Preparation method of self-sacrifice pore-forming binder modified capacitor carbon electrode

Abstract

The invention discloses a preparation method of a self-sacrifice pore-forming binder modified capacitor carbon electrode, a process flow is specifically designed, sodium carboxymethyl cellulose is used as a pore-forming binder, pore-forming and bonding are integrated, the sodium carboxymethyl cellulose exists as a binder at the initial stage, and the sodium carboxymethyl cellulose serves as a pore-forming agent at the post-treatment stage of the electrode, so that the self-sacrifice pore-forming binder modified capacitor carbon electrode is prepared. Volatile small molecules generated by heating can properly expand and communicate pores of the carbon material, electrolyte can fully enter the pore structure due to existence of a proper mesoporous size, the effective specific surface area is increased, the effective adsorption area is increased, the ion transmission path and resistance are reduced, and the rate capability and the capacitance performance of the capacitor are improved.

Description

Technical Field

[0001] This invention relates to the field of capacitor device technology, and specifically to a method for preparing a self-sacrificing pore-forming binder modified capacitor carbon electrode. Background Technology

[0002] In supercapacitors, the energy storage mechanism is the accumulation of particle charge at the electrode / electrolyte interface. The pores of carbon materials provide abundant adsorption sites for ions, and their extremely high specific surface area allows electrolyte ions to fully enter the pores, contributing to increased capacity. However, when the specific surface area increases to a certain extent (>1500 m²), the capacity becomes limited. 2 The narrow and deep pores not only hinder particle transport but also limit the space for charge storage within the pore walls, leading to a decrease in capacitance performance, which needs to be improved. Summary of the Invention

[0003] To address at least one of the aforementioned technical deficiencies, the present invention provides the following technical solution: This invention discloses a method for preparing a self-sacrificing pore-forming binder modified capacitor carbon electrode, comprising the following steps: Step 1: By weight, mix 78-85 parts of activated carbon, 8-12 parts of conductive agent, 5-8 parts of binder, 3-5 parts of pore-forming binder and solvent, heat to 40-60℃ and stir continuously to obtain mixture A, wherein the pore-forming binder is sodium carboxymethyl cellulose. Step 2: Add anhydrous ethanol dropwise to mixture A to obtain mixture B; Step 3: Compress mixture B into tablets and dry them; Step 4: Place the sheet obtained in Step 3 in a sealed container and keep it under inert gas protection for 60-150 minutes. Then raise the temperature to 150-450℃ and keep it at that temperature for 1-6 hours to carbonize it. Then cool it down to room temperature. Step 5: After rinsing and drying the sheet obtained in Step 4, attach it to the current collector plate and dry it again to obtain the desired carbon electrode.

[0004] Sodium carboxymethyl cellulose is a water-soluble cellulose ether obtained by chemical modification of natural cellulose. It has adhesive properties and is relatively stable to heat, but carbon-carbon bonds break at 240-400℃, generating volatile small molecules such as CO (decarboxylation), CO2 (ring cracking), H2O (dehydration), and CH4, which are short-chain hydrocarbons.

[0005] In supercapacitors, the energy storage mechanism is the accumulation of particle charge at the electrode / electrolyte interface. The pores of carbon materials provide abundant adsorption sites for ions, and their extremely high specific surface area allows electrolyte ions to fully enter the pores, contributing to increased capacity. However, when the specific surface area increases to a certain extent (>1500 m²), the capacity becomes limited.2 / g), the narrow and deep channels not only hinder particle transport, but also limit the space for charge to be contained within the pore walls, leading to a decrease in capacitance performance.

[0006] In response, this solution employs a targeted process design, using sodium carboxymethyl cellulose as a pore-forming binder, integrating pore-forming and bonding functions. Initially, it functions as a binder, and later as a pore-forming agent during the electrode post-treatment stage. The volatile small molecules generated upon heating can appropriately expand and connect the pores of the carbon material. The presence of appropriate mesopore size allows the electrolyte to fully penetrate the pore structure, increasing the effective specific surface area, increasing the effective adsorption area, reducing ion transport paths and resistance, and improving the rate performance and capacitance of the capacitor.

[0007] Furthermore, in step one, activated carbon, conductive agent, and binder are first mixed. The pore-forming binder is dissolved in an alcohol solvent to a concentration of 0.5-5%, and stirred at 30-70°C for 30-180 minutes to obtain a pore-forming binder solution. Then, the pore-forming binder solution is mixed with the mixture of activated carbon, conductive agent, and binder, and then the solvent is added. Under the limited mixing process, it helps to improve the uniformity of the mixing of each component.

[0008] Furthermore, in step one, the solvent is N-methylpyrrolidone or anhydrous ethanol, and the amount of solvent added is 10-25 parts by mass.

[0009] Furthermore, in step one, the conductive agent is one or more of carbon black, graphite powder, carbon nanotubes, or graphene, the binder is polytetrafluoroethylene or polyvinylidene fluoride, and the alcohol solvent is anhydrous ethanol.

[0010] Furthermore, in step two, the anhydrous ethanol added is 1-10% of the mass of mixture A by weight.

[0011] Furthermore, in step three, the pressing pressure is 15-30 MPa, and the drying process is vacuum drying at 35-60℃ for 4-10 hours.

[0012] Furthermore, in step five, the sheet obtained in step four is rinsed with clean water, vacuum dried at 45-70°C for at least 6 hours, rinsed with clean water to remove impurities, and dried to remove moisture to avoid affecting subsequent processes.

[0013] Furthermore, in step five, conductive adhesive is applied to the current collector, and then the sheet obtained in step four after rinsing and drying is attached; wherein, the conductive adhesive is any one of carbon-based conductive adhesive, silver-based conductive adhesive, gold-based conductive adhesive or copper-based conductive adhesive, and the current collector is a metal current collector or a carbon current collector.

[0014] Furthermore, the carbonization conditions in step four are as follows: a heating rate of 3-6℃ / min and a pressure of 0.5-5MPa in a sealed container. Limiting the heating rate and pressure helps to improve the degree of activation.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention introduces sodium carboxymethyl cellulose (CMC) into the preparation of carbon electrodes for supercapacitors. Through a relatively simple, controllable, and economical method, starting with the microstructure design of the electrode, it effectively reconciles the contradiction between high capacitance due to high specific surface area and the requirement for rapid ion transport. It overcomes the problems of numerous blind and closed pores and long, complex ion transport paths in traditional electrodes. By generating gas through the thermal decomposition of CMC, microchannels are formed in situ inside the electrode, constructing a more open and interconnected three-dimensional pore network, shortening the ion diffusion distance. The introduction of appropriately sized mesopores allows electrolyte ions to fully enter the pore structure, increasing the effective specific surface area, reducing ion transport resistance, and thus improving the rate performance of the capacitor. Simultaneously, this method integrates pore-forming and electrode preparation steps, eliminating the need for complex post-processing template removal, simplifying the process, and potentially reducing production costs. As a water-soluble polymer derived from natural cellulose, the use of CMC conforms to green chemistry principles and provides a pathway for the high-value utilization of biomass resources.

[0016] 2. The electrodes prepared by this invention can significantly improve the energy density of the device without sacrificing its power characteristics. They can be applied in scenarios that require high power density and fast charging and discharging capabilities, such as energy recovery systems for urban public transportation, starting power supplies for heavy machinery, and frequency regulation devices for smart grids. Detailed Implementation

[0017] The present invention will be further described below with reference to specific embodiments.

[0018] Activated carbon is passed through a 300-mesh sieve and dried at 60°C for 12 hours for later use; the conductive agent is carbon black or graphene; the binder is PVDF (polyvinylidene fluoride) or PTFE (polytetrafluoroethylene); the pore-forming binder is sodium carboxymethyl cellulose; the solvent is anhydrous ethanol; the current collector is a carbon current collector; and the conductive adhesive is silver-based conductive adhesive 503.

[0019] Example 1 A method for preparing a self-sacrificing pore-forming binder modified capacitor carbon electrode includes the following steps: Step 1: Weigh out 85 parts of dried activated carbon, 8 parts of conductive agent (carbon black), 5 parts of binder (PVDF), 3 parts of pore-forming binder, and 10 parts of solvent according to the mass fraction. Mix the activated carbon, conductive agent, and binder, and grind them into powder using a ball mill. Dissolve the pore-forming binder in anhydrous ethanol to a concentration of 0.5%, and stir at 60°C for 90 minutes to obtain a pore-forming binder solution. Mix the powder mixture obtained from the activated carbon, conductive agent, and binder with the pore-forming binder solution, then add the solvent and heat to 60°C, stirring until a large amount of solvent evaporates to obtain a viscous mixture A.

[0020] Step 2: Add anhydrous ethanol dropwise to mixture A to obtain mixture B. The mass of the anhydrous ethanol added is 4% of the mass of mixture A.

[0021] Step 3: Press mixture B into tablets using a tablet press at 20 MPa and vacuum dry at 60°C for 6 hours; place the pressed tablets into a sealed container and introduce excess inert gas (argon) into the sealed container, and then maintain the inert atmosphere for 60 minutes; continue to maintain the inert atmosphere in the reactor, and then raise the temperature to 350°C at a rate of 5°C / min, maintain the pressure inside the sealed container at 1.5 MPa, hold for 2 hours, and then cool down to room temperature.

[0022] Step 4: Remove the sheet from the sealed container, rinse it with plenty of water, vacuum dry it at 60°C for 6 hours, then attach it to a current collector coated with conductive adhesive, and vacuum dry it to carbonize it, thus obtaining the desired carbon electrode.

[0023] The obtained carbon electrode was tested and found to have the following properties: specific capacitance (1 A / g): 198 F / g, internal resistance: 1.6 Ω·cm², rate performance (capacity retention at 10 A / g): 84%, and cycle stability (capacity retention after 5000 cycles): 94%.

[0024] Example 2 Compared with Example 1, the difference is that: 78 parts activated carbon, 12 parts conductive agent (carbon black), 5 parts binder (PVDF), and 3 parts pore-forming adhesive (CMC); the carbonization temperature in the sealed container in step four is 250°C, and the temperature is maintained for 3.5 hours.

[0025] The obtained carbon electrode was tested and found to have the following properties: specific capacitance: 188 F / g, internal resistance: 1.3 Ω·cm², rate performance: 87%, and cycle stability: 95%.

[0026] Example 3 Compared with Example 1, the difference is that: 80 parts activated carbon, 12 parts conductive agent (carbon black), 5 parts binder (PVDF), and 3 parts pore-forming adhesive (CMC); the carbonization temperature in the sealed container in step four is 280°C, and the temperature is maintained for 3 hours.

[0027] The obtained carbon electrode was tested and found to have the following properties: specific capacitance: 195 F / g, internal resistance: 1.0 Ω·cm², rate performance: 90%, and cycle stability: 96%.

[0028] Example 4 Compared with Example 1, the difference is that: 80 parts activated carbon, 8 parts conductive agent (carbon black), 8 parts binder (PVDF), and 4 parts pore-forming adhesive (CMC); the carbonization temperature in the sealed container in step four is 300°C, and the temperature is maintained for 3 hours.

[0029] The obtained carbon electrode was tested and found to have the following properties: specific capacitance: 185 F / g, internal resistance: 1.7 Ω·cm², rate performance: 82%, and cycle stability: 98%.

[0030] Example 5 Compared with Example 1, the difference is that: 80 parts activated carbon, 8 parts conductive agent (carbon black), 5 parts binder (PVDF), and 5 parts pore-forming adhesive (CMC); the carbonization temperature in the sealed container in step four is 300°C, and the temperature is maintained for 3 hours.

[0031] The obtained carbon electrode was tested and found to have the following properties: specific capacitance: 205 F / g, internal resistance: 1.2 Ω·cm², rate performance: 88%, and cycle stability: 93%.

[0032] Example 6 Compared with Example 1, the difference is that: 80 parts activated carbon, 8 parts conductive agent (carbon black), 8 parts binder (PVDF), and 4 parts pore-forming adhesive (CMC); the carbonization temperature in the sealed container in step four is 200°C, and the temperature is maintained for 3 hours.

[0033] The obtained carbon electrode was tested and found to have the following properties: specific capacitance: 175 F / g, internal resistance: 12.2 Ω·cm², rate performance: 80%, and cycle stability: 92%.

[0034] Example 7 Compared with Example 1, the difference is that: 80 parts activated carbon, 8 parts conductive agent (carbon black), 8 parts binder (PVDF), and 4 parts pore-forming adhesive (CMC); the carbonization temperature in the sealed container in step four is 350°C, and the temperature is maintained for 4 hours.

[0035] The obtained carbon electrode was tested and found to have the following properties: specific capacitance: 215 F / g, internal resistance: 1.0 Ω·cm², rate performance: 90%, and cycle stability: 97%.

[0036] Example 8 Compared with Example 1, the difference is that: 80 parts activated carbon, 8 parts conductive agent (carbon black), 8 parts binder (PVDF), and 4 parts pore-forming adhesive (CMC); the carbonization temperature in the sealed container in step four is 450°C, and the temperature is maintained for 4 hours.

[0037] The obtained carbon electrode was tested and found to have the following properties: specific capacitance: 218 F / g, internal resistance: 1.1 Ω·cm², rate performance: 89%, and cycle stability: 94%.

[0038] Example 9 Compared with Example 1, the difference is that: 85 parts activated carbon, 8 parts conductive agent (carbon black), 8 parts binder (PVDF), and 4 parts pore-forming adhesive (CMC); the carbonization temperature in the sealed container in step four is 300°C, and the temperature is maintained for 2 hours.

[0039] The obtained carbon electrode was tested and found to have the following properties: specific capacitance: 195 F / g, internal resistance: 1.3 Ω·cm², rate performance: 89%, and cycle stability: 93%.

[0040] Example 10 Compared with Example 1, the difference is that: 85 parts activated carbon, 8 parts conductive agent (carbon black), 5 parts binder (PVDF), and 3 parts pore-forming adhesive (CMC); the carbonization temperature in the sealed container in step four is 350°C, and the temperature is maintained for 6 hours.

[0041] The obtained carbon electrode was tested and found to have the following properties: specific capacitance: 225 F / g, internal resistance: 0.9 Ω·cm², rate performance: 92%, and cycle stability: 96%.

[0042] Example 11 Compared with Example 1, the difference is that: 80 parts activated carbon, 8 parts conductive agent (graphene), 8 parts binder (PVDF), and 4 parts pore-forming adhesive (CMC); the carbonization temperature in the sealed container in step four is 350°C, and the temperature is maintained for 3 hours.

[0043] The obtained carbon electrode was tested and found to have the following properties: specific capacitance: 235 F / g, internal resistance: 0.7 Ω·cm², rate performance: 95%, and cycle stability: 96%.

[0044] Example 12 Compared with Example 1, the difference is that: 80 parts activated carbon, 8 parts conductive agent (carbon black), 8 parts binder (PTFE), and 4 parts pore-forming adhesive (CMC); the carbonization temperature in the sealed container in step four is 350°C, and the temperature is maintained for 3.5 hours.

[0045] The obtained carbon electrode was tested and found to have the following properties: specific capacitance: 198 F / g, internal resistance: 1.3 Ω·cm², rate performance: 85%, and cycle stability: 98%.

[0046] Comparative Example 1 The difference compared to Example 1 is that no pore-forming adhesive is added.

[0047] The obtained carbon electrode was tested and found to have the following properties: specific capacitance: 128 F / g, internal resistance: 3.5 Ω·cm², rate performance: 59%, and cycle stability: 85%.

[0048] Comparative Example 2 Compared with Example 1, the difference is that the pore-forming adhesive is replaced with the traditional pore-forming agent - NH4HCO3.

[0049] The obtained carbon electrode was tested and found to have the following properties: specific capacitance: 165 F / g, internal resistance: 2.8 Ω·cm², rate performance: 72%, and cycle stability: 88%.

[0050] Comparative Example 3 The difference compared to Example 1 is that the carbonization temperature in step four is 600°C.

[0051] The obtained carbon electrode was tested and found to have the following properties: specific capacitance: 180 F / g, internal resistance: 2.0 Ω·cm², rate performance: 78%, and cycle stability: 90%.

[0052] Comparative Example 4 The difference from Example 1 is that the adhesive used is epoxy resin.

[0053] The obtained carbon electrode was tested and found to have the following properties: specific capacitance: 135 F / g, internal resistance: 3.2 Ω·cm², rate performance: 62%, and cycle stability: 82%.

[0054] Comparative Example 5 The difference compared to Example 1 is that step four is omitted.

[0055] The obtained carbon electrode was tested and found to have the following properties: specific capacitance: 110 F / g, internal resistance: 4.0 Ω·cm², rate performance: 55%, and cycle stability: 80%.

[0056] It can be seen that the core function of sodium carboxymethyl cellulose (CMC) is to form secondary pores inside the electrode by producing small molecules from its decomposition, which can significantly improve specific capacitance and ion transport efficiency. The optimal range for carbonization is 150–450℃, with a holding time of 1–6 hours; excessively high temperatures will lead to structural collapse.

[0057] The specific capacitance of Examples 1-5 and Examples 7-12 is significantly better than that of Comparative Examples 1-5, demonstrating the effectiveness of the self-sacrificing pore-forming strategy. Compared with Example 6, Comparative Example 3 shows that increasing the carbonization temperature can partially improve the specific capacitance, but at the same time it will reduce the rate performance, while a lower carbonization temperature will lead to an increase in internal resistance.

[0058] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principle of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a self-sacrificing pore-forming binder modified capacitor carbon electrode, characterized in that, Includes the following steps: Step 1: By weight, mix 78-85 parts of activated carbon, 8-12 parts of conductive agent, 5-8 parts of binder, 3-5 parts of pore-forming binder and solvent, heat to 40-60℃ and stir continuously to obtain mixture A, wherein the pore-forming binder is sodium carboxymethyl cellulose. Step 2: Add anhydrous ethanol dropwise to mixture A to obtain mixture B; Step 3: Compress mixture B into tablets and dry them; Step 4: Place the sheet obtained in Step 3 in a sealed container and keep it under inert gas protection for 60-150 minutes. Then raise the temperature to 150-450℃ and keep it at that temperature for 1-6 hours to carbonize it. Then cool it down to room temperature. Step 5: After rinsing and drying the sheet obtained in Step 4, attach it to the current collector plate and dry it again to obtain the desired carbon electrode.

2. The method for preparing a self-sacrificing pore-forming binder modified capacitor carbon electrode as described in claim 1, characterized in that: In step one, activated carbon, conductive agent, and binder are first mixed. The pore-forming binder is dissolved in an alcohol solvent to a concentration of 0.5-5%, and stirred at 30-70℃ for 30-180 minutes to obtain a pore-forming binder solution. Then, the pore-forming binder solution is mixed with the mixture of activated carbon, conductive agent, and binder, and then the solvent is added.

3. The method for preparing a self-sacrificing pore-forming binder modified capacitor carbon electrode as described in claim 2, characterized in that: In step one, the solvent is N-methylpyrrolidone or anhydrous ethanol, and the amount of solvent added is 10-25 parts by mass.

4. The method for preparing a self-sacrificing pore-forming binder modified capacitor carbon electrode as described in claim 2, characterized in that: In step one, the conductive agent is one or more of carbon black, graphite powder, carbon nanotubes or graphene, the binder is polytetrafluoroethylene or polyvinylidene fluoride, and the alcohol solvent is anhydrous ethanol.

5. The method for preparing a self-sacrificing pore-forming binder modified capacitor carbon electrode as described in claim 1, characterized in that: In step two, the amount of anhydrous ethanol added is 1-10% of the mass of mixture A.

6. The method for preparing a self-sacrificing pore-forming binder modified capacitor carbon electrode as described in claim 1, characterized in that: In step three, the pressing pressure is 15-30 MPa, and the drying process is vacuum drying at 35-60℃ for 4-10 hours.

7. The method for preparing a self-sacrificing pore-forming binder modified capacitor carbon electrode as described in claim 1, characterized in that: In step five, the tablets obtained in step four are rinsed with clean water and then vacuum dried at 45-70°C for at least 6 hours.

8. The method for preparing a self-sacrificing pore-forming binder modified capacitor carbon electrode as described in claim 1, characterized in that: In step five, conductive adhesive is applied to the current collector, and then the sheet obtained in step four after rinsing and drying is attached; wherein, the conductive adhesive is any one of carbon-based conductive adhesive, silver-based conductive adhesive, gold-based conductive adhesive or copper-based conductive adhesive, and the current collector is a metal current collector or a carbon current collector.

9. The method for preparing a self-sacrificing pore-forming binder modified capacitor carbon electrode as described in claim 1, characterized in that: The carbonization conditions in step four are as follows: heating rate of 3-6℃ / min and pressure of 0.5-5MPa in the sealed container.