Composite material for lithium negative electrode, preparation method of composite material, lithium negative electrode and preparation method and application of lithium negative electrode

Abstract

The invention relates to a composite material for a lithium negative electrode, a preparation method of the composite material, the lithium negative electrode and a preparation method and application of the lithium negative electrode. The composite material comprises a two-dimensional lamellar material and a porous material attached to the surface of the two-dimensional lamellar material through chemical bonds, the two-dimensional lamellar material comprises graphene oxide, the porous material comprises a covalent organic framework, the covalent organic framework is synthesized from a terephthalaldehyde monomer and a melamine monomer, the molar ratio of the melamine monomer to the terephthalaldehyde monomer is 2: 3, and the mass of the graphene oxide is 0.5%-20% of the sum of the mass of the terephthalaldehyde monomer and the mass of the melamine monomer. After the lithium negative electrode modified by the composite material is applied to the lithium battery, the lithium battery has relatively high specific capacity when the cycle performance of the lithium battery is tested.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a composite material for lithium anodes and its preparation method, lithium anodes and their preparation methods and applications. Background Technology

[0002] Due to the non-renewable nature of fossil fuels and environmental requirements, the development and utilization of new energy sources is urgently needed. Lithium-ion batteries possess high energy density and efficiency, have mature technology, and have achieved large-scale industrialization. They dominate the fields of consumer electronics, power batteries, and energy storage. However, at the same time, Earth's lithium resources are relatively scarce, leading to high costs; moreover, lithium-ion batteries use organic electrolytes, which pose safety issues such as lithium dendrite growth piercing the separator and causing short circuits during use. In practical applications, reports of lithium-ion battery combustion and explosions are frequent. Improving the safety of lithium-ion batteries has become a consensus among researchers, and this is an important topic in lithium-ion battery research.

[0003] Lithium-ion batteries typically consist of a positive electrode, a negative electrode, a separator, an electrolyte, and a casing. The requirements for negative electrode materials in lithium-ion batteries mainly include the following: 1. Low redox potential; 2. High capacity density; 3. Structural stability; 4. Good electrical conductivity; 5. Good surface properties; 6. Chemical stability; 7. High diffusion coefficient; 8. Economic efficiency and environmental friendliness. Currently, graphite is the most widely used negative electrode material in lithium-ion batteries. However, graphite materials suffer from drawbacks such as low specific capacity, poor low-temperature performance, and poor rate performance. Many researchers are working on other negative electrode materials, hoping to find better ones. Currently, metal compound negative electrode materials are widely studied, but they suffer from complex synthesis and high metal resource costs. Organic negative electrode materials, with their wide availability, low cost, and flexible design, have become a new research hotspot. Common types of organic negative electrode materials include: 1. Carbonyl compounds: including carboxylates and quinones; 2. Schiff base compounds: containing (methyl)imine groups with carbon-nitrogen double bonds, exhibiting good complexing ability for metal ions. 3. Organic free radical compounds: These possess unpaired electrons and can participate in redox reactions, enabling charge storage. 4. Organic sulfides: These are sulfur-containing organic compounds with certain electrochemical activity, suitable as anode materials. However, current organic anode materials also face several challenges. Most organic anode materials have low intrinsic electronic conductivity, requiring the addition of large amounts of conductive carbon black during electrode fabrication, which reduces the volumetric energy density of the battery system. Furthermore, organic anode materials exhibit high solubility in organic electrolytes, leading to poor cycle stability. Therefore, developing an organic anode material with high conductivity and low organic solubility is crucial for the further development of lithium-ion batteries.

[0004] Covalent organic frameworks (COFs) are porous materials composed of organic units (including elements such as C, N, H, and O) interconnected by covalent bonds. Since the first successful synthesis of COFs by Yaghi's group in 2005, they have been widely used in gas adsorption and separation, catalysis, and proton conduction due to their advantages such as tunable pore size, ease of functionalization, high specific surface area, and strong designability. However, some studies have found that when COF-modified lithium anodes are used in lithium batteries, the specific capacity of the lithium batteries is relatively low during cycle testing, requiring further improvement. Summary of the Invention

[0005] Therefore, it is necessary to provide a composite material for lithium anodes. When the lithium anode modified by this composite material is applied to a lithium battery, the lithium battery exhibits a high specific capacity during cycle performance testing.

[0006] This application provides a composite material for lithium anodes, comprising a two-dimensional sheet material and a porous material attached to the surface of the two-dimensional sheet material by chemical bonds. The two-dimensional sheet material includes graphene oxide, and the porous material includes a covalent organic framework synthesized from terephthalaldehyde monomer and melamine monomer, wherein the molar ratio of the melamine monomer to the terephthalaldehyde monomer is 2:3, and the mass of the graphene oxide is 0.5%-20% of the sum of the masses of the terephthalaldehyde monomer and the melamine monomer.

[0007] In one embodiment, the mass of the two-dimensional sheet material is 3%-12% of the mass of the porous material.

[0008] This application also provides a method for preparing the above-mentioned composite material for lithium anodes, comprising the following steps:

[0009] Terephthalaldehyde and melamine were dissolved in dimethyl sulfoxide to obtain a monomer solution;

[0010] After adding graphene oxide to the monomer solution, the mixture was reacted at 170-190℃ for 60-90 h under an inert atmosphere to obtain a solid-liquid mixture.

[0011] The solid-liquid mixture was filtered to obtain a solid.

[0012] Washing solids; and

[0013] The solid after vacuum drying and washing yields a composite material for lithium anodes.

[0014] In one embodiment, during the step of obtaining the monomer solution, the mixture is stirred and sonicated to dissolve terephthalaldehyde and melamine in dimethyl sulfoxide; and / or

[0015] In the step of obtaining the solid-liquid mixture, after adding graphene oxide to the monomer solution located in the three-necked flask, the three-necked flask is heated in an oil bath, stirred while being heated, and subjected to water-cooled reflux under a nitrogen atmosphere, reacting at 180°C for 72 h; and / or

[0016] In the step of washing the solid, the solid is washed sequentially with dimethyl sulfoxide, tetrahydrofuran, acetone and dichloromethane; and / or

[0017] In the step of vacuum drying the washed solid, the solid is dried at 80°C for 24 hours in a vacuum oven.

[0018] This application also provides a lithium anode, comprising:

[0019] Current collector; and

[0020] A modification layer is disposed on the current collector. The modification layer includes a conductive agent, a binder, and a composite material for lithium anode as described above. The mass ratio of the conductive agent, the binder, and the composite material for lithium anode is (5-15):(5-15):(70-90).

[0021] In one embodiment, the current collector is a copper foil; and / or

[0022] The mass ratio of the conductive agent, the binder, and the composite material for the lithium anode is 10:10:80; and / or

[0023] The conductive agent is conductive carbon black, and the binder is carboxymethyl cellulose; and / or

[0024] The thickness of the modified layer is 30-50 micrometers.

[0025] This application also provides a method for preparing the above-mentioned lithium anode, characterized by comprising the following steps:

[0026] Solvent, conductive agent, binder and composite material for lithium anode are mixed and ground to obtain a slurry mixture;

[0027] The mixture slurry is coated onto the current collector; and

[0028] The current collector coated with the mixed slurry is dried to obtain a lithium anode.

[0029] In one embodiment, in the step of obtaining the slurry mixture, the solvent is water, and the volume ratio of the solvent to the sum of the masses of the conductive agent, the binder, and the composite material for the lithium anode is 5 ml: 100 mg; and / or

[0030] In the step of obtaining the mixture slurry, the grinding time is 20-30 minutes.

[0031] This application also provides a lithium battery, including the lithium anode described above.

[0032] This application also provides an electrical device, including the aforementioned lithium battery.

[0033] Because graphene oxide (GO) contains a large number of oxygen-containing groups such as -OH and -COOH, it can serve as reaction sites to adsorb a large amount of melamine monomers and terephthalaldehyde monomers. A Schiff base reaction between melamine and terephthalaldehyde occurs on the surface of GO, condensing to form a covalent organic framework (COF) material with a porous structure. Since both the COF and GO are almost insoluble in organic electrolytes, the composite material used for lithium anodes can exist stably in organic solvents. Furthermore, the porous structure of the COF results in a high specific surface area and porosity, leading to high conductivity. Combined with the high conductivity of graphene oxide itself, this composite material exhibits high conductivity and can be used as a lithium-ion battery anode material.

[0034] Furthermore, since covalent organic frameworks (COFs) possess a porous structure, and graphene oxide is a two-dimensional sheet material, the composite material used for lithium anodes is a porous sheet composite material. (Electron microscopy image attached) Figure 5 and 6 This confirms that the composite material used for the lithium anode is indeed a layered porous structure. The layered porous structure possesses a high lithium-ion conductivity and can effectively mitigate electrode volume changes during electrochemical processes, thereby enhancing cycle stability and achieving better electrochemical performance. As shown in Examples 1-4 and Comparative Example 1, when the lithium anode modified with this composite material is applied to a lithium battery, the lithium battery exhibits a high specific capacity during cycle performance testing.

[0035] Furthermore, covalent organic frameworks (COFs) possess numerous coordination groups such as amino groups (-NH2) and carbon-carbon double bonds (-C=C-), which can coordinate with lithium ions to inhibit lithium dendrite growth. In addition, melamine and terephthalaldehyde, used in the synthesis of COFs, are inexpensive chemicals, resulting in lower costs compared to other types of COFs, giving them a cost advantage. The molar ratio of terephthalaldehyde monomer to melamine monomer affects the crystallinity of the COF, which in turn affects the macroscopic order of the COF's pores. When the molar ratio of melamine monomer to terephthalaldehyde monomer is 2:3, the macroscopic order of the COF's pores is very high, resulting in very high lithium-ion conduction efficiency. The mass of graphene oxide is 0.5%-20% of the sum of the masses of terephthalaldehyde monomer and melamine monomer, which is very conducive to the formation of porous sheet composite materials and can ensure that the porous sheet composite materials have high specific surface area and porosity. Attached Figure Description

[0036] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0037] Figure 1 This is a flowchart illustrating a method for preparing a composite material for a lithium anode according to an embodiment of this application;

[0038] Figure 2 This is a schematic diagram of the structure of a lithium anode according to an embodiment of this application;

[0039] Figure 3 This is a flowchart of a method for preparing a lithium anode according to an embodiment of this application;

[0040] Figure 4 Electron micrographs of Comparative Example 1 and Examples 1-4 of this application;

[0041] Figure 5 This is an electron microscope image of Embodiment 3 of this application;

[0042] Figure 6 This is an electron microscope image of Embodiment 4 of this application;

[0043] Figure 7 This is an electron microscope image of graphene oxide.

[0044] Figure 8 The diagram shows the cycle performance of the lithium battery of this application, wherein the lithium battery uses the composite material for the lithium anode prepared in Example 4. Detailed Implementation

[0045] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0046] In the description of this application, it should be understood that, where they appear, the terms “center,” “longitudinal,” “lateral,” “length,” “width,” “thickness,” “upper,” “lower,” “front,” “rear,” “left,” “right,” “vertical,” “horizontal,” “top,” “bottom,” “inner,” “outer,” “clockwise,” “counterclockwise,” “axial,” “radial,” and “circumferential” indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0047] Furthermore, where applicable, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0048] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," "fixing," etc., shall be interpreted broadly. For example, they may refer to a fixed connection, a detachable connection, or an integral part; they may refer to a mechanical connection or an electrical connection; they may refer to a direct connection or an indirect connection through an intermediate medium; they may refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0049] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0050] It should be noted that, if an element is described as "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is described as "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0051] One embodiment of this application provides a composite material for a lithium anode comprising a two-dimensional sheet material and a porous material attached to the surface of the two-dimensional sheet material by chemical bonds. The two-dimensional sheet material includes graphene oxide (GO). The porous material includes a covalent organic framework (COF). The covalent organic framework (COF) is synthesized from melamine monomer and terephthalaldehyde monomer.

[0052] Because graphene oxide (GO) contains a large number of oxygen-containing groups such as -OH and -COOH, it can serve as reaction sites to adsorb a large amount of melamine monomers and terephthalaldehyde monomers. A Schiff base reaction between melamine and terephthalaldehyde occurs on the surface of GO, condensing to form a covalent organic framework (COF) material with a porous structure. Since both the COF and GO are almost insoluble in organic electrolytes, the composite material used for lithium anodes can exist stably in organic solvents. Furthermore, the porous structure of the COF results in a high specific surface area and porosity, leading to high conductivity. Combined with the high conductivity of graphene oxide itself, this composite material exhibits high conductivity and can be used as a lithium-ion battery anode material.

[0053] Furthermore, since covalent organic frameworks (COFs) possess a porous structure, and graphene oxide is a two-dimensional sheet material, the composite material used for lithium anodes is a porous sheet composite material. (Electron microscopy image attached) Figure 5 and 6This confirms that the composite material used for the lithium anode is indeed a layered porous structure. The layered porous structure possesses a high lithium-ion conductivity and can effectively mitigate electrode volume changes during electrochemical processes, thereby enhancing cycle stability and achieving better electrochemical performance. As shown in Examples 1-4 and Comparative Example 1, when the lithium anode modified with this composite material is applied to a lithium battery, the lithium battery exhibits a high specific capacity during cycle performance testing.

[0054] Furthermore, covalent organic frameworks (COFs) possess a large number of coordination groups such as amino groups (-NH2) and carbon-carbon double bonds (-C=C-), which can coordinate with lithium ions to inhibit lithium dendrite growth. In addition, melamine and terephthalaldehyde, used in the synthesis of COFs, are inexpensive chemicals, making COFs synthesized using these raw materials more cost-effective than other types of COFs, thus offering a cost advantage.

[0055] In this embodiment, the molar ratio of melamine monomer to terephthalaldehyde monomer is 2:3. Terephthalaldehyde monomer has two aldehyde groups, while melamine monomer has three amino groups. Therefore, a 2:3 molar ratio of melamine monomer to terephthalaldehyde monomer is equivalent to a 1:1 molar ratio of amino to aldehyde groups. The molar ratio of terephthalaldehyde monomer to melamine monomer affects the crystallinity of the covalent organic framework (COF), which in turn affects the macroscopic order of the COF's pores. When the molar ratio of melamine monomer to terephthalaldehyde monomer is 2:3, the macroscopic order of the COF's pores is very high, resulting in very high lithium-ion conduction efficiency.

[0056] In this embodiment, the mass of graphene oxide is 0.5%-20% of the sum of the masses of terephthalaldehyde monomer and melamine monomer. Controlling the mass ratio of graphene oxide to monomers is crucial, as it affects whether a layered structure can be formed and the spreadability of the layers. A mass ratio of 0.5%-20% of the sum of the masses of terephthalaldehyde monomer and melamine monomer is highly conducive to forming porous layered composite materials with excellent spreadability and ensures that the porous layered composite material has a high specific surface area and porosity. Specifically, in this embodiment, the mass of graphene oxide is 3%-12% of the sum of the masses of terephthalaldehyde monomer and melamine monomer. Figure 4 The electron microscope images shown confirm that when the mass of graphene oxide is 3%-12% of the sum of the masses of terephthalaldehyde monomer and melamine monomer, a good porous sheet structure is formed.

[0057] like Figure 1 As shown, this application also provides a method for preparing a composite material for a lithium anode, comprising the following steps:

[0058] In step S210, terephthalaldehyde and melamine are dissolved in dimethyl sulfoxide to obtain a monomer solution.

[0059] In step S120, after adding graphene oxide to the monomer solution, the mixture is reacted at 170-190℃ for 60-90 hours under an inert atmosphere to obtain a solid-liquid mixture.

[0060] Step S130: Filter the solid-liquid mixture to obtain a solid.

[0061] Step S140: Wash the solid.

[0062] Step S150: Vacuum dry the washed solid to obtain a composite material for lithium anode.

[0063] In this embodiment, in step S110, the molar ratio of melamine monomer to terephthalaldehyde monomer is 2:3. In step S110, the mixture is stirred and sonicated to dissolve terephthalaldehyde and melamine in dimethyl sulfoxide.

[0064] In this embodiment, in step S120, the mass of graphene oxide is 0.5%-20% of the sum of the masses of terephthalaldehyde and melamine. In step S120, after adding graphene oxide to the monomer solution in the three-necked flask, the three-necked flask is heated in an oil bath, stirred while being heated, and subjected to water-cooled reflux under a nitrogen atmosphere, and reacted at 180°C for 72 hours.

[0065] In this embodiment, in step S140, the fixative is washed sequentially with dimethyl sulfoxide, tetrahydrofuran, acetone, and dichloromethane. First, washing with dimethyl sulfoxide removes most of the unreacted melamine and terephthalaldehyde, then using a low-boiling-point solvent to remove the high-boiling-point dimethyl sulfoxide, further removing any remaining residual monomers. This effectively removes unreacted raw materials and facilitates subsequent rapid drying.

[0066] In this embodiment, in step S150, the product is dried at 80°C for 24 hours in a vacuum oven.

[0067] like Figure 2 As shown, this application also provides a lithium anode. The lithium anode includes a current collector 210 and a modification layer 220. The modification layer 220 is disposed on both surfaces of the current collector 210. The modification layer 220 includes a conductive agent, a binder, and a composite material for the lithium anode.

[0068] In this embodiment, the mass ratio of the conductive agent, the binder, and the composite material for the lithium anode is (5-15):(5-15):(70-90). Specifically, in this embodiment, the mass ratio of the conductive agent, the binder, and the composite material for the lithium anode is 10:10:80.

[0069] In this embodiment, the current collector 210 is a copper foil.

[0070] In this embodiment, the conductive agent is conductive carbon black, and the binder is carboxymethyl cellulose.

[0071] In this embodiment, the thickness of the modification layer 220 is 30-50 micrometers.

[0072] like Figure 3 As shown, this application also provides a method for preparing a lithium anode, comprising the following steps:

[0073] Step S310: The solvent, conductive agent, binder and composite material for lithium anode are mixed and ground to obtain a slurry mixture.

[0074] Step S320: Apply the mixture slurry onto the current collector.

[0075] Step S330: Dry the current collector coated with the mixed slurry to obtain a lithium anode.

[0076] In this embodiment, in step S310, the solvent is water, and the volume ratio of the solvent to the sum of the masses of the conductive agent, the binder, and the composite material used for the lithium anode is 5 ml: 100 mg. In step S310, the grinding time is 20-30 min.

[0077] This application also provides a lithium battery, including the lithium anode described above.

[0078] This application also provides an electrical device, including the aforementioned lithium battery. The aforementioned electrical device can be a vehicle, mobile phone, portable device, laptop, ship, spacecraft, electric toy, power tool, energy storage device, amusement equipment, elevator, and lifting equipment, etc. Vehicles can be gasoline-powered vehicles, natural gas-powered vehicles, or new energy vehicles; new energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc.; spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc.; electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, or electric airplane toys, etc.; power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc.; energy storage devices can be energy storage walls, base station energy storage, container energy storage, etc.; amusement equipment can be a carousel, a drop tower, etc. This embodiment does not impose any special limitations on the aforementioned electrical device.

[0079] The present application will be further described below with reference to embodiments.

[0080] Example 1

[0081] In a three-necked flask, 180 mL of dimethyl sulfoxide (DMSO), 3.5 g of terephthalaldehyde, and 2.2 g of melamine (molar ratio of terephthalaldehyde to melamine 3:2) were added, stirred, and sonicated until completely dissolved. Then, graphene oxide (GO) (0.5% of the sum of the masses of terephthalaldehyde and melamine) was added. The mixture was stirred continuously in an oil bath at 180 °C and refluxed under a nitrogen atmosphere for 72 h. The resulting black powder was filtered and washed sequentially with dimethyl sulfoxide, tetrahydrofuran, acetone, and dichloromethane. The filter media was then dried in a vacuum oven at 80 °C for 24 h to obtain the composite material (black powder) for lithium anodes.

[0082] Example 2

[0083] In Example 2, the mass of graphene oxide was 1.0% of the sum of the masses of terephthalaldehyde and melamine. Except for the different mass of graphene oxide, everything else was the same as in Example 1.

[0084] Example 3

[0085] In Example 3, the mass of graphene oxide was 3.0% of the sum of the masses of terephthalaldehyde and melamine. Except for the different mass of graphene oxide, everything else was the same as in Example 1.

[0086] Example 4

[0087] In Example 4, the mass of graphene oxide was 12.0% of the sum of the masses of terephthalaldehyde and melamine. Except for the different mass of graphene oxide, everything else was the same as in Example 1.

[0088] Comparative Example 1

[0089] In a three-necked flask, 180 mL of dimethyl sulfoxide (DMSO), 3.5 g of terephthalaldehyde, and 2.2 g of melamine (molar ratio of terephthalaldehyde to melamine 3:2) were added, stirred, and sonicated until completely dissolved. The mixture was continuously stirred in an oil bath at 180 °C and refluxed under a nitrogen atmosphere for 72 h. The resulting white powder was filtered and washed sequentially with dimethyl sulfoxide, tetrahydrofuran, acetone, and dichloromethane. The filtrate was then dried in a vacuum oven at 80 °C for 24 h to obtain a covalent organic framework (COF) (white powder, specifically named SNW-1).

[0090] Figure 4 a, b, c, d, and e are scanning electron microscope images of the covalent organic framework (COF) of Comparative Example 1 and the composite materials for lithium anodes of Examples 1-4, respectively. Figure 5 This is a scanning electron microscope image of the composite material used for the lithium anode in Example 3. Figure 6 This is a scanning electron microscope image of the composite material used for the lithium anode in Example 4. Figure 7 This is an electron microscope image of graphene oxide. The scanning electron microscope used is a HITACHI SU8010 model, manufactured in Japan. Gold sputtering is required before scanning.

[0091] according to Figures 4-6 As can be seen, the mass of graphene oxide in Comparative Example 1 is 0, and its scanning electron microscope (SEM) image only shows that the covalent organic framework (COF) SNW-1 is in an aggregated particulate state, without a layered structure. The SEM images of the composite materials used for lithium anodes in Examples 1-4 show that the layered structure becomes increasingly apparent as the graphene oxide content gradually increases. Figures 4-6 It was demonstrated that the composite material used for the lithium anode has a porous sheet structure.

[0092] Cyclic performance test

[0093] (1) Preparation of lithium anode

[0094] Weigh 10 mg of conductive carbon black, 10 mg of carboxymethyl cellulose (CMC) powder, and 80 mg of modifying material powder, place them in a mortar, add 5 ml of deionized water, and grind evenly for 25 min. Then, evenly coat the ground mixture onto both sides of a copper foil current collector. Finally, place the coated copper foil in an oven to dry and remove the solvent, forming a lithium anode (both sides of the copper foil current collector have a 3 μm thick modifying layer). There are five types of lithium anodes, and the modifying materials for the five lithium anodes correspond to the covalent organic framework (COF) of Comparative Example 1 and the composite materials for lithium anodes in Examples 1-4, respectively.

[0095] (2) Preparation of lithium batteries

[0096] The lithium battery uses a prepared lithium anode as the negative electrode, pure lithium foil as the counter electrode, and a microporous polypropylene membrane as the separator. LiPF6 is dissolved in ethylene carbonate / dimethyl carbonate / diethyl carbonate (EC:DEC:DMC = 1:1:1, V%) as the electrolyte.

[0097] (3) Cyclic performance test

[0098] The cycle performance of the lithium battery was tested at a current density of 500 mA g⁻¹. After 100 cycles, the specific capacity of the lithium battery was recorded, as shown in Table 1. Figure 8 The diagram shows the cycle performance of the lithium battery corresponding to Example 4.

[0099] Table 1 Cyclic performance test results

[0100]

[0101]

[0102] As shown in Table 1, compared with covalent organic frameworks (COFs) that do not contain graphene oxide (specifically named SNW-1), the composite material of this application, when applied to lithium batteries, results in lithium batteries with higher specific capacity when the cycle performance of the lithium batteries is tested.

[0103] As shown in Table 1, the specific capacity of lithium batteries increases with the increase of graphene oxide content. This is because the mass ratio of graphene oxide to monomers affects whether a layered structure can be formed and the extent of the layer expansion. With the increase of graphene oxide content, the graphene oxide changes from its original agglomerated particle state to a layered structure, improving its pore regularity and gaining more lithium-ion storage space, thereby increasing the specific capacity of lithium batteries.

[0104] Considering that a 12wt% graphene oxide content already achieves a high specific capacity, and given the relatively high cost of graphene oxide, adding too much would increase costs, contradicting the idea of ​​obtaining inexpensive COF using cheap chemicals (melamine and terephthalaldehyde). Furthermore, if... Figure 7 As shown in the electron micrograph, pure graphene oxide shrinks into a spherical shape and cannot expand, which is not conducive to the formation of sheet structures. Therefore, we recommend that the amount of graphene oxide used should not exceed 20 wt%.

[0105] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0106] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A composite material for lithium anodes, characterized in that, The invention includes a two-dimensional sheet material and a porous material attached to the surface of the two-dimensional sheet material by chemical bonds. The two-dimensional sheet material includes graphene oxide, and the porous material includes a covalent organic framework. The covalent organic framework is synthesized from terephthalaldehyde monomer and melamine monomer, wherein the molar ratio of the melamine monomer to the terephthalaldehyde monomer is 2:3, and the mass of the graphene oxide is 0.5%-20% of the sum of the masses of the terephthalaldehyde monomer and the melamine monomer.

2. The composite material for lithium anodes as described in claim 1, characterized in that, The mass of the two-dimensional sheet material is 3%-12% of the mass of the porous material.

3. A method for preparing a composite material for a lithium anode as described in claim 1 or 2, characterized in that, Includes the following steps: Terephthalaldehyde and melamine were dissolved in dimethyl sulfoxide to obtain a monomer solution; After adding graphene oxide to the monomer solution, the mixture was reacted at 170-190℃ for 60-90 h under an inert atmosphere to obtain a solid-liquid mixture. The solid-liquid mixture was filtered to obtain a solid. Washing solids; and The solid after vacuum drying and washing yields a composite material for lithium anodes.

4. The method for preparing the composite material for lithium anode as described in claim 3, characterized in that, In the step of obtaining the monomer solution, the mixture is stirred and sonicated to dissolve terephthalaldehyde and melamine in dimethyl sulfoxide; and / or In the step of obtaining the solid-liquid mixture, after adding graphene oxide to the monomer solution located in the three-necked flask, the three-necked flask is heated in an oil bath, stirred while being heated, and subjected to water-cooled reflux under a nitrogen atmosphere, reacting at 180°C for 72 h; and / or In the step of washing the solid, the solid is washed sequentially with dimethyl sulfoxide, tetrahydrofuran, acetone and dichloromethane; and / or In the step of vacuum drying the washed solid, the solid is dried at 80°C for 24 hours in a vacuum oven.

5. A lithium anode, characterized in that, include: current collector; as well as A modification layer is disposed on the current collector, the modification layer comprising a conductive agent, a binder, and a composite material for lithium anode as described in claim 1 or 2, wherein the mass ratio of the conductive agent, the binder, and the composite material for lithium anode is (5-15):(5-15):(70-90).

6. The lithium anode as described in claim 5, characterized in that, The current collector is a copper foil; and / or The mass ratio of the conductive agent, the binder, and the composite material for the lithium anode is 10:10:80; and / or The conductive agent is conductive carbon black, and the binder is carboxymethyl cellulose; and / or The thickness of the modified layer is 30-50 micrometers.

7. A method for preparing a lithium anode as described in claim 5 or 6, characterized in that, Includes the following steps: Solvent, conductive agent, binder and composite material for lithium anode are mixed and ground to obtain a slurry mixture; The mixture slurry is coated onto the current collector; and The current collector coated with the mixed slurry is dried to obtain a lithium anode.

8. The method for preparing a lithium anode as described in claim 7, characterized in that, In the step of obtaining the mixture slurry, the solvent is water, and the volume ratio of the solvent to the sum of the masses of the conductive agent, the binder, and the composite material for the lithium anode is 5 ml: 100 mg; and / or In the step of obtaining the mixture slurry, the grinding time is 20-30 minutes.

9. A lithium battery, characterized in that, Includes the lithium anode as described in claim 5 or 6.

10. An electrical appliance, characterized in that, Including the lithium battery as described in claim 9.

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