A phosphorus-doped carbon-coated co-modified MXene-based nanocomposite and a preparation method thereof

Abstract

The application discloses a kind of phosphorus doped carbon-coated co-modified MXene-based nanocomposites and its preparation method and application.The method is by introducing dopamine self-polymerization on the surface of MXene to form a coating layer, and introducing phosphorus source in the high-temperature carbonization process, realizing the synergistic modification of carbon coating and phosphorus doping.The carbon layer formed not only improves the conductivity of the material and inhibits the self-stacking of the sheet, but also effectively prevents the side reaction between MXene and phosphorus source under high temperature conditions to generate phosphate impurities, thereby maintaining the structural stability of the material;At the same time, the phosphorus element is doped into the carbon layer in the form of P-C bond, providing additional pseudo-capacitive active sites and promoting ion transport.The method is simple, reproducible, without complex additives, with good scalability and environmental friendliness.The prepared composite electrode material has high specific capacitance, excellent rate performance and long-term cycle stability, and has wide application prospects in the field of energy storage such as water-based hybrid supercapacitors.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterials technology and new energy materials and devices, and specifically relates to a phosphorus-doped carbon-coated co-modified MXene-based nanocomposite material and its preparation method. Background Technology

[0002] With the rapid development of various convenient smart electronic devices and new energy electric vehicles, the demand for energy storage devices with high efficiency and long service life is increasing. Hybrid supercapacitors (HSCs), by synergistically integrating the advantages of electric double-layer capacitor (EDLC) materials and pseudocapacitive / battery-type materials, have achieved a breakthrough balance between high energy density and high power density, while also possessing long cycle life, making them a research hotspot for next-generation energy storage systems. However, since the positive electrode of HSCs is mostly a pseudocapacitive / battery-type material, energy storage relies on a limited Faraday reaction and ion diffusion process; while the negative electrode is usually an electric double-layer capacitor material, its energy storage is mainly based on surface adsorption, with faster reaction kinetics but limited specific capacity. The difference between the two in terms of capacity and reaction rate leads to a kinetic imbalance problem for HSCs, urgently requiring a high-performance pseudocapacitive negative electrode material to solve the kinetic imbalance problem of HSCs.

[0003] MXene is considered a promising electrode material for HSCs due to its unique two-dimensional structure, controllable interlayer spacing, excellent specific capacitance, high conductivity, and good mechanical stability. However, the instability caused by defects in the original MXene material and the reduction in active specific surface area due to interlayer self-stacking can lead to blockage of ion diffusion channels, reduce the electrochemical accessibility of ions at the layer level, and result in a serious loss of charge storage capacity.

[0004] In recent years, researchers have developed various strategies to address the severe loss of charge storage capacity mentioned above. Among these, heteroatom doping has proven to be a highly effective method for modulating the electronic structure of MXene, alleviating interlayer self-stacking problems, and improving its capacitance performance. Common heteroatom dopants include nitrogen (N), phosphorus (P), boron (B), vanadium (V), and cobalt (Co). Among these, phosphorus atoms, with their large atomic radius and low electronegativity, can alter the electron distribution and band structure of materials, reducing charge transport resistance, making them a promising doping atom. However, Ti-based materials containing oxygen surface groups are prone to undergo a phase transition reaction with a phosphorus source (PH3 gas) at high temperatures to form titanium phosphate. This type of metal phosphate, due to its dense and aggregated structure, hinders ion intercalation, thereby reducing the active surface area of ​​the material and ultimately leading to a decrease in capacitance performance. Summary of the Invention

[0005] To address the problems in existing technologies, this invention provides a phosphorus-doped carbon-coated co-modified MXene-based nanocomposite material (PC-MXene). Phosphorus atoms are doped into the carbon layer on the MXene surface via PC bonds, allowing for the binding of more protons to introduce additional pseudocapacitance and achieve rapid ion transport. Simultaneously, the carbon layer coating the MXene surface effectively prevents the formation of titanium phosphate impurity phases under high-temperature conditions, protecting the material's structural stability. Furthermore, using electrode fabrication processes, this material is fabricated into electrodes for application in electrochemical energy storage devices such as aqueous hybrid supercapacitors. The prepared electrode material exhibits excellent electrochemical performance.

[0006] To achieve the above objectives, this invention provides a phosphorus-doped carbon-coated co-modified MXene-based nanocomposite material and its preparation method, comprising the following steps: 1) Ti3AlC2 was etched using an etchant in liquid phase to obtain a multilayer MXene nanosheet solution. The multilayer MXene solution was subjected to low-temperature sonication under an inert atmosphere such as argon or nitrogen, and the supernatant was collected by centrifugation to obtain a concentration of 5.0 ~ 8.0 mg / mL. -1 A sol solution of monolayer / few-layer MXene nanosheets is defined as sol solution A.

[0007] 2) Add sol solution A to alkaline buffer solution and mix well to obtain solution B. Quickly add dopamine hydrochloride powder to solution B, stir at room temperature, and centrifuge to collect the lower precipitate. Vacuum dry the lower precipitate and define the obtained powder as powder A.

[0008] 3) Place sodium hypophosphite powder A in the upstream and downstream of a high-temperature tube furnace and perform high-temperature heat annealing treatment to obtain PC-MXene-based nanocomposite material, which is defined as powder B.

[0009] 4) Using powder B as the active material (powder B accounts for 70% to 80% of the total mass of the slurry), polyvinylidene fluoride as the binder, conductive carbon black as the conductive agent, N-methylpyrrolidone as the solvent, and titanium foil as the current collector, phosphorus-doped carbon-coated co-modified MXene-based supercapacitor electrodes were prepared by slurry coating method and vacuum drying.

[0010] Preferably, in step 1), Ti3AlC2 is obtained by mixing Ti powder, Al powder and TiC powder in a molar ratio of 1:(1.1 ~ 1.3):2, and sintering at 1350 ~ 1400 °C for 2 hours under an inert atmosphere such as argon or nitrogen. The Ti3AlC2 layered ceramic material is ground and sieved to a particle size of less than 400 mesh, and the etchant is a mixed solution of HCl and LiF.

[0011] Preferably, the conditions for liquid phase etching in step 1) are: 40-50 ℃, 500-1000 rpm, 1-2 days; the conditions for low-temperature ultrasonication are: 3-12 ℃, 45 kHz frequency, 60-120 minutes; and the conditions for centrifugation are: 3500-5000 rpm, 30-60 minutes.

[0012] Preferably, in step 2), the volume of sol solution A is 10-20 mL, the volume of buffer solution is 40-50 mL, and the mass of dopamine hydrochloride powder is 80-100 mg.

[0013] Preferably, the stirring conditions in step 2) are: 6 to 8 hours; the centrifugation conditions are: 6000 to 9000 rpm for 2 to 5 minutes; and the vacuum drying conditions are: 60 to 80 ℃ for 10 to 12 hours.

[0014] Preferably, in step 3), powder A is placed in a high-temperature tube furnace and heated at 2-5 °C for 1 minute under an inert atmosphere such as argon or nitrogen. -1 Anneal at a heating rate of 400-500℃ and hold for 2-4 hours.

[0015] Preferably, in step 4), the mass of powder B is 40-120 mg, the mass of polyvinylidene fluoride is 5-15 mg, the mass of conductive carbon black is 5-15 mg, the volume of N-methylpyrrolidone is 0.5-1 mL, and the thickness of titanium foil is 0.01-0.1 mm.

[0016] Preferably, the vacuum drying conditions in step 4) are: 80 ~ 120 ℃, 12 ~ 48 hours.

[0017] The present invention also provides a phosphorus-doped carbon-coated co-modified MXene-based nanocomposite material, which is obtained by the above-mentioned preparation method of phosphorus-doped carbon-coated co-modified MXene-based nanocomposite material. It consists of a silver ear-shaped polydopamine carbonized derivative uniformly distributed on the surface of a single / few-layer MXene sheet, forming an open three-dimensional conductive network. The size of the single / few-layer MXene sheet is limited to 5 ~ 10 μm.

[0018] This invention also provides a method for testing the performance of the above-mentioned phosphorus-doped carbon-coated co-modified MXene-based electrode (two-electrode testing system), comprising the following steps: taking a PC-MXene-based supercapacitor electrode with a diameter of 6-12 mm as the negative electrode; and, through capacity and mass ratio, taking an electrode with a certain diameter and a unit area mass of 5-7 mg cm⁻¹. −2Activated carbon was used as the positive electrode, sulfuric acid solution was used as the electrolyte, and a two-electrode system was assembled using a CR2032 button battery case. The specific capacity, energy density, power density and cycle stability of the electrodes were measured using a Shanghai Chenhua CHI 660E electrochemical workstation and a Blue Electric charge-discharge instrument. Cyclic voltammetry (CV), constant current charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS) were used.

[0019] The present invention also provides a hybrid supercapacitor assembled with the above-mentioned phosphorus-doped carbon-coated co-modified MXene-based electrode, which can be applied to new energy electric vehicles, consumer electronic devices, etc.

[0020] Compared with existing technologies, this invention utilizes a monomer self-polymerization method to coat polydopamine onto MXene nanosheets, and simultaneously achieves phosphorus-doped carbon coating co-modification through carbonization treatment. This not only constructs a three-dimensional conductive network on the MXene surface, suppressing the self-stacking phenomenon of MXene, but also allows the phosphorus atoms doped on the surface to bind more protons, introducing additional pseudocapacitance to achieve rapid ion transport. The prepared nanocomposite material exhibits excellent electrochemical performance and superior cycling performance, making it an ideal candidate electrode material for electrochemical energy storage devices such as aqueous supercapacitors, demonstrating great application potential. Therefore, this invention has a simple process route, good reproducibility, no organic additives, widely available and inexpensive raw materials, and low-toxicity byproducts that are easy to treat harmlessly, resulting in good economic and environmental benefits and facilitating large-scale industrial applications. Attached Figure Description

[0021] Figure 1 This is a SEM image of the phosphorus-doped carbon-coated co-modified MXene-based nanocomposite material prepared in Example 1 of the present invention.

[0022] Figure 2 The image shows the XRD pattern of the phosphorus-doped carbon-coated co-modified MXene-based nanocomposite material prepared in Example 1 of this invention.

[0023] Figure 3 The constant current charge-discharge curve of the two-dimensional MXene electrode prepared in Example 1 of the present invention is shown.

[0024] Figure 4 The constant current charge-discharge curve of the phosphorus-doped carbon-coated co-modified MXene-based supercapacitor electrode prepared in Example 1 of this invention is shown.

[0025] Figure 5 The cyclic voltammetry curve of the phosphorus-doped carbon-coated co-modified MXene-based supercapacitor electrode prepared in Example 1 of this invention is shown.

[0026] Figure 6This is a comparison chart of the specific capacitance of the MXene composite electrode and the phosphorus-doped carbon-coated co-modified MXene-based supercapacitor electrode in Example 1 of the present invention. Detailed Implementation

[0027] The present invention will be further explained and described below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0028] This invention provides a phosphorus-doped carbon-coated co-modified MXene-based nanocomposite material and its preparation method, comprising: 1) Ti3AlC2 was etched using an etchant in liquid phase to obtain a multilayer MXene nanosheet solution. The multilayer MXene solution was subjected to low-temperature sonication under an inert atmosphere such as argon or nitrogen, and the supernatant was collected by centrifugation to obtain a concentration of 5.0 ~ 8.0 mg / mL. -1 The sol solution of monolayer / few-layer MXene nanosheets is defined as sol solution A.

[0029] 2) Add sol solution A to alkaline buffer solution and mix well to obtain solution B. Quickly add dopamine hydrochloride powder to solution B, stir at room temperature, and centrifuge to collect the lower precipitate. Vacuum dry the lower precipitate and define the obtained powder as powder A.

[0030] 3) Place sodium hypophosphite powder and powder A in the upstream and downstream of a high-temperature tube furnace respectively for high-temperature heat annealing to obtain PC-MXene-based nanocomposite material, which is defined as powder B.

[0031] 4) Using powder B as the active material (powder B accounts for 70% to 80% of the total mass of the slurry), polyvinylidene fluoride as the binder, conductive carbon black as the conductive agent, N-methylpyrrolidone as the solvent, and titanium foil as the current collector, phosphorus-doped carbon-coated co-modified MXene-based supercapacitor electrodes were prepared by slurry coating method and vacuum drying.

[0032] Specifically, in step 1), the multilayer MXene nanosheet solution is prepared by etching Ti3AlC2 ceramic material using a liquid phase etching method. The layered ceramic material Ti3AlC2 is a mixture of Ti powder, Al powder, and TiC powder in a molar ratio of 1:(1.1 ~ 1.3):2, sintered at 1350 ~ 1400 ℃ for 2 hours under an inert atmosphere such as argon and nitrogen. The Ti3AlC2 layered ceramic material is ground and sieved to a particle size of less than 400 mesh. The etching agent is a mixed solution of HCl and LiF.

[0033] Specifically, the liquid-phase etching conditions for the multilayer MXene nanosheet solution preparation in step 1) are: 40–50 °C, 500–1000 rpm, 1–2 days; the low-temperature ultrasonication conditions for the mono / few-layer MXene nanosheet sol solution preparation are: 3–12 °C, 45 kHz frequency, 60–120 minutes, with argon gas bubbled into the system simultaneously; the centrifugation conditions are: 3500–5000 rpm, 30–60 minutes. The sol concentration is limited to 5.0–8.0 mg / mL. -1 .

[0034] Specifically, in step 2), the volume of sol solution A required for preparing solution B is 10-20 mL, the volume of buffer solution is 40-50 mL, and the mass of dopamine hydrochloride powder is 80-100 mg.

[0035] Specifically, the stirring conditions in step 2) are: 6 to 8 hours; the centrifugation conditions are: 6000 to 9000 rpm for 2 to 5 minutes; and the vacuum drying conditions for obtaining powder A are: 60 to 80 ℃ for 10 to 12 hours.

[0036] Specifically, in step 3), powder A is transferred to a high-temperature tube furnace and heated at 2-5°C for 1 minute under an inert atmosphere such as argon or nitrogen. -1 Anneal at a heating rate of 400-500℃ and hold for 2-4 hours.

[0037] Specifically, in step 4), the mass of powder B required for preparing the composite electrode by the slurry coating method is 40-120 mg, the mass of polyvinylidene fluoride is 5-15 mg, the mass of conductive carbon black is 5-15 mg, the volume of N-methylpyrrolidone is 0.5-1 mL, and the thickness of titanium foil is 0.01-0.1 mm.

[0038] Specifically, the vacuum drying conditions in step 4) are: 80 ~ 120 ℃, 12 ~ 48 hours.

[0039] The present invention also provides a phosphorus-doped carbon-coated co-modified MXene-based nanocomposite material, which is obtained by the above-mentioned preparation method of phosphorus-doped carbon-coated co-modified MXene-based nanocomposite material. It consists of silver ear-shaped polydopamine carbonized derivatives uniformly distributed on the surface of single / few-layer MXene sheets, forming an open three-dimensional conductive network.

[0040] The phosphorus-doped carbon-coated co-modified MXene-based nanocomposite material prepared in this invention utilizes a carbon layer coating on the surface of MXene, allowing phosphorus atoms to be doped into the carbon layer of MXene via PC bonds. This not only allows for the binding of more protons to introduce additional pseudocapacitance and achieve rapid ion transport, but also avoids the formation of titanium phosphate impurities during phosphorus doping, protecting the structural stability of the material and ultimately enhancing the electrochemical performance of the MXene-based composite electrode. The nanocomposite material in this invention can be used in diverse combinations. The phosphorus-doped carbon-coated co-modification strategy can be applied to various two-dimensional MXene nanosheets. The mechanism by which this strategy enhances the electrochemical performance of MXene-based composite electrode materials will be explored, with a focus on verifying its targeted improvement effect on key indicators such as specific capacitance, cycle stability, and rate performance. The preparation of phosphorus-doped carbon-coated co-modified MXene-based supercapacitor electrodes provides a more efficient, reliable, and sustainable energy storage solution for fields such as new energy electric vehicles and consumer electronics.

[0041] The preparation process involved in this invention is characterized by its simple and clear flow and high process stability. Each step has been systematically optimized, and key process parameters are precisely controllable. The raw material system uses widely available and low-cost industrial-grade compounds. This process route strictly follows the principles of green chemistry, resulting in low emissions of waste that are easy to treat harmlessly. This successfully constructs an industrial production system that combines excellent economic efficiency and environmental friendliness.

[0042] The present invention will now be described in detail with reference to specific embodiments.

[0043] Example 1: 1) Prepare an etchant by adding 2 g LiF to 20 mL of HCl with a mass concentration of 36-38%. Add 1 g Ti3AlC2 to the etchant and etch at 50 °C and 1000 rpm for 1 day. Repeat centrifugation with ultrapure water at 3500 rpm until clean, and collect the lower precipitate to obtain a multilayer MXene nanosheet solution. Sonicate the multilayer MXene solution under an argon atmosphere at 10 °C for 60 minutes, and centrifuge at 3500 rpm for 30 minutes. Collect the upper suspension to obtain a concentration of 6.0 mg / mL. -1 A single / few-layer MXene nanosheet sol solution.

[0044] 2) Take 15 mL of the above sol solution A and add it to 40 mL of alkaline buffer solution and mix well to obtain solution B. Take 90 mg of dopamine hydrochloride powder and quickly add it to solution B. Stir at room temperature for 6 hours and centrifuge repeatedly with anhydrous ethanol at 7000 rpm until clean. Collect the lower precipitate and vacuum dry it at 60 °C for 10 hours to obtain powder A.

[0045] 3) Place the sodium hypophosphite powder and powder A above in the upstream and downstream sections of a high-temperature tube furnace, respectively, and heat under an argon atmosphere at 2 °C for 1 minute. -1 Annealing at a heating rate of 400 °C for 2 hours yields phosphorus-doped carbon-coated co-modified MXene-based nanocomposite material, defined as powder B.

[0046] 4) Take 100 mg of powder C, 12.5 mg of polyvinylidene fluoride, and 12.5 mg of conductive carbon black powder respectively and place them in a mortar. Add 0.5 mL of N-methylpyrrolidone to the mixed powder and grind until uniform to form a slightly viscous conductive slurry. Coat the conductive slurry evenly on a titanium foil with a thickness of 0.03 mm and transfer it to a vacuum oven to dry at 80 °C for 12 hours. The result is the phosphorus-doped carbon-coated co-modified MXene-based supercapacitor electrode.

[0047] 5) A PC-MXene-based supercapacitor electrode with a diameter of 8 mm was used as the negative electrode, and an electrode with a diameter of 12 mm and a unit area mass of 5 mg / cm² was used as the negative electrode. −2 Activated carbon was used as the positive electrode, and 1 M H2SO4 solution was used as the electrolyte. The two-electrode system was assembled using a CR2032 button battery case. The specific capacity, energy density, power density and cycle stability of the electrodes were measured using a Shanghai Chenhua CHI 660E electrochemical workstation and a Blue Electric charge-discharge instrument, and methods such as CV, GCD and EIS were used.

[0048] Figure 1 This is a SEM image of the phosphorus-doped carbon-coated co-modified MXene-based nanocomposite material prepared in Example 1. The polydopamine carbon derivative is uniformly coated on the surface of the MXene flakes, exhibiting a silver ear-like three-dimensional open structure.

[0049] Figure 2 The image shows the XRD pattern of the phosphorus-doped carbon-coated co-modified MXene-based nanocomposite material prepared in Example 1. Compared with pure MXene, the (002) of the carbon-doped carbon-coated co-modified MXene-based nanocomposite material showed no significant shift, indicating the stability of the modified structure.

[0050] Figure 4 The image shows the constant current charge-discharge curves of the phosphorus-doped carbon-coated co-modified MXene-based supercapacitor electrode prepared in Example 1. Figure 3Compared to the constant current charge-discharge curve of the MXene electrode shown, the phosphorus-doped carbon-coated co-modified MXene-based supercapacitor electrode prepared in Example 1 exhibits a longer discharge time. This is because the three-dimensional open conductive network formed by the polydopamine carbide derivative on the MXene surface reduces the resistance to electron transport within the electrode material; simultaneously, the doped phosphorus can bind with more protons, thereby enhancing the pseudocapacitance and achieving greater charge storage. The phosphorus-doped carbon-coated co-modification strategy not only suppresses the self-stacking of MXene nanosheets, providing continuous electron transport pathways and ion diffusion channels, but also introduces more surface active sites, endowing it with higher specific capacity.

[0051] Figure 5 The image shows the cyclic voltammetry curves of the phosphorus-doped carbon-coated co-modified MXene-based supercapacitor electrode prepared in Example 1. The CV curve shape of the PC-MXene electrode did not change significantly at different scan rates, indicating good charge-discharge stability.

[0052] Figure 6 This is a comparison chart of the specific capacitance of the phosphorus-doped carbon-coated co-modified MXene-based supercapacitor electrode prepared in Example 1. Calculations using constant current charge-discharge curves show that the MXene-MC composite electrode at a current density of 4 A g⁻¹... -1 The discharge specific capacity is as high as 462 F g. -1 The current density was further increased to 50 A g. -1 There are still 365 F g afterward −1 The discharge specific capacity of the Ti3AlC2 electrode is less than a quarter of that of PC-MXene (4 A g). -1 The specific capacity at the lower discharge level is 106 F g. -1 ).

[0053] Example 2: 1) Prepare an etchant by adding 2 g LiF to 20 mL of HCl with a mass concentration of 36-38%. Add 1 g Ti3AlC2 to the etchant and etch at 1000 rpm for 1 day at 40 °C. Repeat centrifuge with ultrapure water at 3500 rpm until clean, and collect the lower precipitate to obtain a multilayer MXene nanosheet solution. Sonicate the multilayer MXene solution under an argon atmosphere at 12 °C for 90 minutes, and centrifuge at 3500 rpm for 30 minutes. Collect the upper suspension to obtain a concentration of 5.0 mg / mL. -1 A single / few-layer MXene nanosheet sol solution.

[0054] 2) Take 20 mL of the above sol solution A and add it to 40 mL of alkaline buffer solution and mix well to obtain solution B. Take 100 mg of dopamine hydrochloride powder and quickly add it to solution B. Stir at room temperature for 7 hours and centrifuge repeatedly with anhydrous ethanol at 8000 rpm until clean. Collect the lower precipitate and vacuum dry it at 60 °C for 10 hours to obtain powder A.

[0055] 3) Place the sodium hypophosphite powder and powder A above in the upstream and downstream sections of a high-temperature tube furnace, respectively, and heat under an argon atmosphere at 2 °C for 1 minute. -1 Annealing at a heating rate of 500 °C for 2 hours yields phosphorus-doped carbon-coated co-modified MXene-based nanocomposite material, defined as powder B.

[0056] 4) Take 100 mg of powder C, 12.5 mg of polyvinylidene fluoride, and 12.5 mg of conductive carbon black powder respectively and place them in a mortar. Add 0.5 mL of N-methylpyrrolidone to the mixed powder and grind until uniform to form a slightly viscous conductive slurry. Coat the conductive slurry evenly on a titanium foil with a thickness of 0.03 mm and transfer it to a vacuum oven to dry at 80 °C for 12 hours. The result is the phosphorus-doped carbon-coated co-modified MXene-based supercapacitor electrode.

[0057] 5) Use PC-MXene-based supercapacitor electrodes with a diameter of 8 mm as the negative and positive electrodes, and use electrodes with a diameter of 12 mm and a unit area mass of 5 mg / cm³. −2 Activated carbon sheets were used as the positive electrode, 1 M H2SO4 solution was used as the electrolyte, and a two-electrode system was assembled using a CR2032 button battery case. The specific capacity, energy density, power density and cycle stability of the electrodes were measured using a Shanghai Chenhua CHI 660E electrochemical workstation and a Blue Electric charge-discharge instrument, and methods such as CV, GCD and EIS were used.

[0058] Example 3: 1) Prepare an etchant by adding 4 g LiF to 40 mL of HCl with a mass concentration of 36-38%. Add 2 g Ti3AlC2 to the etchant and etch at 50 °C and 1000 rpm for 1 day. Repeat centrifuge with ultrapure water at 3500 rpm until clean, and collect the lower precipitate to obtain a multilayer MXene nanosheet solution. Sonicate the multilayer MXene solution under an argon atmosphere at 10 °C for 90 minutes, and centrifuge at 3500 rpm for 30 minutes. Collect the upper suspension to obtain a concentration of 8.0 mg / mL. -1 A single / few-layer MXene nanosheet sol solution.

[0059] 2) Take 10 mL of the above sol solution A and add it to 40 mL of alkaline buffer solution and mix well to obtain solution B. Take 80 mg of dopamine hydrochloride powder and quickly add it to solution B. Stir at room temperature for 6 hours and centrifuge repeatedly with anhydrous ethanol at 6000 rpm until clean. Collect the lower precipitate and vacuum dry it at 60 °C for 10 hours to obtain powder A.

[0060] 3) Place the sodium hypophosphite powder and powder A above in the upstream and downstream sections of a high-temperature tube furnace, respectively, and heat at 4 °C for 1 minute under an argon atmosphere. -1 Annealing at a heating rate of 500 °C for 2 hours yields phosphorus-doped carbon-coated co-modified MXene-based nanocomposite material, defined as powder B.

[0061] 4) Take 100 mg of powder C, 12.5 mg of polyvinylidene fluoride, and 12.5 mg of conductive carbon black powder respectively and place them in a mortar. Add 0.5 mL of N-methylpyrrolidone to the mixed powder and grind until uniform to form a slightly viscous conductive slurry. Coat the conductive slurry evenly on a titanium foil with a thickness of 0.03 mm and transfer it to a vacuum oven to dry at 80 °C for 12 hours. The result is the phosphorus-doped carbon-coated co-modified MXene-based supercapacitor electrode.

[0062] 5) Use PC-MXene-based supercapacitor electrodes with a diameter of 8 mm as the negative and positive electrodes, and use electrodes with a diameter of 12 mm and a unit area mass of 5 mg / cm³. −2 Activated carbon sheets were used as the positive electrode, 1 M H2SO4 solution was used as the electrolyte, and a two-electrode system was assembled using a CR2032 button battery case. The specific capacity, energy density, power density and cycle stability of the electrodes were measured using a Shanghai Chenhua CHI 660E electrochemical workstation and a Blue Electric charge-discharge instrument, and methods such as CV, GCD and EIS were used.

Claims

1. A phosphorus-doped carbon-coated co-modified MXene-based nanocomposite material (PC-MXene) and its preparation method, comprising the following steps: (1) Ti3AlC2 was etched using an etchant in liquid phase to obtain a multilayer MXene nanosheet solution. The multilayer MXene solution was subjected to low-temperature sonication under an inert atmosphere such as argon or nitrogen, and the upper suspension was collected by centrifugation to obtain a concentration of 5.0 ~ 8.0 mg / mL. -1 The sol solution of monolayer / few-layer MXene nanosheets is defined as sol solution A. (2) Add sol solution A to alkaline buffer solution and mix well to obtain solution B. Add dopamine hydrochloride powder to solution B quickly, stir at room temperature, and centrifuge to collect the lower precipitate. Dry the lower precipitate under vacuum. The obtained powder is defined as powder A. (3) Place sodium hypophosphite powder A in the upstream and downstream of a high-temperature tube furnace and perform high-temperature heat annealing treatment to obtain PC-MXene-based nanocomposite material, which is defined as powder B.

2. The method for preparing a phosphorus-doped carbon-coated co-modified MXene-based nanocomposite material according to claim 1, characterized in that, In step 1), Ti3AlC2 is obtained by mixing Ti powder, Al powder and TiC powder in a molar ratio of 1:(1.1 ~ 1.3):2 and sintering at 1350 ~ 1400 °C for 2 hours under an inert atmosphere such as argon and nitrogen. The Ti3AlC2 layered ceramic material is ground and sieved to a particle size of less than 400 mesh, and the etchant is a mixed solution of HCl and LiF.

3. The method for preparing a phosphorus-doped carbon-coated co-modified MXene-based nanocomposite material according to claim 1, characterized in that, The conditions for liquid phase etching in step 1) are: 40 ~ 50 ℃, 500 ~ 1000 rpm, 1 ~ 2 days; the conditions for low-temperature ultrasonic etching are: 3 ~ 12 ℃, frequency 45 KHz, 60 ~ 120 minutes; the conditions for centrifugation are: 3500 ~ 5000 rpm, 30 ~ 60 minutes.

4. The method for preparing a phosphorus-doped carbon-coated co-modified MXene-based nanocomposite material according to claim 1, characterized in that, In step 2), the volume of sol solution A is 10-20 mL, the volume of buffer solution is 40-50 mL, and the mass of dopamine hydrochloride powder is 80-100 mg.

5. The method for preparing a phosphorus-doped carbon-coated co-modified MXene-based nanocomposite material according to claim 1, characterized in that, The stirring conditions in step 2) are: 6 to 8 hours; the centrifugation conditions are: 6000 to 9000 rpm for 2 to 5 minutes; and the vacuum drying conditions are: 60 to 80 ℃ for 10 to 12 hours.

6. The method for preparing a phosphorus-doped carbon-coated co-modified MXene-based nanocomposite material according to claim 1, characterized in that, In step 3), powder A is placed in a high-temperature tube furnace and heated at 2-5 °C for 1 minute under an inert atmosphere such as argon or nitrogen. -1 Anneal at a heating rate of 400-500℃ and hold for 2-4 hours.

7. A phosphorus-doped carbon-coated co-modified MXene-based nanocomposite material, characterized in that, The MXene-based nanocomposite material is prepared by the method described in any one of claims 1 to 6. It consists of a silver ear-shaped polydopamine carbonized derivative uniformly distributed on the surface of a single / few-layer MXene sheet, forming an open three-dimensional conductive network. The size of the single / few-layer MXene sheet is limited to 5 to 10 μm.

8. A phosphorus-doped carbon-coated co-modified MXene-based nanocomposite material as described in claim 7, used as an electrode active material, in electrochemical energy storage devices such as hybrid supercapacitors.

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