Preparation method of negative electrode material for improving cycle performance of sodium battery

Abstract

The invention discloses a preparation method of a negative electrode material for improving the cycle performance of a sodium battery, and relates to the technical field of battery preparation. Comprising the following steps: preparing a sodium battery negative electrode material through ball-milling calcination and hydrothermal synthesis methods, mixing the prepared negative electrode material with an adhesive and modified carbon black, uniformly stirring, coating an aluminum foil of 12-15 microns with the mixture, drying, rolling, and drying at 120-150 DEG C for 12-15 hours to obtain a negative electrode piece. The sodium battery negative electrode material has the beneficial effects that the sodium battery negative electrode material is prepared through ball-milling calcination and hydrothermal synthesis methods, the binder with a three-dimensional cross-linked structure is obtained through modification, the mechanical property and electrochemical stability of the sodium battery negative electrode material are remarkably improved, in addition, in order to improve the compatibility of the conductive carbon black and the binder, a polyamide acid chain segment is introduced to the surface of the conductive carbon black, and the conductivity of the conductive carbon black is improved. And the conductivity and the structural stability of the electrode are enhanced.

Description

Technical Field

[0001] The invention relates to the technical field of battery preparation, and in particular to a method for preparing a negative electrode material for improving the cycle performance of a sodium battery. Background Art

[0002] As the global demand for renewable energy continues to grow, the scarcity of traditional energy and the limited lithium resources have become urgent problems to be solved. In order to meet these challenges, sodium battery technology, which is lower in cost and more abundant in resources, has gradually become a research hotspot in academia. Unlike lithium batteries, the negative electrode materials of sodium batteries need to have a larger interlayer spacing and a lower volume expansion coefficient to accommodate the insertion and extraction of sodium ions. As a highly potential negative electrode material for sodium ion batteries, red phosphorus has a theoretical capacity of up to 2596mAh·g⁻¹, showing significant advantages. However, red phosphorus faces two major problems in practical applications: first, its poor conductivity leads to limited electrochemical reaction rate; second, during the charging and discharging process, red phosphorus undergoes a large volume change, which causes the destruction of the electrode structure and rapid capacity decay.

[0003] In addition, the battery binders in the prior art have significant defects, especially in terms of cycle performance. Traditional binders have poor mechanical properties and electrochemical stability, and cannot effectively inhibit the volume expansion of electrode materials during charging and discharging, resulting in gradual destruction of the electrode structure, accelerated capacity decay, and significantly shortened cycle life. At the same time, the compatibility between the conductive agent and the binder is poor, which not only reduces the conductivity of the electrode, but also affects the overall structural stability of the electrode, further exacerbating the deterioration of the cycle performance.

[0004] In summary, in order to solve the above problems, the present invention obtains a negative electrode material for improving the cycle performance of sodium batteries. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing a negative electrode material for improving the cycle performance of a sodium battery, so as to solve the problems raised in the prior art.

[0006] To achieve the above object, the present invention provides the following technical solutions: A method for preparing a negative electrode material for improving the cycle performance of a sodium battery comprises the following steps: Step 1: mechanically mix red phosphorus and sulfide polyacrylonitrile and perform ball milling, then transfer to a tube furnace, introduce argon gas, and calcine at 300-350° C. for 10-12 h to obtain a red phosphorus-sulfide polyacrylonitrile sample; Step 2: Dissolve the red phosphorus-sulfurized polyacrylonitrile sample in pure water, then add a few layers of MXene, stir evenly, bake at 180-200°C for 16-18h, and finally obtain the modified negative electrode material after filtering, washing and drying.

[0007] More optimally, the mass ratio of the red phosphorus to the sulfide polyacrylonitrile is (60-65):1; the mass ratio of the red phosphorus to the few-layer MXene is (20-22):1.

[0008] More optimally, during the baking process, the heating rate is 40-45°C / min, and the annealing rate is 10-15°C / min.

[0009] A method for preparing a negative electrode sheet comprises the following steps: mixing the above-mentioned negative electrode material with a binder and modified carbon black, stirring evenly, then coating on a 12-15 μm aluminum foil, drying and rolling, and drying at 120-150° C. for 12-15 hours to obtain a negative electrode sheet.

[0010] More optimally, the mass ratio of the negative electrode material, the binder, and the modified carbon black is (8-9):1:1.

[0011] More optimally, the preparation process of the adhesive is: S1: under a protective atmosphere, diaminodiphenyl ether is added to N-methylpyrrolidone, stirred for several times until all dissolved, and then 4,4'-oxydiphthalic anhydride is added in batches, and reacted at 0-5°C for 4-6h to obtain anhydride-terminated polyamic acid; S2: 2,4-diaminobutyric acid, anhydrous sodium carbonate and deionized water are mixed, mechanically stirred to be uniform, and cyanuric chloride solution is slowly added dropwise at 0-5°C, and the addition is completed within 2-3 hours, and stirring is continued for 6-8 hours, and then filtered, washed and recrystallized to obtain triaminocarboxylic acid triazine; S3: Add triaminocarboxylic acid triazine to N-methylpyrrolidone, and after fully dissolving, slowly drip it into anhydride-terminated polyamic acid at 0-5°C, and react for 3-4 hours. After the reaction is completed, continue to add N-methylpyrrolidone for dilution to obtain an adhesive.

[0012] More optimally, the anhydride-terminated polyamic acid comprises the following substances: by weight, 5-8 parts of diaminodiphenyl ether, 40-50 parts of N-methylpyrrolidone, and 7.5-12 parts of 4,4'-oxydiphthalic anhydride; The triaminocarboxylic acid triazine comprises the following substances: by weight, 35-40 parts of 2,4-diaminobutyric acid, 40-42 parts of anhydrous sodium carbonate, 300-320 parts of deionized water, and 18-20 parts of cyanuric chloride solution; wherein the mass fraction of the cyanuric chloride solution is 8-10wt%, and the solvent is dioxane; The adhesive raw material comprises the following substances: by weight, 0.5-0.8 parts of triaminocarboxylic acid triazine, 50-55 parts of N-methylpyrrolidone, and 30-35 parts of anhydride-terminated polyamic acid; wherein the solid content of the adhesive is 6-8wt%.

[0013] More optimally, the preparation process of the modified carbon black is as follows: (1) the conductive carbon black is evenly dispersed in ethanol, the pH is adjusted to 6-6.5, γ-aminopropyltriethoxysilane is added dropwise, the temperature is raised to 60-70°C, and the reaction is carried out for 3-4 hours to obtain amino carbon black; (2) the amino carbon black is mixed with anhydride-terminated polyamic acid, and the mixture is reacted at 0-5°C for 4-5 hours to obtain modified carbon black.

[0014] More optimally, the mass ratio of the conductive carbon black to γ-aminopropyltriethoxysilane is (9-10):1; the mass ratio of the amino carbon black to the anhydride-terminated polyamic acid is 1:(2-3).

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention prepares the negative electrode material of the sodium battery by ball milling calcination and hydrothermal synthesis, and obtains a binder with a three-dimensional cross-linked structure by modification, which significantly improves its mechanical properties and electrochemical stability. In addition, in order to improve the compatibility of the conductive carbon black and the binder, a polyamic acid segment is introduced on the surface of the conductive carbon black to enhance the conductivity and structural stability of the electrode. The details are as follows: First: This scheme forms a PS bond between red phosphorus and polyacrylonitrile sulfide through ball milling and calcination, which significantly improves the conductivity of red phosphorus and constructs a stable electrode structure, effectively alleviating the volume expansion problem during the charge and discharge process and improving the cycle stability. The calcined sample is further compounded with a few-layer MXene through hydrothermal synthesis to form a PC bond, which enhances the contact characteristics between red phosphorus and MXene, stabilizes the material structure, and achieves highly stable cycle performance. In addition, the large interlayer spacing of MXene provides a fast channel for sodium ion transmission, further improving the kinetic performance of the electrode; Second: By reacting triaminocarboxylic acid triazine with anhydride-terminated polyamic acid, a binder system with a three-dimensional cross-linked structure is formed, which significantly improves its performance. The three-dimensional cross-linked structure gives the binder excellent mechanical strength and flexibility, effectively inhibits the volume expansion of the electrode material during the charge and discharge process, and reduces powdering and shedding. At the same time, the resulting binder system contains more carboxyl groups, which effectively enhances the interfacial bonding force with the electrode material, improves the structural stability of the electrode, and helps maintain the integrity of the electrode during long cycles. In addition, the three-dimensional network structure of the binder provides a continuous channel for ion transport and optimizes the electrode kinetics. Third: The introduction of polyamic acid segments on the surface of conductive carbon black improves the interface bonding between conductive carbon black and the binder, reduces interface defects, and improves the overall structural stability of the electrode. At the same time, the introduction of polyamic acid segments makes the conductive carbon black more evenly dispersed in the electrode material, forming a continuous and efficient conductive network, which improves the conductivity and charge transfer efficiency of the electrode. DETAILED DESCRIPTION

[0016] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative work shall fall within the scope of protection of the present invention.

[0017] It should be noted that the following parts are parts by weight, and the purchase manufacturers of all raw materials involved in the present invention are not subject to any special restrictions and are exemplified as follows: in the following embodiments, diaminodiphenyl ether CAS is 101-80-4; 4,4'-oxydiphthalic anhydride CAS is 1823-59-2; 2,4-diaminobutyric acid CAS is 305-62-4; and cyanuric chloride CAS is 108-77-0.

[0018] Example 1: A method for preparing a negative electrode material for improving the cycle performance of a sodium battery, comprising the following steps: Step 1: Red phosphorus and polyacrylonitrile sulfide are mechanically mixed and ball-milled, and then transferred into a tube furnace, introduced with argon gas, and calcined at 300° C. for 10 h to obtain a red phosphorus-polyacrylonitrile sulfide sample; Step 2: Dissolve the red phosphorus-sulfurized polyacrylonitrile sample in pure water, then add a few-layer MXene, stir evenly, bake at 180°C for 16 hours, and finally filter, wash, and dry to obtain a modified negative electrode material; wherein the mass ratio of red phosphorus to sulfurized polyacrylonitrile is 65:1; the mass ratio of red phosphorus to few-layer MXene is 22:1; A method for preparing a negative electrode sheet, comprising the following steps: mixing the above-mentioned negative electrode material with a binder and modified carbon black, stirring evenly, then coating on a 12 μm aluminum foil, drying and rolling, and drying at 120° C. for 12 hours to obtain a negative electrode sheet; the mass ratio of the negative electrode material, the binder, and the modified carbon black is 8:1:1; Wherein, the preparation process of the adhesive is: S1: under nitrogen, 5 parts of diaminodiphenyl ether were added to 40 parts of N-methylpyrrolidone, stirred several times until all dissolved, and then 7.5 parts of 4,4'-oxydiphthalic anhydride were added in batches, and reacted at 0°C for 4 hours to obtain anhydride-terminated polyamic acid; S2: 35 parts of 2,4-diaminobutyric acid, 40 parts of anhydrous sodium carbonate and 300 parts of deionized water are mixed, mechanically stirred evenly, 18 parts of cyanuric chloride solution are slowly added dropwise at 0-5°C, the addition is completed within 2 hours, stirring is continued for 6 hours, filtering, washing and recrystallizing to obtain triaminocarboxylic acid triazine; S3: 0.5 parts of triaminocarboxylic acid triazine are added to 45 parts of N-methylpyrrolidone, and after being fully dissolved, the mixture is slowly dripped into 30 parts of anhydride-terminated polyamic acid at 0°C, and reacted for 3 hours. After the reaction is completed, 6 parts of N-methylpyrrolidone are continuously added for dilution to obtain an adhesive; The preparation process of modified carbon black is: (1) Disperse 9 parts of conductive carbon black evenly in ethanol, adjust the pH to 6, add 1 part of γ-aminopropyltriethoxysilane dropwise, raise the temperature to 60°C, and react for 3 hours to obtain amino carbon black; (2) Mix 1 part of amino carbon black with 2 parts of anhydride-terminated polyamic acid, react at 0°C for 4 hours to obtain modified carbon black.

[0019] Example 2: It is basically the same as Example 1, except that the mass ratio of red phosphorus material to sulfide polyacrylonitrile is 55:1.

[0020] Example 3: It is basically the same as Example 1, except that the mass ratio of red phosphorus material to sulfide polyacrylonitrile is 60:1.

[0021] Example 4: It is basically the same as Example 1, except that the mass ratio of red phosphorus material to sulfide polyacrylonitrile is 70:1.

[0022] Example 5: is basically the same as Example 1, except that the mass ratio of red phosphorus material to sulfide polyacrylonitrile is 75:1.

[0023] Example 6: Basically the same as Example 1, except that the mass ratio of red phosphorus material to few-layer MXene is 18:1.

[0024] Example 7: Basically the same as Example 1, except that the mass ratio of red phosphorus material to few-layer MXene is 20:1.

[0025] Example 8: Basically the same as Example 1, except that the mass ratio of red phosphorus material to few-layer MXene is 24:1.

[0026] Example 9: Basically the same as Example 1, except that the mass ratio of red phosphorus material to few-layer MXene is 26:1.

[0027] Comparative Example 1: basically the same as Example 1, except that no sulfurized polyacrylonitrile is introduced.

[0028] Comparative Example 2: is basically the same as Example 1, except that: no few-layer MXene material is introduced.

[0029] Comparative Example 3: is basically the same as Example 1, except that: traditional red phosphorus material is used as the positive electrode material.

[0030] Comparative Example 4: It is basically the same as Example 1, except that PVDF is used and the conductive carbon black is not modified accordingly, as follows: Step 1: Red phosphorus and polyacrylonitrile sulfide are mechanically mixed and ball-milled, and then transferred into a tube furnace, introduced with argon gas, and calcined at 300° C. for 10 h to obtain a red phosphorus-polyacrylonitrile sulfide sample; Step 2: Dissolve the red phosphorus-sulfurized polyacrylonitrile sample in pure water, then add a few-layer MXene, stir evenly, bake at 180°C for 16 hours, and finally filter, wash, and dry to obtain a modified negative electrode material; wherein the mass ratio of red phosphorus to sulfurized polyacrylonitrile is 65:1; the mass ratio of red phosphorus to few-layer MXene is 22:1; A method for preparing a negative electrode sheet comprises the following steps: weighing 0.5 parts of white powdered PVDF (the molecular weight of PVDF is 500,000), dissolving it in 15 parts of N-methylpyrrolidone, stirring evenly, adding the above-mentioned negative electrode material and conductive carbon black, stirring evenly, and then coating it on a 12 μm aluminum foil, drying and rolling it, and drying it at 100° C. for 2 hours to obtain a negative electrode sheet; the mass ratio of the negative electrode material, the binder, and the conductive agent is 8:1:1.

[0031] Comparative Example 5: It is basically the same as Example 1, except that the conductive carbon black is not modified, as follows: Step 1: Red phosphorus and polyacrylonitrile sulfide are mechanically mixed and ball-milled, and then transferred into a tube furnace, introduced with argon gas, and calcined at 300° C. for 10 h to obtain a red phosphorus-polyacrylonitrile sulfide sample; Step 2: Dissolve the red phosphorus-sulfurized polyacrylonitrile sample in pure water, then add a few-layer MXene, stir evenly, bake at 180°C for 16 hours, and finally filter, wash, and dry to obtain a modified negative electrode material; wherein the mass ratio of red phosphorus to sulfurized polyacrylonitrile is 65:1; the mass ratio of red phosphorus to few-layer MXene is 22:1; A method for preparing a negative electrode sheet, comprising the following steps: mixing the negative electrode material with a binder and conductive carbon black, stirring evenly, coating the mixture on a 12 μm aluminum foil, drying the mixture, and rolling the mixture at 120° C. for 12 hours to obtain a negative electrode sheet; the mass ratio of the negative electrode material, the binder, and the conductive carbon black is 8:1:1; Wherein, the preparation process of the adhesive is: S1: under nitrogen, 5 parts of diaminodiphenyl ether were added to 40 parts of N-methylpyrrolidone, stirred several times until all dissolved, and then 7.5 parts of 4,4'-oxydiphthalic anhydride were added in batches, and reacted at 0°C for 4 hours to obtain anhydride-terminated polyamic acid; S2: 35 parts of 2,4-diaminobutyric acid, 40 parts of anhydrous sodium carbonate and 300 parts of deionized water are mixed, mechanically stirred evenly, 18 parts of cyanuric chloride solution are slowly added dropwise at 0-5°C, the addition is completed within 2 hours, stirring is continued for 6 hours, filtering, washing and recrystallizing to obtain triaminocarboxylic acid triazine; S3: Add 0.5 parts of triaminocarboxylic acid triazine to 45 parts of N-methylpyrrolidone. After fully dissolved, slowly drip it into 30 parts of anhydride-terminated polyamic acid at 0°C and react for 3 hours. After the reaction is completed, continue to add 6 parts of N-methylpyrrolidone for dilution to obtain an adhesive.

[0032] Comparative Example 6: It is basically the same as Example 1, except that triaminocarboxylic acid triazine is not introduced, and the rest is the same, as follows: Step 1: Red phosphorus and polyacrylonitrile sulfide are mechanically mixed and ball-milled, and then transferred into a tube furnace, introduced with argon gas, and calcined at 300° C. for 10 h to obtain a red phosphorus-polyacrylonitrile sulfide sample; Step 2: Dissolve the red phosphorus-sulfurized polyacrylonitrile sample in pure water, then add a few-layer MXene, stir evenly, bake at 180°C for 16 hours, and finally filter, wash, and dry to obtain a modified negative electrode material; wherein the mass ratio of red phosphorus to sulfurized polyacrylonitrile is 65:1; the mass ratio of red phosphorus to few-layer MXene is 22:1; A method for preparing a negative electrode sheet, comprising the following steps: mixing the above-mentioned negative electrode material with a binder and modified conductive carbon black, stirring evenly, coating on a 12 μm aluminum foil, drying and rolling, and drying at 120° C. for 12 hours to obtain a negative electrode sheet; the mass ratio of the negative electrode material, the binder, and the modified carbon black is 8:1:1; Wherein, the preparation process of the adhesive is: S1: under nitrogen, 5 parts of diaminodiphenyl ether were added to 40 parts of N-methylpyrrolidone, stirred several times until all dissolved, and then 7.5 parts of 4,4'-oxydiphthalic anhydride were added in batches, and reacted at 0°C for 4 hours to obtain anhydride-terminated polyamic acid, which was used as a binder; The preparation process of modified carbon black is: (1) Disperse 9 parts of conductive carbon black evenly in ethanol, adjust the pH to 6, add 1 part of γ-aminopropyltriethoxysilane dropwise, raise the temperature to 60°C, and react for 3 hours to obtain amino carbon black; (2) Mix 1 part of amino carbon black with 2 parts of anhydride-terminated polyamic acid, react at 0°C for 4 hours to obtain modified carbon black.

[0033] Performance Test: Preparation of positive electrode sheets: NaFePO4 material is used as the positive electrode active material, PVDF (Solvay 5130) is used as the binder, and SuperP (Swiss Termeco) is used as the conductive agent; the active material: binder: conductive agent = 8:1:1 ratio is stirred and mixed, and after mixing evenly, it is coated on 12um aluminum foil, dried and rolled, and then dried in a vacuum drying oven at 120°C for 12h.

[0034] Assembly of soft pack batteries: The negative electrode sheets obtained in the embodiment and the comparative example and the positive electrode sheets obtained above are subjected to the steps of rolling-die-cutting-lamination-shelling-packaging-formation-capacity separation and sorting to obtain a 3.1Ah soft-pack battery.

[0035] Test experiment 1: Use a soft-pack battery charge and discharge tester (Xinwei) to perform 100, 300, and 500 cycles of 0.5C charge and discharge tests on the soft-pack battery. The voltage range is 1.8-4.0V. The results are shown in the following table: Table 1

[0036] Test experiment 2: The negative electrode materials obtained in Example 1 and Comparative Examples 4-6 were cut into 50×20 mm rectangular strips, and the strips were adhered to the aluminum plate using 3M tape. The 3M tape was then adhered to the surface of the negative electrode sheet using a universal testing machine at a speed of 10 mm×min. -1 Pull the tape down at a speed of 100° and record the peeling data. The obtained data are shown in the following table: Table 2

[0037] Conclusion: The present invention significantly improves the mechanical properties and electrochemical stability of the battery by preparing a negative electrode material for a sodium battery, a binder with a three-dimensional cross-linked structure, and introducing polyamic acid segments on the surface of the conductive carbon black, which is suitable for practical applications. Among them, Example 1 is the best example with the highest cycle performance and bonding strength; In Comparative Example 1, the lack of sulfide polyacrylonitrile results in poor conductivity of red phosphorus, insufficient stability of the electrode structure, and significantly reduced cycle performance; in Comparative Example 2, the lack of a few-layer MXene results in poor structural stability of the composite material, reduced ion transfer efficiency, and reduced cycle performance; in Comparative Example 3, the traditional red phosphorus material has the worst cycle performance due to poor conductivity and volume expansion problems; in Comparative Example 4, the mechanical properties and electrochemical stability of the PVDF binder are poor, and the volume expansion of the electrode material cannot be effectively suppressed, resulting in gradual destruction of the electrode structure and accelerated capacity decay; in Comparative Example 5, the conductive carbon black is not modified, resulting in poor compatibility with the binder, and the conductivity and structural stability of the electrode are reduced; in Comparative Example 6, triaminocarboxylic acid triazine is not introduced, resulting in the lack of a three-dimensional cross-linked structure of the binder, insufficient mechanical strength and flexibility of the binder, and the volume expansion of the electrode material cannot be effectively suppressed, the electrode structure stability is reduced, and the cycle performance is significantly reduced.

[0038] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a negative electrode material for improving the cycle performance of a sodium battery, characterized in that: The following steps are involved: Step 1: mechanically mix red phosphorus and sulfide polyacrylonitrile and perform ball milling, then transfer to a tube furnace, introduce argon gas, and calcine at 300-350° C. for 10-12 h to obtain a red phosphorus-sulfide polyacrylonitrile sample; Step 2: Dissolve the red phosphorus-sulfurized polyacrylonitrile sample in pure water, then add a few layers of MXene, stir evenly, bake at 180-200°C for 16-18h, and finally obtain the negative electrode material after filtering, washing and drying.

2. The method for preparing a negative electrode material for improving the cycle performance of a sodium battery according to claim 1, characterized in that: The mass ratio of the red phosphorus to the sulfide polyacrylonitrile is (60-65):1; the mass ratio of the red phosphorus to the few-layer MXene is (20-22):

1.

3. The method for preparing a negative electrode material for improving the cycle performance of a sodium battery according to claim 1, characterized in that: During the baking process, the heating rate is 40-45°C / min, and the annealing rate is 10-15°C / min.

4. A negative electrode material, characterized in that: The negative electrode material is obtained by the preparation method according to claim 1.

5. A method for preparing a negative electrode sheet, characterized in that: The method comprises the following steps: mixing the negative electrode material according to claim 4 with a binder and modified carbon black, stirring evenly, coating the mixture on a 12-15 μm aluminum foil, drying the mixture and rolling the mixture, drying the mixture at 120-150° C. for 12-15 hours, and obtaining a negative electrode sheet.

6. The method for preparing a negative electrode sheet according to claim 5, characterized in that: The mass ratio of the negative electrode material, the binder and the modified carbon black is (8-9):1:

1.

7. The method for preparing a negative electrode sheet according to claim 5, characterized in that: The preparation process of the adhesive is: S1: under a protective atmosphere, diaminodiphenyl ether is added to N-methylpyrrolidone, stirred for several times until all dissolved, and then 4,4'-oxydiphthalic anhydride is added in batches, and reacted at 0-5°C for 4-6h to obtain anhydride-terminated polyamic acid; S2: 2,4-diaminobutyric acid, anhydrous sodium carbonate and deionized water are mixed, mechanically stirred to be uniform, and cyanuric chloride solution is slowly added dropwise at 0-5°C, and the addition is completed within 2-3 hours, and stirring is continued for 6-8 hours, and then filtered, washed and recrystallized to obtain triaminocarboxylic acid triazine; S3: Add triaminocarboxylic acid triazine to N-methylpyrrolidone, and after fully dissolving, slowly drip it into anhydride-terminated polyamic acid at 0-5°C, and react for 3-4 hours. After the reaction is completed, continue to add N-methylpyrrolidone for dilution to obtain an adhesive.

8. The method for preparing a negative electrode sheet according to claim 7, characterized in that: The anhydride-terminated polyamic acid comprises the following substances: by weight, 5-8 parts of diaminodiphenyl ether, 40-50 parts of N-methylpyrrolidone, and 7.5-12 parts of 4,4'-oxydiphthalic anhydride; The triaminocarboxylic acid triazine comprises the following substances: by weight, 35-40 parts of 2,4-diaminobutyric acid, 40-42 parts of anhydrous sodium carbonate, 300-320 parts of deionized water, and 18-20 parts of cyanuric chloride solution; wherein the mass fraction of the cyanuric chloride solution is 8-10wt%, and the solvent is dioxane; The adhesive raw material comprises the following substances: by weight, 0.5-0.8 parts of triaminocarboxylic acid triazine, 50-55 parts of N-methylpyrrolidone, and 30-35 parts of anhydride-terminated polyamic acid; wherein the solid content of the adhesive is 6-8wt%.

9. The method for preparing a negative electrode sheet according to claim 5, characterized in that: The preparation process of the modified carbon black is as follows: (1) uniformly dispersing conductive carbon black in ethanol, adjusting the pH to 6-6.5, dropping γ-aminopropyltriethoxysilane, heating to 60-70° C., reacting for 3-4 hours, and obtaining amino carbon black; (2) mixing the amino carbon black with anhydride-terminated polyamic acid, reacting at 0-5° C. for 4-5 hours, and obtaining modified carbon black.

10. The method for preparing a negative electrode sheet according to claim 9, characterized in that: The mass ratio of the conductive carbon black to γ-aminopropyltriethoxysilane is (9-10):1; the mass ratio of the amination carbon black to the anhydride-terminated polyamic acid is 1:(2-3).

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