Method for making activated carbon material for supercapacitor

Abstract

A method for preparing activated carbon material for supercapacitors includes: (A) subjecting heavy oil to a first heat treatment at a pressure between 2 and 3 atm to generate a soft carbon precursor with a mesophase structure ratio greater than 50 vol%, a quinoline insoluble value (QI value) between 78 and 98 wt%, and a toluene insoluble value between 88 and 100 wt%; (B) mixing the soft carbon precursor with an activator to obtain a mixture; (C) subjecting the mixture to a second heat treatment to induce an activation reaction and a carbonization reaction to obtain a component containing activated carbon and a residual activator; (D) removing the residual activator from the component to obtain an activated carbon material; (E) grinding and classifying the activated carbon material; and (F) subjecting the activated carbon material to a third heat treatment to obtain an activated carbon material for supercapacitors. In step (A), the operating temperature and operating time are between 480 and 580°C and at least 4 hours, respectively.

Description

Technical Field

[0001] This invention relates to a method for preparing a carbon material, and more particularly to a method for preparing an activated carbon material for use in supercapacitors. Prior Technology

[0002] Supercapacitors are also known as electrostatic double-layer capacitors. As is widely known in the industry, supercapacitors are electrochemical capacitors with high energy density, whose capacitance and performance fall between those of traditional electrolytic capacitors and batteries. Furthermore, supercapacitors are a primary tool in power supply systems due to their fast charge / discharge speed and long cycle life. Currently, carbon is the most common electrode material used in supercapacitors. It is worth noting that carbon materials can be produced from heavy hydrocarbon oil, which is sold cheaply by oil refineries, through multiple processing steps. This further enhances the economic benefits of using cheaply sold heavy hydrocarbon oil.

[0003] For example, Chinese patent application CN117342554A (hereinafter referred to as Case 1) discloses a method for preparing activated carbon based on coal pitch, which includes step a, step b, step c, step d and step e in sequence.

[0004] Step a involves placing coal pitch into a high-temperature oxidation furnace and introducing air from the bottom of the furnace to oxidize it for 2 to 5 hours to obtain oxidized material.

[0005] Step b involves crushing the oxidant and sieving it through a 4- to 30-mesh sieve to obtain oxidant particles for later use.

[0006] Step c involves adding the oxidized material particles into a rotary carbonization furnace, introducing steam into the furnace, and carrying out a carbonization reaction at 100°C to 450°C to obtain a carbonized material with a certain strength.

[0007] Step d involves activating the carbonized material using physical activation. Specifically, the carbonized material is added to a rotary activation furnace at a temperature between 650°C and 800°C, and an activation gas is introduced. The oxygen concentration in the rotary activation furnace is controlled to not exceed 5 vol% for activation for 1 to 5 hours, resulting in an activated material with a porous structure.

[0008] Step e involves crushing and sieving or grinding the activated material to obtain granular or powdered activated carbon. While the preparation method described in Case 1 can produce activated carbon suitable for electrode materials in supercapacitors, the physical activation method used in Case 1 results in granular activated carbon with a specific surface area (BET) of only 971 m² / g and a total pore volume of only 0.65 cm³ / g, and powdered activated carbon with a BET of only 958 m² / g and a total pore volume of only 0.66 cm³ / g. Therefore, its contribution to the specific capacitance of supercapacitors is minimal.

[0009] As explained above, improving the preparation method of activated carbon materials to increase the BET and total pore volume of activated carbon materials and increase the specific capacitance of supercapacitors is a problem that needs to be solved by those skilled in the art to which this case pertains. Summary of the Invention

[0010] Therefore, the object of the present invention is to provide a method for preparing an activated carbon material for supercapacitors that can improve BET and total pore volume.

[0011] Therefore, the method for preparing the activated carbon material for supercapacitors of the present invention includes the following steps: step (A), step (B), step (C), step (D), step (E), and step (F).

[0012] Step (A) involves subjecting a heavy oil to a first heat treatment at a pressure between 2 atm and 3 atm to undergo a coking reaction and generate a soft carbon precursor with a quinoline insoluble (QI) value between 78 wt% and 98 wt% and a toluene insoluble (TI) value between 88 wt% and 100 wt%.

[0013] Step (B) involves mixing the soft carbon precursor with an activator to obtain a mixture.

[0014] Step (C) involves subjecting the mixture to a second heat treatment to induce an activation reaction and a carbonization reaction, thereby obtaining a component containing activated carbon and a residual activator.

[0015] Step (D) is to remove the residual activator from the component to obtain an activated carbon material.

[0016] Step (E) involves grinding and grading the activated carbon material.

[0017] Step (F) involves subjecting the ground and graded activated carbon material to a third heat treatment to obtain an activated carbon material for supercapacitors.

[0018] In step (A), the proportion of a mesophase structure contained in the soft carbon precursor is greater than 50 vol%, and the working temperature and working time of the coking reaction are between 480°C and 580°C and at least 4 hours, respectively.

[0019] The advantage of this invention is that the soft carbon precursor obtained by the first heat treatment in step (A) is mixed with the activator to form a mixture and then subjected to the second heat treatment to form a component containing activated carbon and residual activator. After removing the residual activator in the component to obtain activated carbon material, the activated carbon material for supercapacitors obtained by sequentially performing grinding, grading and the third heat treatment has high BET and total pore volume. Simple Explanation of the Diagram

[0020] Other features and effects of the present invention will be clearly presented in the embodiments with reference to the drawings, wherein: Figures 1A to 1E are polarizing microscope (PM) images, illustrating a soft carbon precursor obtained in step (A) of a comparative example 1 (CE1), a comparative example 2 (CE2), a specific example 1 (E1), a specific example 2 (E2), and a specific example 3 (E3) according to the method for preparing activated carbon material for supercapacitors according to the present invention. Figure 2 is a capacitor-to-cycle life curve, illustrating the electrical properties of activated carbon materials for supercapacitors obtained by the method of the present invention in Example 1a (E1a), Example 1g (E1g), Example 1i (E1i), and Example 3 (E3), and assembled into a soft-pack supercapacitor. Figure 3 is a graph showing the relationship between energy density and power density, obtained by summarizing from Figure 2. Figure 4 is a capacitor-to-discharge current relationship diagram, illustrating the capacitance retention of the supercapacitors of Example 1a (E1a), Example 1g (E1g), Example 1i (E1i), and Example 3 (E3) of this invention under low current (0.5A / g) and high current (25A / g). Figure 5A is a graph showing the relationship between capacitance retention and cycle life, illustrating the charge-discharge characteristics of a supercapacitor made from activated carbon material for a supercapacitor obtained by a specific example 1f (E1f) of the method of the present invention and a commercially available activated carbon material (hereinafter referred to as Comparative Example 3 (CE3)), each assembled into a supercapacitor under a charge-discharge condition of 26A; and Figure 5B is a graph showing the relationship between capacitance retention and cycle life, illustrating the charge-discharge characteristics of the supercapacitors of this specific example 1f (E1f) and the comparative example 3 (CE3) under a charge-discharge condition of 52A. Implementation

[0021] An embodiment of the method for preparing activated carbon material for supercapacitors according to the present invention includes the following steps: step (A), step (B), step (C), step (D), step (E), and step (F).

[0022] Step (A) involves subjecting a heavy oil to a first heat treatment at a pressure between 2 and 3 atm to induce a coking reaction and generate a soft carbon precursor with a QI value between 78 wt% and 98 wt% and a toluene-insoluble content between 88 wt% and 100 wt%. In step (A), the soft carbon precursor contains a mesophase structure comprising more than 50 vol%, and the coking reaction is carried out at a temperature between 480°C and 580°C for at least 4 hours. More specifically, step (A) involves first transferring the heavy oil to a reaction vessel (not shown) and subjecting it to a first heat treatment at the specified temperature and pressure for at least 4 hours, causing the heavy oil in the reaction vessel to undergo cracking and condensation polymerization to generate the soft carbon precursor.

[0023] Step (B) involves mixing the soft carbon precursor with an activator to obtain a mixture. In some embodiments, the weight ratio of the soft carbon precursor to the activator in step (B) is between 0.125 and 0.25; that is, the weight ratio is between 1:4 and 1:8. In step (B) of this embodiment of the invention, an impregnation method is used, and potassium hydroxide (KOH) is used as an example of the activator, but the method is not limited thereto. Specifically, step (B) involves placing a mixed solution containing the soft carbon precursor, the activator, and water in a constant temperature bath of an ultrasonic oscillator (not shown) and subjecting it to ultrasonic oscillation for 3 hours; then, the mixed solution is placed in a vacuum oven (not shown) and dried at 110°C for 6 hours to obtain the mixture.

[0024] Step (C) involves subjecting the mixture to a second heat treatment to induce an activation reaction and a carbonization reaction, resulting in a component containing activated carbon and a residual activator. In some embodiments, step (C) involves heating to 700°C to 900°C at a heating rate of 1°C / min to 10°C / min under a nitrogen atmosphere.

[0025] Step (D) removes residual activator from the component to obtain an activated carbon material. In step (D) of this embodiment of the invention, the component is subjected to an acid washing treatment, a water washing treatment, and a drying treatment in sequence. Specifically, the acid washing treatment involves introducing an aqueous solution containing hydrochloric acid (HCl) into the component to neutralize the residual KOH and generate potassium chloride (KCl); the water washing treatment involves introducing deionized water into the aqueous solution to control the pH of the aqueous solution to around 7; the drying treatment involves heating the aqueous solution containing the activated carbon at a temperature of 100-150°C for at least 4 hours to remove the deionized water and obtain the activated carbon material of step (D). In step (D) of this embodiment of the invention, the acid washing treatment is described using an aqueous solution containing hydrochloric acid (HCl) as an example, but is not limited to this.

[0026] Step (E) involves grinding and classifying the activated carbon material. Specifically, in this invention, step (E) involves grinding the activated carbon material and classifying it to obtain activated carbon with a D50 between 10 μm and 12 μm, a D10 between 4 μm and 6 μm, and a D90 between 18 μm and 20 μm. More specifically, in step (E) of this embodiment of the invention, a cyclone classifier is used to sieve the ground activated carbon material to classify it to obtain activated carbon with a D50 between 8 μm and 10 μm, a D10 between 2 μm and 4 μm, and a D90 between 14 μm and 16 μm.

[0027] Step (F) involves subjecting the ground and graded activated carbon material to a third heat treatment to obtain an activated carbon material for supercapacitors. In some embodiments, step (F) involves heating to less than 1000°C at a heating rate of 1°C / min to 10°C / min under nitrogen atmosphere. In this step (F), the activated carbon material for supercapacitors has a plurality of micropores and a plurality of mesopores with a pore size larger than the individual micropores, and the ratio of the total number of micropores to the total number of mesopores is between 7.5 and 0.45.

[0028] The present invention provides the following specific examples and comparative examples based on the manufacturing method of this embodiment to illustrate in detail the specific manufacturing method, the activated carbon material for supercapacitors obtained by the manufacturing method, the carbon electrode made from the activated carbon material, the supercapacitor assembled from the carbon electrode, and the electrical characteristics of the supercapacitor.

[0029] <Preparation method of activated carbon material for supercapacitors>

[0030] <Comparative Example 1 (CE1)>

[0031] Comparative Example 1 (CE1) of the preparation method of the present invention was implemented according to Example 5 disclosed in the applicant's invention patent application No. TWI656094B of the Republic of China. Specifically, the preparation method of Comparative Example 1 (CE1) involved subjecting homophase asphalt to a three-stage first heat treatment under normal pressure to obtain a soft carbon precursor of Comparative Example 1 (CE1). In Comparative Example 1 (CE1), the first stage heat treatment conditions, the second stage heat treatment conditions, and the third stage heat treatment conditions were respectively: heating from 30°C to 100°C at a heating rate of 2°C / min and holding at that temperature for 0.5 hours; heating from 100°C to 200°C at a heating rate of 2°C / min and holding at that temperature for 0.5 hours; and heating from 200°C to 430°C at a heating rate of 2°C / min and holding at that temperature for 1 hour. Next, the soft carbon precursor and KOH were mixed by impregnation at a weight ratio of 1:4 to obtain a mixture of Comparative Example 1 (CE1). Subsequently, the mixture of Comparative Example 1 (CE1) was heated from 30°C to 800°C at a heating rate of 5°C / min and held at that temperature for 1 hour to perform a second heat treatment and obtain a component of Comparative Example 1 (CE1) containing activated carbon and residual KOH. Further, an aqueous solution containing HCl (concentration of 1M) was introduced into the component of Comparative Example 1 (CE1) to neutralize the residual KOH and generate KCl. Next, deionized water was introduced into the aqueous solution of Comparative Example 1 (CE1) to adjust the pH value of the aqueous solution to about 7 to remove the residual HCl in the aqueous solution. Then, the deionized water in the aqueous solution containing the activated carbon was dried at a temperature of 100-150°C to obtain an activated carbon material of Comparative Example 1 (CE1). Subsequently, the activated carbon material of Comparative Example 1 (CE1) was heated from 30°C to 700°C at a heating rate of 10°C / min in an argon (Ar) atmosphere and held at that temperature for 1 hour to perform a third heat treatment and obtain the activated carbon material for a supercapacitor of Comparative Example 1 (CE1).

[0032] <Comparative Example 2 (CE2)>

[0033] Comparative Example 2 (CE2) of the preparation method of the present invention was carried out according to this embodiment and was substantially the same as Comparative Example 1 (CE1), except that Comparative Example 2 (CE2) underwent a first heat treatment, used a certain amount of KOH, and underwent a third heat treatment, while Comparative Example 1 (CE1) was subjected to grinding and classification before the third heat treatment. Specifically, Comparative Example 2 (CE2) underwent a first heat treatment of a heavy oil at a pressure between 2 atm and 3 atm and a working temperature of 450°C for at least 4 hours, causing a coking reaction and generating a soft carbon precursor containing a mesophase structure, as in Comparative Example 2 (CE). Then, the soft carbon precursor and KOH were mixed by impregnation at a weight ratio of 1:6 to obtain a mixture of Comparative Example 2 (CE2). In addition, the activated carbon material of Comparative Example 2 (CE2) was ground and graded, and the activated carbon material of Comparative Example 2 (CE) was heated to 700°C at a heating rate of 10°C / min in a nitrogen atmosphere and held at that temperature for 0.5 hours to complete the third heat treatment.

[0034] The specific examples 1a (E1a), 1b (E1b), 1c (E1c), 1d (E1d), 1e (E1e), 1f (E1f), 1g (E1g), 1h (E1h), 1i (E1i), 2 (E2), and 3 (E3) of the present invention for the preparation of activated carbon material for supercapacitors are substantially the same as Comparative Example 2 (CE2). To reduce the overall length of this specification, the applicant has compiled the different process parameters of each specific example and Comparative Example 2 (CE2) in Table 1 below, which will not be described in detail here.

[0035] Table 1 Example Step (A)1 Step (B)2 Step (C) 3 Step (F)4 Operating temperature (°C) soft carbon precursor weight parts KOH (by weight) temperature (°C) time (hr) temperature (°C) time (hr) CE2 450 1 6 800 1.0 700 0.5 E1a 480 1 4 800 1.0 700 0.5 E1b 480 1 5 800 1.0 700 0.5 E1c 480 1 6 800 1.0 700 0.5 E1d 480 1 7 800 1.0 700 0.5 E1e 480 1 8 800 1.0 700 0.5 E1f 480 1 5 800 1.0 800 2.0 E1g 480 1 6 800 1.5 850 2.0 E1h 480 1 7 800 1.0 700 1.0 E1i 480 1 5 800 0.5 700 0.5 E2 550 1 6 800 1.0 700 0.5 E3 580 1 5 800 1.0 700 0.5 The first heat treatment is to hold the temperature for more than 4 hours. 2. Use impregnation method. 3. The heating rate for the second heat treatment is 5℃ / min. 4. The heating rate for the third heat treatment is 10℃ / min.

[0036] <Measurement Items for Soft Carbon Precursors and Activated Carbon Materials for Supercapacitors>

[0037] The quinoline insoluble content (QI value) was measured according to the specifications of ASTM D7280-06 (2011) for each soft carbon precursor obtained by the CE1, CE2, E1, E2 and E3 methods.

[0038] The toluene insoluble content (TI value) was measured according to the ASTM D4312-95a (2010) standard for each soft carbon precursor obtained by the CE1, CE2, E1, E2 and E3 methods.

[0039] The measurement of the mesophase structure was first performed by taking PM images of each soft carbon precursor obtained by methods CE1, CE2, E1, E2 and E3 using a polarizing microscope (brand: Nikon Polarizing Microscope; model: Eclipse LV100POL) (Figures 1A to 1E). The soft carbon precursors in each PM image of Figures 1A to 1E were analyzed according to ASTM D4616-95 (2013) to calculate the proportion of mesophase structure in each soft carbon precursor obtained by methods CE1, CE2, E1, E2 and E3.

[0040] The yield of activated carbon material is obtained by the following formula (1).

[0041] (Wa / W)×100%................................(1)

[0042] In formula (1), Wa is the weight of the activated carbon material, and W in formula (1) is the weight of the same phase pitch or soft carbon precursor.

[0043] BET was measured using a nitrogen adsorption-desorption instrument (brand: Micromeritics Instrument Corp. USA; model: ASAP 2020M) to measure the activated carbon materials of each comparative example and each specific example, and obtained a graph showing the relationship between the nitrogen adsorption capacity (V, cm3 / g) and the relative pressure (P / P0) at equilibrium pressure. The BET adsorption isotherm relationship was then used ( By plotting P / V(P0-P) against P / P0, the slope (C-1 / CVm) and intercept (1 / CVm) of the relationship between various adsorption amounts and relative pressure can be obtained. Then, using... The specific surface area is calculated using formula (2). In the BET adsorption isotherm, P represents the equilibrium pressure, P0 represents the saturated vapor pressure, C represents the BET constant, V represents the amount of gas adsorbed at the equilibrium pressure, and Vm represents the monolayer saturated adsorption amount. In formula (2), Nm represents the number of adsorbed gas molecules, N represents the Avogadro constant, σ represents the adsorption cross-sectional area of ​​the adsorbed gas molecules, and ν represents the molar volume of the adsorbed gas molecules. In BET measurement, the relative pressure (P / P0) ranges from 0 to 1.

[0044] The BET of mesopores and micropores was measured by using curves from the relationship between various adsorption amounts and relative pressure, combined with the analysis model of heterogeneous surface-2-dimension non-localized density functional theory (HS-2D-NLDFT).

[0045] The total pore volume (unit: cm3 / g) was measured using a nitrogen adsorption-desorption instrument on the activated carbon materials of each comparative example and each specific example, and a nitrogen adsorption-desorption relationship graph was obtained for each gas at equilibrium pressure as a function of relative pressure (P / P0). The total pore volume of the activated carbon materials of each comparative example and each specific example was calculated by combining the curves from each nitrogen adsorption-desorption relationship graph with the HS-2D-NLDFT analytical model.

[0046] The distribution of micropores was measured by using the curves in the nitrogen adsorption-desorption relationship diagram in conjunction with the HS-2D-NLDFT analysis model to calculate the distribution of micropores in the activated carbon materials of each comparative example and each specific example.

[0047] The distribution of mesopores was measured by using the curves in the nitrogen adsorption-desorption relationship diagram in conjunction with the HS-2D-NLDFT analytical model to calculate the distribution of mesopores in the activated carbon materials of each comparative example and each specific example.

[0048] The ratio of micropores to mesopores is calculated using a value obtained by measuring the total pore volume of the activated carbon materials of each comparative example and each specific example; wherein the ratio of micropores is obtained by the following formula (3).

[0049] (Vμ / Vtotal)×100%................................(3)

[0050] In formula (3), Vμ represents the pore volume of micropores with a pore width of less than 2nm, and Vtotal represents the total pore volume.

[0051] Referring to Figures 1A to 1E, the PM images of the soft carbon precursors CE1, CE2, E1, E2, and E3 are shown respectively. The black areas represent the homophase structure of each soft carbon precursor, while the green areas represent the mesophase structure of each soft carbon precursor. The PM images of the soft carbon precursors CE1, CE2, E1, E2, and E3 were analyzed according to ASTM D4616-95 (2013) to calculate the proportions of mesophase structures in each precursor as 78 vol%, 65 vol%, 52 vol%, 60 vol%, and 85 vol% (see also Table 2 compiled by the applicant).

[0052] Table 2 CE1 CE2 E1 E2 E3 Softening point (°C) 185 - - - - First heat treatment temperature (°C) 430 450 480 550 580 First heat treatment pressure (atm) 1 2-3 2-3 2-3 2-3 Mesophase content (vol%) 78 65 52 60 85 Toluene insoluble content (wt%) 45.0 95.0 89.9 99.6 96.4 Quinoline insoluble matter value (wt%) 16.0 78.1 96.4 97.4 88.8

[0053] As shown in Table 2, the toluene-insoluble values ​​of each soft carbon precursor of CE1, CE2, E1, E2 and E3, measured according to ASTM D4312-95a (2010), are 45.0 wt%, 95.0 wt%, 89.9 wt%, 99.6 wt% and 96.4 wt%, respectively. Furthermore, the quinoline-insoluble values ​​of each soft carbon precursor of CE1, CE2, E1, E2 and E3, measured according to ASTM D7280-06 (2011), are 16.0 wt%, 78.1 wt%, 96.4 wt%, 97.4 wt% and 88.8 wt%, respectively. Although the proportion of mesophase structure in the soft carbon precursor of CE1 can reach 78 vol%, the toluene insoluble value and quinoline insoluble value of the soft carbon precursor of CE1 are too low, and they are easily removed by KOH, resulting in a decrease in the yield of activated carbon material.

[0054] Referring to the results for E1a, E1b, E1c, E1d, and E1e shown in Table 3 below, it can be seen that the total pore volume of the activated carbon material used in supercapacitors gradually increases with the gradual increase in the amount of activator used. This result indicates that the activated carbon materials of E1a, E1b, E1c, E1d, and E1e, when each is fabricated into an electrode and assembled into a supercapacitor, are beneficial for improving the power density of the supercapacitor.

[0055] Table 3 P1:A2 BET (m2 / g) Micropore BET (m2 / g) Total pore volume (cm3 / g) Micropore ratio (%) Medium hole ratio (%) CE1 1:4 2802 2028 1.24 72 28 CE2 1:6 2269 2001 1.09 88 12 E1a 1:4 2616 1727 1.13 81 19 E1b 1:5 2895 2487 1.21 85 15 E1c 1:6 2696 2243 1.30 83 17 E1d 1:7 2900 1302 1.68 45 55 E1e 1:8 2820 944 1.73 33 67 E1f 1:5 2409 1856 0.86 81 19 E1g 1:6 2847 2034 1.33 66 34 E1h 1:7 2824 1938 1.36 59 41 E1i 1:5 2555 1889 1.16 71 29 E2 1:6 2301 1977 1.11 86 14 E3 1:5 2116 1640 0.95 74 26 1 part by weight of soft carbon precursor. 2 parts by weight of activator.

[0056] It should be noted that when activated carbon material is used in a supercapacitor, the micropores contained in the activated carbon material can provide a large adsorption area for electrolyte ions during the formation of the electric double layer in the supercapacitor during operation. This helps to increase the specific capacitance of the supercapacitor and thus improve its energy density. In addition, the pore size of the mesopores in the activated carbon material is relatively larger than that of the micropores, resulting in less resistance to the electrolyte, which helps to reduce the resistance to the movement of electrolyte ions and charges. Therefore, it can provide rapid transfer of electrolyte ions and charges within the supercapacitor. Especially when used in environments with a current density of at least 100 A / g, the supercapacitor can still maintain a high specific capacitance and thus improve its power density. As shown in Table 3 above, the ratio of the total micropores to the total mesopores in the activated carbon material used in the supercapacitors E1a, E1b, E1c, E1d, E1e, E1f, E1g, E1h, E1i, E2, and E3 is calculated to be between 6.14 and 0.49. Therefore, it can be deduced that the activated carbon material used in the supercapacitors of these specific examples of the present invention, when applied to a supercapacitor, can provide rapid transfer of electrolyte ions and charges within each supercapacitor, and can also maintain a high specific capacitance value in each supercapacitor under high current density conditions.

[0057] Therefore, after completing the preparation method of the activated carbon material for supercapacitors, the applicant further prepared an electrode slurry and a set of carbon electrode sheets for each of the activated carbon materials used in supercapacitors CE1, E1a, E1b, E1f, E1g, E1h, E1i, and E3 in sequence according to the analysis results in Table 3, and then assembled each set of carbon electrode sheets into a plurality of supercapacitors. The preparation of the electrode slurry was divided into a first electrode slurry and a second electrode slurry, and the set of carbon electrode sheets was also divided into a first carbon electrode sheet and a second carbon electrode sheet. Specifically, the first electrode slurry was used to prepare the first set of carbon electrode sheets and then assemble them into a plurality of test supercapacitors, and the second electrode slurry was used to prepare the second set of carbon electrode sheets and then assemble them into a plurality of pouch cells. It should be noted that the capacitance of each pouch cell is greater than the capacitance of each test supercapacitor, and the capacitance of each pouch cell is approximately 1 F.

[0058] <Starting materials for electrode paste>

[0059] Carboxymethyl cellulose (CMC) powder, model JSR-104A, was purchased from JSR Corporation.

[0060] Conductive carbon black purchased from Timcal under the trade name Super P.

[0061] Styrene-butadiene rubber (hereinafter referred to as SBR) was purchased from Nippon Paper Corporation and is model number MAC350HC.

[0062] Activated carbon material (hereinafter referred to as AC) for supercapacitors of CE1, E1a, E1b, E1f, E1g, E1h, E1i and E3.

[0063] <Preparation of Electrode Paste>

[0064] CMC powder was added to a first deionized water solution (12 ml) and homogenized for 30 minutes at room temperature using a homogenizer to completely dissolve the CMC powder in the first deionized water, thus obtaining a high-viscosity and completely transparent first solution. Next, Super P was added to the first solution and homogenized for 30 minutes, followed by AC, which was homogenized for approximately 150 minutes until the AC was completely and uniformly dispersed in the first solution. Finally, SBR was added to the first solution and homogenized for approximately 15 minutes to obtain the first electrode slurry. The weight percentages (wt%) of CMC, SBR, Super P, and AC in the first electrode slurry are summarized in Table 4 below, and the weight of the dry powder (i.e., CMC, SBR, Super P, and AC) in the first electrode slurry is 0.2 g.

[0065] Table 4 CMC SBR Super P AC 1.5% 5% 3.5% 90%

[0066] The ratio of CMC, SBR, Super P, and AC in the dry powder of the second electrode slurry is the same as that of the first electrode slurry, and its preparation is also largely the same as that of the first electrode slurry. The difference is that the weight of the dry powder of the second conductive slurry is 0.5 g. Specifically, CMC powder is added to a second deionized water (volume 12 ml) and homogenized at room temperature for 40 minutes using a homogenizer to completely dissolve the CMC powder in the second deionized water, thereby obtaining a high-viscosity and completely transparent second solution. Then, Super P is added to the second solution and homogenized for 40 minutes. Subsequently, AC is added to the second solution and homogenized for about 180 minutes until AC is completely and uniformly dispersed in the second solution. Finally, SBR is added to the second solution and homogenized for about 30 minutes to obtain the second electrode slurry.

[0067] <Starting materials for carbon electrode sheets>

[0068] Aluminum foil, model number 30C054, was purchased from Japan Electric Machinery Co., Ltd.

[0069] <Preparation of carbon electrode sheets>

[0070] The first electrode slurry is fed into a coating doctor blade machine with a gap size adjusted to 150 μm, allowing the slurry to be uniformly coated onto the aluminum foil used as a first aluminum current collector to obtain a first electrode coating. Next, the first electrode coating and the first aluminum current collector are placed in a vacuum oven and heated at 110°C for at least 4 hours to ensure complete evaporation of the first deionized water in the first electrode coating. Subsequently, the dried first electrode coating and the first aluminum current collector are placed in a roller and rolled at a rolling rate between 30% and 40%, thereby forming a first carbon electrode layer with a thickness between 40 μm and 50 μm on the first aluminum current collector, so that the first carbon electrode layer and the first aluminum current collector together constitute a first carbon electrode. Finally, the first carbon electrode is cut into a plurality of first carbon electrode sheets to obtain a set of first carbon electrode sheets. It should be noted that each first carbon electrode sheet has a working area (with an area of ​​1.0 cm × 1.0 cm) and a welding area protruding outward from the working area.

[0071] The preparation of the second carbon electrode sheet is largely the same as that of the first carbon electrode sheet, except that the gap size of the coating doctor blade is adjusted to 200 μm. This allows the second electrode slurry to be sequentially coated, heated, and rolled to form a second carbon electrode layer with a thickness of approximately 80 μm on a second aluminum current collector, thus forming a second carbon electrode together with the second aluminum current collector. Finally, the second carbon electrode is cut into multiple second carbon electrode sheets to obtain the set of second carbon electrode sheets. It should be noted that each second carbon electrode sheet has a working area (3.5 cm × 3.5 cm) and a welding area protruding outward from the working area.

[0072] <Starting materials for supercapacitors>

[0073] Triethylmethylammonium tetrafluoroborate (TEMABF4) was purchased from Tokyo Chemical Industry Co., Ltd. and is designated as model T2198.

[0074] Propylene carbonate (hereinafter referred to as PC) was purchased from Sigma and its model number is 107913.

[0075] Acrylonitrile (hereinafter referred to as AN) was purchased from Sigma and its model number is 605310.

[0076] The aluminum tabs were purchased from Ubiquitous and have a thickness of 0.1mm, a width of 3mm, and a length of 65mm.

[0077] Nickel tabs purchased from Ubiquiti, with thicknesses of 0.1mm, widths of 3mm, and lengths of 65mm.

[0078] A separator, model TF40-30, purchased from Liuhe Chemical Co., Ltd., was used as the separator membrane for the supercapacitor.

[0079] The aluminum laminated film (ALF) was purchased from Ubiquitous and has a thickness of 113μm, a width of 480mm, and a length of 10m.

[0080] Assembly of Supercapacitors

[0081] It should be noted that two first carbon electrode sheets are used as a group to serve as the first positive electrode and the first negative electrode of each supercapacitor used for testing. First, the carbon electrode layer remaining on each welding area of ​​each group of first positive and first negative electrode sheets is wiped clean. Then, an aluminum tab and a nickel tab are welded to the welding area of ​​each group of first positive and first negative electrode sheets using an ultrasonic spot welder. Each aluminum tab and each nickel tab has an adhesive film covering an opposite surface corresponding to its welding area. Next, a first separator of appropriate size is sandwiched between the working areas of each group of first positive and first negative electrode sheets and wound to cover each group of first positive and first negative electrode sheets. Subsequently, the wound and covering first separator is placed in a plastic bag and vacuum dried to remove excess moisture from each group of first positive and first negative electrode sheets. Next, each plastic bag containing the first positive electrode, the first negative electrode, and the first separator was placed in a glove box filled with argon (Ar) atmosphere. A first electrolyte (containing TEMABF4 and PC, with TEMABF4 concentration of 1M) was dripped into each plastic bag to completely wet the first positive electrode, the first negative electrode, and the first separator. Finally, a vacuum sealing machine was used to seal one opening of each plastic bag, ensuring that each aluminum tab and each nickel tab was exposed outside the plastic bag, and that the adhesive film on each aluminum tab and each nickel tab was cut flush with the opening of each plastic bag and sealed inside the plastic bag, thereby obtaining each supercapacitor for testing.

[0082] The assembly of each soft-pack supercapacitor is largely the same as that of the test supercapacitors. The difference lies in that two second carbon electrode sheets are grouped together to serve as the second positive and second negative electrode sheets for each soft-pack supercapacitor. Specifically, two aluminum-plastic films of the same size are grouped together and overlapped. The three sides of each group of overlapping aluminum-plastic films are sealed using a vacuum sealing machine to obtain a soft-pack bag with an opening. A second separator film, which is wound and covers each group of second positive and second negative electrode sheets, is placed inside the soft-pack bag and vacuum dried to further remove excess moisture from the second positive and second negative electrode sheets. Next, each soft-pack bag containing each group of second positive and second negative electrode sheets and the second separator film is placed in the glove box, and a second electrolyte (containing TEMABF4 and AN, with the concentration of TEMABF4 being 1M) is dripped into each soft-pack bag to completely wet the second positive electrode sheet, second negative electrode sheet, and second separator film. Finally, the vacuum sealing machine is used to seal the openings of each soft-pack bag, thereby obtaining each soft-pack supercapacitor.

[0083] In addition, based on the analysis results in Table 3, the applicant also sent activated carbon material for the E1f supercapacitor and activated carbon material (model YP-50F) purchased from Corona to a supercapacitor assembly plant to assemble them into a supercapacitor (E1f) and a supercapacitor of Comparative Example 3 (CE3).

[0084] Capacitor Performance Testing

[0085] The specific capacitance (unit: F / g) was measured using an electrochemical apparatus (Solartron Analytical equipment; Model 1470E) on the test supercapacitors and pouch supercapacitors of CE1, CE3, E1a, E1b, E1f, E1g, E1h, E1i, and E3. First, the first positive and first negative electrodes of each test supercapacitor, and the second positive and second negative electrodes of each pouch supercapacitor, were activated using cyclic voltammetry (CV). The scan rate and scan voltage of this cyclic voltammetry were 50 mV / s and 0 to 2.7 V, respectively. Next, each test supercapacitor and each pouch supercapacitor was charged at a current density of 2 A / g. Then, constant current discharge tests were performed on the supercapacitors CE1, E1a, E1b, E1g, and E1h in a voltage range of 0 to 2.7V using current densities of 2 A / g and 100 A / g. Meanwhile, soft-pack supercapacitors E3, E1a, E1g, and E1i were tested using current densities of 0.5 A / g, 5 A / g, 10 A / g, 12.5 A / g, 15 A / g, 20 A / g, and 25 A / g in a voltage range of 0 to 2.7V. Five constant current charge-discharge tests were performed on each capacitor. One constant current charge-discharge test was also performed on each of the E3, E1a, E1g, and E1i soft-pack supercapacitors at current densities of 0.5 A / g, 1.0 A / g, 2.5 A / g, 5 A / g, 7.0 A / g, 10 A / g, 12.5 A / g, 15 A / g, 17.5 A / g, 20 A / g, 22.5 A / g, and 25 A / g within a voltage range of 0 to 2.7 V. Finally, the specific capacitance of each supercapacitor and each soft-pack supercapacitor was calculated using the following formula (4).

[0086] Mass-specific capacitance = 4 × I × td / (M × ΔV) ……………………(4)

[0087] In formula (4), I represents the discharge rate, td represents the discharge time (seconds), M represents the weight of the carbon electrode layer in the electrode of each supercapacitor, and ΔV represents the potential difference after deducting the voltage drop (internal resistance drop, or IR drop).

[0088] The capacitance retention rate (unit: %) is measured as (capacitance value at a current density of 25 A / g) / (capacitance value at a current density of 0.5 A / g) × 100%.

[0089] As shown in Table 5 below, the specific capacitance of the supercapacitors E1a, E1b, E1g, and E1h under a detection condition of 2 A / g are 154 F / g, 156 F / g, 147 F / g, and 153 F / g, respectively, all lower than the specific capacitance of CE1 (160 F / g). However, the specific capacitance of the supercapacitors E1a, E1b, E1g, and E1h under a high current density (100 A / g) detection condition are 130 F / g, 130 F / g, 121 F / g, and 117 F / g, respectively, all higher than the specific capacitance of CE1 (110 F / g). This result indicates that the supercapacitors E1a, E1b, E1g, and E1h under a high current density (100 A / g) test condition have a higher power density than the supercapacitor of CE1.

[0090] Table 5 BET (m2 / g) Micropore ratio (%) Medium hole ratio (%) Mass ratio capacitor F / g; 2A / g F / g; 100A / g CE1 2802 78 twenty two 160 110 E1a 2616 81 19 154 130 E1b 2895 85 15 156 130 E1g 2989 66 34 147 121 E1h 2824 59 41 153 117

[0091] Referring to the capacitance-to-cycle life curves shown in Figure 2, it can be seen that after five constant current charge-discharge tests were conducted on the E3, E1a, E1g, and E1i soft-pack supercapacitors at current densities of 0.5 A / g, 5 A / g, 10 A / g, 12.5 A / g, 15 A / g, 20 A / g, and 25 A / g, respectively, the capacitance gradually decreased. However, when these soft-pack supercapacitors were subjected to a constant current charge-discharge test again at a current density of 0.5 A / g, the capacitance of the E1a, E1g, and E1i soft-pack supercapacitors after five constant current charge-discharge tests was close to the capacitance after the first five constant current charge-discharge tests at a current density of 0.5 A / g. This indicates that the E1a, E1g, and E1i soft-pack supercapacitors of this invention have excellent capacitance retention.

[0092] Further referring to the energy density to power density relationship diagram compiled from Figure 2 (see Figure 3), it can be seen that the power density and energy density of the E3, E1a, E1g, and E1i soft-pack supercapacitors of the present invention are all greater than those of most existing supercapacitors (see the skin-colored area in Figure 3). Furthermore, referring to Figure 4, it can be seen that the capacitance retention rate of the E3, E1a, E1g, and E1i soft-pack supercapacitors of the present invention can be maintained above 93.0% after constant current charge-discharge testing at current densities ranging from 0.5 A / g to 25 A / g.

[0093] Referring to Figure 5A, it can be seen that the cycle life of both the E1f supercapacitor and the CE3 supercapacitor under 26A charge-discharge conditions is close to 18,000 cycles, and the trends of their curves are similar, with their capacitance retention rates both remaining above 80%. Referring to Figure 5B, it can be seen that the cycle life of both the E1f supercapacitor and the CE3 supercapacitor under 56A charge-discharge conditions is also close to 40,000 cycles, and the trends of their curves are similar, with their capacitance retention rates both remaining around 80%. This indicates that the activated carbon material used in the supercapacitors obtained by the method of the present invention, after being made into carbon electrode sheets and assembled into supercapacitors, has charge-discharge characteristics close to those of commercially available activated carbon material (CE3). Therefore, it can be seen that the method of the present invention can improve the economic benefits of selling heavy oil at a low price.

[0094] In summary, the method for preparing activated carbon material for supercapacitors according to the present invention not only improves the economic benefits of selling heavy oil at low prices, but also has high BET and total pore volume. After being prepared into carbon electrode sheets and assembled into supercapacitors, the supercapacitors also have high energy density, high power density and excellent capacitance retention, thus achieving the purpose of the present invention.

[0095] However, the above description is merely an embodiment of the present invention and should not be construed as limiting the scope of the present invention. Any simple equivalent changes and modifications made in accordance with the scope of the patent application and the contents of the patent specification of the present invention shall still fall within the scope of the patent of the present invention.

[0096] none

Claims

1. A method for preparing an activated carbon material for supercapacitors, comprising the following steps: Step (A), subjecting a heavy oil to a first heat treatment at a pressure between 2 atm and 3 atm to undergo a coking reaction and generate a soft carbon precursor with a quinoline insoluble value (QI value) between 78 wt% and 98 wt% and a toluene insoluble value between 88 wt% and 100 wt%; Step (B), mixing the soft carbon precursor with an activator to obtain a mixture, wherein the weight ratio of the soft carbon precursor to the activator is between 0.125 and 0.167; Step (C), subjecting the mixture to a second heat treatment to undergo an activation reaction and a carbonization reaction, and obtaining a component containing activated carbon and a residual activator; Step (D), removing the residual activator from the component to obtain an activated carbon material. Step (E) involves grinding and classifying the activated carbon material; and step (F) involves subjecting the ground and classified activated carbon material to a third heat treatment to obtain an activated carbon material for a supercapacitor. In step (A), the proportion of a mesophase structure contained in the soft carbon precursor is greater than 50 vol%, and the operating temperature and operating time of the coking reaction are respectively between 480°C and 580°C and at least 4 hours. In step (F), the activated carbon material for the supercapacitor has a plurality of micropores and a plurality of mesopores with a pore size larger than each micropore, wherein the micropores represent pore widths of less than 2 nm, and the ratio of the total pore volume of the micropores to the total pore volume of the mesopores is between 7.5 and 0.

45.

2. The method for preparing the activated carbon material for supercapacitors as described in claim 1, wherein, In step (C), the temperature is increased to 700°C to 900°C at a heating rate of 1°C / min to 10°C / min under a nitrogen atmosphere.

3. The method for preparing the activated carbon material for supercapacitors as described in claim 1, wherein, In step (F), the temperature is increased to 700°C to 1000°C in a nitrogen atmosphere at a heating rate of 1°C / min to 10°C / min.

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