Performance test method and preparation method of coconut shell charcoal secondary carbonization capacitor carbon-based material

Abstract

The invention belongs to the field of carbon-based material preparation, and discloses a performance test method and a preparation method of a coconut shell charcoal secondary carbonization capacitor carbon-based material. The preparation method comprises the steps of pretreatment of coconut shell charcoal, secondary carbonization, activation and the like. According to the method, coconut shell charcoal and potassium hydroxide are used as raw materials, complex equipment is not needed, the cost is low, and the prepared capacitor carbon-based material is stable in physical structure and large in specific surface area, has a good multi-layer porous structure and has the advantages of being large in specific capacitance, good in heat stability, high in capacity density, good in cycling stability and the like.

Description

Technical Field

[0001] The invention belongs to the field of carbon-based material preparation, and in particular relates to a performance testing method and a preparation method of a coconut shell charcoal secondary carbonization capacitor carbon-based material. Background Art

[0002] With the rapid development of economy and the increase of organic solid waste, waste treatment has become an urgent environmental problem. Using pyrolysis technology to harmlessly treat and efficiently transform organic waste resources and produce high value-added carbon-based functional materials has become an effective technical path to solve the current problems of resource shortage and environmental pollution.

[0003] Coconut shell is the outer shell of coconut fruit, which is usually discarded after coconuts are picked. Coconut shell is a hard shell biomass resource rich in cellulose, with high density and high carbon content, and is an ideal raw material for preparing biomass activated carbon. The preparation of coconut shell activated carbon not only realizes the resource utilization of waste, but also reduces the demand for traditional resources such as wood, which is in line with the concept of sustainable development. Supercapacitors (Super Capacitors) as a high conversion efficiency and high energy density energy storage device have attracted widespread attention and are considered to be a practical low-carbon energy storage device. Among them, the difference in electrode materials has a relatively large impact on the performance of supercapacitors. Commonly used supercapacitor electrode materials include carbon materials, transition metal oxides, hydroxides and conductive polymers, among which carbon materials have attracted much attention from scientific researchers for their good performance. Activated carbon is a commonly used carbon material. As an electrode material for supercapacitors, it can improve the capacitor's specific capacitance and power density. Due to its low preparation cost, simple process and stable electrochemical properties, it is extremely suitable as a supercapacitor electrode material. A preparation method that can effectively use coconut shells to prepare capacitor carbon-based materials is now needed. Summary of the invention

[0004] In order to solve the shortcomings of the prior art, the present invention aims to provide a method for preparing coconut shell charcoal secondary carbonization capacitor carbon-based materials. The method does not require complex equipment and is low in cost. The prepared capacitor carbon-based material has a stable physical structure, a large specific surface area, a good multi-layer pore structure, and has the advantages of large specific capacitance, good thermal stability, high capacity density, and good cycle stability.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] The present invention also proposes a performance testing method for coconut shell carbon secondary carbonization capacitor carbon-based material, comprising the following steps:

[0007] (1) Cut a piece of nickel foam material, mark its number, accurately weigh its initial mass M1 and record it;

[0008] (2) taking out the prepared capacitor carbon-based material, mixing the capacitor carbon-based material, acetylene black and polytetrafluoroethylene (PTFE) in proportion, dropping a small amount of ethanol solution during the mixing and stirring, and stirring into a mixed slurry;

[0009] (3) The mixed slurry is evenly applied on the nickel foam, and the mixture is placed in a constant temperature drying oven for drying. After drying, the electrode sheets are pressed into sheets, and their weights are respectively weighed and recorded as M2; the electrode sheets are then placed in a potassium hydroxide solution and soaked for a period of time;

[0010] (4) Determine the mass composition of the active material on the nickel foam substrate, and the calculation formula is:

[0011] m = 80% (M2 - M1);

[0012] (5) starting the three-electrode system of the electrochemical workstation, selecting the Hg / HgO electrode as the reference electrode, the platinum electrode as the counter electrode, and the prepared nickel foam electrode as the working electrode;

[0013] (6) Use an electrochemical workstation to test the electrochemical performance of the electrode sheet, select cyclic voltammetry, change the voltage window by measuring and adjusting, select the voltage window when the image is optimal, test the preset number of cycles at different scanning rates, save the data, select the last cycle data and calculate the specific capacitance according to the following formula and record it;

[0014] Cm = S integrated area / (2m·△V·r);

[0015] Where Cm is the mass specific capacitance, S is the integrated area of ​​the CV curve, m is the mass of the active component, △V is the width of the voltage window, and r is the scan rate;

[0016] (7) Select the same voltage window for constant current charge-discharge method and cyclic voltammetry, set the current density to 6 segments, select the middle segment of the discharge curve and calculate the specific capacitance according to the following formula and record it;

[0017] Cs=I·△t / (△V·m);

[0018] Among them, Cs is the mass specific capacitance, I is the current intensity, △t is the discharge time, m is the mass of the active component, and △V is the width of the voltage window.

[0019] (8) Select electrochemical impedance spectroscopy (EIS) to measure and draw an image;

[0020] (9) Selecting capacitor carbon-based materials prepared at different activation temperatures, and repeating steps (1)-(8) respectively;

[0021] (10) The capacitor carbon-based materials prepared under different conditions were tested separately to explore the effects of different mixing ratios of slurry and activation temperature on the experimental products, so as to analyze the optimal preparation conditions for the capacitor carbon-based materials.

[0022] Furthermore, in step (2), the capacitor carbon-based material, acetylene black and polytetrafluoroethylene (PTFE) are mixed in a ratio of 8:1:1.

[0023] Preferably, in step (3), the drying temperature is 80° C. and the drying time is 12 h; the pressure and time used in pressing to make the electrode sheet are 15 MPa and 10 min; the electrode sheet is placed in a 6 mol / L KOH solution and soaked for 12 h.

[0024] Preferably, in step (8), the electrochemical impedance spectroscopy is between 0.01 and 10 5 The measurement was performed in the Hz frequency range with an AC amplitude of 10mV.

[0025] Correspondingly, the present invention also proposes a method for preparing a coconut shell carbon secondary carbonization capacitor carbon-based material, which is implemented based on the following steps:

[0026] S1. Pretreatment: Wash the coconut shell charcoal in deionized water for 3-5 times by ultrasonic oscillation, the oscillation time is 10-20min, and the water temperature is controlled at 30-40℃. After washing, place it in a constant temperature drying oven at 70-90℃ to dry for 8-12h, and perform coarse crushing; Wash the coconut shell charcoal in deionized water for 3-5 times by ultrasonic oscillation, the oscillation time is 10-20min, and the water temperature is controlled at 30-40℃. After washing, place it in a constant temperature drying oven at 70-90℃ to dry for 8-12h, and perform coarse crushing;

[0027] S2. Secondary carbonization:

[0028] S2-1. The coconut shell charcoal after pretreatment in step S1 is placed in a tubular furnace and introduced into an inert gas for secondary carbonization. The carbonization temperature is 500-800 ° C, the carbonization time is 2-5h, and the heating rate during the secondary carbonization process is 5-10 ° C / min;

[0029] S2-2. After the carbonization, the coconut shell charcoal is cooled to room temperature at a cooling rate of 5-10 ° C / min, and inert gas protection is continuously introduced during the period;

[0030] S2-3. The cooled coconut shell charcoal is ground into a charcoal powder with uniform particle size and set aside;

[0031] S3. Activation:

[0032] S3-1. Take the ground carbon powder in step S2-3, add the carbon powder to potassium hydroxide in a mass ratio of 1:2-1:4 to a potassium hydroxide solution having a mass fraction of 85%, and mix thoroughly at a stirring speed of 100-300rpm under a magnetic stirrer for 3-5h until a uniform precipitate is formed;

[0033] S3-2. The precipitate obtained in step S3-1 is placed in a constant temperature drying oven at 70-90°C and dried for 12-24 hours until the precipitate is completely dehydrated to form a dry sample;

[0034] S3-3. The solid sample dried in step S3-2 is placed in a tube furnace and an inert gas is introduced for activation reaction. The activation temperature is 700-900 ° C. The heating rate during the activation reaction is 5-10 ° C / min. The activation time is maintained for 2-6h until the activation reaction is completed;

[0035] S4. Purification: The activated product in step S3-3 is cooled to room temperature, washed with hydrochloric acid solution to remove impurities, and then washed with deionized water to neutrality. Finally, the product is placed in a constant temperature drying oven at 70-90°C and dried to constant weight to obtain the final product.

[0036] Preferably, in step S1, the coconut shell charcoal is washed 3 times in ultrasonic oscillation, the oscillation time is 15 minutes, the water temperature is set to 35° C., the drying temperature of the constant temperature drying oven is 80° C., and the drying time is 10 hours.

[0037] Preferably, the inert gas introduced during the secondary carbonization in step S2-1 is high-purity argon with a purity of ≥99.999%, the flow rate is 100 ml / min, the carbonization temperature is 600°C, and the heating rate and cooling rate are both 5°C / min.

[0038] Furthermore, the coconut shell charcoal cooled in step S2-3 is ground into charcoal powder and then passed through a 100-mesh sieve.

[0039] Preferably, in step S3-1, the mass ratio of carbon powder to potassium hydroxide is 1:2-1:4, the stirring speed is 150 rpm, and the stirring time is 4 h.

[0040] Furthermore, in step S3-2, the drying temperature of the constant temperature drying oven is 80° C., and the drying time is 24 hours.

[0041] Furthermore, in step S3-3, the inert gas introduced during activation is high-purity argon gas, the flow rate is 120 mL / min, the activation temperature is 800° C., the activation time is 3 h, and the heating rate is 5° C. / min.

[0042] Furthermore, the hydrochloric acid concentration in step S4 is 1 mol / L, washed to a neutral pH of 6.5-7.5, and dried at 80°C.

[0043] The beneficial effects of the present invention are:

[0044] 1. The present invention uses coconut shell charcoal as the carbon source of the capacitor carbon-based material. In the preparation process, only low cost is required to prepare an activated carbon material with stable physical structure, large specific surface area and good multi-layer pore structure. And no complex equipment is required. The electrode material synthesized at low cost has the advantages of large specific capacitance, good thermal stability, high energy density, good cycle stability, etc.

[0045] 2. In the process of preparing electrode materials, the present invention adds activation of biochar. By changing the mass ratio of biochar and KOH, an activated carbon material with excellent performance can be prepared, which has a large specific surface area, rich porous structure, high degree of graphitization, and good stability. The electrode material prepared by the present invention has excellent electrochemical properties, improves specific capacitance, and prolongs service life. At a scanning rate of 10mV / s, 800℃, C:KOH=1:3, the specific capacitance increases by more than 1.5 times compared with other proportions. At a scanning rate of 5mV / s, 800℃, C:KOH=1:3, the specific capacitance increases by more than 2 times compared with other proportions.

[0046] 3. The electrode material prepared by the present invention can ensure the stability of specific capacitance even at a high current density, and the cycle stability of the electrode material is very good. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 CV curve comparison diagram of each sample of the present invention at different scanning rates;

[0048] Figure 2 This is a comparison diagram of GCD curves of various samples of the present invention at different current densities;

[0049] Figure 3 The samples of the present invention are 0.01-10 5 Comparison of EIS curves in the frequency range of Hz;

[0050] Figure 4 The SEM morphology characterization of different samples of the present invention;

[0051] Figure 5 It is a comparison diagram of adsorption-desorption curves and pore size distribution of different samples of the present invention.

[0052] in, Figure 1 (a), (b), (c), (d), (e), and (f) are CV graphs of CSC, CSC-1:2-800, CSC-1:3-800, CSC-1:4-800, CSC-1:3-700, and CSC-1:3-900 at different scanning rates, respectively;

[0053] Figure 2 (a), (b), (c), (d), (e), and (f) are comparison diagrams of GCD curves of CSC, CSC-1:2-800, CSC-1:3-800, CSC-1:4-800, CSC-1:3-700, and CSC-1:3-900 at different current densities;

[0054] Figure 3 (a) is the EIS graph of CSC, CSC-1:2-800, CSC-1:3-800 and CSC-1:4-800, (b) is the EIS graph of CSC-1:3-700, CSC-1:3-800 and CSC-1:3-900;

[0055] Figure 4 (a), (b), (c), (d), (e), and (f) are SEM images of CSC, CSC-1:2-800, CSC-1:3-800, CSC-1:4-800, CSC-1:3-700, and CSC-1:3-900, respectively;

[0056] Figure 5 (a), (b), (c), (d), (e), and (f) are the adsorption curves and pore size distribution comparisons of CSC, CSC-1:2-800, CSC-1:3-800, CSC-1:4-800, CSC-1:3-700, and CSC-1:3-900, respectively. DETAILED DESCRIPTION

[0057] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not intended to limit the scope of use of the present invention.

[0058] Coconut shell charcoal, as the carbon source of capacitor carbon-based materials, is an activated carbon material prepared from biomass charcoal. The present invention proposes a method for preparing coconut shell charcoal secondary carbonization capacitor carbon-based materials, and coconut shell charcoal is applied to the electrode material of supercapacitors. During the preparation process, an activated carbon material with stable physical structure, large specific surface area, and good multi-layer pore structure can be prepared at a low cost. And no complex equipment is required, and the electrode material synthesized at a low cost has the advantages of large specific capacitance, good thermal stability, high capacity density, and good cycle stability. As described below, the following method can be used when the preparation method of the coconut shell charcoal secondary carbonization capacitor carbon-based material is specifically implemented.

[0059] Embodiment 1:

[0060] (1) Wash the coconut shell charcoal in deionized water for 3 times by ultrasonic oscillation, the oscillation time is 15 minutes, and the water temperature is controlled at 35°C. After cleaning, place it in a constant temperature drying oven at 80°C for 10 hours and coarsely grind it to obtain coconut shell charcoal powder;

[0061] (2) The dried coconut shell carbon powder is placed in a quartz boat, covered with a lid, placed in a tube furnace, and the flanges at both ends are closed. Inert gas argon with a purity of ≥99.999% is introduced at a flow rate of 100 mL / min. The heating rate is set to 5-10°C / min (5°C / min is selected in this embodiment) to 600°C, and the heat preservation time is 2 hours. Then, the temperature is cooled to room temperature at a cooling rate of 5-10°C / min (10°C / min is selected in this embodiment) to ensure argon protection throughout the process, and the coconut shell carbon powder is obtained by secondary carbonization.

[0062] (3) The carbonized coconut shell charcoal powder is ground, passed through 100 mesh, and sealed in a centrifuge tube for storage, which is marked as "CSC".

[0063] Embodiment 2:

[0064] (1) 3.0 g of coconut shell charcoal was cleaned by ultrasonic vibration, dried in a constant temperature drying oven at 80° C. for 10 h, and coarsely crushed to obtain 2.0 g of coconut shell charcoal powder;

[0065] (2) 2.0 g of dried coconut shell carbon powder was placed in a quartz boat, covered with a lid, placed in a tubular furnace, the flanges at both ends were closed, and inert gas argon was introduced at a flow rate of 100 mL / min. The heating rate was set to 5 °C / min to 600 °C, the heat preservation time was 2 hours, and then the temperature was cooled to room temperature at a cooling rate of 10 °C / min to ensure argon protection throughout the process. 1.66 g of coconut shell carbon powder was obtained by secondary carbonization.

[0066] (3) The carbonized coconut shell charcoal powder is ground, passed through 100 mesh, and sealed into a centrifuge tube for storage; the tube is marked as "CSC".

[0067] (4) Weigh 1.5 g of C2-600 with an electronic balance, take 3.0 g of KOH according to the ratio of carbon powder C: potassium hydroxide KOH = 1:2, add water and mix well, pour into a beaker, stir thoroughly with a magnetic stirrer, and stir for 4 hours.

[0068] (5) Place the precipitate in a drying oven, set the drying temperature to 80°C, and dry for 12 hours.

[0069] (6) Grind the dried precipitate, pass it through a 100 mesh, pour it into a quartz boat, and put it into a tube furnace. Tighten the flanges at both ends, introduce inert gas argon, set the flow rate to 120 ml / min, set the heating rate to 5 °C / min to 800 °C, and set the activation holding time to 2-6 h, preferably 3 hours; then cool it down to room temperature at a cooling rate of 10 °C / min to ensure argon protection throughout the process.

[0070] (7) The activated product was taken out, washed with 1 mol / L hydrochloric acid and deionized water until it was neutral, and dried at 80° C., which was recorded as CSC-1:2-800.

[0071] Embodiment 3:

[0072] (1) 10.5 g of coconut shell charcoal was cleaned by ultrasonic vibration, dried in a constant temperature drying oven at 80° C. for 10 h, and coarsely crushed to obtain 10.0 g of coconut shell charcoal powder;

[0073] (2) 10.0 g of dried coconut shell carbon powder was placed in a quartz boat, covered with a lid, placed in a tubular furnace, the flanges at both ends were closed, and inert gas argon was introduced at a flow rate of 100 mL / min. The heating rate was set to 5 °C / min to 600 °C, the heat preservation time was 2 hours, and then the temperature was cooled to room temperature at a cooling rate of 10 °C / min to ensure argon protection throughout the process. 8.4 g of coconut shell carbon powder was obtained by secondary carbonization.

[0074] (3) The carbonized coconut shell charcoal powder is ground, passed through 100 mesh, and sealed into a centrifuge tube for storage; the tube is marked as "CSC".

[0075] (4) Weigh 2.0 g of C2-600 using an electronic balance, take 6.0 g of KOH according to the ratio of C:KOH = 1:3, add water and mix well, pour into a beaker, stir thoroughly with a magnetic stirrer, and stir for 4 h.

[0076] (5) Place the precipitate in a drying oven, set the drying temperature to 80°C, and dry for 12 hours.

[0077] (6) The dried precipitate was ground and passed through a 100-mesh sieve, poured into a quartz boat, and placed in a tubular furnace. The flanges at both ends were tightened, and inert gas argon was introduced with a flow rate of 120 ml / min. The heating rate was set to 5 °C / min to 800 °C, and the temperature was kept at this temperature for 3 hours. The temperature was then cooled to room temperature at a cooling rate of 10 °C / min to ensure argon protection throughout the process.

[0078] (7) The activated product was taken out, washed with 1 mol / L hydrochloric acid and deionized water until it was neutral, and dried at 80° C., which was recorded as CSC-1:3-800.

[0079] Embodiment 4:

[0080] (1) 6.0 g of coconut shell charcoal was cleaned by ultrasonic vibration, placed in a constant temperature drying oven at 80° C. for 10 h, and coarsely ground to obtain 5.0 g of coconut shell charcoal powder;

[0081] (2) 5.0 g of dried coconut shell carbon powder was placed in a quartz boat, covered with a lid, placed in a tubular furnace, the flanges at both ends were closed, and inert gas argon was introduced at a flow rate of 100 mL / min. The heating rate was set to 5 °C / min to 600 °C, the heat preservation time was 2 hours, and then the temperature was cooled to room temperature at a cooling rate of 10 °C / min to ensure argon protection throughout the process. 4.2 g of coconut shell carbon powder was obtained by secondary carbonization.

[0082] (3) The carbonized coconut shell charcoal powder is ground, passed through 100 mesh, and sealed into a centrifuge tube for storage; the tube is marked as "CSC".

[0083] (4) Weigh 1.0 g of C2-600 using an electronic balance, take 4.0 g of KOH according to the ratio of C:KOH = 1:4, add water and mix well, pour into a beaker, stir thoroughly with a magnetic stirrer, and stir for 4 h.

[0084] (5) Place the precipitate in a drying oven, set the drying temperature to 80°C, and dry for 12 hours.

[0085] (6) The dried precipitate was ground and passed through a 100-mesh sieve, poured into a quartz boat, and placed in a tubular furnace. The flanges at both ends were tightened, and inert gas argon was introduced with a flow rate of 120 ml / min. The heating rate was set to increase from 5 °C to 800 °C, and the temperature was kept at this temperature for 3 hours. The temperature was then cooled to room temperature at a cooling rate of 10 °C / min to ensure argon protection throughout the process.

[0086] (7) The activated product was taken out, washed with 1 mol / L hydrochloric acid and deionized water until it was neutral, and dried at 80° C., which was recorded as CSC-1:4-800.

[0087] Embodiment 5-6:

[0088] The difference from the above-mentioned Example 2 is that in Examples 5 and 6, the activation temperature in the tube furnace is set to 700° C. and 900° C., respectively, and finally recorded as CSC-1:3-700 and CSC-1:3-900, respectively.

[0089] The structural parameters of the activated carbon prepared in Examples 1 to 6 are shown in Table 1 below:

[0090] Table 1

[0091]

[0092] In addition, for the coconut shell charcoal secondary carbonization capacitor carbon-based material prepared by the above preparation method, the present invention also proposes a method for testing the electrochemical properties of the coconut shell charcoal secondary carbonization capacitor carbon-based material, the method comprising the following steps:

[0093] (1) Cut the nickel foam material into 1×1 cm 2 Shape, make corresponding marks, accurately weigh its initial mass as M1, and keep records.

[0094] (2) Take out the CSC-1:3-800 prepared above and mix them in a ratio of CSC-1:3-800: acetylene black: polytetrafluoroethylene PTFE = 8:1:1. 0.048 g of CSC-1:3-800 and 0.006 g of acetylene black can be weighed, and 5.0 μl of PTFE can be taken with a pipette. During the mixing and stirring, a small amount of ethanol solution is dropped and stirred into a mixed slurry.

[0095] (3) The mixed slurry was evenly applied on the nickel foam and dried in a constant temperature drying oven at 80°C for 12 h. After drying, the electrode sheets were pressed to obtain electrode sheets (15 MPa, 10 min). The weights were weighed and recorded as M2. The electrode sheets were placed in a 6 mol / L KOH solution and soaked for 12 h.

[0096] (4) Determine the mass composition of the active material on the nickel foam substrate, and the calculation formula is as follows:

[0097] m=80%(M2-M1).

[0098] (5) Start the three-electrode system of the electrochemical workstation, select the Hg / HgO electrode as the reference electrode, the platinum electrode as the counter electrode, and the prepared nickel foam electrode as the working electrode.

[0099] (6) Using an electrochemical workstation to test the electrochemical performance of the electrode sheet, select cyclic voltammetry (CV), change the voltage window by measuring and adjusting, select the voltage window -1.0-0.0 V when the image is optimal (i.e., the graph is closest to a rectangle), test six cycles at scan rates of 5, 10, 20, 50, 70, and 100 mV / s, save the data, select the sixth cycle data and calculate the specific capacitance according to the following formula and record it;

[0100] Cm=S integrated area / (2m·△V·r)

[0101] Where Cm is the mass specific capacitance, S is the integrated area of ​​the CV curve, m is the mass of the active component, △V is the width of the voltage window, and r is the scan rate.

[0102] (7) Select the constant current charge-discharge method (CP), with the same voltage window as the CV method, and set the current density to 0.5, 1, 2, 5, and 10 A / g. Select the middle discharge curve and calculate the specific capacitance according to the following formula and record it;

[0103] Cs=I·△t / (△V·m);

[0104] Among them, Cs is the mass specific capacitance, I is the current intensity, △t is the discharge time, m is the mass of the active component, and △V is the width of the voltage window.

[0105] (8) Select electrochemical impedance spectroscopy (EIS) at 0.01-10 5 The measurements were performed in the Hz frequency range with an AC amplitude of 10mV and the graph was plotted.

[0106] (9) Take out the prepared CSC, CSC-1:2-800, CSC-1:4-800, CSC-1:3-700 and CSC-1:3-900, and repeat the above experiment respectively.

[0107] (10) The present invention tests the preparation of capacitor carbon-based materials under different conditions, with the aim of exploring the effects of conditions such as C:KOH and activation temperature on the experimental products and obtaining the optimal preparation conditions for capacitor carbon-based materials.

[0108] The performance test method proposed in the present invention can more directly and comprehensively verify the influence of experimental conditions on material properties by comparing and analyzing materials prepared by preparation methods under different conditions (such as C:KOH, activation temperature, etc.), thereby optimizing the preparation process and obtaining the best preparation conditions. Using electrochemical performance testing, the following conclusions can be obtained:

[0109] In the voltage window of -1.0-0.0V, under different scanning rate conditions, such as Figure 1 As shown in (c), the curve integral area of ​​CSC-1:3-800 is the largest at a scan rate of 100mV / s. After calculation using the above formula, it is known that the specific capacitance of CSC-1:3-800 at different scan rates is 267F / g, 251F / g, 233.5F / g, 202.1F / g, 187F / g and 169.3F / g, respectively. It can be seen that the calculated specific capacitance of CSC-1:3-800 is the largest, indicating that CSC-1:3-800 has superior capacitance performance and this condition is the best experimental preparation condition. Figure 1 The CV curves of (a)-(f) are shown in Table 2 below.

[0110] Table 2:

[0111]

[0112] It can be concluded from Table 2 that the specific capacitance of different samples shows a downward trend under the change of scan rate. Among them, CSC-1:3-800 shows the highest specific capacitance at the same scan rate, showing excellent capacitive performance.

[0113] In the same voltage window, under different current density conditions, such as Figure 2 As shown in (c), CSC-1:3-800 has a longer discharge time at a current density of 0.5A / g. After calculation using the above formula, it is known that the specific capacitance of CSC-1:3-800 at different current densities is 272.8F / g, 260F / g, 220.6F / g, 206F / g and 189.5F / g. The calculation shows that CSC-1:3-800 has the largest specific capacitance, indicating that it has a longer charge and discharge time and excellent capacitance performance. Figure 2 The GCD curves of (a)-(f) are shown in Table 3 below, and the specific capacitance results of each sample are calculated.

[0114] Table 3:

[0115]

[0116] It can be seen from Table 3 that the specific capacitance decreases with the increase of current density. It is worth noting that CSC-1:3-800 exhibits a higher specific capacitance value at the same current density, highlighting its superior electrochemical performance.

[0117] like Figure 3 As shown in (a), when the open circuit voltage is 0.01V and the frequency range is 0.01-10 5 Under the condition of 1:3 Hz, CSC-1:3-800 has the lowest resistance. The fitting results show that its charge transfer resistance (Rct) is 0.75Ω and its equivalent series resistance (Rs) is 0.27Ω. There are obvious differences in the resistance characteristics of different C:KOH samples, among which the Rct and Rs of CSC are 1.47Ω and 0.42Ω, 1.22Ω and 0.41Ω for CSC-1:2-800, and 1.11Ω and 0.39Ω for CSC-1:4-800. This shows that the appropriate C:KOH (1:3) can significantly reduce the resistance of the sample and improve the conductivity.

[0118] like Figure 3As shown in (b), under the same conditions, the activation temperature also has an important influence on the resistance performance of the samples. CSC-1:3-800 exhibits the lowest resistance values (Rct is 0.75 Ω and Rs is 0.27 Ω), while the Rct and Rs of CSC-1:3-700 and CSC-1:3-900 are 1.19 Ω and 0.32 Ω, and 0.79 Ω and 0.28 Ω, respectively. It can be seen that too high or too low activation temperature will lead to an increase in resistance, indicating that an appropriate activation temperature (800 °C) helps to optimize the conductivity performance.

[0119] As Figure 4 As shown in (a)-(f), they are the SEM images of CSC, CSC-1:2-800, CSC-1:3-800, CSC-1:4-800, CSC-1:3-700 and CSC-1:3-900, respectively. As Figure 4 As shown in (c), CSC-1:3-800 has a hierarchical porous structure, with a large number of micropores, a small amount of macropores and mesopores, and a larger specific surface area, so it has a higher specific capacitance.

[0120] To further study the pore structure and surface porosity of each sample, all samples were subjected to N 2 adsorption-desorption tests at 77.3 K. Figure 5 (a)-(f) show the adsorption-desorption curves of each sample. In the low relative pressure region (P / Po < 0.2), the curve of CSC-1:3-800 shows an obvious steepness, indicating the existence of a large number of micropores. As the relative pressure increases, at a relative pressure of P / Po > 0.4, a hysteresis loop is observed, indicating the existence of mesopores in the material. At 0.9 < P / Po < 1.0, the curve increases slightly, indicating the existence of macropores in the material. Figure 5 The insets in (a)-(f) show the pore size distribution curves of each sample, confirming the existence of a large number of micropores as well as a small amount of mesopores and macropores. The adsorption and desorption amount of CSC-1:3-800 is the largest, and the steepness of the curve is higher than that of CSC-1:2-800 and CSC-1:4-800, indicating that the number of micropores in CSC-1:3-800 is higher than that in CSC-1:2-800 and CSC-1:4-800.

[0121] Through experimental comparative analysis, it can be known that the CSC-1:3-800 prepared under the conditions of C:KOH = 1:3 and an activation temperature of 800 °C has a larger specific surface area (1883 m 2 / g) and a more abundant porous structure (0.97 cm 3 / g), showing a CV curve with a larger rectangular shape and a GCD curve with a longer discharge time, indicating that it has a higher specific capacitance (272.8F / g), and the EIS curve shows that it has a smaller semicircle diameter, indicating that it has a lower high-frequency resistance (0.75Ω), and the material prepared under this condition exhibits excellent electrochemical properties. The present invention can explore the optimal preparation conditions for capacitor carbon-based materials through a performance testing method, which is beneficial to improving the reliability of the preparation process, improving the overall performance of the material, reducing production consumption, and reducing production costs.

[0122] Obviously, the embodiments described above are only some embodiments of the present application, rather than all embodiments. The preferred embodiments of the present application are given in the accompanying drawings, but they do not limit the patent scope of the present application. The present application can be implemented in many different forms. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present application more thorough and comprehensive. Although the present application is described in detail with reference to the aforementioned embodiments, for those skilled in the art, it is still possible to modify the technical solutions recorded in the aforementioned specific implementation methods, or to perform equivalent replacement of some of the technical features therein. Any equivalent structure made using the contents of the specification and drawings of this application, directly or indirectly used in other related technical fields, is similarly within the scope of patent protection of this application.

Claims

1. The performance test method of coconut shell carbon secondary carbonization capacitor carbon-based material is characterized by: The following steps are involved: (1) Cut a piece of nickel foam material, mark its number, accurately weigh its initial mass M1 and record it; (2) taking out the prepared capacitor carbon-based material, mixing the capacitor carbon-based material, acetylene black and polytetrafluoroethylene (PTFE) in proportion, dropping a small amount of ethanol solution during the mixing and stirring, and stirring into a mixed slurry; (3) The mixed slurry is evenly applied on the nickel foam, and the mixture is placed in a constant temperature drying oven for drying. After drying, the electrode sheets are pressed into sheets, and their weights are respectively weighed and recorded as M2; the electrode sheets are then placed in a potassium hydroxide solution and soaked for a period of time; (4) Determine the mass composition of the active material on the nickel foam substrate, and the calculation formula is: m = 80% (M2 - M1); (5) starting the three-electrode system of the electrochemical workstation, selecting the Hg / HgO electrode as the reference electrode, the platinum electrode as the counter electrode, and the prepared nickel foam electrode as the working electrode; (6) Use an electrochemical workstation to test the electrochemical performance of the electrode sheet, select cyclic voltammetry, change the voltage window by measuring and adjusting, select the voltage window when the image is optimal, test the preset number of cycles at different scanning rates, save the data, select the last cycle data and calculate the specific capacitance according to the following formula and record it; Cm = S integrated area / (2m·△V·r); Where Cm is the mass specific capacitance, S is the integrated area of ​​the CV curve, m is the mass of the active component, △V is the width of the voltage window, and r is the scan rate; (7) Select the same voltage window for constant current charge-discharge method and cyclic voltammetry, set the current density to 6 segments, select the middle segment of the discharge curve and calculate the specific capacitance according to the following formula and record it; Cs=I·△t / (△V·m); Where Cs is the mass specific capacitance, I is the current intensity, △t is the discharge time, m is the mass of the active component, and △V is the width of the voltage window; (8) Select electrochemical impedance spectroscopy (EIS) to measure and draw an image; (9) Selecting capacitor carbon-based materials prepared at different activation temperatures, and repeating steps (1)-(8) respectively; (10) The capacitor carbon-based materials prepared under different conditions were tested separately to explore the effects of different mixing ratios of slurry and activation temperature on the experimental products, so as to analyze the optimal preparation conditions for the capacitor carbon-based materials.

2. The performance testing method of the coconut shell charcoal secondary carbonization capacitor carbon-based material according to claim 1 is characterized in that: The size of the nickel foam cut in step (1) is 1 cm×1 cm.

3. The performance testing method of the coconut shell charcoal secondary carbonization capacitor carbon-based material according to claim 1 is characterized in that: In step (2), the capacitor carbon-based material, acetylene black and polytetrafluoroethylene (PTFE) are mixed in a ratio of 8:1:

1.

4. The performance testing method of the coconut shell charcoal secondary carbonization capacitor carbon-based material according to claim 1 is characterized in that: In step (3), the drying temperature is 80° C. and the drying time is 12 h. The pressure and time used in pressing to make the electrode sheet are 15 MPa and 10 min. The electrode sheet is placed in a 6 mol / L KOH solution and soaked for 12 h.

5. The performance testing method of the coconut shell charcoal secondary carbonization capacitor carbon-based material according to claim 1 is characterized in that: In step (8), the electrochemical impedance spectroscopy is between 0.01 and 10 5 The measurement was performed in the Hz frequency range with an AC amplitude of 10mV.

6. The method for preparing the coconut shell charcoal secondary carbonization capacitor carbon-based material used in the performance testing method according to claim 1 is characterized in that: The preparation method is achieved based on the following steps: S1. Pretreatment: Wash the coconut shell charcoal in deionized water for 3-5 times by ultrasonic oscillation, the oscillation time is 10-20min, and the water temperature is controlled at 30-40°C; after washing, dry it in a constant temperature drying oven at 70-90°C for 8-12h and coarsely crush it; S2. Secondary carbonization: S2-1. The coconut shell charcoal after pretreatment in step S1 is placed in a tubular furnace and introduced into an inert gas for secondary carbonization. The carbonization temperature is 500-800 ° C, the carbonization time is 2-5h, and the heating rate during the secondary carbonization process is 5-10 ° C / min; S2-2. The coconut shell charcoal after carbonization is cooled to room temperature at a cooling rate of 5-10 ° C / min, during which inert gas protection is continuously introduced; S2-3. The cooled coconut shell charcoal is ground into a charcoal powder having a uniform particle size and set aside; S3. Activation: S3-1. Take the ground carbon powder in step S2-3, add the carbon powder to potassium hydroxide in a mass ratio of 1:2-1:4 to a potassium hydroxide solution having a mass fraction of 85%, and mix thoroughly at a stirring speed of 100-300rpm under a magnetic stirrer for 3-5h until a uniform precipitate is formed; S3-2. The precipitate obtained in step S3-1 is placed in a constant temperature drying oven at 70-90°C and dried for 12-24 hours until the precipitate is completely dehydrated to form a dry sample; S3-3. The solid sample dried in step S3-2 is placed in a tube furnace and an inert gas is introduced for activation reaction. The activation temperature is 700-900 ° C. The heating rate during the activation reaction is 5-10 ° C / min. The activation time is maintained for 2-6h until the activation reaction is completed; S4. Purification: Cool the activated product in step S3-3 to room temperature, first wash it with hydrochloric acid solution to remove impurities, and then wash it with deionized water until it is neutral; finally, place the product in a constant temperature drying oven at 70-90°C and dry it to constant weight to obtain the final product.

7. The method for preparing coconut shell charcoal secondary carbonization capacitor carbon-based material according to claim 6, characterized in that: In step S1, the coconut shell charcoal is washed 3 times in ultrasonic oscillation, the oscillation time is 15 minutes, the water temperature is set to 35° C., the drying temperature of the constant temperature drying oven is 80° C., and the drying time is 10 hours.

8. The method for preparing coconut shell charcoal secondary carbonization capacitor carbon-based material according to claim 6, characterized in that: In step S2-1, the inert gas introduced during the secondary carbonization is high-purity argon gas with a purity of ≥99.999%, the flow rate is 100 ml / min, the carbonization temperature is 600° C., and the heating rate and cooling rate are both 5° C. / min; The cooled coconut shell charcoal in step S2-3 is ground into charcoal powder and then passed through a 100-mesh sieve.

9. The method for preparing coconut shell charcoal secondary carbonization capacitor carbon-based material according to claim 6, characterized in that: In step S3-1, the mass ratio of carbon powder to potassium hydroxide is 1:2-1:4, the stirring speed is 150 rpm, and the stirring time is 4 h; In step S3-2, the drying temperature of the constant temperature drying oven is 80°C and the drying time is 24h; During activation in step S3-3, the inert gas introduced was high-purity argon gas with a flow rate of 120 mL / min, an activation temperature of 800° C., an activation time of 3 h, and a heating rate of 5° C. / min.

10. The method for preparing coconut shell charcoal secondary carbonization capacitor carbon-based material according to claim 6, characterized in that: The hydrochloric acid concentration in step S4 is 1 mol / L, washed to a neutral pH of 6.5-7.5, and dried at 80°C.

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