Preparation method of biomass-based nitrogen-doped capacitor carbon, electrode and capacitor

Abstract

According to the preparation method, a co-sintering pretreatment step is added, potassium carbonate and urea are co-sintered at a limited temperature to form a eutectic mixture, so that a nitrogen-containing group (such as NH3) generated by urea decomposition and the potassium carbonate are synergistically embedded into a carbon skeleton precursor, and the carbon skeleton precursor is formed. Meanwhile, urea decomposition provides a nitrogen source, efficient nitrogen doping is achieved, the nitrogen doping efficiency is improved by 50% or above compared with a traditional process, continuous production can be achieved, the production efficiency is improved, continuous activation of the rotary furnace is matched with segmented temperature control, construction of a micropore-dominated hierarchical pore structure (the micropore rate is larger than 85%) is facilitated, and the specific surface area is increased; the capacitance carbon prepared by the method has the advantages of high specific surface area, reasonable pore size distribution and the like, the specific capacitance can reach 220F / g and is increased by 40% compared with that of an undoped sample, the tap density is greater than or equal to 0.4 g / cm, and the specific capacitance is increased by 30%.

Description

Technical Field

[0001] This invention relates to the field of electrode technology, specifically to a method for preparing biomass-based nitrogen-doped capacitive carbon, as well as electrodes and capacitors. Background Technology

[0002] Supercapacitors, as a novel energy storage device, possess advantages such as high power density, fast charge / discharge speed, and long cycle life, and have broad application prospects in the field of energy storage. Capacitor carbon, as a key electrode material in supercapacitors, directly affects the energy density and power density of the device.

[0003] Traditional capacitor carbon is mostly prepared using fossil raw materials (such as coal and petroleum coke), which has problems such as high cost and environmental pollution. Biomass raw materials (such as lignin, rice husks, and straw) have become ideal precursors for the preparation of capacitor carbon due to their renewable nature, low cost, and wide availability.

[0004] To improve the performance of biomass-based capacitor carbon, chemical activation (such as KOH and NaOH activation) and heteroatom doping (such as nitrogen, phosphorus, and boron doping) are commonly used. For example, Chinese invention application CN117438221A discloses a method for preparing biomass-based capacitor carbon, using KOH activation and ammonia post-treatment for nitrogen doping. However, the process is cumbersome, the nitrogen doping amount is low (<2%), and KOH causes severe corrosion to equipment. CN106744788A uses urea as a nitrogen source, but the direct high-temperature decomposition of urea results in low nitrogen utilization and uneven doping. CN113620287A uses an "internal immersion-external coating" technology, but this process is cumbersome and requires improvement. Summary of the Invention

[0005] To address at least one of the aforementioned technical deficiencies, the present invention provides the following technical solution: This application discloses a method for preparing biomass-based nitrogen-doped capacitive carbon, comprising the following steps: Step 1: Sinter the mixture of biomass, potassium carbonate and urea in a mass ratio of 1:0.5-3:0.2-1.5 at 120-150℃ for 1-4 hours to form a homogeneous eutectic mixture; Step 2: Under an inert atmosphere, the homogeneous eutectic mixture is pre-carbonized in a rotary kiln at 300-450℃ for 10-60 minutes, and then the pre-carbonized product is carbonized at 650-850℃. Step 3: First, wash the carbonized product with hydrochloric acid until the pH of the filtrate is 5-7, and then wash it with water until the conductivity is ≤10μS / cm; Step 4: Dry the washed product to obtain capacitor carbon.

[0006] Furthermore, in step two, the temperature inside the rotary kiln is increased to 300-450℃ at a rate of 5-15℃ / min, and then increased to 650-850℃ at a rate of 10-20℃ / min.

[0007] Furthermore, in step three, the rotary kiln speed is 2-10 rpm and the inert gas flow rate is 1-3 L / min.

[0008] Furthermore, in step one, the biomass is one or more of lignin, coconut shell, bamboo shavings, rice husk, and straw.

[0009] Furthermore, in step one, the biomass has a particle size of 100-200 mesh and a moisture content of ≤5%, and the biomass is first placed in an oven and dried at 100-120℃ for 10-15 hours.

[0010] Furthermore, in step four, the washed product is dried until the moisture content is ≤3%.

[0011] This application also discloses an electrode comprising the capacitor carbon prepared by the above method.

[0012] Furthermore, by weight, the electrode composition is: 80-90% capacitive carbon, 5-10% conductive carbon black, and 5-10% binder.

[0013] This application discloses a capacitor including the electrodes described above.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Co-sintering pretreatment: Potassium carbonate and urea are co-sintered at a limited temperature to form a eutectic mixture, which allows nitrogen-containing groups (such as NH3) generated by urea decomposition to be synergistically embedded with the carbon skeleton precursor with potassium carbonate, avoiding the wall sticking problem of traditional molten alkali. At the same time, urea decomposition provides a nitrogen source, achieving efficient nitrogen doping, which is more than 50% higher than the traditional process, enabling continuous production and improving production efficiency.

[0015] 2. Rotary furnace continuous activation: The rotary furnace ensures uniform heat and material transfer through centrifugal force, avoiding local overheating caused by static heating. Combined with segmented temperature control, it helps to build a microporous structure with micropores as the main feature (micropore rate > 85%), thereby increasing the specific surface area.

[0016] 3. Pore structure control: By adjusting the ratio of potassium carbonate to urea, activation temperature and time, the specific surface area, pore size distribution and nitrogen content of the capacitor carbon can be precisely controlled.

[0017] 4. Post-treatment optimization: Hydrochloric acid washing removes residual alkali metal salts, facilitating subsequent recycling and reducing environmental pollution. At the same time, protonation of nitrogen-containing functional groups helps enhance the pseudocapacitive effect.

[0018] 5. The capacitor carbon prepared by this invention has advantages such as high specific surface area and reasonable pore size distribution. In 6 mol / L KOH electrolyte, the specific capacitance can reach 220 F / g, which is 40% higher than that of the undoped sample. The tap density is ≥0.4 g / cm³, and the volumetric specific capacitance is increased by 30%. Detailed Implementation

[0019] The present invention will be further described below with reference to specific embodiments.

[0020] The preparation methods of biomass nitrogen-doped capacitor carbon in each embodiment are as follows: Step 1: The mass ratios of biomass, potassium carbonate, and urea are shown in Table 1. The biomass, potassium carbonate, and urea are mixed according to the mass ratio. The mixture is added to a sintering furnace and sintered at 135°C for 3 hours to form a homogeneous eutectic mixture.

[0021] Standard for biomass: Select biomass with a moisture content of ≤5%, crush it to 100-200 mesh, and dry it in an oven at 105℃ for 12 hours.

[0022] Step 2: Add the homogeneous eutectic mixture to the rotary kiln with a filling rate of 65%. Inert gas (argon, flow rate of 2 L / min) is introduced into the rotary kiln. Under the inert atmosphere, the temperature is increased to 380°C at a rate of 10°C / min and held for 45 min for pre-carbonization. Then, the temperature is increased to the activation temperature shown in Table 1 at a rate of 15°C / min for carbonization. During this period, the rotary kiln speed is 7 rpm.

[0023] Step 3: Cool the final product in the rotary kiln to room temperature and immerse it in 1 mol / L hydrochloric acid. Stir and wash three times, 40 min each time, until the pH of the filtrate is 6. Then wash with deionized water until the conductivity is ≤10 μS / cm.

[0024] Step 4: Dry the washed product in a vacuum drying oven at 120℃ for 12 hours until the moisture content is ≤3%. After drying, pass the material through a 200-sieve to obtain capacitor carbon.

[0025] The electrode composition is as follows: by mass, the above-prepared capacitor carbon is 85%, conductive carbon black is 6%, and binder (PVDF binder) is 9%. The preparation method can be referred to conventionally.

[0026] Table 1 Configuration Table for Each Embodiment

[0027] Examples 1, 3, and 5: When biomass (such as lignin, coconut shell, and bamboo chips) reacts with potassium carbonate and urea at a relatively high activation temperature (750-850℃), superior overall performance can be obtained, indicating that by controlling the ratio of potassium carbonate to urea and the activation temperature, the specific surface area and pore size distribution of capacitive carbon can be adjusted. Examples 6 and 7: Different biomass composite materials have adjustable carbon skeleton structures and performance between those of single raw materials, demonstrating the designability of the formulation. Example 8: Increasing the urea ratio can effectively increase the nitrogen content to 4.8%, and the specific capacitance increases accordingly to 241 F / g, proving the effective contribution of nitrogen doping to the specific capacitance. Example 9: Although reducing the amount of activator leads to a decrease in performance, the specific capacitance still reaches 185 F / g, providing a feasible solution for cost-sensitive applications.

[0028] High-performance capacitor carbon can be successfully prepared from different biomass raw materials, proving the versatility of the preparation process of this invention.

[0029] A control example is also provided, as shown below.

[0030] Comparative Example 1 The difference compared to Example 1 is that urea is not added in this example.

[0031] The specific capacitance (F / g) of the capacitor carbon obtained in this comparative example is 165, and the nitrogen content is 0.8%.

[0032] This indicates that the comparative sample lacks an effective nitrogen source and has an extremely low nitrogen doping level, confirming the necessity of urea as a nitrogen source. The nitrogen-containing groups produced by its decomposition are the key to achieving efficient doping. Comparative Example 2 The difference from Example 1 is that potassium hydroxide is used in place of potassium carbonate in this example.

[0033] The specific capacitance (F / g) of the capacitor carbon obtained in this comparative example is 205, and the nitrogen content is 2.7%.

[0034] Potassium hydroxide easily causes equipment corrosion and activation products are difficult to wash. Potassium carbonate has significant advantages in terms of corrosion resistance and environmental protection, and is more suitable for continuous production. Comparative Example 3 Compared with Example 1, the difference is that in this example, physical mixing is performed directly in step one, and the co-sintering step is omitted.

[0035] The specific capacitance (F / g) of the capacitor carbon obtained in this comparative example is 183, and the nitrogen content is 2.3%.

[0036] In this example, the nitrogen source distribution was uneven, the nitrogen doping efficiency was low, and the example also suffered from problems such as easy adhesion to the walls and poor material uniformity, making continuous operation impossible. This indicates that the co-sintering pretreatment step can significantly reduce wall adhesion, thereby enabling continuous operation.

[0037] Comparative Example 4 The difference from Example 1 is that a static fixed-bed reactor is used instead of a rotary kiln in this example.

[0038] The specific capacitance (F / g) of the capacitor carbon obtained in this comparative example is 196, and the nitrogen content is 3.1%.

[0039] This indicates that dynamic activation of the rotary kiln has a significant advantage in ensuring uniform heat and material transfer, while a static fixed bed cannot achieve the same effect. Comparative Example 5 The difference compared to Example 1 is that the hydrochloric acid washing step is omitted in this example.

[0040] The specific capacitance (F / g) of the capacitor carbon obtained in this comparative example is 190, and the nitrogen content is 3.0%.

[0041] This indicates that post-acid washing treatment is crucial for removing residual alkali metal salts and exposing active sites.

[0042] Comparative Example 6 The difference compared to Example 1 is that the pre-carbonization process is omitted in this example.

[0043] The specific capacitance (F / g) of the capacitor carbon obtained in this comparative example is 205, and the nitrogen content is 3.1%.

[0044] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principle of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing biomass-based nitrogen-doped capacitive carbon, characterized in that, Includes the following steps: Step 1: Sinter the mixture of biomass, potassium carbonate and urea in a mass ratio of 1:0.5-3:0.2-1.5 at 120-150℃ for 1-4 hours to form a homogeneous eutectic mixture; Step 2: Under an inert atmosphere, the homogeneous eutectic mixture is pre-carbonized in a rotary kiln at 300-450℃ for 10-60 minutes, and then the pre-carbonized product is carbonized at 650-850℃. Step 3: First, wash the carbonized product with hydrochloric acid until the pH of the filtrate is 5-7, and then wash it with water until the conductivity is ≤10μS / cm; Step 4: Dry the washed product to obtain capacitor carbon.

2. The method for preparing biomass-based nitrogen-doped capacitive carbon as described in claim 1, characterized in that: In step two, the temperature inside the rotary kiln is increased to 300-450℃ at a rate of 5-15℃ / min, and then increased to 650-850℃ at a rate of 10-20℃ / min.

3. The method for preparing biomass-based nitrogen-doped capacitive carbon as described in claim 2, characterized in that: In step three, the rotary kiln speed is 2-10 rpm and the inert gas flow rate is 1-3 L / min.

4. The method for preparing biomass-based nitrogen-doped capacitive carbon as described in claim 1, characterized in that: In step one, the biomass is one or more of lignin, coconut shell, bamboo shavings, rice husk, and straw.

5. The method for preparing biomass-based nitrogen-doped capacitive carbon as described in claim 1, characterized in that: In step one, the biomass has a particle size of 100-200 mesh and a moisture content of ≤5%, and the biomass is first placed in an oven and dried at 100-120℃ for 10-15 hours.

6. The method for preparing biomass-based nitrogen-doped capacitive carbon as described in claim 1, characterized in that: In step four, the washed product is dried until the moisture content is ≤3%.

7. An electrode, characterized in that: Including the capacitor carbon prepared by any one of claims 1-6.

8. An electrode as described in claim 7, characterized in that: By weight, the electrode composition is: 80-90% capacitive carbon, 5-10% conductive carbon black, and 5-10% binder.

9. A capacitor, characterized in that: Includes the electrode as described in any one of claims 7-8.

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