Composite flexible electrode material and preparation method thereof

Abstract

The present invention belongs to the field of electrochemistry and specifically relates to a composite flexible electrode material and its preparation method. The method comprises modifying carbon nanotubes with sulfonic acid to add sulfur-containing groups to their surfaces, thereby obtaining sulfur-containing carbon nanotubes. Manganese-modified carbon nanotubes are then obtained using potassium permanganate. A copper salt and a manganese salt are mixed to prepare a manganese-based oxide. The manganese-based oxide is treated with acid to obtain an acidified oxide. The acidified oxide is mixed with the modified carbon nanotubes, and dilute ammonia is added for full reaction, followed by heat treatment. After film formation, the composite flexible electrode material is obtained. The composite flexible electrode material of the present invention exhibits good flexibility, high specific capacity, and excellent cycle stability.

Description

Technical Field

[0001] The present invention belongs to the field of electrochemistry, and in particular relates to a composite flexible electrode material and a preparation method thereof. Background Art

[0002] The rapid development of wearable electronics has fueled the rapid development of flexible energy storage devices. Flexible supercapacitors and flexible aqueous zinc-ion batteries (ZIBs) hold broad application prospects in wearable energy storage. Aqueous zinc-ion batteries (ZIBs), which store energy in multiple valence states in aqueous electrolytes, boast high energy density, excellent safety, ease of fabrication, and low cost. They have been a highly researched class of high-performance rechargeable batteries over the past decade. However, for high-energy-density flexible energy storage devices, the fabrication of flexible electrode materials with high capacity and long operating life is crucial for the fabrication of flexible energy storage and conversion devices. However, the preparation of flexible electrode materials with high capacity and excellent electrochemical performance currently faces several challenges, such as low active material loading, slow ion diffusion caused by material accumulation, and complex and demanding preparation methods, which severely limit their practical application. Composites with flexible conductive substrates, such as carbon nanotubes and graphene, can enhance conductivity, improve battery flexibility, and enhance cycling stability. However, there are strong van der Waals forces between carbon nanotubes and they have a high aspect ratio, which makes them prone to agglomeration or entanglement, increasing the difficulty of dispersion and affecting their electrochemical performance. Summary of the Invention

[0003] To address the existing issues of low active material loading, easy agglomeration of carbon nanotube conductive substrates, and easy material accumulation, the present invention provides a composite flexible electrode material with good dispersibility, uniform dispersion of carbon nanotubes and manganese dioxide, and high loading. The technical solution is as follows:

[0004] A method for preparing a composite flexible electrode material comprises the following steps: subjecting carbon nanotubes to sulfonic acid modification to increase sulfur-containing groups on their surfaces to obtain sulfur-containing carbon nanotubes; then subjecting the carbon nanotubes to manganese modification using potassium permanganate to obtain modified carbon nanotubes; mixing copper salt and manganese salt to prepare manganese-based oxides; subjecting the manganese-based oxides to acid treatment to obtain acidified oxides; mixing the acidified oxides with the modified carbon nanotubes, adding dilute ammonia water for reaction, and then heat treating; and obtaining the composite flexible electrode material after film formation.

[0005] Furthermore, the mass ratio of the potassium permanganate to the sulfur-containing carbon nanotubes is 1:2-6; the mass ratio of the acidified oxide to the modified carbon nanotubes is 0.2-1:1.

[0006] Furthermore, the copper salt and manganese salt are one or more of acetate, oxalate, and formate; and the molar ratio of the copper salt to the manganese salt is 1:3-6.

[0007] Further, the following steps are included:

[0008] a. Preparation of sulfur-containing carbon nanotubes: Prepare a potassium permanganate solution, then add the sulfur-containing carbon nanotubes to the potassium permanganate solution, react at 30-55°C for 1-2 hours, separate and collect the precipitate, wash, and then dry to obtain modified carbon nanotubes;

[0009] b. Mix a copper salt and a manganese salt to prepare a manganese-based oxide; disperse the manganese-based oxide in a dilute hydrochloric acid solution, then soak for 2-6 hours. Collect the precipitate and wash it several times with dilute hydrochloric acid to obtain an acidified oxide;

[0010] c. Grind the acidified oxide and the modified carbon nanotubes into powder in water, mix and disperse them, and stir at a low speed for 0.5-2 hours. Add dilute ammonia solution dropwise to adjust the system to neutrality. Continue stirring at a low speed for 0.5-1 hour, then raise the temperature to a slight boil and maintain it for 20-40 minutes. Add a binder during the boiling process, stop heating, mix thoroughly, and then form a film to obtain a composite flexible electrode material.

[0011] Furthermore, the carbon nanotubes are dispersed in dichloromethane, and then chlorosulfonic acid is added, and the reaction is stirred at 0-10°C for 1.5-2.5 hours, and then stirred at room temperature until the system reaches room temperature, and stirring is continued for 0.5-1 hour; the precipitate is separated and collected, washed and dried to obtain sulfur-containing carbon nanotubes.

[0012] Furthermore, the mass ratio of the carbon nanotubes to chlorosulfonic acid is 1:0.2-1.

[0013] Furthermore, copper salt, manganese salt and potassium nitrate are placed in water, ammonia water is slowly added dropwise until the system is clarified, mixed and evaporated to dryness, and then calcined at 700-850°C for 8-16 hours to obtain manganese-based oxide.

[0014] Furthermore, the molar ratio of the manganese salt to potassium nitrate is 1:0.5-1.2.

[0015] Furthermore, the low-speed stirring speed in step c is 100-200 rpm; and the binder in step c is polyvinylidene fluoride or carboxymethyl cellulose.

[0016] A composite flexible electrode material prepared by the above method.

[0017] By adopting the above scheme, the method of the present invention has the following advantages:

[0018] 1. The carbon nanotubes and active materials of the composite flexible electrode of the present invention have good dispersion. The manganese-based oxide active material is nanoscale, uniform in size, has a high specific surface area, has many active sites, and is tightly connected to the carbon nanotubes, resulting in good electrochemical performance.

[0019] 2. The present invention uses potassium permanganate to directly generate manganese dioxide on carbon nanotubes, which not only improves the conductivity of the material, but also protects the manganese dioxide, alleviates the direct contact between the electrolyte and the active material, and provides manganese dioxide materials with various exposure levels with manganese-based oxides, thereby improving the cycle stability of the electrode.

[0020] 3. The present invention introduces sulfonic acid groups into carbon nanotubes to increase the hydrophilicity of carbon nanotubes, thereby improving their dispersibility and adsorption in the reaction system. It can also increase the pores and improve the binding stability between carbon nanotubes and active materials. The multiple lone pairs of electrons in sulfur atoms are beneficial to improving the conductivity and capacity of the material.

[0021] 4. The sulfonic acid groups introduced into the carbon nanotubes of the present invention, under the action of ammonia, produce complexation and electrostatic interaction with the partially ionized copper ions in the manganese-based oxide, forming electrostatic attraction with the manganese-based oxide, thereby promoting the dispersion and combination of the carbon nanotubes and the manganese-based oxide and reducing the agglomeration of the raw materials.

[0022] 5. The present invention utilizes easily removable ammonia water to react with the acidified manganese-based oxide, reacts with the hydrogen ions in the manganese-based oxide, and then heat treats to remove ammonia, thereby promoting the miniaturization of manganese-based oxide particles and increasing the specific surface area and active sites of the manganese-based oxide.

[0023] 6. The present invention dopes copper into manganese-based oxides. Part of the copper is released from the structure under the action of ammonia and sulfonic acid, promoting the nano-sizing of the manganese-based oxides. The copper atoms remaining in the structure can increase the number of active sites, improve the ion transfer / electron transfer efficiency, reduce the energy band of manganese dioxide, enhance the conductivity, and improve the capacitance performance of the material.

[0024] 7. The preparation method of the present invention is simple, the raw materials are easily available, and the active substances in the prepared positive electrode material have good dispersibility, good flexibility, high specific capacity, and good cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a scanning electron microscope image of Example 1;

[0026] Figure 2 The battery prepared by the electrode material of Example 1 is at 2A·g -1 Specific capacity curve of long cycle charge and discharge under current density;

[0027] Figure 3 The battery prepared by the electrode material of Example 2 is 2A·g -1 Specific capacity curve of long cycle charge and discharge under current density;

[0028] Figure 4 The battery prepared by the electrode material of Comparative Example 1 was -1Specific capacity curve of long cycle charge and discharge under current density;

[0029] Figure 5 The battery prepared by the electrode material of Comparative Example 2 was -1 Specific capacity curve of long cycle charge and discharge under current density. DETAILED DESCRIPTION

[0030] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0031] Example 1: (1) 1 g of carbon nanotubes was fully dispersed in dichloromethane, and then 0.6 g of chlorosulfonic acid was added, and the mixture was stirred at 5°C for 2 h, and then stirred at room temperature until the system reached room temperature, and the stirring was continued for 1 h; the precipitate was separated and collected, and then washed thoroughly and dried to obtain sulfur-containing carbon nanotubes; 250 mg of potassium permanganate was taken to prepare a potassium permanganate solution, and then 1 g of sulfur-containing carbon nanotubes was added to the potassium permanganate solution, and the mixture was reacted at 45°C for 1.5 h, and the precipitate was separated and collected, and then washed thoroughly and dried to obtain modified carbon nanotubes;

[0032] (2) 0.5 g of copper oxalate, 2 g of manganese oxalate, and 1.2 g of potassium nitrate were placed in water, and ammonia water was slowly added dropwise until the system was clear. After thorough mixing, the mixture was evaporated to dryness. The mixture was then calcined at 750°C for 12 h to obtain a manganese-based oxide. The manganese-based oxide was placed in a 0.5 mol / L dilute hydrochloric acid solution and fully dispersed. The mixture was then soaked for 4 h, and the precipitate was collected and washed several times with dilute hydrochloric acid to obtain an acidified oxide.

[0033] (3) Grind 0.6 g of the acidified oxide and place it in water with 1 g of modified carbon nanotubes, mix and disperse them thoroughly, and stir at 150 rpm for 1 h. Add dilute ammonia water to adjust the system to neutrality, continue stirring for 0.5 to 1 h, and then heat it to a slight boil and maintain it for 30 min. During the boiling process, add 20 mL of 10% (w / w) polyvinylidene fluoride solution. After the addition is complete, stop heating and mix well to obtain a mixed solution.

[0034] (4) Cut 40 cm 2 Place the dust-free filter cloth in the funnel, ensuring that it fits the funnel wall completely without bubbles. Slowly pour 50 mL of the mixed solution into the funnel, turn on the pump to filter, and filter the mixed solution onto the dust-free filter cloth. After drying, remove the formed film from the dust-free filter cloth to obtain a composite flexible electrode material.

[0035] The obtained samples were characterized and the Figure 1As shown in the scanning electron microscope photo, it can be seen that the active particles are evenly distributed between the carbon nanotubes, and the particle size is extremely small, and they are all nanoparticles.

[0036] The obtained electrode material has excellent flexibility and can be bent well or even folded in half.

[0037] Example 2: (1) 1 g of carbon nanotubes was fully dispersed in dichloromethane, and then 0.6 g of chlorosulfonic acid was added, and the mixture was stirred at 5°C for 2 h, and then stirred at room temperature until the system reached room temperature, and the stirring was continued for 1 h; the precipitate was separated and collected, and then washed thoroughly and dried to obtain sulfur-containing carbon nanotubes; 170 mg of potassium permanganate was taken to prepare a potassium permanganate solution, and then 1 g of sulfur-containing carbon nanotubes was added to the potassium permanganate solution, and the mixture was reacted at 45°C for 1.5 h, and the precipitate was separated and collected, and then washed thoroughly and dried to obtain modified carbon nanotubes;

[0038] (2) 0.5 g of copper oxalate, 2 g of manganese oxalate, and 1.2 g of potassium nitrate were placed in water, and ammonia water was slowly added dropwise until the system was clear. After thorough mixing, the mixture was evaporated to dryness. The mixture was then calcined at 800 °C for 8 h to obtain a manganese-based oxide. The manganese-based oxide was placed in a 0.5 mol / L dilute hydrochloric acid solution and fully dispersed. The mixture was then soaked for 2 h, and the precipitate was collected and washed with dilute hydrochloric acid several times to obtain an acidified oxide.

[0039] (3) Grind 0.6 g of the acidified oxide and place it in water with 0.6 g of modified carbon nanotubes, mix and disperse them thoroughly, and stir at 150 rpm for 1 h; add dilute ammonia water to adjust the system to neutrality, continue stirring for 0.5-1 h, then heat it to a slight boil and maintain it for 30 min; add 20 mL of 10% (w / w) polyvinylidene fluoride solution during the boiling process, stop heating after addition, and mix evenly to obtain a mixed solution;

[0040] (4) Cut 40 cm 2 Place the dust-free filter cloth in the funnel, ensuring that it fits the funnel wall completely without bubbles. Slowly pour 50 mL of the mixed solution into the funnel, turn on the pump to filter, and filter the mixed solution onto the dust-free filter cloth. After drying, remove the formed film from the dust-free filter cloth to obtain a composite flexible electrode material.

[0041] Example 3: (1) 1 g of carbon nanotubes was fully dispersed in dichloromethane, and then 0.6 g of chlorosulfonic acid was added, and the mixture was stirred at 5°C for 2 h, and then stirred at room temperature until the system reached room temperature, and the stirring was continued for 1 h; the precipitate was separated and collected, and then washed thoroughly and dried to obtain sulfur-containing carbon nanotubes; 450 mg of potassium permanganate was taken to prepare a potassium permanganate solution, and then 1 g of sulfur-containing carbon nanotubes was added to the potassium permanganate solution, and the mixture was reacted at 55°C for 1 h, and the precipitate was separated and collected, and then washed thoroughly and dried to obtain modified carbon nanotubes;

[0042] (2) 0.5 g of copper oxalate, 2 g of manganese oxalate, and 1.2 g of potassium nitrate were placed in water, and ammonia water was slowly added dropwise until the system was clear. After thorough mixing, the mixture was evaporated to dryness. The mixture was then calcined at 750°C for 12 h to obtain a manganese-based oxide. The manganese-based oxide was placed in a 0.5 mol / L dilute hydrochloric acid solution and thoroughly dispersed. The mixture was then soaked for 6 h, and the precipitate was collected and washed several times with dilute hydrochloric acid to obtain an acidified oxide.

[0043] (3) Grind 0.6 g of the acidified oxide and place it in water with 1.5 g of modified carbon nanotubes, mix and disperse them thoroughly, and stir at 150 rpm for 1 h. Add dilute ammonia water to adjust the system to neutrality, continue stirring for 0.5 to 1 h, and then heat it to a slight boil and maintain it for 30 min. Add 20 mL of 10% (w / w) polyvinylidene fluoride solution during the boiling process. After the addition is complete, stop heating and mix well to obtain a mixed solution.

[0044] (4) Cut 40 cm 2 Place the dust-free filter cloth in the funnel, ensuring that it fits the funnel wall completely without bubbles. Slowly pour 50 mL of the mixed solution into the funnel, turn on the pump to filter, and filter the mixed solution onto the dust-free filter cloth. After drying, remove the formed film from the dust-free filter cloth to obtain a composite flexible electrode material.

[0045] Comparative Example 1: The difference from Example 1 is:

[0046] (1) Disperse 1 g of carbon nanotubes in dichloromethane, then add 0.6 g of chlorosulfonic acid, stir and react at 5 °C for 2 h, then stir at room temperature until the system reaches room temperature, and continue stirring for 1 h; separate and collect the precipitate, wash it thoroughly, and then dry it to obtain modified carbon nanotubes.

[0047] Comparative Example 2: The difference from Example 1 is:

[0048] (1) Prepare potassium permanganate solution with 250 mg of potassium permanganate, then add 1 g of carbon nanotubes to the potassium permanganate solution and react at 30-55 °C for 1-2 h. Separate and collect the precipitate, wash it thoroughly, and then dry it to obtain modified carbon nanotubes.

[0049] Comparative Example 3: The difference from Example 1 is:

[0050] (2) 0.5 g of copper oxalate, 2 g of manganese oxalate, and 1.2 g of potassium nitrate were placed in water, and ammonia water was slowly added dropwise until the system was clear. After thorough mixing, the mixture was evaporated to dryness. The mixture was then calcined at 750 °C for 12 h to obtain a manganese-based oxide.

[0051] (3) Grind 0.6 g of manganese-based oxide and place it in water with 1 g of modified carbon nanotubes, mix and disperse them thoroughly, and stir at 100-200 rpm for 0.5-2 h. Then, heat the system to a slight boil and add 20 mL of 10% (w / w) polyvinylidene fluoride solution. After adding, stop heating and mix evenly to obtain a mixed solution.

[0052] The active substance of the composite flexible electrode material prepared in Comparative Example 3 has poor affinity with the modified carbon nanotubes, low dispersion, and relatively large particles of manganese-based oxide, which are only micron particles.

[0053] Electrochemical performance test:

[0054] The flexible positive electrode materials prepared in Example 1, Example 2, and Comparative Examples 1 and 2 were used as positive electrodes, Zn sheets were used as negative electrodes, 1M zinc sulfate aqueous solution was used as electrolyte, and glass fiber separators were used as separators to assemble button-type zinc ion batteries. The button-type zinc ion batteries were tested for their specific capacity over a long cycle of 300 cycles at a current density of 2 A / g in the voltage range of 1.0-1.8 V to evaluate the electrochemical performance of the electrode materials of the present invention. The test results are shown in Figure 2. Figures 2 to 5 shown.

[0055] Depend on Figure 2 It can be seen that under high current, the initial discharge specific capacity of the electrode material of Example 1 of the present invention is around 80 mAh / g. At 300 cycles, the discharge specific capacity exceeds 100 mAh / g, which is higher than the initial value. After 400 cycles, it can still maintain a specific capacity of nearly 80 mAh / g, with a high capacity retention rate, indicating that the electrode material prepared by the present invention has excellent cycling performance. Although there is a significant decrease after 300 cycles, the highest discharge specific capacity can reach 200 mAh / g during the cycling process, indicating that the electrode material of the present invention has many active sites and good capacity potential.

[0056] The amount of potassium permanganate added in Example 2 is less, and the content of modified carbon nanotubes is also reduced. The cycle test results of Example 2 are as follows: Figure 3 As shown. Figure 2 and Figure 3 It can be seen that the initial discharge specific capacity of Comparative Example 1 exceeds 100 mAh / g, but after 300 cycles it can only reach about 80 mAh / g, and the capacity retention ability is not as good as that of Example 1.

[0057] The cycle test results of Comparative Example 1 in which manganese dioxide is not directly generated on carbon nanotubes are as follows: Figure 4 As shown in the figure, it can be seen that after 200 cycles, the specific capacity of the sample has a cliff-like drop, indicating that the direct generation of manganese dioxide on carbon nanotubes has a significant impact on the cycle stability of the battery and the capacity retention ability in the later stage of the cycle.

[0058] The cycle test results of Comparative Example 2 without sulfonic acid modification are as follows: Figure 5 As shown in the figure, it can be seen that the coulombic efficiency of the sample of Comparative Example 2 fluctuates greatly, and the coulombic efficiency is low, the charge and discharge energy loss is large, the charge transfer efficiency is low, and the activity of the electrode material decreases rapidly, indicating that the step of sulfonic acid modification is beneficial to promote the full contact between carbon nanotubes and manganese-based oxides, reduce the accumulation of materials, and have a significant effect on improving the performance of the electrode material.

[0059] Those skilled in the art can make various other corresponding changes and deformations based on the technical solutions and concepts described above, and all of these changes and deformations should fall within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a composite flexible electrode material, characterized in that: The following steps are involved: The carbon nanotubes are modified with sulfonic acid to add sulfur-containing groups on their surface to obtain sulfur-containing carbon nanotubes; then, potassium permanganate is used to modify the carbon nanotubes with manganese, and manganese dioxide is directly generated on the carbon nanotubes by potassium permanganate to obtain modified carbon nanotubes; Mixing copper salt and manganese salt to prepare manganese-based oxide; treating the manganese-based oxide with acid to obtain an acidified oxide; mixing the acidified oxide with modified carbon nanotubes, adding dilute ammonia water to fully react, and then heat treating; After film formation, a composite flexible electrode material is obtained.

2. The method for preparing a composite flexible electrode material according to claim 1, characterized in that: The mass ratio of the potassium permanganate to the sulfur-containing carbon nanotubes is 1:2-6; the mass ratio of the acidified oxide to the modified carbon nanotubes is 0.2-1:

1.

3. The method for preparing a composite flexible electrode material according to claim 1, wherein: The copper salt and manganese salt are one or more of acetate, oxalate, and formate; and the molar ratio of the copper salt to the manganese salt is 1:3-6.

4. The method for preparing a composite flexible electrode material according to claim 3, wherein: The following steps are involved: a. Preparation of sulfur-containing carbon nanotubes: Prepare a potassium permanganate solution, then add the sulfur-containing carbon nanotubes to the potassium permanganate solution and react at 30-55°C for 1-2 hours. Separate and collect the precipitate, thoroughly wash it, and then dry it to obtain the modified carbon nanotubes. b. Mix a copper salt and a manganese salt to prepare a manganese-based oxide; fully disperse the manganese-based oxide in a dilute hydrochloric acid solution, then soak for 2-6 hours. Collect the precipitate and wash it several times with dilute hydrochloric acid to obtain an acidified oxide; c. Grind the acidified oxide and the modified carbon nanotubes into powder in water, thoroughly mix and disperse them, and stir at a low speed for 0.5-2 hours. Add dilute ammonia solution dropwise to adjust the system to neutrality, continue stirring at a low speed for 0.5-1 hour, then raise the temperature to a slight boil and maintain it for 20-40 minutes. Add the binder during the boiling process, stop heating, mix thoroughly, and then form a physical film to obtain a composite flexible electrode material.

5. The method for preparing a composite flexible electrode material according to claim 1 or 4, characterized in that: The carbon nanotubes are fully dispersed in dichloromethane, and then chlorosulfonic acid is added. The reaction is stirred at 0-10°C for 1.5-2.5 hours, and then stirred at room temperature until the system reaches room temperature, and stirring is continued for 0.5-1 hour. The precipitate is separated and collected, fully washed, and then dried to obtain sulfur-containing carbon nanotubes.

6. The method for preparing a composite flexible electrode material according to claim 5, characterized in that: The mass ratio of the carbon nanotubes to chlorosulfonic acid is 1:0.2-1.

7. The method for preparing a composite flexible electrode material according to claim 4, characterized in that: Copper salt, manganese salt and potassium nitrate are placed in water, and ammonia water is slowly added dropwise until the system is clear. After thorough mixing, the mixture is evaporated to dryness, and then calcined at 700-850°C for 8-16 hours to obtain manganese-based oxide.

8. The method for preparing a composite flexible electrode material according to claim 7, characterized in that: The molar ratio of the manganese salt to potassium nitrate is 1:0.5-1.

2.

9. The method for preparing a composite flexible electrode material according to claim 8, characterized in that: The low-speed stirring speed in step c is 100-200 rpm; the binder in step c is polyvinylidene fluoride or carboxymethyl cellulose.

10. A composite flexible electrode material prepared by the method according to claim 1.

Images