Super-capacitor carbon based on heat treatment doping of coffee grounds and preparation method and application of super-capacitor carbon

Abstract

The invention belongs to the technical field of electrode materials, and relates to coffee residue heat treatment doping-based super capacitor carbon and a preparation method and application thereof, coffee residue is used as a raw material, and after hydrothermal carbonization, staged gradient activation and ultrasonic-acid etching coupling treatment, the super capacitor carbon with a rich pore structure is prepared. According to the process, through precise matching of intrinsic characteristics of coffee grounds and process parameters, a hierarchical porous structure is constructed and is matched with an electron transport network formed by self-doping, so that the technical bottleneck that a traditional biomass carbon material is poor in electrical conductivity and difficult to achieve both ion diffusion efficiency is broken through; the super-capacitor carbon with extremely high specific surface area, excellent electricity storage performance and high energy density is finally obtained; a supercapacitor electrode prepared from the supercapacitor carbon has good charge-discharge performance, large specific capacitance, high energy density and good cycle efficiency; moreover, efficient recycling of the coffee grounds can be achieved, the environment-friendly requirement is met, the process is simple, cost is low, and application and popularization are easy.

Description

Technical Field

[0001] This invention belongs to the field of electrode material technology, and relates to supercapacitor carbon based on coffee grounds heat treatment doping, its preparation method and application. Background Technology

[0002] Current socio-economic development heavily relies on the extensive consumption of fossil fuels. However, the drawbacks of this energy utilization model have created a systemic crisis. The short-term benefits of the high-carbon economy are severely imbalanced with the long-term environmental costs, and extreme weather events triggered by the greenhouse effect are frequent. The limitations of traditional energy storage technologies (such as lithium batteries) in terms of cycle life and power density make it difficult to meet the demand for efficient energy storage in the new energy system. Against this backdrop, supercapacitors, with their ultra-long cycle life and millisecond-level charge and discharge capabilities, have become core components in fields such as regenerative braking in new energy vehicles and frequency regulation in smart grids.

[0003] Electrode materials are a decisive factor in the performance of supercapacitors, and their development focuses on carbon-based material systems. Although graphene and carbon nanotubes possess excellent theoretical properties, their complex preparation processes and high costs severely restrict their industrial application. In contrast, biomass-derived carbon materials have advantages in raw material renewability, cost, and ease of processing, making them highly promising for application.

[0004] Coffee, a widely consumed beverage globally, generates a large amount of coffee grounds waste annually. Currently, the main methods for treating coffee grounds are incineration and landfill, with little research on their high-value recycling. However, coffee grounds are characterized by high carbon content, low ash content, and higher nitrogen and trace amounts of sulfur / phosphorus heteroatoms than conventional biomass. This natural doping characteristic allows them to spontaneously form a nitrogen-doped carbon framework during carbonization, significantly enhancing their pseudocapacitive contribution compared to biomass-based carbon materials that require additional doping treatment. In the prior art, Chinese invention patent CN111223684A discloses a method for preparing a coffee grounds-based supercapacitor electrode material. This method involves loading graphene nanosheets and carbon nanotubes onto coffee grounds and then carbonizing and activating them at high temperature under a nitrogen atmosphere. Although the introduction of graphene nanosheets and carbon nanotubes improves the material's performance, this method still has significant shortcomings: firstly, the additional loading of graphene nanosheets and carbon nanotubes significantly increases the preparation cost; secondly, the specific surface area of ​​the resulting electrode material is only 460.1 m². 2At a current density of 1 A / g, the specific capacitance is only 68 F / g, indicating low performance and poor economic efficiency. Furthermore, another Chinese invention patent, CN111017924A, discloses a method for preparing electrode materials, employing a process of high-temperature pyrolysis pretreatment, impregnation chemical activation, and high-temperature calcination under a protective atmosphere. Although the two-step pyrolysis process is relatively clear and easy to operate, this method also has significant drawbacks: on the one hand, the two high-temperature carbonization processes are energy-intensive and time-consuming; on the other hand, the resulting electrode material has a specific capacitance of only 100 F / g to 350 F / g at a current density of 1 A / g, indicating unsatisfactory electrochemical performance.

[0005] In summary, existing methods for preparing carbon materials for coffee grounds-based supercapacitors generally suffer from problems such as high cost, high energy consumption, small specific surface area, and poor electrochemical performance. There is an urgent need to develop an economical, efficient, green, environmentally friendly, and high-performance preparation method. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides supercapacitor carbon based on the thermal treatment and doping of coffee grounds, its preparation method, and its application. Through hydrothermal carbonization, staged gradient activation, and ultrasonic-acid etching coupling treatment, supercapacitor carbon with rich pore structure is obtained. The supercapacitor electrode prepared by supercapacitor carbon has good charge and discharge performance, large specific capacitance, high energy density, and good cycle efficiency. It can also realize the efficient recycling of coffee grounds, meet environmental protection requirements, and has a simple process, low cost, and is easy to promote and apply.

[0007] This invention is achieved through the following technical solution: In a first aspect, the present invention provides a method for preparing supercapacitor carbon based on heat treatment of coffee grounds, comprising the following steps: Coffee grounds powder is mixed with a reaction medium and then subjected to hydrothermal carbonization. The resulting product is then separated and washed to obtain a carbon precursor. After mixing the carbon precursor with the activator, the carbon is subjected to a staged gradient activation treatment under an inert atmosphere to obtain activated carbon. After ultrasonic-acid etching coupled treatment, activated carbon is washed, dried and pulverized to obtain supercapacitor carbon.

[0008] Preferably, the mass ratio of the coffee grounds powder to the reaction medium is 1:(5~20); the mass ratio of the carbon precursor to the activator is 1:(1~4).

[0009] Preferably, the reaction medium is a mixed solution of deionized water and ethanol; the volume fraction of ethanol in the mixed solution is 10% to 90%.

[0010] Preferably, the specific conditions for the hydrothermal carbonization treatment are as follows: The temperature is increased to 200-300℃ at a heating rate of 5℃ / min, and the mixture is stirred at a speed of 90-150 r / min for 0.5-2 h.

[0011] Preferably, the particle size of the carbon precursor is 5~10 μm.

[0012] Preferably, the activator is a mixture of KOH and K2CO3; the mass ratio of KOH to K2CO3 is (2:1) to (1:1).

[0013] Preferably, the specific process of the staged gradient activation treatment is as follows: The reactants, after mixing the carbon precursor and the activator, are subjected to a low-temperature activation reaction for 0.5 to 1 hour under a nitrogen atmosphere and a first temperature gradient of 400 to 500 °C. Then, the temperature is raised to a second temperature gradient of 600 to 800 °C and subjected to a high-temperature activation reaction for 0.5 to 1 hour to obtain activated carbon.

[0014] Preferably, the activated carbon is subjected to ultrasonic-acid etching coupling treatment, followed by washing, drying, and pulverization to obtain supercapacitor carbon, specifically: Activated carbon is immersed in a hydrochloric acid solution with a concentration of 0.5~1.5 mol / L and ultrasonically treated for 30~60 min at an ultrasonic frequency of 28~40 kHz and a temperature of 30~50℃. After ultrasonic treatment, the solid product is allowed to stand and separated. The separated solid product is washed with deionized water and anhydrous ethanol, dried at 80~105℃ for 12~24 h, and then pulverized to obtain supercapacitor carbon. The mass ratio of activated carbon to hydrochloric acid solution is 1:(150~200).

[0015] Secondly, the present invention provides supercapacitor carbon based on heat treatment of coffee grounds, which is prepared by the aforementioned method for preparing supercapacitor carbon based on heat treatment of coffee grounds.

[0016] Thirdly, the present invention provides the application of the supercapacitor carbon based on the heat treatment of coffee grounds in supercapacitors, including: A supercapacitor electrode was prepared from the supercapacitor carbon based on the heat treatment of coffee grounds. When the supercapacitor electrode is placed in a three-electrode system in a 6 mol / L potassium hydroxide (KOH) electrolyte, the specific capacitance is 411.82~526.93 F / g at a current density of 1 A / g; when the supercapacitor electrode is assembled into a symmetrical supercapacitor, the energy density reaches 10.67~13.69 Wh / kg.

[0017] Compared with the prior art, the present invention has the following beneficial technical effects: This invention provides a method for preparing supercapacitor carbon based on thermal treatment doping of coffee grounds, using widely available and inexpensive coffee grounds as raw material. By fully utilizing the natural doping characteristics of coffee grounds (containing 1.8wt%~2.5wt% nitrogen and 0.1wt%~0.4wt% sulfur), a nitrogen-doped carbon framework is spontaneously formed during carbonization, eliminating the need for additional doping treatment. This not only achieves efficient recycling of coffee grounds but also aligns with the concept of green and environmentally friendly development. This invention employs a process route combining hydrothermal carbonization with staged gradient activation treatment. By efficiently transferring carbon elements from coffee grounds to the solid phase, a carbon precursor with a surface rich in oxygen-containing groups is generated, effectively retaining the natural nitrogen, sulfur, and other heteroatoms in the coffee grounds, significantly improving the pseudocapacitive performance of the material. The carbon precursor obtained by hydrothermal carbonization has a preliminary porous structure and its surface is rich in oxygen-containing groups, making it easier to be etched into a porous network during the subsequent staged gradient activation process. Simultaneously, this invention employs an ultrasonic-acid etching coupled process, which, through the synergistic effect of cavitation and chemical etching, significantly reduces the concentration of residual alkali metal ions (K2) in the carbon of the supercapacitor. + The content was reduced to below 0.1 wt%, which effectively removed impurities in the pores and optimized the pore structure. In addition, the chemical etching selectively removed the amorphous areas on the surface of the supercapacitor carbon, exposed more edge sites, increased the density of oxygen-containing functional groups (such as carboxyl and hydroxyl groups) on the surface, and significantly improved the surface wettability and ion transport efficiency of the supercapacitor carbon.

[0018] The supercapacitor carbon based on heat-treated coffee grounds provided by this invention has an excellent porous structure and a specific surface area of ​​2440.3 m². 2 / g, pore volume 1.7cm 3 / g. A supercapacitor electrode was prepared using this supercapacitor carbon and placed in a three-electrode system in a 6 mol / L potassium hydroxide (KOH) electrolyte. The specific capacity reached 411.82~526.93 F / g at a current density of 1 A / g. After 30,000 continuous charge-discharge cycles at a high current density of 10 A / g, the supercapacitor electrode maintained a capacity retention of 95.36% and a coulombic efficiency of over 99.5%, demonstrating excellent electrochemical energy storage performance and cycle stability.

[0019] Furthermore, the preparation method of the present invention utilizes a mixture of KOH and potassium carbonate (K2CO3) as an activator. During the phased heating process, KOH and K2CO3 generate a dynamic coupling effect. KOH preferentially reacts to construct microporous energy storage sites, while K2CO3 thermally decomposes during the heating phase to generate CO2 gas. Through vapor-phase etching, a uniform mesoporous structure is formed. The synergistic distribution of micropores and mesopores not only significantly improves the specific surface area and charge storage capacity of the supercapacitor carbon, but also promotes the rapid migration of electrolyte ions, thereby optimizing the electrochemical reaction kinetics performance.

[0020] Furthermore, the reaction medium of the present invention is a mixed solution of deionized water and ethanol. The addition of ethanol can promote the occurrence of esterification, etherification and other reactions during the hydrothermal carbonization process, and increase the density of oxygen-containing functional groups on the surface of the carbon precursor.

[0021] Furthermore, this invention employs ultrasonic-acid etching coupling treatment with hydrochloric acid solution. By controlling the acid etching conditions, residual alkaline substances and metal ions in the activated carbon can be effectively removed, resulting in a lower concentration of K in the final product. + The content is reduced to below 0.1wt%, while avoiding excessive corrosion of the carbon skeleton structure due to excessively high local acid concentration. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a flowchart of the method for preparing supercapacitor carbon based on heat treatment of coffee grounds according to the present invention; Figure 2 This is a scanning electron microscope image of the supercapacitor carbon prepared in Example 3 of the present invention; Figure 3 The nitrogen adsorption / desorption curves of carbon in supercapacitors of Examples 1-4 of this invention are shown below. Figure 4 The pore size distribution diagrams are shown for the carbon in the supercapacitors of Examples 1-4 of this invention. Figure 5 Cyclic voltammetry curves of supercapacitor electrodes at different scan rates were obtained for the supercapacitor carbon preparation of Example 3 of the present invention. Figure 6 The supercapacitor carbon preparation of Example 3 of the present invention yielded constant current charge-discharge curves of supercapacitor electrodes under different current densities; Figure 7The cycling stability curve of the supercapacitor electrode prepared from the supercapacitor carbon in Example 3 of this invention is shown. Detailed Implementation

[0024] To achieve the above objectives, the present invention employs the following technical solution: This invention discloses a method for preparing supercapacitor carbon based on heat treatment of coffee grounds, comprising the following steps: Step (1) Raw material pretreatment: Place the coffee grounds in an oven and dry them at 80~105℃ for 12~24h to ensure that the moisture content of the coffee grounds is less than 5%. Use a planetary ball mill to crush the dried coffee grounds, and then transfer the crushed coffee grounds to a vibrating screen and pass them through a 100~200 mesh screen to collect coffee ground powder with uniform particle size; Step (2) Preparation of carbon precursor: The coffee grounds powder obtained in step (1) is mixed with the reaction medium at a mass ratio of 1:(5~20). The mixture is transferred to a high-pressure reactor, sealed, and placed in a temperature-controlled heating jacket. The temperature is increased to 200~300℃ at a heating rate of 5℃ / min, and mechanically stirred at a speed of 90~150r / min for 0.5~2h. After the reaction is completed, the reactants are naturally cooled to room temperature. The product is taken out, and the solid is separated by filtration through a Buchner funnel. The product is washed with deionized water and anhydrous ethanol in sequence, and then dried at a temperature of 80~105℃ for 12~24h. The product is then ground in a planetary ball mill until the average particle size is 5~10μm to obtain the carbon precursor. Step (3) Preparation of activated carbon: The carbon precursor obtained in step (2) and the activator are ground and mixed in an agate mortar at a mass ratio of 1: (1~4). The mixture is evenly spread in a corundum boat and placed in a tube furnace. High-purity nitrogen is introduced at a rate of 500~800 mL / min as a protective gas. The temperature is increased at a rate of 5~10℃ / min for a staged gradient activation treatment. Specifically, the temperature is increased to 400~500℃ for the first gradient, and the low-temperature activation reaction is carried out for 0.5~1h. Then, the temperature is increased to 600-800℃ for the second gradient, and the high-temperature activation reaction is carried out for 0.5~1h. After the reaction is completed, the product is naturally cooled to room temperature under nitrogen protection. The product is taken out, ground, and passed through an 80~150 mesh sieve to obtain activated carbon. Step (4) Post-treatment of activated carbon: The activated carbon obtained in step (3) is immersed in a hydrochloric acid solution with a concentration of 0.5~1.5 mol / L at a mass ratio of 1:(150~200), and placed in a constant temperature ultrasonic cleaner. It is ultrasonically treated for 30~60 min at an ultrasonic frequency of 28~40 kHz and a temperature of 30~50℃. After ultrasonic treatment, it is allowed to stand for 6 h, and the solid is separated by suction filtration through a Buchner funnel. It is then washed with deionized water and anhydrous ethanol in sequence, and then dried at a temperature of 80~105℃ for 12~24 h. It is then processed by an air jet mill to a particle size of less than 5 μm to obtain supercapacitor carbon.

[0025] Preferably, in step (2), the mass ratio of coffee grounds powder to the reaction medium is 1:(5~20) to ensure that the reaction system has suitable mass transfer and heat transfer efficiency and promote the full progress of the hydrothermal reaction.

[0026] Preferably, in step (2), the reaction medium is a mixed solution of deionized water and ethanol, wherein the volume fraction of ethanol is 10%~90%. The addition of ethanol can promote the occurrence of esterification, etherification and other reactions in the hydrothermal carbonization process and increase the density of oxygen-containing functional groups on the surface of carbon precursor.

[0027] Preferably, in step (2), the reaction temperature of the hydrothermal carbonization treatment is 200~300℃ and the reaction time is 0.5~2h. This condition can ensure that the polysaccharides in the coffee grounds powder are fully hydrolyzed and dehydrated, while avoiding excessive aromatization that leads to the loss of natural heteroatoms and oxygen-containing functional groups.

[0028] Preferably, in step (3), the mass ratio of carbon precursor to activator is 1:(1~4). By precisely controlling the amount of activator, the specific surface area and pore volume of the material can be precisely controlled.

[0029] Preferably, in step (3), the activator is a mixture of KOH and K2CO3 in a mass ratio of (2:1) to (1:1). KOH and K2CO3 generate a dynamic coupling effect during the stage heating process. KOH preferentially reacts to construct microporous energy storage sites, while K2CO3 thermally decomposes during the heating stage to generate CO2 gas. Through vapor-phase etching, a uniform mesoporous structure is formed. The synergistic distribution of micropores and mesopores not only significantly improves the specific surface area and charge storage capacity of the supercapacitor carbon, but also promotes the rapid migration of electrolyte ions, thereby optimizing the electrochemical reaction kinetics performance.

[0030] Preferably, in step (3), the conditions for the staged gradient activation treatment are as follows: under the first gradient temperature condition of 400~500℃, a low-temperature activation reaction is carried out for 0.5~1h, so that KOH and K2CO3 are partially decomposed to generate K2O and CO2, which are uniformly dispersed in the carbon skeleton, providing a uniform etching environment for subsequent high-temperature activation; then, under the second gradient temperature condition of 600~800℃, a high-temperature activation reaction is carried out for 0.5~1h, so that KOH or K2CO3 reacts violently with the carbon skeleton to generate a large number of micropores, which significantly increases the specific surface area.

[0031] Preferably, in step (4), an ultrasonic-acid etching coupled treatment is performed using a hydrochloric acid solution with a concentration of 0.5~1.5 mol / L, wherein the mass ratio of activated carbon to hydrochloric acid solution is 1:(150~200); by controlling the above acid washing conditions, residual alkaline substances and metal ions in the activated carbon can be effectively removed, so that the K in the final product is reduced. + The content is reduced to below 0.1wt%, while avoiding excessive corrosion of the carbon skeleton structure due to excessively high local acid concentration.

[0032] Preferably, in step (4), the ultrasonic frequency is 28~40kHz, and the cavitation effect generated by low-frequency ultrasound can effectively remove impurities in the pores while maintaining the integrity of the carbon skeleton structure; the ultrasonic temperature is 30~50℃, which can improve the solubility of hydrochloric acid and the ultrasonic cavitation effect by moderately raising the temperature, while avoiding excessive temperature that could cause hydrochloric acid to volatilize or the carbon skeleton to be destroyed; the ultrasonic time is 30~60 minutes, which can ensure that the impurity removal rate in the activated carbon is higher than 95% and optimize the pore structure.

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0034] The coffee grounds used in the following embodiments of the present invention were provided by Changsha San Dun Ban Coffee Co., Ltd., and were dried and stored in self-sealing bags after being retrieved.

[0035] Example 1 Supercapacitor carbon based on heat-treated coffee grounds, its preparation method and application, including the following steps: Step (1) Raw material pretreatment: Place the coffee grounds in an oven and dry them at 80℃ for 24 hours to ensure that the moisture content of the coffee grounds is less than 5%. Use a planetary ball mill to crush the dried coffee grounds, transfer the crushed coffee grounds to a vibrating screen, pass them through a 200-mesh screen, and collect coffee ground powder with uniform particle size.

[0036] Step (2) Preparation of carbon precursor: Mix 5g of coffee grounds powder and 100g of reaction medium (10% ethanol by volume, the remainder being deionized water), transfer to a high-pressure reactor, seal, and place in a temperature-controlled heating mantle. Heat to 200℃ at a rate of 5℃ / min, and mechanically stir for 2h at a speed of 90r / min. After the reaction, remove the reactor from the heating mantle and allow it to cool naturally to room temperature. Remove the product from the reactor, separate the solid by filtration through a Buchner funnel, and wash with deionized water and anhydrous ethanol in sequence. Dry the solid product in an oven at 80℃ for 24h, and grind it with a planetary ball mill until the average particle size is 5μm to obtain the carbon precursor.

[0037] Step (3) Preparation of activated carbon: 0.6g of carbon precursor and 0.6g of activator (wherein the mass ratio of KOH to K2CO3 is 2:1) are placed in an agate mortar and ground thoroughly until homogeneous. The mixture is evenly spread in a corundum boat and placed in a tube furnace. High-purity nitrogen is introduced at a rate of 500mL / min as a protective gas, and a staged gradient activation treatment is carried out at a heating rate of 10℃ / min. Specifically, the first gradient is a low-temperature activation reaction at 400℃ for 0.5h, and then the temperature is raised to the second gradient at 600℃ for a high-temperature activation reaction for 0.5h. After the reaction is completed, the product is naturally cooled to room temperature under nitrogen protection, ground, and passed through a 100-mesh sieve to obtain activated carbon.

[0038] Step (4) Post-treatment of activated carbon: 1g of activated carbon was immersed in 150g of hydrochloric acid solution with a concentration of 1.5mol / L, and placed in a constant temperature ultrasonic cleaner. The ultrasonic frequency was set to 28kHz, the temperature to 30℃, and the ultrasonic treatment time to 60min. After ultrasonic treatment, the carbon was allowed to stand for 6h, and the solid was separated by filtration through a Buchner funnel. The solid was washed successively with deionized water and anhydrous ethanol. The solid product was placed in an oven and dried at 105℃ for 12h. The solid was then processed by an air jet mill to a particle size of 4.7μm to obtain supercapacitor carbon.

[0039] Example 2 The method for preparing supercapacitor carbon based on heat treatment of coffee grounds includes the following steps: Step (1) Raw material pretreatment: Place the coffee grounds in an oven and dry them at 90℃ for 18 hours to ensure that the moisture content of the coffee grounds is less than 5%. Use a planetary ball mill to crush the dried coffee grounds, transfer the crushed coffee grounds to a vibrating screen, pass them through a 150-mesh screen, and collect coffee ground powder with uniform particle size.

[0040] Step (2) Preparation of carbon precursor: Mix 5g of coffee grounds powder and 50g of reaction medium (50% ethanol by volume, the remainder being deionized water), transfer to a high-pressure reactor, seal, and place in a temperature-controlled heating mantle. Heat to 240℃ at a rate of 5℃ / min, and mechanically stir at 120r / min for 1.5h. After the reaction, remove the reactor from the heating mantle and allow it to cool naturally to room temperature. Remove the product from the reactor, separate the solid by filtration through a Buchner funnel, and wash with deionized water and anhydrous ethanol in sequence. Dry the solid product in an oven at 90℃ for 18h, and grind it with a planetary ball mill until the average particle size is 7μm to obtain the carbon precursor.

[0041] Step (3) Preparation of activated carbon: 0.6g of carbon precursor and 1.2g of activator (wherein the mass ratio of KOH to K2CO3 is 1.5:1) are placed in an agate mortar and ground thoroughly until homogeneous. The mixture is evenly spread in a corundum boat and placed in a tube furnace. High-purity nitrogen is introduced at a rate of 600mL / min as a protective gas, and a staged gradient activation treatment is carried out at a heating rate of 10℃ / min. Specifically, the first gradient is a low-temperature activation reaction at 450℃ for 0.75h, and then the temperature is increased to a second gradient of 700℃ for a high-temperature activation reaction for 0.75h. After the reaction is completed, the product is naturally cooled to room temperature under nitrogen protection, ground, and passed through a 100-mesh sieve to obtain activated carbon.

[0042] Step (4) Post-treatment of activated carbon: 1g of activated carbon was immersed in 175g of hydrochloric acid solution with a concentration of 1mol / L, and placed in a constant temperature ultrasonic cleaner. The ultrasonic frequency was set to 30kHz, the temperature to 40℃, and the ultrasonic treatment time to 45min. After ultrasonic treatment, the carbon was allowed to stand for 6h, and the solid was separated by filtration through a Buchner funnel. The solid was washed successively with deionized water and anhydrous ethanol. The solid product was placed in an oven and dried at 90℃ for 18h. After drying, the solid was processed by an air jet mill to a particle size of 4.5μm to obtain supercapacitor carbon.

[0043] Example 3 The method for preparing supercapacitor carbon based on heat treatment of coffee grounds includes the following steps: Step (1) Raw material pretreatment: Place the coffee grounds in an oven and dry them at 105℃ for 12 hours to ensure that the moisture content of the coffee grounds is less than 5%. Use a planetary ball mill to crush the dried coffee grounds, transfer the crushed coffee grounds to a vibrating screen, pass them through a 100-mesh screen, and collect coffee ground powder with uniform particle size.

[0044] Step (2) Preparation of carbon precursor: Mix 5g of coffee grounds powder and 60g of reaction medium (25% ethanol by volume, the remainder being deionized water), transfer to a high-pressure reactor, seal, and place in a temperature-controlled heating mantle. Heat to 280℃ at a rate of 5℃ / min, and mechanically stir for 1h at 100r / min. After the reaction, remove the reactor from the heating mantle and allow it to cool naturally to room temperature. Remove the product from the reactor and separate the solid by filtration through a Buchner funnel. Wash the solid product with deionized water and anhydrous ethanol in sequence. Dry the solid product in an oven at 105℃ for 12h, and grind it with a planetary ball mill until the average particle size is 10μm to obtain the carbon precursor.

[0045] Step (3) Preparation of activated carbon: 0.6g of carbon precursor and 1.8g of activator (wherein the mass ratio of KOH to K2CO3 is 2:1) are placed in an agate mortar and ground thoroughly until homogeneous. The mixture is evenly spread in a corundum boat and placed in a tube furnace. High-purity nitrogen is introduced at a rate of 500mL / min as a protective gas, and a staged gradient activation treatment is carried out at a heating rate of 7℃ / min. Specifically, the first gradient is a low-temperature activation reaction at 400℃ for 0.5h, and then the temperature is raised to the second gradient at 800℃ for a high-temperature activation reaction for 1h. After the reaction is completed, the product is naturally cooled to room temperature under nitrogen protection, ground, and passed through a 100-mesh sieve to obtain activated carbon.

[0046] Step (4) Post-treatment of activated carbon: Immerse 1g of activated carbon in 150g of 1mol / L hydrochloric acid solution, place it in a constant temperature ultrasonic cleaner, set the ultrasonic frequency to 30kHz, the temperature to 30℃, and the ultrasonic treatment time to 30min. After ultrasonic treatment, let it stand for 6h, separate the solid by filtration through a Buchner funnel, and wash it successively with deionized water and anhydrous ethanol. Place the solid product in an oven and dry it at 105℃ for 12h, then process it with an air jet mill to a particle size of 4.5μm to obtain supercapacitor carbon.

[0047] Example 4 The method for preparing supercapacitor carbon based on heat treatment of coffee grounds includes the following steps: Step (1) Raw material pretreatment: Place the coffee grounds in an oven and dry them at 105℃ for 12 hours to ensure that the moisture content of the coffee grounds is less than 5%. Use a planetary ball mill to crush the dried coffee grounds, transfer the crushed coffee grounds to a vibrating screen, pass them through a 100-mesh screen, and collect coffee ground powder with uniform particle size.

[0048] Step (2) Preparation of carbon precursor: Mix 5g of coffee grounds powder and 75g of reaction medium (25% ethanol by volume, the remainder being deionized water), transfer to a high-pressure reactor, seal, and place in a temperature-controlled heating mantle. Heat to 300℃ at a rate of 5℃ / min, and mechanically stir at 150r / min for 0.5h. After the reaction, remove the reactor from the heating mantle and allow it to cool naturally to room temperature. Remove the product from the reactor and separate the solid by filtration through a Buchner funnel. Wash the solid product with deionized water and anhydrous ethanol in sequence. Dry the solid product in an oven at 80℃ for 12h, and then grind it in a planetary ball mill until the average particle size is 10μm to obtain the carbon precursor.

[0049] Step (3) Preparation of activated carbon: 0.6g of carbon precursor and 1.8g of activator (wherein the mass ratio of KOH to K2CO3 is 1:1) are placed in an agate mortar and ground thoroughly until homogeneous. The mixture is evenly spread in a corundum boat and placed in a tube furnace. High-purity nitrogen is introduced at a rate of 800mL / min as a protective gas, and a staged gradient activation treatment is carried out at a heating rate of 10℃ / min. Specifically, the first gradient is a low-temperature activation reaction at 500℃ for 1h, followed by a high-temperature activation reaction at 800℃ for 1h. After the reaction is completed, the product is naturally cooled to room temperature under nitrogen protection, ground, and passed through a 150-mesh sieve to obtain activated carbon.

[0050] Step (4) Post-treatment of activated carbon: Immerse 1g of activated carbon in 200g of 1mol / L hydrochloric acid solution, place it in a constant temperature ultrasonic cleaner, set the ultrasonic frequency to 35kHz, the temperature to 30℃, and the ultrasonic treatment time to 30min. After ultrasonic treatment, let it stand for 6h, separate the solid by filtration through a Buchner funnel, and wash it successively with deionized water and anhydrous ethanol. Place the solid product in an oven and dry it at 105℃ for 12h, then process it with an air jet mill to a particle size of 5μm to obtain supercapacitor carbon.

[0051] Example 5 The method for preparing supercapacitor carbon based on heat treatment of coffee grounds includes the following steps: Step (1) Raw material pretreatment: Place the coffee grounds in an oven and dry them at 95°C for 18 hours to ensure that the moisture content of the coffee grounds is less than 5%. Use a planetary ball mill to crush the dried coffee grounds, transfer the crushed coffee grounds to a vibrating screen, pass them through a 150-mesh screen, and collect coffee ground powder with uniform particle size.

[0052] Step (2) Preparation of carbon precursor: Mix 5g of coffee grounds powder and 25g of reaction medium (90% ethanol by volume, the remainder being deionized water), transfer to a high-pressure reactor, seal, and place in a temperature-controlled heating mantle. Heat to 280℃ at a rate of 5℃ / min, and mechanically stir for 1h at a speed of 150r / min. After the reaction, remove the reactor from the heating mantle and allow it to cool naturally to room temperature. Remove the product from the reactor, separate the solid by filtration through a Buchner funnel, and wash with deionized water and anhydrous ethanol in sequence. Dry the solid product in an oven at 105℃ for 12h, and grind it with a planetary ball mill until the average particle size is 8μm to obtain the carbon precursor.

[0053] Step (3) Preparation of activated carbon: 0.6g of carbon precursor and 2.4g of activator (where the mass ratio of KOH to K2CO3 is 2:1) are placed in an agate mortar and ground thoroughly until homogeneous. The mixture is evenly spread in a corundum boat and placed in a tube furnace. High-purity nitrogen is introduced at a rate of 700mL / min as a protective gas, and a staged gradient activation treatment is carried out at a heating rate of 5℃ / min. Specifically, the first gradient is a low-temperature activation reaction at 450℃ for 0.75h, and then the temperature is raised to the second gradient at 750℃ for a high-temperature activation reaction for 0.75h. After the reaction is completed, the product is naturally cooled to room temperature under nitrogen protection, ground, and passed through an 80-mesh sieve to obtain activated carbon.

[0054] Step (4) Post-treatment of activated carbon: Immerse 1g of activated carbon in 180g of 0.5mol / L hydrochloric acid solution, place it in a constant temperature ultrasonic cleaner, set the ultrasonic frequency to 40kHz, the temperature to 50℃, and the ultrasonic treatment time to 30min. After ultrasonic treatment, let it stand for 6h, separate the solid by filtration through a Buchner funnel, and wash it successively with deionized water and anhydrous ethanol. Place the solid product in an oven and dry it at 80℃ for 24h, then process it with an air jet mill to a particle size of 4μm to obtain supercapacitor carbon.

[0055] Performance testing The prepared supercapacitor carbon, conductive acetylene black, and polytetrafluoroethylene (PTFE) binder were weighed and placed in anhydrous ethanol at a mass ratio of 16:3:1. The mixture was ultrasonically treated for 30 minutes to ensure uniform mixing. Subsequently, the mixture was dried at 105℃ for 12 hours. The dried mixture was pressed into six circular electrode sheets with a diameter of 10 mm (each sheet weighing approximately 3-4 mg). Finally, the pressed electrode sheets and a nickel strip serving as tabs were sandwiched between two pieces of 15 mm diameter nickel foam and pressed under 10 MPa pressure for 30 seconds to form the supercapacitor electrode.

[0056] Three-electrode system test: The supercapacitor electrode prepared by supercapacitor carbon based on coffee grounds heat treatment was used as the working electrode, the platinum sheet electrode was used as the counter electrode, and the mercury / mercury oxide (Hg / HgO) electrode was used as the reference electrode. Cyclic voltammetry and constant current charge-discharge tests were performed in a KOH solution with a concentration of 6 mol / L to determine its specific capacitance. The results are shown in Table 1, which shows the specific capacitance of Examples 1-5 in the three-electrode system when the measured current density is 1 A / g. Dual-electrode system test: Two coffee grounds-based supercapacitor electrodes were assembled into a symmetrical supercapacitor, and its energy density was tested in a 6 mol / L KOH solution. The results are shown in Table 1, which shows the energy density of Examples 1-5 in the dual-electrode system when the measured current density is 1 A / g. Table 1 shows the test data of specific capacitance and energy density of the supercapacitor electrodes prepared from supercapacitor carbon in Examples 1-5.

[0057] from Figure 2 It can be seen that the supercapacitor carbon prepared in Example 3 formed a large number of pores during the hydrothermal carbonization and staged gradient activation processes, exhibiting a good porous structure and a specific surface area of ​​2440.3 m². 2 / g, pore volume 1.7cm 3 / g, the presence of numerous pores can promote electrolyte permeation and improve the availability of electrochemical active sites.

[0058] from Figure 3 It can be seen that the amount of nitrogen adsorption increases rapidly in the low-pressure region and then tends to level off. The nitrogen adsorption / desorption curve is a typical type I curve, indicating that the supercapacitor carbon is mainly composed of micropores. The adsorption-desorption curves of Examples 3 and 4 show H4 type hysteresis loops, indicating that the supercapacitor carbon contains some mesopores. Figure 4 The pore size distribution curves show that the pore size of the supercapacitor carbon is mainly concentrated below 10 nm, containing a large number of micropores and a small number of mesopores. This hierarchical pore structure provides the supercapacitor carbon with excellent electrochemical performance. The abundant micropores significantly increase the specific surface area of ​​the supercapacitor carbon, providing a large number of charge storage sites; the mesoporous network optimizes the ion transport pathway, effectively promoting the rapid migration of electrolyte ions, thereby improving the rate performance and cycle stability of the supercapacitor electrode.

[0059] from Figure 5 , Figure 6 and Figure 7 It can be seen that the supercapacitor carbon prepared in Example 3 exhibits excellent electrochemical performance: Figure 5In the cyclic voltammetry curves, the curves exhibit a typical rectangular shape and maintain good capacitance characteristics even at a high scan rate of 200 mV / s, indicating that the supercapacitor carbon has excellent reversibility and fast charge transport dynamics. Figure 6 In the process, the charge-discharge curves all exhibit highly symmetrical triangular characteristics under different current densities, further confirming the high reversibility and excellent charge storage capacity of the supercapacitor carbon. Figure 7 In this study, a supercapacitor electrode prepared from supercapacitor carbon exhibited a capacity retention of 95.36% after 30,000 charge-discharge cycles at a high current density of 10 A / g, while maintaining a coulombic efficiency consistently above 99.5%. This demonstrates the excellent cycling stability and electrochemical reversibility of the supercapacitor carbon. These performance advantages are primarily attributed to the hierarchical porous structure and abundant surface functional groups of the supercapacitor carbon, which effectively promote ion transport and charge storage in the electrolyte.

[0060] In summary, the supercapacitor carbon prepared by this invention has promising applications in the field of electrochemistry, with the following specific advantages: 1. Raw Material Selection and Environmental Benefits: This invention uses coffee grounds as raw material, which is widely available and inexpensive. By fully utilizing the natural doping characteristics of coffee grounds (containing 1.8 wt%~2.5 wt% nitrogen and 0.1 wt%~0.4 wt% sulfur), a nitrogen-doped carbon framework is spontaneously formed during carbonization. This framework includes active sites for pyridine N (398.4 eV), pyrrole N (399.9 eV), graphite N (401.1 eV), and thiophene sulfur (163.9 eV), requiring no additional doping treatment. This method not only achieves efficient recycling of coffee grounds but also aligns with the concept of green and environmentally friendly development.

[0061] 2. Innovative Process of Hydrothermal Carbonization and Staged Gradient Activation: This invention employs a process route combining hydrothermal carbonization with staged gradient activation. By efficiently transferring carbon elements from coffee grounds to the solid phase, a hydrothermal carbon precursor with a surface rich in oxygen-containing groups is generated. This effectively retains the natural nitrogen, sulfur, and other heteroatoms in the coffee grounds, significantly improving the pseudocapacitive performance of the material. The carbon precursor obtained through hydrothermal carbonization has a preliminary porous structure and a surface rich in oxygen-containing groups, making it easier to be etched into a porous network during the subsequent staged gradient activation process. Simultaneously, a mixture of KOH and K2CO3 is used as an activator. Staged temperature increases during activation improve the dispersion of the activator in the carbon framework, further optimizing the hierarchical pore structure and significantly improving the specific surface area and ion transport efficiency of the supercapacitor carbon.

[0062] 3. Optimization of Ultrasonic-Acid Etching Coupled Treatment Process: This invention employs an ultrasonic-acid etching coupled treatment process, which, through the synergistic effect of cavitation and chemical etching, significantly reduces the concentration of residual alkali metal ions (K2) in the carbon of supercapacitors.+ The content was reduced to below 0.1 wt%, which effectively removed impurities in the pores and optimized the pore structure. In addition, the chemical etching selectively removed the amorphous regions on the surface of the supercapacitor carbon, exposing more edge sites and increasing the density of oxygen-containing functional groups (such as carboxyl and hydroxyl groups) on the surface, which significantly improved the surface wettability and ion transport efficiency of the material.

[0063] 4. Electrochemical performance of high-performance supercapacitors: The supercapacitor carbon prepared in this invention has an excellent porous structure with a specific surface area of ​​2440.3 m². 2 / g, pore volume 1.7cm 3 / g. A supercapacitor electrode prepared using supercapacitor carbon was placed in a three-electrode system in a 6 mol / L KOH electrolyte. At a current density of 1 A / g, the specific capacitance reached 526.93 F / g. After 30,000 charge-discharge cycles at a high current density of 10 A / g, the supercapacitor electrode maintained a capacity retention of 95.36%, and the coulombic efficiency remained stable above 99.5%. A symmetrical supercapacitor assembled using supercapacitor carbon achieved an energy density of 13.69 Wh / kg at a current density of 1 A / g.

[0064] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Those skilled in the art can readily implement the present invention based on the accompanying drawings and the above description. However, any modifications, alterations, or variations made by those skilled in the art without departing from the scope of the present invention, utilizing the disclosed technical content, are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, or variations made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing supercapacitor carbon based on heat-treated coffee grounds, characterized in that, Includes the following steps: Coffee grounds powder is mixed with a reaction medium and then subjected to hydrothermal carbonization. The resulting product is then separated and washed to obtain a carbon precursor. After mixing the carbon precursor with the activator, the carbon is subjected to a staged gradient activation treatment under an inert atmosphere to obtain activated carbon. After ultrasonic-acid etching coupled treatment, activated carbon is washed, dried and pulverized to obtain supercapacitor carbon.

2. The method for preparing supercapacitor carbon based on heat-treated coffee grounds according to claim 1, characterized in that, The mass ratio of coffee grounds powder to reaction medium is 1:(5~20); the mass ratio of carbon precursor to activator is 1:(1~4).

3. The method for preparing supercapacitor carbon based on heat-treated coffee grounds according to claim 1, characterized in that, The reaction medium is a mixed solution of deionized water and ethanol; the volume fraction of ethanol in the mixed solution is 10% to 90%.

4. The method for preparing supercapacitor carbon based on heat-treated coffee grounds according to claim 1, characterized in that, The specific conditions for the hydrothermal carbonization treatment are as follows: The temperature is increased to 200-300℃ at a heating rate of 5℃ / min, and the mixture is stirred at a speed of 90-150 r / min for 0.5-2 h.

5. The method for preparing supercapacitor carbon based on heat-treated coffee grounds according to claim 1, characterized in that, The particle size of the carbon precursor is 5~10 μm.

6. The method for preparing supercapacitor carbon based on heat-treated coffee grounds according to claim 1, characterized in that, The activator is a mixture of KOH and K2CO3; the mass ratio of KOH to K2CO3 is (2:1) to (1:1).

7. The method for preparing supercapacitor carbon based on heat-treated coffee grounds according to claim 1, characterized in that, The specific process of the phased gradient activation process is as follows: The reactants, after mixing the carbon precursor and the activator, are subjected to a low-temperature activation reaction for 0.5 to 1 hour under a nitrogen atmosphere and a first temperature gradient of 400 to 500 °C. Then, the temperature is raised to a second temperature gradient of 600 to 800 °C and subjected to a high-temperature activation reaction for 0.5 to 1 hour to obtain activated carbon.

8. The method for preparing supercapacitor carbon based on heat-treated coffee grounds according to claim 1, characterized in that, The activated carbon, after being subjected to ultrasonic-acid etching coupling treatment, and then washed, dried, and pulverized, yields supercapacitor carbon, specifically: Activated carbon is immersed in a hydrochloric acid solution with a concentration of 0.5~1.5 mol / L and ultrasonically treated for 30~60 min at an ultrasonic frequency of 28~40 kHz and a temperature of 30~50℃. After ultrasonic treatment, the solid product is allowed to stand and separated. The separated solid product is washed with deionized water and anhydrous ethanol, dried at 80~105℃ for 12~24 h, and then pulverized to obtain supercapacitor carbon. The mass ratio of activated carbon to hydrochloric acid solution is 1:(150~200).

9. Supercapacitor carbon based on heat treatment of coffee grounds, prepared according to the preparation method of supercapacitor carbon based on heat treatment of coffee grounds as described in any one of claims 1-8.

10. The application of supercapacitor carbon based on heat-treated coffee grounds doping in supercapacitors according to claim 9, characterized in that, include: A supercapacitor electrode was prepared from the supercapacitor carbon based on the heat treatment of coffee grounds. When the supercapacitor electrode is placed in a three-electrode system in a KOH electrolyte with a concentration of 6 mol / L, the specific capacitance is 411.82~526.93 F / g at a current density of 1 A / g; when the supercapacitor electrode is assembled into a symmetrical supercapacitor, the energy density reaches 10.67~13.69 Wh / kg.

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