electrode material.

[0048] The ternary cathode materials prepared in the examples of the present invention and the comparative examples were characterized and their performance tested.

[0049] The ternary cathode materials obtained in Example 1 and Comparative Example 1 were characterized by SEM. Figure 1 and Figure 2 It can be seen from the comparison that the surface of the ternary positive electrode material in Example 1 is uniformly coated with polypyrrole.

[0050] The ternary cathode materials in Example 1 and Comparative Examples 1-2 were made into wound soft-pack batteries, and were subjected to 25°C rate discharge and 45°C high-temperature cycle tests at a test voltage of 3.0-4.3V. The test results are shown in Tables 1 and Figure 3 As shown in .

[0051] Depend on Figure 3 It can be seen from the test results in that the discharge capacity retention rate and high temperature cycle performance of the polypyrrole-coated ternary positive electrode material in the present invention are significantly improved at a 3C rate.

[0052] Table 1 Results of 3C rate discharge and 45°C high temperature cycle tests on soft pack batteries

[0053] Example 1 Comparative Example 1 Comparative Example 2 3C discharge capacity retention rate (100%) 98.36％ 88.72％ 94.79％ Capacity retention after 600 cycles (100%) 95.49％ 84.26％ 90.33％

[0054] The test results in Table 1 show that the high-temperature cycle performance of the polypyrrole-coated ternary cathode material in Example 1 is significantly better than that of the uncoated ternary cathode material. This is because the uncoated ternary cathode material is unstable and its structure will slowly break down during the cycle, resulting in poor cycle performance. Compared with the mechanical mixing coating method in Comparative Example 2, the coating effect of the present invention is better. This is mainly because the expansion and decompression process of the supercritical solution containing the coating material through the nozzle in the present invention is very fast (10 -8 ~10 -5 ), thus instantly achieving uniform conditions within the expansion solution, resulting in the precipitation of a very small and evenly distributed powder. When the ternary cathode material to be coated also expands rapidly with the supercritical solution ejected from the nozzle at a certain speed, the coating material can be uniformly and stably coated on the surface of the ternary cathode material.

[0055] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0056] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing high-performance ternary cathode materials by using supercritical fluid rapid expansion, characterized in that: The following steps are involved: S1. Placing the coating material in a reactor, pumping in a solvent, and adjusting the temperature and pressure in the reactor to make the solvent reach a supercritical state; maintaining the temperature and pressure in the reactor until the coating material reaches a saturated state in the supercritical solvent to obtain a supercritical solution; S2. The supercritical solution is further heated to 70-130°C and rapidly sprayed into the reaction chamber through the first nozzle at a flow rate of v1. At the same time, the ternary cathode material to be coated is rapidly sprayed into the reaction chamber through the second nozzle at a flow rate of v2 under the influence of air flow. The two materials collide and react, and the product in the reaction chamber is collected, which is a uniformly coated high-performance ternary cathode material; wherein, the first nozzle and the second nozzle are located on the same horizontal line and spray the materials horizontally so that the flow paths of the materials intersect; v1=50~85m / s, v2=50-75m / s; v1≥v2.

2. The method for preparing high-performance ternary cathode materials by using supercritical fluid rapid expansion according to claim 1, characterized in that: The chemical formula of the ternary cathode material is LiNi 1-x-y Co x Mn y O2, where 0<x≤0.5, 0<y≤0.

35.

3. The method for preparing high-performance ternary cathode materials by utilizing supercritical fluid rapid expansion according to claim 1 or 2, characterized in that: In S1, the coating material is a conductive material; the conductive material is one or more of a conductive polymer and a carbon material; wherein the conductive polymer includes one or more of polyacetylene, polyaniline, polypyrrole, polythiophene, and polyphenylene vinylene; the carbon material includes one or more of carbon black, carbon nanotubes, and graphene.

4. The method for preparing high-performance ternary cathode materials by utilizing rapid expansion of supercritical fluid according to any one of claims 1 to 3, characterized in that: In S1, the solvent is a mixture of one or more of carbon dioxide, ethane, ethylene, and propane.

5. The method for preparing high-performance ternary cathode materials by utilizing rapid expansion of supercritical fluid according to any one of claims 1 to 3, characterized in that: In S1, the mass percentage of the coating material to the solvent is 0.1-5:95-99.

9.

6. The method for preparing high-performance ternary cathode materials by utilizing rapid expansion of supercritical fluid according to any one of claims 1 to 3, characterized in that: In S1, the temperature in the reactor is adjusted to 20-60° C. and the pressure is adjusted to 5-20 MPa so that the solvent reaches a supercritical state; the temperature and pressure in the reactor are maintained for 10-45 minutes until the coating material reaches a saturated state in the supercritical solvent.

7. The method for preparing high-performance ternary cathode materials by utilizing supercritical fluid rapid expansion according to any one of claims 1 to 3, characterized in that: In S2, the mass ratio of the ternary positive electrode material and the coating material is 20-200:

1.

8. The method for preparing high-performance ternary cathode materials by utilizing rapid expansion of supercritical fluid according to any one of claims 1 to 3, characterized in that: In S2, the two materials collide and react for 1-10 minutes.

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