Preparation method of mixed carbon source derived hierarchical porous carbon electrode material

Abstract

The application discloses a preparation method of mixed carbon source derived hierarchical porous carbon. The steps of the preparation method of the mixed carbon source derived hierarchical porous carbon are as follows: firstly, starch and disaccharide are added into N-methylmorpholine-N-oxide aqueous solution and heated to be dissolved; the obtained mixture is melt-blended and extruded through a double screw extruder to prepare uniform mixed granules; then, the granules are subjected to pre-carbonization treatment to obtain a carbon precursor; the carbon precursor is ground into powder, mixed with an activating agent aqueous solution, dried, and subjected to activation carbonization at high temperature; finally, the carbonized product is subjected to acid pickling, water washing and drying to obtain the mixed carbon source derived hierarchical porous carbon electrode material. The disaccharide is white granulated sugar or maltose. The preparation method realizes uniform compounding of multiple carbon sources by using a melt-blending process, has the advantages of easy availability of raw materials and easy scale production, and the prepared product shows excellent electrochemical performance and good cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of electrode materials for supercapacitors, and specifically relates to a method for preparing a hierarchical porous carbon electrode material derived from a mixed carbon source. Background Technology

[0002] Against the backdrop of global energy shortages and environmental pollution control, supercapacitors, as one of the most promising energy storage devices, require careful consideration of practicality, economy, and environmental compatibility in the selection and preparation of their electrode materials. In this regard, biomass-derived carbon materials are highly favored in existing electrode material systems due to their abundant raw materials, low cost, high specific surface area, good chemical stability, excellent conductivity, and wide operating potential window. However, the inherent non-graphite carbon structure of biomass precursors often makes it difficult to effectively control their microstructure, pore distribution, and surface chemistry using conventional preparation methods. This results in porous carbon electrodes that may face limitations such as long ion diffusion paths, low electronic conductivity, and high interfacial impedance.

[0003] In recent years, research has focused on the following directions to effectively regulate the microstructure and surface chemical properties of biomass carbon materials: First, introducing heteroatoms (such as N, B, S, and P) using hydrothermal and template methods to induce abundant surface active sites, thereby significantly improving the utilization efficiency of the specific surface area of ​​carbon-based materials, while enhancing surface wettability and contributing additional pseudocapacitance; Second, constructing rich hierarchical channels through activation and carbonization methods, as suitable pore structures facilitate rapid ion diffusion. In practical processes, multiple preparation methods (such as hydrothermal-activation combination and template-carbonization combination) are usually integrated to simultaneously optimize specific surface area and electrochemical performance. However, the currently widely used hydrothermal and template methods often suffer from complex processes and high costs, becoming bottlenecks for their large-scale preparation. Furthermore, while forcibly introducing dopants for elemental doping can introduce active sites, the integrity of the carbon framework structure is often difficult to maintain, affecting conductivity. In contrast to traditional research directions, there is relatively little research on the use of mixed carbon sources as biomass precursors. This may be because: traditional research focuses more on single precursors or post-processing, neglecting the active design and composite composition of precursor components; the interaction mechanisms of mixed systems during pyrolysis are complex and difficult to characterize and control precisely; and there is a lack of theoretical prediction of the potential synergistic effects of the two components during carbonization. To achieve the widespread adoption of supercapacitors and meet the demands of commercial production, it is urgent to find a mixed carbon source method for the preparation of carbon electrode materials, in addition to the traditional single carbon source approach. Summary of the Invention

[0004] The purpose of this invention is to provide a method for producing hierarchical porous carbon electrode materials derived from mixed carbon sources without the need for introducing dopants.

[0005] The technical solution to achieve the objective of this invention is: a method for preparing a hierarchical porous carbon electrode material derived from a mixed carbon source, comprising the following steps:

[0006] Step 1: Obtain an aqueous solution of N-methylmorpholine-N-oxide with a content of ≥75% by vacuum distillation;

[0007] Step 2: Mix starch, disaccharide, and N-methylmorpholine-N-oxide aqueous solution in a certain mass ratio and heat to dissolve;

[0008] Step 3: The mixture obtained by dissolution is melt-blended and extruded through a twin-screw extruder to obtain mixed granules;

[0009] Step 4: The mixed granules are pre-carbonized in a tube furnace under nitrogen atmosphere protection to obtain pre-carbonized carbon.

[0010] Step 5: Grind the pre-carbonized carbon into powder, mix it evenly with the activator aqueous solution, evaporate it to dryness, and then activate and carbonize the mixture at high temperature in a tube furnace. After the activated carbonized product is cooled to room temperature, it is acid-washed with dilute hydrochloric acid, then washed with water until neutral, and dried to obtain the final mixed carbon source-derived hierarchical porous carbon electrode material.

[0011] In the second step of the preparation method of the mixed carbon source-derived hierarchical porous carbon electrode material of the present invention, the disaccharide is granulated sugar or maltose.

[0012] In the second step of the preparation method of the mixed carbon source-derived hierarchical porous carbon electrode material of the present invention, the amount of N-methylmorpholine-N-oxide aqueous solution is 25% to 40%, the amount of starch is 40% to 50%, and the amount of dopant is 15% to 30%.

[0013] In step 3 of the preparation method of the mixed carbon source-derived hierarchical porous carbon electrode material of the present invention, the melt blending temperature is ≤130℃.

[0014] In step 4 of the preparation method of the mixed carbon source-derived hierarchical porous carbon electrode material of the present invention, the pre-carbonization temperature is 400-600℃.

[0015] In step 5 of the preparation method of the mixed carbon source-derived hierarchical porous carbon electrode material of the present invention, the high-temperature activation carbonization temperature is 600-800℃.

[0016] In step 5 of the preparation method of the mixed carbon source-derived hierarchical porous carbon electrode material of the present invention, the activator used is potassium hydroxide, and the mass ratio of potassium hydroxide to carbon is (2-4):1.

[0017] Compared with the prior art, the advantages of the present invention are: (1) The starch and disaccharide (such as white sugar) used in the present invention are mixed biomass carbon sources. They have high yield, are renewable, abundant in source and low in cost. They can be converted into carbon materials with rich pore structure through pyrolysis, carbonization and other processes; (2) The present invention achieves uniform blending by extrusion blending N-methylmorpholine-N-oxide solvent containing heteroatoms and disaccharide with starch to improve the electrochemical energy storage performance of carbonized materials. The method is simple and easy to implement industrially. Detailed Implementation

[0018] The present invention discloses a method for preparing a hierarchical porous carbon electrode material derived from a mixed carbon source, comprising the following steps:

[0019] Step 1: Obtain an aqueous solution of N-methylmorpholine-N-oxide with a content of ≥75% by vacuum distillation;

[0020] Step 2: Mix starch with disaccharide and N-methylmorpholine-N-oxide aqueous solution in a certain mass ratio and heat to dissolve;

[0021] Step 3: The mixture obtained by dissolution is melt-blended and extruded through a twin-screw extruder to obtain mixed granules;

[0022] Step 4: The mixed granules are pre-carbonized in a tube furnace under nitrogen atmosphere protection to obtain pre-carbonized carbon.

[0023] Step 5: Grind the pre-carbonized carbon into powder, mix it evenly with the activator aqueous solution, evaporate it to dryness, and then activate and carbonize the mixture at high temperature in a tube furnace. After the activated carbonized product is cooled to room temperature, it is acid-washed with dilute hydrochloric acid, then washed with water until neutral, and dried to obtain the final mixed carbon source-derived hierarchical porous carbon electrode material.

[0024] In the second step of the preparation method of the mixed carbon source-derived hierarchical porous carbon electrode material of the present invention, the disaccharide is granulated sugar or maltose.

[0025] In the second step of the preparation method of the mixed carbon source-derived hierarchical porous carbon electrode material of the present invention, the amount of N-methylmorpholine-N-oxide aqueous solution is 25% to 40%, the amount of starch is 40% to 50%, and the amount of disaccharide is 15% to 30%.

[0026] In step 3 of the preparation method of the mixed carbon source-derived hierarchical porous carbon electrode material of the present invention, the melt blending temperature is ≤130℃.

[0027] In step 4 of the preparation method of the mixed carbon source-derived hierarchical porous carbon electrode material of the present invention, the pre-carbonization temperature is 400-600℃.

[0028] In step 5 of the preparation method of the mixed carbon source-derived hierarchical porous carbon electrode material of the present invention, the high-temperature activation carbonization temperature is 600-800℃.

[0029] In step 5 of the preparation method of the mixed carbon source-derived hierarchical porous carbon electrode material of the present invention, the activator used is potassium hydroxide, and the mass ratio of alkali to carbon is (2-4):1.

[0030] Electrochemical performance testing (including constant current charge-discharge testing and cyclic charge-discharge testing) was conducted using a standard three-electrode testing system. A mixed slurry was prepared by mixing the prepared carbon material, acetylene black (conductive agent), and polytetrafluoroethylene (binder) in an appropriate amount of anhydrous ethanol at a ratio of 8:1:1. This slurry was then uniformly coated onto a cleaned nickel foam current collector. The dried nickel foam was then pressed using a tablet press at 10 MPa for 1 minute to obtain the working electrode. A Hg / HgO reference electrode, a platinum sheet counter electrode, and a 6 mol·L⁻¹ electrode were used. -1 A three-electrode system consisting of KOH solution electrolyte was used for electrochemical testing using an AUTO electrochemical workstation (Metroën STAT302N).

[0031] Example 1

[0032] Weigh 56 grams of N-methylmorpholine-N-oxide hydrate with a water content of 13.3%, mix and dissolve it with 42 grams of food-grade wheat starch and 14 grams of white sugar at 100°C. The mixture is then melt-blended and extruded twice in a micro twin-screw extruder. The operating temperatures of the four sections of the extruder are set to 115°C, 120°C, 120°C, and 120°C, respectively. After cooling by an air-cooled conveyor, the mixture is pelletized by a micro pelletizer to obtain the pretreated starch-based material.

[0033] The pretreated starch-based material was placed in a tube furnace and heated at 5°C / min under a N2 atmosphere. -1 The temperature was increased to 500℃ at a certain rate and held for 2 hours to obtain pre-carbonized carbon. The pre-carbonized carbon was mixed with 3 times its mass of KOH in deionized water and impregnated for 30 minutes. The mixture was then evaporated to dryness at 100℃ with stirring. The evaporated mixture was transferred to a tube furnace and heated at 5℃·min. -1 After heating to 700℃ at a certain rate and holding for 2 hours, the product was removed, cooled, and then treated with 1 mol·L⁻¹ water. -1 The material is acid-washed with dilute hydrochloric acid, then washed with a large amount of deionized water until neutral, and dried to obtain the mixed carbon source-derived hierarchical porous carbon electrode material of the present invention, which exhibits performance at a current density of 1 A·g⁻¹. -1 The specific capacitance is 198.3 F·g. -1 .

[0034] Example 2

[0035] Weigh 48 grams of N-methylmorpholine-N-oxide hydrate with a water content of 13.3%, mix and dissolve it with 30 grams of food-grade wheat starch and 18 grams of white sugar at 100°C. The mixture is then melt-blended and extruded twice in a micro twin-screw extruder. The operating temperatures of the four sections of the extruder are set to 115°C, 120°C, 120°C, and 120°C, respectively. After cooling by an air-cooled conveyor, the mixture is pelletized by a micro pelletizer to obtain the pretreated starch-based material.

[0036] The pretreated starch-based material was placed in a tube furnace and heated at 5°C / min under a N2 atmosphere. -1 The temperature was increased to 500℃ at a certain rate and held for 2 hours to obtain pre-carbonized carbon. The pre-carbonized carbon was mixed with 3 times its mass of KOH in deionized water and impregnated for 30 minutes. The mixture was then evaporated to dryness at 100℃ with stirring. The evaporated mixture was transferred to a tube furnace and heated at 5℃·min. -1 After heating to 700℃ at a certain rate and holding for 2 hours, the product was removed, cooled, and then treated with 1 mol·L⁻¹ water. -1 The material is acid-washed with dilute hydrochloric acid, then washed with a large amount of deionized water until neutral, and dried to obtain the mixed carbon source-derived hierarchical porous carbon electrode material of the present invention, which exhibits performance at a current density of 1 A·g⁻¹. -1 The specific capacitance is 202.3 F·g. -1 .

[0037] Example 3

[0038] Weigh 48 grams of N-methylmorpholine-N-oxide hydrate with a water content of 13.3%, mix and dissolve it with 30 grams of food-grade wheat starch and 18 grams of maltose at 100°C. The mixture is then melt-blended and extruded twice in a micro twin-screw extruder. The operating temperatures of the four sections of the extruder are set to 115°C, 120°C, 120°C, and 120°C, respectively. After cooling by an air-cooled conveyor, the mixture is pelletized by a micro pelletizer to obtain the pretreated starch-based material.

[0039] The pretreated starch-based material was placed in a tube furnace and heated at 5°C / min under a N2 atmosphere. -1 The temperature was increased to 500℃ at a certain rate and held for 2 hours to obtain pre-carbonized carbon. The pre-carbonized carbon was mixed with 3 times its mass of KOH in deionized water and impregnated for 30 minutes. The mixture was then evaporated to dryness at 100℃ with stirring. The evaporated mixture was transferred to a tube furnace and heated at 5℃·min. -1 After heating to 700℃ at a certain rate and holding for 2 hours, the product was removed, cooled, and then treated with 1 mol·L⁻¹ water. -1 The material is acid-washed with dilute hydrochloric acid, then washed with a large amount of deionized water until neutral, and dried to obtain the mixed carbon source-derived hierarchical porous carbon electrode material of the present invention, which exhibits performance at a current density of 1 A·g⁻¹. -1 The specific capacitance is 201.8 F·g. -1 .

Claims

1. A method for preparing a hierarchical porous carbon electrode material derived from a mixed carbon source, characterized in that: Includes the following steps: Step 1: Obtain an aqueous solution of N-methylmorpholine-N-oxide with a content of ≥75% by vacuum distillation; Step 2: Mix starch, disaccharide and N-methylmorpholine-N-oxide aqueous solution in a certain mass ratio and heat to dissolve; Step 3: The mixture obtained by dissolution is melt-blended and extruded through a twin-screw extruder to obtain mixed granules; Step 4: The mixed granules are pre-carbonized in a tube furnace under nitrogen atmosphere protection to obtain pre-carbonized carbon. Step 5: Grind the pre-carbonized carbon into powder, mix it evenly with the activator aqueous solution, evaporate it to dryness, and then activate and carbonize the mixture at high temperature in a tube furnace. After the activated carbonized product is cooled to room temperature, it is acid-washed with dilute hydrochloric acid, then washed with water until neutral, and dried to obtain the final mixed carbon source-derived hierarchical porous carbon electrode material.

2. The method for preparing the hierarchical porous carbon electrode material derived from the mixed carbon source according to claim 1, characterized in that: In step 2, the disaccharide is either granulated sugar or maltose.

3. The method for preparing the mixed carbon source-derived hierarchical porous carbon electrode material according to claim 1 or 2, characterized in that: In step 2, the amount of N-methylmorpholine-N-oxide aqueous solution used is 25%–40%, the amount of starch is 40%–50%, and the amount of disaccharide is 15%–30%.

4. The method for preparing the mixed carbon source-derived hierarchical porous carbon electrode material according to any one of claims 1 to 3, characterized in that: In step 3, the melt blending temperature is ≤130℃.

5. The method for preparing the mixed carbon source-derived hierarchical porous carbon electrode material according to any one of claims 1 to 4, characterized in that: The pre-carbonization temperature in step 4 is 400–600℃.

6. The method for preparing the mixed carbon source-derived hierarchical porous carbon electrode material according to any one of claims 1 to 5, characterized in that: In step 5, the high-temperature activation and carbonization temperature is 600–800℃.

7. The method for preparing a mixed carbon source-derived hierarchical porous carbon electrode material according to any one of claims 1 to 6, characterized in that: The activator used in step 5 is potassium hydroxide, and the mass ratio of potassium hydroxide to carbon is 2 to 4:1.