A vertically oriented composite cathode and a preparation method and application thereof

Abstract

This invention relates to a vertically oriented composite cathode, its preparation method, and its application, relating to the field of solid-state batteries. The vertically oriented composite cathode includes a conductive agent, which comprises a graphene nanomesh. The graphene nanomesh has a microporous structure and exhibits a preferred orientation perpendicular to the current collector in the electrode thickness direction. The composite cathode provided by this invention contains a microporous structure and a vertically oriented graphene nanomesh. Through a dual strategy of "opening" and "aligning," a "high-speed tunnel" for ion transport is constructed, significantly shortening the lithium-ion transport path. The tortuosity is reduced from >3.5 in traditional structures to below 1.2, overcoming the shortcomings of existing technologies.

Description

Technical Field

[0001] This invention relates to the field of solid-state batteries, and more particularly to a vertically oriented composite cathode, its preparation method, and its application. Background Technology

[0002] All-solid-state lithium batteries are considered the next generation of power batteries due to their superior safety and potential high energy density. Among all-solid-state batteries, sulfide solid electrolytes (such as Li6PS5Cl) possess ionic conductivity (>10⁻⁶) comparable to liquid electrolytes. -3 It has been extensively studied due to its S / cm ratio.

[0003] However, in practical cathode composite systems, graphene, a two-dimensional material with a high aspect ratio, is typically added to construct an efficient electron transport network. While graphene can significantly improve the electronic conductivity of the electrode, its inherent two-dimensional planar structure often exhibits random arrangement or horizontal stacking within the electrode. This structure produces two negative effects: (1) Tortuosity Issue: The graphene plane provides a barrier to lithium ions (Li ions). + The graphene is impermeable; ions must navigate around graphene sheets several micrometers wide to reach the surface of the active material. This extremely high tortuosity leads to severe polarization during high-current charging and discharging, limiting the fast-charging rate performance of solid-state batteries.

[0004] (2) Poor interfacial wettability: Original graphene is chemically inert and has poor compatibility with sulfur-containing solid electrolyte interfaces, which easily generates physical gaps and increases interfacial impedance.

[0005] Currently, although there are reports on porous carbon materials in existing technologies, it is difficult to achieve synergistic control of "atomic-level perforation" and "macroscopic vertical orientation". Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by providing a vertically oriented composite cathode, its preparation method, and its applications.

[0007] In a first aspect, the present invention provides a vertically oriented composite positive electrode, the vertically oriented composite positive electrode comprising a conductive agent, the conductive agent comprising a graphene nanowire network; The graphene nanonet has a microporous structure, and the graphene nanonet exhibits a preferred orientation perpendicular to the current collector in the electrode thickness direction.

[0008] Furthermore, the orientation degree of the graphene nanonet perpendicular to the preferred orientation of the current collector, characterized by the texture coefficient of the (002) crystal plane by XRD, is greater than 1.5, for example, it can be 1.8, 2.0, 2.2, 2.4 or any of the aforementioned values.

[0009] Furthermore, the microporous structure is a two-dimensional structure with atomic-level micropores, and the planar micropore density is 102. 11 cm -2 Up to 10 14 cm -2 For example, it can be 10 11 cm -2 10 12 cm -2 10 13 cm -2 10 14 cm -2 Or any of the aforementioned values; the aperture range is 0.5 nm to 5 nm, for example, it can be 0.5 nm, 1 nm, 1.5 nm, 2.0 nm, 2.5 nm, 4 nm, 5 nm or any of the aforementioned values.

[0010] Furthermore, sulfur-containing functional groups are grafted onto the pore edges of the microporous structure.

[0011] Furthermore, the surface of the graphene nanonet is modified with ferromagnetic metal nanoparticles, the loading of which is 0.1wt%~1wt%, and the ferromagnetic metal nanoparticles include paramagnetic Fe3O4 nanoparticles.

[0012] Furthermore, the vertically oriented composite positive electrode also includes a positive electrode active material and a solid electrolyte; The positive electrode active material includes a high-nickel positive electrode active material, and the high-nickel positive electrode active material includes at least one of NCM811 and NCM622; The solid electrolyte comprises sulfides, including silver-germanium sulfide electrolyte, which includes Li3PS4 and Li 10 GeP2S 12 At least one of Li6PS5Cl.

[0013] Secondly, the present invention provides a method for preparing the vertically oriented composite positive electrode as described in the first aspect, comprising the following steps: Graphene is perforated to form a graphene nanomesh with a nanomesh structure. Magnetic particles are loaded onto the surface of the graphene nanonet and then mixed with the remaining components to form a mixed slurry; The mixed slurry is coated onto the current collector and then placed in a vertical magnetic field to induce orientation. The magnetic field is then removed and the material is cured to obtain the vertically oriented composite positive electrode.

[0014] Furthermore, prior to the step of loading magnetic particles onto the surface of the graphene nanonet, the method further includes: The graphene nanonets were heat-treated in a sulfur-containing atmosphere to achieve edge sulfidation.

[0015] Furthermore, the above preparation method includes the following steps: (1) Hole formation treatment: High-density vacancy defects are introduced on the graphene surface by thermochemical etching or electrochemical oxidation to form a nano-network structure. Then, heat treatment at 400~600℃ is carried out in H2S atmosphere to achieve edge sulfurization modification. (2) Magnetic loading: Ultrafine paramagnetic particles are loaded onto the surface of graphene nanonets by in-situ reduction method; (3) Slurry preparation: The treated graphene nanonet, sulfide electrolyte and active material are mixed in anhydrous solvent and stirred at a pressure of 0.1~0.5 MPa; (4) Magnetic field induced orientation: After the slurry is coated on the current collector, before the solvent has completely evaporated, it is placed in a steady vertical magnetic field of 0.5~1.5 T for 10~30 minutes to induce the vertical rotation of the graphene sheets. (5) Compacting and curing: Remove the magnetic field and cold press the material under a pressure of 200~400 MPa.

[0016] Thirdly, the present invention provides an application of the vertically oriented composite cathode described in the first aspect or the vertically oriented composite cathode obtained by the preparation method of the vertically oriented composite cathode described in the second aspect in the preparation of solid-state batteries.

[0017] Furthermore, the solid-state battery includes an all-solid-state battery.

[0018] The technical solutions provided in the embodiments of the present invention have at least the following advantages compared with the prior art: This invention provides a vertically oriented composite cathode, its preparation method, and its application. The composite cathode provided by this invention contains a microporous structure and a vertically oriented graphene nanonet. Through a dual strategy of "opening" and "aligning," a "high-speed tunnel" for ion transport is constructed, greatly shortening the lithium-ion transport path. The tortuosity is reduced from >3.5 in traditional structures to below 1.2, overcoming the shortcomings of existing technologies. Specifically: (1) Significantly reduced tortuosity: Lithium ions can either pass directly through the micropores of the graphene plane or move in a straight line along the vertically arranged interlayer gaps, shortening the ion transport path by more than 60%.

[0019] (2) Excellent rate performance: Experimental verification shows that the capacity retention rate of the composite electrode of the present invention at a high rate of 5C is more than 3 times that of the traditional randomly distributed electrode.

[0020] (3) Reduced interfacial impedance: The micropore edges of the graphene nanonet are grafted with sulfur-containing functional groups, which enhances the interfacial compatibility with the sulfide electrolyte; at the same time, the edge sulfide groups provide a chemical environment similar to the sulfide electrolyte, eliminating the interfacial charge transfer barrier. Attached Figure Description

[0021] Figure 1 : A schematic diagram of the structure of the graphene nanonet in the vertically oriented composite cathode provided in this embodiment of the invention.

[0022] Figure 2 : TEM high-resolution transmission electron microscope image of the atomic-level micropores on the surface of the graphene nanonet in the vertically oriented composite cathode provided in this embodiment of the invention.

[0023] Figure 3 Comparison chart of discharge capacity at 0.1C, 1C, 3C and 5C rates in Embodiment 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0024] The present invention will be specifically described below through embodiments. It should be noted that these embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of the present invention. Those skilled in the art can make some non-essential improvements and adjustments based on the above description of the present invention.

[0025] Unless otherwise specified, all raw materials, reagents, instruments, and equipment used in this invention can be purchased commercially or prepared using existing methods. Furthermore, unless otherwise specified or detailed, the steps and parameters involved can be performed according to existing processing techniques or using existing equipment; these will not be elaborated upon in detail in this invention document.

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0027] Example 1 This example provides a vertically oriented composite positive electrode, comprising a positive electrode active material (specifically NCM811), a solid electrolyte (specifically Li6PS5Cl), and a conductive agent. The solid electrolyte comprises a sulfide, and the conductive agent is as follows: Figure 1 The graphene nanonet shown (Note: Figure 1 The yellow spheres in the image represent sulfur-containing functional groups grafted onto the edges of the micropores in the graphene nanomesh. The graphene nanomesh has a microporous structure, and the graphene nanomesh exhibits a preferred orientation perpendicular to the current collector in the electrode thickness direction. The degree of orientation of the graphene nanomesh perpendicular to the current collector, characterized by an XRD-represented (002) crystal plane texture coefficient greater than 1.5, specifically 2.1; the microporous structure is a two-dimensional structure with atomic-level micropores, and the planar micropore density is 102. 12 cm -2 The pore size ranges from 1 nm to 2 nm; sulfur-containing functional groups are grafted onto the pore edges of the microporous structure; and 0.5 wt% Fe3O4 nanoparticles are loaded on the surface of the graphene nanonet.

[0028] The above-mentioned method for preparing a vertically oriented composite cathode includes the following steps: (1) Take a single layer of graphene and place it in a solution containing dilute nitric acid and potassium permanganate for mild oxidation to create pores (specific conditions include: dilute nitric acid concentration: 0.1 M; potassium permanganate concentration: 2.0 mM; solid-liquid ratio (graphene / solution): 1 mg / 20 mL; reaction temperature: 40℃; reaction time: 60 min; stirring rate: 60 rpm), control the pore size to 1-2 nm, and obtain a graphene nanonet with a microporous structure.

[0029] (2) The graphene nanonet with microporous structure was annealed in an Ar / H2S mixed atmosphere (H2S volume fraction of 20%) at 500℃ for 2 hours to obtain edge-sulfurized graphene nanonet.

[0030] (3) Using the polyol method, 0.5 wt% of Fe3O4 nanoparticles were loaded onto the surface of edge-sulfurized graphene nanonets; Furthermore, the steps and parameters of the polyol method are as follows: A. High-purity ethylene glycol is used as a reducing agent and reaction medium; ferric chloride hexahydrate (FeCl3·6H2O) is used as an iron source with a concentration controlled at 0.03 M; anhydrous sodium acetate solution (0.3 M) and polyethylene glycol PEG-4000 (0.5 mg / mL) are used to regulate the alkalinity of the solution, assist in the nucleation and dispersion of nanoparticles, avoid the aggregation of Fe3O4 particles, and achieve monodisperse loading.

[0031] B. Hydrothermal reactor filling rate ~70%; reaction temperature: 180~190℃, constant temperature reaction time 10~12 h.

[0032] C. After completion, dry at a constant temperature of 60°C for 12 h in a vacuum drying oven. (4) In an argon glove box, mix the graphene nanonet, Li6PS5Cl and NCM811 obtained in step (3) above in a mass ratio of 1:2:15:82, and add xylene to make a slurry.

[0033] (5) After coating on aluminum foil (thickness of 50 μm), place it in a 1.2 T vertical magnetic field for 20 minutes until dry.

[0034] (6) Finally, the vertically oriented composite cathode is obtained by pressurizing and encapsulating it under a pressure of 300 MPa.

[0035] The high-resolution transmission electron microscope (TEM) image of the atomic-level micropores on the surface of the graphene nanomesh in the vertically oriented composite cathode provided in this embodiment is shown below. Figure 2 As shown.

[0036] Example 2 This example provides a vertically oriented composite cathode, which differs from Example 1 in that the pore size of the microporous structure in the graphene nanonet is 4-5 nm.

[0037] Example 3 This example provides a vertically oriented composite cathode, which differs from Example 1 in that the loading of Fe3O4 nanoparticles in the graphene nanonet is 0.1wt%.

[0038] Example 4 This example provides a vertically oriented composite cathode, which differs from Example 1 in that the loading of Fe3O4 nanoparticles in the graphene nanonet is 1wt%.

[0039] Example 5 This example provides a vertically oriented composite cathode, which differs from Example 1 in that the graphene nanonet is not subjected to edge sulfidation treatment (i.e., the graphene nanonet obtained in step (1) of Example 1 is directly subjected to step (3) in the preparation method).

[0040] Comparative Example 1 A composite cathode differs from Example 1 in that it uses the exact same raw material ratio, but no external magnetic field is applied during the coating process, and it uses untreated raw graphene.

[0041] The preparation method of the above-mentioned composite cathode includes the following processes: (1) Take the same single-layer graphene as in Example 1 and anneal it in an Ar / H2S mixed atmosphere (H2S volume fraction of 20%) at 500°C for 2 hours. Then, load 0.5wt% Fe3O4 nanoparticles on the surface in the same manner as in Example 1.

[0042] (2) In an argon glove box, the graphene, Li6PS5Cl and NCM811 obtained in step (1) above are mixed in a mass ratio of 1:2:15:82, and xylene is added to make a slurry.

[0043] (3) After coating the aluminum foil with the same thickness as in Example 1 and drying it, it is pressurized and encapsulated under a pressure of 300 MPa to obtain a composite positive electrode.

[0044] Comparative Example 2 A composite cathode differs from Example 1 in that it uses the exact same raw material ratio, but does not apply an external magnetic field during the coating process, and uses microporous graphene that has been treated with open pores.

[0045] The preparation method of the above-mentioned composite cathode includes the following processes: (1) Take the same single-layer graphene as in Example 1 and place it in a solution containing dilute nitric acid and potassium permanganate for mild oxidation to create pores (specific conditions and parameters are the same as in Example 1). Control the pore size to 1-2 nm to obtain a graphene nanonet with a microporous structure. Anneal it in an Ar / H2S mixed atmosphere (H2S volume fraction is 20%) at 500℃ for 2 hours. Then, load 0.5wt% Fe3O4 nanoparticles on the surface in the same manner as in Example 1.

[0046] (2) In an argon glove box, the graphene, Li6PS5Cl and NCM811 obtained in step (1) above are mixed in a mass ratio of 1:2:15:82, and xylene is added to make a slurry.

[0047] (3) After coating the aluminum foil with the same thickness as in Example 1 and drying it, it is pressurized and encapsulated under a pressure of 300 MPa to obtain a composite positive electrode.

[0048] Comparative Example 3 A composite cathode differs from Example 1 in that it uses the exact same raw material ratio and employs untreated raw graphene, but applies an external magnetic field during the coating process.

[0049] The preparation method of the above-mentioned composite cathode includes the following processes: (1) Take the same single-layer graphene as in Example 1 and anneal it in an Ar / H2S mixed atmosphere (H2S volume fraction of 20%) at 500°C for 2 hours. Then, load 0.5wt% Fe3O4 nanoparticles on the surface in the same manner as in Example 1.

[0050] (2) In an argon glove box, the graphene, Li6PS5Cl and NCM811 obtained in step (1) above are mixed in a mass ratio of 1:2:15:82, and xylene is added to make a slurry.

[0051] (3) After coating the aluminum foil with the same thickness as in Example 1 and drying it, it is pressurized and encapsulated under a pressure of 300 MPa to obtain a composite positive electrode.

[0052] Test case In this example, the composite positive electrodes obtained from the above embodiments and comparative examples were assembled into an all-solid-state mold battery (the negative electrode uses a 150 μm thick lithium-indium alloy, the electrolyte layer uses a 500 μm thick Li6PS5Cl, and it is encapsulated under pressure of 0.5~1.0 MPa using a sealing machine) and its electrical performance was tested. The test results are shown in Table 1. Furthermore, the discharge capacity of Embodiment 1 and Comparative Example 1 at 0.1C, 1C, 3C, and 5C rates is compared. Figure 3 As shown.

[0053] Table 1. Comparison of discharge specific capacity between each embodiment and the comparative example. As shown in Table 1: As shown in Examples 1 and 2, larger pore sizes can reduce the cycle life of the battery to some extent. This may be because larger pores lead to a decrease in the sulfation content, increasing the interfacial contact resistance between the electrolyte and the positive electrode. At the same time, larger pores mean a lower areal density of the loaded Fe3O4, which may be detrimental to the orientation growth of graphite. Examples 1, 3, and 4 further verify that the loading of Fe3O4 has a significant impact on capacity. Examples 1 and 5 further verify that sulfation significantly reduces the battery capacity. By designing Comparative Examples 1, 2, and 3 and Example 1, it was found that whether graphene has pores and whether it is oriented has a significant impact on battery performance. Furthermore, by comparing the capacity difference between Example 1 and Comparative Example 1 with the capacity difference between different comparative examples, it was found that pore size and orientation have a significant synergistic effect.

[0054] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A vertically oriented composite positive electrode, characterized in that, Includes a conductive agent, wherein the conductive agent includes graphene nanowires; The graphene nanonet has a microporous structure, and the graphene nanonet exhibits a preferred orientation perpendicular to the current collector in the electrode thickness direction.

2. The vertically oriented composite positive electrode according to claim 1, characterized in that, The orientation degree of the graphene nanonet perpendicular to the preferred orientation of the current collector is characterized by an XRD texture coefficient of (002) crystal plane greater than 1.

5.

3. The vertically oriented composite positive electrode according to claim 1, characterized in that, The microporous structure is a two-dimensional structure with atomic-level micropores, and the planar micropore density is 10. 11 cm -2 Up to 10 14 cm -2 The aperture ranges from 0.5 nm to 5 nm.

4. The vertically oriented composite positive electrode according to claim 1, characterized in that, The microporous structure has sulfur-containing functional groups grafted onto the pore edges.

5. The vertically oriented composite positive electrode according to claim 1, characterized in that, The surface of the graphene nanomesh is modified with ferromagnetic metal nanoparticles, the loading of which is 0.1wt%~1wt%, and the ferromagnetic metal nanoparticles include paramagnetic Fe3O4 nanoparticles.

6. The vertically oriented composite positive electrode according to claim 1, characterized in that, The vertically oriented composite cathode also includes a cathode active material and a solid electrolyte; The positive electrode active material includes a high-nickel positive electrode active material, and the high-nickel positive electrode active material includes at least one of NCM811 and NCM622; The solid electrolyte comprises sulfides, including silver-germanium sulfide electrolyte, which includes Li3PS4 and Li 10 GeP2S 12 At least one of Li6PS5Cl.

7. A method for preparing a vertically oriented composite positive electrode according to any one of claims 1 to 6, characterized in that, Includes the following steps: Graphene is perforated to form a graphene nanomesh with a nanomesh structure. Magnetic particles are loaded onto the surface of the graphene nanonet and then mixed with the remaining components to form a mixed slurry; The mixed slurry is coated onto the current collector and then placed in a vertical magnetic field to induce orientation. The magnetic field is then removed and the material is cured to obtain the vertically oriented composite positive electrode.

8. The method for preparing the vertically oriented composite positive electrode according to claim 7, characterized in that, Before the step of loading magnetic particles onto the surface of the graphene nanonet, the method further includes: The graphene nanonets were heat-treated in a sulfur-containing atmosphere to achieve edge sulfidation.

9. The application of a vertically oriented composite cathode according to any one of claims 1 to 6, or a vertically oriented composite cathode obtained by the preparation method of the vertically oriented composite cathode according to any one of claims 7 to 8, in the preparation of solid-state batteries.

10. The application according to claim 9, characterized in that, The solid-state battery includes an all-solid-state battery.

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