Positive electrode material, positive electrode plate containing positive electrode material and electrochemical device

Abstract

The invention relates to the field of electrochemistry, and particularly discloses a positive electrode material, a positive electrode plate containing the positive electrode material and an electrochemical device. The positive electrode material comprises a ternary transition metal oxide and a coating layer existing on the ternary transition metal oxide, the coating layer is an MOF structure layer containing C, N and O elements, and is formed by mixing a ternary transition metal oxide with an organic ligand and coordinating the organic ligand with metal ions on the surface of the ternary transition metal oxide by adopting a low-pressure vapor deposition method. When the positive electrode material is applied to a battery system, the structural stability of the material can be greatly improved, and the cycle life of an electrochemical device is effectively prolonged. Moreover, the coating layer on the surface of the positive electrode material can effectively inhibit the phenomena of oxygen release and metal ion dissolution in the circulation process, and effectively improve the gas production problem in the circulation process of an electrochemical device, thereby improving the safety performance.

Description

Technical Field

[0001] The present application relates to the field of electrochemistry, and more specifically, to a positive electrode material, a positive electrode sheet containing the material, and an electrochemical device. Background Art

[0002] As an important component of current energy storage technology, lithium-ion batteries have become core indicators of concern in terms of energy density, cycle performance, and safety with the popularization of portable electronic devices and new energy vehicles. In the field of ternary materials, they are particularly popular due to their high energy density. However, ternary materials are prone to irreversible phase changes during the cycle, releasing oxygen and reacting with the electrolyte, leading to thermal runaway and even deflagration. Especially for high-nickel ternary materials (such as NCM811 and NCA), the increase in nickel content will aggravate structural instability and thermal sensitivity, further reducing safety. In addition, such materials are easily affected by moisture and deterioration in the air, and are prone to gassing and metal ion dissolution during the battery cell cycle, which greatly affects the energy density, cycle performance, and safety of lithium-ion batteries.

[0003] At present, in order to improve the cycle performance and safety of ternary positive electrode materials, the industry generally adopts a variety of modification methods. Common methods include surface coating, doping, and regulating material morphology. Among them, the surface coating technology forms a protective layer on the surface of the ternary material to inhibit the occurrence of side reactions. However, the surface coating layer in the existing technology usually has the problem of insufficient stability. Traditional coating layers are difficult to effectively inhibit the release of oxygen and the dissolution of metal ions during the electrochemical cycle. Especially under high voltage and high temperature conditions, the coating layer is prone to cracking or falling off, resulting in the cycle performance and safety of the electrochemical device still unable to meet high performance requirements.

[0004] Therefore, it is urgent to develop a new type of ternary positive electrode material and coating technology to solve the above problems. Summary of the Invention

[0005] In order to solve the above technical problems, the present application provides a positive electrode material, a positive electrode sheet containing the material, and an electrochemical device.

[0006] This application provides the following technical solutions: In a first aspect, the present application provides a positive electrode material comprising a ternary transition metal oxide and a coating layer present on the ternary transition metal oxide, wherein the coating layer has a thickness of 1 nm to 20 nm; The coating layer is a MOF structure layer containing C, N, and O elements, which is formed by mixing a ternary transition metal oxide with an organic ligand and using a low-pressure vapor deposition method to coordinate the organic ligand with the metal ions on the surface of the ternary transition metal oxide.

[0007] Furthermore, the above-mentioned ternary transition metal oxide includes one or more of NCM811, NCM622, NCM523, NCM111, NCA and ultra-high nickel 9 series ternary materials.

[0008] Among them, NCM811 is Ni:Co:Mn=8:1:1, NCM622 is Ni:Co:Mn=6:2:2, NCM523 is Ni:Co:Mn=5:2:3, NCM111 is Ni:Co:Mn=1:1:1; NCA is Ni:Co:Al=89:9:2; in the ultra-high nickel 9 series ternary, Ni accounts for greater than or equal to 90% of all transition metal elements. These materials have a high nickel content and can significantly improve the energy density of electrochemical devices. However, high nickel content can easily lead to structural instability and thermal sensitivity problems. Combined with the MOF structure of the coating layer, it can effectively inhibit oxygen release and metal ion dissolution, thereby improving the cycle performance and safety of the electrochemical device. In addition, the selection of the above-mentioned specific type of ternary transition metal oxide can further optimize the comprehensive performance of the material while maintaining high energy density, so that the electrochemical device exhibits more stable characteristics during long cycles.

[0009] Furthermore, the organic ligand is an aromatic or heterocyclic compound containing a multidentate ligand group, wherein the multidentate ligand group is selected from carboxyl, amino, hydroxyl or nitrogen-containing heterocycle, and the aromatic or heterocyclic skeleton is selected from benzene ring, naphthalene ring or imidazole ring.

[0010] Furthermore, the organic ligand is one or more of terephthalic acid, trimesic acid, 2-aminoisophthalic acid, 2-methylimidazole or N-methylimidazole.

[0011] By adopting the above technical solution, the organic ligand is selected from aromatic or heterocyclic compounds containing multidentate ligands. The multidentate ligands can form a stable coordination structure with the metal ions on the surface of the ternary transition metal oxide, thereby enhancing the binding force between the coating layer and the material surface. Among them, carboxyl, amino, hydroxyl or nitrogen-containing heterocyclic rings as coordination groups can effectively promote the occurrence of coordination reactions and improve the uniformity and density of the coating layer. At the same time, benzene rings, naphthalene rings or imidazole rings as aromatic or heterocyclic skeletons give the organic ligands good thermal stability and chemical stability, further enhancing the protective effect of the coating layer on the positive electrode material, thereby effectively suppressing oxygen release and metal ion dissolution during the cycle, and improving the cycle performance and safety of the electrochemical device.

[0012] Furthermore, the mass ratio of the ternary transition metal oxide and the organic ligand when mixed is 1:0.3-8.

[0013] By adopting the above technical solution, the ternary transition metal oxide and the organic ligand are mixed within a specific mass ratio range and can be fully coordinated to form a coating layer of the MOF structure.

[0014] Furthermore, the process parameters of the low pressure vapor deposition method are: Vacuum conditions are 100-150 Pa, temperature is 120°C-250°C, and reaction time is 4-12h.

[0015] Furthermore, the specific surface area of the positive electrode material is 10m 2 / g~100m 2 / g; the average particle size D50 of the positive electrode material is 3μm to 15μm.

[0016] In the second aspect, the present application provides a method for preparing the above-mentioned positive electrode material, which comprises: mixing an appropriate amount of a ternary transition metal oxide with an appropriate amount of an organic ligand, wherein the mass ratio of the ternary transition metal oxide to the organic ligand is 1:0.3 to 8, heating at 120°C to 250°C under vacuum conditions of 100 to 150Pa, and reacting for 4-12 hours to obtain the positive electrode material.

[0017] In a third aspect, the present application provides a positive electrode plate comprising the above-mentioned positive electrode material.

[0018] In a fourth aspect, the present application provides an electrochemical device comprising: a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte as described above.

[0019] In summary, this application has the following beneficial effects: 1. The cathode materials provided herein, with a ternary transition metal oxide core, have a high nickel content and can significantly enhance the energy density of electrochemical devices. However, high nickel content can easily lead to structural instability and thermal sensitivity. Combined with the MOF structure of the coating layer, this can effectively inhibit oxygen release and metal ion dissolution, thereby improving the cycling performance and safety of electrochemical devices.

[0020] 2. This application uses aromatic or heterocyclic compounds containing multidentate ligands as organic ligands, which can form stable metal-organic framework materials with metal ions on the surface of ternary transition metal oxide materials. This coordination structure effectively improves the stability and uniformity of the coating layer, thereby further suppressing the oxygen release and metal ion dissolution of the positive electrode material during the cycle. At the same time, due to the presence of multidentate ligands, the weather resistance and deliquescence resistance of the coating layer are also significantly improved, which enhances the stability of the positive electrode material and thereby improves the overall energy density, cycle performance and safety of the electrochemical device.

[0021] 3. This application adopts low-pressure vapor deposition method to prepare the coating layer. The organic ligand and the metal ions on the surface of the ternary transition metal oxide are formed through coordination. It has strong binding force and high interface stability. It can maintain good protection during long-term circulation and improve the cycle performance of the electrochemical device. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a TEM image of the positive electrode material provided in Example 4 of the present application; Figure 2 1 is the XRD diagram of the positive electrode material corresponding to Example 4 and Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0023] The embodiments of the present invention will be described in detail below with reference to the examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. Specific conditions not specified in the examples are carried out according to conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used without indicating the manufacturer are all conventional products that can be purchased commercially.

[0024] The following is a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0025] Example 1 This embodiment provides a positive electrode material, and the preparation method thereof includes: 1. Using NCM523 as a ternary transition metal oxide and 2-methylimidazole as an organic ligand, NCM523 and 2-methylimidazole are mixed in a mass ratio of 1:2 to obtain a mixed material; 2. The obtained mixed material was subjected to low-pressure vapor deposition under vacuum conditions of 100 Pa, a temperature of 140°C, and a deposition time of 4 hours to obtain a coated positive electrode material.

[0026] Example 2 The difference between this embodiment and embodiment 1 is that the temperature of low-pressure vapor deposition is 140° C., and the time of low-pressure vapor deposition is 8 hours.

[0027] Example 3 The difference between this embodiment and embodiment 1 is that the temperature of low-pressure vapor deposition is 150° C. and the time is 4 hours.

[0028] Example 4 The difference between this embodiment and embodiment 1 is that the temperature of low-pressure vapor deposition is 150° C. and the time is 8 hours.

[0029] Example 5 The difference between this embodiment and embodiment 4 is that the mass ratio of NCM523 to 2-methylimidazole in the mixture is 1:0.3.

[0030] Example 6 The difference between this embodiment and embodiment 4 is that the mass ratio of NCM523 to 2-methylimidazole in the mixture is 1:8.

[0031] Example 7 The difference between this embodiment and embodiment 4 is that NCM811 is used as the ternary transition metal oxide and 2-methylimidazole is used as the organic ligand.

[0032] Example 8 The difference between this embodiment and embodiment 4 is that NCM622 is used as the ternary transition metal oxide and 2-methylimidazole is used as the organic ligand.

[0033] Example 9 The difference between this embodiment and embodiment 4 is that NCM111 is used as the ternary transition metal oxide and 2-methylimidazole is used as the organic ligand.

[0034] Example 10 The difference between this embodiment and embodiment 1 is that NCA is used as the ternary transition metal oxide and N-methylimidazole is used as the organic ligand.

[0035] Comparative Example 1 NCM523 is directly used as the positive electrode material without coating.

[0036] Comparative Example 2 The commercial positive electrode material 1 purchased has NCM523 as the core and a carbon coating layer.

[0037] Comparative Example 3 The commercial cathode material 2 purchased has NCM523 as the core and a transition metal-doped LiAlO2 coating layer.

[0038] Comparative Example 4 The difference between this comparative example and Example 4 is that the mass ratio of NCM523 to 2-methylimidazole in the mixture is 1:10.

[0039] Comparative Example 5 The difference between this comparative example and Example 4 is that the temperature of low-pressure vapor deposition is 260° C. and the time is 4 hours.

[0040] Comparative Example 6 The difference between this comparative example and Example 1 is that the temperature of low-pressure vapor deposition is 110° C. and the time is 10 h.

[0041] Comparative Example 7 The difference between this comparative example and Example 1 is that 2,5-dihydroxyterephthalic acid is used as the organic ligand.

[0042] Performance testing 1. Assemble half-cell electrochemical performance test: (1) Assembling button half-cell Positive electrode sheet: The positive electrode material, conductive agent Super P, and binder polyvinylidene fluoride (PVDF) are thoroughly stirred and mixed in an N-methylpyrrolidone solvent system at a weight ratio of 96.8:1.5:1.7, and then coated on Al foil, dried, and cold pressed to obtain a positive electrode sheet.

[0043] Negative electrode: lithium sheet with a diameter of 16 mm.

[0044] Diaphragm: PP porous polymer film as the separator Electrolyte: 1M LiPF6 in EC:EMC:DMC=1:1:1(Vol%) Lithium-ion battery assembly: Lithium-ion batteries are assembled in an inert glove box in the order of lithium metal sheet-diaphragm-electrolyte-positive electrode sheet.

[0045] 1. The assembled lithium-ion battery was subjected to electrochemical performance testing at a voltage range of 2.8-4.3V and a current density of 0.1C. The results are shown in Table 1: Table 1. Material properties and electrochemical performance 2. Assemble the full battery electrochemical performance test (1) Assemble the soft pack battery: Positive electrode sheet: The positive electrode material, conductive agent Super P, and binder polyvinylidene fluoride (PVDF) are thoroughly stirred and mixed in an N-methylpyrrolidone solvent system at a weight ratio of 96.8:1.5:1.7, and then coated on Al foil, dried, and cold pressed to obtain a positive electrode sheet.

[0046] Negative electrode sheet: The active material artificial graphite, conductive agent Super P, binder styrene-butadiene rubber (SBR), and thickener carbon methyl cellulose sodium (CMC) are thoroughly stirred and mixed in a deionized water solvent system in a weight ratio of 95.5:1.5:1.2:1.8, and then coated on Cu foil, dried, and cold pressed to obtain the negative electrode sheet.

[0047] Diaphragm: PP porous polymer film as the separator Electrolyte: 1M LiPF6 in EC:EMC:DMC=1:1:1(Vol%) The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the cathode and anode to provide isolation, to obtain a bare cell. The bare cell is then placed in outer packaging and injected with the prepared basic electrolyte. After vacuum packaging, standing, formation (charging to 4.25V at a constant current of 0.1C), and capacity testing, a lithium-ion battery is obtained.

[0048] The obtained lithium-ion battery was subjected to electrochemical cycling test at a voltage range of 2.8-4.25V and a current density of 0.1C. After 800 cycles, the performance of each cell is shown in Table 2: Table 2. Material properties and battery cell performance It can be seen from Table 1 and Table 2 that: The ternary cathode materials provided in Examples 1-10 of the present application exhibited excellent gram capacity and capacity retention. The assembled soft-pack cells also exhibited excellent cycling performance, with no flatulence and low transition metal ion dissolution.

[0049] Combining Examples 1-4 and Comparative Examples 1-3, it can be seen that the MOF structure coating layer provided by the present invention can effectively inhibit the dissolution of metal ions and the release of oxygen, thereby improving the cycle performance and safety performance of the battery cell.

[0050] Combining Examples 4-6 and Comparative Example 4, it can be seen that when the mass ratio of transition metal oxide to organic ligand is 1:0.3-8, the coating effect is best. When the proportion of organic ligand is too high, it not only increases the preparation cost, but also leads to a thicker coating layer, thereby reducing the discharge specific capacity of the ternary material.

[0051] Combining Examples 1-4 and Comparative Examples 5 and 6, it can be seen that during the low-pressure vapor deposition process, the temperature and time parameters of low-pressure vapor deposition have a significant impact on the performance of the ternary cathode material. When the temperature is too high or too low, the coating layer thickness will be inappropriate, resulting in a reduced coating effect.

[0052] Combining Example 1 and Comparative Example 7, it can be seen that the selection of organic ligands is critical in the coating process and will directly affect the coating effect.

[0053] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A positive electrode material, characterized in that It includes a ternary transition metal oxide and a coating layer on the ternary transition metal oxide, wherein the thickness of the coating layer is 1 nm to 20 nm; The coating layer is a MOF structure layer containing C, N, and O elements, which is formed by mixing a ternary transition metal oxide with an organic ligand and using a low-pressure vapor deposition method to coordinate the organic ligand with the metal ions on the surface of the ternary transition metal oxide.

2. The positive electrode material according to claim 1, characterized in that The ternary transition metal oxide includes one or more of NCM811, NCM622, NCM523, NCM111, NCA and ultra-high nickel 9 series ternary materials.

3. The positive electrode material according to claim 1, characterized in that The organic ligand is an aromatic or heterocyclic compound containing a multidentate ligand group, the multidentate ligand group is selected from carboxyl, amino, hydroxyl or nitrogen-containing heterocycle, and the aromatic or heterocyclic skeleton is selected from benzene ring, naphthalene ring or imidazole ring.

4. The positive electrode material according to claim 3, characterized in that The organic ligand is one or more of terephthalic acid, trimesic acid, 2-aminoisophthalic acid, 2-methylimidazole or N-methylimidazole.

5. The positive electrode material according to claim 1, characterized in that In the process of forming the coating layer, the mass ratio of the ternary transition metal oxide and the organic ligand when mixed is 1:0.3~8.

6. The positive electrode material according to claim 1, characterized in that The process parameters of the low pressure vapor deposition method are: Vacuum conditions are 100~150Pa, temperature is 120℃~250℃, and reaction time is 4-12h.

7. The positive electrode material according to any one of claims 1 to 6, characterized in that The specific surface area of the positive electrode material is 10 m 2 / g ~ 100 m 2 / g; the average particle size D50 of the positive electrode material is 3 μm~15 μm.

8. A method for preparing the positive electrode material according to any one of claims 1 to 7, characterized in that: It includes: An appropriate amount of the ternary transition metal oxide is mixed with an appropriate amount of an organic ligand, with a mass ratio of the ternary transition metal oxide to the organic ligand being 1:0.3-8. The mixture is heated at 120°C-250°C under vacuum conditions of 100-150 Pa and reacted for 4-12 hours to obtain the positive electrode material.

9. A positive electrode plate, characterized in that: It comprises the positive electrode material according to any one of claims 1 to 7.

10. An electrochemical device, characterized in that It includes: A positive electrode sheet, a negative electrode sheet, a separator and an electrolyte; wherein the positive electrode sheet is the positive electrode sheet according to claim 9.

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