Modified graphene and preparation method and application thereof

Abstract

The application provides modified graphene and a preparation method and application thereof, the modified graphene has a structure shown in formula (I): wherein R1 is selected from any one of benzene, naphthalene, anthracene, phenanthrene, perylene, naphthacene, pyrene groups; R2 and R3 are each independently any one of H, -CH3 and -CH2CH3; m is 0, 1, 2, 3 or 4; n is 0, 1 or 2; the modified graphene provided by the application enables the carbon-coated aluminum foil to have the function of sodium storage, and can reduce the contact resistance of the carbon-coated aluminum foil and the positive electrode material, improve the peeling strength of the carbon-coated aluminum foil and the positive electrode material, and improve the battery charging capacity and cycle life.

Description

Technical Field

[0001] This invention relates to the field of carbon-coated aluminum foil, specifically to a modified graphene, its preparation method, and its applications. Background Technology

[0002] Because sodium ions have a larger radius than lithium ions, materials such as graphite, soft carbon, conductive carbon black, and graphene have difficulty storing sodium. Soft carbon has insufficient capacity, and the interlayer spacing and pore size of graphite and conductive carbon black are small, making it difficult for sodium ions to insert and extract. Sheet-shaped graphene does not have sodium storage sites. Therefore, carbon-coated aluminum foil using soft carbon, graphite, conductive carbon black, graphene, and other materials as coatings does not have sodium storage performance.

[0003] Since sodium does not alloy with aluminum, carbon-coated aluminum foil can be used as a current collector for both the positive and negative electrodes of sodium-ion batteries. As a current collector, the primary function of carbon-coated aluminum foil is to collect current; its coating typically incorporates graphene. While graphene has strong conductivity, its sodium storage capacity is insufficient. Due to the poor sodium storage capacity of ordinary carbon coatings, the contact resistance between the carbon-coated aluminum foil and the positive and negative electrode materials increases, leading to a decrease in battery energy density and a faster decline in cycle life.

[0004] To balance conductivity and sodium storage requirements, existing carbon-coated aluminum foils use hard carbon in combination with other conductive agents. Hard carbon is carbon that cannot be graphitized after high-temperature treatment above 2800℃. Hard carbon has a disordered internal crystal arrangement, more pores, and sodium can be stored between layers, on the surface of micropores, and at defect sites. Its pore size and interlayer spacing meet the requirements of sodium-ion batteries, resulting in high capacity. However, because hard carbon has a low degree of graphitization, its conductivity is lower than that of graphite, conductive carbon black, and graphene. While the addition of hard carbon enhances the sodium storage performance of the coating, it also increases the coating's resistance.

[0005] Existing technologies use three-dimensional organic framework materials (COFs) containing PN-type groups as sodium storage materials. Although COFs exhibit good electrochemical performance, their two-dimensional or three-dimensional framework structure results in stable molecular structures, large molecular weights, and large particle sizes. Therefore, when adding COFs to conductive pastes, it is difficult to achieve uniform and fine particle sizes through milling, leading to poor leveling and uneven coating during application. Furthermore, the preparation process of COFs is complex and costly, hindering large-scale application.

[0006] Therefore, there is an urgent need for a conductive agent that has strong sodium storage capacity, good electrochemical performance, simple preparation process, and can reduce coating resistance. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a modified graphene, its preparation method, and its applications, which at least partially solve the problems mentioned above.

[0008] In a first aspect, the present invention provides a modified graphene having the structure shown in formula (I):

[0009]

[0010] in,

[0011] R1 is selected from any one of the following groups: benzene, naphthalene, anthracene, phenanthrene, perylene, tetraphenylene, and pyrene.

[0012] R2 and R3 are each independently one of H, -CH3, and -CH2CH3;

[0013] m can be 0, 1, 2, 3, or 4;

[0014] n is 0, 1, or 2.

[0015] In this invention, each R2 can be the same or different; each R3 can be the same or different.

[0016] In this invention, PN-type groups are introduced into graphene, so that graphene contains both N-type imide groups and P-type triazine groups. The N-type imide groups enable the carbon-coated aluminum foil coating to have sodium storage capacity, increasing the battery's charging capacity, energy density, and cycle life, while reducing the resistance of the carbon-coated aluminum foil coating. The P-type triazine groups stabilize anions, helping to increase battery capacity. The PN-type groups' ability to combine with sodium ions and anions can improve the peel strength between the carbon-coated aluminum foil and the positive and negative electrode materials.

[0017] This invention provides a modified graphene having one of the following structures:

[0018]

[0019] Secondly, the present invention provides a method for preparing modified graphene, the method comprising the following steps:

[0020]

[0021] 1) The amino-based graphene reacts with compound 1 to obtain intermediate 1;

[0022] 2) The intermediate 1 obtained in step 1) reacts with acid anhydride and organic amine to obtain graphene containing N-type groups;

[0023] 3) The graphene containing N-type groups obtained in step 2) reacts with compound 2 to obtain intermediate 2;

[0024] 4) Dehydrate and cyclize intermediate 2 obtained in step 3) to obtain graphene containing PN-type groups with the structure shown in formula (I).

[0025] In this invention, step 1) may further include at least one of the following technical features:

[0026] According to an embodiment of the present invention, step 1) is performed under nitrogen protection.

[0027] According to an embodiment of the present invention, in step 1), compound 1 is selected from 1,4,5,8-naphthalenetetracarboxylic anhydride (CAS: 81-30-1, with the specific structure as follows: ), 2-methyl-1,4,5,8-naphthalenetetracarboxylic anhydride (CAS: 259154-36-4, specific structure is: ), 2,6-dimethyl-1,4,5,8-naphthalenetetracarboxylic anhydride (CAS: 147647-47-0, specific structure is: ), 2,7-dimethyl-1,4,5,8-naphthalenetetracarboxylic anhydride (CAS: 259154-38-6, specific structure is: ), benzo[1,2,3-de:4,5,6-d'e']diisochrome-1,3,7,9-tetraone (CAS: 158494-90-7, specific structure is: ), benzo[h]isochromone[6,5,4-def]isochromene-1,3,6,8-tetraone (CAS: 158494-92-9, specific structure is: ), benzo[1,2,3-de:6,5,4-d']diisochrome-1,3,10,12-tetraone (CAS: 17873-48-2, specific structure is: ), 3,4,9,10-perylenetetracarboxylic acid dianhydride (CAS: 128-69-8, specific structure is: ), benzo[h]benzo[7,8]isochromone[6,5,4-def]isochromene-1,3,8,10-tetraone (CAS: 944926-30-1, specific structure is: ), naphtho[2,1,8-def:6,5,4-d'f']diisochrome-1,3,7,9(5a1H, 11a1H)-tetraone (CAS: 101395-59-9, specific structure is: At least one of the following.

[0028] Preferably, compound 1 is selected from 1,4,5,8-naphthalenetetracarboxylic anhydride (Naphthalenetetracarboxylic anhydride). ), 3,4,9,10-perylenetetracarboxylic acid dianhydride ( At least one of the following.

[0029] According to an embodiment of the present invention, in step 1), the mass ratio of the amino-graphene to compound 1 is 1:(0.5-1.5).

[0030] Specifically, the mass ratio of the aminographene to compound 1 is any value within the range of 1:0.5, 1:0.75, 1:1, 1:1.25, 1:1.5 or 1:(0.5-1.5).

[0031] According to an embodiment of the present invention, in step 1), the reaction temperature is 20-100°C, preferably 25-75°C; the reaction time is 1-48h, preferably 2-30h.

[0032] Specifically, the reaction temperature is any value within the range of 20℃, 25℃, 50℃, 60℃, 70℃, 75℃, 80℃, 90℃, 100℃ or 20-100℃; the reaction time is any value within the range of 1h, 2h, 5h, 10h, 15h, 20h, 24h, 25h, 30h, 35h, 40h, 45h, 48h or 1-48h.

[0033] According to an embodiment of the present invention, step 1) is carried out in solvent 1.

[0034] Specifically, solvent 1 is selected from at least one of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), and N-methylpyrrolidone (NMP).

[0035] According to an embodiment of the present invention, step 1) further includes a water-removing agent 1.

[0036] Specifically, the water-removing agent 1 is selected from at least one of toluene and benzene.

[0037] According to an embodiment of the present invention, in step 1), the volume ratio of the water-removing agent 1 to the solvent 1 is 1:(1-10).

[0038] Specifically, the volume ratio of water-removing agent 1 to solvent 1 is any value within the range of 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10 or 1:(1-10).

[0039] In this invention, step 1) specifically involves: under nitrogen protection, after the aminated graphene and compound 1 react in solvent 1 for a period of time, a dehydrating agent 1 is added, and the water is removed by azeotropic reaction. After the reaction is complete, the mixture is filtered, the precipitate is washed with solvent 1 to remove unreacted compound 1, and the mixture is dried under vacuum to obtain intermediate 1.

[0040] According to an embodiment of the present invention, in step 1), the azeotropic temperature is 100-150°C, preferably 110-130°C; the azeotropic dehydration time is 0.5-2h.

[0041] Specifically, the azeotropic temperature is any value within the range of 100℃, 110℃, 120℃, 130℃, 140℃, 150℃ or 100-150℃; the azeotropic dehydration time is any value within the range of 0.5h, 0.75h, 1h, 1.25h, 1.5h, 2h or 0.5-2h.

[0042] In this invention, step 2) may further include at least one of the following technical features:

[0043] According to an embodiment of the present invention, step 2) is performed under nitrogen protection.

[0044] According to an embodiment of the present invention, in step 2), the acid anhydride is selected from at least one of acetic anhydride and trifluoroacetic anhydride.

[0045] According to an embodiment of the present invention, in step 2), the organic amine is selected from at least one of pyridine and triethylamine.

[0046] According to an embodiment of the present invention, in step 2), the mass ratio of the amino-graphene, acid anhydride and organic amine is 1:(0.5-1.5):(0.5-1.5).

[0047] Specifically, the mass ratio of the aminated graphene, acid anhydride, and organic amine is any value within the range of 1:0.5:0.5, 1:0.75:0.75, 1:1:1, 1:1.25:1.25, 1:1.35:1.35, 1:1.4:1.4, 1:1.5:1.5, or 1:(0.5-1.5):(0.5-1.5).

[0048] According to an embodiment of the present invention, in step 2), the reaction temperature is 20-100°C, preferably 25-75°C; the reaction time is 1-24h, preferably 2-12h.

[0049] Specifically, the reaction temperature is any value within the range of 20℃, 30℃, 40℃, 50℃, 60℃, 70℃, 75℃, 80℃, 90℃, 100℃ or 20-100℃; the reaction time is any value within the range of 2h, 4h, 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, 24h or 1-24h.

[0050] According to an embodiment of the present invention, step 2) is carried out in solvent 2.

[0051] Specifically, solvent 2 is selected from at least one of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), and N-methylpyrrolidone (NMP).

[0052] In this invention, step 2) specifically involves: under nitrogen protection, intermediate 1, acid anhydride and organic amine react in solvent 2. After the reaction is complete, the mixture is filtered, the precipitate is washed with solvent 2 and water to remove excess raw materials, and the mixture is vacuum dried to obtain graphene containing N-type groups.

[0053] In this invention, step 3) may further include at least one of the following technical features:

[0054] According to an embodiment of the present invention, step 3) is performed under nitrogen protection.

[0055] According to an embodiment of the present invention, in step 3), compound 2 is selected from 4-(1,3,5-triazine-2-yl)aniline (CAS: 75207-71-5, with the specific structure as follows: ), 4-(4,6-dimethyl-1,3,5-triazin-2-yl)aniline (CAS: 1195207-38-5, specific structure is: ), 4-(4,6-dimethyl-1,3,5-triazin-2-yl)-2-methylaniline (CAS: 1368971-51-0, specific structure is as follows) ), 2-methyl-4-(1,3,5-triazin-2-yl)aniline (CAS: 1368718-24-4, specific structure is as follows) ), 3-(1,3,5-triazin-2-yl)aniline (CAS: 75207-70-4, specific structure is as follows) ), 2-methyl-5-(1,3,5-triazin-2-yl)aniline (CAS: 1369006-22-3, specific structure is as follows) ), 3-(4-methyl-1,3,5-triazine-2-yl)aniline (CAS: 2167543-71-5, specific structure is as follows) ), 2-methyl-3-(1,3,5-triazin-2-yl)aniline (CAS: 1368468-24-9, specific structure is as follows) ), 3-(4,6-dimethyl-1,3,5-triazin-2-yl)aniline (CAS: 1368525-31-8, specific structure is as follows) ), 2-(1,3,5-triazin-2-yl)aniline (CAS: 1368659-00-0, specific structure is as follows) ), 2-(4,6-dimethyl-1,3,5-triazin-2-yl)aniline (CAS: 1368948-25-7, specific structure is as follows) ), 4-methyl-2-(1,3,5-triazin-2-yl)aniline (CAS: 1368935-06-1, specific structure is as follows) At least one of the following.

[0056] Preferably, compound 2 is selected from 4-(1,3,5-triazin-2-yl)aniline. 4-(4,6-Dimethyl-1,3,5-triazin-2-yl)aniline At least one of them.

[0057] According to an embodiment of the present invention, in step 3), the mass ratio of the graphene containing the N-type group to compound 2 is 1:(0.5-1.5).

[0058] Specifically, the mass ratio of the graphene containing the N-type group to compound 2 is any value within the range of 1:0.5, 1.09:0.75, 1.15:0.75, 1.07:1, 1.1:1, 1:1.5 or 1:(0.5-1.5).

[0059] According to an embodiment of the present invention, in step 3), the reaction temperature is 20-100°C, preferably 25-75°C; the reaction time is 1-48h, preferably 2-30h.

[0060] Specifically, the reaction temperature is any value within the range of 20℃, 30℃, 40℃, 50℃, 60℃, 70℃, 75℃, 80℃, 90℃, 100℃ or 20-100℃; the reaction time is any value within the range of 1 h, 5 h, 10 h, 15 h, 20 h, 24 h, 25 h, 30 h, 35 h, 40 h, 45 h, 48 h or 1-48 h.

[0061] According to an embodiment of the present invention, step 3) is carried out in solvent 3.

[0062] Specifically, solvent 3 is selected from at least one of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), and N-methylpyrrolidone (NMP).

[0063] According to an embodiment of the present invention, step 3) further includes a water-removing agent 2.

[0064] Specifically, the water-removing agent 2 is selected from at least one of toluene and benzene.

[0065] According to an embodiment of the present invention, in step 3), the volume ratio of the water-removing agent 2 to the solvent 3 is 1:(1-10).

[0066] Specifically, the volume ratio of the water-removing agent 2 to the solvent 3 is any value within the range of 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10 or 1:(1-10).

[0067] In this invention, step 3) specifically involves: under nitrogen protection, graphene containing N-type groups and compound 2 react in solvent 3 for a period of time, then adding dehydrating agent 2, azeotropically removing water, and after the reaction is complete, filtering, washing the precipitate with solvent 3 to remove unreacted compound 2, and vacuum drying to obtain intermediate 2.

[0068] According to an embodiment of the present invention, in step 3), the azeotropic temperature is 100-150°C, preferably 110-130°C; the azeotropic dehydration time is 0.5-2h.

[0069] Specifically, in step 3), the azeotropic temperature is any value within the range of 100℃, 110℃, 120℃, 130℃, 140℃, 150℃ or 100-150℃; the azeotropic dehydration time is any value within the range of 0.5h, 0.75h, 1h, 1.25h, 1.5h, 2h or 0.5-2h.

[0070] In this invention, step 4) may further include at least one of the following technical features:

[0071] According to an embodiment of the present invention, step 4) is performed under nitrogen protection.

[0072] According to an embodiment of the present invention, in step 4), the temperature of dehydration cyclization is 200-400°C, preferably 250-350°C; the time of dehydration cyclization is 1-48h, preferably 2-30h.

[0073] Specifically, in step 4), the temperature of the dehydration cyclization is any value within the range of 200℃, 250℃, 300℃, 350℃, 400℃ or 200-400℃; the time of the dehydration cyclization is any value within the range of 1h, 5h, 10h, 15h, 20h, 25h, 30h, 35h, 40h, 45h, 48h or 1-48h.

[0074] In this invention, step 4) specifically involves: under nitrogen protection, intermediate 2 undergoes dehydration and cyclization at a certain temperature. After the reaction is complete, it is dried under vacuum to obtain graphene containing PN-type groups (the compound shown in formula (I)).

[0075] In this invention, aminated graphene is grafted with aromatic compounds containing dianhydrides, triazine compounds, etc., to obtain graphene containing PN-type groups. Aminated graphene undergoes a condensation reaction with aromatic compounds containing dianhydrides to obtain compounds containing imide groups, where the imide groups are N-type groups. Then, triazine compounds are introduced, where the triazine groups are P-type groups.

[0076] Thirdly, the present invention provides a carbon coating slurry, the carbon coating slurry comprising a conductive agent, wherein the conductive agent comprises graphene and conductive carbon black Super P;

[0077] The graphene is the modified graphene described in the first aspect or the graphene containing PN-type groups prepared by the method described in the second aspect.

[0078] In this invention, the carbon coating slurry may further include at least one of the following technical features:

[0079] According to an embodiment of the present invention, the carbon coating slurry further includes at least one of a binder, a dispersant, and a thickener.

[0080] According to an embodiment of the present invention, the adhesive is selected from at least one of acrylic resins, polyvinyl alcohol resins, epoxy resins, and styrene-butadiene rubber.

[0081] Specifically, the adhesive is selected from at least one of K-702, K-7028, K-732, K-739, and K-766.

[0082] According to embodiments of the present invention, the dispersant is selected from at least one of sodium dodecyl sulfate, BYK-ET3000, BYK-ET3001, BYK-ET3003, BYK-ET3004, BYK-ET 3032, BYK-ET 3031, BYK-ET3002, BYK-ET 3033, BYK-ET 3034, Electro-Rite AL003, and octadecyltrimethylammonium bromide.

[0083] According to an embodiment of the present invention, the thickener is selected from at least one of polyvinylpyrrolidone, polyoxyethylene, methylcellulose, carboxymethylcellulose, sodium carboxymethylcellulose, hydroxymethylcellulose, and sodium hydroxymethylcellulose.

[0084] According to an embodiment of the present invention, the mass ratio of graphene to conductive carbon black Super P is 1:(0.1-10).

[0085] Specifically, the mass ratio of graphene to conductive carbon black Super P is any value within the range of 1:0.1, 1:0.5, 1:1, 1:5, 1:10 or 1:(0.1-10).

[0086] According to an embodiment of the present invention, the mass ratio of the total mass of the conductive agent to the mass of the binder is 1:(1-10).

[0087] Specifically, the mass ratio of the total mass of the conductive agent to the mass of the binder is any value within the range of 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10 or 1:(1-10).

[0088] According to an embodiment of the present invention, the mass ratio of the dispersant to the binder is 1:(20-100).

[0089] Specifically, the mass ratio of the dispersant to the binder is any value within the range of 1:20, 1:40, 1:60, 1:80, 1:100 or 1:(20-100).

[0090] According to an embodiment of the present invention, the mass ratio of the thickener to the binder is 1:(10-100).

[0091] Specifically, the mass ratio of the thickener to the binder is any value within the range of 1:10, 1:20, 1:30, 1:40, 1:50, 1:60, 1:70, 1:80, 1:90, 1:100 or 1:(10-100).

[0092] According to an embodiment of the present invention, the carbon coating slurry further includes deionized water.

[0093] Fourthly, the present invention provides a method for preparing the carbon coating slurry described in the third aspect, comprising: mixing deionized water, binder, conductive agent, dispersant and thickener, pre-dispersing and milling to obtain the carbon coating slurry.

[0094] According to an embodiment of the present invention, mechanical stirring is used for pre-dispersion.

[0095] According to an embodiment of the present invention, the mechanical stirring speed is 500-2000 r / min.

[0096] Specifically, the mechanical stirring speed is any value within the range of 500 r / min, 1000 r / min, 1500 r / min, 2000 r / min, or 500-2000 r / min.

[0097] According to an embodiment of the present invention, the sanding time is 1-5 hours and the sanding temperature is 10-30°C.

[0098] Specifically, the grinding time is any value within the range of 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, or 1-5h; the grinding temperature is any value within the range of 10℃, 15℃, 20℃, 25℃, 30℃, or 10-30℃.

[0099] Fifthly, the present invention provides a method for preparing carbon-coated aluminum foil, the method comprising: coating a carbon-coating slurry onto the surface of an aluminum foil substrate, and drying the coated aluminum foil;

[0100] in,

[0101] The carbon coating slurry is the carbon coating slurry described in the third aspect or is prepared by the method described in the fourth aspect.

[0102] According to an embodiment of the present invention, the wet film thickness is 3-10 μm.

[0103] Specifically, the thickness of the coated wet film is any value within the range of 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm or 3-10μm.

[0104] According to an embodiment of the present invention, the thickness of the aluminum foil substrate is 12-15 μm.

[0105] Specifically, the thickness of the aluminum foil substrate is any value within the range of 12μm, 13μm, 14μm, 15μm or 12-15μm.

[0106] According to an embodiment of the present invention, the drying temperature is 80-200℃; the drying time is 0.5-10min.

[0107] Specifically, the drying temperature is any value within the range of 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃ or 80-200℃; the drying time is any value within the range of 0.5min, 1min, 2.5min, 5min, 7.5min, 10min or 0.5-10min.

[0108] In a sixth aspect, the present invention provides a carbon-coated aluminum foil, the carbon-coated aluminum foil comprising the carbon coating slurry described in the third aspect or prepared by the method described in the fifth aspect.

[0109] In a seventh aspect, the present invention provides an application of the carbon-coated aluminum foil described in the sixth aspect in a sodium-ion battery; wherein the carbon-coated aluminum foil is applied to the positive electrode current collector and / or the negative electrode current collector of the sodium-ion battery.

[0110] Specifically, the carbon-coated aluminum foil is used in both the positive and negative current collectors of sodium-ion batteries.

[0111] Specifically, the carbon-coated aluminum foil is used as the positive electrode current collector in a sodium-ion battery.

[0112] Specifically, the carbon-coated aluminum foil is used as the negative electrode current collector in a sodium-ion battery.

[0113] Specifically, the sodium-ion battery is a polyanion type.

[0114] In this invention, the conductive agent used includes the modified graphene described in the first aspect or the graphene containing PN-type groups prepared by the method described in the second aspect. The carbonyl group in the N-type group (imide structure) can gain an electron and then combine with sodium ions through an enolization reaction to achieve sodium storage capacity. The imide group combined with sodium ions can reversibly release sodium ions, achieving sodium ion insertion / extraction. During charging, sodium ions move from the positive electrode to the negative electrode. The carbon-coated aluminum foil located in the negative electrode current collector combines with sodium ions through the N-type groups in the coating to achieve sodium storage, increasing the charging capacity of the sodium-ion battery and improving its energy density. During discharging, sodium ions are released from the N-type groups again, achieving reversible charging and discharging. The p-type group (triazine structure) can lose an electron to form an amine cation, which then combines with an anion to achieve coordination with the anion. Polyanionic compounds are the positive electrode materials of sodium-ion batteries. Their anions include orthophosphate, pyrophosphate, sulfate, fluorophosphate, and silicate. The triazine group that combines with the anion can reversibly release the anion. During charging, the carbon-coated aluminum foil located in the positive electrode current collector combines with the anion through the p-type group in the coating, which can stabilize the anion after charging and play an auxiliary role in increasing the charging capacity. During discharging, the anion is released from the p-type group and recombines with sodium ions to achieve reversible charging and discharging.

[0115] The carbon-coated aluminum foil provided by this invention can be used as a current collector for the positive / negative electrodes of sodium-ion batteries, improving the performance of sodium-ion batteries. The N-type and P-type groups in graphene containing PN-type groups have stable insertion / extraction potentials, allowing sodium ions to reversibly insert and extract, thus achieving sodium storage function. This can improve the conductivity of the carbon-coated aluminum foil. For rocking chair-type sodium-ion batteries, it is beneficial to reduce the contact resistance between the carbon-coated aluminum foil and the positive and negative electrode materials, increase the battery energy density, and improve the battery's cycle capacity and lifespan.

[0116] In this invention, graphene containing PN-type groups exhibits good compatibility with sodium electrode positive and negative electrode materials, improving the peel strength between the carbon-coated aluminum foil and the positive and negative electrode materials. The PN-type groups can combine with sodium ions or anions, which is beneficial for improving the compatibility between the carbon-coated aluminum foil coating and the positive and negative electrode materials. Simultaneously, amide bonds can form hydrogen bonds with the positive and negative electrode materials, enhancing the interfacial forces and improving the peel strength between them.

[0117] The principles of sodium storage and anion stabilization in graphene containing PN-type groups are as follows:

[0118]

[0119] Graphene containing PN-type groups contains both N-type and P-type group structures.

[0120] The N-type group can gain an electron and bind to a sodium ion. Typical N-type groups include imide, quinone, quinoxaline, and azo groups. Among them, imide contains two carbonyl groups, which can gain an electron and then bind to lithium, sodium, potassium, etc., through an enolization reaction to achieve the function of storing sodium. It can also release the bound lithium, sodium, potassium, etc., through a reversible reaction to achieve the function of inserting / extracting lithium, sodium, potassium, etc.

[0121]

[0122] Specifically, the carbonyl group on the N-type group can reversibly bind sodium ions, achieving the function of insertion / extraction. During charging, sodium ions move from the positive electrode to the negative electrode, and the carbonyl group on the N-type group in the carbon-coated aluminum foil of the negative electrode gains an electron and combines with sodium ions through an enolization reaction; during discharging, sodium ions are released back from the carbonyl group.

[0123] P-type groups can lose electrons and then combine with anions. Typical P-type groups include triazine, nitrogen-substituted phenazine, and triphenylamine groups. Among them, triazine, nitrogen-substituted phenazine, and triphenylamine groups can lose electrons to form amine cations, which then coordinate with anions to stabilize the anions.

[0124]

[0125] Specifically, the triazine group on the p-type group can reversibly bind to anions. During charging, the triazine group on the p-type group loses electrons to form an amine cation, which combines with the anion, stabilizing the anion. During discharging, the anion is released and recombines with sodium ions, achieving reversible charging and discharging.

[0126] The working principle of graphene containing PN-type groups is as follows:

[0127] Carbon-coated aluminum foil containing graphene with PN-type groups can be used as positive and negative current collectors in sodium-ion batteries.

[0128] During battery charging: Sodium ions move from the positive electrode to the negative electrode. The carbon-coated aluminum foil on the negative electrode can increase the charging capacity and improve the energy density of the sodium-ion battery through the sodium storage performance of the N-type groups in the coating. At the same time, the carbon-coated aluminum foil on the positive electrode can combine with anions through the P-type groups in the coating, which can stabilize the anions and help increase the charging capacity.

[0129] During battery discharge: the N-type groups that bind to sodium ions reversibly release sodium ions, achieving reversible insertion / extraction of sodium ions; at the same time, the P-type groups that bind to anions also release anions, which re-bind to sodium ions, thus improving the battery's cycle capacity.

[0130] Compared with the prior art, the modified graphene provided by the present invention enables carbon-coated aluminum foil to have the function of storing sodium, which can reduce the contact resistance between carbon-coated aluminum foil and positive electrode material, improve the peel strength between carbon-coated aluminum foil and positive electrode material, and improve battery charging capacity and cycle life. Detailed Implementation

[0131] Embodiments of the present invention are described in detail below. Unless otherwise stated, all technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. All patents and publications related to this invention are incorporated herein by reference in their entirety. The terms "comprising" or "including" are open-ended expressions, meaning they include the contents specified in this invention but do not exclude other aspects.

[0132] According to embodiments provided by the present invention, the present invention specifically provides a method for preparing graphene containing PN-type groups, the method comprising the following steps:

[0133]

[0134] 1) Under nitrogen protection, amino-based graphene and compound 1 react in solvent 1 for a period of time. Then, dehydrating agent 1 is added, and water is removed by azeotropic reaction. After the reaction is complete, the mixture is filtered, and the precipitate is washed with solvent 1 to remove unreacted compound 1. The mixture is then dried under vacuum to obtain intermediate 1.

[0135] 2) Under nitrogen protection, intermediate 1, acid anhydride and organic amine react in solvent 2. After the reaction is complete, filter, wash the precipitate with solvent 2 and water to remove excess raw materials, and vacuum dry to obtain graphene containing N-type groups.

[0136] 3) Under nitrogen protection, graphene containing N-type groups and compound 2 react in solvent 3 for a period of time. Then, dehydrating agent 2 is added, and water is removed by azeotropic reaction. After the reaction is complete, the mixture is filtered, the precipitate is washed with solvent 3 to remove unreacted compound 2, and then vacuum dried to obtain intermediate 2.

[0137] 4) Add intermediate 2 to the reactor, heat the mixture under nitrogen protection, dehydrate and cyclize it, and obtain graphene containing PN type groups after the reaction is completed.

[0138] Preparation of carbon coating paste

[0139] Deionized water, binder, the above-prepared graphene containing PN-type groups, conductive carbon black Super P, dispersant, and thickener are mixed and pre-dispersed at high speed using mechanical stirring until homogeneous. The pre-dispersed slurry is then sand-milled to obtain a carbon-coated slurry.

[0140] Preparation of carbon-coated aluminum foil

[0141] The carbon-coated slurry prepared above is applied to the surface of an aluminum foil substrate with a thickness of 12-15 μm using a micro-grooving roller, doctor blade, or wire rod coating. The wet film thickness is controlled to be 3-10 μm. The coated aluminum foil is then placed in a dryer and heated at 80-200℃ for 0.5-10 min to form a film, thus obtaining the carbon-coated aluminum foil.

[0142] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific conditions are not specified in the examples, they are performed according to the conditions described in the instruction manual, conventional conditions, or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0143] Example 1

[0144]

[0145] The graphene containing PN-type groups shown in formula (I-1) is prepared as follows:

[0146] 1) Add 100 mL of N-methylpyrrolidone and 1 g of aminographene to a reaction vessel, evacuate and replace with nitrogen, add 0.75 g of 1,4,5,8-naphthalenetetracarboxylic anhydride at 50 °C, and react for 24 h. Then add 20 mL of toluene, azeotropically react at 120 °C for 1 h, and reflux to separate the water. After the reaction is complete, filter, wash the filter cake with N-methylpyrrolidone, and dry under vacuum at 50 °C to obtain intermediate 1-A1.

[0147] 2) Add 100 mL of N-methylpyrrolidone and intermediate 1-A1 to the reaction vessel, evacuate and replace with nitrogen, add 1.25 g of acetic anhydride and 1.25 g of pyridine at 50 °C, and react for 10 h. After the reaction is complete, add 200 mL of water, filter, and wash the filter cake with N-methylpyrrolidone and water. Dry under vacuum at 50 °C. The product weighs 1.09 g, with a yield of 93.4%, yielding graphene containing N-type groups.

[0148] FTIR(KBr):ν=1784,1707,1563,1514,1301,1235,1149,1128,971,606cm -1 .

[0149] 3) Add 100 mL of N-methylpyrrolidone and 1.09 g of N-type graphene to the reaction vessel, evacuate and replace with nitrogen, add 0.75 g of 4-(1,3,5-triazin-2-yl)aniline at 50 °C, and react for 24 h. Then add 20 mL of toluene, azeotropically react at 120 °C for 1 h, and reflux to separate water. After the reaction is complete, filter, wash the filter cake with N-methylpyrrolidone, and dry under vacuum at 50 °C to obtain intermediate 2-B1.

[0150] 4) Add intermediate 2-B1 to the reactor, evacuate and replace with nitrogen, dehydrate and cyclize at 300℃ for 10h. After the reaction is complete, dry under vacuum at 50℃. The product weighs 1.12g and has a yield of 88.3%, thus obtaining graphene containing PN-type groups (product 1).

[0151] FTIR(KBr):ν=1711,1549,1526,1484,1405,1363,1278,1214,1184,1107,805,728cm -1 .

[0152] Preparation of carbon coating paste:

[0153] By weight, 100 parts of deionized water, 20 parts of K-702 binder, 5 parts of graphene containing PN-type groups (product 1), 5 parts of conductive carbon black Super P, 0.5 parts of BYK-ET3003 and 1 part of carboxymethyl cellulose are mixed and stirred at high speed until uniform at a stirring speed of 1000 r / min. The pre-dispersed slurry is then milled in a sand mill at 10℃ for 2 hours to obtain carbon-coated slurry (slurry 1).

[0154] Preparation of carbon-coated aluminum foil:

[0155] Carbon-coated slurry (slurry 1) was coated onto a bright aluminum foil using a 5μm wire rod and dried at 150℃ for 5 minutes to form a film. After drying, carbon-coated aluminum foil (carbon-coated aluminum foil 1) was obtained.

[0156] Example 2

[0157]

[0158] The graphene containing PN-type groups shown in formula (I-2) is prepared as follows:

[0159] 1) Add 100 mL of N-methylpyrrolidone and 1 g of aminographene to a reaction vessel, evacuate and replace with nitrogen, add 1 g of 3,4,9,10-perylenetetracarboxylic acid dianhydride at 50 °C, and react for 24 h. Then add 20 mL of toluene, azeotropically react at 120 °C for 1 h, and reflux to separate water. After the reaction is complete, filter, wash the filter cake with N-methylpyrrolidone, and dry under vacuum at 50 °C to obtain intermediate 1-A2.

[0160] 2) Add 100 mL of N-methylpyrrolidone and intermediate 1-A2 to the reaction vessel, evacuate and replace with nitrogen, add 1.35 g of acetic anhydride and 1.35 g of pyridine at 50 °C, and react for 10 h. After the reaction is complete, add 200 mL of water, filter, and wash the filter cake with N-methylpyrrolidone and water. Dry under vacuum at 50 °C. The product weighs 1.15 g, with a yield of 92.5%, yielding graphene containing N-type groups.

[0161] FTIR(KBr):ν=1777,1704,1595,1403,1306,1234,1035,920,731,663cm -1 .

[0162] 3) Add 100 mL of N-methylpyrrolidone and 1.15 g of N-type graphene to the reaction vessel, evacuate and replace with nitrogen, add 0.75 g of 4-(1,3,5-triazin-2-yl)aniline at 50 °C, and react for 24 h. Then add 20 mL of toluene, azeotropically react at 120 °C for 1 h, and reflux to separate water. After the reaction is complete, filter, wash the filter cake with N-methylpyrrolidone, and dry under vacuum at 50 °C to obtain intermediate 2-B2.

[0163] 4) Add intermediate 2-B2 to the reactor, evacuate and replace with nitrogen, dehydrate and cyclize at 300℃ for 10h. After the reaction is complete, dry under vacuum at 50℃. The product weighs 1.21g, with a yield of 90.1%, and graphene containing PN type groups (product 2) is obtained.

[0164] FTIR(KBr):ν=1694,1597,1487,1468,1453,1358,1245,1147,964,809,741,603cm -1 .

[0165] Preparation of carbon coating paste:

[0166] By weight, 100 parts of deionized water, 20 parts of K-702 binder, 5 parts of graphene containing PN-type groups (product 2), 5 parts of conductive carbon black Super P, 0.5 parts of BYK-ET3003 and 1 part of carboxymethyl cellulose were mixed and stirred at high speed until uniform. The stirring speed was 1000 r / min. The pre-dispersed slurry was then milled in a sand mill at 10℃ for 2 h to obtain carbon-coated slurry (slurry 2).

[0167] Preparation of carbon-coated aluminum foil:

[0168] Carbon-coated slurry (slurry 2) is coated onto bright aluminum foil using a 5μm wire rod, dried at 150℃ for 5 minutes to form a film, and then compacted by roller pressing to obtain carbon-coated aluminum foil (carbon-coated aluminum foil 2).

[0169] Example 3

[0170]

[0171] The graphene containing PN-type groups shown in formula (I-3) is prepared as follows:

[0172] 1) Add 100 mL of N-methylpyrrolidone and 1 g of aminographene to a reaction vessel, evacuate and replace with nitrogen, add 0.75 g of 1,4,5,8-naphthalenetetracarboxylic anhydride at 50 °C, and react for 24 h. Then add 20 mL of toluene, azeotropically react at 120 °C for 1 h, and reflux to separate water. After the reaction is complete, filter, wash the filter cake with N-methylpyrrolidone, and dry under vacuum at 50 °C to obtain intermediate 1-A3.

[0173] 2) Add 100 mL of N-methylpyrrolidone and intermediate 1-A3 to the reaction vessel, evacuate and replace with nitrogen, add 1.25 g of acetic anhydride and 1.25 g of pyridine at 50 °C, and react for 10 h. After the reaction is complete, add 200 mL of water, filter, and wash the filter cake with N-methylpyrrolidone and water. Dry under vacuum at 50 °C. The product weighs 1.07 g, with a yield of 91.6%, yielding graphene containing N-type groups.

[0174] FTIR(KBr):ν=1784,1707,1563,1514,1301,1235,1149,1128,971,606cm -1 .

[0175] 3) Add 100 mL of N-methylpyrrolidone and 1.07 g of N-type graphene to the reaction vessel, evacuate and replace with nitrogen, add 1 g of 4-(4,6-dimethyl-1,3,5-triazin-2-yl)aniline at 50 °C, and react for 24 h. Then add 20 mL of toluene, and reflux at 120 °C for 1 h to separate the water. After the reaction is complete, filter, wash the filter cake with N-methylpyrrolidone, and dry under vacuum at 50 °C to obtain intermediate 2-B3.

[0176] 4) Add intermediate 2-B3 to the reactor, evacuate and replace with nitrogen, dehydrate and cyclize at 300℃ for 10h. After the reaction is complete, dry under vacuum at 50℃. The product weighs 1.15g and has a yield of 90.5%, yielding graphene containing PN-type groups (product 3).

[0177] FTIR(KBr):ν=1701,1601,1506,1483,1477,1421,1360,1298,1254,1107,802,728,691cm -1 .

[0178] Preparation of carbon coating paste:

[0179] By weight, 100 parts of deionized water, 20 parts of K-702 binder, 5 parts of graphene containing PN-type groups (product 3), 5 parts of conductive carbon black Super P, 0.5 parts of BYK-ET3003 and 1 part of carboxymethyl cellulose were mixed and stirred at high speed until uniform. The stirring speed was 1000 r / min. The pre-dispersed slurry was then milled in a sand mill at 10℃ for 2 h to obtain carbon-coated slurry (slurry 3).

[0180] Preparation of carbon-coated aluminum foil:

[0181] Carbon-coated slurry (slurry 3) is coated onto bright aluminum foil using a 5μm wire rod, dried at 150℃ for 5 minutes to form a film, and then compacted by roller pressing to obtain carbon-coated aluminum foil (carbon-coated aluminum foil 3).

[0182] Example 4

[0183]

[0184] The graphene containing PN-type groups shown in formula (I-4) was prepared as follows:

[0185] 1) Add 100 mL of N-methylpyrrolidone and 1 g of aminographene to a reaction vessel, evacuate and replace with nitrogen, add 1 g of 3,4,9,10-perylenetetracarboxylic acid dianhydride at 50 °C, and react for 24 h. Then add 20 mL of toluene, azeotropically react at 120 °C for 1 h, and reflux to separate water. After the reaction is complete, filter, wash the filter cake with N-methylpyrrolidone, and dry under vacuum at 50 °C to obtain intermediate 1-A4.

[0186] 2) Add 100 mL of N-methylpyrrolidone and intermediate 1-A4 to the reaction vessel, evacuate and replace with nitrogen, add 1.4 g of acetic anhydride and 1.4 g of pyridine at 50 °C, and react for 10 h. After the reaction is complete, add 200 mL of water, filter, and wash the filter cake with N-methylpyrrolidone and water. Dry under vacuum at 50 °C. The product weighs 1.10 g, with a yield of 88.5%, yielding graphene containing N-type groups.

[0187] FTIR(KBr):ν=1777,1704,1595,1403,1306,1234,1035,920,731,663cm -1 .

[0188] 3) Add 100 mL of N-methylpyrrolidone and 1.1 g of N-type graphene to the reaction vessel, evacuate and replace with nitrogen, add 1 g of 4-(4,6-dimethyl-1,3,5-triazin-2-yl)aniline at 50 °C, and react for 24 h. Then add 20 mL of toluene, azeotropically react at 120 °C for 1 h, and reflux to separate water. After the reaction is complete, filter, wash the filter cake with N-methylpyrrolidone, and dry under vacuum at 50 °C to obtain intermediate 2-B4.

[0189] 4) Add intermediate 2-B4 to the reactor, evacuate and replace with nitrogen, dehydrate and cyclize at 300℃ for 10h. After the reaction is complete, dry under vacuum at 50℃. The product weighs 1.15g and has a yield of 85.8%, thus obtaining graphene containing PN-type groups (product 4).

[0190] FTIR(KBr):ν=1707,1582,1563,1485,1449,1366,1305,1237,944,810,721,621,604cm -1 .

[0191] Preparation of carbon coating paste:

[0192] By weight, 100 parts of deionized water, 20 parts of K-702 binder, 5 parts of graphene containing PN-type groups (product 4), 5 parts of conductive carbon black Super P, 0.5 parts of BYK-ET3003 and 1 part of carboxymethyl cellulose were mixed and stirred at high speed until uniform. The stirring speed was 1000 r / min. The pre-dispersed slurry was then milled in a sand mill at 10℃ for 2 h to obtain carbon-coated slurry (slurry 4).

[0193] Preparation of carbon-coated aluminum foil:

[0194] Carbon-coated slurry (slurry 4) is coated onto bright aluminum foil using a 5μm wire rod, dried at 150℃ for 5 minutes to form a film, and then compacted by roller pressing to obtain carbon-coated aluminum foil (carbon-coated aluminum foil 4).

[0195] Comparative Example 1

[0196] Preparation of carbon coating paste:

[0197] By weight, 100 parts deionized water, 20 parts K-702 binder, 5 parts commercially available graphene, 5 parts conductive carbon black Super P, 0.5 parts BYK-ET3003 and 1 part carboxymethyl cellulose were mixed and stirred at high speed until uniform at a stirring speed of 1000 r / min. The pre-dispersed slurry was then milled in a sand mill at 10℃ for 2 h to obtain carbon-coated slurry (slurry 5).

[0198] Preparation of carbon-coated aluminum foil:

[0199] Carbon-coated slurry (slurry 5) is coated onto bright aluminum foil using a 5μm wire rod, dried at 150℃ for 5 minutes to form a film, and then compacted by roller pressing to obtain carbon-coated aluminum foil (carbon-coated aluminum foil 5).

[0200] Comparative Example 2

[0201] Preparation of carbon coating paste:

[0202] By weight, 100 parts deionized water, 20 parts K-702 binder, 5 parts commercially available hard carbon, 5 parts conductive carbon black Super P, 0.5 parts BYK-ET3003 and 1 part carboxymethyl cellulose are mixed and stirred at high speed until uniform. The stirring speed is 1000 r / min. The pre-dispersed slurry is then milled in a sand mill at 10℃ for 2 hours to obtain carbon coating slurry (slurry 6).

[0203] Preparation of carbon-coated aluminum foil:

[0204] Carbon-coated slurry (slurry 6) is coated onto bright aluminum foil using a 5μm wire rod, dried at 150℃ for 5 minutes to form a film, and then compacted by roller pressing to obtain carbon-coated aluminum foil (carbon-coated aluminum foil 6).

[0205] Comparative Example 3

[0206] Preparation of carbon coating paste:

[0207] By weight, 100 parts deionized water, 20 parts K-702 binder, 5 parts commercially available graphene, 5 parts commercially available hard carbon, 5 parts conductive carbon black Super P, 0.5 parts BYK-ET3003 and 1 part carboxymethyl cellulose are mixed and stirred at high speed until uniform. The stirring speed is 1000 r / min. The pre-dispersed slurry is then milled in a sand mill at 10℃ for 2 h to obtain carbon-coated slurry (slurry 7).

[0208] Preparation of carbon-coated aluminum foil:

[0209] Carbon-coated slurry (slurry 7) is coated onto bright aluminum foil using a 5μm wire rod, dried at 150℃ for 5 minutes to form a film, and then compacted by roller pressing to obtain carbon-coated aluminum foil (carbon-coated aluminum foil 7).

[0210] Performance testing:

[0211] Preparation of electrode sheets and batteries

[0212] The positive electrode materials sodium iron pyrophosphate, conductive carbon black Super P, and PVDF are mixed and ground in a mass ratio of 8:1:1. An appropriate amount of N-methylpyrrolidone is added and stirred into a homogenous slurry. The positive electrode slurry is then coated onto carbon-coated aluminum foil 1-7 and dried in a blower dryer at 95°C for 12 hours. After rolling, the positive electrode sheet 1-7 is obtained.

[0213] Mix hard carbon, conductive carbon black Super P, and PVDF in a mass ratio of 8:1:1, grind them, and add an appropriate amount of N-methylpyrrolidone to form a slurry. Then, coat the negative electrode slurry on the carbon-coated aluminum foil 1-7. Dry the obtained negative electrode in a vacuum drying oven at 95°C for 12 hours to obtain the negative electrode sheet 1-7.

[0214] Correspond the positive electrode sheet 1-7 and the negative electrode sheet 1-7 one by one, and further cut and wind them to obtain the 26650 cylindrical sodium-ion secondary battery 1-7.

[0215] Test method:

[0216] (1) Resistance value test of carbon-coated aluminum foil

[0217] Use the ST2258C tester to test the resistance, resistivity, and conductivity of the carbon-coated aluminum foil.

[0218] (2) Peel strength test

[0219] Use the INSTRON tensile testing machine to test the peel strength.

[0220] (3) NMP resistance and water resistance tests of carbon-coated aluminum foil

[0221] Use a two-way abrasion tester. Soak cotton fully with test solvents such as NMP or water, wipe back and forth once every 2 seconds for 200 times. If it can be wiped more than 200 times and there is no phenomenon of the carbon-coated layer leaking the substrate, it is qualified. When the substrate leaks before 200 wipes, record the maximum number of wiping times.

[0222] (4) Scratch resistance test

[0223] Adopt the cross-cut method to test the peel strength according to the method of GB-T9286-1998: When using the cross-cut method, grade 0 means no peeling, grade 1 means less than 5% peeling, grade 2 means more than 5% and less than 15% peeling, grade 3 means more than 15% and less than 35% peeling, grade 4 means more than 35% and less than 65% peeling, and grade 5 means the peeling degree is greater than grade 4.

[0224] (5) Electrolyte resistance test of carbon-coated aluminum foil

[0225] Let the carbon-coated foil stand in the electrolyte for 120 days. If the coating shows no obvious peeling and the electrolyte does not change color, it is qualified.

[0226] (6) Discharge specific capacity test of the battery

[0227] The operating voltage range is 1.5 - 3.0V, the current density is 1C, and it cycles 100 times.

[0228] (7) Battery cycle life test

[0229] Charge-discharge tests were conducted at 25℃ for N cycles. The specific capacity of the battery discharge after the first and Nth cycles was recorded, and the discharge capacity retention rate was calculated. Discharge capacity retention rate = (Nth discharge capacity / First discharge capacity) * 100%. The test was terminated and the number of cycles was recorded when the discharge capacity retention rate reached 80%.

[0230] The carbon-coated aluminum foil, positive electrode sheet, and sodium-ion battery obtained in Examples 1-4 and Comparative Examples 1-3 were tested respectively, and the results are shown in the table below:

[0231] Table 1: Test data for carbon-coated aluminum foil

[0232]

[0233]

[0234] Table 2: Test Data for Positive Electrode

[0235] Thickness / μm 80 79 78 82 79 80 79 Conductivity / S / cm 14.077 13.956 13.617 14.004 12.041 10.234 11.107 Peel strength / N / m 12.6 11.9 12.4 11.7 9.81 9.74 9.64

[0236] Table 3: Test Data for Sodium-ion Batteries

[0237]

[0238] As shown in Table 1, in Examples 1-4, graphene containing PN-type groups was incorporated. During charging and discharging, its structure can gain or lose electrons, which is beneficial for forming a conductive network and increasing the electron flow in the coating, thereby reducing the resistance of the carbon-coated aluminum foil. Simultaneously, the imide and triazine groups can form hydrogen bonds with the groups in the binder, enabling the graphene to bond more firmly to the binder and increasing the peel strength of the carbon-coated aluminum foil coating. Even after incorporating graphene containing PN-type groups, the resistance to NMP wiping, water wiping, cross-cut adhesion testing, and electrolyte resistance remained excellent.

[0239] As shown in Table 2, in Examples 1-4, a positive electrode slurry was coated onto a carbon-coated aluminum foil containing PN-type groups. The PN-type group structure has a sodium storage function, enabling sodium ion insertion / extraction during charging and discharging. This reduces the contact resistance between the carbon-coated aluminum foil current collector and the positive electrode slurry, increasing the conductivity of the coating. Simultaneously, its imide and triazine groups can form hydrogen bonds with the surface of the positive electrode material, increasing the peel strength between the carbon-coated aluminum foil and the positive electrode material.

[0240] As shown in Table 3, the carbon-coated aluminum foils of Examples 1-4, which incorporated graphene containing PN-type groups, exhibited higher initial discharge specific capacities at both 0.1C and 1C than those of Comparative Examples 1-3. This indicates that the insertion / extraction properties of PN-type groups can increase the charge / discharge capacity of sodium-ion batteries.

[0241] Comparative Example 1 did not include hard carbon that can store sodium, while Comparative Examples 2 and 3 included hard carbon. The initial discharge capacity of Comparative Examples 2-3 was greater than that of Comparative Example 1, indicating that the addition of hard carbon can improve the charge and discharge capacity. However, the initial discharge capacity of Comparative Examples 2-3 was less than that of Examples 1-4, indicating that although hard carbon can improve the charge and discharge capacity, its effect is not as good as that of graphene containing PN-type groups.

[0242] The capacity retention rates of Examples 1-4 after 100 cycles at 1C are all greater than those of Comparative Examples 1-3, and the cycle life of Examples 1-4 is also greater than that of Comparative Examples 1-3. This indicates that graphene containing PN-type groups facilitates the insertion / extraction of sodium ions, which is beneficial to improving the charge and discharge performance of sodium-ion batteries.

[0243] In the description of this specification, the references to terms such as "some embodiments," "other embodiments," "examples," and "examples" 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.

[0244] Although embodiments and examples of the present invention have been shown and described above, it is understood that the above embodiments and examples are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments and examples within the scope of the present invention.

Claims

1. A modified graphene, characterized in that, The modified graphene has the structure shown in formula (I): ； in, R1 is selected from any one of the following groups: benzene, naphthalene, anthracene, phenanthrene, perylene, tetraphenylene, and pyrene. R2 and R3 are each independently one of H, -CH3, and -CH2CH3; m can be 0, 1, 2, 3, or 4; n is 0, 1, or 2.

2. The modified graphene according to claim 1, characterized in that, The modified graphene has one of the following structures: , , or .

3. A method for preparing the modified graphene according to claim 1 or 2, characterized in that, The preparation method includes the following steps: 1) Aminographene reacts with compound 1 to obtain intermediate 1; 2) The intermediate 1 obtained in step 1) reacts with acid anhydride and organic amine to obtain graphene containing N-type groups; 3) The graphene containing N-type groups obtained in step 2) reacts with compound 2 to obtain intermediate 2; 4) Dehydrate and cyclize intermediate 2 obtained in step 3) to obtain graphene containing PN-type groups with the structure shown in formula (I).

4. The method for preparing modified graphene according to claim 3, characterized in that, In step 1), compound 1 is selected from... , , , , , , , , , At least one of them; The mass ratio of the amino-based graphene to compound 1 is 1:(0.5-1.5). The reaction temperature is 20-100℃; The reaction time is 1-48 h.

5. The method for preparing modified graphene according to claim 3, characterized in that, In step 1), the reaction temperature is 25-75℃; The reaction time is 2-30 h.

6. The method for preparing modified graphene according to claim 3, characterized in that, In step 2), the acid anhydride is selected from at least one of acetic anhydride and trifluoroacetic anhydride; The organic amine is selected from at least one of pyridine and triethylamine; The mass ratio of the amino-based graphene, acid anhydride, and organic amine is 1:(0.5-1.5):(0.5-1.5). The reaction temperature is 20-100℃; The reaction time is 1-24 h.

7. The method for preparing modified graphene according to claim 3, characterized in that, In step 2), the reaction temperature is 25-75℃; The reaction time is 2-12 h.

8. The method for preparing modified graphene according to claim 3, characterized in that, In step 3), compound 2 is selected from... , , , , , , , , , , , At least one of them; The mass ratio of the N-type graphene to compound 2 is 1:(0.5-1.5). The reaction temperature is 20-100℃; The reaction time is 1-48 h.

9. The method for preparing modified graphene according to claim 3, characterized in that, In step 3), the reaction temperature is 25-75℃; The reaction time is 2-30 h.

10. The method for preparing modified graphene according to claim 3, characterized in that, In step 4), the temperature for dehydration cyclization is 200-400℃; The dehydration cyclization time is 1-48 h.

11. The method for preparing modified graphene according to claim 3, characterized in that, In step 4), the temperature for dehydration cyclization is 250-350℃; The dehydration cyclization time is 2-30 h.

12. A carbon coating paste, characterized in that, The carbon coating slurry includes a conductive agent, wherein the conductive agent includes graphene and conductive carbon black Super P; The graphene is the modified graphene according to any one of claims 1 or 2, or the graphene containing PN-type groups prepared by any one of claims 3-11.

13. The carbon coating paste according to claim 12, characterized in that, The carbon coating slurry also includes at least one of a binder, dispersant, and thickener; The adhesive is selected from at least one of acrylic resins, polyvinyl alcohol resins, epoxy resins, and styrene-butadiene rubber; The dispersant is selected from sodium dodecyl sulfate, BYK ET3000, BYK ET3001, BYK ET3003, BYK ET3004, BYK ET 3032, BYK ET 3031, BYK ET3002, BYK ET 3033, BYK ET 3034, Electro At least one of Rite AL003 and octadecyltrimethylammonium bromide; The thickener is selected from at least one of polyvinylpyrrolidone, polyoxyethylene, methylcellulose, carboxymethylcellulose, sodium carboxymethylcellulose, hydroxymethylcellulose, and sodium hydroxymethylcellulose. in, The mass ratio of graphene to conductive carbon black Super P is 1:(0.1-10). The mass ratio of the total mass of the conductive agent to the mass of the binder is 1:(1-10). The mass ratio of the dispersant to the binder is 1:(20-100); The mass ratio of the thickener to the binder is 1:(10-100).

14. A carbon-coated aluminum foil, characterized in that, The carbon-coated aluminum foil comprises the carbon-coating paste as described in any one of claims 12 or 13.

15. The application of the carbon-coated aluminum foil according to claim 14 in a sodium-ion battery, characterized in that, The carbon-coated aluminum foil is used in the positive electrode current collector and / or negative electrode current collector of sodium-ion batteries.

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