Millimeter-level bamboo-based supercapacitor electrode material and preparation method and application thereof

Abstract

The invention relates to the technical field of preparation and electrochemical performance of bamboo-based supercapacitors and electrode materials, in particular to a millimeter-level bamboo-based supercapacitor electrode material and a preparation method and application thereof. Mixing bamboo chips with potassium hydroxide, absolute ethyl alcohol and water, dipping, and drying to obtain a dipping material; and carrying out heat treatment on the impregnated material in a nitrogen atmosphere to obtain the millimeter-scale bamboo-based supercapacitor electrode material. And the temperature of the heat treatment is 700-900 DEG C. The ABCM-700 with the thickness of 2 mm realizes the ultrahigh area specific capacitance of 30 F cm <-2 > at 1 mA cm <-2 >, and the area specific capacitance of the ABCM-700 is the highest in all reported carbon electrodes. The symmetric supercapacitor assembled by using the two ABCM-700 electrodes has high energy / power density (3.6 mW h cm <-3 > / 2.5 mW cm <-3 >) and excellent cycling stability (the capacitance retention rate is 89% after 5000 times of charge and discharge cycles).

Description

Technical Field

[0001] This invention relates to the technical field of bamboo-based supercapacitors, electrode material preparation and electrochemical performance, and in particular to a millimeter-scale bamboo-based supercapacitor electrode material, its preparation method and application. Background Technology

[0002] In recent years, the rapid development of portable electronic devices and miniaturized energy supply devices has led to increasingly demanding requirements for supercapacitor performance. Therefore, thick electrodes with high areal mass loading and stability are ideal for supercapacitor design because they maximize the energy density of the supercapacitor device by maximizing the packing density of the electroactive material. However, achieving high capacitance through the thickness direction of the electrode material for electrolyte and ion exchange, while maintaining low deformability and lightweight, presents challenges for practical applications. It has been reported that reducing the tortuosity of the internal pores of the electrode material accelerates electrolyte transport throughout the electrode, which is beneficial for thick electrodes. Various layers of porous materials, including wood, enzyme-treated wood, and graphene, have been explored to achieve thick electrode materials with low tortuosity and high ion accessibility. However, due to structural limitations, the thickness of such electrode materials remains limited to below millimeters. Therefore, developing a new strategy for millimeter-scale electrodes with high areal mass loading, high capacitance, low deformability (safety), and lightweight (portability) is crucial for the design of novel supercapacitors.

[0003] One way to increase the thickness of electrode materials is to improve their structural efficiency, thereby promoting the synchronous and multidirectional transport of electrolyte ions within the electrode. Furthermore, the capacity of an electrode also depends on the sufficiency and effectiveness of its active sites. For example, in supercapacitors, micropores with pore sizes suitable for electrolyte ion shuttles can serve as active sites, and their effectiveness and abundance determine the electrode's capacitance. In this case, bamboo charcoal, inheriting the interconnected, layered porous structure of natural bamboo, particularly meets these requirements. However, the insufficient micropores in bamboo charcoal, the unbalanced distribution of micropores and other pores, and the unsuitability of micropore sizes for electrolyte ions weaken the structural effectiveness of bamboo charcoal, thus delaying its role as a millimeter-scale carbon electrode. Therefore, endowing bamboo charcoal with controllable micropores through structural design, enabling it to fully utilize its structural efficiency in thick electrodes, is of great significance. Summary of the Invention

[0004] To address the aforementioned issues, this invention provides a millimeter-scale bamboo-based supercapacitor electrode material, its preparation method, and its application. Based on the unique anisotropic structure of natural bamboo with numerous open channels along its growth direction, this invention proposes a one-step customizable activation strategy to enrich the micropores in these channels, thereby enabling the construction of millimeter-scale supercapacitor electrode materials.

[0005] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for preparing millimeter-scale bamboo-based supercapacitor electrode materials, comprising the following steps: 1) Bamboo strips are mixed with potassium hydroxide, anhydrous ethanol, and water, then impregnated and dried to obtain the impregnated material; 2) The impregnation material described in step 1) is heat-treated in a nitrogen atmosphere to obtain millimeter-scale bamboo-based supercapacitor electrode material; The heat treatment temperature is 700~900℃.

[0006] Preferably, the bamboo strip in step 1) has a thickness of 2 mm and a weight of 5 g.

[0007] Preferably, the mass ratio of the bamboo strips in step 1) to the mass of potassium hydroxide, the volume of anhydrous ethanol, and the volume of water is 5g:9g:135mL:15mL.

[0008] Preferably, the impregnation conditions in step 1) include stirring at a temperature of 20°C for 4 hours.

[0009] Preferably, the drying conditions in step 1) include: a temperature of 70°C and a time of 12 hours.

[0010] Preferably, the heat treatment temperature in step 2) is 800°C.

[0011] Preferably, the heat treatment time in step 2) is 1 hour, and the heating rate is 1℃ / min.

[0012] Preferably, a pretreatment is performed before the heat treatment in step 2), and the pretreatment conditions include: treatment at 350°C for 5 hours in a nitrogen atmosphere, with a heating rate of 1°C / min.

[0013] The present invention also provides a millimeter-scale bamboo-based supercapacitor electrode material prepared by the preparation method described in the above technical solution.

[0014] This invention also provides the application of the millimeter-scale bamboo-based supercapacitor electrode material described in the above technical solution in the preparation of bamboo-based supercapacitors.

[0015] The beneficial effects of this invention are: Inspired by the unique layered porous network of natural bamboo, this invention demonstrates for the first time the design and fabrication of a 2 mm thick activated bamboo charcoal (ABCM) electrode using a one-step KOH activation strategy. Thanks to the improved overall structural efficiency of ABCM, a typical 2 mm thick ABCM-700 achieves a performance of 1 mA cm⁻¹. -2 30 F cm was achieved -2The ultra-high areal capacitance is the highest among all reported carbon electrodes. The symmetrical supercapacitor assembled using two ABCM-700 electrodes exhibits a high energy / power density (3.6 mW h cm⁻¹). -3 / 2.5 mW cm -3 It also boasts excellent cycle stability (capacitance retention of 89% after 5000 charge-discharge cycles). Due to these unique properties, activated carbon represents a promising electrochemical device for enabling high-quality load, high capacitance, lightweight, non-deformable, scalable, and sustainable green and renewable energy storage. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the embodiments will be briefly described below.

[0017] Figure 1 SEM image of the microstructure of the prepared ABCM-700; Figure 2 XRD patterns at different activation temperatures; Figure 3 Electrochemical performance under a three-electrode system at different activation temperatures; Figure 4 Cyclic performance of the ABCM-700 dual-electrode system. Detailed Implementation

[0018] This invention provides a method for preparing millimeter-scale bamboo-based supercapacitor electrode materials, comprising the following steps: 1) Bamboo strips are mixed with potassium hydroxide, anhydrous ethanol, and water, then impregnated and dried to obtain the impregnated material; 2) The impregnation material described in step 1) is heat-treated in a nitrogen atmosphere to obtain millimeter-scale bamboo-based supercapacitor electrode material; the heat treatment temperature is 700~900℃.

[0019] This invention involves impregnating bamboo strips with a mixture of potassium hydroxide, anhydrous ethanol, and water, followed by drying to obtain an impregnated material. In this invention, the thickness of the bamboo strips is preferably 2 mm, and the weight is preferably 5 g. The preferred mass ratio of the bamboo strips to the potassium hydroxide, anhydrous ethanol, and water is 5 g:9 g:135 mL:15 mL. In this invention, potassium hydroxide acts as an activator, etching the bamboo surface to increase micropores; being a strong alkali, it provides optimal etching. The anhydrous ethanol removes excess impurities, disinfects, and improves the permeability of the bamboo. The preferred impregnation conditions include stirring at 20°C for 4 hours. Preferably, the impregnated material is repeatedly washed with anhydrous ethanol and water until the filtrate is neutral before drying. The preferred drying conditions include a temperature of 70°C and a drying time of 12 hours.

[0020] This invention involves heat-treating the impregnated material under a nitrogen atmosphere to obtain millimeter-scale bamboo-based supercapacitor electrode materials; the heat treatment temperature is 600~900℃. Preferably, the heat treatment time is 1 hour, and the heating rate is 1℃ / min. Pretreatment is preferably performed before the heat treatment, and the pretreatment conditions preferably include: treatment at 350℃ under a nitrogen atmosphere for 5 hours, with a heating rate of 1℃ / min. Preferably, the heat-treated material is repeatedly washed with 10% hydrochloric acid and water until the filtrate is neutral to obtain millimeter-scale bamboo-based supercapacitor electrode materials.

[0021] The present invention also provides a millimeter-scale bamboo-based supercapacitor electrode material prepared by the preparation method described in the above technical solution.

[0022] This invention also provides the application of the millimeter-scale bamboo-based supercapacitor electrode material described in the above technical solution in the preparation of bamboo-based supercapacitors.

[0023] To further illustrate the present invention, the following detailed description is provided in conjunction with embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0024] Experimental materials: Natural bamboo, potassium hydroxide, anhydrous ethanol, deionized water, hydrochloric acid, etc., were all purchased from Aladdin (Shanghai, China). All chemicals were used as is, without further purification.

[0025] Example 1 Natural bamboo was cut into 5 g slices, 2 mm thick, and then placed in a mixed solution of potassium hydroxide (9 g), anhydrous ethanol (135 ml), and water (15 ml), and stirred at room temperature (20 °C) for 4 hours. The treated bamboo slices were repeatedly washed with anhydrous ethanol and water until the filtrate was neutral, and finally dried at 70 °C for 12 hours. The impregnated samples were then subjected to a 1 °C min... -1 Heat to the set temperature of 350℃ at a rising rate and hold for 5 hours, then increase the temperature by 1℃ per minute. -1 The temperature was increased to the set temperature of 700℃ and held for 1 hour. The entire heating process was carried out in a nitrogen atmosphere. The resulting carbon body was repeatedly washed with 10% (w) hydrochloric acid and water until the filtrate was neutral. The bamboo charcoal material obtained through one-step activation was labeled ABCM-700.

[0026] Example 2 Natural bamboo was cut into 5 g slices, 2 mm thick, and then placed in a mixed solution of potassium hydroxide (9 g), anhydrous ethanol (135 ml), and water (15 ml), and stirred at room temperature (20 °C) for 4 hours. The treated bamboo slices were repeatedly washed with anhydrous ethanol and water until the filtrate was neutral, and finally dried at 70 °C for 12 hours. The impregnated samples were then subjected to a 1 °C min... -1 Heat to the set temperature of 350℃ at a rising rate and hold for 5 hours, then increase the temperature by 1℃ per minute. -1 The temperature was increased to the set temperature of 800℃ and held for 1 hour. The entire heating process was carried out in a nitrogen atmosphere. The resulting carbon body was repeatedly washed with 10% (w) hydrochloric acid and water until the filtrate was neutral. The bamboo charcoal material obtained through one-step activation was labeled ABCM-800.

[0027] Example 3 Natural bamboo was cut into 5 g slices, 2 mm thick, and then placed in a mixed solution of potassium hydroxide (9 g), anhydrous ethanol (135 ml), and water (15 ml), and stirred at room temperature (20 °C) for 4 hours. The treated bamboo slices were repeatedly washed with anhydrous ethanol and water until the filtrate was neutral, and finally dried at 70 °C for 12 hours. The impregnated samples were then subjected to a 1 °C min... -1 Heat to the set temperature of 350℃ at a rising rate and hold for 5 hours, then increase the temperature by 1℃ per minute. -1 The temperature was increased to the set temperature of 900℃ and held for 1 hour. The entire heating process was carried out in a nitrogen atmosphere. The resulting carbon body was repeatedly washed with 10% (w) hydrochloric acid and water until the filtrate was neutral. The bamboo charcoal material obtained through one-step activation was labeled ABCM-900.

[0028] Comparative Example 1 Natural bamboo was cut into 5 g slices, 2 mm thick, and then placed in a mixture of anhydrous ethanol (135 ml) and water (15 ml) and stirred at room temperature (20°C) for 4 hours. The treated bamboo slices were repeatedly washed with anhydrous ethanol and water until the filtrate was neutral, and finally dried at 70°C for 12 hours. The impregnated samples were then subjected to a 1°C min... -1 Heat to the set temperature of 350℃ at a rising rate and hold for 5 hours, then increase the temperature by 1℃ per minute. -1 The temperature was increased to the set temperature of 700℃ and held for 1 hour. The entire heating process was carried out in a nitrogen atmosphere. The resulting carbon body was repeatedly washed with 10% (w) hydrochloric acid and water until the filtrate was neutral. The bamboo charcoal material obtained without adding KOH was labeled BCM.

[0029] Material characterization testing: The morphology of the samples was measured using a field emission scanning electron microscope (SEM, Thermo Scientific, USA) at a working voltage of 100 kV. The crystal phase analysis of the prepared materials was performed using a wide-angle X-ray diffractometer (XRD, PANalytical BV, Netherlands) with a Ni-filtered Cu-Ka radiation source on an X'Pert PRO MPD X-ray diffractometer.

[0030] Electrochemical characterization tests: Electrochemical measurements were performed using both a three-electrode system and a two-electrode symmetrical supercapacitor, with a 6M KOH aqueous solution as the electrolyte. In the three-electrode system, activated carbon (ABCM) was used as the working electrode, a platinum sheet as the counter electrode, and a mercury / mercury oxide (Hg / HgO) electrode as the reference electrode. In the two-electrode system, the symmetrical supercapacitor consisted of two identical bamboo charcoal electrodes separated by a cellulose membrane containing 6M KOH electrolyte. Cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) were performed on a CHI660D electrochemical workstation (Shanghai Chenhua Instrument Co., Ltd.). CV measurements were performed within a potential window from -1.0 to 0 V, at intervals from 1 to 20 mV s. -1 Different scan rates were performed. GCD experiments were conducted within a potential window of -1.0 to 0 V, at scan rates of 1–20 mA cm⁻¹. -2 Different current densities were used.

[0031] Performance testing: Figure 1 Image a shows a scanning electron microscope image where several channels form vascular bundles, acting as straight channels surrounded by almost uniform cell cavities. This is from a magnified top view (…). Figure 1As shown in diagram b), the openings of the pit chambers are evenly distributed on the surface of the straight channel and connected to the battery. This is the reason why the electrolyte moves rapidly from the channel to adjacent battery chambers. Simultaneously, the cell chambers (20-30µm) are interconnected by tiny pits, such as... Figure 1 As shown in Figure c. Furthermore, all constructed micropores (active sites) are embedded in the cell lumen and further connected to straight channels. The large cell lumen can serve as a "reservoir" for electrolytes, which significantly shortens the transport distance of electrolytes from the cell lumen to the micropores.

[0032] like Figure 2 As shown, BCM and ABCM both exhibit two broader diffraction peaks at 23° and 43°, corresponding to the reflections of the (002) and (100) type graphite interlayer spacing and the graphene-like in-plane structure, respectively.

[0033] Figure 3 In the figure, 'a' represents a scan rate of 10 mV / s. -1 The CV curves of all samples were obtained, and their approximate rectangular shape indicates that the capacitive response of BCM and ABCM mainly originates from the double-layer capacitance. Generally, the area enclosed by the CV profile is proportional to the specific capacitance of the electrode, indicating that ABCM-700 has the highest specific capacitance among all carbons. Figure 3 Figure b shows the ABCM-700 in the range of 1~20 mV s -1 The CV curves at different scan rates show that the rectangular shape of the CV curves is well maintained at different scan rates. The results indicate that ABCM-700 exhibits a rapid electrochemical response.

[0034] All samples were tested at a current density of 10 mA cm⁻¹. -2 The GCD curve at time is as follows Figure 3 As shown in Figure c, the curve exhibits a regular isosceles symmetrical shape, demonstrating the superior electrochemical reversibility of the obtained sample as a thick electrode. Among all the obtained samples, ABCM-700 exhibits the longest charge-discharge time and the largest capacitance. Furthermore, Figure 3 The ABCM-700 is shown in the image below at current densities of 1~20 mA cm⁻¹. -2 The capacitance remains an isosceles triangle. Meanwhile, the charge-discharge curves of ABCM-700 exhibit good symmetry at various current densities, particularly at 1 mA cm⁻¹. -2 30 F cm was achieved -2 The ultra-high areal capacitance indicates that ABCM-700 has good capacitive properties and electrochemical reversibility.

[0035] like Figure 4As shown, in a two-electrode system, a symmetrical supercapacitor assembled using two ABCM-700 electrodes exhibits a high energy / power density (3.6 mW h cm⁻¹). -3 / 2.5 mW cm -3 ). At 20 mA cm -2 After 5000 charge-discharge cycles under certain conditions, the assembled supercapacitor maintained almost 100% coulombic efficiency with 89% of its initial specific capacitance, indicating that the assembled supercapacitor has excellent electrochemical stability and variability even at a thickness of millimeters.

[0036] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing millimeter-scale bamboo-based supercapacitor electrode material, characterized in that, Includes the following steps: 1) Bamboo strips are mixed with potassium hydroxide, anhydrous ethanol, and water, then impregnated and dried to obtain the impregnated material; 2) The impregnation material described in step 1) is heat-treated in a nitrogen atmosphere to obtain millimeter-scale bamboo-based supercapacitor electrode material; The heat treatment temperature is 700~900℃.

2. The preparation method according to claim 1, characterized in that, Step 1) The bamboo strip has a thickness of 2mm and a weight of 5g.

3. The preparation method according to claim 1, characterized in that, Step 1) The mass ratio of the bamboo strips to the mass of potassium hydroxide, the volume of anhydrous ethanol, and the volume of water is 5g:9g:135mL:15mL.

4. The preparation method according to claim 1, characterized in that, Step 1) The impregnation conditions include stirring at a temperature of 20°C for 4 hours.

5. The preparation method according to claim 1, characterized in that, The drying conditions in step 1) include a temperature of 70°C and a time of 12 hours.

6. The preparation method according to claim 1, characterized in that, Step 2) The heat treatment temperature is 800℃.

7. The preparation method according to claim 1, characterized in that, Step 2) The heat treatment time is 1 hour, and the heating rate is 1℃ / min.

8. The preparation method according to claim 1, characterized in that, Step 2) Pretreatment is performed before the heat treatment. The pretreatment conditions include: treatment at 350°C for 5 hours in a nitrogen atmosphere, with a heating rate of 1°C / min.

9. A millimeter-scale bamboo-based supercapacitor electrode material prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the millimeter-scale bamboo-based supercapacitor electrode material according to claim 9 in the preparation of bamboo-based supercapacitors.

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