A method for preparing a high specific capacitance supercapacitor electrode based on carbon material

Abstract

The application discloses a preparation method of a high specific capacitance supercapacitor electrode based on carbon materials, which comprises the following steps: mixing carbon materials with sodium alginate or a carboxymethyl cellulose aqueous solution to obtain a slurry; coating the slurry on a substrate to form a slurry film, immersing the slurry film together with the substrate in a crosslinking agent to perform crosslinking, and then separating the hydrogel film from the substrate; cleaning the hydrogel film with distilled water to remove residual crosslinking agent, and then immersing the hydrogel film in an electrolyte to perform electrochemical treatment, so as to obtain a high specific capacitance supercapacitor electrode. The application can widen the electrochemical stable potential window of the carbon materials and the electrolyte by 30% and improve the specific capacitance of the carbon materials by about 100% under the condition that the carbon materials and the electrolyte are used in existing commercial applications, and the preparation method is simple, compatible with existing commercial production lines, and can realize large-scale preparation.

Description

Technical Field

[0001] This invention belongs to the field of supercapacitor technology, and particularly relates to a method for preparing a high specific capacitance supercapacitor electrode based on carbon materials. Background Technology

[0002] Supercapacitors have attracted widespread attention due to their high power density and long cycle life, making them particularly suitable for applications requiring frequent, short-term energy storage and release. However, their low energy density (approximately one-tenth that of lead-acid batteries) severely limits their wider application. The relationship between the energy density (E) of a supercapacitor and its capacitance (C) and operating voltage (U) is E = CU. 2 / 2. Therefore, E can be increased by expanding U and enhancing C, which are determined by the electrochemical stability potential window and specific capacitance of the electrode, respectively.

[0003] Carbon materials (such as porous activated carbon, graphene, and carbon nanotubes) are considered the most attractive electrode materials for supercapacitors due to their advantages such as lightweight, high ionic surface area, high electronic conductivity, high electrochemical stability, and fast ion transport kinetics. Currently, commercially available supercapacitor devices are primarily constructed using activated carbon as the active material. However, the electrochemical stability window of carbon materials in acidic and alkaline aqueous electrolytes with high ionic conductivity, small ion size, and high safety is mostly ≤1.0V, and their energy storage primarily relies on the electric double layer (EDLC) mechanism, resulting in relatively low specific capacitance (mostly <300F / g). This severely limits the improvement of energy density in widely used carbon-based supercapacitors.

[0004] To improve the electrochemical stability window of carbon materials, previous studies have mainly focused on altering the composition of the electrolyte, such as water-in-salt electrolytes, organic electrolytes, and ionic liquid electrolytes. However, these electrolytes have significant drawbacks, including large ion sizes and low conductivity, and also introduce problems related to cost and safety. Assembling carbon materials into electrodes often requires the use of binders to bond them into a single unit to ensure the mechanical stability and electronic pathway of the electrode. However, commonly used binders are ionically insulating (such as polyvinylidene fluoride), which prevents the active area blocked by the binder from participating in energy storage, resulting in "dead capacitors" and hindering the full utilization of the carbon material's capacitance. To further improve the capacitance of carbon materials, pseudocapacitors can be introduced. Previous researchers have mainly achieved this by doping carbon materials with nitrogen or compositing them with pseudocapacitor materials. However, these approaches often involve complex synthesis steps and can lead to problems with cycling stability and rate performance degradation.

[0005] Currently, research on expanding the electrochemical stability window of carbon materials, enhancing their capacitance, and simultaneously retaining high rate performance and high cycling stability is still lacking. Solving this problem has significant theoretical and practical implications. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, this invention proposes a method for preparing a high specific capacitance supercapacitor electrode based on carbon materials.

[0007] In one aspect, the present invention provides a method for preparing a high specific capacitance supercapacitor electrode based on carbon materials, comprising:

[0008] Step 1: Mix the carbon material with an aqueous solution of sodium alginate or carboxymethyl cellulose to obtain a slurry;

[0009] Step 2: Coat the slurry onto the substrate to form a slurry film, immerse the slurry film and the substrate together in a crosslinking agent for crosslinking, and then separate the hydrogel film from the substrate;

[0010] Step 3: Wash the hydrogel film with distilled water to remove residual crosslinking agent, and then immerse it in the electrolyte for electrochemical treatment to obtain a high specific capacitance supercapacitor electrode.

[0011] In some embodiments, in step 1, the carbon material is selected from activated carbon, graphene, carbon black, carbon nanotubes, or combinations thereof.

[0012] In some embodiments, in step 1, the ratio of the carbon material to sodium alginate or carboxymethyl cellulose is 2% to 20 wt%, preferably 2% to 10 wt%.

[0013] In some embodiments, in step 2, a blade coater is used to coat the slurry onto a substrate, which may be a glass plate. Preferably, the coating thickness is 200–1000 μm, more preferably 400–600 μm. When the thickness is less than 200 μm, it will be difficult to separate the hydrogel film from the substrate; when the thickness is greater than 1000 μm, it will result in uneven film thickness.

[0014] In some embodiments, in step 2, the crosslinking agent is a calcium chloride or aluminum chloride solution, and the concentration of the calcium chloride or aluminum chloride solution is 0.01 to 1 mol / L.

[0015] In some embodiments, in step 3, the electrolyte is selected from H2SO4, Li2SO4, ZnSO4, CaCl2 and Al2(SO4)3 electrolytes, preferably 3M H2SO4, 0.5M Li2SO4, 1M ZnSO4, 1M CaCl2 and 0.5M Al2(SO4)3 electrolytes.

[0016] In some embodiments, in step 3, the electrochemical treatment is achieved by 20-200 cycles of CV at a scan rate of 5-50 mV / s.

[0017] In some embodiments, in step 3, the oxidation potential of the electrochemical treatment is 0.5-1.0V (relative to Hg / Hg2SO4), preferably 0.5-0.7V. When the oxidation potential is less than 0.5V, the electrochemical stability window and capacitance improvement of the electrode are limited; when the oxidation potential is greater than 1.0V, the electrode will be over-oxidized, leading to performance degradation.

[0018] In a second aspect, the present invention provides a high specific capacitance supercapacitor electrode based on carbon materials obtained by the above-described preparation method.

[0019] In some embodiments, the electrochemically stable potential window of the supercapacitor electrode reaches 1.3V.

[0020] In some embodiments, the specific capacitance of the supercapacitor electrode is increased to 395 F / g.

[0021] In some implementations, the supercapacitor electrodes still exhibit 99% capacitance retention after 20,000 cycles.

[0022] Technical effect

[0023] The high specific capacitance supercapacitor electrode prepared by this invention uses a highly ionicly conductive polymer hydrogel as a binder. Compared to the hydrogel formed by the self-crosslinking of graphene, the polymer hydrogel is simple to prepare and meets the conditions for large-scale preparation. As a binder, it can be conveniently used to form hydrogel electrodes based on various active materials. Furthermore, the polymer hydrogel has high ionic conductivity, allowing ions to penetrate the capping layer and reach all active sites when used as a binder. This avoids the "dead capacitance" caused by the blocking effect of ion-insulating binders, thereby releasing the intrinsic capacitance of carbon materials and achieving a capacitance increase of approximately 40%. In addition, controlled electrochemical oxidation can introduce oxygen-containing functional groups into the electrochemically active surface of carbon materials. This not only improves the oxidation resistance of carbon materials and widens their electrochemical stability potential window by 30%, expanding the electrochemical stability potential window of activated carbon, graphene, and carbon nanotube electrodes to 1.3V, but also introduces pseudocapacitance, further increasing the specific capacitance of carbon materials by approximately 45% (total increase exceeding 100%), and exhibiting high cycling stability.

[0024] By adjusting the electrochemical oxidation potential, the degree of oxidation of carbon materials can be controlled. Appropriate oxidation levels can avoid damage to the conductive carbon framework and prevent the collapse of the porous structure. Controlling the oxidation potential between 0.5 and 0.7 V simultaneously achieves high specific capacitance, high rate performance, and high cycle stability, thus balancing electrochemical stability window, specific capacitance, and rate performance. This electrode can serve as both the positive and negative electrode in symmetric supercapacitors. Due to its high oxidation resistance, it is also suitable as the positive electrode in asymmetric supercapacitors. The fabrication method for this high specific capacitance supercapacitor electrode is simple, allows for large-scale production, and exhibits flexibility and robustness.

[0025] This invention can broaden the electrochemical stability potential window by 30% and increase the specific capacitance by approximately 100% using existing commercially available carbon materials and electrolytes. Furthermore, the preparation method is simple, compatible with existing commercial production lines, and can achieve large-scale production. This method provides an electrode for high-energy-density carbon-based supercapacitors. Attached Figure Description

[0026] Figure 1 A schematic diagram of ion transport within an electrode based on an ion-insulating binder and a polymer hydrogel binder is shown. Figure 1 a is an electrode based on an ion-insulating binder. Figure 1 b is an electrode based on a polymer hydrogel binder;

[0027] Figure 2 The preparation and characterization of the activated carbon / sodium alginate hydrogel electrode are shown. Figure 2 a is the preparation process of activated carbon / sodium alginate hydrogel electrode. Figure 2 b is the obtained flexible activated carbon / sodium alginate hydrogel electrode. Figure 2 c and 2d are scanning electron microscope images of the activated carbon / sodium alginate electrode surface orientation. Figure 2 e and 2f are scanning electron microscope images of the cross-section of the activated carbon / sodium alginate electrode;

[0028] Figure 3 The capacitance performance of activated carbon / sodium alginate hydrogel electrodes and activated carbon / polyvinylidene fluoride electrodes in a series of electrolytes is compared. Figure 3 a is the CV curve in 3M H2SO4. Figure 3 b is the CV curve in 0.5M Li2SO4. Figure 3 c is the CV curve in 1M ZnSO4. Figure 3 d is the CV curve in 1M CaCl2. Figure 3 e is the CV curve in 0.5M Al2(SO4)3. Figure 3 f is the weight-to-capacitance ratio at a sweep rate of 10 mV / s.

[0029] Figure 4 The electrochemical oxidation of the activated carbon electrode and its effect on capacitance performance in 3M H2SO4 are shown. Figure 4 a is the CV curve of the activated carbon electrode from -0.7V to +1.2V (relative to Hg / Hg2SO4). Figure 4 b is the process of oxidizing the electrode at an oxidation potential of +0.6V. Figure 4 c represents the CV curves for electrodes with different oxidation potentials. Figure 4 d represents the electrochemical stability window and weight-to-weight capacitance of electrodes with different oxidation potentials.

[0030] Figure 5 Characterization of the activated carbon electrode undergoing electrochemical oxidation is shown. Figure 5 'a' represents the C / O atom ratio at electrodes with different oxidation potentials. Figure 5 b represents the Raman spectra of electrodes with different oxidation potentials. Figure 5 c represents the infrared spectra of electrodes with different oxidation potentials. Figure 5 df is the X-ray photoelectron spectrum (C1s peak) of electrodes with different oxidation potentials;

[0031] Figure 6 The electrochemical performance of activated carbon electrodes with different oxidation potentials is shown. Figure 6 a represents the ion storage kinetics of electrodes with different oxidation potentials. Figure 6 b represents the rate performance of electrodes with different oxidation potentials based on their specific capacitance. Figure 6 c represents the rate performance of electrodes with different oxidation potentials based on volumetric specific capacitance. Figure 6 Figure d shows the cycling stability of the electrode with an oxidation potential of +0.6V;

[0032] Figure 7 The electrochemical properties of other electrochemically oxidized carbon materials are shown. Figure 7 a is the CV curve of the reduced graphene oxide (rGO) electrode before and after oxidation. Figure 7 b is the CV curve of the electrochemically exfoliated graphene (EG) electrode before and after oxidation. Figure 7 c is the CV curve of the multi-walled carbon nanotube (MWCNT) electrode before and after oxidation. Detailed Implementation

[0033] The preferred embodiments of the present invention are described below with reference to the accompanying drawings to make the technical content clearer and easier to understand. The present invention can be embodied in many different forms, and the scope of protection of the present invention is not limited to the embodiments mentioned herein.

[0034] Example 1

[0035] This embodiment describes the preparation of a high specific capacitance activated carbon / sodium alginate electrode. The specific steps are as follows:

[0036] Prepare a 10 mg / mL sodium alginate (SA) aqueous solution for later use. Figure 2 As shown in a, activated carbon (AC), carbon black (CB, content fixed at 10.0 wt%) and sodium alginate (SA) were water-soluble and stirred for 12 hours to obtain a uniform AC / SA slurry.

[0037] An adjustable blade applicator is used to coat the slurry onto a glass plate, forming a uniform slurry film.

[0038] The slurry film, along with the glass plate, was then immersed in a 1M CaCl2 aqueous solution for crosslinking. After 3 minutes, the AC / SA hydrogel film could be peeled off the glass plate.

[0039] Comparative Example 1

[0040] The electrodes are fabricated using commercially available ion-insulating binders, and the specific steps are as follows:

[0041] AC, CB (with a fixed content of 10 wt%) and polyvinylidene fluoride (PVDF) were mixed in an NMP (N-methylpyrrolidone) solution for 12 h to obtain a homogeneous AC / PVDF slurry.

[0042] The slurry is applied to a glass plate using an adjustable doctor blade applicator and then dried at 60°C for 12 hours. After drying, the AC / PVDF electrode can be peeled off the glass plate.

[0043] The areal load of the electrode is controlled by adjusting the coating thickness of the coater.

[0044] Figure 2 b shows a photograph of an AC / SA electrode (5.0%-SA) with an SA content of 5.0 wt%, which shows that it has good flexibility and can be easily wound onto a glass rod with a diameter of 6 mm.

[0045] Figure 2 The image shown in cf is a scanning electron microscope (SEM) image of the cross-section and surface of the 5.0% SA electrode. The results indicate that the SA region consists of a network of SA lines and voids. Figure 1 As shown, in the hydrogel state, these hydrophilic pores are filled with free water, allowing for rapid ion transport. This allows ions to penetrate the SA capping layer and reach all electrochemically active surfaces, releasing the "dead capacitance" of the AC. The areal loading of the electrode is controlled by adjusting the coating thickness of the coater. The resulting AC / SA hydrogel electrode was washed five times with distilled water to remove residual Ca. 2+ They are then immersed in the electrolyte for 2 hours for subsequent electrochemical treatment.

[0046] like Figure 3As shown, the capacitance performance of the 5.0%-SA electrode in various electrolytes was evaluated using a three-electrode architecture, and its specific capacitance was significantly improved in all cases. In 3M H2SO4, the specific capacitance of 5.0%-SA at 10mV / s was 267F / g, which is 39% higher than that of the activated carbon electrode (5.0%-PVDF) using 5.0wt% polyvinylidene fluoride (PVDF) as a binder. Its capacitance increased by 31%, 33%, 36%, and 34% in 0.5M Li2SO4, 1M ZnSO4, 1M CaCl2, and 0.5M Al2(SO4)3, respectively. It can be seen that the ion-conductive binder 5.0%-SA of the present invention can improve the capacitance of carbon materials in various electrolytes.

[0047] The electrochemical partial oxidation of the activated carbon electrode was achieved by 50 cycles of CV at a scan rate of 20 mV / s in a 3M H2SO4 electrolyte (e.g., Figure 4 (As shown in a and b). CV scans were performed with a fixed minimum potential (-0.7V vs. Hg / Hg₂SO₄) and different maximum oxidation potentials (+0.5V to +0.8V vs. Hg / Hg₂SO₄). After oxidation at +0.7V, the electrochemical stability potential window of the electrode increased from 1.0V to 1.3V, and its specific capacitance also increased from 267F / g to 395F / g. Figure 4 c,d).

[0048] like Figure 5 As shown, characterization by X-ray photoelectron spectroscopy, Raman spectroscopy, and infrared spectroscopy revealed that the aforementioned changes were caused by the introduction of oxygen-containing functional groups into the activated carbon during the oxidation process. These oxygen-containing functional groups not only enhance the oxidation resistance of the activated carbon but also introduce pseudocapacitance with high specific capacitance.

[0049] like Figure 6 As shown, because the degree of oxidation is controlled within a reasonable range, the electrode with an oxidation potential ≤0.7V also exhibits excellent rate performance and still shows 99% capacitance retention after 20,000 cycles.

[0050] Example 2

[0051] This embodiment describes the preparation of a high specific capacitance reduced graphene / sodium alginate electrode. The specific steps are as follows:

[0052] A 10 mg / mL sodium alginate (SA) aqueous solution was prepared for use. Graphene (including reduced graphene oxide and electrochemically exfoliated graphene), carbon black (CB, fixed at 10.0 wt%), and sodium alginate (SA) were dissolved in water and stirred for 12 hours to obtain a uniform graphene / SA slurry. The slurry was then coated onto a glass plate using an adjustable blade coater to form a uniform slurry film. The slurry film, along with the glass plate, was then immersed in a 1 M CaCl2 aqueous solution for crosslinking. After 3 minutes, the AC / SA hydrogel film could be peeled off the glass plate; it exhibited good flexibility and could be easily wound onto a 6 mm diameter glass rod. The obtained graphene / SA hydrogel electrode was washed five times with distilled water to remove residual Ca. 2+ They are then immersed in the electrolyte for 2 hours for subsequent electrochemical treatment.

[0053] Electrochemical partial oxidation of the graphene electrode was achieved by 50 cycles of CV at a scan rate of 20 mV / s in a 3 M H2SO4 electrolyte. CV scans were performed with a fixed minimum potential (-0.7 V vs. Hg / Hg2SO4) and different maximum oxidation potentials (+0.5 V to +0.8 V vs. Hg / Hg2SO4).

[0054] like Figure 7 As shown in a and b, after oxidation at a potential of +0.7V, the electrochemical stability potential window of the electrode increases from 1.0V to 1.3V, and its specific capacitance also increases significantly.

[0055] Example 3

[0056] This embodiment describes the preparation of a high specific capacitance reduction activated carbon / sodium carboxymethyl cellulose electrode. The specific steps are as follows:

[0057] Prepare a 10 mg / mL sodium carboxymethyl cellulose (CMC) aqueous solution for later use. Activated carbon (AC), carbon black (CB, fixed content 10.0 wt%), and CMC are dissolved and mixed in water for 12 hours to obtain a uniform AC / CMC slurry. The slurry is then coated onto a glass plate using an adjustable blade coater to form a uniform slurry film. The slurry film, along with the glass plate, is then immersed in a 1 M AlCl3 aqueous solution for crosslinking. After 3 minutes, the AC / SA hydrogel film can be peeled off the glass plate. It exhibits good flexibility and can be easily wound onto a 6 mm diameter glass rod.

[0058] The electrochemical partial oxidation of the activated carbon electrode was achieved by 50 cycles of CV at a scan rate of 20 mV / s in a 3M H2SO4 electrolyte (e.g., Figure 4(As shown in a and b). CV scans were performed with a fixed minimum potential (-0.7V vs. Hg / Hg2SO4) and different maximum oxidation potentials (+0.5V to +0.8V vs. Hg / Hg2SO4).

[0059] Example 4

[0060] This embodiment describes the preparation of a high specific capacitance multi-walled carbon nanotube / sodium alginate electrode. The specific steps are as follows:

[0061] A 10 mg / mL sodium alginate (SA) aqueous solution was prepared for use. Multi-walled carbon nanotubes (MWCNTs) and sodium alginate (SA) were mixed in water and stirred for 12 hours to obtain a uniform graphene / SA slurry. The slurry was then coated onto a glass plate using an adjustable blade coater to form a uniform slurry film. The slurry film, along with the glass plate, was then immersed in a 1 M CaCl2 aqueous solution for crosslinking. After 3 minutes, the MWCNT / SA hydrogel film could be easily peeled off the glass plate, exhibiting good flexibility and readily wound onto a 6 mm diameter glass rod. The resulting MWCNT / SA hydrogel electrode was washed five times with distilled water to remove residual Ca. 2+ They are then immersed in the electrolyte for 2 hours for subsequent electrochemical treatment.

[0062] Electrochemical partial oxidation of the MWCNT electrode was achieved by 50 CV cycles at a scan rate of 20 mV / s in a 3 M H2SO4 electrolyte. CV scans were performed with a fixed minimum potential (-0.7 V vs. Hg / Hg2SO4) and different maximum oxidation potentials (+0.5 V to +0.8 V vs. Hg / Hg2SO4).

[0063] like Figure 7 As shown in c, after oxidation at a potential of +0.7V, the electrochemical stability potential window of the electrode increases from 1.0V to 1.3V, and its specific capacitance also increases significantly.

[0064] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for preparing a high specific capacitance supercapacitor electrode based on carbon materials, comprising the following steps: Step 1: Mix the carbon material with an aqueous solution of sodium alginate or carboxymethyl cellulose to obtain a slurry; the carbon material is selected from activated carbon, graphene, carbon black, carbon nanotubes, or a combination thereof; Step 2: Coat the slurry onto the substrate to form a slurry film, immerse the slurry film and the substrate together in a crosslinking agent for crosslinking, and then separate the hydrogel film from the substrate; Step 3: Wash the hydrogel film with distilled water to remove residual crosslinking agent, and then immerse it in the electrolyte for electrochemical treatment to obtain a high specific capacitance supercapacitor electrode; In step 3, the electrochemical treatment is achieved by CV cycling at a scan rate of 5-50 mV / s for 20-200 cycles; the oxidation potential of the electrochemical treatment is 0.5-0.7 V vs. Hg / Hg2SO4.

2. The preparation method according to claim 1, wherein, In step 1, the ratio of the carbon material to sodium alginate or carboxymethyl cellulose is 2% to 20 wt%.

3. The preparation method according to claim 1, wherein, In step 2, the coating thickness is 200~1000μm.

4. The preparation method according to claim 1, wherein, In step 2, the crosslinking agent is a calcium chloride or aluminum chloride solution, and the concentration of the calcium chloride or aluminum chloride solution is 0.01~1 mol / L.

5. The preparation method according to claim 1, wherein, In step 3, the electrolyte is selected from H2SO4, Li2SO4, ZnSO4, CaCl2 and Al2(SO4)3 electrolyte.

6. A high specific capacitance supercapacitor electrode based on carbon materials obtained by the preparation method according to any one of claims 1-5.

7. The high specific capacitance supercapacitor electrode based on carbon material according to claim 6, wherein it satisfies at least one of the following conditions: (1) The electrochemical stable potential window of the supercapacitor electrode is 1.3V; (2) The specific capacitance of the supercapacitor electrode is 395 F / g; (3) The supercapacitor electrode has a capacitance retention rate of 99% after 20,000 cycles.

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