Preparation method of current collector, current collector, pole piece, secondary battery and electrical equipment

Abstract

The present disclosure provides a method for preparing a current collector, a current collector, an electrode, a secondary battery, and an electrical device. The preparation method comprises the following steps: dissolving polyacrylonitrile in a solvent and mixing carbon nanotubes with the resulting polyacrylonitrile solution to form a mixed slurry; removing the solvent from the mixed slurry to form a polyacrylonitrile-coated carbon nanotube material; and carbonizing the polyacrylonitrile-coated carbon nanotube material at a temperature above 800°C. The current collector prepared by this preparation method can provide abundant attachment sites for active materials, inhibiting the detachment of active material particles from the current collector, thereby improving the reversible cycle capacity of the battery and enhancing the stability of the electrode structure.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a method for preparing a current collector, a current collector, a pole piece, a secondary battery and an electrical device. Background Art

[0002] Lithium-ion batteries are currently the most widely used secondary batteries in commercial applications. Lithium-ion batteries typically require lithium salts and organic electrolytes. The high material cost of lithium salts contributes to the high production costs of lithium-ion batteries, while organic electrolytes easily decompose in air, posing a significant safety risk. Compared to lithium-ion batteries, rechargeable zinc-manganese secondary batteries have lower material costs and can use aqueous electrolytes to conduct ions, resulting in greater safety and higher ionic conductivity.

[0003] Secondary zinc-manganese batteries typically use materials such as manganate and manganese oxide as the positive electrode active material. In secondary zinc-manganese batteries using aqueous electrolytes, the positive electrode active material gradually detaches from the current collector and dissolves into the electrolyte during charge and discharge, significantly reducing the battery's reversible cycle capacity and affecting battery stability. Summary of the Invention

[0004] Based on this, it is necessary to provide a method for preparing a current collector to address the problems in the above background technology, and the current collector prepared by the method can effectively improve the reversible cycle capacity of the positive electrode active material.

[0005] In a first aspect, according to some embodiments of the present disclosure, a method for preparing a current collector is provided, comprising the following steps:

[0006] dissolving polyacrylonitrile in a solvent, and mixing carbon nanotubes with the formed polyacrylonitrile solution to form a mixed slurry;

[0007] removing the solvent from the mixed slurry to form a polyacrylonitrile-coated carbon nanotube material; and

[0008] The polyacrylonitrile-coated carbon nanotube material is carbonized at a temperature above 800°C.

[0009] In some embodiments of the present disclosure, after the polyacrylonitrile-coated carbon nanotube material is carbonized, the specific surface area of ​​the formed carbonized material is ≥50m 2 / g; and / or, the pore volume of the formed carbonized material is ≥0.2cm 3 / g; and / or, the average pore size of the formed carbonized material is ≥5nm.

[0010] In some embodiments of the present disclosure, in the mixed slurry, the mass ratio of the polyacrylonitrile to the carbon nanotubes is 1:(4~29).

[0011] In some embodiments of the present disclosure, in the polyacrylonitrile-coated carbon nanotube material, the mass proportion of the carbon nanotubes is 80% to 96.7%, and the mass proportion of the polyacrylonitrile is 3.3% to 20%.

[0012] In some embodiments of the present disclosure, before the polyacrylonitrile-coated carbon nanotube material is carbonized, the following steps are also included: placing the polyacrylonitrile-coated carbon nanotube material in a gas environment containing oxygen for annealing treatment; during the annealing treatment, heating the polyacrylonitrile-coated carbon nanotube material to 150°C~250°C, keeping it warm for 1h~2h, and then cooling it naturally.

[0013] In some embodiments of the present disclosure, the carbonization treatment of the polyacrylonitrile-coated carbon nanotube material is carried out in a protective gas, and the carbonization treatment time is 1 hour to 4 hours.

[0014] In some embodiments of the present disclosure, before the polyacrylonitrile-coated carbon nanotube material is carbonized, the following step is further included: placing the polyacrylonitrile-coated carbon nanotube material in an oxidant containing nitric acid to pre-oxidize the polyacrylonitrile-coated carbon nanotube material.

[0015] In some embodiments of the present disclosure, before removing the solvent from the mixed slurry, the step of coating the mixed slurry on a surface of a conductive substrate to form a coating layer is further included.

[0016] In a second aspect, the present disclosure further provides a current collector, which is prepared by the method for preparing the current collector according to the above embodiment.

[0017] In a third aspect, the present disclosure further provides a pole piece, which includes an active material layer and a current collector according to the above embodiment, wherein the active material layer is disposed on the current collector.

[0018] In some embodiments of the present disclosure, the active material layer includes a manganese-based material.

[0019] In a fourth aspect, the present disclosure further provides a secondary battery, comprising a positive electrode and a negative electrode arranged opposite to each other, wherein the positive electrode and / or the negative electrode comprises a pole piece as described in any of the above embodiments.

[0020] In a fifth aspect, the present disclosure further provides an electrical device, which includes a functional body and a secondary battery as described in any of the above embodiments, wherein the secondary battery is used to supply power to the functional body.

[0021] In the preparation method of the current collector disclosed in the present invention, polyacrylonitrile is first dissolved in a solvent and carbon nanotubes are added. A plurality of carbon nanotubes are staggered to form a conductive skeleton, and there are abundant gaps between the staggered carbon nanotubes. After removing the solvent, polyacrylonitrile can be coated on the surface of the carbon nanotube skeleton. The polyacrylonitrile coating layer undergoes pyrolysis and carbonization during the carbonization treatment at a temperature above 800°C, and a carbon coating layer with a large number of pores with moderate pore diameters is formed on the basis of the gaps in the carbon nanotube skeleton. The current collector prepared by this preparation method can provide abundant attachment sites for the active material, inhibit the particles of the active material from falling off from the current collector, thereby improving the reversible cycle capacity of the battery and improving the stability of the electrode structure.

[0022] This current collector is particularly suitable for the positive electrode of aqueous zinc-manganese batteries. Specifically, the rich and complex mesopore and macropore structure formed on the carbonized surface can accommodate particles of manganese-based active materials and inhibit their shedding. Furthermore, the carbon coating acts as a conductive attachment site, and the carbon nanotubes serve as a conductive backbone within the current collector, effectively promoting electron transfer from the active material to the current collector, thereby improving the active material's poor conductivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the steps of a method for preparing a current collector according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0024] To facilitate understanding of this document, a more comprehensive description of this document is provided below. Preferred embodiments of this document are provided herein. However, this document can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the present document.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this document pertains. The terms used herein in the specification are for the purpose of describing specific embodiments only and are not intended to limit this document.

[0026] The purpose of the terms used herein is only to describe specific embodiments and is not intended to limit the present disclosure. When used herein, the singular forms "a," "an," and "the" are intended to include the plural forms, unless the context clearly indicates otherwise. It should also be understood that the terms "comprising" and / or "including," when used in this specification, identify the presence of features, integers, steps, operations, elements, and / or parts, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, parts, and / or groups. When used herein, the term "and / or" includes any and all combinations of the relevant listed items.

[0027] The present disclosure provides a method for preparing a current collector, which includes the following steps: dissolving polyacrylonitrile in a solvent and adding carbon nanotubes to the solvent to form a mixed slurry; coating the mixed slurry on a conductive substrate, and removing the solvent in the mixed slurry to form a coating layer on the conductive substrate; and carbonizing the polyacrylonitrile in the coating layer, wherein the temperature of the carbonization treatment is above 800°C.

[0028] In the preparation method of the current collector disclosed in the present invention, polyacrylonitrile is first dissolved in a solvent and carbon nanotubes are added. A plurality of carbon nanotubes are staggered to form a conductive skeleton, and there are abundant gaps between the staggered carbon nanotubes. After removing the solvent, polyacrylonitrile can be coated on the surface of the carbon nanotube skeleton. The polyacrylonitrile coating undergoes pyrolysis and carbonization during the carbonization process, and a carbon coating layer with a large number of pores with moderate pore diameters is formed on the basis of the gaps in the carbon nanotube skeleton. The current collector prepared by this preparation method can provide abundant attachment sites for the active material, inhibit the particles of the active material from falling off from the current collector, thereby improving the reversible cycle capacity of the battery and improving the stability of the electrode structure.

[0029] This current collector is particularly suitable for the positive electrode of aqueous zinc-manganese batteries. Specifically, the rich and complex pore structure formed on the carbonized surface can accommodate particles of manganese-based active materials and inhibit their shedding. Furthermore, the carbon coating acts as a conductive attachment site, and the carbon nanotubes serve as a conductive backbone within the current collector, effectively facilitating electron transfer from the active material to the current collector, thereby improving the active material's poor conductivity.

[0030] Figure 1 Schematic diagram of the steps of a method for preparing a current collector disclosed in the present invention. Figure 1 As shown, the preparation method of the current collector includes steps S1 to S3, which are specifically as follows.

[0031] In step S1 , polyacrylonitrile is dissolved in a solvent, and carbon nanotubes are mixed with the polyacrylonitrile solution to form a mixed slurry.

[0032] As an example of this embodiment, the molecular weight of polyacrylonitrile is 50,000-300,000, which is conducive to forming a dense and uniform coating layer.

[0033] It is understood that the solvent should be selected from a solvent capable of dissolving polyacrylonitrile. As an example of this embodiment, the solvent may include an organic solvent selected from dimethyl sulfoxide. Further, the solvent may also include water, that is, the solvent may be a mixture of an organic solvent and water.

[0034] As an example of this embodiment, the step of dissolving polyacrylonitrile in a solvent includes: adding polyacrylonitrile to the solvent, heating the solvent, and stirring the solvent.

[0035] In some examples, when heating the solvent, the temperature of the solvent is controlled to be 80° C. to 120° C.

[0036] As an example of this embodiment, after polyacrylonitrile is dissolved in a solvent, the mass concentration of polyacrylonitrile can be 0.005 g / mL to 0.05 g / mL. This mass concentration of polyacrylonitrile is conducive to forming a relatively uniform coating layer on the surface of the carbon nanotubes.

[0037] As an example of this embodiment, in the step of mixing the carbon nanotubes with the formed polyacrylonitrile solution, a dispersion containing the carbon nanotubes may be mixed with the formed polyacrylonitrile solution to promote sufficient dispersion of the carbon nanotubes in the polyacrylonitrile solution.

[0038] In some examples, a method for preparing a dispersion containing carbon nanotubes includes: mixing an aqueous carbon nanotube dispersion with an organic solvent and then performing a heating treatment.

[0039] In some examples, the organic solvent used in mixing the aqueous carbon nanotube dispersion with the organic solvent is the same as the organic solvent in the polyacrylonitrile solution.

[0040] In some examples, the solid content of the carbon nanotubes in the aqueous carbon nanotube dispersion may be 2% to 8%.

[0041] In some examples, in the step of mixing the aqueous carbon nanotube dispersion with the organic solvent, the mass ratio of the aqueous carbon nanotube dispersion to the organic solvent is (1-8):1.

[0042] In some examples, during the heating process after mixing the aqueous carbon nanotube dispersion with the organic solvent, the heating temperature can be controlled to be 100° C. to 140° C., and the heating time can be controlled to be 1 hour to 4 hours to promote sufficient mixing of the aqueous carbon nanotube dispersion and the organic solvent.

[0043] As an example of this embodiment, the mass ratio of polyacrylonitrile to carbon nanotubes in the mixed slurry is 1:(4-29). The mass of the carbon nanotubes is significantly greater than that of the polyacrylonitrile, primarily because the carbon nanotubes serve as the primary matrix structure, while the polyacrylonitrile forms a thinner coating, thereby enabling the formation of abundant mesopores and macropores during the carbonization process. Using this mass ratio of polyacrylonitrile to carbon nanotubes as raw materials facilitates obtaining a carbonized material with a large pore volume and average pore diameter.

[0044] In some examples, the mass ratio of polyacrylonitrile to carbon nanotubes can be 1:4, 1:6, 1:8, 1:10, 1:12, 1:15, 1:20, 1:25, or 1:29, or the mass ratio of polyacrylonitrile to carbon nanotubes can be between any two of the above mass ratios.

[0045] As an example of this embodiment, the step of mixing the carbon nanotubes with the formed polyacrylonitrile solution includes: mixing the dispersion containing the carbon nanotubes with the polyacrylonitrile solution, and then heating and stirring the mixture.

[0046] In the step of heating and stirring, the heating temperature may be 30° C. to 50° C., and stirring may be continued for 1 hour to 2 hours during the heating process.

[0047] After the above step S1 , a mixed slurry in which carbon nanotubes and polyacrylonitrile are uniformly dispersed can be formed.

[0048] Step S2: removing the solvent from the mixed slurry to form a polyacrylonitrile-coated carbon nanotube material.

[0049] As an example of this embodiment, the method of removing the solvent from the mixed slurry may be drying, such as freeze drying or oven drying.

[0050] It is understood that in this embodiment, the mixed slurry can be first applied to the support material to form a coating layer on the surface of the support material. Further, as an example of this embodiment, before removing the solvent from the mixed slurry, the mixed slurry can also be applied to the surface of the conductive substrate to form a coating layer.

[0051] As a further example of this embodiment, after forming the coating layer, the conductive substrate with the coating layer can be placed in a forced air oven to evaporate the solvent in the coating layer, so that the coating layer forms a polyacrylonitrile-coated carbon nanotube material.

[0052] The temperature of the blast oven can be set to 60°C~100°C.

[0053] As a further example of this embodiment, after removing the solvent from the mixed slurry, the polyacrylonitrile-coated carbon nanotube material can be washed in ethanol and deionized water in sequence to remove impurities therein, and then dried in a forced air oven.

[0054] As an example of this embodiment, the polyacrylonitrile-coated carbon nanotube material contains only carbon nanotubes and polyacrylonitrile except for impurities.

[0055] As a further example of this embodiment, in the polyacrylonitrile-coated carbon nanotube material, the mass proportion of the carbon nanotubes is 80% to 96.7%. For example, the mass proportion of the carbon nanotubes can be 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, or 96.7%, or the mass proportion of the carbon nanotubes can be between any two of the above mass proportions.

[0056] As a further example of this embodiment, in the polyacrylonitrile-coated carbon nanotube material, the mass proportion of polyacrylonitrile is 3.3% to 20%. For example, the mass proportion of polyacrylonitrile can be 3.3%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, or 20%. Alternatively, the mass proportion of polyacrylonitrile can be between any two of the above mass proportions.

[0057] As a further example of this embodiment, the conductive substrate is selected from carbon cloth, carbon paper, stainless steel mesh, stainless steel foil, titanium mesh, titanium foil or nickel foam. It is understood that the conductive substrate and the carbonized polyacrylonitrile-coated carbon nanotube material can serve as a current collector.

[0058] Step S3: performing carbonization treatment on the polyacrylonitrile-coated carbon nanotube material.

[0059] As an example of this embodiment, before the polyacrylonitrile-coated carbon nanotube material is carbonized, the following step is further included: placing the polyacrylonitrile-coated carbon nanotube material in an oxidant containing nitric acid to perform a pre-oxidation treatment on the coating layer.

[0060] The pre-oxidation treatment removes certain residual reducing impurities in the material. More importantly, it also oxidizes the surfaces of the polyacrylonitrile and carbon nanotubes, creating surface defects in the polyacrylonitrile coating, which helps increase the number of mesopores and mesopores produced during the subsequent calcination process.

[0061] As a further example of this embodiment, the nitric acid may be concentrated nitric acid, in which the mass concentration of nitric acid is greater than 50%.

[0062] As a further example of this embodiment, the polyacrylonitrile-coated carbon nanotube material is immersed in the oxidant for a period of 20 minutes to 60 minutes.

[0063] As an example of this embodiment, before the carbonization treatment is performed on the polyacrylonitrile-coated carbon nanotube material, the following step is further included: placing the polyacrylonitrile-coated carbon nanotube material in a gas environment containing oxygen for annealing treatment.

[0064] As a further example of this embodiment, annealing can be performed after pre-oxidation. Pre-oxidation can produce certain defects on the surface of polyacrylonitrile, and the subsequent annealing can further decompose the polyacrylonitrile, thereby forming a certain microporous structure on the surface of the polyacrylonitrile before carbonization. This microporous structure will expand during the subsequent calcination process to form abundant mesopores and mesopores. In addition, the annealing process can also make the structure of the polyacrylonitrile-coated carbon nanotubes more stable, which is conducive to ensuring a stable bond between the formed carbon coating and the carbon nanotubes during the subsequent carbonization process.

[0065] As a further example of this embodiment, during the annealing process, the polyacrylonitrile-coated carbon nanotube material is heated to 150° C. to 250° C., kept at this temperature for 1 h to 2 h, and then cooled naturally.

[0066] The carbonization step can be performed after the annealing step. As an example of this embodiment, the carbonization process of the polyacrylonitrile-coated carbon nanotube material is performed in a protective gas. The protective gas can be selected from at least one of argon and nitrogen.

[0067] In this embodiment, the temperature of the carbonization treatment is above 800° C. As an example of this embodiment, during the carbonization treatment, the temperature of the carbonization treatment is 800° C. to 1300° C.

[0068] The carbonization process creates a large number of nanopores on the surface of polyacrylonitrile. The number of these pores is correlated with the carbonization temperature. Lower temperatures result in a slower carbonization rate and lower carbonization degree, resulting in a significantly lower number of micropores. Overall, a carbonization temperature between 800°C and 1300°C is beneficial for obtaining a carbon coating with a higher number of micropores.

[0069] As an example of this embodiment, during the carbonization process, the carbonization time is 1 hour to 4 hours.

[0070] As an example of this embodiment, after the polyacrylonitrile-coated carbon nanotube material is carbonized, the specific surface area of ​​the formed carbonized material is ≥50m 2 / g.

[0071] As a further example of this embodiment, after the polyacrylonitrile-coated carbon nanotube material is carbonized, the specific surface area of ​​the formed carbonized material is 50 m 2 / g~500m 2 / g.

[0072] As an example of this embodiment, the pore volume of the carbonized material formed is ≥ 0.2 cm 3 / g.

[0073] As a further example of this embodiment, after the polyacrylonitrile-coated carbon nanotube material is carbonized, the pore volume of the formed carbonized material is 0.2 cm 3 / g~1cm 3 / g.

[0074] As an example of this embodiment, the carbonized material is formed to have an average pore size of ≥5 nm.

[0075] As a further example of this embodiment, after the polyacrylonitrile-coated carbon nanotube material is carbonized, the average pore diameter of the formed carbonized material is 5 nm to 20 nm.

[0076] After steps S1 to S3, the method for preparing the current collector disclosed herein can be completed.

[0077] In a second aspect, the present disclosure further provides a current collector prepared by the above-described current collector preparation method. This current collector is particularly suitable for use in aqueous zinc-manganese batteries. As a positive electrode current collector in aqueous zinc-manganese batteries, it can effectively address the problems of positive electrode material pulverization and poor conductivity.

[0078] In a third aspect, the present disclosure further provides a pole piece, which includes an active material layer and a current collector as described in the above embodiment. The active material layer is disposed on the current collector.

[0079] As an example of this embodiment, the active material layer includes a positive electrode active material, and the positive electrode active material includes a manganese-based compound.

[0080] As a further example of this embodiment, the manganese-based compound includes one or more of manganate and manganese oxide, wherein the manganate may include but is not limited to one or more of lithium manganate and nickel manganate, and the manganese oxide may include but is not limited to manganese dioxide.

[0081] As an example of this embodiment, the positive electrode active material may be formed into a positive electrode active layer by electrodeposition or coating.

[0082] In a fourth aspect, the present disclosure further provides a secondary battery, which includes a positive electrode and a negative electrode arranged opposite to each other, and the positive electrode and / or the negative electrode includes a pole piece as in the above embodiment.

[0083] As an example of this embodiment, the secondary battery may be a zinc-manganese battery. In other examples, the secondary battery may also be, but is not limited to, one of a lithium-ion battery, a lithium metal battery, a lithium-air battery, and a zinc-air battery.

[0084] As an example of this embodiment, the secondary battery is a zinc-manganese battery, and the electrolyte in the zinc-manganese battery is an aqueous electrolyte. It can be understood that the solvent in the aqueous electrolyte includes water, and the solute in the aqueous electrolyte includes an electrolyte salt.

[0085] As a further example of this embodiment, the electrolyte in the aqueous electrolyte may include one or more of zinc sulfate and manganese sulfate.

[0086] As a further example of this embodiment, in the secondary battery, the negative electrode may include one or more of metallic zinc and a zinc alloy.

[0087] In a fifth aspect, the present disclosure further provides an electric device, which includes a functional body and a secondary battery as described in the above embodiment, wherein the secondary battery is used to supply power to the functional body.

[0088] As some examples of this embodiment, the power-consuming device may be a mobile phone, a laptop computer, a smartwatch, an electric car, a medical device, a portable charging station, a spacecraft, a smart home, or an energy storage power station. The energy storage power station may be a photovoltaic energy storage station, a wind power energy storage station, a hydropower energy storage station, a thermal power energy storage station, or the like.

[0089] The present disclosure also provides the following more specific examples and comparative examples.

[0090] Example 1

[0091] Prepare a mixed slurry: Add 0.8g of polyacrylonitrile to 8mL of dimethyl sulfoxide (DMSO), then add 2mL of deionized water. Stir magnetically and heat to 120°C until completely dissolved to form a polyacrylonitrile solution. Add an aqueous carbon nanotube dispersion (containing 5% solids of carbon nanotubes) to the DMSO. Mix the aqueous carbon nanotube dispersion and DMSO in a mass ratio of 1:5. Heat to 120°C and hold for 2 hours to form a carbon nanotube dispersion. Mix the prepared polyacrylonitrile solution and carbon nanotube dispersion, heat to 40°C, and stir for 2 hours to form a mixed slurry. The mass ratio of polyacrylonitrile to carbon nanotubes is 1:15.

[0092] Preparation of polyacrylonitrile-coated carbon nanotubes: The mixed slurry was applied to the surface of carbon cloth to form a coating layer, which was then dried in an 80°C forced air oven to form the polyacrylonitrile-coated carbon nanotube material. The material was then soaked in ethanol for 10 minutes, rinsed with deionized water, and dried in an 80°C forced air oven until ready for use.

[0093] Preparation of carbon-coated carbon nanotube material: The carbon arrangement formed with the polyacrylonitrile-coated carbon nanotube material is soaked in concentrated nitric acid for 30 minutes for pre-oxidation, then rinsed with deionized water and dried in a forced air oven at 80°C. The pre-oxidized polyacrylonitrile-coated carbon nanotube material is transferred to a tube furnace, heated to 200°C in air, held at this temperature for 2 hours, and then naturally cooled for annealing. After annealing, argon gas is introduced into the tube furnace, and the temperature is raised to 900°C and held at this temperature for 3 hours, followed by natural cooling to complete the carbonization process and form the carbon-coated carbon nanotube material.

[0094] Example 2

[0095] Example 2 is substantially the same as Example 1, with the only difference being that in the mixed slurry, the mass ratio of polyacrylonitrile to carbon nanotubes is 1:4.

[0096] Example 3

[0097] Example 3 is basically the same as Example 1, with the only difference being that in the mixed slurry, the mass ratio of polyacrylonitrile to carbon nanotubes is 1:2.

[0098] Example 4

[0099] Example 4 is basically the same as Example 1, with the only difference being that in the mixed slurry, the mass ratio of polyacrylonitrile to carbon nanotubes is 1:29.

[0100] Example 5

[0101] Example 5 is basically the same as Example 1, with the only difference being that in the mixed slurry, the mass ratio of polyacrylonitrile to carbon nanotubes is 1:39.

[0102] Example 6

[0103] Example 6 is basically the same as Example 1, with the only difference being that after the annealing treatment, argon gas is introduced into the tube furnace, the temperature is raised to 800° C. and kept at that temperature for 3 hours, and then naturally cooled to complete the carbonization treatment to form a carbon-coated carbon nanotube material.

[0104] Example 7

[0105] Example 7 is basically the same as Example 1, with the only difference being that after the annealing treatment, argon gas is introduced into the tube furnace, the temperature is raised to 1100° C. and kept at this temperature for 3 hours, and then naturally cooled to complete the carbonization treatment to form a carbon-coated carbon nanotube material.

[0106] Example 8

[0107] Example 8 is basically the same as Example 1, with the only difference being that during the process of preparing the carbon-coated carbon nanotube material, neither pre-oxidation treatment nor annealing treatment is performed, and carbonization treatment is performed directly.

[0108] Example 9

[0109] Example 9 is basically the same as Example 1, with the only difference being that, in the process of preparing the carbon-coated carbon nanotube material, the carbonization treatment is performed directly after the pre-oxidation treatment without the annealing treatment.

[0110] Example 10

[0111] Example 10 is substantially the same as Example 1, with the only difference being that, during the process of preparing the carbon-coated carbon nanotube material, no pre-oxidation treatment is performed, and the carbonization treatment is performed directly after the annealing treatment.

[0112] Comparative Example 1

[0113] Comparative Example 1 is substantially the same as Example 1, except that no carbon nanotube slurry is added, and the carbon material is directly prepared using polyacrylonitrile solution.

[0114] Comparative Example 2

[0115] Comparative Example 2 is substantially the same as Example 1, except that the temperature of the carbonization treatment is 600°C.

[0116] Comparative Example 3

[0117] Carbon nanotubes, conductive carbon black and polyvinylidene fluoride are mixed in a mass ratio of 8:1:1 to form a slurry, which is then coated on the surface of the carbon cloth and dried in a forced air oven at 80°C to serve as a current collector.

[0118] Experiment 1: The specific surface area (S) of the carbon materials prepared in each embodiment and comparative example was measured using the BET method. BET ), total pore volume (V), and average pore diameter (D). The total pore volume includes the volume of micropores with a pore diameter less than 2 nm and the volume of mesopores with a pore diameter greater than 2 nm. The test results are shown in Table 1.

[0119] Experiment 2: The sheet resistance of the carbon material layer on the surface of the current collector prepared in each embodiment and comparative example was tested using a four-probe method. The test results are shown in Table 1.

[0120] Test 3: Manganese dioxide powder was applied to the surface of the current collector of each Example and Comparative Example by coating to serve as the positive electrode. Zinc foil was used as the negative electrode. A glass fiber membrane was used as the separator. An aqueous solution containing zinc sulfate (ZnSO4) and manganese sulfate (MnSO4) was used as the electrolyte, wherein the molar concentration of zinc sulfate was 2 mol / L and the molar concentration of manganese sulfate was 0.1 mol / L. An aqueous zinc-manganese battery was assembled using the above-described positive electrode, negative electrode, separator, and electrolyte. Using a Xinwei battery testing system, 100 charge and discharge cycles were performed at a constant current of 0.1 A / g. The first-cycle discharge specific capacity and the discharge specific capacity after 100 cycles were recorded for each Example and Comparative Example, and the corresponding capacity retention was calculated. The results are shown in Table 2.

[0121] Table 1

[0122]

[0123] As shown in Table 1, the carbon materials prepared in Examples 1 to 10 all have large specific surface areas and large pore volumes. Among them, the specific surface area of ​​the carbon material prepared in Example 1 can reach 150.4 m 2 / g, which is conducive to achieving more complete contact with the active material. In addition, the carbon material has a low square resistance, which is also conducive to sufficient electron conduction. More importantly, the carbon material prepared in Example 1 has a pore volume of 0.515cm 3 / g while still maintaining a pore diameter of 13.09nm, indicating that it contains a large number of larger mesopores and mesopores. This is beneficial for the carbon material to accommodate and fix the particles of the active material and prevent them from falling off. Compared with Examples 1 to 10, Comparative Example 1 did not use carbon nanotubes, but only used polyacrylonitrile solution as the raw material. The specific surface area, pore volume and pore diameter of Comparative Example 1 were significantly lower than those of Examples 1 to 10. Its pore volume was extremely small and all were micropores of about 2nm. This shows that in the absence of the support of carbon nanotubes, it is difficult for a single polyacrylonitrile to form a large number of mesopores and mesopores during the carbonization process, and it also shows that the presence of carbon nanotubes plays a key role in the formation of the porous structure. The carbonization temperature of Comparative Example 2 was only 600℃. Although polyacrylonitrile can be carbonized and has a large pore diameter at this temperature, the pore volume is very low. It is speculated that this is mainly because the lower temperature leads to a slower carbonization rate of polyacrylonitrile, which results in polyacrylonitrile having more time to slowly deform when heated, which is not conducive to the formation of a large number of mesopores and mesopores.

[0124] Compared with Example 1, the proportion of polyacrylonitrile in Example 2 and Example 3 decreases successively, which results in that the surface of the carbon nanotubes is not easily uniformly coated by polyacrylonitrile during the preparation process, thereby resulting in a reduction in the pore structure generated during the carbonization process. Therefore, the specific surface area, pore volume and pore diameter of Example 2 and Example 3 are all lower than those of Example 1. In addition, the pore volume and pore diameter of Example 3 have decreased significantly, which indicates that when the content of polyacrylonitrile is on the low side, the number of pores in the carbon material will be reduced. In Example 4 and Example 5, the proportion of polyacrylonitrile increases successively, which results in that there are fewer carbon nanotubes as the skeleton in the finally formed carbon material. Polyacrylonitrile lacks the support of carbon nanotubes, which is not conducive to the formation of pores with larger pore diameters. Therefore, the pore volume and pore diameter of Example 4 and Example 5 are both lower than those of Example 1. In addition, the specific surface pore diameter of Example 5 has decreased significantly, indicating that when the content of polyacrylonitrile is on the high side, the pore size of the carbon material will also be significantly reduced.

[0125] Compared with Example 1, the carbonization temperatures of Example 6 and Example 7 are 800°C and 1100°C, respectively. The specific surface area and pore volume of Example 6 are slightly lower than those of Example 1, and the specific surface area and pore volume of Example 7 are similar to those of Example 1. This indicates that when the carbonization temperature is above 800°C, polyacrylonitrile can be quickly and fully decomposed during the carbonization process, thereby producing a rich porous structure in the carbon material.

[0126] Compared with Example 1, Example 8 was not subjected to pre-oxidation and annealing, Example 9 was only subjected to pre-oxidation, and Example 10 was only subjected to annealing, and its specific surface area, pore volume and pore diameter were significantly lower than those of Example 1. Among them, compared with Example 8, the specific surface area, pore volume and pore diameter of Example 9 were all increased, which is mainly because the pre-oxidation treatment can form defects on the surface of polyacrylonitrile, and these defects can serve as sites for pore generation during the subsequent calcination process. The specific surface area, pore volume and pore diameter of Example 10 were all reduced, which is mainly because the annealing process makes the surface of polyacrylonitrile smoother, which is not conducive to the generation of holes. In addition, compared with Example 9, the specific surface area, pore volume and pore diameter of Example 1, which was subjected to annealing after pre-oxidation, were greatly improved, which shows that the two steps of pre-oxidation and annealing have a synergistic effect in obtaining a richer porous structure and increasing the specific surface area and pore volume of the carbon material. It is speculated that this phenomenon occurs mainly because the annealing process promotes the deformation of the defective areas formed during the pre-oxidation process into depressions, and then a large number of mesoporous and mesoporous structures are generated based on the depressions during the calcination process.

[0127] Table 2

[0128]

[0129] Furthermore, referring to Table 2, Examples 1 through 10 all exhibited initial discharge specific capacities exceeding 275 mAh / g and capacity retention rates exceeding 90%. This is primarily due to the large pore volume and average pore diameter of the carbon materials in Examples 1 through 10, providing abundant attachment sites for the active material and inhibiting the shedding of manganese dioxide powder. The carbon materials with a large specific surface area also ensure sufficient charge and discharge of the active material. In contrast, while Comparative Example 1 also possesses a certain specific surface area, it lacks the carbon nanotubes as a scaffold support, resulting in extremely low pore volume and average pore diameter, making it difficult to accommodate the active material. This results in the active material still easily shedding from the current collector, resulting in a significantly lower cycle capacity retention rate than Examples 1 through 10. The carbon material in Comparative Example 2, while having a large average pore diameter, has a very small pore volume, also making it difficult to accommodate the active material. Furthermore, its significantly poor electrical conductivity prevents the active material from effectively and fully discharging. Therefore, the initial discharge specific capacity and capacity retention rate of the carbon material in Comparative Example 2 are even lower than those in Comparative Example 1. In Comparative Example 3, a conductive coating was prepared on the surface of the carbon cloth, which also resulted in a large amount of manganese dioxide powder falling off during the charge and discharge cycle, and showed an extremely low charge and discharge specific capacity after 50 cycles.

[0130] From the above, it can be seen that the current collector prepared by the preparation method of the present disclosure can provide abundant attachment sites for the active material, inhibit the particles of the active material from falling off from the current collector, thereby improving the reversible cycle capacity of the battery and improving the stability of the electrode structure.

[0131] It should be understood that, unless otherwise expressly stated herein, there is no strict order in which the steps are to be performed, and the steps may be performed in other orders. Furthermore, at least a portion of the steps in the preparation process may include multiple sub-steps or multiple stages, and these sub-steps or stages are not necessarily performed at the same time and may be performed at different times, and the order in which these sub-steps or stages are performed is not necessarily sequential.

[0132] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, 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.

Claims

1. A method for preparing a current collector, characterized in that: The steps include: Dissolving polyacrylonitrile in a solvent, and mixing carbon nanotubes with the formed polyacrylonitrile solution to form a mixed slurry, wherein the mass ratio of the polyacrylonitrile to the carbon nanotubes is 1:(4-29); Applying the mixed slurry on the surface of a conductive substrate to form a coating layer, and then removing the solvent in the mixed slurry to form a polyacrylonitrile-coated carbon nanotube material; as well as, placing the polyacrylonitrile-coated carbon nanotube material in an oxidant containing nitric acid to perform a pre-oxidation treatment on the polyacrylonitrile-coated carbon nanotube material; the nitric acid is concentrated nitric acid, and the mass concentration of nitric acid in the concentrated nitric acid is greater than 50%; placing the pre-oxidized polyacrylonitrile-coated carbon nanotube material in a gas environment containing oxygen for annealing, during the annealing process, heating the polyacrylonitrile-coated carbon nanotube material to 150° C. to 250° C., keeping the temperature for 1 hour to 2 hours, and then cooling naturally; The polyacrylonitrile-coated carbon nanotube material after annealing is carbonized at a temperature of above 800°C.

2. The method for preparing a current collector according to claim 1, wherein: After the polyacrylonitrile-coated carbon nanotube material is carbonized, the specific surface area of ​​the formed carbonized material is ≥50m 2 / g; and / or, the pore volume of the formed carbonized material is ≥0.2cm 3 / g; and / or, the average pore size of the formed carbonized material is ≥5nm.

3. The method for preparing a current collector according to claim 1, wherein: The solvent in the mixed slurry is removed to form a polyacrylonitrile-coated carbon nanotube material, in which the carbon nanotubes account for 80% to 96.7% by weight and the polyacrylonitrile accounts for 3.3% to 20% by weight.

4. The method for preparing a current collector according to any one of claims 1 to 3, wherein: The carbonization treatment of the polyacrylonitrile-coated carbon nanotube material is carried out in a protective gas atmosphere, and the carbonization treatment time is 1 hour to 4 hours.

5. A current collector, characterized in that: The current collector is prepared by the method for preparing the current collector according to any one of claims 1 to 4.

6. A pole piece, characterized in that: The device comprises an active material layer and the current collector according to claim 5, wherein the active material layer is disposed on the current collector.

7. The pole piece according to claim 6, characterized in that: The active material layer includes a manganese-based material.

8. A secondary battery, characterized in that: The secondary battery comprises a positive electrode and a negative electrode arranged opposite to each other, and the positive electrode and / or the negative electrode comprises the electrode sheet according to any one of claims 6 to 7.

9. An electrical device, characterized in that: The device comprises a functional body and the secondary battery according to claim 8, wherein the secondary battery is used to supply power to the functional body.

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