Lignin-based supercapacitor carbon and preparation method and application thereof

Abstract

This invention discloses a lignin-based supercapacitor carbon, its preparation method, and its applications, aiming to solve the technical problems in existing supercapacitor carbon preparation processes, such as low utilization rate of potassium-based activators, susceptibility to "potassium explosion," poor product purity and electrochemical stability, and high production costs. The method includes the following steps: First, the lignin solvent is purified, then mixed with a binder, water, and an activator to form pellets with uniform structure. The pellets undergo a low-temperature curing-high-temperature activation synergistic treatment to achieve controlled radial slow diffusion of potassium vapor, improving activator utilization, suppressing "potassium explosion," and reducing costs. The activated product is then acid-washed with organic acid and dried to obtain the lignin-based supercapacitor carbon. This invention achieves low-cost, high-purity, and high-stability lignin-based supercapacitor carbon preparation. The process route is simple and controllable, with good environmental compatibility, suitable for large-scale industrial production, and has broad application prospects and significant industrial application value in the field of supercapacitor carbon materials.

Description

Technical Field

[0001] This invention belongs to the field of supercapacitor carbon preparation, specifically relating to a lignin-based supercapacitor carbon, its preparation method, and its application. Background Technology

[0002] Supercapacitors, as a type of energy storage device that combines high power density, long cycle life, and relatively high energy density, have broad application prospects in fields such as new energy vehicles, data storage, and rail transportation.

[0003] Currently, maturely applied supercapacitors primarily rely on the reversible adsorption and desorption of electrolyte ions through the material's pores to achieve energy storage—a double-layer capacitor. Carbon materials, with their advantages of excellent stability, tunable pore structure, and low preparation cost, have become the only electrode material to achieve successful commercial application in the field of double-layer supercapacitors. While my country's demand for supercapacitor carbon has been increasing year by year, it has long been dependent on imports. The current mainstream preparation process for supercapacitor carbon is the KOH activation method, which faces two major bottlenecks:

[0004] (1) The product has poor charge-discharge cycle stability, the core problem being the low purity of the product. During long-term charge-discharge cycles, residual metal ions are prone to undergo Faraday side reactions, causing pore blockage and damaging the stability of the pore wall structure, which in turn significantly reduces the capacitance performance.

[0005] (2) Alkali activation has the risk of "potassium explosion" and strong alkali severely corrodes the equipment, which restricts large-scale production. The reason is that when potassium-containing compounds such as KOH and K2CO3 are used as activators, the potassium vapor generated in the high-temperature activation stage will be converted into potassium metal element during the cooling process. When it comes into contact with air, it will cause the "potassium explosion" phenomenon.

[0006] Therefore, screening suitable biomass raw materials, improving the purity of raw materials and products, optimizing the pellet preparation process, reducing the amount of activator and improving its utilization efficiency, and avoiding potassium metal deposition to solve the "potassium explosion" problem have become the two core objectives that those skilled in the art need to overcome.

[0007] Chinese patent application CN119296990A uses lignite as a carbon source to prepare a series of supercapacitor carbons. However, the amount of KOH activator used is generally as high as 4:1 or more, which significantly increases the production cost. Moreover, after 10,000 charge-discharge cycles, the specific capacitance of this sample decreased to 93.3% of its original value. Chinese patent application CN108163855A uses molten KOH for activation, reducing the alkali ratio from 4:1 to 2:1. However, molten KOH places extremely stringent requirements on the equipment. Taking a common rotary kiln as an example, the nickel alloy liner in contact with the activator at high temperatures will produce severe adhesion, peeling corrosion, and other phenomena, resulting in a significant increase in the nickel content of the product, increased impurities in the supercapacitor carbon, and affected stability. After 10,000 charge-discharge cycles, the capacitance retention rate is only 95%. Chinese patent application CN120709084A uses biomass-based supercapacitor carbon technology, employing walnut shells as the carbon source and a 2:1 alkali-to-carbon ratio. It uses hydrochloric acid for purification, which inevitably introduces chloride ion impurities, significantly reducing cycle life. It can be seen that in current alkali activation methods, the alkali-to-carbon ratio is mainly concentrated around 2:1, inevitably leading to alkali corrosion and potassium explosion problems. Chinese patent CN116573642B uses biomass biochar as raw material, improving efficiency through a "pelletizing-activation" process, but it has two key limitations: First, the carbon spheres have a "spherical shell structure" (carbon source coated with activator). When the binder or mixed carbon powder is dissolved in water, the alkali activator in the sphere core easily dissolves, damaging the sphere morphology and affecting activation uniformity. Second, the mass ratio of activator to carbon source (alkali-to-carbon ratio) can only be reduced to 1:1, making it difficult to reduce costs and failing to avoid equipment corrosion and potassium explosion hazards. Japanese patent application JP 2024103325A uses biomass as raw material and organic polymer (polyvinyl alcohol) as binder for pelletizing and activation. However, it mainly uses a mild physical activation method. Moreover, the patent application aims to improve the particle strength of activated carbon products, but does not focus on purity, cycle stability, or solve the "potassium explosion" problem when the pelletizing method is applied to the alkaline process for producing capacitor carbon. Summary of the Invention

[0008] Addressing the shortcomings of domestically produced supercapacitor carbon production processes (high alkali usage, risk of potassium explosion) and performance (low purity, poor cycle stability), this invention provides a low-alkali pelletizing and activation method. The core innovations are twofold: First, optimized purification process: pre-purification of lignin raw materials and post-treatment with organic acids in the product reduce the content of metallic impurities while avoiding the introduction of anionic impurities, improving the uniformity and purity of raw materials and products, and enhancing the long-term cycle stability of the supercapacitor carbon. Second, low-temperature curing-assisted pelletizing and activation: unlike conventional pelletizing, low-temperature curing first slightly sintersulates the lignin pellets, increasing their strength (reducing process losses); during high-temperature activation, the dense pellets inhibit potassium vapor escape, allowing it to slowly diffuse radially within the pellets and fully etch micropores, achieving efficient utilization of the activator. Ultimately, the KOH to carbon source ratio is reduced to 0.5:1 (only 1 / 4 of the conventional process), significantly reducing costs, and the product's electrochemical performance is significantly superior to commercially available supercapacitor carbon, while simultaneously avoiding the risk of potassium explosion.

[0009] The present invention is achieved through the following technical solution.

[0010] A method for preparing lignin-based supercapacitor carbon includes the following steps:

[0011] Step 1: Mix the adhesive with water and stir until dissolved to obtain an adhesive solution;

[0012] Step 2: Mix the adhesive solution, purified lignin, and activator to form pellets. First, solidify at low temperature in a nitrogen atmosphere, then activate at high temperature. After washing with water and acid to remove impurities, obtain lignin-based supercapacitor carbon until the filtrate is colorless and clear.

[0013] Preferably, the adhesive in step 1 is at least one of polyethylene glycol and polyvinyl alcohol;

[0014] The concentration of the adhesive after dissolution in step 1 is 11~25 wt.%.

[0015] More preferably, the concentration of the adhesive after dissolution in step 1 is 11~16 wt.%.

[0016] Preferably, the activator used in step 2 is one or more of KOH, K2CO3 and KHCO3.

[0017] Preferably, the mass ratio of the activator to the purified lignin in step 2 is 0.5 to 1:1.

[0018] More preferably, the mass ratio of the activator to the purified lignin in step 2 is 0.5:1.

[0019] Preferably, the low-temperature curing temperature in step 2 is 100~120℃ and the time is 4~6h; the high-temperature activation temperature is 700~800℃ and the time is 1~2h.

[0020] More preferably, the low-temperature curing temperature in step 2 is 120°C and the time is 6 hours; the high-temperature activation temperature is 800°C and the time is 2 hours.

[0021] Preferably, in step 2, the pickling uses a compound organic acid, which includes an organic acid and a hydrogen peroxide solution; wherein the organic acid refers to at least one of oxalic acid, citric acid, acetic acid, and ascorbic acid; the concentration of the organic acid in the compound organic acid is 3-10 wt.%, and the concentration of the hydrogen peroxide in the compound organic acid is 2-5 wt.%.

[0022] More preferably, the concentration of the hydrogen peroxide solution is 30 wt.%.

[0023] Preferably, in step 2, after pelleting and mixing, the mass ratio of purified lignin, binder, water and activator is 100:(3~5):25:(50~100).

[0024] Preferably, the nitrogen flow rate in step 2 is 50~100 mL / min.

[0025] Further preferably, the nitrogen flow rate in step 2 is 50 mL / min.

[0026] In step 2, "ball making" refers to preparing the material into pellets.

[0027] Preferably, the diameter of the pellets obtained in step 2 is 0.2~0.5cm.

[0028] More preferably, the diameter of the pellets obtained in step 2 is 0.5 cm.

[0029] The ash content of the purified lignin described in step 2 is less than 0.15 wt.%.

[0030] The purified lignin is obtained by purifying lignin with ammonia and acetone in sequence, followed by drying, pulverizing and sieving.

[0031] The purification process of the lignin is as follows: The lignin raw material is placed in 8-12 wt.% ammonia water for primary purification, with a liquid-to-solid ratio of 4-6 mL:1 g. It is heated at 80-90℃ and 0.3-0.4 MPa for 2-3 hours. After filtering to remove impurities, the filtrate is distilled under reduced pressure and then centrifuged and filtered to obtain primary purified lignin. Subsequently, the primary purified lignin is dissolved in acetone for secondary purification, filtered to remove impurities, and dried to finally obtain secondary purified lignin.

[0032] More preferably, the lignin purification process is as follows: the lignin raw material is placed in 10wt.% ammonia water for primary purification, with a liquid-to-solid ratio of 5 mL / g, heated at 80℃ and 0.3MPa for 2 hours, filtered to remove impurities, and the filtrate is subjected to vacuum distillation, followed by centrifugal filtration to obtain primary purified lignin; subsequently, the primary purified lignin is dissolved in acetone for secondary purification, filtered to remove impurities and dried, finally obtaining secondary purified lignin with an ash content of less than 0.15%.

[0033] Further preferred, the purified lignin is pulverized and passed through a 200-mesh sieve.

[0034] Further preferred, the raw material is enzymatically hydrolyzed lignin, but it can also be crude products whose main component is lignin, such as lignin char.

[0035] This invention uses an organic polymer binder to prepare pellets and incorporates a low-temperature curing process. Through slight sintering or bonding at low temperatures, the carbon-alkali contact structure inside the pellets is fixed, locking in the carbon-alkali mixed state and preventing local segregation. Therefore, during high-temperature activation, gases generated by alkali etching (such as CO2 and potassium vapor) can diffuse uniformly, resulting in a more complete and synchronized carbon-alkali reaction. This avoids potassium vapor escape and the resulting "potassium explosion," and ultimately forms a more rationally distributed pore structure with a "micropore-mesopore" hierarchical distribution.

[0036] A lignin-based supercapacitor carbon prepared by any of the above preparation methods.

[0037] Preferably, the supercapacitor carbon ash is composed of A%, 0 ≤ A ≤ 0.2%; and has a specific surface area of ​​SA m². 2 / g, pore volume is V cm 3 / g, wherein the mesoporous proportion is P%, 1000≤SA≤2000, 0.55≤V≤0.8, 5≤P≤25.

[0038] The above describes the applications of supercapacitor carbon in supercapacitor energy storage devices.

[0039] The lignin-based supercapacitor carbon prepared by this invention has excellent pore structure control effect. After being prepared as a self-supporting electrode, the specific capacitance can reach 53.3 F / g in a symmetrical dual-electrode test system (both positive and negative electrodes are self-supporting electrodes prepared by the carbon material of this invention), which is 25.1% higher than the specific capacitance of the product prepared without the balling process. The ash content of the product is only 0.93‰. After 30,000 cycles of charge and discharge test, the specific capacitance retention rate is still 96.1%, which shows excellent electrochemical cycle stability.

[0040] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0041] (1) The core advantage of this invention is achieved through pelleting and activation: the pellet structure is dense and the activator is evenly distributed, which can ensure that the activator and the carbon source are in full contact, and significantly improve the utilization efficiency of the activator. Compared with the 2:1 alkali-to-carbon ratio commonly used in the prior art, the amount of alkali used in this invention can be reduced to one-quarter of the conventional amount, while the product still maintains good performance.

[0042] (2) Based on the pellet activation process, this invention can effectively suppress the escape and deposition of alkali metals during the activation process, which not only reduces the corrosiveness of the activator to the equipment, but also greatly reduces the risk of "potassium explosion".

[0043] (3) In the pellet activation system of the present invention, the organic binder can decompose at high temperature and at the same time partially cross-link with the lignin substrate to form stable channels; combined with the organic acid purification process, it avoids the introduction of additional metal or anionic impurities, so that the product has excellent cycle stability.

[0044] (4) By taking advantage of the activation characteristics of pellets, even at a low alkali-to-carbon ratio, the present invention can activate and generate mesopores and build abundant micropores, which not only ensures excellent electrochemical performance, but also provides a technical path to significantly reduce production costs.

[0045] (5) The present invention pre-treats and purifies lignin raw materials with alkali solution, which can further improve the purity of raw materials and reduce ash content, laying the foundation for higher cycle stability of capacitor carbon products. Attached Figure Description

[0046] Figure 1 The current-voltage characteristic (CV) curve of the supercapacitor carbon prepared in Example 2 is shown.

[0047] Figure 2 The constant current charge-discharge curves of the supercapacitor carbon prepared in Example 2, Comparative Example 1, and commercial carbon 1 are shown.

[0048] Figure 3 The graphs show the rate performance of the supercapacitor carbon prepared in Example 2, Comparative Example 1, and commercial carbon 1, and the rate performance of commercial capacitor carbon 1.

[0049] Figure 4 This is a long-cycle comparison diagram of the supercapacitor carbon prepared in Example 2, Comparative Example 2, Comparative Example 3, and Commercial Carbon 1 with Commercial Carbon 1.

[0050] Figure 5 The figure shows a comparison of the nitrogen adsorption-desorption curves and pore size distribution curves of the supercapacitor carbon prepared in Example 2 and that of Comparative Example 1.

[0051] Figure 6 This is a schematic diagram comparing pelletizing activation and ordinary activation. Detailed Implementation

[0052] The raw materials used in this invention can be purified lignin and lignin-like byproducts obtained by various purification methods, such as lignin char. For process parameters not specified, conventional techniques can be referred to.

[0053] Example 1

[0054] A method for preparing lignin-based supercapacitor carbon material for energy storage includes the following steps:

[0055] Weigh 2 kg of lignin raw material and dissolve it in 10% ammonia water at a liquid-to-solid ratio of 5 mL / g. React at 80℃ and 0.3 MPa for 2 hours. After vacuum distillation, the resulting reaction solution is centrifuged, filtered, and dried to obtain crude purified lignin. This crude lignin is then dissolved in acetone for secondary purification, filtered to remove impurities, and dried to obtain purified lignin. The purified lignin is then thoroughly crushed in a pulverizer and passed through a 200-mesh sieve to obtain fine purified lignin powder. If the purified lignin is already in powder form, it can be directly sieved. Take 1 kg of the sieved purified lignin powder for later use. Dissolve 50 g of polyvinyl alcohol (type 1788) binder in 250 mL of hot water to obtain a 16 wt.% binder solution. Finally, pulverize 500 g of potassium hydroxide activator into powder, mix it evenly with the purified lignin powder, add 250 mL of the 16 wt.% polyvinyl alcohol (type 1788) solution, stir thoroughly, and form into pellets with a diameter of 0.2 cm. The carbon spheres were heated to 120℃ in a nitrogen atmosphere for low-temperature curing for 6 hours, and then activated at 800℃ for 2 hours. During activation, the nitrogen flow rate was 50 mL / min. After activation, the product was washed once with 1000 mL of water, and then washed three times with a 3 wt.% oxalic acid + 3 wt.% hydrogen peroxide compound solution, with 1000 mL of acid used each time, until the filtrate was colorless and clear. Then, the product was dried to obtain the capacitor carbon product.

[0056] Example 2

[0057] Weigh 2 kg of lignin raw material and dissolve it in 10% ammonia water at a liquid-to-solid ratio of 5 mL / g. React at 80℃ and 0.3 MPa for 2 hours. After vacuum distillation, the resulting reaction solution is centrifuged, filtered, and dried to obtain crude purified lignin. This crude lignin is then dissolved in acetone for secondary purification, filtered to remove impurities, and dried to obtain purified lignin. The purified lignin is then thoroughly crushed in a pulverizer and passed through a 200-mesh sieve to obtain fine purified lignin powder. If the purified lignin is already in powder form, it can be directly sieved. Take 1 kg of the sieved purified lignin powder for later use. Dissolve 50 g of polyethylene glycol (molecular weight 6000, the same below) in 250 mL of water to obtain a 16 wt.% binder solution. Finally, pulverize 500 g of potassium hydroxide activator into powder, mix it evenly with the purified lignin powder, add 250 mL of the 16 wt.% polyethylene glycol solution, stir thoroughly, and form into pellets with a diameter of 0.2 cm. The carbon spheres were heated to 120℃ in a nitrogen atmosphere for low-temperature curing for 6 hours, and then activated at 800℃ for 2 hours. During activation, the nitrogen flow rate was 50 mL / min. After activation, the product was washed once with 1000 mL of water, and then washed three times with a 3 wt.% oxalic acid + 3 wt.% hydrogen peroxide compound solution, with 1000 mL of acid used each time, until the filtrate was colorless and clear. Then, the product was dried to obtain the capacitor carbon product.

[0058] Example 3

[0059] Weigh 2 kg of lignin raw material and dissolve it in 10% ammonia water at a liquid-to-solid ratio of 5 mL / g. React at 80℃ and 0.3 MPa for 2 hours. After vacuum distillation, the resulting reaction solution is centrifuged, filtered, and dried to obtain crude purified lignin. This crude lignin is then dissolved in acetone for secondary purification, filtered to remove impurities, and dried to obtain purified lignin. The purified lignin is then thoroughly crushed in a pulverizer and passed through a 200-mesh sieve to obtain fine purified lignin powder. If the purified lignin is already in powder form, it can be directly sieved. Take 1 kg of the sieved purified lignin powder for later use. Dissolve 30 g of polyethylene glycol in 250 mL of water to obtain a binder solution with a concentration of 11 wt.%. Finally, pulverize 500 g of potassium hydroxide activator into powder, mix it evenly with the purified lignin powder, add 250 mL of the 11 wt.% polyethylene glycol solution, stir thoroughly, and form into pellets with a diameter of 0.2 cm. The carbon spheres were heated to 120℃ in a nitrogen atmosphere for low-temperature curing for 6 hours, and then activated at 800℃ for 2 hours. During activation, the nitrogen flow rate was 50 mL / min. After activation, the product was washed once with 1000 mL of water, and then washed three times with a 3 wt.% oxalic acid + 3 wt.% hydrogen peroxide compound solution, with 1000 mL of acid used each time, until the filtrate was colorless and clear. Then, the product was dried to obtain the capacitor carbon product.

[0060] Comparative Example 1

[0061] Weigh 2 kg of lignin raw material and dissolve it in 10% ammonia water at a liquid-to-solid ratio of 5 mL / g. React at 80℃ and 0.3 MPa for 2 hours. After vacuum distillation, the resulting reaction solution is centrifuged, filtered, and dried to obtain crude purified lignin. Dissolve the crude lignin in acetone for secondary purification, filter to remove impurities, and dry to obtain purified lignin. Place the purified lignin in a pulverizer and grind it thoroughly. Then pass it through a 200-mesh sieve to obtain fine purified lignin powder. If the purified lignin is already in powder form, it can be directly sieved. Grind 500 g of potassium hydroxide activator into powder (alkali-to-carbon ratio of 0.5:1), mix it evenly with the purified lignin powder, and heat to 800℃ for 2 hours. During the activation process, the nitrogen flow rate is 50 mL / min. After activation, the product was washed once with 1000 mL of water, and then washed three times with a 3 wt.% oxalic acid + 3 wt.% hydrogen peroxide compound solution, with 1000 mL of acid used each time, until the filtrate was colorless and clear. Then it was dried to obtain the capacitor carbon product.

[0062] Comparative Example 2

[0063] Weigh 2 kg of lignin raw material and dissolve it in 10% ammonia water at a liquid-to-solid ratio of 5 mL / g. React at 80℃ and 0.3 MPa for 2 hours. After vacuum distillation, the resulting reaction solution is centrifuged, filtered, and dried to obtain crude purified lignin. This crude lignin is then dissolved in acetone for secondary purification, filtered to remove impurities, and dried to obtain purified lignin. The purified lignin is then thoroughly crushed in a pulverizer and passed through a 200-mesh sieve to obtain fine purified lignin powder. If the purified lignin is already in powder form, it can be directly sieved. Take 1 kg of the sieved purified lignin powder for later use. Dissolve 50 g of polyethylene glycol in 250 mL of water to obtain a 16 wt.% binder solution. Finally, pulverize 500 g of potassium hydroxide activator into powder, mix it evenly with the purified lignin powder, add 250 mL of the 16 wt.% polyethylene glycol solution, stir thoroughly, and form into pellets with a diameter of 0.2 cm. The carbon spheres were heated to 120℃ in a nitrogen atmosphere for low-temperature curing for 6 hours, and then activated at 800℃ for 2 hours. During activation, the nitrogen flow rate was 50 mL / min. After activation, the product was washed three times with 1000 mL of water each time until the filtrate was clear. Then, it was dried to obtain the capacitor carbon product.

[0064] Comparative Example 3

[0065] Weigh 2 kg of lignin raw material and dissolve it in 10% ammonia water at a liquid-to-solid ratio of 5 mL / g. React at 80℃ and 0.3 MPa for 2 hours. After vacuum distillation, the resulting reaction solution is centrifuged, filtered, and dried to obtain crude purified lignin. This crude lignin is then dissolved in acetone for secondary purification, filtered to remove impurities, and dried to obtain purified lignin. The purified lignin is then thoroughly crushed in a pulverizer and passed through a 200-mesh sieve to obtain fine purified lignin powder. If the purified lignin raw material is already in powder form, it can be directly sieved. Take 1 kg of the sieved purified lignin powder for later use. Dissolve 50 g of polyethylene glycol in 250 mL of water to obtain a 16 wt.% binder solution. Finally, pulverize 500 g of potassium hydroxide activator into powder, mix it evenly with the purified lignin powder, add 250 mL of the 16 wt.% polyethylene glycol solution, stir thoroughly, and form into pellets with a diameter of 0.2 cm. The pellets were directly heated to 800℃ and activated for 2 hours, with a nitrogen flow rate of 50 mL / min during activation. After activation, the product was washed once with 1000 mL of water, and then washed three times with a 3 wt.% oxalic acid + 3 wt.% hydrogen peroxide compound solution, with 1000 mL of acid used each time, until the filtrate was colorless and clear. Then, it was dried to obtain the capacitor carbon product.

[0066] Comparative Example 4

[0067] Weigh 2 kg of lignin raw material and dissolve it in 10% ammonia water at a liquid-to-solid ratio of 5 mL / g. React at 80℃ and 0.3 MPa for 2 hours. After vacuum distillation, the resulting reaction solution is centrifuged, filtered, and dried to obtain crude purified lignin. This crude lignin is then dissolved in acetone for secondary purification, filtered to remove impurities, and dried to obtain purified lignin. The purified lignin is then thoroughly crushed in a pulverizer and passed through a 200-mesh sieve to obtain fine purified lignin powder. If the purified lignin is already in powder form, it can be directly sieved. Take 1 kg of the sieved purified lignin powder for later use. Dissolve 50 g of hydroxymethyl cellulose in 250 mL of water to obtain a 16 wt.% binder solution. Finally, pulverize 500 g of potassium hydroxide activator into powder, mix it evenly with the purified lignin powder, add 250 mL of the 16 wt.% hydroxymethyl cellulose solution, stir thoroughly, and form into pellets with a diameter of 0.2 cm. The carbon balls were heated to 120℃ in a nitrogen atmosphere for low-temperature curing for 6 hours, and then the temperature was raised to 800℃ for activation for 2 hours. During the activation process, the nitrogen flow rate was 50 mL / min. After activation, the product was washed once with 1000 mL of water, and then washed three times with a compound solution of 3 wt.% oxalic acid + 3 wt.% hydrogen peroxide, with 1000 mL of acid used each time, until the filtrate was colorless and clear. Then the product was dried to obtain the capacitor carbon product.

[0068] Gray content test

[0069] Weigh a certain amount of the dried charcoal material and place it in a ceramic boat. Transfer the ceramic boat to a tube furnace and ignite it at 850°C for 30 minutes each time, until the mass change after ignition is <0.001g.

[0070] A ad =(m2−m1) / m0×100%

[0071] In the formula:

[0072] A ad —Ash content of air-dried sample, mass fraction (%)

[0073] m0 — Mass of the air-dried sample, in grams (g)

[0074] m1 — The mass of the porcelain ark, in grams (g).

[0075] m2 — Mass of the porcelain ark and ash after firing, in grams (g)

[0076] Performance testing

[0077] The electrochemical performance of Examples 1-3, Comparative Examples 1-4, and commercial supercapacitor carbon 1 (Kuraray 50F capacitor carbon from Japan) was evaluated. The pore structure of the prepared carbon materials was characterized using an ASAP-2460 surface area pore size analyzer from Micromeritics, Inc., USA. The pore structure and specific capacitance data are shown in Table 1 below.

[0078] Yield = m1 / m2 × 100%

[0079] Where m1 is the total mass of lignin raw materials; m2 is the mass of supercapacitor carbon products.

[0080] Table 1. Pore structure and specific capacitance of Examples 1-3, Comparative Examples 1-4, and commercial supercapacitor carbon 1.

[0081]

[0082] As can be seen from the pore structure data, under the same alkali-to-carbon ratio and activation temperature, the specific surface area and mesopore volume of Example 2 are significantly better than those of Comparative Example 1. This indicates that the pelletizing method can significantly promote the formation of mesopores and micropores under low alkali-to-carbon ratio conditions. Micropores are the main area for energy storage, while mesopores are the key ion transport channels for capacitor carbon. Both can directly optimize its electrochemical performance.

[0083] Table 2. Elemental contents obtained from lignin ash content and ICP testing.

[0084]

[0085] Table 2 above shows the elemental content obtained from ash content and ICP testing. The ash content test shows that the ash content of the unpurified lignin raw material is as high as 1.876%. The ash comes from impurities such as metal oxides that cannot be combusted and volatilized in the sample. These impurities, if retained during the activation process, will greatly affect the stability of the capacitive carbon pores, causing pore wall collapse and blockage after long cycles. After purification, the ash content of the lignin raw material is significantly reduced, with the product of Example 2 even decreasing to one-thousandth, lower than that of commercial carbon. Furthermore, due to the use of organic acid purification, its anion content is significantly lower than that of commercial carbon 1.

[0086] Examples 1-3, Comparative Examples 1-4, and commercial carbon 1 (Kuraray 50F capacitor carbon from Japan) were assembled into symmetrical capacitors (button capacitors). The specific steps were as follows: 0.1g of capacitor carbon and 0.0125g of SuperP conductive carbon were weighed and ground in an agate mortar for at least 40 minutes. Then, 13μL of 60% PTFE solution and an appropriate amount of anhydrous ethanol were added, and the mixture was pressed into a self-supporting sheet using a roller press. The sheet was then vacuum-dried at 100°C for at least 8 hours and cut into circular electrode sheets with a diameter of 12 mm using a slicing machine. Using CR2032 as the battery casing, 60 μL of 6 M KOH was added to each device as the electrolyte, and cellulose paper was used as the separator to assemble a button-type supercapacitor. The button capacitors were extruded and encapsulated at 5MPa, and after standing for at least 8 hours to allow the electrolyte to fully impregnate them, they were tested.

[0087] Figure 1 The figure shows the cyclic voltammetric characteristics of the electrode material obtained in Example 2 after it was assembled into a button capacitor at scan rates of 5, 20, and 100 mV / s, with a voltage window of 0–1 V. Testing showed that when the scan rate was increased to 100 mV / s, the cyclic voltammetric characteristic curve still exhibited an approximately rectangular shape, indicating that the electrode material has excellent double-layer capacitance behavior. Furthermore, the large area enclosed by the curve further supports the claim that the electrode material possesses high specific capacitance.

[0088] Figure 2 The graph shows the constant current charge-discharge curves of Example 2, Comparative Example 1, and Commercial Carbon 1 assembled into button capacitors at a current density of 0.5 A / g, with a voltage window of 0~1V. As can be seen from the graph, the voltage drop in the initial stage of discharge is relatively small for all three materials, and they exhibit good symmetry. Specifically, the discharge time of the curve corresponding to Example 2 is significantly longer than that of Comparative Example 1 and Commercial Carbon 1, and the specific capacitance of the material obtained in Example 2 is significantly better than the other two samples.

[0089] Figure 3The graph shows the specific capacitance calculated from the constant current charge-discharge curves of Example 2, Comparative Example 1, and commercial carbon 1 after they were assembled into button capacitors at current densities of 0.5, 1, 2, 4, 10, 20, and 30 A / g. The voltage window for constant current charge-discharge is 0~1V. The preparation conditions of the supercapacitor carbon obtained in Example 2 and Comparative Example 1 are the same, both activated at 800℃ with a low alkali carbon ratio of 0.5:1. The difference is that Example 2 adds a pelletizing activation process. After modification by this process, the specific capacitance of the supercapacitor carbon obtained in Example 2 is significantly improved, and is much higher than that of commercial carbon 1. At the same time, under the condition of increased current density, the specific capacitance of the supercapacitor carbon obtained in Example 2 decreases less. This performance advantage is attributed to: 1. Increased utilization of activator after pelletizing, resulting in increased micropore volume, which is the main contributor to specific capacitance. 2. Its unique mesoporous structure, which can provide channels for rapid ion transport at high current densities.

[0090] Figure 4 This is a comparison curve of the long-cycle performance of the three samples assembled into button capacitors after 30,000 constant current charge-discharge cycles at a current density of 1 A / g, with a voltage window of 0~1V. The specific capacitance retention rate of commercial carbon 1 is only 77% of the initial value; while the specific capacitance retention rate of Example 2 can still reach 96.1%. In addition, Comparative Example 2 is an activated sample without organic acid washing treatment, and the rest of the process is the same as Example 2, and its capacitance retention rate is 90.1%. Comparative Example 3 is a sample without low-temperature curing process, and the rest of the process is the same as Example 2, and its capacitance retention rate is only 91.3%. Comparative Example 2 shows that organic acid purification can significantly improve product purity, thereby improving stability. Comparative Example 3 shows that in the pelletizing activation process, low-temperature curing promotes the cross-linking reaction between the binder and lignin functional groups, further improving pore strength and cycle stability.

[0091] Figure 5 These are nitrogen adsorption-desorption isotherms for Example 2 and Comparative Example 1. The results show that even under the preparation conditions of a low alkali-to-carbon ratio, the nitrogen adsorption-desorption isotherm curve corresponding to Example 2 still shows a significant hysteresis loop, indicating that it possesses a mesoporous structure. In contrast, Comparative Example 1, due to insufficient activator, has a weak activation etching effect, making it difficult to form a mesoporous structure and resulting in a significantly lower nitrogen adsorption capacity. This proves that the micropore-mesopore hierarchical pore structure of the material obtained in Comparative Example 1 is not fully developed.

[0092] In summary, as Figure 6 As shown, the present invention achieves slow radial diffusion of alkaline activator with low dosage through pelletizing and low-temperature curing activation in the activation process, thereby improving pore formation efficiency. This allows the potassium activator to be fully etched and consumed inside the pellets without escaping to the outside, thus optimizing the pore structure and electrochemical performance while avoiding the "potassium explosion" problem.

[0093] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a lignin-based supercapacitive carbon, characterized in that, Includes the following steps: Step 1: Mix the adhesive with water and stir until dissolved to obtain an adhesive solution; Step 2: Mix the adhesive solution, purified lignin and activator and pelletize them. First, solidify them at low temperature in a nitrogen atmosphere, then activate them at high temperature. After washing with water and acid washing to remove impurities, the filtrate becomes colorless and clear, and then lignin-based supercapacitor carbon is obtained. The adhesive mentioned in step 1 is at least one of polyethylene glycol and polyvinyl alcohol; The mass ratio of the activator to the purified lignin in step 2 is 0.5~1:1; the low-temperature curing temperature is 100~120℃ and the time is 4~6h; In step 2, the pickling uses a compound organic acid, which includes organic acid and hydrogen peroxide solution.

2. The method for preparing lignin-based supercapacitor carbon according to claim 1, characterized in that, The adhesive used in step 1 has a dissolved concentration of 11-25 wt.%; The activator used in step 2 is one or more of KOH, K2CO3 and KHCO3.

3. The method for preparing lignin-based supercapacitor carbon according to claim 1, characterized in that, The high-temperature activation in step 2 is performed at a temperature of 700~800℃ for 1~2 hours.

4. The method for preparing lignin-based supercapacitor carbon according to claim 1, characterized in that, The organic acid refers to at least one of oxalic acid, citric acid, acetic acid, and ascorbic acid; the concentration of the organic acid in the compound organic acid is 3 to 10 wt.%, and the concentration of hydrogen peroxide in the compound organic acid is 2 to 5 wt.%.

5. The method for preparing lignin-based supercapacitor carbon according to claim 1, characterized in that, In step 2, after pelleting and mixing, the mass ratio of purified lignin, binder, water, and activator is 100:(3~5):25:50; In step 2, the nitrogen flow rate is 50~100 mL / min; The diameter of the pellets obtained in step 2 is 0.2~0.5cm.

6. The method for preparing lignin-based supercapacitor carbon according to claim 1, characterized in that, The ash content of the purified lignin described in step 2 is less than 0.15 wt.%. The purified lignin is obtained by purifying lignin with ammonia and acetone in sequence, followed by drying, pulverizing and sieving. The purification process of the lignin is as follows: The lignin raw material is placed in 8-12 wt.% ammonia water for primary purification, with a liquid-to-solid ratio of 4-6 mL:1 g. It is heated at 80-90℃ and 0.3-0.4 MPa for 2-3 hours. After filtering to remove impurities, the filtrate is distilled under reduced pressure and then centrifuged and filtered to obtain primary purified lignin. Subsequently, the primary purified lignin is dissolved in acetone for secondary purification, filtered to remove impurities, and dried to finally obtain purified lignin.

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