Preparation method and application of carbon dot-based electrode slurry

Abstract

The invention discloses a preparation method and application of carbon dot-based electrode slurry. Comprising the following steps: mixing a conductive agent with mixed acid, and carrying out a heating reaction in a closed container to obtain the carbon dot-based electrode slurry, the conductive agent contains KB and Super P; the mixed acid contains concentrated sulfuric acid and concentrated nitric acid. Compared with a hydrothermal method from bottom to top, the TDs prepared by the method provided by the invention are uniform in granularity, high in purity and high in yield. The product does not need to be separated from mother liquor, does not need subsequent water washing, and can be directly used for preparing electrode slurry.

Description

Technical Field

[0001] This application relates to a method for preparing and applying a carbon dot-based electrode slurry, belonging to the field of flow battery materials. Background Technology

[0002] Supercapacitors are a new type of energy storage device developed in recent years. They have advantages such as high power density, long cycle life, environmental friendliness, and safety and reliability, and can meet the needs of smoothing and power quality control in distributed renewable energy generation systems. However, the small capacity and low energy density of individual units lead to problems such as overly complex module integration, high system cost, and high operation and maintenance costs, thus restricting the widespread application of supercapacitors in the field of large-scale energy storage. Flow supercapacitors are a type of supercapacitor with a novel structure that uses a flowable electrode slurry composed of electrode active materials and an electrolyte solution to store electrical energy. The electrode slurry is charged as it flows between the two electrodes, during which a double electric layer is formed on the surface and within the pores of the electrode active materials, or a rapid reversible electrochemical reaction occurs to achieve energy storage. The charged electrode slurry is then transported to an external container for storage. During discharge, the charged electrode slurry flows between the two electrodes, releasing electrical energy. The discharged electrode slurry is then transported to another pair of containers for storage. One of the important characteristics of flow supercapacitors is that energy density and power density are no longer interdependent. The energy density of traditional supercapacitors decreases with increasing power density, while the energy stored in flow supercapacitors is determined by the size of the electrode slurry tank, and the output power is determined by the size of the capacitor cell. The development of electrode slurries with high suspension stability, high capacity, and high rate performance is of particular significance to the technological development and application of flow supercapacitors. Compared with other types of carbon materials, activated carbon has advantages such as high specific surface area and low cost. However, to use activated carbon in the preparation of electrode slurries for flow supercapacitors, the problem of its poor suspension characteristics must be solved.

[0003] Carbon dots (CDs) are a novel type of zero-dimensional carbon-based nanomaterial with outstanding advantages such as good electrical conductivity, high chemical stability, low toxicity, and environmental friendliness. CDs exhibit a high degree of graphitization and their surface contains abundant oxygen- or nitrogen-containing functional groups. Due to their high water solubility and the high stability of the resulting aqueous solution, CDs hold promise as active materials for high-performance flow supercapacitor electrodes. The preparation of CDs typically employs two technical routes: "top-down" and "bottom-up." The "top-down" method involves exfoliating carbon materials such as graphite using physical or chemical methods to reduce their size and obtain nanoscale carbon particles, i.e., CDs. The "bottom-up" method involves preparing nanoscale CDs from a carbon source using physical methods such as vapor deposition or hydrothermal methods. Both of these methods generally suffer from difficulties in large-scale preparation or separation from the mother liquor, and require significant water consumption for washing and purification, limiting their widespread application. Summary of the Invention

[0004] The technical problems to be solved by this application include: (1) the difficulty in preparing large quantities of carbon dots and the difficulty in separating them from the mother liquor. (2) the problem that activated carbon slurry for liquid-flow supercapacitors is prone to agglomeration and blockage in carbon felt and pipes. (3) the problem that it is difficult to obtain both high specific surface area and high conductivity of electrode active materials.

[0005] According to one aspect of this application, a method for preparing a carbon dot-based electrode paste (TDs electrode paste) is provided, comprising the following steps:

[0006] The conductive agent is mixed with mixed acid and heated in a sealed container to obtain the carbon dot-based electrode slurry.

[0007] The conductive agent contains KB and Super P;

[0008] The mixed acid contains concentrated sulfuric acid and concentrated nitric acid.

[0009] The concentrated sulfuric acid has a mass fraction of 70-98%.

[0010] The concentrated nitric acid has a mass fraction of 50-68%.

[0011] In the conductive agent, the mass ratio of KB to Super P is 95:5 to 6:4.

[0012] Optionally, the mass ratio of KB to Super P in the conductive agent is any value or a range between any two of 95:5, 95:4, 90:4, 80:4, 70:4, 60:4, 50:4, 40:4, 30:4, 20:4, 10:4, and 6:4.

[0013] In the mixed acid, the volume ratio of concentrated sulfuric acid to concentrated nitric acid is 1:9 to 9:1.

[0014] Optionally, the volume ratio of concentrated sulfuric acid to concentrated nitric acid is any value from 1:9, 2:9, 3:9, 4:9, 5:9, 6:9, 7:9, 8:9, 9:9, 9:8, 9:7, 9:6, 9:5, 9:4, 9:3, 9:2, 9:1 or any range between the two.

[0015] The ratio of the conductive agent to the mixed acid is 0.1-10g:100ml.

[0016] Optionally, the ratio of the conductive agent to the mixed acid is any value or a range between 0.1g:100ml, 0.5g:100ml, 1g:100ml, 2g:100ml, 3g:100ml, 4g:100ml, 5g:100ml, 6g:100ml, 7g:100ml, 8g:100ml, 9g:100ml, and 10g:100ml.

[0017] The temperature of the heating reaction is 90–150°C;

[0018] Optionally, the temperature of the heating reaction is any value or a range between 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, and 150°C.

[0019] The heating reaction time is 0.1 to 24 hours.

[0020] Optionally, the heating reaction time is any value among 0.1h, 0.5h, 1h, 2h, 4h, 8h, 12h, 16h, 20h, and 24h, or a range between any two.

[0021] The sealed container is a hydrothermal reactor.

[0022] Optionally, the following steps are included:

[0023] (1) Mix concentrated sulfuric acid and concentrated nitric acid in a ratio of 1:9 to 9:1.

[0024] (2) Add KB and Super P powder to the mixed acid and stir until homogeneous. The mass ratio of KB to Super P is 95:5-6:4.

[0025] (3) Transfer the mixture obtained in step (2) into the polytetrafluoroethylene sleeve of the hydrothermal reactor, seal and tighten it, and heat it to 90-150℃ and keep it at that temperature for 0.1-24h.

[0026] (4) After the hydrothermal reactor cools to room temperature, the reaction product is taken out and diluted with deionized water to obtain TDs-based electrode slurry.

[0027] According to another aspect of this application, an electrode slurry prepared by the above-described preparation method is provided for use in a flow supercapacitor.

[0028] According to another aspect of this application, an electrode slurry prepared by the above-described preparation method is provided for use in a symmetrical flow supercapacitor.

[0029] After diluting the electrode slurry, it is added to the positive and negative electrodes of the flow supercapacitor, and then circulated between the positive electrode and the positive electrode slurry pool, and between the negative electrode and the negative electrode slurry pool, to form a symmetrical flow supercapacitor.

[0030] The substance is added by pumping it in using a circulation pump.

[0031] The symmetrical flow supercapacitor is charged using a constant voltage and current limiting method and discharged using a constant current method.

[0032] This application relates to a top-down method for preparing CDs (capacitors and precipitates). This method uses a hydrothermal process to treat highly conductive KB and Super P with a mixed acid solution of concentrated sulfuric acid and concentrated nitric acid, reducing the particle size of KB and Super P to obtain mixed CDs. Unlike the traditional bottom-up hydrothermal method for CD preparation, the method described in this invention offers significant advantages such as ease of large-scale production, high product purity, uniform particle size, and good dispersibility. When applied to flow supercapacitors, it eliminates the need for separation from the mother liquor and washing / purification processes, reducing energy consumption and wastewater discharge, thus benefiting environmental protection. By adjusting the ratio of KB and Super P, the electrode slurry possesses both high specific surface area and high conductivity, significantly improving the specific capacity and rate performance of the flow supercapacitor.

[0033] The beneficial effects that this application can produce include:

[0034] (1) Using KB and Super P as raw materials and mixed acid as the reaction medium, large-scale preparation of TDs was achieved by hydrothermal method. Compared with the "bottom-up" hydrothermal method, the TDs prepared by the method provided by this invention have uniform particle size, high purity and high yield.

[0035] (2) The hydrothermal products obtained by the method provided by the present invention do not need to be separated from the mother liquor or washed with water, and can be directly used to prepare electrode slurry.

[0036] (3) TDs in hydrothermal products serve as electrode active materials. Among them, TDs derived from KB have a high specific surface area, and their main function is to provide a site for the formation of the electric double layer, thereby achieving energy storage. TDs derived from Super P have higher electronic conductivity, which can provide channels for electron transport in the electrode slurry, reduce the ohmic polarization of the electrode, and thus improve the electrode capacity and rate performance. By adjusting the ratio of hydrothermal raw materials KB and Super P, the ratio of KB-based and Super P-based CDs in the electrode slurry can be flexibly adjusted, thereby optimizing the capacity and rate performance of the electrode slurry.

[0037] (4) Sulfuric acid and nitric acid in hydrothermal products can be used directly as electrolytes in electrode slurry.

[0038] (5) By adjusting the ratio of concentrated sulfuric acid and concentrated nitric acid in the hydrothermal feedstock, the types and ratios of oxygen-containing and nitrogen-containing functional groups on the surface of TDs can be optimized, thereby improving the pseudocapacitance, hydrophilicity and suspension stability of the electrode active material.

[0039] (6) By adjusting the ratio of KB / Super P and mixed acid and the amount of deionized water added during the dilution process, the specific capacity and suspension stability of the balanced electrode slurry can be optimized.

[0040] (7) By optimizing the hydrothermal reaction temperature, the suspension characteristics and specific capacity of the electrode slurry can be controlled. Attached Figure Description

[0041] Figure 1 The image shown is a transmission electron microscope image of KB used in Example 1, with a scale of 100 nm.

[0042] Figure 2 The image shown is a transmission electron microscope image of the Super P used in Example 1, with a scale of 100 nm.

[0043] Figure 3 The image shown is a transmission electron microscope image of the TDs electrode paste prepared in Example 1, at a scale of 50 nm. Detailed Implementation

[0044] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0045] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.

[0046] Example 1

[0047] (1) Preparation of TDs electrode paste

[0048] Mix 60 ml of 98% concentrated sulfuric acid and 20 ml of 68% concentrated nitric acid thoroughly. Add 4.5 g of KB and 0.5 g of Super P, and stir until homogeneous. Transfer the resulting mixture to a PTFE inner liner, place it inside a stainless steel sleeve of a hydrothermal reactor, seal it tightly, and place it in a constant temperature oven. Heat to 100°C and maintain the temperature for 4 hours. Cool the hydrothermal reactor to room temperature, remove the hydrothermal product, and dilute it with deionized water to 160 ml to obtain the TDs electrode slurry.

[0049] TDs in the electrode slurry were observed using a transmission electron microscope.

[0050] Figure 1The image shown is a transmission electron microscope image of KB used in Example 1, with a scale of 100 nm.

[0051] Figure 2 The image shown is a transmission electron microscope image of the Super P used in Example 1, with a scale of 100 nm.

[0052] Figure 3 The image shown is a transmission electron microscope image of the TDs electrode paste prepared in Example 1, at a scale of 50 nm.

[0053] The results are attached. Figure 3 As shown. For comparison, KB and Super P powders were observed simultaneously using transmission electron microscopy, and the results are as follows. Figure 1 , Figure 2 As shown, the particle size of KB and Super P before hydrothermal mixed acid treatment is relatively large and the dispersibility is poor. After hydrothermal treatment, the particle size of KB and Super P-based TDs in the product is 5-10 nm, and the dispersion is uniform without agglomeration.

[0054] 10 ml of electrode slurry was taken out and allowed to stand for 120 hours; no stratification occurred. The remaining electrode slurry was divided into two portions, one for the positive electrode and the other for the negative electrode, to be used for constructing a flow supercapacitor and for performance testing.

[0055] (2) Construction of flow supercapacitor

[0056] The structure of this patented flow supercapacitor is basically the same as that of a flow battery. The constructed flow supercapacitor consists of end plates, a graphite current collector, carbon felt, a separator, a frame, a sealing gasket, positive and negative electrode slurry storage tanks, a delivery pump, and piping. The separator used is a Daramic 900μm polyethylene porous membrane. The effective area of ​​the capacitor is 6cm*8cm.

[0057] The test conditions for capacitor performance were as follows: the flow rate of the positive and negative electrode slurries in the capacitor was 50 ml / min. The capacitor was subjected to constant voltage and current-limited charging, with a charging cutoff voltage of 1.0V and a charging current limit of 50 mA / cm². 2 The capacitor is subjected to constant current discharge, with a discharge cutoff voltage of 0V. Calculate the coulombic efficiency and energy efficiency of the capacitor based on its charge / discharge capacity.

[0058] Test results show that the supercapacitor using the TDs electrode slurry of this embodiment achieves a flow rate of 20 mA / cm². 2 The constant current discharge specific capacity is 175 F / g, the coulombic efficiency is 98%, and the energy efficiency is 95%. (100 mA / cm) 2 The constant current discharge specific capacity is 145 F / g, the coulombic efficiency is 97%, and the energy efficiency is 93%.

[0059] Example 2

[0060] Mix 60 ml of 98% concentrated sulfuric acid and 20 ml of 68% concentrated nitric acid thoroughly. Add 3 g of KB and 2 g of Super P, and stir until homogeneous. Transfer the resulting mixture to a PTFE-lined container, place it inside a stainless steel sleeve of a hydrothermal reactor, seal tightly, and place it in a constant temperature chamber. Heat to 100°C and maintain this temperature for 4 hours. Cool the hydrothermal reactor to room temperature, remove the hydrothermal product, and dilute it with deionized water to 160 ml to obtain the TDs electrode slurry. Take out 10 ml of the electrode slurry and let it stand for 120 hours; no stratification occurred.

[0061] The remaining electrode slurry was divided into two portions, one for the positive electrode and the other for the negative electrode, used to construct a flow supercapacitor and for performance testing. The construction method and testing conditions for the flow supercapacitor were the same as in Example 1.

[0062] Test results show that the liquid flow supercapacitor assembled using the electrode slurry of this embodiment achieves a current of 20 mA / cm². 2 The constant current discharge specific capacity is 162 F / g, the coulombic efficiency is 97.5%, and the energy efficiency is 95%. (100 mA / cm) 2 The constant current discharge specific capacity is 148 F / g, the coulombic efficiency is 97%, and the energy efficiency is 94.8%.

[0063] Example 3

[0064] Mix 60 ml of 98% concentrated sulfuric acid and 20 ml of 68% concentrated nitric acid thoroughly, add 4 g of KB and 1 g of Super P, and stir until homogeneous. Transfer the resulting mixture to a PTFE inner liner, place it inside a stainless steel sleeve of a hydrothermal reactor, seal tightly, and place it in a constant temperature chamber. Heat to 100°C and maintain the temperature for 4 hours. Cool the hydrothermal reactor to room temperature, remove the hydrothermal product, and dilute it with deionized water to 160 ml to obtain the TDs electrode slurry. Take out 10 ml of the electrode slurry and let it stand for 120 hours; no layering of the electrode slurry occurred.

[0065] The remaining electrode slurry was divided into two portions, one for the positive electrode and the other for the negative electrode, used to construct a flow supercapacitor and for performance testing. The construction method and testing conditions for the flow supercapacitor were the same as in Example 1.

[0066] Test results show that the supercapacitor using the TDs electrode slurry of this embodiment achieves a flow rate of 20 mA / cm². 2 The constant current discharge specific capacity is 171 F / g, the coulombic efficiency is 98.5%, and the energy efficiency is 94.5%. (100 mA / cm) 2The constant current discharge specific capacity is 152 F / g, the coulombic efficiency is 97.6%, and the energy efficiency is 94.2%.

[0067] Example 4

[0068] Mix 60 ml of 98% concentrated sulfuric acid and 20 ml of 68% concentrated nitric acid thoroughly. Add 4.5 g of KB and 0.5 g of Super P, and stir until homogeneous. Transfer the resulting mixture to a PTFE-lined container, place it inside a stainless steel sleeve of a hydrothermal reactor, seal tightly, and place in a constant temperature chamber. Heat to 100°C and maintain the temperature for 20 hours. Cool the hydrothermal reactor to room temperature, remove the hydrothermal product, and dilute with deionized water to 160 ml to obtain the TDs electrode slurry. Take out 10 ml of the electrode slurry and let it stand for 120 hours; no stratification occurred.

[0069] The remaining electrode slurry was divided into two portions, one for the positive electrode and the other for the negative electrode, used to construct a flow supercapacitor and for performance testing. The construction method and testing conditions for the flow supercapacitor were the same as in Example 1.

[0070] Test results show that the supercapacitor using the electrode slurry of this embodiment achieves a flow rate of 20 mA / cm². 2 The constant current discharge specific capacity is 128 F / g, the coulombic efficiency is 96.2%, and the energy efficiency is 94.4%. (100 mA / cm) 2 The constant current discharge specific capacity is 125 F / g, the coulombic efficiency is 95.6%, and the energy efficiency is 92.5%.

[0071] Example 5

[0072] Mix 60 ml of 98% concentrated sulfuric acid and 20 ml of 68% concentrated nitric acid thoroughly. Add 3 g of KB and 2 g of Super P, and stir until homogeneous. Transfer the resulting mixture to a PTFE-lined container, place it inside a stainless steel sleeve of a hydrothermal reactor, seal tightly, and place it in a constant temperature chamber. Heat to 120°C and maintain this temperature for 4 hours. Cool the hydrothermal reactor to room temperature, remove the hydrothermal product, and dilute it with deionized water to 160 ml to obtain the TDs electrode slurry. Take out 10 ml of the electrode slurry and let it stand for 120 hours; no stratification occurred.

[0073] The remaining TDs electrode slurry was divided into two portions, one for the positive electrode and the other for the negative electrode, used to construct a flow supercapacitor and for performance testing. The construction method and testing conditions for the flow supercapacitor were the same as in Example 1.

[0074] Test results show that the supercapacitor using the TDs electrode slurry of this embodiment achieves a flow rate of 20 mA / cm². 2The constant current discharge specific capacity is 150 F / g, the coulombic efficiency is 98.5%, and the energy efficiency is 96%. (100 mA / cm) 2 The constant current discharge specific capacity is 144 F / g, the coulombic efficiency is 98%, and the energy efficiency is 95.4%.

[0075] Example 6

[0076] Mix 60 ml of 98% concentrated sulfuric acid and 20 ml of 68% concentrated nitric acid thoroughly. Add 3 g of KB and 2 g of Super P, and stir until homogeneous. Transfer the resulting mixture to a PTFE-lined container, place it inside a stainless steel sleeve of a hydrothermal reactor, seal tightly, and place it in a constant temperature oven. Heat to 150°C and maintain this temperature for 4 hours. Cool the hydrothermal reactor to room temperature, remove the hydrothermal product, and dilute it with deionized water to 160 ml to obtain the TDs electrode slurry. Take out 10 ml of the electrode slurry and let it stand for 120 hours; no stratification occurred.

[0077] The remaining TDs electrode slurry was divided into two portions, one for the positive electrode and the other for the negative electrode, used to construct a flow supercapacitor and for performance testing. The construction method and testing conditions for the flow supercapacitor were the same as in Example 1.

[0078] Test results show that the supercapacitor using the electrode slurry of this embodiment achieves a flow rate of 20 mA / cm². 2 The constant current discharge specific capacity is 128 F / g, the coulombic efficiency is 96.2%, and the energy efficiency is 94.4%. (100 mA / cm) 2 The constant current discharge specific capacity is 125 F / g, the coulombic efficiency is 95.6%, and the energy efficiency is 92.5%.

[0079] Example 7

[0080] Mix 10 ml of 98% concentrated sulfuric acid and 70 ml of 68% concentrated nitric acid thoroughly. Add 4.5 g of KB and 0.5 g of Super P, and stir until homogeneous. Transfer the resulting mixture to a PTFE-lined container, place it inside a stainless steel sleeve of a hydrothermal reactor, seal tightly, and place it in a constant temperature chamber. Heat to 100°C and maintain the temperature for 4 hours. Cool the hydrothermal reactor to room temperature, remove the hydrothermal product, and dilute it with deionized water to 160 ml to obtain the TDs electrode slurry. Take out 10 ml of the electrode slurry and let it stand for 120 hours; no stratification occurred.

[0081] The remaining electrode slurry was divided into two portions, one for the positive electrode and the other for the negative electrode, used to construct a flow supercapacitor and for performance testing. The construction method and testing conditions for the flow supercapacitor were the same as in Example 1.

[0082] Test results show that the supercapacitor using the electrode slurry of this embodiment achieves a flow rate of 20 mA / cm².2 The constant current discharge specific capacity is 118 F / g, the coulombic efficiency is 96.5%, and the energy efficiency is 94.3%. (100 mA / cm) 2 The constant current discharge specific capacity is 110 F / g, the coulombic efficiency is 95.8%, and the energy efficiency is 92.9%.

[0083] Example 8

[0084] Mix 70 ml of 98% concentrated sulfuric acid and 10 ml of 68% concentrated nitric acid thoroughly. Add 4.5 g of KB and 0.5 g of Super P, and stir until homogeneous. Transfer the resulting mixture to a PTFE-lined container, place it inside a stainless steel sleeve of a hydrothermal reactor, seal tightly, and place it in a constant temperature chamber. Heat to 100°C and maintain the temperature for 4 hours. Cool the hydrothermal reactor to room temperature, remove the hydrothermal product, and dilute it with deionized water to 160 ml to obtain the TDs electrode slurry. Take out 10 ml of the electrode slurry and let it stand for 120 hours; no stratification occurred.

[0085] The remaining electrode slurry was divided into two portions, one for the positive electrode and the other for the negative electrode, used to construct a flow supercapacitor and for performance testing. The construction method and testing conditions for the flow supercapacitor were the same as in Example 1.

[0086] Test results show that the supercapacitor using the electrode slurry of this embodiment achieves a flow rate of 20 mA / cm². 2 The constant current discharge specific capacity is 165 F / g, the coulombic efficiency is 98%, and the energy efficiency is 97%. (100 mA / cm) 2 The constant current discharge specific capacity is 155 F / g, the coulombic efficiency is 97%, and the energy efficiency is 95%.

[0087] Comparative Example 1

[0088] Mix 60 ml of 98% concentrated sulfuric acid and 20 ml of 68% concentrated nitric acid thoroughly, add 4.5 g KB and 0.5 g Super P, and stir until homogeneous to obtain the TDs electrode slurry. Take out 10 ml of the electrode slurry and let it stand for 120 h; no layering of the electrode slurry was observed.

[0089] The remaining electrode slurry was divided into two portions, one for the positive electrode and the other for the negative electrode, used to construct a flow supercapacitor and for performance testing. The construction method and testing conditions for the flow supercapacitor were the same as in Example 1.

[0090] Test results show that the liquid flow supercapacitor using this comparative electrode slurry achieves a flow rate of 20 mA / cm². 2 The constant current discharge specific capacity is 135 F / g, the coulombic efficiency is 97.5%, and the energy efficiency is 95.4%. (100 mA / cm) 2The constant current discharge specific capacitance is 64 F / g, the coulombic efficiency is 97.5%, and the energy efficiency is 80%. The TDs slurry prepared by this comparative method has poor rate performance and is not suitable as an electrode slurry for flow supercapacitors.

[0091] Comparative Example 2

[0092] Mix 60 ml of 98% concentrated sulfuric acid and 20 ml of 68% concentrated nitric acid thoroughly, add 3 g of KB, and stir until homogeneous. Transfer the resulting mixture to a PTFE-lined container, place it inside a stainless steel sleeve of a hydrothermal reactor, seal tightly, and place in a constant temperature chamber. Heat to 120°C and maintain this temperature for 4 hours. Cool the hydrothermal reactor to room temperature, remove the hydrothermal product, and dilute it with deionized water to 160 ml to obtain the TDs electrode slurry. Take out 10 ml of the electrode slurry and let it stand for 120 hours; no stratification occurred.

[0093] The remaining electrode slurry was divided into two portions, one for the positive electrode and the other for the negative electrode, used to construct a flow supercapacitor and for performance testing. The construction method and testing conditions for the flow supercapacitor were the same as in Example 1.

[0094] Test results show that the liquid flow supercapacitor using this comparative electrode slurry achieves a flow rate of 20 mA / cm². 2 The specific capacitance under constant current discharge is 17 F / g, the coulombic efficiency is 98.6%, and the energy efficiency is 96.5%. The specific capacitance of the TDs slurry prepared by this comparative method is too low and is not suitable for use as an electrode slurry for flow supercapacitors.

[0095] Comparative Example 3

[0096] Mix 60 ml of 98% concentrated sulfuric acid and 20 ml of 68% concentrated nitric acid thoroughly, add 2 g of Super P, and stir until homogeneous. Transfer the resulting mixture to a PTFE-lined container, place it inside a stainless steel sleeve of a hydrothermal reactor, seal tightly, and place it in a constant temperature oven. Heat to 120°C and maintain this temperature for 4 hours. Cool the hydrothermal reactor to room temperature, remove the hydrothermal product, and dilute it with deionized water to 160 ml to obtain the TDs electrode slurry. Take out 10 ml of the electrode slurry and let it stand for 120 hours; no active stratification occurred.

[0097] The remaining electrode slurry was divided into two portions, one for the positive electrode and the other for the negative electrode, used to construct a flow supercapacitor and for performance testing. The construction method and testing conditions for the flow supercapacitor were the same as in Example 1.

[0098] Test results show that the liquid flow supercapacitor using this comparative electrode slurry achieves a flow rate of 20 mA / cm². 2The specific capacitance under constant current discharge is 8.8 F / g, the coulombic efficiency is 85.6%, and the energy efficiency is 82.5%. The specific capacitance of the TDs slurry prepared by this comparative method is too low and is not suitable for use as an electrode slurry for flow supercapacitors.

[0099] Comparative Example 4

[0100] Mix 60 ml of 98% concentrated sulfuric acid and 20 ml of 68% concentrated nitric acid thoroughly. Add 3 g of KB and 2 g of Super P, and stir until homogeneous. Transfer the resulting mixture to a PTFE-lined container, place it inside a stainless steel sleeve of a hydrothermal reactor, seal tightly, and place it in a constant temperature chamber. Heat to 180°C and maintain this temperature for 4 hours. Cool the hydrothermal reactor to room temperature, remove the hydrothermal product, and dilute it with deionized water to 160 ml to obtain the TDs electrode slurry. Take out 10 ml of the electrode slurry and let it stand for 120 hours; no stratification occurred.

[0101] The remaining electrode slurry was divided into two portions, one for the positive electrode and the other for the negative electrode, used to construct a flow supercapacitor and for performance testing. The construction method and testing conditions for the flow supercapacitor were the same as in Example 1.

[0102] Test results show that the liquid flow supercapacitor using this comparative electrode slurry achieves a flow rate of 20 mA / cm². 2 The specific capacitance under constant current discharge is 35 F / g, the coulombic efficiency is 97%, and the energy efficiency is 95%. The TDs slurry prepared using this comparative method is unsuitable for use as an electrode slurry for flow supercapacitors due to its excessively low specific capacitance.

[0103] Comparative Example 5

[0104] Mix 60 ml of 98% concentrated sulfuric acid and 20 ml of 68% concentrated nitric acid thoroughly, add 3 g of KB and 2 g of Super P, and stir until homogeneous. Transfer the resulting mixture to a PTFE inner liner, place it inside a stainless steel sleeve of a hydrothermal reactor, seal it tightly, and place it in a constant temperature chamber. Heat to 60°C and maintain the temperature for 4 hours. Cool the hydrothermal reactor to room temperature, remove the hydrothermal product, and dilute it with deionized water to 160 ml to obtain the TDs electrode slurry.

[0105] The remaining electrode slurry was divided into two portions, one for the positive electrode and the other for the negative electrode, used to construct a flow supercapacitor and for performance testing. The construction method and testing conditions for the flow supercapacitor were the same as in Example 1.

[0106] Test results show that the liquid flow supercapacitor assembled using this comparative electrode slurry achieves a performance of 20 mA / cm². 2The specific capacitance under constant current discharge is 45 F / g, the coulombic efficiency is 98.5%, and the energy efficiency is 96%. The TDs slurry prepared using this comparative method is unsuitable for use as an electrode slurry for flow supercapacitors due to its excessively low specific capacitance.

[0107] As can be seen from Examples 5 and 6 and Comparative Examples 4 and 5, higher temperatures help increase the number of oxygen-containing functional groups on the surface of activated carbon particles, thereby improving the suspension stability of the electrode slurry. However, excessively high reaction temperatures will reduce the specific surface area of ​​the product, thus reducing the specific capacity of the electrode slurry. Furthermore, excessively high reaction temperatures will oxidize some of the carbon material into carbon dioxide, reducing the product yield. Conversely, excessively low reaction temperatures result in insufficient oxidizing power of the mixed acid, leading to a lower number of oxygen-containing functional groups on the surface of the carbon material particles, thus reducing the hydrophilicity of the reaction product. Insufficient hydrophilicity will affect the suspension characteristics of the activated carbon particles.

[0108] Comparative Example 6

[0109] Mix 75 ml of 98% concentrated sulfuric acid and 5 ml of 68% concentrated nitric acid thoroughly. Add 3 g of KB and 2 g of Super P, and stir until homogeneous. Transfer the resulting mixture to a PTFE-lined container, place it inside a stainless steel sleeve of a hydrothermal reactor, seal tightly, and place it in a constant temperature chamber. Heat to 120°C and maintain this temperature for 4 hours. Cool the hydrothermal reactor to room temperature, remove the hydrothermal product, and dilute it with deionized water to 160 ml to obtain the TDs electrode slurry. Take out 10 ml of the electrode slurry and let it stand for 120 hours; no stratification occurred.

[0110] The remaining electrode slurry was divided into two portions, one for the positive electrode and the other for the negative electrode, used to construct a flow supercapacitor and for performance testing. The construction method and testing conditions for the flow supercapacitor were the same as in Example 1.

[0111] Test results show that the supercapacitor using this comparative electrode slurry achieves a flow rate of 20 mA / cm². 2 The specific capacitance under constant current discharge is 24.5 F / g, the coulombic efficiency is 94.5%, and the energy efficiency is 91.5%. The TDs slurry prepared using this comparative method is unsuitable for use as an electrode slurry for flow supercapacitors due to its excessively low specific capacitance.

[0112] Comparative Example 7

[0113] Mix 5 ml of 98% concentrated sulfuric acid and 75 ml of 68% concentrated nitric acid thoroughly. Add 3 g of KB and 2 g of Super P, and stir until homogeneous. Transfer the resulting mixture to a PTFE-lined container, place it inside a stainless steel sleeve of a hydrothermal reactor, seal tightly, and place it in a constant temperature chamber. Heat to 120°C and maintain the temperature for 4 hours. Cool the hydrothermal reactor to room temperature, remove the hydrothermal product, and dilute it with deionized water to 160 ml to obtain the TDs electrode slurry. Take out 10 ml of the electrode slurry and let it stand for 10 hours; stratification occurs.

[0114] The TDs slurry prepared by this comparative method is not suitable for use as an electrode slurry for flow supercapacitors.

[0115] Comparative Examples 6 and 7 show that if the ratio of concentrated sulfuric acid to concentrated nitric acid in the hydrothermal feedstock is less than 1:9, the oxidizing power of the mixed acid is low, resulting in larger carbon dots and a higher number of oxygen-containing functional groups on the surface, thus reducing the suspension characteristics and pseudocapacitance of the electrode slurry. If the ratio of concentrated sulfuric acid to concentrated nitric acid in the hydrothermal feedstock is less than 9:1, the oxidizing power of the mixed acid is too strong, resulting in smaller carbon dots and a lower specific surface area, significantly reducing the capacity of the electrode slurry.

[0116] Comparative Example 8

[0117] Mix 60 ml of 98% concentrated sulfuric acid and 20 ml of 68% concentrated nitric acid thoroughly. Add 4.9 g of KB and 0.1 g of Super P, and stir until homogeneous. Transfer the resulting mixture to a PTFE-lined container, place it inside a stainless steel sleeve of a hydrothermal reactor, seal tightly, and place in a constant temperature chamber. Heat to 100°C and maintain this temperature for 4 hours. Cool the hydrothermal reactor to room temperature, remove the hydrothermal product, and dilute it with deionized water to 160 ml to obtain the TDs electrode slurry. Take out 10 ml of the electrode slurry and let it stand for 120 hours; no stratification occurred.

[0118] The remaining electrode slurry was divided into two portions, one for the positive electrode and the other for the negative electrode, used to construct a flow supercapacitor and for performance testing. The construction method and testing conditions for the flow supercapacitor were the same as in Example 1.

[0119] Test results show that the supercapacitor using this comparative electrode slurry achieves a flow rate of 20 mA / cm². 2 The constant current discharge specific capacity is 158 F / g, the coulombic efficiency is 97.2%, and the energy efficiency is 95.5%. (100 mA / cm) 2 The constant current discharge specific capacitance is 34 F / g, the coulombic efficiency is 97.5%, and the energy efficiency is 84%. The TDs slurry prepared by this comparative method has poor rate performance and is not suitable as an electrode slurry for flow supercapacitors.

[0120] Comparative Example 9

[0121] Mix 60 ml of 98% concentrated sulfuric acid and 20 ml of 68% concentrated nitric acid thoroughly. Add 0.1 g KB and 4.9 g Super P, and stir until homogeneous. Transfer the resulting mixture to a PTFE-lined container, place it inside a stainless steel sleeve of a hydrothermal reactor, seal tightly, and place it in a constant temperature chamber. Heat to 100°C and maintain the temperature for 4 hours. Cool the hydrothermal reactor to room temperature, remove the hydrothermal product, and dilute it with deionized water to 160 ml to obtain the TDs electrode slurry. Take out 10 ml of the electrode slurry and let it stand for 120 hours; no stratification occurred.

[0122] The remaining electrode slurry was divided into two portions, one for the positive electrode and the other for the negative electrode, used to construct a flow supercapacitor and for performance testing. The construction method and testing conditions for the flow supercapacitor were the same as in Example 1.

[0123] Test results show that the supercapacitor assembled using this comparative electrode slurry achieves a flow rate of 20 mA / cm². 2 The specific capacitance under constant current discharge is 36 F / g, the coulombic efficiency is 96.4%, and the energy efficiency is 94.7%. The TDs slurry prepared using this comparative method is unsuitable for use as an electrode slurry for flow supercapacitors due to its excessively low specific capacitance.

[0124] As shown in Comparative Examples 8 and 9, if the mass ratio of KB to Super P in the raw materials is higher than 95:5, the content of Super P-based quantum dots in the resulting electrode paste will be too low, leading to low electronic conductivity and thus affecting the electrode paste's capacity. If the mass ratio of KB to Super P in the raw materials is lower than 6:4, the content of KB-based carbon dots in the resulting electrode paste will be low, resulting in a low content of KB-based carbon dots with high specific surface area, which will also affect the electrode paste's capacity.

[0125] Comparative Example 10

[0126] Mix 60 ml of 98% concentrated sulfuric acid and 20 ml of 37% concentrated hydrochloric acid thoroughly. Add 3 g of KB and 2 g of Super P, and stir until homogeneous. Transfer the resulting mixture to a PTFE inner liner, place it inside a stainless steel sleeve of a hydrothermal reactor, seal tightly, and place it in a constant temperature oven. Heat to 100°C and maintain the temperature for 4 hours. Cool the hydrothermal reactor to room temperature, remove the hydrothermal product, and dilute it with deionized water to 160 ml to obtain the TDs electrode slurry. Take out 10 ml of the electrode slurry and let it stand for 24 hours; stratification occurs.

[0127] In this comparative example, concentrated hydrochloric acid lacks oxidizing properties. Adding it to concentrated sulfuric acid reduces the concentration of the sulfuric acid, thus decreasing the oxidizing power of the mixed acid and resulting in a lower number of oxygen-containing functional groups on the TDs surface. Insufficient hydrophilicity reduces the suspension stability of the TDs, causing sedimentation and stratification of the electrode slurry after standing. The TDs slurry prepared using this comparative method is unsuitable for use as an electrode slurry for flow supercapacitors.

[0128] Comparative Example 11

[0129] Mix 60 ml of 98% concentrated sulfuric acid and 20 ml of 68% concentrated nitric acid thoroughly. Add 3 g of KB and 2 g of acetylene black, and stir until homogeneous. Transfer the resulting mixture to a PTFE-lined container, place it inside a stainless steel sleeve of a hydrothermal reactor, seal tightly, and place in a constant temperature chamber. Heat to 100°C and maintain this temperature for 4 hours. Cool the hydrothermal reactor to room temperature, remove the hydrothermal product, and dilute it with deionized water to 160 ml to obtain the electrode slurry. Take out 10 ml of the electrode slurry and let it stand for 24 hours; stratification occurs.

[0130] The acetylene black used in this comparative example has an uneven particle size. After treatment with mixed acid, uniform carbon dots cannot be obtained, and the residual large acetylene black particles will cause stratification of the electrode slurry. This slurry containing TDs and large acetylene black particles with poor suspension stability is not suitable as an electrode slurry for flow supercapacitors.

[0131] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing a carbon dot-based electrode paste, characterized in that, Includes the following steps: The conductive agent is mixed with mixed acid and heated in a sealed container to obtain the carbon dot-based electrode slurry. The conductive agent contains KB and Super P; The mixed acid contains concentrated sulfuric acid and concentrated nitric acid.

2. The preparation method according to claim 1, characterized in that, In the conductive agent, the mass ratio of KB to Super P is 95:5 to 6:

4.

3. The preparation method according to claim 1, characterized in that, In the mixed acid, the volume ratio of concentrated sulfuric acid to concentrated nitric acid is 1:9 to 9:

1.

4. The preparation method according to claim 1, characterized in that, The ratio of the conductive agent to the mixed acid is 0.1–10 g: 100 ml.

5. The preparation method according to claim 1, characterized in that, The temperature of the heating reaction is 90–150°C; The heating reaction time is 0.1 to 24 hours.

6. The application of an electrode slurry prepared by the preparation method according to any one of claims 1 to 5 in a flow supercapacitor.

7. The application of an electrode slurry prepared by the preparation method according to any one of claims 1 to 5 in a symmetrical flow supercapacitor.

8. The application according to claim 7, characterized in that, After diluting the electrode slurry, it is added to the positive and negative electrodes of the flow supercapacitor, and then circulated between the positive electrode and the positive electrode slurry pool, and between the negative electrode and the negative electrode slurry pool, to form a symmetrical flow supercapacitor.

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