Carbon fiber structure battery negative electrode material, preparation method, negative electrode sheet and lithium ion battery

Abstract

The present invention relates to a carbon fiber structure battery negative electrode material, a preparation method, a negative electrode plate, and a lithium-ion battery. The carbon fiber structure battery negative electrode material comprises carbon fibers, carbon nanotubes, and polydopamine; the carbon nanotubes and polydopamine are coated on the surface of the carbon fibers; and the polydopamine connects the carbon fibers and the carbon nanotubes in a strong interaction between the carbon fibers and the carbon nanotubes. The present invention selects carbon nanotubes to modify the carbon fibers, and the carbon nanotubes and polydopamine are coated on the surface of the carbon fibers, thereby improving the mechanical properties and interfacial properties while increasing the specific capacity of the structural battery negative electrode. The polydopamine connects the carbon fibers and the carbon nanotubes in a strong interaction between the carbon fibers and the carbon nanotubes, further improving the bonding force between the carbon nanotubes and the carbon fibers, thereby providing good mechanical properties.

Description

Technical Field

[0001] The present invention relates to the technical field of structural battery negative electrode materials, and in particular to a carbon fiber structural battery negative electrode material, a preparation method, a negative electrode plate and a lithium ion battery. Background Art

[0002] Carbon fiber has good electrical conductivity (1000S·cm -1 ), excellent mechanical properties (high specific strength, high modulus, high compressive strength, high shear modulus) and low density (1.7-2.0g / cm 3 As an essential component of structural battery electrodes, carbon fiber boasts lightweight properties, enabling both energy storage and mechanical load resistance. However, the surface of carbon fiber is inert, resulting in poor interfacial properties with the resin. Furthermore, as anodes in structural batteries, carbon fiber has a low specific capacity, hindering its potential in structural batteries.

[0003] Currently, structured lithium-ion batteries (LIBs) generally use carbon fibers (CFs) as multifunctional anode materials to provide Li + However, the development of structured LIBs is hampered by the shortcomings of CF, such as low specific capacity, chemically inert surface, and significant volume expansion during lithiation.

[0004] There are reports of synthesizing iron oxide (Fe3O4) crystals on acidified carbon fibers through in-situ growth methods, and then coating the surface with a layer of PDA molecules to accommodate the deformation of Fe3O4 due to volume expansion. At the same time, Fe3O4 also brings a large specific capacity to the structural battery. However, when prepared in this way, the carbon fibers are damaged by acidification, and the bonding force between Fe3O4 and carbon fibers, and between PDA and iron oxide is very weak, which is not conducive to the mechanical properties and interfacial properties of the structural battery. In addition, the ability of Fe3O4 particles to conduct electrons is weak, which is not conducive to the rate performance of the structural battery.

[0005] Another report has used a mixture of graphite powder, conductive carbon black, and a binder called PVDF in a specific ratio to create a slurry, which was then coated on a carbon fiber cloth to create a negative electrode. However, this method has a limit on the battery's specific capacity. A thick layer of active material compromises the battery's mechanical and interfacial properties. Furthermore, the gaps between the carbon fiber cloth hinder electron transfer between the fibers.

[0006] Since the carbon fiber negative electrode materials in the existing technology cannot have both excellent mechanical strength and good electrical conductivity, how to develop a carbon fiber structure battery negative electrode material with both high mechanical strength and high electrochemical performance has become an urgent problem to be solved. Summary of the Invention

[0007] To solve the above-mentioned technical problems, the present invention aims to provide a carbon fiber structure battery negative electrode material, preparation method, negative electrode plate and lithium ion battery. The carbon fiber structure battery negative electrode material of the present invention has high mechanical strength and excellent electrochemical properties, while solving the problem of easy shedding of the coating layer. The negative electrode plate of the present invention has excellent mechanical and electrical properties, and can significantly improve the problem of poor interfacial bonding strength between the carbon fiber negative electrode material and the resin / electrolyte material. Its excellent mechanical strength can also be used as a positive and negative electrode current collector. The provided lithium ion battery not only has excellent mechanical properties, but also has excellent rate performance and high specific capacity.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a carbon fiber structure battery negative electrode material, which includes carbon fiber, carbon nanotubes and polydopamine; the carbon nanotubes and polydopamine are coated on the surface of the carbon fiber to form a carbon nanotube and polydopamine coating layer; the polydopamine connects the carbon fiber and the carbon nanotube in the form of strong interaction between the carbon fiber and the carbon nanotube.

[0010] The present invention uses carbon nanotubes to modify carbon fibers. The carbon nanotubes and polydopamine are coated on the surface of the carbon fibers, improving mechanical and interfacial properties while also increasing the specific capacity of the negative electrode of structural batteries. This design can also be used as a current collector for the positive electrode of structural batteries. Compared to aluminum foil, carbon nanotube-modified carbon fibers not only have good electrical conductivity, but also possess excellent mechanical properties and deformation resistance of the positive electrode active material. The polydopamine forms a strong interaction between the carbon fibers and the carbon nanotubes, further enhancing the bonding between the carbon nanotubes and the carbon fibers, resulting in excellent mechanical properties.

[0011] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0012] Preferably, the carbon fiber structure battery negative electrode material has a porous structure.

[0013] The porous structure contained in the carbon fiber structure battery negative electrode material of the present invention can increase the specific surface area of ​​the material, improve the interface contact between the battery negative electrode and the resin material, and at the same time improve the infiltration effect of the electrolyte, increase the contact between the electrolyte and the electrode material, and improve the electrochemical stability of the battery.

[0014] Preferably, the thickness of the carbon nanotube and polydopamine coating layer is 20-250 nm, for example, it can be 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, 210 nm, 220 nm, 230 nm, 240 nm or 250 nm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0015] Preferably, the carbon nanotubes include single-walled carbon nanotubes or multi-walled carbon nanotubes.

[0016] In a second aspect, the present invention provides a method for preparing the carbon fiber structure battery negative electrode material as described in the first aspect, the preparation method comprising the following steps:

[0017] (1) uniformly mixing carbon nanotubes, polyvinyl pyrrolidone and water to obtain a CNT / PVP solution;

[0018] (2) mixing a pH buffer with a CNT / PVP solution, adjusting the pH of the solution, and then adding dopamine hydrochloride to obtain a CNT / PVP / DA solution; impregnating the CNT / PVP / DA solution into the pretreated carbon fiber, and reacting, washing, and drying to obtain a CF@PDA@CNT material;

[0019] (3) The obtained CF@PDA@CNT material is subjected to heat treatment to obtain the carbon fiber structure battery negative electrode material.

[0020] The present invention utilizes the synergistic effect of polydopamine (PDA) and polyvinylpyrrolidone (PVP) to comprehensively improve the mechanical and electrical properties of carbon fiber materials. Among them, the addition of carbon nanotubes improves the conductivity of individual carbon fibers and enhances the electronic conduction between carbon fibers in the resin electrolyte; the present invention uses polyvinylpyrrolidone as a dispersant to promote the dispersion of carbon nanotubes. Compared with other dispersants, on the one hand, PVP can form a stronger interaction with dopamine in the dopamine solution, attracting dopamine to adhere and polymerize along the CNT with PVP as the center. On the other hand, PVP can be removed in the subsequent heat treatment stage, thereby leaving pores in the negative electrode material. The formation of pores increases the specific surface area of ​​the carbon fiber negative electrode material, improves the wettability of the interface, and thus improves the contact between the electrolyte and the carbon fiber negative electrode material.

[0021] In addition, the addition of PDA can achieve modification on a single carbon fiber without damage, thereby enhancing the interface performance between the carbon fiber negative electrode material and the resin electrolyte; after the CNT / PVP / DA solution is impregnated into the carbon fiber, dopamine hydrochloride undergoes a polymerization reaction. During this process, polydopamine can connect the carbon nanotubes and the carbon fiber, so that the carbon nanotubes can be tightly connected to the surface of the carbon fiber and form a strong and stable coating together with the polydopamine, so that the carbon nanotubes will not fall off during the battery cycle; on this basis, impurities are removed by heat treatment, and at the same time, part of the polydopamine undergoes a crystal transformation, thereby obtaining a carbon fiber negative electrode material with higher specific capacity and better rate performance.

[0022] Preferably, the mass ratio of the carbon nanotubes, polyvinyl pyrrolidone and water is (1-2):(0.5-5):(1-10), for example, it can be 1:1:1, 1:1:2, 1:2:1, 2:1:1, 2:2:1, 1:1:2, 1:2:3, 2:1:4, 2:2:6, 1:3:10, 1:3:2, 1:3:3, 1:3:10, 1:4:10 or 2:1:2, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0023] The present invention further controls the mass ratio of carbon nanotubes, polyvinyl pyrrolidone and water to (1-2): (0.5-5): (1-10) to obtain a uniformly dispersed carbon nanotube dispersion. By regulating the mass ratio of carbon nanotubes to polyvinyl pyrrolidone, the dispersion state of the carbon nanotubes in the dispersion and the subsequent distribution state on the carbon fibers can be controlled.

[0024] Preferably, the diameter of the carbon nanotubes is 7nm-20nm, for example, it can be 7.1nm, 7.2nm, 7.3nm, 7.4nm, 7.5nm, 7.6nm, 7.7nm, 7.8nm, 7.9nm, 8.0nm, 8.1nm, 8.2nm, 8.3nm, 8.4nm, 8.5nm, 8.6nm, 8.7nm, 8.8nm, 8.9nm, 9.0nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 16nm, 17nm, 18nm, 19nm or 20nm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0025] Preferably, the length of the carbon nanotubes is 10μm-200μm, for example, it can be 10μm, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, 160μm, 170μm, 180μm, 190μm or 200μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0026] Preferably, the mixing method includes ultrasound and high-pressure homogeneous dispersion.

[0027] Preferably, the mixing is firstly carried out by ultrasonic dispersion and then by high-pressure homogenous dispersion.

[0028] In order to improve the dispersion uniformity of carbon nanotubes, the present invention uses ultrasonic dispersion plus a high-pressure homogenizer to perform dispersion, thereby improving the dispersion effect and efficiency.

[0029] Preferably, the ultrasonic time is 10 min-20 min, for example, 10 min, 12 min, 14 min, 16 min, 18 min or 20 min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0030] Preferably, the dispersion pressure of the high-pressure homogenizer is 300 bar-500 bar, for example, 300 bar, 350 bar, 400 bar, 450 bar or 500 bar, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0031] Preferably, the dispersion time of the high-pressure homogenizer is 20 min-30 min, for example, it can be 20 min, 22 min, 24 min, 26 min, 28 min or 30 min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0032] Preferably, the carbon fiber pretreatment method comprises the following steps:

[0033] The carbon fiber is heated to 400-500° C. at a heating rate of 5-10° C. / min, and calcined for 20-60 minutes to perform degumming treatment to obtain pretreated carbon fiber.

[0034] The heating rate may be, for example, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min or 10°C / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0035] The calcination temperature may be, for example, 400° C., 420° C., 440° C., 460° C., 480° C. or 500° C., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0036] The calcination time can be, for example, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0037] The carbon fibers of the present invention are pretreated to remove the sizing agent on the surface of the carbon fibers, so that the PDA can directly connect the carbon fibers and the carbon nanotubes, thereby helping to improve the interface bonding strength and electrical conductivity between the carbon fibers and the carbon nanotubes.

[0038] Preferably, the pH buffer in step (2) comprises tris(hydroxymethyl)aminomethane.

[0039] Preferably, the pH of the solution is adjusted to 8.0-9.0, for example, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9 or 9.0, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0040] Preferably, the mass ratio of CNT to dopamine hydrochloride in the CNT / PVP / DA solution is (1-2):(1-2), for example, it can be 1:1, 1:1.5, 1:2, 1.5:1, 1.5:2 or 2:1, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0041] The present invention further controls the mass ratio of CNTs to dopamine hydrochloride in the CNT / PVP solution to be (1-2):(1-2), thereby regulating the progress of subsequent reactions and the thickness of the coating layer. Furthermore, since the polydopamine generated by the reaction acts as a bridge between the carbon nanotubes and the carbon fibers to achieve a connecting effect, the amount of dopamine hydrochloride added affects the stability of the coating layer. When the amount of dopamine hydrochloride added is too much, the coating layer becomes too thick, and the excess polydopamine forms a coating layer on the outer layer of the carbon nanotubes, which hinders electron transmission and is not conducive to improving the conductivity of the negative electrode material.

[0042] Preferably, the impregnation step comprises: pouring the solution into a rectangular tank, fixing the pretreated carbon fibers in the rectangular tank, the reaction temperature being 25° C.-40° C., and the reaction time being 5 h-8 h.

[0043] The temperature of the impregnation reaction can be, for example, 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, 31°C, 32°C, 33°C, 34°C, 35°C, 36°C, 37°C, 38°C, 39°C or 40°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0044] The present invention immediately brings the mixed CNT / PVP / DA solution into contact with carbon fibers. During this process, a polymerization reaction of dopamine hydrochloride occurs. After the reaction, polydopamine is connected to the carbon nanotubes and carbon fibers through adhesion, so that the carbon nanotubes can be firmly fixed on the carbon fibers. During the reaction, the reaction temperature and time are controlled, and the polymerization degree of dopamine hydrochloride is controlled, thereby forming a structure in which the polydopamine and carbon nanotubes jointly coat the carbon fibers.

[0045] The impregnation reaction time can be, for example, 5 h, 6 h, 7 h or 8 h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0046] Preferably, the cleaning solvent in step (2) includes water.

[0047] Preferably, the drying temperature in step (2) is 60°C-80°C, for example, 60°C, 65°C, 70°C, 75°C or 80°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0048] Preferably, the drying time in step (2) is 12h-24h, for example, it can be 12h, 14h, 16h, 18h, 20h, 22h or 24h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0049] Preferably, the temperature of the heat treatment in step (3) is 400°C-2000°C, for example, it can be 400°C, 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, 1100°C, 1200°C, 1300°C, 1400°C, 1500°C, 1600°C, 1700°C, 1800°C, 1900°C or 2000°C, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable, preferably 400°C-750°C.

[0050] The purpose of the heat treatment step of the present invention is to remove unreacted impurities and completely remove PVP to form a porous structure on the surface of the carbon fiber. In addition, within this temperature range, part of the polydopamine can undergo partial graphitization, which can further improve the conductivity of the carbon fiber negative electrode material. The more preferred heat treatment temperature range of the present invention is 400°C-750°C. If the temperature is too low, the PVP cannot be completely removed; if the temperature is too high, the preparation time is extended and the energy consumption is too high.

[0051] Preferably, the heat treatment time in step (3) is 0.5h-5h, for example, it can be 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h or 5h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0052] Preferably, the atmosphere of the heat treatment in step (3) includes a nitrogen atmosphere.

[0053] As a preferred technical solution of the preparation method of the present invention, the preparation method comprises the following steps:

[0054] (1) placing the carbon fiber in a muffle furnace, heating the temperature to 400-500°C at a heating rate of 5-10°C / min, and calcining the temperature for 20-60 min to remove the glue, thereby obtaining pretreated carbon fiber;

[0055] (2) uniformly mixing carbon nanotubes, polyvinyl pyrrolidone, and water in a mass ratio of (1-2):(0.5-5):(1-10), ultrasonicating for 10 min-20 min, and using a high-pressure homogenizer for dispersion at a pressure of 300 bar-500 bar for 20 min-30 min to obtain a CNT / PVP solution;

[0056] (3) After adjusting the pH of the solution to 8.0-9.0 by mixing tris(hydroxymethyl)aminomethane and CNT / PVP solution, the CNT / PVP solution and dopamine hydrochloride were mixed in a mass ratio of CNT to dopamine hydrochloride of (1-2):(1-2) to obtain a CNT / PVP / DA solution; impregnating the CNT / PVP / DA solution into the pretreated carbon fiber for 5 h-8 h, washing with water to remove impurities, and drying at 60 ° C-80 ° C for 12 h-24 h to obtain a CF@PDA@CNT material;

[0057] (4) The obtained CF@PDA@CNT material is heat treated at 400°C-2000°C in a nitrogen atmosphere of a vacuum tube furnace for 0.5h-5h to obtain the carbon fiber structure battery negative electrode material.

[0058] In a third aspect, the present invention provides a negative electrode plate, which includes the carbon fiber structure battery negative electrode material described in the first aspect, such as the carbon fiber structure battery negative electrode material prepared by the preparation method described in the second aspect.

[0059] The negative electrode sheet of the present invention has excellent mechanical and electrical properties, can significantly improve the problem of poor interface contact between carbon fiber negative electrode materials and resin / electrolyte materials, and its excellent mechanical strength can also be used as positive and negative electrode current collectors.

[0060] In a fourth aspect, the present invention provides a lithium-ion battery, comprising the negative electrode sheet described in the third aspect.

[0061] The lithium-ion battery provided by the present invention not only has excellent mechanical properties, but also has excellent rate performance and high specific capacity.

[0062] The numerical range described in the present invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0063] Compared with the prior art, the present invention has at least the following beneficial effects:

[0064] (1) The present invention selects carbon nanotubes to modify carbon fibers, and carbon nanotubes and polydopamine are coated on the surface of the carbon fibers, thereby improving the mechanical properties and interfacial properties while increasing the specific capacity of the negative electrode of the structural battery. In addition, this design can also be used as a current collector for the positive electrode of the structural battery, because compared to aluminum foil, carbon nanotube-modified carbon fibers not only have good electrical conductivity, but also have excellent mechanical properties and deformation resistance of the positive electrode active material. Among them, polydopamine connects the carbon fibers and carbon nanotubes in the form of strong interaction between the carbon fibers and the carbon nanotubes, further improving the bonding force between the carbon nanotubes and the carbon fibers, so that they have good mechanical properties.

[0065] (2) The present invention utilizes the synergistic effect of polydopamine (PDA) and polyvinylpyrrolidone (PVP) to comprehensively improve the mechanical and electrical properties of carbon fiber materials. Among them, the addition of carbon nanotubes improves the conductivity, specific surface area and interaction sites with the electrolyte of a single carbon fiber, and enhances the electronic conduction between carbon fibers in the resin electrolyte; while polyvinylpyrrolidone promotes the dispersion of carbon nanotubes, it leaves pores in the negative electrode material after heat treatment. The formation of pores further increases the specific surface area of ​​the carbon fiber negative electrode material, improves the wettability of the interface, and improves the contact between the electrolyte and the carbon fiber negative electrode material; in addition, the addition of PDA enhances the interface performance between the carbon fiber negative electrode material and the resin electrolyte; polydopamine can connect carbon nanotubes and carbon fibers, so that the carbon nanotubes can be tightly connected to the surface of the carbon fibers, and together with polydopamine, form a stable coating layer, so that the carbon nanotubes will not fall off during the battery cycle, thereby obtaining a carbon fiber negative electrode material with higher specific capacity and better rate performance.

[0066] (3) The negative electrode sheet of the present invention has excellent mechanical and electrical properties, significantly improving the poor interfacial contact between carbon fiber negative electrode materials and resin materials. Its excellent mechanical strength also allows it to be used as a positive and negative electrode current collector. The provided lithium-ion battery not only has excellent mechanical properties, but also has excellent rate capability and high specific capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 Schematic diagram of the structure of the CF@PDA@SWCNTs negative electrode material prepared in Example 1 of the present invention;

[0068] Figure 2 This is a schematic diagram of the process for preparing CF@PDA@SWCNTs negative electrode material according to Example 1 of the present invention;

[0069] Figure 3 This is an SEM image of the CF@PDA@SWCNTs material prepared in Example 1 of the present invention and a locally enlarged SEM image of the morphology;

[0070] Figure 4 It is a bar chart of the interfacial shear strength of the negative electrode materials prepared in Example 1 of the present invention and Comparative Examples 1-4.

[0071] Figure 5 It is a rate performance curve diagram of the negative electrode materials prepared in Example 1, Comparative Example 1 and Comparative Example 4 of the present invention for lithium metal half-cells.

[0072] Figure 6 This is a charge and discharge curve diagram of the CF@PDA@SWCNTs sample prepared in Example 1 of the present invention during the cycle process. DETAILED DESCRIPTION

[0073] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0074] In the following examples, unless otherwise specified, all reagents and consumables were purchased from conventional reagent manufacturers in the field; unless otherwise specified, the experimental methods and technical means used were conventional methods and means in the field.

[0075] Example 1

[0076] This embodiment provides a carbon fiber structure battery negative electrode material, and its specific structural diagram is as follows Figure 1 As shown, the carbon fiber structure battery negative electrode material includes carbon fiber, single-walled carbon nanotubes and polydopamine; the single-walled carbon nanotubes and polydopamine are coated on the surface of the carbon fiber; the polydopamine connects the carbon fiber and the single-walled carbon nanotubes through strong interaction between the carbon fiber and the single-walled carbon nanotubes.

[0077] The schematic diagram of the preparation process of the carbon fiber structure battery negative electrode material provided in this embodiment is as follows Figure 2 As shown, the specific preparation method comprises the following steps:

[0078] (1) Carbon fiber (T700, Toray, Japan) was placed in a muffle furnace, heated to 450°C at a heating rate of 5°C / min, and calcined for 30 min to remove the glue and obtain pretreated carbon fiber;

[0079] (2) Single-walled carbon nanotubes (95% purity, OCSIAL), polyvinyl pyrrolidone (K30, Sinopharm Group) and water were uniformly mixed in a mass ratio of 1:1:1, ultrasonicated for 10 min, and dispersed for 25 min at a pressure of 400 bar using a high-pressure homogenizer (AH-BASIC 2, Suzhou Antosi) to obtain a SWCNTs / PVP solution;

[0080] (3) After adjusting the pH of the solution to 8.5 by mixing tris(hydroxymethylaminomethane) (AR-grade, Sinopharm Group) with SWCNTs / PVP solution, the SWCNTs / PVP solution and dopamine hydrochloride (98%, Aladdin) were mixed in a mass ratio of 1:1 to obtain a SWCNTs / PVP / DA solution; the SWCNTs / PVP / DA solution was poured into a rectangular tank, and the pretreated carbon fiber was fixed in the rectangular tank and immersed at 30°C for 6 hours. After that, the CF@PDA@SWCNTs material was obtained by washing with water to remove impurities and drying at 60°C for 12 hours;

[0081] (4) The obtained CF@PDA@SWCNTs material was heat treated at 500°C for 2h in a nitrogen atmosphere in a vacuum tube furnace to obtain the carbon fiber structure battery negative electrode material.

[0082] The SEM image of the prepared carbon fiber structure battery negative electrode material is as follows Figure 3 As shown, from Figure 3 It can be seen that under the synergistic effect of PVP and PDA, carbon nanotubes are evenly coated on the surface of carbon fibers. After pyrolysis, the carbon nanotubes are more clearly visible and the surface becomes rougher.

[0083] The shear strength of the negative electrode material obtained by testing is as follows Figure 4 As shown, the interfacial shear strength of the negative electrode material is 108.11 MPa, and the shear strength of the negative electrode material is significantly improved.

[0084] The obtained carbon fiber structure battery negative electrode material was used to assemble button batteries, and the battery rate performance was tested. Figure 5 As shown, the battery has excellent rate performance.

[0085] The obtained carbon fiber structure battery negative electrode material was used to assemble button batteries, and the battery charge and discharge performance was tested. Figure 6 As shown, it can be seen that the battery has a high charge-discharge specific capacity and capacity retention rate.

[0086] Example 2

[0087] This embodiment provides a carbon fiber structure battery negative electrode material, the carbon fiber structure battery negative electrode material includes carbon fiber, single-walled carbon nanotubes and polydopamine; the single-walled carbon nanotubes and polydopamine are coated on the surface of the carbon fiber;

[0088] The polydopamine connects the carbon fibers and the single-walled carbon nanotubes through a strong interaction between the carbon fibers and the single-walled carbon nanotubes;

[0089] The method for preparing the carbon fiber structure battery negative electrode material provided in this embodiment includes the following steps:

[0090] (1) Carbon fiber (T700, Toray, Japan) was placed in a muffle furnace, heated to 400°C at a heating rate of 8°C / min, and calcined for 60 min to remove the glue and obtain pretreated carbon fiber;

[0091] (2) Single-walled carbon nanotubes (95% purity, OCSIAL), polyvinyl pyrrolidone (K30, Sinopharm Group) and water were uniformly mixed in a mass ratio of 1:2:1, ultrasonicated for 10 min, and dispersed for 30 min at a pressure of 350 bar using a high-pressure homogenizer (AH-BASIC2, Suzhou Antosi) to obtain a SWCNTs / PVP solution;

[0092] (3) After adjusting the pH of the solution to 8.0 by mixing tris(hydroxymethyl)aminomethane (AR-grade, Sinopharm Group) and SWCNTs / PVP solution, the SWCNTs / PVP solution and dopamine hydrochloride (98%, Aladdin) were mixed at a mass ratio of 1:1.5 to obtain a SWCNTs / PVP / DA solution; the SWCNTs / PVP / DA solution was poured into a rectangular tank, and the pretreated carbon fiber was fixed in the rectangular tank and immersed in the reaction at 25°C for 8 hours. After that, the CF@PDA@SWCNTs material was obtained by washing with water to remove impurities and drying at 70°C for 12 hours;

[0093] (4) The obtained CF@PDA@SWCNTs material was heat treated at 400°C for 5 h in a nitrogen atmosphere in a vacuum tube furnace to obtain the carbon fiber structure battery negative electrode material.

[0094] Example 3

[0095] This embodiment provides a carbon fiber structure battery negative electrode material, the carbon fiber structure battery negative electrode material includes carbon fiber, multi-walled carbon nanotubes and polydopamine; the multi-walled carbon nanotubes and polydopamine are coated on the surface of the carbon fiber;

[0096] The polydopamine connects the carbon fibers and the multi-walled carbon nanotubes in a strong interaction between the carbon fibers and the multi-walled carbon nanotubes;

[0097] The method for preparing the carbon fiber structure battery negative electrode material provided in this embodiment includes the following steps:

[0098] (1) placing the carbon fiber in a muffle furnace, heating it to 500°C at a heating rate of 10°C / min, and calcining it for 20 minutes to remove the glue, thereby obtaining pretreated carbon fiber;

[0099] (2) Multi-walled carbon nanotubes (95% purity, OCSIAL), polyvinyl pyrrolidone, and water were uniformly mixed in a mass ratio of 2:1:1, ultrasonicated for 10 min, and dispersed for 20 min using a high-pressure homogenizer at a pressure of 500 bar to obtain a MWCNTs / PVP solution;

[0100] (3) After adjusting the pH of the solution to 9.0 by mixing tris(hydroxymethyl)aminomethane and MWCNTs / PVP solution, the MWCNTs / sPVP solution and dopamine hydrochloride were mixed in a mass ratio of CNTs to dopamine hydrochloride of 2:1 to obtain a MWCNTs / PVP / DA solution; the MWCNTs / PVP / DA solution was poured into a rectangular tank, the pretreated carbon fiber was fixed in the rectangular tank, and the carbon fiber was immersed in the tank at 30°C for 6 hours, and then washed with water to remove impurities and dried at 60°C for 12 hours to obtain the CF@PDA@MWCNTs material;

[0101] (4) The obtained CF@PDA@MWCNTs material was heat treated at 750°C for 0.5h in a nitrogen atmosphere in a vacuum tube furnace to obtain the carbon fiber structure battery negative electrode material.

[0102] Example 4

[0103] This embodiment provides a carbon fiber structure battery negative electrode material, which differs from Example 1 only in that, when preparing the carbon fiber structure battery negative electrode material, the mass ratio of the carbon nanotubes, polyvinyl pyrrolidone and water in step (2) is 1:6:1.

[0104] Example 5

[0105] This embodiment provides a carbon fiber structure battery negative electrode material, which differs from Example 1 only in that, when preparing the carbon fiber structure battery negative electrode material, the mass ratio of the carbon nanotubes, polyvinyl pyrrolidone and water in step (2) is 3:1:1.

[0106] Example 6

[0107] This embodiment provides a carbon fiber structure battery negative electrode material, which differs from Example 1 only in that, when preparing the carbon fiber structure battery negative electrode material, the mass ratio of CNT to dopamine hydrochloride in the CNT / PVP solution in step (3) is 1:3.

[0108] Example 7

[0109] This embodiment provides a carbon fiber structure battery negative electrode material, which differs from Example 1 only in that, when preparing the carbon fiber structure battery negative electrode material, the mass ratio of CNT to dopamine hydrochloride in the CNT / PVP solution in step (3) is 3:1.

[0110] Example 8

[0111] This embodiment provides a carbon fiber structure battery negative electrode material, which differs from Example 1 only in that, when preparing the carbon fiber structure battery negative electrode material, the temperature of the heat treatment in step (4) is 300°C.

[0112] Example 9

[0113] This embodiment provides a carbon fiber structure battery negative electrode material, which differs from Example 1 only in that, when preparing the carbon fiber structure battery negative electrode material, the temperature of the heat treatment in step (4) is 800°C.

[0114] Example 10

[0115] This embodiment provides a carbon fiber structure battery negative electrode material, which differs from Example 1 only in that, when preparing the carbon fiber structure battery negative electrode material, the temperature of the heat treatment in step (4) is 2200°C.

[0116] Comparative Example 1

[0117] This comparative example provides a negative electrode material, which differs from Example 1 only in that, when preparing the carbon fiber structure battery negative electrode material, carbon nanotubes are not added in step (2) and dopamine hydrochloride is not added in step (3), and the remaining steps remain unchanged.

[0118] The shear strength of the negative electrode material obtained by testing is as follows Figure 4 As shown, it can be seen that if carbon nanotubes are not added, the interface shear strength of the negative electrode material is 61.54 MPa, which is significantly lower than the shear strength of the carbon fiber structure battery negative electrode material obtained in Example 1.

[0119] The obtained negative electrode material was used to assemble a button battery, and the rate performance of the battery was tested. Figure 5 As shown, it can be seen that if carbon nanotubes and dopamine hydrochloride are not added, the rate performance of the battery assembled with the obtained negative electrode material is significantly lower than that of Example 1.

[0120] Comparative Example 2

[0121] This comparative example provides a negative electrode material, which differs from Example 1 only in that, when preparing the carbon fiber structure battery negative electrode material, carbon nanotubes are not added in step (2), and the other steps remain unchanged.

[0122] The shear strength of the negative electrode material obtained by testing is as follows Figure 4 As shown, it can be seen that if carbon nanotubes are not added, the interface shear strength of the negative electrode material is 86.87 MPa, which is significantly lower than the shear strength of the carbon fiber structure battery negative electrode material obtained in Example 1.

[0123] Comparative Example 3

[0124] This comparative example provides a negative electrode material, which differs from Example 1 only in that, when preparing the carbon fiber structure battery negative electrode material, dopamine hydrochloride is not added in step (3), and the remaining steps remain unchanged.

[0125] The shear strength of the negative electrode material obtained by testing is as follows Figure 4 As shown, it can be seen that if dopamine hydrochloride is not added, the interfacial shear strength of the negative electrode material is 92.09 MPa, which is significantly lower than the shear strength of the carbon fiber structure battery negative electrode material obtained in Example 1.

[0126] Comparative Example 4

[0127] This comparative example provides a negative electrode material, which differs from Example 1 only in that, when preparing the carbon fiber structure battery negative electrode material, the heat treatment in step (4) is not performed, and the other steps remain unchanged.

[0128] The shear strength of the negative electrode material obtained by testing is as follows Figure 4As shown, it can be seen that if the heat treatment in step (4) is not performed, the interface shear strength of the negative electrode material is 102.97 MPa, which is significantly lower than the shear strength of the carbon fiber structure battery negative electrode material obtained in Example 1.

[0129] The obtained negative electrode material was used to assemble a button battery, and the rate performance of the battery was tested. Figure 5 As shown, it can be seen that if carbon nanotubes are not added, the rate performance of the battery assembled with the obtained negative electrode material is significantly lower than that of Example 1.

[0130] Comparative Example 5

[0131] This comparative example provides a negative electrode material, which differs from Example 1 only in that, when preparing the carbon fiber structure battery negative electrode material, polyvinyl pyrrolidone is not added in step (2), and the other steps remain unchanged.

[0132] Comparative Example 6

[0133] This comparative example provides a negative electrode material, which differs from Example 1 only in that, when preparing the carbon fiber structure battery negative electrode material, step (3) is prepared using the method disclosed in patent CN117166019A.

[0134] Testing Method: The carbon fiber negative electrode materials obtained in Examples 1-10 and Comparative Examples 1-6 were cut into multiple 1 x 0.8 cm strips and combined with a PVDF binder (MTI, >99.5%) (fiber to PVDF mass ratio of 9:1) to form a robust electrode sheet. Coin cells were then assembled in a glove box, following the sequence of negative electrode shell → fiber electrode sheet → fiber separator → lithium metal sheet → gasket → spring clip → positive electrode shell.

[0135] The test results showed that the battery's first discharge capacity and battery capacity after 100 charge and discharge cycles were tested at 0.5C, with the electrolyte using 1M LiPF6 in DEC:EC:EMC=2:1:2wt%.

[0136] Table 1

[0137]

[0138]

[0139] The test results show that:

[0140] (1) It can be seen from Examples 1-3 that the present invention selects carbon nanotubes to modify carbon fibers, and utilizes the synergistic effect of polydopamine (PDA) and polyvinylpyrrolidone (PVP) to comprehensively improve the mechanical and electrical properties of carbon fiber materials.

[0141] (2) By comparing Example 1 with Examples 4-5, it can be seen that the present invention obtains a uniformly dispersed carbon nanotube dispersion by further controlling the mass ratio of carbon nanotubes, polyvinyl pyrrolidone and water to (1-2):(0.5-5):(1-10). By regulating the mass ratio of carbon nanotubes and polyvinyl pyrrolidone, the dispersion state of the carbon nanotubes in the dispersion and the distribution state on the carbon fibers in the later stage can be controlled.

[0142] (3) By comparing Example 1 with Examples 6-7, it can be seen that the present invention further regulates the progress of the subsequent reaction and the thickness of the coating layer by further adjusting the mass ratio of CNT to dopamine hydrochloride in the CNT / PVP solution to (1-2): (1-2). At the same time, since the polydopamine generated by the reaction acts as a bridge between the carbon nanotubes and the carbon fibers to play a connecting role, the addition amount of dopamine hydrochloride will affect the stability of the coating layer. When the amount of dopamine hydrochloride added is too much, the thickness of the coating layer will be too thick, and the excess polydopamine will form a coating layer on the outer layer of the carbon nanotubes, which will hinder the transmission of electrons and is not conducive to the improvement of the conductivity of the negative electrode material.

[0143] (4) By comparing Example 1 with Examples 8-10, it can be seen that the present invention further removes unreacted impurities through heat treatment and completely removes PVP to form a porous structure on the surface of the carbon fiber. In addition, within this temperature range, part of the polydopamine can undergo graphitization, which can further improve the conductivity of the carbon fiber negative electrode material. The more preferred temperature range of the present invention is 400°C-750°C. If the temperature is too low, the PVP cannot be completely removed; if the temperature is too high, the preparation time is extended and the energy consumption is too high.

[0144] (5) It can be seen from Example 1 and Comparative Example 1 that the present invention can obtain excellent mechanical and electrical properties by simultaneously introducing carbon nanotubes and polydopamine. When carbon nanotubes and polydopamine are not used to coat carbon fibers, the mechanical and electrical properties of the obtained negative electrode material are significantly reduced.

[0145] (6) It can be seen from Example 1 and Comparative Example 2 that the present invention can significantly improve the mechanical strength of the carbon fiber negative electrode by introducing carbon nanotubes. However, when carbon nanotubes are added, the shear strength of the negative electrode material is significantly reduced, and the electrical performance of the assembled battery is also significantly reduced.

[0146] (7) It can be seen from Example 1 and Comparative Example 3 that when dopamine hydrochloride is not added, the shear strength of the electrode is greatly reduced, the mechanical and interface properties of the battery are reduced, and the service life is even shorter.

[0147] (8) It can be seen from Example 1 and Comparative Example 4 that the present invention can improve the electrical conductivity and mechanical properties of the carbon fiber negative electrode material by further heat treatment. When no heat treatment is performed, it is impossible to achieve the transformation of the polydopamine crystal form, and the electrical conductivity of the negative electrode material is lower than that of the material after heat treatment.

[0148] (9) It can be seen from Example 1 and Comparative Example 5 that the present invention introduces PVP as a dispersant, which makes PVP more environmentally friendly and easy to obtain, and has lower material cost. On the other hand, PVP can be removed in the subsequent heat treatment stage, thereby leaving pores in the negative electrode material. The formation of pores increases the specific surface area of ​​the carbon fiber negative electrode material, improves the wettability of the interface, and thus improves the contact between the electrolyte and the carbon fiber negative electrode material.

[0149] (10) It can be seen from Example 1 and Comparative Example 6 that the present invention impregnates the mixed CNT / PVP / DA solution into the pretreated carbon fiber, and dopamine hydrochloride undergoes a polymerization reaction during the impregnation. During the reaction, polydopamine can connect the carbon nanotubes and the carbon fiber, so that the carbon nanotubes can be tightly connected to the surface of the carbon fiber, and together with the polydopamine, a firm and stable coating layer is formed. The carbon nanotubes will not fall off during the battery cycle, thereby improving the stability of the coating layer. If the CNT / DA solvent is allowed to complete the polymerization reaction, the CNT / PDA solution obtained by the reaction is deposited on the carbon fiber by electrophoretic deposition technology. This process is to first obtain carbon nanotubes coated with polydopamine, and then deposit the carbon nanotubes coated with polydopamine on the carbon fiber by electrophoretic deposition. The carbon fiber obtained by this method only contains a coating layer of carbon nanotubes, and the electrophoretic deposition method can only make the carbon fiber adsorb on the surface of the carbon fiber. There is no polydopamine as an intermediate connecting bridge, and a firm coating layer cannot be formed.

[0150] In summary, the present invention comprehensively improves the mechanical and electrical properties of carbon fiber materials by utilizing the synergistic effect of polydopamine (PDA) and polyvinyl pyrrolidone (PVP). Among them, the addition of carbon nanotubes improves the conductivity of single carbon fibers and enhances the electronic conduction between carbon fibers in the resin electrolyte; while polyvinyl pyrrolidone promotes the dispersion of carbon nanotubes, it leaves pores in the negative electrode material after heat treatment. The formation of pores increases the specific surface area of ​​the carbon fiber negative electrode material, improves the wettability of the interface, and improves the contact between the electrolyte and the carbon fiber negative electrode material; in addition, the addition of PDA enhances the interface performance between the carbon fiber negative electrode material and the resin electrolyte; polydopamine can connect carbon nanotubes and carbon fibers, so that the carbon nanotubes can be tightly connected to the surface of the carbon fibers, and together with polydopamine, form a stable coating layer, so that the carbon nanotubes will not fall off during the battery cycle, thereby obtaining a carbon fiber negative electrode material with higher specific capacity and better rate performance.

[0151] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A carbon fiber structure battery negative electrode material, characterized in that: The carbon fiber structure battery negative electrode material comprises carbon fibers, carbon nanotubes and polydopamine; the carbon nanotubes and polydopamine are coated on the surface of the carbon fibers to form a carbon nanotube and polydopamine coating layer; The polydopamine connects the carbon fibers and the carbon nanotubes through a strong interaction between the carbon fibers and the carbon nanotubes; The carbon fiber structure battery negative electrode material is obtained by the following preparation method, which includes: (1) uniformly mixing carbon nanotubes, polyvinyl pyrrolidone and water to obtain a CNT / PVP solution; (2) Mixing a pH buffer with a CNT / PVP solution, adjusting the pH of the solution, and then adding dopamine hydrochloride to obtain a CNT / PVP / DA solution; impregnating the pretreated carbon fiber into the CNT / PVP / DA solution, reacting, washing, and drying to obtain a CF@PDA@CNT material; (3) heat-treating the obtained CF@PDA@CNT material to obtain the carbon fiber structure battery negative electrode material; The mass ratio of CNT to dopamine hydrochloride in the CNT / PVP / DA solution in step (2) is 1-2:1-2.

2. The carbon fiber structure battery negative electrode material according to claim 1, characterized in that: The carbon fiber structure battery negative electrode material has a porous structure.

3. The carbon fiber structure battery negative electrode material according to claim 1, characterized in that: The thickness of the carbon nanotube and polydopamine coating layer is 20-250 nm.

4. The carbon fiber structure battery negative electrode material according to claim 1, characterized in that: The carbon nanotubes include single-walled carbon nanotubes or multi-walled carbon nanotubes.

5. A method for preparing the carbon fiber structure battery negative electrode material according to any one of claims 1 to 4, characterized in that: The preparation method comprises the following steps: (1) uniformly mixing carbon nanotubes, polyvinyl pyrrolidone and water to obtain a CNT / PVP solution; (2) Mixing a pH buffer with a CNT / PVP solution, adjusting the pH of the solution, and then adding dopamine hydrochloride to obtain a CNT / PVP / DA solution; impregnating the pretreated carbon fiber into the CNT / PVP / DA solution, reacting, washing, and drying to obtain a CF@PDA@CNT material; (3) heat-treating the obtained CF@PDA@CNT material to obtain the carbon fiber structure battery negative electrode material; The mass ratio of CNT to dopamine hydrochloride in the CNT / PVP / DA solution in step (2) is 1-2:1-2.

6. The preparation method according to claim 5, characterized in that The mass ratio of the carbon nanotubes, polyvinyl pyrrolidone and water is 1-2:0.5-5:1-10.

7. The preparation method according to claim 5, characterized in that The diameter of the carbon nanotubes is 7nm-20nm.

8. The preparation method according to claim 5, characterized in that The length of the carbon nanotubes is 10 μm-200 μm.

9. The preparation method according to claim 5, characterized in that The mixing method in step (1) includes ultrasonic and high-pressure homogenous dispersion.

10. The preparation method according to claim 9, characterized in that The ultrasonic time is 10 min-20 min.

11. The preparation method according to claim 9, characterized in that The high-pressure homogenizer used for the high-pressure homogenization dispersion has a dispersion pressure of 300 bar to 500 bar.

12. The preparation method according to claim 9, characterized in that The high-pressure homogenizer used in the high-pressure homogenization dispersion has a dispersion time of 20 min to 30 min.

13. The preparation method according to claim 5, characterized in that The carbon fiber pretreatment method comprises the following steps: The carbon fiber is heated to 400-500° C. at a heating rate of 5-10° C. / min, and calcined for 20-60 minutes to perform degumming treatment to obtain pretreated carbon fiber.

14. The preparation method according to claim 5, characterized in that The pH buffer in step (2) includes tris(hydroxymethyl)aminomethane.

15. The preparation method according to claim 5, characterized in that The pH of the solution is adjusted to be between 8.0 and 9.

0.

16. The preparation method according to claim 5, characterized in that The reaction temperature of the impregnation is 25°C-40°C.

17. The preparation method according to claim 5, characterized in that The impregnation reaction time is 5h-8h.

18. The preparation method according to claim 5, characterized in that The cleaning solvent in step (2) includes water.

19. The preparation method according to claim 5, characterized in that The drying temperature in step (2) is 60°C-80°C.

20. The preparation method according to claim 5, characterized in that The drying time in step (2) is 12h-24h.

21. The preparation method according to claim 5, characterized in that The temperature of the heat treatment in step (3) is 400°C-2000°C.

22. The preparation method according to claim 21, characterized in that The temperature of the heat treatment in step (3) is 400°C-750°C.

23. The preparation method according to claim 5, characterized in that The heat treatment time in step (2) is 0.5h-5h.

24. The preparation method according to claim 5, characterized in that The atmosphere of the heat treatment in step (2) includes a nitrogen atmosphere.

25. The preparation method according to claim 5, characterized in that The preparation method comprises the following steps: (1) The carbon fiber is placed in a muffle furnace, heated to 400-500°C at a heating rate of 5-10°C / min, and calcined for 20-60 minutes to remove the glue, thereby obtaining pretreated carbon fiber; (2) uniformly mixing carbon nanotubes, polyvinyl pyrrolidone and water in a mass ratio of 1-2:0.5-5:1-10, ultrasonicating for 10 min-20 min, and using a high-pressure homogenizer to disperse for 20 min-30 min at a pressure of 300 bar-500 bar to obtain a CNT / PVP solution; (3) After adjusting the pH of the solution to 8.0-9.0 by mixing tris(hydroxymethyl)aminomethane with a CNT / PVP solution, the CNT / PVP solution and dopamine hydrochloride were mixed in a mass ratio of CNT to dopamine hydrochloride of 1-2:1-2 to obtain a CNT / PVP / DA solution; the pretreated carbon fiber was immersed in the CNT / PVP / DA solution for 5 h-8 h, washed with water to remove impurities, and dried at 60 ° C-80 ° C for 12 h-24 h to obtain a CF@PDA@CNT material; (4) The obtained CF@PDA@CNT material is heat treated at 400°C-2000°C for 0.5h-5h in a nitrogen atmosphere in a vacuum tube furnace to obtain the carbon fiber structure battery negative electrode material.

26. A negative electrode plate, characterized in that: The negative electrode plate comprises the carbon fiber structure battery negative electrode material according to any one of claims 1 to 4, or the carbon fiber structure battery negative electrode material prepared by the preparation method according to any one of claims 5 to 25.

27. A lithium ion battery, characterized in that: The lithium-ion battery comprises the negative electrode sheet according to claim 26.

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