A porous carbon fiber supported black phosphorus / nitrogen-doped carbon composite material, a preparation method and application thereof

Abstract

The application discloses a porous carbon fiber supported black phosphorus / nitrogen-doped carbon composite material and a preparation method and application thereof, and belongs to the field of new energy materials and devices. A nitrogen-doped carbon coated porous carbon fiber conductive framework is prepared by using a metal-assisted chemical etching technology, then a solvent thermal and limited growth strategy is adopted to convert red phosphorus into black phosphorus and in-situ limit the growth of the black phosphorus in the pores of the nitrogen-doped carbon coated porous carbon fiber framework, so that a high-performance self-supported phosphorus / carbon heterostructure electrode material is constructed. The three-dimensional nitrogen-doped carbon coated porous carbon fiber conductive framework realizes high-speed electron / ion transmission and limits the expansion of the electrode structure; the rich nitrogen-doped defects are beneficial to abundant reaction active sites and enhance the reaction kinetics; the in-situ formed phosphorus / carbon heterojunction can promote electron transfer and ion diffusion, stabilize the electrode structure, and realize stable and fast reversible sodium storage.

Description

Technical Field

[0001] The present invention belongs to the field of new energy materials and devices, and specifically relates to a porous carbon fiber-supported black phosphorus / nitrogen-doped carbon composite material and a preparation method and application thereof. Background Art

[0002] New secondary energy storage technologies are developing rapidly. Sodium ion batteries have the characteristics of abundant resources, low solvation effect and high safety, and may become the new main force of next-generation energy storage batteries in the future. However, the larger radius of sodium ions This leads to slow ion diffusion, electrode structural damage, and poor solid electrolyte interface (SEI) stability; the high redox potential (-2.71V) reduces its open circuit voltage and energy density. Developing electrode materials with fast electrochemical reaction kinetics, robust structure, high reversible capacity, and low redox potential through electrode component and structural design is key to ensuring sodium-ion batteries exhibit excellent rate performance, cycling stability, and high energy density.

[0003] Phosphorus has a high theoretical capacity (2596 mAh g -1 ), low charge and discharge potential (~0.2V / ~0.5V vs.Na + / Na) and other characteristics have attracted much attention, and as a negative electrode material, it is expected to significantly improve the energy density of sodium ion batteries. Phosphorus exists in three allotropes: white phosphorus, red phosphorus and black phosphorus, and their properties are different. Among them, white phosphorus is highly toxic and flammable, and is not suitable as an electrode material; red phosphorus is low in cost and non-toxic, and has been widely studied as a negative electrode for sodium ion batteries. However, the intrinsic conductivity of red phosphorus is low (10 -14 S m -1 ) and significant volume effect, resulting in sluggish electrochemical reaction kinetics, poor cycle reversibility and rapid capacity decay. The new nanomaterial black phosphorus has a two-dimensional folded layered structure and has high conductivity (300S m -1 ), high carrier mobility, good thermal stability and high anisotropy, making it an ideal negative electrode material for sodium ion batteries. Single block black phosphorus has serious volume expansion and large voltage hysteresis during the sodium insertion / extraction process. Nanosizing black phosphorus can alleviate the volume effect, shorten the ion diffusion distance, and enhance the reaction activity. However, the self-aggregation effect of nanoparticles leads to a decrease in the electrode / electrolyte contact area, an increase in the interface resistance, and slow ion diffusion kinetics. Anchoring the nanoparticles in conductive carbon with a hierarchical pore structure can effectively limit their self-aggregation through spatial confinement, thereby enriching the reaction interface. In addition, the lone pair electrons in the phosphorus atoms make black phosphorus extremely sensitive to water and oxygen in the environment and have poor cyclic stability. When it is composited with conductive porous carbon, a phosphorus / carbon heterogeneous interface is formed in situ through bonding, which can promote electron transfer and sodium ion diffusion and stabilize the electrode structure.

[0004] Innovation of traditional electrode structures, integrated design of electrode materials and current collectors, and development of new self-supporting sodium-ion battery negative electrode materials have become a new hotspot in sodium-ion battery research. By optimizing the microstructure of electrode materials and combining self-supporting hierarchical porous carbon networks with alloy-type black phosphorus negative electrode materials, high-performance self-supporting electrode materials with phosphorus / carbon heterostructures can be constructed. When hierarchical porous carbon is used as a conductive support skeleton, rapid electron transport and excellent ion diffusion kinetics can be achieved, while effectively limiting the self-aggregation effect of nanomaterials and the volume effect during the cycle. The abundant pore structure gives it a large specific surface area, which can enhance the infiltration of the electrolyte into the active components. Heteroatom doping introduces defect structures, which can enrich the reaction active sites and enhance the reaction kinetics, thereby effectively improving the electrochemical performance of the electrode material. Summary of the Invention

[0005] The present invention aims to address the serious volume effect of black phosphorus and the instability of lone-pair electrons in phosphorus atoms by providing a porous carbon fiber-supported black phosphorus / nitrogen-doped carbon composite and its preparation method. When used as a negative electrode material for sodium-ion batteries, this self-supporting composite exhibits high specific capacity, excellent rate performance, and cycling reversibility.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A porous carbon fiber-supported black phosphorus / nitrogen-doped carbon composite material is prepared. Tiny rod-shaped black phosphorus nanoparticles are dispersed within a nitrogen-doped carbon-coated porous carbon fiber conductive framework, forming a porous carbon fiber-supported black phosphorus / nitrogen-doped carbon (BP@NC / PCF) composite material. The areal loading of the active material (BP@NC) in the composite material is 1.8-2.0 mg cm -2 The mass ratio of black phosphorus in the composite material is 30 to 50%.

[0008] A method for preparing a porous carbon fiber-supported black phosphorus / nitrogen-doped carbon composite material comprises the following steps: first, metal-assisted chemical etching is used to prepare a nitrogen-doped carbon-coated porous carbon fiber conductive framework; then, solvent thermal and confined growth strategies are used to convert red phosphorus into black phosphorus and in situ confinedly grow it in the pores of the nitrogen-doped carbon-coated porous carbon fiber framework, thereby constructing a high-performance phosphorus / carbon heterostructure composite material, namely, a porous carbon fiber-supported black phosphorus / nitrogen-doped carbon (BP@NC / PCF) composite material.

[0009] As a preferred technical solution of the present invention, the specific steps of the preparation method of the porous carbon fiber supported black phosphorus / nitrogen-doped carbon composite material are as follows:

[0010] (1) Commercial carbon fiber cloth was ultrasonically cleaned with acetone, ethanol, and deionized water in sequence, and then dried; nickel hydroxide was electrochemically deposited on the carbon fiber cloth using a three-electrode system with a platinum sheet as a counter electrode, the carbon fiber cloth as a working electrode, and Ag / AgCl as a reference electrode, and then dried for use;

[0011] (2) Weigh a certain amount of polyacrylonitrile and polyvinylpyrrolidone and dissolve them in an appropriate amount of N,N-dimethylformamide solvent. Stir for a period of time to obtain a viscous solution.

[0012] (3) fully immersing the carbon fiber cloth with nickel hydroxide loaded on the surface obtained in step (1) in the above-mentioned viscous solution for 5 minutes, taking it out and drying it; then calcining it at high temperature in an argon / hydrogen mixed atmosphere; finally, washing it in a hydrochloric acid solution to remove nickel particles, washing it, and drying it to obtain a nitrogen-doped carbon-coated porous carbon fiber (NC / PCF) composite material;

[0013] (4) A certain amount of purified red phosphorus was dissolved in an appropriate amount of ethylenediamine solution, and then the nitrogen-doped carbon-coated porous carbon fiber composite material was fully immersed in this mixed solution, and then transferred into a high-pressure reactor for solvent thermal reaction; finally, the product was washed and dried to obtain a porous carbon fiber supported black phosphorus / nitrogen-doped carbon (BP@NC / PCF) composite material.

[0014] As a further preferred technical solution of the present invention, in the preparation method:

[0015] In step (1), during the electrochemical deposition of nickel hydroxide, 1 mol L -1 Nickel nitrate (Ni(NO3)2) and 0.1 mol L -1 The electrolyte is a mixed solution of sodium nitrate (NaNO3), with a volume ratio of 1:1 between nickel nitrate solution and sodium nitrate solution; the current density is 7-9 mA cm -2 , the deposition time is 10 to 30 minutes.

[0016] In step (2), the mass volume concentration of polyacrylonitrile in the viscous solution is 0.08 g mL -1 The mass ratio of polyacrylonitrile and polyvinyl pyrrolidone is 1:1~3.

[0017] In step (3), the high temperature calcination temperature is 800-1000°C, the calcination time is 1-3h, and the heating rate is 5-10°C min -1 .

[0018] In step (4), the specific steps of red phosphorus purification are as follows: first, 3.0 g of commercial red phosphorus is weighed and dispersed in 80 mL of deionized water, followed by hydrothermal purification in an autoclave at a hydrothermal temperature of 200° C. for 12 h, and finally, the product is centrifuged, washed with ethanol, and dried to obtain purified red phosphorus.

[0019] In step (4), the solvent thermal reaction temperature is 180-200° C. and the time is 10-12 h.

[0020] The porous carbon fiber supported black phosphorus / nitrogen-doped carbon (BP@NC / PCF) composite material prepared by the present invention is used as a negative electrode material in sodium ion batteries, avoiding the use of additional conductive agents, binders and current collectors, thereby improving the battery energy density.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1) The present invention uses nitrogen-doped carbon-coated porous carbon fibers with high mechanical strength and stable structure as a conductive support skeleton to accelerate electron / ion transmission and limit electrode volume expansion; the three-dimensional hierarchical pore structure gives the composite material a high specific surface area, which is beneficial to enhance the infiltration of the electrolyte into the active material; nitrogen-doped defects are beneficial to enrich the reaction active sites and enhance the reaction kinetics; the dispersed black phosphorus particles can effectively shorten the ion diffusion distance; the in situ formed phosphorus / carbon heterogeneous interface can promote electron transfer and sodium ion diffusion, stabilize the electrode structure, and achieve stable and rapid reversible sodium storage.

[0023] 2) The self-supporting anode material for sodium-ion batteries (BP@NC / PCF) prepared in the present invention does not require the use of current collectors, conductive agents, and binders when assembling batteries. The manufacturing process is simple, low-cost, and environmentally friendly, which is conducive to industrial promotion and is of great significance to the development of self-supporting anode materials for sodium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 3 is the XRD curve of the nitrogen-doped carbon-coated porous carbon fiber composite material (NC / PCF) in Example 1.

[0025] Figure 2 XRD curves of (a) black phosphorus and (b) porous carbon fiber supported black phosphorus / nitrogen-doped carbon composite material (BP@NC / PCF) in Example 1.

[0026] Figure 3 (a) low and (b) high magnification SEM morphologies of the nitrogen-doped carbon-coated porous carbon fiber composite material (NC / PCF) in Example 1.

[0027] Figure 4 (a) SEM and (b) TEM morphologies of the porous carbon fiber supported black phosphorus / nitrogen-doped carbon composite material (BP@NC / PCF) in Example 1.

[0028] Figure 5(a) N2 adsorption-desorption isotherm and (b) DFT pore size distribution diagram of the porous carbon fiber supported black phosphorus / nitrogen-doped carbon composite material (BP@NC / PCF) in Example 1 (the inset is a curve diagram of the pore size distribution ≤ 2 nm).

[0029] Figure 6 (a) XPS full spectrum and (b) C 1s, (c) N 1s, and (d) high-resolution spectra of P 2p elements of the porous carbon fiber-supported black phosphorus / nitrogen-doped carbon composite material (BP@NC / PCF) in Example 1.

[0030] Figure 7 The sodium ion half-cell assembled based on the BP@NC / PCF electrode material in Example 1 was -1 Lower cycle performance test results.

[0031] Figure 8 These are the rate performance test results of the sodium ion half-cell assembled based on the BP@NC / PCF electrode material in Example 1.

[0032] Figure 9 The results of the cycling performance test of the sodium ion full battery assembled based on the BP@NC / PCF negative electrode material in Example 1 at 0.5C.

[0033] Figure 10 These are the rate performance test results of the sodium ion full battery assembled based on the BP@NC / PCF negative electrode material in Example 1.

[0034] Figure 11 The sodium ion half-cell assembled based on NC / PCF electrode material in Comparative Example 1 was -1 Lower cycle performance test results.

[0035] Figure 12 These are the rate performance test results of the sodium ion half-cell assembled based on NC / PCF electrode materials in Comparative Example 1. DETAILED DESCRIPTION

[0036] The porous carbon fiber-supported black phosphorus / nitrogen-doped carbon composite material provided by the present invention and its preparation method and application are further described in detail below with reference to the examples and drawings.

[0037] Example 1

[0038] This embodiment provides a method for preparing a porous carbon fiber-supported black phosphorus / nitrogen-doped carbon composite material. First, a nitrogen-doped carbon-coated porous carbon fiber conductive framework is prepared using metal-assisted chemical etching technology. Then, a solvent thermal and confined growth strategy is used to convert red phosphorus into black phosphorus and in situ confined growth is achieved in the pores of the nitrogen-doped carbon-coated porous carbon fiber framework to construct a high-performance phosphorus / carbon heterostructure composite material for use as a negative electrode material for sodium ion batteries.

[0039] The specific steps include:

[0040] (1) Commercial carbon fiber cloth was ultrasonically cleaned with acetone, ethanol, and deionized water for 10 to 30 minutes, and then dried at 60°C for 8 hours. A three-electrode system was used to electrochemically deposit nickel hydroxide on the carbon fiber cloth, using a platinum sheet as the counter electrode, carbon fiber cloth as the working electrode, and Ag / AgCl as the reference electrode. During the electrochemical deposition process, 1 mol L -1 Nickel nitrate (Ni(NO3)2) and 0.1 mol L -1 A mixed solution of sodium nitrate (NaNO3) (volume ratio of 1:1) was used as the electrolyte, and the current density was 8 mA cm -2 , the deposition time is 20 min; then the prepared sample is dried at 60°C for 12 h for use.

[0041] (2) Weigh polyacrylonitrile and polyvinylpyrrolidone in a mass ratio of 1:2 and dissolve them in N,N-dimethylformamide solvent. Stir continuously at 60°C for 12 hours to obtain a viscous solution. The mass volume concentration of polyacrylonitrile in this solution is 0.08 g / mL -1 .

[0042] (3) The carbon fiber cloth loaded with nickel hydroxide on the surface was fully immersed in the above viscous solution, taken out after 5 minutes, and dried at 60°C for 8 hours; then calcined at high temperature in an argon / hydrogen mixed atmosphere with a volume ratio of 5:1, the calcination temperature was 900°C, the calcination time was 2 hours, and the heating rate was 10°C min -1 ; Finally, place it in 3 mol L -1 The nickel particles were removed by pickling in a hydrochloric acid solution at 80°C for 5 h, and then the composite was washed and dried to obtain a nitrogen-doped carbon-coated porous carbon fiber (NC / PCF) composite material.

[0043] (4) The specific steps of red phosphorus purification are as follows: first, 3.0 g of commercial red phosphorus was weighed and dispersed in 80 mL of deionized water. Then, the product was hydrothermally purified in an autoclave at a temperature of 200 °C for 12 h. Finally, the product was centrifuged, washed with ethanol, and dried to obtain purified red phosphorus.

[0044] (5) 0.3 g of purified red phosphorus was dissolved in 50 mL of ethylenediamine solution. The NC / PCF composite material was then fully immersed in the mixed solution and then transferred to a high-pressure reactor for a solvothermal reaction at 200 °C for 12 h. Finally, the product was washed and dried to obtain a porous carbon fiber-supported black phosphorus / nitrogen-doped carbon composite material (BP@NC / PCF). When the BP@NC / PCF composite material was used as a self-supporting negative electrode material for sodium ion batteries, the areal loading of the active material was 1.8 mg cm -2 The mass ratio of black phosphorus in BP@NC / PCF composite material is 47.3%.

[0045] See also Figure 1 , which is the XRD curve of the nitrogen-doped carbon-coated porous carbon fiber composite material (NC / PCF) prepared in this embodiment. As can be seen from the figure, after metal-assisted chemical etching and pickling treatment, the NC / PCF composite material can be obtained. The diffraction peaks at 25.7° and 43.8° correspond to the (002) and (100) crystal planes of graphitized carbon, respectively. Combined with the SEM morphology of the NC / PCF composite material ( Figure 3 ) It can be seen that the hierarchical pores in the composite material are cross-linked and interconnected, which can provide convenient channels for electron migration and ion diffusion, and at the same time can significantly expand the specific surface area of ​​the composite material, which is beneficial to enhance the electrolyte penetration and improve the reaction activity of the active material; in addition, the pore structure has a good pore confinement effect.

[0046] See also Figure 2 , This figure shows the XRD curves of black phosphorus and porous carbon fiber supported black phosphorus / nitrogen-doped carbon composite material (BP@NC / PCF). Figure 2 It can be seen from a that 17.4°, 27.4°, 35.3°, 35.5°, 41.4° and 57.5° correspond to the (020), (021), (040), (111), (041) and (151) crystal planes of BP, respectively (PDF#76-1967). In addition, during the solvent thermal reaction of ethylenediamine, since two P atoms in a unit cell are replaced by vacancies or H atoms, the crystal structure along the c-axis direction is dislocated or periodically distorted, and the lattice spacing is changed from Increase to Thus, obvious diffraction peaks appear at 10.3° and 31.1°. Figure 2 b It can be seen that NC / PCF was placed as a conductive support skeleton in an ethylenediamine solution containing red phosphorus, and a BP@NC / PCF composite material was prepared by solvent thermal reaction. In the XRD spectrum of BP@NC / PCF, diffraction peaks of BP at 10.3° and 17.4° can be observed, while the diffraction peaks at other positions are obscured by the high-intensity diffraction peaks of the graphitized carbon (002) crystal plane and are difficult to observe. Combined with the SEM morphology of the BP@NC / PCF composite material ( Figure 4 It can be seen from a) that the tiny black phosphorus nanoparticles cannot be directly observed in the pores. The main reason is that the confinement effect of the three-dimensional hierarchical pore structure in the NC / PCF composite material can inhibit the continuous growth of black phosphorus nanoparticles. Figure 4 b) It can be seen that the rod-shaped black phosphorus nanoparticles are about 8 nm in length, and the porous carbon tightly wraps the black phosphorus nanoparticles, which can effectively alleviate the large stress and strain of black phosphorus during the electrochemical reaction and enhance the stability of the electrode structure.

[0047] See also Figure 5 , the figure shows the (a) N2 adsorption-desorption isotherm and (b) DFT pore size distribution of porous carbon fiber supported black phosphorus / nitrogen-doped carbon composite material (BP@NC / PCF) (the inset is the curve of pore size distribution ≤ 2nm). As can be seen from the figure, the N2 adsorption-desorption isotherm of BP@NC / PCF composite material contains obvious hysteresis loop, which is due to the capillary condensation phenomenon caused by the presence of rich mesoporous structure, proving that the material contains rich mesoporous structure. The specific surface area of ​​BP@NC / PCF composite material calculated by Brunauer-Emmett-Teller (BET) method is 435.85m 2 g -1 , the pore volume is 0.623cm 3 g -1 The pore size distribution ranges from 0.3 to 290 nm. This indicates that the larger specific surface area of ​​the BP@NC / PCF composite material facilitates electrolyte wetting of active components while also providing abundant channels for sodium ion diffusion. The hierarchical pore structure provides more reactive sites and helps mitigate the volume effect of black phosphorus nanoparticles. The spatial confinement effect of the porous carbon facilitates the formation of a phosphorus / carbon heterogeneous interface, promoting electron transfer and ion diffusion, and stabilizing the electrode structure.

[0048] See also Figure 6 The figure shows (a) the full XPS spectrum and (b) the high-resolution spectra of C 1s, (c) N 1s, and (d) P 2p elements of the porous carbon fiber-supported black phosphorus / nitrogen-doped carbon composite (BP@NC / PCF). The full XPS spectrum shows that the BP@NC / PCF composite contains four elements: C, O, N, and P. In the C1s high-resolution spectrum, the characteristic peaks with binding energies of 284.0, 284.7, 285.8, and 288.2 eV correspond to the CP bond, CC / C=C bond, CO / C=N bond, and C=O bond, respectively; in the N1s high-resolution spectrum, there are characteristic peaks corresponding to the pyridine-N bond (399.1 eV), pyrrole-N bond (400.3 eV), and graphite-N bond (401.5 eV); in the P2p high-resolution spectrum, the binding energies of 130.8 and 131.4 correspond to the P 2p of the phosphorus element. 3 / 2and P2p 1 / 2 Characteristic peaks with binding energies of 133.6 and 1134.5 eV correspond to POC and PC bonds, respectively. XPS analysis indicates that the BP@NC / PCF composite contains elemental phosphorus and nitrogen-doped carbon, which act as active materials in the electrochemical reactions of sodium-ion batteries and contribute to the capacity of the self-supporting sodium-ion battery electrode material. Furthermore, the strong chemical bonds formed by the heterogeneous nucleation and growth of black phosphorus in the hierarchical pores stabilize the lone pairs of electrons on the black phosphorus surface, enhancing its stability.

[0049] The BP@NC / PCF self-supporting electrode material prepared in this example was used as the working electrode, the sodium sheet was used as the counter electrode, the GF / D glass microfiber membrane was used as the separator, sodium perchlorate NaClO4 was used as the solute, and ethylene carbonate EC and dimethyl carbonate DMC with a volume ratio of 1:1 were used as the solvent. The concentration of the prepared solution was 1 mol L -1 The solution was prepared and 5 wt% of fluoroethylene carbonate (FEC) was added as the electrolyte; finally, a 2032-type button-type sodium ion half-cell was assembled and a charge and discharge test was performed, with the test voltage window being 0.01-2V.

[0050] See also Figure 7 The figure shows the sodium ion half-cell assembled based on BP@NC / PCF electrode material in this embodiment at 100mA g -1 Cycling performance test results of BP@NC / PCF||Na half-cell at 100mA g -1 The initial charge and discharge specific capacities were 721 and 1015 mAh g -1 The initial coulombic efficiency is 70.9%. The main reasons for the low initial coulombic efficiency are: (1) side reactions between inactive components in the electrolyte and sodium metal; (2) decomposition of the electrolyte and formation of a solid electrolyte interface film (SEI) on the electrode surface; (3) partial Na + Irreversible embedding occurs in the host material. During the first 40 cycles, the charge and discharge capacity shows an upward trend. This is because the electrolyte continues to penetrate and infiltrate, and the electrode active material is in a continuously activated state. After 150 cycles, the capacity can reach 890mAh g -1 , the coulombic efficiency is 99.9%, compared with the reversible capacity at the 40th cycle (926 mAh g -1 ), the capacity retention rate was 96.1%, showing excellent cycle stability.

[0051] See also Figure 8 The figure shows the rate performance test results of the sodium ion half-cell assembled based on the BP@NC / PCF electrode material in Example 1. As shown in the figure, the current density is 0.1~2.0A g -1The BP@NC / PCF||Na half-cell has a step-by-step increase in the range of 0.1, 0.2, 0.4, 0.6, 0.8, 1.0 and 2.0 A g -1 The average capacities at 400 nm and 800 nm were 989, 864, 708, 606, 507, 415, and 304 mAh g-1, respectively. -1 When the current density returns to 0.1 A g -1 When the capacity is still up to 926mAh g -1 , showing excellent rate performance.

[0052] See also Figure 9 The figure shows the cycling performance test results of the sodium ion full battery assembled based on the BP@NC / PCF negative electrode material in Example 1 at 0.5C. As shown in the figure, at a current density of 0.5C, the initial capacity of the full battery in this example is 128mAh g -1 After 200 cycles, the battery capacity is 99 mAh g -1 , showing good cycle stability.

[0053] See also Figure 10 The figure shows the rate performance test results of the sodium ion full battery assembled based on the BP@NC / PCF negative electrode material in Example 1. As shown in the figure, the current density increases stepwise in the range of 0.2-3.0C. The average capacity of the full battery in this example at 0.2, 0.5, 0.8, 1.0, 1.5, 2.0 and 3.0C is 130, 120, 115, 109, 104, 100 and 91 mAh g, respectively. -1 When the current density returned to 0.2C, the capacity reached 116 mAh g -1 , showing good rate performance.

[0054] The above battery performance test results show that the porous carbon fiber supported black phosphorus / nitrogen-doped carbon composite material (BP@NC / PCF) provided by the present invention has good electrochemical performance, which is mainly attributed to the three-dimensional conductive NC / PCF framework in this composite material accelerating electron / ion transport and limiting electrode volume expansion; rich nitrogen-doped defects are conducive to abundant reaction active sites and enhanced reaction kinetics; the in situ formed phosphorus / carbon heterogeneous interface promotes electron transfer and sodium ion diffusion, stabilizes the electrode structure, and realizes stable and rapid reversible sodium storage.

[0055] Comparative Example 1

[0056] In order to compare and illustrate the effect of the black phosphorus nanoparticles, an active substance in the BP@NC / PCF composite material provided by the present invention, on the electrochemical properties of the electrode material, the method for preparing the negative electrode material of a sodium ion battery in this comparative example is basically the same as that in Example 1, except that the red phosphorus purification step (4) and the solvent thermal reaction step (5) are removed to prepare nitrogen-doped carbon-coated porous carbon fibers (NC / PCF) as a self-supporting negative electrode material for a sodium ion battery.

[0057] The NC / PCF electrode material prepared in this comparative example was used as the working electrode, the sodium sheet was used as the counter electrode; the GF / D glass microfiber membrane was used as the diaphragm; sodium perchlorate NaClO4 was used as the solute, and ethylene carbonate EC and dimethyl carbonate DMC with a volume ratio of 1:1 were used as the solvent, and the concentration was 1 mol L -1 The solution was prepared by adding 5 wt% of fluoroethylene carbonate (FEC) as an electrolyte; a 2032 button-type sodium ion half-cell was assembled and a charge and discharge test was performed, with a test voltage window of 0.01-2V.

[0058] See also Figure 11 The figure shows the sodium ion half-cell assembled based on NC / PCF electrode material in Comparative Example 1 at 100mA g -1 Cycling performance test results of NC / PCF||Na half-cell at 100mA g -1 The initial charge and discharge specific capacities were 90 and 151 mAh g -1 The initial coulombic efficiency is 59.6%; after 150 cycles, the capacity is 88 mAh g -1 The reversible capacity of NC / PCF electrode material is significantly lower than that of BP@NC / PCF electrode material. The main reason is that Na + In the NC / PCF composite material, only adsorption / intercalation reactions occur, and the initial Coulombic efficiency is also low, further reducing the capacity output during subsequent cycles. In contrast, the BP@NC / PCF electrode material has both intercalation-alloying and adsorption / intercalation reactions, providing a higher reversible capacity. However, it is worth noting that the NC / PCF composite material exhibits a lower capacity decay rate and excellent cycling stability due to its good electrical conductivity.

[0059] See also Figure 12 , This figure shows the rate performance test results of the sodium ion half-cell assembled based on the NC / PCF electrode material in Comparative Example 1. NC / PCF||Na at 0.1, 0.2, 0.4, 0.6, 0.8, 1.0 and 2.0 A g -1 The average capacities at 103, 95, 89, 85, 81, 75, and 68 mAh g -1 When the current density returns to 0.1 A g -1The reversible capacity is 94 mAh g -1 , the rate performance is significantly lower than that of the negative electrode material in Example 1.

[0060] The half-cell performance test results in Comparative Example 1 show that when the BP@NC / PCF composite material is used as the negative electrode material of the sodium ion battery, the active material black phosphorus based on the reversible embedding-alloying reaction can provide a higher reversible capacity for the electrode material, while the capacity provided by the porous carbon based on the adsorption / embedding reaction is limited.

[0061] Since the performance test results of the sodium ion half-cell assembled based on NC / PCF electrode material are inferior to those of BP@NC / PCF electrode material, performance testing of the full battery assembled based on BP@NC / PCF negative electrode material was not carried out.

[0062] Example 2

[0063] The preparation method of this embodiment is the same as that of embodiment 1, except that the current density during electrochemical deposition in step (1) is reduced to 7 mA cm -2 , other conditions remain unchanged. Compared with Example 1, the current density during electrochemical deposition in this embodiment is reduced, resulting in a decrease in the content of nickel hydroxide deposited in the carbon fiber cloth. This is not conducive to the formation of a hierarchical porous carbon network during high-temperature reduction and etching, and reduces the electrochemical performance of the BP@NC / PCF electrode material. In the half-cell test, the current density is 100mA g -1 When the initial charge and discharge specific capacities of the electrodes are 617 and 913 mAh g -1 The initial coulombic efficiency is about 67.5%; after 150 cycles, the reversible capacity is 523 mAh g -1 The capacity retention rate was 84.7%, which was significantly lower than the electrode material in Example 1. In addition, the electrochemical performance of the full battery was also reduced.

[0064] Example 3

[0065] The preparation method of this embodiment is the same as that of Example 1, except that the temperature of the high-temperature reduction and etching treatment in step (3) is reduced to 800°C, and other conditions remain unchanged. Compared with Example 1, the temperature of the high-temperature reduction and etching treatment in this embodiment is reduced, resulting in insufficient etching of the nitrogen-doped carbon-coated carbon fibers, and the inability to form a porous carbon network with a confined area, which limits the black phosphorus content in the NC / PCF composite material and leads to a decrease in the electrochemical performance of the BP@NC / PCF electrode material. In the half-cell test, the current density is 100mA g -1 When the initial charge and discharge specific capacities of the electrodes are 481 and 783 mAh g -1 The initial coulombic efficiency is about 61.4%; after 150 cycles, the reversible capacity is only 324 mAh g-1 The capacity retention rate was 67.3%, and the performance was obviously lower than that of the electrode material in Example 1. In addition, the electrochemical performance of the full battery was also reduced.

[0066] Example 4

[0067] The preparation method of this example is the same as that of Example 1, except that the solvothermal reaction in step (4) is performed using unpurified red phosphorus, and other conditions remain unchanged. Compared with Example 1, in this example, the BP@NC / PCF composite material prepared using unpurified red phosphorus not only contains residual red phosphorus, but also produces other impurities, which is not conducive to the performance of the BP@NC / PCF electrode material. In the half-cell test, when the current density is 100 mA g -1 , the initial charge and discharge specific capacity of the electrode is 354, 618 mAh g -1 , and the initial coulombic efficiency is about 57.2%; after 150 cycles, the reversible capacity is only 207 mAh g -1 , and the capacity retention rate is 58.4%, which is obviously lower than that of the electrode material in Example 1. In addition, the electrochemical performance of the full battery is also reduced.

[0068] The above is only an example and description of the concept of the present application. Those skilled in the art can make various modifications or supplements to the described specific examples or use similar ways to replace them, as long as they do not deviate from the concept of the present application or exceed the scope defined by the present claims, and they should belong to the protection scope of the present application.

Claims

1. A porous carbon fiber-supported black phosphorus / nitrogen-doped carbon composite material, characterized by: The composite material is used as a negative electrode material in sodium-ion batteries. Tiny rod-shaped black phosphorus nanoparticles are dispersed in a nitrogen-doped carbon-coated porous carbon fiber conductive framework to form a porous carbon fiber-supported black phosphorus / nitrogen-doped carbon (BP@NC / PCF) composite material. The areal loading of black phosphorus / nitrogen-doped carbon (BP@NC) in the composite material is 1.8-2.0 mg cm -2 , the mass ratio of black phosphorus in the composite material is 30~50%; The composite material is prepared by first using metal-assisted chemical etching technology to prepare a nitrogen-doped carbon-coated porous carbon fiber conductive framework, and then using solvent thermal and confined growth strategies to convert red phosphorus into black phosphorus and in situ confined growth in the pores of the nitrogen-doped carbon-coated porous carbon fiber framework to construct a porous carbon fiber-supported black phosphorus / nitrogen-doped carbon (BP@NC / PCF) composite material.

2. A method for preparing the porous carbon fiber-supported black phosphorus / nitrogen-doped carbon composite material according to claim 1, characterized in that: First, a nitrogen-doped carbon-coated porous carbon fiber conductive framework was prepared using metal-assisted chemical etching technology. Then, a solvent thermal and confined growth strategy was used to convert red phosphorus into black phosphorus and in situ confined growth was achieved in the pores of the nitrogen-doped carbon-coated porous carbon fiber framework to construct a porous carbon fiber-supported black phosphorus / nitrogen-doped carbon (BP@NC / PCF) composite material.

3. The preparation method according to claim 2, wherein: The specific steps are as follows: (1) Commercial carbon fiber cloth was ultrasonically cleaned with acetone, ethanol, and deionized water in sequence, and then dried. Nickel hydroxide was electrochemically deposited on the carbon fiber cloth using a three-electrode system with a platinum sheet as the counter electrode, the carbon fiber cloth as the working electrode, and Ag / AgCl as the reference electrode, and then dried for use. (2) Weigh a certain amount of polyacrylonitrile and polyvinylpyrrolidone and dissolve them in an appropriate amount of N, N-dimethylformamide solvent. Stir for a period of time to obtain a viscous solution. (3) The carbon fiber cloth with nickel hydroxide loaded on the surface obtained in step (1) is fully immersed in the above-mentioned viscous solution for 5 minutes, taken out and dried; then calcined at high temperature in an argon / hydrogen mixed atmosphere; finally, it is placed in a hydrochloric acid solution for pickling to remove nickel particles, washed and dried to obtain a nitrogen-doped carbon-coated porous carbon fiber (NC / PCF) composite material; (4) A certain amount of purified red phosphorus was dissolved in an appropriate amount of ethylenediamine solution, and then the nitrogen-doped carbon-coated porous carbon fiber composite material was fully immersed in this mixed solution, and then transferred to a high-pressure reactor for solvent thermal reaction; finally, the product was washed and dried to obtain a porous carbon fiber supported black phosphorus / nitrogen-doped carbon (BP@NC / PCF) composite material.

4. The preparation method according to claim 3, wherein: In step (1), during the electrochemical deposition of nickel hydroxide, 1 mol L -1 Nickel nitrate (Ni(NO3)2) and 0.1 mol L -1 The electrolyte is a mixed solution of sodium nitrate (NaNO3), with a volume ratio of 1:1 between nickel nitrate solution and sodium nitrate solution; the current density is 7-9 mA cm -2 , the deposition time is 10~30 min.

5. The preparation method according to claim 3, wherein: In step (2), the mass volume concentration of polyacrylonitrile in the viscous solution is 0.08 g mL -1 , the mass ratio of polyacrylonitrile and polyvinyl pyrrolidone is 1:1~3.

6. The preparation method according to claim 3, wherein: In step (3), the high temperature calcination temperature is 800-1000 ° C, the calcination time is 1-3 h, and the heating rate is 5-10 ° C min -1 .

7. The preparation method according to claim 3, wherein: In step (4), the specific steps for purifying red phosphorus are as follows: first, 3.0 g of commercial red phosphorus is weighed and dispersed in 80 mL of deionized water, and then hydrothermal purification is performed in a high-pressure reactor at a hydrothermal temperature of 200°C and a hydrothermal time of 12 h. Finally, the product is centrifuged, washed with ethanol, and dried to obtain purified red phosphorus.

8. The preparation method according to claim 3, wherein: In step (4), the solvent thermal reaction temperature is 180-200°C and the time is 10-12 h.

9. A use of the porous carbon fiber supported black phosphorus / nitrogen-doped carbon (BP@NC / PCF) composite material according to claim 1, characterized in that: The composite material is used as a negative electrode material in sodium ion batteries.

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