Single-atom copper-doped porous carbon fiber and its preparation method and application

Abstract

The present invention discloses a single-atom copper-doped porous carbon fiber and its preparation method and application, and relates to the technical field of material preparation. The porous carbon fiber has a pore diameter of 100-600 nm and a specific surface area of ​​1000-3500 m 2 g ‑1 ; And the surface of porous carbon fiber is doped with uniformly dispersed single-atom copper, and the content of single-atom copper is 0.5 wt%~10.0 wt%;Its preparation method comprises the following steps:Polyvinyl pyrrolidone and polytetrafluoroethylene dispersion are added into water and stirred to form a precursor solution, the precursor solution is prepared into a fiber membrane by electrostatic spinning, and then the fiber membrane is subjected to pre-oxidation and high-temperature carbonization to obtain porous carbon fiber;Porous carbon fiber is put into a solution containing 1,10 phenanthroline and cupric acetate and soaked and dried, and single-atom copper-doped porous carbon fiber is obtained after subsequent high-temperature treatment. In the present invention, the preparation method is simple and controllable, suitable for large-scale production, and the single-atom copper-doped porous carbon fiber is first applied in potassium metal batteries, with super strong cycle stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of material preparation, and in particular relates to single-atom copper-doped porous carbon fibers and a preparation method thereof, and applications in potassium metal batteries. Background Art

[0002] With the development of electricity, lithium-ion batteries are facing huge consumption demands, which has caused concerns about limited resources. Therefore, alternative battery systems that utilize earth-abundant elements have become a focus of attention. For example, potassium-ion batteries are attracting widespread attention due to their comparable operating voltage and power density compared to lithium-ion batteries and their high abundance of potassium resources. To date, several types of potassium-ion battery anode materials have been developed, such as intercalation type (graphite, hard / soft carbon), conversion type (SnS2, MoS2) and alloy type (Sn, Sb). In order to achieve high specific energy of potassium batteries, potassium metal is an optimal choice, which has the lowest redox potential (-2.93 V vs. SHE) and the highest specific capacity (687mA hg) among all anode materials. -1 ).

[0003] However, the potassium metal anode will also encounter the inevitable problem of dendrite growth during the electroplating / stripping process, resulting in low Coulomb efficiency, internal short circuit and other problems, which seriously hinders its practical application. Therefore, it is considered to use a conductive substrate to stabilize the potassium anode so that the potassium metal can be encapsulated in the substrate, thereby reducing the chance of side reactions, buffering volume changes, providing a conductive network, and further inhibiting dendrite growth. Generally, modified metal substrates such as copper and aluminum are a type of potential substrate for stable and dendrite-free composite potassium anodes, but their high density and relatively low space utilization hinder the application of metal substrates. In contrast, carbon substrates with lower density and electrochemical stability are more advantageous for potassium accommodation, which is conducive to achieving high specific energy and energy density.

[0004] Therefore, in order to achieve high energy density and stable cycling of potassium metal batteries, we need to consider the following aspects: (1) Introducing more active sites, such as single atoms, clusters, particles, etc., to achieve low nucleation overpotential and improve potassium affinity; (2) Increasing the conductivity and specific surface area of ​​the substrate, such as porous carbon, can induce rapid ion / electron transfer, reduce local current density, and hinder dendrite growth; (3) A three-dimensional structure with sufficient internal space can effectively guide a uniform electric field and a smooth potassium plating layer to achieve the inhibition of dendrite growth during the cycle. Therefore, constructing a three-dimensional porous substrate material with a large number of distributed active sites is an effective solution to improve the cycling stability of potassium metal batteries.

[0005] The present invention provides a single-atom copper-doped porous carbon fiber and a preparation method thereof, and its application in potassium metal batteries. The porous carbon fiber with uniformly dispersed single-atom copper is prepared by electrospinning. The single-atom copper content is 0.5 wt% to 10.0 wt%, the pore diameter of the porous carbon fiber is 100 to 600 nm, and the specific surface area is 1000 to 3500 m 2 g -1 , and the prepared single-atom copper-doped porous carbon fibers have super strong cycle stability when applied to potassium metal batteries. Summary of the Invention

[0006] The purpose of the present invention is to provide single-atom copper-doped porous carbon fibers and a preparation method thereof, and their application in potassium metal batteries, so as to solve the problems in the prior art proposed in the above-mentioned background technology that the potassium metal negative electrode will inevitably encounter dendrite growth problems during the electroplating / stripping process, resulting in low Coulomb efficiency, internal short circuit and other problems.

[0007] To achieve the above objectives, the present invention adopts the following technical solutions:

[0008] The first aspect of the present invention provides a single-atom copper-doped porous carbon fiber having a three-dimensional porous structure with a pore diameter of 100-600 nm and a specific surface area of ​​1000-3500 m 2 g -1 ;

[0009] The surface of the porous carbon fiber is doped with uniformly dispersed single-atom copper, and the content of single-atom copper is 0.5 wt%~10.0wt%.

[0010] A second aspect of the present invention provides a method for preparing single-atom copper-doped porous carbon fibers, comprising the following steps:

[0011] (1) Preparation of porous carbon fibers: Polyvinyl pyrrolidone (PVP) and polytetrafluoroethylene dispersion (PTFE) are added to water and stirred to form a precursor solution, the precursor solution is prepared by electrospinning to obtain a fiber membrane, and the fiber membrane is then pre-oxidized and carbonized at high temperature to obtain porous carbon fibers;

[0012] (2) Preparation of single-atom copper-doped porous carbon fibers: The porous carbon fibers were immersed in a solution containing 1,10-phenanthroline and copper acetate and then dried, and then treated at high temperature to obtain single-atom copper-doped porous carbon fibers.

[0013] Preferably, the precursor solution is formed in step (1) as follows:

[0014] The mass fraction of polyvinyl pyrrolidone in water is 5-20 wt%, and the mass ratio of polytetrafluoroethylene dispersion to polyvinyl pyrrolidone is 0.5-4:1;

[0015] The stirring temperature is 30-70° C., and the stirring time is 5-24 h.

[0016] Preferably, the electrospinning method in step (1) is specifically as follows: the propulsion speed is 0.2-1.5 mL / h, the spinning voltage is 13-22 kV, the receiving distance is 10-20 cm, the temperature is 20-40 °C, and the humidity is 30-60%.

[0017] Preferably, the pre-oxidation temperature in step (1) is 200-300°C, the heating rate is 2-6°C / min, and the holding time is 1-3 h.

[0018] Preferably, in step (1), the high-temperature carbonization is carried out at a temperature of 600-1000°C, a heating rate of 2-6°C / min, a holding time of 1-6 h, and an argon or nitrogen protective atmosphere.

[0019] Preferably, the molar ratio of 1,10-phenanthroline to copper acetate in the solution in step (2) is 5-30:1.

[0020] Preferably, the soaking time in the solution in step (2) is 5 to 60 minutes.

[0021] Preferably, the drying temperature in step (2) is 40-80°C, and the drying time is 12-48 hours.

[0022] Preferably, in step (2), the high temperature treatment is performed at a temperature of 600-1000°C, a heating rate of 2-6°C / min, a holding time of 1-6 h, and an argon or nitrogen protective atmosphere.

[0023] The third aspect of the present invention proposes an application of single-atom copper-doped porous carbon fiber in the negative electrode of a potassium metal battery, as follows:

[0024] The potassium metal battery negative electrode is a single-atom copper-doped porous carbon fiber / potassium composite negative electrode; the single-atom copper-doped porous carbon fiber is made into an anode, and potassium metal is made into a cathode. The anode and cathode are immersed in a potassium ion electrolyte, and current is loaded at both poles to obtain the single-atom copper-doped porous carbon fiber / potassium composite negative electrode through an electrochemical deposition method.

[0025] Preferably, the single-atom copper-doped porous carbon fiber is cut into discs with a diameter of 8 to 16 mm as the anode, and potassium metal is rolled into discs of the same size as the cathode.

[0026] Preferably, the anode and cathode are immersed in the potassium ion electrolyte, specifically, the two are assembled into a button battery in a glove box (water and oxygen content is less than 0.01 ppm).

[0027] Specifically, the potassium ion electrolyte is an electrolyte containing KPF6 or KTFSI, the concentration of potassium ions in the electrolyte is 0.8~4 M, and the organic solvent in the electrolyte is one or more of EC (ethylene carbonate), DEC (diethyl carbonate), EMC (ethyl methyl carbonate), DMC (dimethyl carbonate), and DME (ethylene glycol dimethyl ether).

[0028] Preferably, the current is 0.1-0.4 mA cm -2 ; The deposition time is 10~50 h.

[0029] The fourth aspect of the present invention proposes an application of single-atom copper-doped porous carbon fiber in a potassium metal battery, wherein the potassium metal battery includes a single-atom copper-doped porous carbon fiber / potassium composite negative electrode, and the single-atom copper-doped porous carbon fiber / potassium composite negative electrode includes multiple single-atom copper-doped porous carbon fibers as a substrate and potassium metal deposited on the substrate.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The single-atom copper-doped porous carbon fiber of the present invention is a three-dimensional porous carbon material with high conductivity and large specific surface area. It can not only accommodate more potassium metal, but also buffer the volume change of potassium metal during the potassium plating / stripping process. At the same time, it can provide a conductive network, induce rapid charge transfer and reduce local current density, thereby slowing down the growth of dendrites.

[0032] (2) The present invention introduces high-load single-atom copper, which maximizes the atomic utilization rate, tunable electronic structure and surface properties of the material, can achieve a low nucleation potential, improve the potassium affinity of carbon fibers, promote uniform electroplating of potassium metal, and thus improve the cycle stability of the battery. The single-atom copper-doped porous carbon fibers prepared by the present invention were first used in potassium metal batteries and exhibited a cycle life of more than 400 h.

[0033] (3) The present invention uses polyvinyl pyrrolidone (PVP), polytetrafluoroethylene dispersion (PTFE), and water as raw materials to prepare porous carbon fibers through electrospinning and carbonization. The porous carbon fibers are then immersed in an ethanol solution of 1,10-phenanthroline and copper acetate and sintered at high temperature to obtain single-atom copper-doped porous carbon fibers. This preparation method is simple and controllable, low-cost, and uses readily available raw materials, making it suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a scanning electron microscope (SEM) image of the single-atom copper-doped porous carbon fiber in Example 1 of the present invention;

[0035] Figure 2is an X-ray diffraction (XRD) pattern of the single-atom copper-doped porous carbon fiber in Example 1 of the present invention;

[0036] Figure 3 This is a scanning transmission electron microscope (STEM) image of the single-atom copper-doped porous carbon fiber in Example 1 of the present invention;

[0037] Figure 4 This is a cycle performance diagram of the single-atom copper-doped porous carbon fiber / potassium composite negative electrode symmetrical battery in Example 1 of the present invention;

[0038] Figure 5 This is a cycle performance diagram of the porous carbon fiber / potassium composite negative electrode symmetrical battery in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0039] The following will provide a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0040] Example 1:

[0041] Preparation method of single-atom copper-doped porous carbon fiber:

[0042] (1) 1.0 g of PVP was added to 9 mL of water and stirred at 60 °C for 6 h. Then 1.8 g of PTFE was added and stirred for 12 h to obtain a uniform and stable precursor solution.

[0043] (2) Take 10 mL of the precursor solution for electrospinning at a propulsion speed of 0.8 mL / h, a spinning voltage of 16 kV, a receiving distance of 18 cm, a temperature of 25 °C, and a humidity of 50% to obtain a fiber membrane.

[0044] (3) The obtained fiber membrane was pre-oxidized in air at 260 °C for 2 h at a heating rate of 2 °C / min. After pre-oxidation, it was carbonized in a tubular furnace at 800 °C for 3 h in a nitrogen atmosphere at a heating rate of 3 °C / min to obtain porous carbon fibers.

[0045] (4) The porous carbon fibers were immersed in a 10 mL ethanol solution containing 3.9 g of 1,10-phenanthroline and 0.18 g of copper acetate for 10 min, then taken out and dried in a vacuum oven at 60 °C for 24 h. Subsequently, the carbon fibers were heated at 800 °C for 2 h in a nitrogen atmosphere in a tube furnace at a heating rate of 5 °C / min to obtain single-atom copper-doped porous carbon fibers.

[0046] The scanning electron microscope (SEM) image of the single-atom copper-doped porous carbon fiber is shown in Figure 2. Figure 1 As shown in the figure, it can be seen that carbon fiber has a rich pore structure. X-ray diffraction (XRD) was used to test the material. Figure 2 It can be seen that there is no diffraction peak of copper, indicating that copper exists in the form of single atoms. Scanning transmission electron microscopy (STEM) was used to characterize the material. Figure 3 It can be seen that single-atom copper is evenly dispersed on the carbon fiber.

[0047] The application of single-atom copper-doped porous carbon fibers in the negative electrode of potassium metal batteries is as follows:

[0048] The single-atom copper-doped porous carbon fibers prepared above were cut into 12 mm diameter discs as anodes, and 12 mm diameter potassium metal discs as cathodes. They were assembled into button cells in a glove box (water and oxygen contents were both less than 0.01 ppm) for electrodeposition. The electrolyte was 3 M KTFSI dissolved in DME, and the constant current was 0.1 mA cm -2 After 40 hours of deposition, a single-atom copper-doped porous carbon fiber / potassium composite anode was obtained. The composite anode served as the counter and working electrodes in a button cell with a glass fiber separator and 3M KFSI dissolved in dimethylbenzene (DME) as the electrolyte. The potassium deposition / stripping cycling performance was measured.

[0049] Figure 4 The cycling performance diagram of the single-atom copper doped porous carbon fiber / potassium composite negative electrode symmetric battery. At a current density of 0.5 mA cm -2 , with an areal capacity of 0.5 mAh cm -2 It has excellent performance under high temperature and can cycle stably for 460 hours.

[0050] Example 2:

[0051] The difference from Example 1 is that the preparation method of single-atom copper-doped porous carbon fiber is:

[0052] (1) 1.5 g of PVP was added to 8 mL of water and stirred at 50 °C for 12 h. Then 3.2 g of PTFE was added and stirred for 18 h to obtain a uniform and stable precursor solution.

[0053] (2) Take 8 mL of the precursor solution for electrospinning at a propulsion speed of 0.6 mL / h, a spinning voltage of 18 kV, a receiving distance of 16 cm, a temperature of 25 °C, and a humidity of 40% to obtain a fiber membrane.

[0054] (3) The obtained fiber membrane was pre-oxidized in air at 280 °C for 2 h at a heating rate of 5 °C / min. After pre-oxidation, it was carbonized in a tubular furnace at 700 °C for 2 h in a nitrogen atmosphere at a heating rate of 2 °C / min to obtain porous carbon fibers.

[0055] (4) The porous carbon fibers were immersed in a 10 mL ethanol solution containing 4.3 g of 1,10-phenanthroline and 0.15 g of copper acetate for 20 min, then taken out and dried in a vacuum oven at 70 °C for 20 h. Subsequently, the carbon fibers were heated at 700 °C for 3 h in a tube furnace under a nitrogen atmosphere at a heating rate of 3 °C / min to obtain single-atom copper-doped porous carbon fibers.

[0056] Example 3:

[0057] The difference from Example 1 is that the preparation method of single-atom copper-doped porous carbon fiber is:

[0058] (1) Add 0.8 g of PVP to 10 mL of water and stir at 70 °C for 5 h. Then add 2.5 g of PTFE and continue stirring for 10 h to obtain a uniform and stable precursor solution.

[0059] (2) Take 7 mL of the precursor solution for electrospinning at a propulsion speed of 0.9 mL / h, a spinning voltage of 20 kV, a receiving distance of 15 cm, a temperature of 25 °C, and a humidity of 45% to obtain a fiber membrane.

[0060] (3) The obtained fiber membrane was pre-oxidized in air at 230 °C for 4 h at a heating rate of 3 °C / min. After pre-oxidation, it was carbonized in a tubular furnace at 900 °C in a nitrogen atmosphere for 6 h at a heating rate of 5 °C / min to obtain porous carbon fibers.

[0061] (4) The porous carbon fibers were immersed in a 12 mL ethanol solution containing 5.4 g of 1,10-phenanthroline and 0.12 g of copper acetate for 15 min, then taken out and dried in a vacuum oven at 80 °C for 18 h. Subsequently, the carbon fibers were heated at 900 °C for 2 h in a nitrogen atmosphere in a tube furnace at a heating rate of 4 °C / min to obtain single-atom copper-doped porous carbon fibers.

[0062] Comparative Example 1:

[0063] The steps and parameters are similar to those of Example 1, except that there is no subsequent immersion treatment in 1,10-phenanthroline and copper acetate solution.

[0064] The porous carbon fibers prepared in Comparative Example 1 were cut into 12 mm diameter discs as anodes, and 12 mm diameter potassium metal discs were used as cathodes. They were assembled into button cells in a glove box (water and oxygen contents were both less than 0.01 ppm) for electrodeposition. The electrolyte was 3 M KTFSI dissolved in DME, and the constant current was 0.1 mA cm -2 After 40 hours of deposition, a porous carbon fiber / potassium composite anode was obtained. The porous carbon fiber / potassium composite anode was used as the counter and working electrodes in a button cell with a glass fiber separator and 3M KFSI dissolved in dimethylbenzene (DME) as the electrolyte. The potassium deposition / stripping cycling performance was measured.

[0065] Figure 5 The cycling performance diagram of the porous carbon fiber / potassium composite negative electrode symmetrical battery. At a current density of 0.5 mA cm -2 , with an areal capacity of 0.5 mAh cm -2 The short circuit occurred after only 240 h of stable cycling under these conditions, indicating severe dendrite growth.

[0066] In summary, the present invention prepares single-atom copper-doped porous carbon fibers through Examples 1-3, and the content of single-atom copper in the porous carbon fibers is 0.5 wt%~10.0 wt%, the pore diameter of the porous carbon fibers is 100~600 nm, and the specific surface area is 1000~3500 m 2 g -1 .

[0067] The single-atom copper-doped porous carbon fiber / potassium composite negative electrode symmetrical battery prepared in Example 1 is compared with the porous carbon fiber / potassium composite negative electrode symmetrical battery in Comparative Example 1. It can be proved that the single-atom copper-doped porous carbon fiber prepared by the present invention can effectively inhibit dendrite growth and improve cycle stability, which has a good guiding significance in the application of potassium metal battery negative electrode. This method is conducive to the large-scale application of dendrite-free potassium metal negative electrode.

[0068] The above description is only used to help understand the method and core essence of the present invention, but the scope of protection of the present invention is not limited thereto. For those skilled in the art, equivalent replacements or modifications based on the technical solutions and inventive concepts of the present invention within the technical scope disclosed by the present invention should be included in the scope of protection of the present invention. In summary, the contents of this specification should not be understood as limiting the present invention.

Claims

1. Single-atom copper-doped porous carbon fiber, characterized in that: The porous carbon fiber has a three-dimensional porous structure with a pore diameter of 100-600 nm and a specific surface area of ​​1000-3500 m 2 g -1 ; The surface of the porous carbon fibers is doped with uniformly dispersed single-atom copper, with the content of single-atom copper ranging from 0.5 wt% to 10.0 wt%. The single-atom copper-doped porous carbon fiber is used as a substrate for the single-atom copper-doped porous carbon fiber / potassium composite negative electrode, and potassium metal is deposited on the substrate; Single-atom copper-doped porous carbon fibers were prepared as follows: Preparation of porous carbon fibers: adding polyvinyl pyrrolidone and polytetrafluoroethylene dispersion to water and stirring to form a precursor solution, preparing a fiber membrane from the precursor solution by electrospinning, and then pre-oxidizing and carbonizing the fiber membrane at high temperature to obtain porous carbon fibers; The stirring temperature is 30-70°C and the stirring time is 5-24 hours; The high-temperature carbonization temperature is 600-1000°C, the heating rate is 2-6°C / min, the holding time is 1-6 h, and the protective atmosphere is argon or nitrogen; Preparation of single-atom copper-doped porous carbon fibers: The porous carbon fibers are immersed in a solution containing 1,10-phenanthroline and copper acetate, dried, and then subjected to high-temperature treatment to obtain single-atom copper-doped porous carbon fibers; The temperature of the high-temperature treatment is 600-1000°C, the heating rate is 2-6°C / min, the holding time is 1-6 h, and the protective atmosphere is argon or nitrogen.

2. A method for preparing single-atom copper-doped porous carbon fibers as claimed in claim 1, characterized in that: The following steps are involved: (1) Preparation of porous carbon fibers: adding polyvinyl pyrrolidone and polytetrafluoroethylene dispersion to water and stirring to form a precursor solution, preparing the precursor solution into a fiber membrane by electrospinning, and then pre-oxidizing and high-temperature carbonizing the fiber membrane to obtain porous carbon fibers; The stirring temperature is 30-70°C and the stirring time is 5-24 hours; The high-temperature carbonization temperature is 600-1000°C, the heating rate is 2-6°C / min, the holding time is 1-6 h, and the protective atmosphere is argon or nitrogen; (2) Preparation of single-atom copper-doped porous carbon fibers: The porous carbon fibers were immersed in a solution containing 1,10-phenanthroline and copper acetate, dried, and then subjected to high-temperature treatment to obtain single-atom copper-doped porous carbon fibers; The temperature of the high-temperature treatment is 600-1000°C, the heating rate is 2-6°C / min, the holding time is 1-6 h, and the protective atmosphere is argon or nitrogen.

3. The method for preparing single-atom copper-doped porous carbon fibers according to claim 2, wherein: In step (1), a precursor solution is formed as follows: The mass fraction of polyvinyl pyrrolidone in water is 5-20 wt%, and the mass ratio of polytetrafluoroethylene dispersion to polyvinyl pyrrolidone is 0.5-4:

1.

4. The method for preparing single-atom copper-doped porous carbon fibers according to claim 2, wherein: In step (1), the pre-oxidation temperature is 200-300 °C, the heating rate is 2-6 °C / min, and the holding time is 1-3 h.

5. The method for preparing single-atom copper-doped porous carbon fibers according to claim 2, wherein: The molar ratio of 1,10-phenanthroline to copper acetate in the solution in step (2) is 5-30:

1.

6. The method for preparing single-atom copper-doped porous carbon fibers according to claim 2, wherein: The soaking time in the solution in step (2) is 5 to 60 minutes.

7. The method for preparing single-atom copper-doped porous carbon fibers according to claim 2, wherein: The drying temperature in step (2) is 40-80°C, and the drying time is 12-48 hours.

8. Application of single-atom copper-doped porous carbon fibers prepared by the preparation method according to any one of claims 2 to 7 in potassium metal batteries, characterized in that: The potassium metal battery includes a single-atom copper-doped porous carbon fiber / potassium composite negative electrode, which includes single-atom copper-doped porous carbon fiber as a substrate and potassium metal deposited on the substrate.

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