A MOF-derived amorphous carbon / metal oxide composite undercoat layer, a preparation method and application thereof, and a positive electrode sheet and a lithium ion battery

Abstract

The application belongs to the technical field of electrode material preparation, and discloses a MOF-derived amorphous carbon / metal oxide composite undercoat layer, a preparation method and application thereof, and a positive electrode sheet and a lithium ion battery. The composite undercoat layer is formed by in-situ pyrolysis of MOF crystals on the surface of a current collector, and comprises an amorphous carbon skeleton and metal oxide nanoparticles. In the application, the MOF crystals are used as a precursor to perform in-situ pyrolysis on the surface of a positive electrode current collector, so as to form a MOF-derived amorphous carbon / metal oxide composite undercoat layer. Different from the existing MOF original form application and active material coating, the application forms a chemical bond between the coating and the current collector through in-situ pyrolysis, thereby solving the problem of weak adhesion between the traditional undercoat layer and the current collector.

Description

Technical Field

[0001] This invention relates to the field of electrode material preparation technology, and in particular to a MOF-derived amorphous carbon / metal oxide composite undercoating, its preparation method and application, as well as a positive electrode and a lithium-ion battery. Background Technology

[0002] Metal-organic frameworks (MOFs) have attracted attention in the lithium-ion battery field due to their high specific surface area and well-organized pore structure. Existing technologies have reported the use of MOFs or MOF derivatives for coating and modifying the surface of cathode active material particles. For example, lithium iron phosphate particles are embedded in MOF-derived porous carbon networks. Utilizing the characteristics of MOFs, such as easy high-temperature decomposition, large specific surface area, and three-dimensional network structure, a uniform porous carbon network is obtained by pyrolysis and reduction on the particle surface. Other technologies involve directly adding MOF materials to high-nickel ternary cathode materials for modification, or calcining transition metal MOFs to generate MOF derivatives, which are then ball-milled and mixed with nickel-cobalt-manganese ternary materials for coating.

[0003] However, in the above technologies, MOFs are all used for coating and modifying active material particles, and there are no reports of in-situ pyrolysis of MOFs on the surface of the cathode current collector to form an amorphous carbon / metal oxide composite undercoating.

[0004] In addition, traditional base coatings (such as boehmite / conductive agent / PVDF system) bond with current collectors through physical adhesion, and their peel strength is usually less than 15 N / m and their conductivity is less than 1 S / cm, which makes it difficult to meet the dual requirements of conductivity and adhesion for high energy density batteries. Summary of the Invention

[0005] The purpose of this invention is to provide a MOF-derived amorphous carbon / metal oxide composite undercoating, its preparation method and application, as well as a positive electrode and a lithium-ion battery, to solve the problems of weak bonding between existing positive electrode undercoatings and current collectors, and the limited application of MOFs in undercoatings.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a MOF-derived amorphous carbon / metal oxide composite undercoat, which is formed by in-situ pyrolysis of MOF crystals on the surface of a current collector and comprises: an amorphous carbon framework and metal oxide nanoparticles; The amorphous carbon framework is formed by the carbonization of organic ligands in MOF crystals during pyrolysis; The metal oxide nanoparticles are formed by the pyrolysis of metal ions in MOF crystals.

[0007] Preferably, the thickness of the MOF-derived amorphous carbon / metal oxide composite undercoat is 1~5 μm.

[0008] Preferably, the mass fraction of the amorphous carbon skeleton in the MOF-derived amorphous carbon / metal oxide composite undercoat is 40~70 wt%.

[0009] Preferably, the mass fraction of metal oxide nanoparticles in the MOF-derived amorphous carbon / metal oxide composite undercoat is 30~60 wt%.

[0010] Preferably, the metal oxide nanoparticles in the MOF-derived amorphous carbon / metal oxide composite undercoat are one or more of ZnO, ZrO2, and Co3O4.

[0011] This invention also provides a method for preparing a MOF-derived amorphous carbon / metal oxide composite undercoat, comprising the following steps: S1, MOF precursor coating: MOF crystals are dispersed in a solvent to form a slurry, the slurry is coated on the surface of the current collector, and after drying, a MOF precursor layer is formed; S2. In-situ pyrolysis: The current collector coated with the MOF precursor layer is placed in a protective atmosphere for in-situ pyrolysis to form the MOF-derived amorphous carbon / metal oxide composite undercoating.

[0012] Preferably, the MOF crystal is one or more of ZIF-8, UiO-66, and ZIF-67.

[0013] Preferably, the solvent is methanol or ethanol; the protective atmosphere is argon or nitrogen.

[0014] Preferably, the in-situ pyrolysis temperature is 400~600℃, the time is 0.5~4 h, and the heating rate is 1~10℃ / min.

[0015] This invention also provides an application of MOF-derived amorphous carbon / metal oxide composite undercoating in lithium-ion battery cathode materials.

[0016] The present invention also provides a positive electrode sheet, the positive electrode sheet comprising a positive current collector, a base coating, and a positive active material layer disposed on the base coating; the base coating is the above-mentioned MOF-derived amorphous carbon / metal oxide composite base coating.

[0017] The present invention also provides a lithium-ion battery, wherein the lithium-ion battery includes the above-mentioned positive electrode sheet.

[0018] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects: This invention uses MOF crystals as a precursor and performs in-situ pyrolysis on the surface of the positive electrode current collector to form an amorphous carbon / metal oxide composite undercoat derived from MOF. Unlike existing MOF applications in their original form and active material coatings, this invention achieves chemical bonding between the coating and the current collector through in-situ pyrolysis: during in-situ pyrolysis under a protective atmosphere, the metal nodes in the MOF crystals transform into metal oxide nanoparticles, which react interfacially with the alumina layer on the surface of the current collector (e.g., aluminum foil), forming Al-OM (M is Zn, Zr, Co, etc.) chemical bonds; simultaneously, the amorphous carbon formed by the carbonization of organic ligands generates strong carbon-aluminum interactions with the current collector surface, enabling the undercoat to adhere to the current collector at a chemical bonding level, significantly improving peel strength and solving the problem of weak adhesion between traditional undercoats and current collectors. Specifically: Strong interfacial bonding: In-situ pyrolysis forms chemical bonds, and the peel strength can reach 24.5 N / m (compared to only 12~13 N / m by traditional wet process). Excellent electrical conductivity: The MOF-derived carbon framework forms a continuous conductive network with a conductivity of up to 2.8 S / cm; Good thermal stability: The metal oxide components are stable at high temperatures, improving battery safety performance. Detailed Implementation

[0019] The present invention provides a MOF-derived amorphous carbon / metal oxide composite undercoat, which is formed by in-situ pyrolysis of MOF crystals on the surface of a current collector and includes: an amorphous carbon framework and metal oxide nanoparticles.

[0020] In this invention, the amorphous carbon framework is preferably formed by the carbonization of organic ligands in MOF crystals during pyrolysis, thus constituting a continuous conductive network.

[0021] In this invention, the metal oxide nanoparticles are preferably formed by metal ions in MOF crystals during pyrolysis and are uniformly dispersed in an amorphous carbon framework.

[0022] In this invention, the thickness of the MOF-derived amorphous carbon / metal oxide composite undercoat is preferably 1~5 μm, and more preferably 2~3 μm.

[0023] In this invention, the mass fraction of the amorphous carbon skeleton in the MOF-derived amorphous carbon / metal oxide composite undercoat is preferably 40-70 wt%, and more preferably 45-60 wt%.

[0024] In this invention, the mass fraction of metal oxide nanoparticles in the MOF-derived amorphous carbon / metal oxide composite undercoat is preferably 30-60 wt%, and more preferably 40-55 wt%.

[0025] In this invention, the metal oxide nanoparticles in the MOF-derived amorphous carbon / metal oxide composite undercoat are preferably one or more of ZnO, ZrO2, and Co3O4, and more preferably ZnO or ZrO2.

[0026] This invention also provides a method for preparing a MOF-derived amorphous carbon / metal oxide composite undercoat, comprising the following steps: S1, MOF precursor coating: MOF crystals are dispersed in a solvent to form a slurry, the slurry is coated on the surface of the current collector, and after drying, a MOF precursor layer is formed; S2. In-situ pyrolysis: The current collector coated with the MOF precursor layer is placed in a protective atmosphere for in-situ pyrolysis to form the MOF-derived amorphous carbon / metal oxide composite undercoating.

[0027] In this invention, the MOF crystal is preferably one or more of ZIF-8, UiO-66, and ZIF-67, and more preferably ZIF-8, UiO-66, or ZIF-67.

[0028] In this invention, the solvent is preferably methanol or ethanol, and more preferably methanol.

[0029] In this invention, the protective atmosphere is preferably argon or nitrogen, and more preferably argon.

[0030] In this invention, the temperature of the in-situ pyrolysis is preferably 400~600℃, more preferably 450~550℃, the time is preferably 0.5~4 h, more preferably 1~3 h, and the heating rate is preferably 1~10 ℃ / min, more preferably 3~6℃ / min.

[0031] This invention also provides an application of MOF-derived amorphous carbon / metal oxide composite undercoating in lithium-ion battery cathode materials.

[0032] The present invention also provides a positive electrode sheet, the positive electrode sheet comprising a positive current collector, a base coating, and a positive active material layer disposed on the base coating; the base coating is the above-mentioned MOF-derived amorphous carbon / metal oxide composite base coating.

[0033] The present invention also provides a lithium-ion battery, wherein the lithium-ion battery includes the above-mentioned positive electrode sheet.

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] Example 1

[0036] (1) MOF precursor coating: ZIF-8 crystals (particle size of about 200 nm) were dispersed in methanol to prepare a slurry with a solid content of 15%. The slurry was coated on the surface of a 15 μm aluminum foil using a microgravure coating method and dried at 80 °C to form a MOF precursor layer with a thickness of about 3 μm.

[0037] (2) In-situ pyrolysis: The aluminum foil coated with the MOF precursor layer was placed in a tube furnace and heated to 500℃ at 5℃ / min under Ar atmosphere and held for 2 h. ZIF-8 was transformed into an amorphous carbon / ZnO composite base coating with a thickness of about 2.2 μm. Thermogravimetric analysis and energy dispersive spectroscopy (EDS) showed that the mass fraction of the amorphous carbon skeleton in the coating was about 55 wt% and the mass fraction of ZnO nanoparticles was about 45 wt%.

[0038] X-ray diffraction (XRD) analysis revealed that the amorphous carbon framework exhibited broadened characteristic peaks of amorphous carbon in the range of 2θ = 15° to 30°, while the metal oxide nanoparticles showed characteristic peaks of the hexagonal wurtzite structure of ZnO. Scanning electron microscopy (SEM) observation showed that the undercoat layer had a uniform thickness, a dense interface with the current collector, and no cracks or peeling.

[0039] (3) Battery assembly: NCM811 positive electrode active material layer is coated on the base coating and assembled with graphite negative electrode and PP / PE separator into 5 Ah soft pack battery.

[0040] Example 2

[0041] UiO-66 was used instead of ZIF-8, and the pyrolysis temperature was 550℃. The temperature was maintained for 2 h to obtain an amorphous carbon / ZrO2 composite base coating. The mass fraction of the amorphous carbon skeleton in the coating was about 50 wt%, and the mass fraction of ZrO2 was about 50 wt%. The rest was the same as in Example 1.

[0042] Example 3

[0043] ZIF-67 was used instead of ZIF-8, and the pyrolysis temperature was 450℃. The temperature was maintained for 2 h to obtain an amorphous carbon / Co3O4 composite base coating. The mass fraction of the amorphous carbon skeleton in the coating was about 50 wt%, the mass fraction of Co3O4 was about 50 wt%, and the rest was the same as in Example 1.

[0044] Comparative Example 1

[0045] The difference from Example 1: ZIF-8 was pyrolyzed into powder at 500°C for 2 hours, then mixed with PVDF and conductive carbon black in NMP at a ratio of 85:10:5, and coated onto aluminum foil with a thickness of 2.5 μm.

[0046] Comparative Example 2

[0047] The difference from Example 1: The traditional wet process was used, in which boehmite (Dv50=300 nm), PVDF and conductive carbon black were mixed in NMP at a ratio of 85:10:5 and coated onto aluminum foil with a thickness of 2.5 μm.

[0048] The performance test results of Examples 1-3 and Comparative Examples 1-2 are shown in Table 1.

[0049] Table 1 Summary of performance results for both examples and comparative examples

[0050] Results Analysis: The performance of Examples 1-3 was significantly better than that of Comparative Examples 1-2. The peel strength of Comparative Example 1 was only 14.2 N / m, far lower than that of Example 1 (24.5 N / m), Example 2 (23.8 N / m), and Example 3 (23.6 N / m). This proves that the chemical bonding formed between the MOF and the current collector surface during in-situ pyrolysis is the key to improved adhesion, and this effect cannot be achieved by pre-pyrolysis followed by coating. The peel strength of Comparative Example 2 was only 12.8 N / m, and the conductivity was only 0.5 S / cm. The peel strength of Example 1 was nearly twice that of Comparative Example 2, and the conductivity was 5.6 times that of Comparative Example 2. The peel strength of Example 3 was also close to 24 N / m, and the conductivity reached 2.6 S / cm. The above results demonstrate that the in-situ pyrolysis process of the present invention can construct a highly adhered and highly conductive amorphous carbon / metal oxide composite undercoating on the surface of the current collector using different MOF precursors (ZIF-8, UiO-66, ZIF-67), significantly improving interfacial adhesion and electrochemical performance.

[0051] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A MOF-derived amorphous carbon / metal oxide composite undercoat, characterized in that, The MOF-derived amorphous carbon / metal oxide composite undercoat is formed by in-situ pyrolysis of MOF crystals on the surface of the current collector, and includes: an amorphous carbon framework and metal oxide nanoparticles; The amorphous carbon framework is formed by the carbonization of organic ligands in MOF crystals during pyrolysis; The metal oxide nanoparticles are formed by the pyrolysis of metal ions in MOF crystals.

2. The MOF-derived amorphous carbon / metal oxide composite undercoat according to claim 1, characterized in that, The thickness of the MOF-derived amorphous carbon / metal oxide composite undercoat is 1~5 μm.

3. The MOF-derived amorphous carbon / metal oxide composite undercoat according to claim 1, characterized in that, The mass fraction of the amorphous carbon skeleton in the MOF-derived amorphous carbon / metal oxide composite undercoat is 40~70 wt%.

4. The MOF-derived amorphous carbon / metal oxide composite undercoat according to claim 1, characterized in that, The mass fraction of metal oxide nanoparticles in the MOF-derived amorphous carbon / metal oxide composite undercoat is 30-60 wt%; the metal oxide nanoparticles are one or more of ZnO, ZrO2, and Co3O4.

5. A method for preparing a MOF-derived amorphous carbon / metal oxide composite undercoat according to any one of claims 1 to 4, characterized in that, Includes the following steps: S1, MOF precursor coating: MOF crystals are dispersed in a solvent to form a slurry, the slurry is coated on the surface of the current collector, and after drying, a MOF precursor layer is formed; S2. In-situ pyrolysis: The current collector coated with the MOF precursor layer is placed in a protective atmosphere for in-situ pyrolysis to form the MOF-derived amorphous carbon / metal oxide composite undercoating.

6. The method for preparing a MOF-derived amorphous carbon / metal oxide composite undercoat according to claim 5, characterized in that, The MOF crystal is one or more of ZIF-8, UiO-66, and ZIF-67; the solvent is methanol or ethanol; and the protective atmosphere is argon or nitrogen.

7. The method for preparing a MOF-derived amorphous carbon / metal oxide composite undercoat according to claim 6, characterized in that, The in-situ pyrolysis temperature is 400~600℃, the time is 0.5~4 h, and the heating rate is 1~10 ℃ / min.

8. The application of the MOF-derived amorphous carbon / metal oxide composite undercoating as described in any one of claims 1 to 4 in lithium-ion battery cathode materials.

9. A positive electrode sheet, characterized in that, The positive electrode sheet includes a positive current collector, a base coating, and a positive active material layer disposed on the base coating; The base coating is a MOF-derived amorphous carbon / metal oxide composite base coating as described in any one of claims 1 to 4.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the positive electrode sheet as described in claim 9.

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