Positive pole piece containing metal organic framework derived amorphous composite coating as well as preparation method and application of positive pole piece

Abstract

The invention belongs to the field of electrochemistry, and particularly relates to a positive pole piece containing a metal organic framework derived amorphous composite coating as well as a preparation method and application of the positive pole piece. The positive pole piece comprises a current collector, a first positive functional coating and a second positive functional coating. The first positive functional coating is arranged on at least one side surface of the current collector and contains a positive active material, a binder and a conductive material; and the second positive electrode functional coating is arranged on the surface of the first positive electrode functional coating and contains an aluminum-based metal organic framework (MOF) derived amorphous material, a binder and a conductive material. The structure can significantly inhibit the dissolution of transition metal ions and oxygen, has excellent performance in a wide temperature range and high rate, and is suitable for electrochemical devices such as lithium ion batteries and the like.

Description

Technical Field

[0001] This invention belongs to the field of electrochemistry, specifically relating to positive electrode sheets containing metal-organic framework-derived amorphous composite coatings, their preparation methods, and applications. Background Technology

[0002] With the development of high-energy-density lithium-ion batteries, high-nickel cathode materials have become a key choice due to their high specific capacity. However, capacity decay and interfacial side reactions caused by the dissolution of transition metal ions and the evolution of lattice oxygen during cycling severely limit battery life. Traditional solutions, such as inorganic oxide coatings like Al2O3 and TiO2, suffer from drawbacks such as rigid interfaces prone to cracking, low ionic conductivity, and inability to selectively adsorb electrolyte byproducts. Polymer coatings, on the other hand, are limited by poor high-temperature stability and insufficient chemical anchoring ability.

[0003] Metal-organic frameworks (MOFs) have been explored for electrode modification due to their controllable pore structure; however, their crystal structure is prone to collapse during charge and discharge, and they exhibit poor conductivity. Existing patent CN115006603A uses direct MOF crystal coating, but fails to resolve the conflict between structural stability and electronic conduction. Therefore, it is necessary to develop composite coatings that combine interface protection, ion conduction, and electron transport functions. Through structural transformation and component synergy, the balance between cycle stability and kinetic performance of high-nickel cathodes can be addressed. Summary of the Invention

[0004] To address the problems of existing technologies, this invention provides a positive electrode sheet containing a metal-organic framework-derived amorphous composite coating, its preparation method, and its application. In this invention, the aluminum-based MOF glass transition coating and the aluminum-containing high-nickel positive electrode have a synergistic effect. Aluminum-based MOF-derived amorphous materials, such as products formed by glass transition of aluminum-based MOFs like Al-MIL-53 and Al-MIL-120, have a disordered atomic arrangement structure with micropore sizes ≤0.6nm, enabling them to construct a three-dimensional interpenetrating conductive network structure with conductive materials. This coating continuously covers the surface of the first positive electrode functional coating containing the aluminum-containing high-nickel positive electrode material, effectively suppressing metal ion and oxygen dissolution. After 500 cycles at 1C charge / discharge rate within a voltage range of 3.0-4.3V and 25℃, the amount of transition metal elements dissolved is ≤50ppm, demonstrating significant advantages over traditional technologies in improving battery stability and cycle life.

[0005] This invention provides a positive electrode sheet, its preparation method, and an electrochemical device to solve the stability and kinetic problems of nickel-cobalt-aluminum positive electrodes. The electrode sheet contains a current collector and first and second positive electrode functional coatings. The first coating contains a positive electrode active material, a binder, and a conductive agent; the second coating is an aluminum-based MOF-derived amorphous material, a binder, and a conductive material, forming a three-dimensional interpenetrating network, with the amorphous material having channels ≤ 0.6 nm.

[0006] During preparation, the first coating is formed by applying and curing a corresponding slurry; the second coating is achieved by dispersing an aluminum-based MOF, a conductive agent, and a binder in a polar solvent, followed by gradient drying to achieve a glass transition. This design combines interface protection, ion conduction, and electron transport functions, improving cycling stability and rate performance.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] In a first aspect, this application provides a positive electrode sheet, including a current collector, a first positive electrode functional coating disposed on at least one side surface of the current collector along the thickness direction, the first positive electrode functional coating comprising a positive electrode active material, a binder and a conductive agent, and a second positive electrode functional coating continuously covering the entire surface of the first positive electrode functional coating away from the current collector, the second positive electrode functional coating comprising an aluminum-based MOF-derived amorphous material, a binder and a conductive agent.

[0009] Preferably, the current collector is an aluminum foil, an aluminum alloy foil, or a surface-treated metal composite foil with a thickness of 5μm-20μm.

[0010] Preferably, the thickness of the first positive electrode functional coating is 50μm-400μm, and the thickness of the second positive electrode functional coating is 100nm-500nm.

[0011] Preferably, the areal density of the second positive electrode functional coating is 0.1 mg / cm²-2 mg / cm², and the interfacial bonding force with the first positive electrode functional coating is ≥ 500 mN.

[0012] Preferably, the positive electrode active material is a high-nickel positive electrode material LiNi. 1-x-y-z Co x Mn y Al z O2, where 0≤x≤0.15, 0≤y≤0.1, 0≤z≤0.1.

[0013] Preferably, the aluminum-based MOF-derived amorphous material is a product of MOF glass transition, including one of Al-MIL-53 and Al-MIL-120 aluminum-based MOFs;

[0014] Preferably, the adhesive comprises a fluoropolymer or a hydrophobic polyolefin derivative;

[0015] Preferably, the conductive agent comprises a carbonaceous conductive agent or a metal-based conductive agent, or a mixture thereof;

[0016] Preferably, the aluminum-based MOF-derived amorphous material has a disordered atomic arrangement structure with a micropore size ≤0.6nm, and forms a three-dimensional interpenetrating conductive network structure with the conductive agent;

[0017] Secondly, this application provides a method for preparing a positive electrode sheet, characterized by comprising the following steps:

[0018] (a) A first positive electrode slurry is coated on the surface of the current collector and dried to form a first positive electrode functional coating;

[0019] (b) A second positive electrode slurry is coated on the surface of the first positive electrode functional coating, and the second positive electrode functional coating is formed by multi-stage drying process;

[0020] The first positive electrode slurry comprises a positive electrode active material, a binder, a conductive agent, and a polar organic solvent; the second positive electrode slurry comprises an aluminum-based MOF, a binder, a conductive agent, and a polar organic solvent.

[0021] Preferably, the solid content of the first positive electrode slurry is 50wt%-80wt%, and the solid content of the second positive electrode slurry is 1.0wt%-30wt%.

[0022] The preparation method for step (b) is as follows:

[0023] (i) Dissolve aluminum nitrate and terephthalic acid in N,N-dimethylformamide at a certain molar ratio, react with hydrothermal method at 80-180℃ for 12-48 hours, and finally activate by vacuum drying for 12 hours to obtain aluminum-based MOF;

[0024] (ii) Disperse aluminum-based MOF, conductive material, and binder in N-methylpyrrolidone solvent to form a second positive electrode slurry;

[0025] (iii) Cover the surface of the first positive electrode functional coating with the second positive electrode slurry;

[0026] (iv) Gradient temperature drying: The electrode is vacuum dried at 80℃-120℃ for 0.5h-2h to remove most of the solvent, and then annealed at 150℃-250℃ for 0.5h-2h. After that, it is quenched to room temperature to inhibit MOF recrystallization and promote the formation of amorphous structure, and finally obtains glassy coating to form the second positive electrode functional coating. The thickness after drying is controlled at 100-500nm.

[0027] Preferably, the mass ratio of aluminum-based MOF, conductive material and binder in step (ii) is 95wt%-99wt%: 0.6wt%-3wt%: 0.4wt%-2wt%.

[0028] Thirdly, this application provides an electrochemical device, the specific structure of which and its testing are as follows:

[0029] Positive electrode sheet: The composite coating positive electrode sheet according to claims 1-6 is adopted, wherein the thickness of the first positive electrode functional coating is 50μm-400μm and the thickness of the second positive electrode functional coating is 100nm-500nm. For specific solutions, please refer to the embodiments.

[0030] Negative electrode sheet: Silicon carbon, conductive carbon black, and acrylonitrile multi-component copolymer are slurried in a mass fraction ratio of 91:3:6, then coated on copper foil, dried, and rolled into a negative electrode sheet with a compaction density of 1.5 g / cm3.

[0031] Electrolyte: A ternary + silicon-carbon system electrolyte is used.

[0032] The membrane is made of polyethylene porous membrane with a thickness of 12μm and a porosity of 45%.

[0033] Battery assembly: Aluminum-plastic composite film is used for soft pack packaging. Before packaging, the stacking and electrolyte injection are completed in a dry room (dew point ≤ -40℃) with an injection volume of 3g / Ah. After vacuum packaging, formation and capacity testing are carried out.

[0034] Rate testing: At 25℃, charge and discharge cycles were performed at current densities of 0.2C, 0.5C, 1C, 2C, and 5C, respectively. The discharge specific capacity and capacity retention rate relative to 0.2C were recorded at each rate.

[0035] High and low temperature tests: The charge and discharge capacity was tested at a 1C rate under environments of -20℃, 0℃, 45℃ and 60℃, and the capacity retention rate relative to 25℃ was calculated at different temperatures.

[0036] Cyclic performance test: Using a battery testing system, at a room temperature of 25℃ and a voltage range of 3.0-4.3V, the battery was cycled 500 times at a 1C charge-discharge rate to test its cyclic performance and record its discharge capacity retention rate after 500 cycles.

[0037] Metal ion dissolution test: After 500 cycles, the battery was disassembled and the amount of dissolution of metal ions such as Ni, Co, Mn, and Al in the negative electrode was detected by inductively coupled plasma mass spectrometry (ICP-MS).

[0038] Oxygen dissolution detection: Gas chromatography is used to monitor the composition and content of gases such as O2 and CO2 released during battery cycling.

[0039] Compared with existing technologies, the beneficial effects of this invention are as follows: The positive electrode sheet includes a current collector, a first positive electrode functional coating, and a second positive electrode functional coating. The first positive electrode functional coating is disposed on at least one side of the current collector surface and contains positive electrode active material, binder, and conductive material; the second positive electrode functional coating is disposed on the surface of the first positive electrode functional coating and contains aluminum-based metal-organic framework (MOF) derived amorphous material, binder, and conductive material. This structure can significantly suppress the dissolution of transition metal ions and oxygen, and performs excellently over a wide temperature range and at high rates, making it suitable for electrochemical devices such as lithium-ion batteries. Through the design of the positive electrode sheet structure, especially the innovative materials and processes of the second positive electrode coating, the overall performance of aluminum-containing high-nickel positive electrode lithium-ion batteries is significantly improved. By constructing an amorphous glassy functional coating made of aluminum-based MOF through gradient thermal treatment on the surface of a conventional positive electrode sheet and adding conductive material to form a conductive network, the dissolution of transition metal ions and oxygen is significantly suppressed, and excellent performance is achieved over a wide temperature range and at high rates, making it suitable for electrochemical devices such as lithium-ion batteries. Detailed Implementation

[0040] The present invention will be further described in detail below through embodiments. These embodiments are only used to illustrate the present invention and do not limit the scope of the present invention.

[0041] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0042] Example 1

[0043] Preparation of the first positive electrode coating

[0044] Nickel-cobalt-aluminum based cathode material LiNi 0.80 Co 0.10 Al 0.10 O2 (97.6 wt%), PVDF binder (1.2 wt%), carbon nanotubes and conductive carbon black (mass ratio 1:3, total percentage 1.2 wt%) were added to N-methylpyrrolidone solvent, and the solid content was controlled to 70 wt% to obtain the first positive electrode slurry. The first positive electrode slurry was coated on the surface of a 13 μm aluminum foil with a wet film thickness of 200 μm. It was dried at 120℃ for 2 h, and then rolled to achieve a compaction density of 3.5 g / cm³ to obtain the first positive electrode coating.

[0045] Preparation of the second positive electrode coating

[0046] (i) Aluminum nitrate and terephthalic acid were dissolved in N,N-dimethylformamide in a 1:1 molar ratio, and the mixture was reacted at 100°C for 12 hours by hydrothermal method. Finally, it was activated by vacuum drying for 12 hours to obtain aluminum-based MOF.

[0047] (ii) Disperse aluminum-based MOF, conductive material and binder in N-methylpyrrolidone solvent at a mass ratio of 95wt%:3wt%:2wt% and a solid content of 5wt% to form a second positive electrode slurry;

[0048] (iii) Spray the second positive electrode slurry onto the surface of the first positive electrode coating, and control the coating thickness to be 200 nm;

[0049] (iv) Vacuum drying at 80℃ for 1h to remove solvent, followed by annealing at 220℃ for 1h, and then quenching to room temperature to transform aluminum-based MOF crystals into amorphous glass, thus obtaining the target positive electrode.

[0050] Example 2

[0051] The difference between Example 2 and Example 1 is that the active material of the first positive electrode coating is LiNi. 0.80 Co 0.15 Al 0.05 O2, the rest is the same as in Example 1.

[0052] Example 3

[0053] The difference between Example 3 and Example 1 is that the active material of the first positive electrode coating is LiNi. 0.92 Co 0.03 Al 0.05 O2, the rest is the same as in Example 1.

[0054] Example 4

[0055] The difference between Example 4 and Example 1 is that the active material of the first positive electrode coating is LiNi. 0.80 Co 0.05 Mn 0.10 Al 0.05 O2, the rest is the same as in Example 1.

[0056] Example 5

[0057] The difference between Example 5 and Example 1 is that the active material of the first positive electrode coating is LiNi. 0.8 Co 0.1 Mn 0.1 O2, without aluminum doping, otherwise consistent with Example 1.

[0058] Comparative Example 1

[0059] The difference between Comparative Example 1 and Example 1 is that there is no second positive electrode coating, but otherwise it is the same as Example 1.

[0060] Comparative Example 2

[0061] The difference between Comparative Example 2 and Example 1 is that the second positive electrode coating is dried at a single temperature, vacuum dried at 80°C for 1 hour to remove the solvent, without gradient treatment, and the MOF is not vitrified to maintain the crystal structure. The rest is the same as Example 1.

[0062] Comparative Example 3

[0063] The difference between Comparative Example 3 and Example 1 is that the second positive electrode coating does not contain a conductive agent, while the rest is the same as in Example 1.

[0064] The core value of this patented solution lies in its significantly improved overall performance of aluminum-containing high-nickel cathode lithium-ion batteries through innovative cathode structure design, particularly the innovative materials and processes used in the second cathode coating. Its core innovation involves constructing an amorphous glassy functional coating on the surface of a traditional cathode, formed by gradient thermal treatment of an aluminum-based MOF, and adding conductive materials to form a conductive network. This significantly suppresses the dissolution of transition metal ions and oxygen, exhibiting excellent performance over a wide temperature range and at high rates, making it suitable for electrochemical devices such as lithium-ion batteries.

[0065]

[0066] Table 1

[0067] Based on the performance test data of the examples and comparative examples in Table 1, this design is universally applicable to various high-nickel cathode materials, such as NCA, NCMA, and ultra-high-nickel systems, with LiNi being a particularly suitable candidate. 0.80 Co 0.10 Al 0.10 Example 1, with O2 as the active material, exhibited the best overall performance: after 500 cycles at 1C, the capacity retention rate reached 92.1%, an improvement of 16.3% compared to Comparative Example 1 without the second coating; the capacity retention rate at -20℃ was as high as 87.5%, far exceeding the 48.1% of Comparative Example 1; at the same time, the capacity retention rate at 5C was improved by approximately 15.7%. The effect of inhibiting transition metal dissolution was particularly outstanding, with the nickel dissolution amount in Example 1 being only 5% of that in Comparative Example 1, proving that the aluminum-based MOF glass transition coating can effectively isolate electrolyte corrosion and delay interfacial side reactions.

[0068] The comparative experiments further revealed the key technical points. The omission of the second coating in Comparative Example 1 resulted in a comprehensive deterioration in cycling, low-temperature and metal leaching performance. The cycle retention rate of Comparative Example 2, which did not undergo glass transition treatment at 220℃, decreased to 72.1%, confirming the necessity of amorphous transformation for interface stability. Meanwhile, the capacity retention rate of Comparative Example 3, which did not contain conductive agent, was significantly reduced at a 5C rate, indicating the key role of the conductive network in the second positive electrode coating for ion / electron transport.

[0069] This invention discloses a positive electrode and an electrochemical device comprising it, relating to the field of electrochemical technology. In this invention, the aluminum-based MOF glass transition coating and the aluminum-containing high-nickel positive electrode have a synergistic effect. This coating continuously covers the surface of the first positive electrode functional coating where the aluminum-containing high-nickel positive electrode material is located, effectively suppressing metal ion dissolution and oxygen dissolution. After 500 cycles at a 1C charge-discharge rate within a voltage range of 3.0-4.3V and 25℃, the amount of transition metal elements dissolved is ≤50ppm, significantly improving the cycle life, high-temperature performance, and safety of lithium-ion batteries.

[0070] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0071] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A positive electrode sheet containing a metal-organic framework-derived amorphous composite coating, characterized in that, include: Current collector, first positive electrode functional coating, second positive electrode functional coating; A first positive electrode functional coating is disposed on at least one side surface of the current collector along the thickness direction, and the first positive electrode functional coating comprises a positive electrode active material, a binder, and a conductive material; The second positive electrode functional coating continuously covers the entire surface of the first positive electrode functional coating away from the current collector, and the second positive electrode functional coating comprises an aluminum-based MOF-derived amorphous material, a binder, and a conductive material.

2. The positive electrode sheet with a metal-organic framework-derived amorphous composite coating according to claim 1, characterized in that: The thickness of the first positive electrode functional coating is 50μm-400μm, and the thickness of the second positive electrode functional coating is 100nm-500nm.

3. The positive electrode sheet with a metal-organic framework-derived amorphous composite coating according to claim 1, characterized in that: The areal density of the second positive electrode functional coating is 0.1 mg / cm²-2 mg / cm², and the interfacial bonding force with the first positive electrode functional coating is ≥ 500 mN.

4. The positive electrode sheet with a metal-organic framework-derived amorphous composite coating according to claim 1, characterized in that: The positive electrode active material is a high-nickel positive electrode material LiNi. 1-x-y-z Co x Mn y Al z O2, where 0≤x≤0.15, 0≤y≤0.1, 0≤z≤0.

1.

5. The positive electrode sheet with a metal-organic framework-derived amorphous composite coating according to claim 1, characterized in that: The aluminum-based MOF-derived amorphous materials are products formed by the glass transition of MOFs, including one of Al-MIL-53 and Al-MIL-120 aluminum-based MOFs.

6. The positive electrode sheet with a metal-organic framework-derived amorphous composite coating according to claim 1, characterized in that: The aluminum-based MOF-derived amorphous material has a disordered atomic arrangement structure with a micropore size ≤ 0.6 nm, and forms a three-dimensional interpenetrating conductive network structure with the conductive material.

7. A method for preparing a positive electrode sheet containing a metal-organic framework-derived amorphous composite coating according to any one of claims 1-6, characterized in that, Includes the following steps: (a) A first positive electrode slurry is coated on the surface of the current collector and dried to form a first positive electrode functional coating; (b) A second positive electrode slurry is coated on the surface of the first positive electrode functional coating, and the second positive electrode functional coating is formed by multi-stage drying process; The first positive electrode slurry comprises a positive electrode active material, a binder, a conductive material, and a polar organic solvent; the second positive electrode slurry comprises an aluminum-based MOF, a binder, a conductive material, and a polar organic solvent.

8. The preparation method according to claim 7, characterized in that: The first positive electrode slurry has a solid content of 50wt%-80wt%, and the second positive electrode slurry has a solid content of 1.0wt%-30wt%.

9. The preparation method according to claim 7, characterized in that, Step (b) includes: (i) Dissolve aluminum nitrate and terephthalic acid in N,N-dimethylformamide at a certain molar ratio, react with hydrothermal method at 80-180℃ for 12-48 hours, and finally activate by vacuum drying for 12 hours to obtain aluminum-based MOF; (ii) Disperse aluminum-based MOF, conductive material, and binder in N-methylpyrrolidone solvent to form a second positive electrode slurry; (iii) Cover the surface of the first positive electrode functional coating with the second positive electrode slurry; (iv) Gradient temperature drying: The electrode is vacuum dried at 80℃-120℃ for 0.5h-2h; annealed at 150℃-250℃ for 0.5h-2h, and then quenched to room temperature to form the second positive electrode functional coating.

10. An application of a positive electrode sheet containing a metal-organic framework-derived amorphous composite coating according to claim 7, characterized in that, The positive electrode is used in an electrochemical device, which includes a positive electrode, wherein the thickness of the first positive electrode functional coating is 50μm-400μm and the thickness of the second positive electrode functional coating is 100nm-500nm. Negative electrode sheet: Silicon carbon, conductive carbon black and acrylonitrile multi-component copolymer are slurried in a mass fraction ratio of 91:3:6, then coated on copper foil, dried and rolled into a negative electrode sheet with a compaction density of 1.5 g / cm3. Electrolyte: A ternary + silicon-carbon system electrolyte is used; The membrane is made of polyethylene porous membrane with a thickness of 12μm and a porosity of 45%.

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