Preparation method and application of nickel-cobalt bimetallic phosphide for in-situ growth of nitrogen-doped carbon nanotubes

Abstract

The invention discloses a preparation method and application of nickel-cobalt bimetallic phosphide for in-situ growth of nitrogen-doped carbon nanotubes. The preparation method comprises the following steps: preparing a graphene oxide dispersion liquid; sequentially adding a cobalt source, a nickel source, a segmented copolymer, a phosphorus source and a nitrogen source into the graphene oxide dispersion liquid, and uniformly mixing to obtain a mixed solution; drying the mixed solution to obtain a precursor; and annealing the precursor in an inert atmosphere to obtain the product. According to the nitrogen-doped carbon material coated phosphide nano-particle composite material and the preparation method thereof, by regulating and controlling the ratio of Ni to Co, a carbon source grows on graphene in situ to form a carbon nano-tube, nickel-cobalt bimetal phosphide nano-particles are uniformly distributed on a nitrogen-doped carbon material to form the nitrogen-doped carbon material coated phosphide nano-particle composite material, and the nitrogen-doped carbon material coated phosphide nano-particle composite material is used as a modified diaphragm material of a lithium-sulfur battery. The preparation method disclosed by the invention has the advantages of mild reaction conditions and easiness in amplification and regulation, and the prepared composite material has a relatively high specific surface area and can be applied to the field of energy sources, especially the field of lithium-sulfur batteries.

Description

Technical Field

[0001] This invention relates to the field of functional materials technology, specifically to a method for preparing and applying nickel-cobalt bimetallic phosphides with in-situ grown nitrogen-doped carbon nanotubes. Background Technology

[0002] Lithium-sulfur (LSB) batteries are considered one of the most promising next-generation energy storage systems due to their high theoretical specific capacity and high energy density. However, the polysulfide shuttle effect and slow redox kinetics hinder the development of LSBs. Catalytic polysulfide conversion is an effective strategy to address these challenges. However, because polysulfide conversion involves complex multi-step phase transitions, single-function catalysts are difficult to effectively promote the entire redox process. Transition metal phosphides (TMPs) are highly attractive due to their unique metalloid physicochemical properties, high electrical conductivity, and good catalytic performance, and are widely used in electrocatalysis, energy storage, and photocatalysis. In recent years, combining transition metal phosphides with carbon-based materials doped with heteroatoms has been considered an effective strategy to improve catalytic performance. The synergistic effect of Ni / Co bimetals can modulate the electronic state of the material, thereby enhancing the catalytic ability of metal phosphides for polysulfide conversion.

[0003] Patent CN118308747A discloses a nickel-cobalt bimetallic / mesoporous graphene@nickel foam composite material, its preparation method, and its application. The prepared mesoporous graphene@nickel foam undergoes a hydrothermal reaction with a nitrogen source, a cobalt source, and a nickel source, followed by phosphating to obtain nickel-cobalt bimetallic phosphide / mesoporous graphene@nickel foam. This material preparation process is complex. Patent CN201810525236.5 discloses a hydrothermal method for growing seaweed-like NiCo salt compound precursors on nickel foam, followed by phosphating. This preparation process is also complex. Some methods utilize MOF or MXene materials as templates or supports for composites with this material, but these methods typically involve the pre-synthesis of MOF or MXene, increasing the complexity and cost of preparation. Existing methods require high-temperature treatment, and the product morphology is closely related to the preparation environment, such as gas type, gas flow rate, reaction temperature, and furnace pressure. Therefore, precise control of the reaction is difficult, the steps are relatively cumbersome, and the efficiency is low.

[0004] Therefore, developing a simple, controllable, and low-cost preparation method to achieve in-situ growth of nitrogen-doped carbon nanotubes on nickel-cobalt bimetallic phosphides is of great significance for improving the catalytic performance of the material and the electrochemical performance of lithium-sulfur batteries. Summary of the Invention

[0005] To address the problems existing in the background technology, this invention provides a method for preparing and applying nickel-cobalt bimetallic phosphides with in-situ grown nitrogen-doped carbon nanotubes. This invention achieves in-situ growth of carbon nanotubes on graphene by controlling the ratio of Ni to Co, resulting in the uniform distribution of nickel-cobalt bimetallic phosphide nanoparticles on the nitrogen-doped carbon material, forming a nitrogen-doped carbon material-coated phosphide nanoparticle composite material. This composite material is then used as a modified separator material for lithium-sulfur batteries. The preparation method of this invention has the advantages of mild reaction conditions, ease of scale-up and control, and the prepared composite material has a high specific surface area, enabling its application in the energy field, especially in lithium-sulfur batteries.

[0006] This invention is implemented through the following technical solutions: A method for preparing nickel-cobalt bimetallic phosphide with in-situ grown nitrogen-doped carbon nanotubes includes the following steps: (1) Graphene oxide is dispersed in water and ultrasonically treated to obtain a graphene oxide dispersion. (2) Under stirring conditions, cobalt source, nickel source, block copolymer, phosphorus source and nitrogen source are added sequentially to the graphene oxide dispersion and mixed evenly to obtain a mixed solution; (3) The mixed solution is dried to obtain the precursor; (4) The precursor is annealed in an inert atmosphere to obtain a nickel-cobalt bimetallic phosphide with in-situ grown nitrogen-doped carbon nanotubes.

[0007] Further, in step (1), the concentration of the graphene oxide dispersion is 0.1-2 g / L.

[0008] Further, in step (2), the cobalt source is selected from one or more of cobalt acetate, cobalt nitrate, cobalt chloride, and cobalt sulfate; the nickel source is selected from one or more of nickel acetate, nickel nitrate, nickel chloride, and nickel sulfate. In the cobalt source and the nickel source, the molar ratio of cobalt to nickel is (1-2):(1-2).

[0009] Further, in step (2), the block copolymer is Pluronic P123 or Pluronic F127; the phosphorus source is ammonium dihydrogen phosphate, diammonium hydrogen phosphate or sodium hypophosphite; and the nitrogen source is dicyandiamide or cyanamide.

[0010] Furthermore, in step (2), based on the mass of graphene oxide, the amount of cobalt source is 50-150 times, the amount of nickel source is 50-150 times, the amount of block copolymer is 200-400 times, the amount of phosphorus source is 10-30 times, and the amount of nitrogen source is 400-600 times.

[0011] Furthermore, in step (3), the drying temperature of the mixed solution is 50-70℃.

[0012] Further, in step (4), the inert gas is nitrogen or argon; the annealing temperature is 800-1000℃, the annealing time is 1-2 hours, and the heating rate is 3-10℃ / min.

[0013] The present invention also discloses nickel-cobalt bimetallic phosphide prepared by the above method for in-situ growth of nitrogen-doped carbon nanotubes, wherein the nickel-cobalt bimetallic phosphide nanoparticles are coated in the in-situ grown nitrogen-doped carbon nanotubes, and the particle size of the nanoparticles is 30-60 nm.

[0014] The present invention also discloses the application of the in-situ grown nitrogen-doped carbon nanotube nickel-cobalt bimetallic phosphide as a lithium-sulfur battery separator modification material.

[0015] Furthermore, the application specifically involves mixing the in-situ grown nitrogen-doped carbon nanotubes with the nickel-cobalt bimetallic phosphide, carbon nanotubes, and polyvinylidene fluoride in N-methylpyrrolidone at a mass ratio of (6-8):(1-3):1 to form a slurry, coating it onto a polypropylene diaphragm, and then vacuum drying to obtain a modified diaphragm.

[0016] The beneficial effects of this invention are: 1. This invention achieves in-situ growth of carbon nanotubes on graphene by controlling the ratio of cobalt and nickel sources, forming a unique composite material structure. The prepared composite material has a high specific surface area, uniform distribution of nickel-cobalt bimetallic phosphide nanoparticles, and excellent catalytic performance. When used as a lithium-sulfur battery separator modification material, it exhibits excellent electrochemical performance and shows good prospects for practical application.

[0017] 2. This invention employs a one-step solution method combined with high-temperature annealing, avoiding the cumbersome steps of multiple reactions and transfers in traditional methods. The reaction conditions are mild, facilitating large-scale production. The method of this invention allows for controllable reaction conditions and easy adjustment of component ratios to optimize material performance. The prepared composite material shows promising practical application prospects in the field of lithium-sulfur batteries. Attached Figure Description

[0018] The accompanying drawings are provided to further explain the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 Cycling performance curves of the materials prepared in Example 1, Comparative Example 1, and Comparative Example 2 at a current density of 1C; Figure 2 Rate performance curves of the materials prepared in Example 1, Comparative Example 1, and Comparative Example 2; Figure 3 SEM images, TEM images, and elemental mapping spectra of the material prepared in Example 1; Figure 4 XRD spectra of the materials prepared in Example 1, Comparative Example 1, and Comparative Example 2; Figure 5 SEM images of the materials prepared for Comparative Example 1 and Comparative Example 2. Detailed Implementation

[0019] The technical solution of the present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0020] Example 1: This embodiment prepares in-situ grown nitrogen-doped carbon nanotubes into nickel-cobalt bimetallic phosphide, and the specific steps are as follows: (1) Add 15 mg of graphene oxide to 50 ml of water and sonicate for 2 hours; (2) Under stirring, 1 gram of Co(CH3COO)2·4H2O, 1 gram of Ni(CH3COO)2·4H2O, 4 grams of P123, 0.25 grams of NH4H2PO4, and 8 grams of dicyandiamide solution (50wt%) were dissolved into the above solution; (3) The blue precursor can be obtained by drying the mixture at 60°C; (4) The precursor is annealed at 900°C in a nitrogen atmosphere and held for 1 hour at a heating rate of 5°C / min to obtain in-situ grown nitrogen-doped carbon nanotubes nickel-cobalt bimetallic phosphide.

[0021] The application of the nickel-cobalt bimetallic phosphide with in-situ grown nitrogen-doped carbon nanotubes prepared above in lithium-sulfur batteries includes the following steps: (5) The nickel-cobalt bimetallic phosphide of in-situ grown nitrogen-doped carbon nanotubes obtained above is mixed with CNT and PVDF in NMP at a mass ratio of 7:2:1. The mixture is stirred vigorously to form a uniform slurry, which is then coated onto Celgard 2500 polypropylene (PP) membrane. After vacuum drying, it is cut into round slices with a diameter of about 19 mm. (6) The sulfur cathode material (CNT / S) was mixed with Super P and PVDF in NMP at a weight ratio of 8:1:1. The mixture was stirred to obtain a uniform slurry, which was then coated onto aluminum foil and vacuum dried overnight. The slurry was cut into 12 mm diameter discs to form the sulfur electrode. Lithium metal and the modified separator described above were used as the anode and separator, respectively. The battery was assembled in an argon-protected glove box with water and oxygen contents both below 1 ppm, using 1.0 M LiTFSI in DOL and DME (v / v=1:1) and 1 wt% LiNO3 additive as the electrolyte. (7) The assembled battery uses the LAND CT2001A system (China) in different groups (1C=1675mA g) -1Constant current discharge / charge measurements were performed under these conditions, with a voltage window of 1.7-2.8V.

[0022] Performance test results: from Figure 3 SEM images ( Figure 3 ac) and TEM images ( Figure 3 As can be seen from the df (database diagram), the nanoparticles are encapsulated within in-situ grown carbon nanotubes, and the size of the nanoparticles is approximately 40-50 nm. From the elemental mapping spectrum (database diagram),... Figure 3 As can be seen from the gm, C, N, Ni, Co, and P elements are uniformly distributed, proving that nickel-cobalt bimetallic phosphide nanoparticles are uniformly dispersed on nitrogen-doped carbon nanotubes.

[0023] from Figure 4 The XRD spectrum shows that the diffraction peaks of NiCoP are consistent with those of the standard PDF 71-2336 card, indicating that the nickel-cobalt bimetallic phosphide was successfully prepared.

[0024] Electrochemical performance: such as Figure 1 As shown, the initial specific capacity of the NiCoP modified separator at 1C rate is 1007 mAh g. -1 It can still provide 420mAh g after 1000 cycles. -1 With a specific capacity, the coulombic efficiency remains at approximately 100%. For example... Figure 2 As shown, NiCoP exhibits excellent rate performance at different rates from 0.1C to 5C, and can still provide 277mAh g at a high rate of 5C. -1 The specific capacity of the NiCoP modified separator is shown in the results. These results indicate that the NiCoP modified separator exhibits excellent cycle stability and rate performance in lithium-sulfur batteries.

[0025] Example 2: The difference between this embodiment and Embodiment 1 is that in step (2), cobalt acetate is replaced with cobalt nitrate, and nickel acetate is replaced with nickel nitrate. 1g of cobalt nitrate and 1g of nickel nitrate are used for preparation. The other steps are the same as in Embodiment 1.

[0026] Example 3: The difference between this embodiment and Embodiment 1 is that in step (2), Pluronic P123 is replaced with Pluronic F127 of the same quality. The other steps are the same as in Embodiment 1.

[0027] Example 4: The difference between this embodiment and Embodiment 1 is that in step (2), dicyandiamide is replaced with 8g of monocyandiamide. The other steps are the same as in Embodiment 1.

[0028] Example 5: The difference between this embodiment and Embodiment 1 is that the heat treatment temperature in step (4) is set to 800°C and the holding time is 2 hours. The other steps are the same as in Embodiment 1.

[0029] Comparative Example 1: The difference between this comparative example and Example 1 is that the weight ratio of cobalt acetate and nickel acetate in step (2) is replaced by 0:2 instead of 1:1. The other steps are the same as in Example 1.

[0030] Performance test results: from Figure 5 The SEM images from ab show that Ni2P nanoparticles are encapsulated within graphene oxide in the Ni2P material. From... Figure 4 The XRD spectrum shows that the diffraction peaks of Ni2P are consistent with those of the standard PDF 03-0953 card, indicating that nickel phosphide was successfully prepared.

[0031] Electrochemical performance: Initial specific capacity at 1C rate is only 393 mAh g. -1 After 1000 cycles, the specific capacity is 365 mAh g. -1 ( Figure 1 The specific capacity at 5C rate is only 35mAh g. -1 ( Figure 2 ).

[0032] Comparative Example 2: The difference between this comparative example and Example 1 is that the weight ratio of cobalt acetate and nickel acetate in step (2) is changed from 1:1 to 2:0. The other steps are the same as in Example 1.

[0033] Performance test results: From Figure 5 The SEM images of the CD show that Co2P nanoparticles are encapsulated within in-situ grown carbon nanotubes in the Co2P material. From... Figure 4 The XRD spectrum shows that the diffraction peaks of Co2P are consistent with those of the standard PDF 32-0306 card, indicating that cobalt phosphide was successfully prepared.

[0034] Electrochemical performance: Initial specific capacity at 1C rate is 560 mAh g. -1 After 1000 cycles, the specific capacity is 312 mAh g. -1 ( Figure 1 The specific capacity at 5C rate is 144 mAh g. -1 ( Figure 2 ).

[0035] The electrochemical performance test results of Examples 1-5 and Comparative Examples 1-2 are shown in Table 1: Table 1. Electrochemical performance test results of the examples and comparative examples. As can be seen from the data in Table 1, the nickel-cobalt bimetallic phosphide materials prepared in Examples 1-5 all exhibit excellent electrochemical performance, with specific capacities ranging from 381 to 420 mAh g after 1000 cycles at 1C rate. -1 Within this range, the specific capacity at 5C rate is consistently between 237-277 mAh g. -1 Within the specified range, it is significantly superior to Comparative Example 1 and Comparative Example 2. This indicates that the synergistic effect of nickel-cobalt bimetal and the in-situ grown nitrogen-doped carbon nanotube structure play an important role in improving the catalytic and electrochemical performance of the material.

[0036] The results of Comparative Examples 1 and 2 show that a single metal phosphide (Ni2P) cannot achieve in-situ growth of carbon nanotubes, and the electrochemical performance is significantly poor, especially at high magnification.

[0037] The preparation method provided by this invention is simple, mild, and easy to control. The in-situ grown nitrogen-doped carbon nanotube nickel-cobalt bimetallic phosphide has a unique structure and excellent electrochemical performance, and has good application prospects in the field of lithium-sulfur batteries.

[0038] Finally, it should be noted that the above embodiments are merely illustrative of several implementations of the present invention and are not intended to limit the scope of the invention. For those skilled in the art, any modifications, equivalent substitutions, or improvements made without departing from the concept of the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing nickel-cobalt bimetallic phosphide with in-situ grown nitrogen-doped carbon nanotubes, characterized in that, Includes the following steps: (1) Graphene oxide is dispersed in water and ultrasonically treated to obtain a graphene oxide dispersion. (2) Under stirring conditions, cobalt source, nickel source, block copolymer, phosphorus source and nitrogen source are added sequentially to the graphene oxide dispersion and mixed evenly to obtain a mixed solution; (3) The mixed solution is dried to obtain the precursor; (4) The precursor is annealed in an inert atmosphere to obtain a nickel-cobalt bimetallic phosphide with in-situ grown nitrogen-doped carbon nanotubes.

2. The preparation method according to claim 1, characterized in that, In step (1), the concentration of the graphene oxide dispersion is 0.1-2 g / L.

3. The preparation method according to claim 1, characterized in that, In step (2), the cobalt source is selected from one or more of cobalt acetate, cobalt nitrate, cobalt chloride, and cobalt sulfate; the nickel source is selected from one or more of nickel acetate, nickel nitrate, nickel chloride, and nickel sulfate. In the cobalt source and the nickel source, the molar ratio of cobalt to nickel is (1-2):(1-2).

4. The preparation method according to claim 1, characterized in that, In step (2), the block copolymer is Pluronic P123 or Pluronic F127; the phosphorus source is ammonium dihydrogen phosphate, diammonium hydrogen phosphate or sodium hypophosphite; and the nitrogen source is dicyandiamide or cyanamide.

5. The preparation method according to claim 1, characterized in that, In step (2), based on the mass of graphene oxide, the amount of cobalt source is 50-150 times, the amount of nickel source is 50-150 times, the amount of block copolymer is 200-400 times, the amount of phosphorus source is 10-30 times, and the amount of nitrogen source is 400-600 times.

6. The preparation method according to claim 1, characterized in that, In step (3), the drying temperature of the mixed solution is 50-70℃.

7. The preparation method according to claim 1, characterized in that, In step (4), the inert gas is nitrogen or argon; the annealing temperature is 800-1000℃, the annealing time is 1-2 hours, and the heating rate is 3-10℃ / min.

8. A nickel-cobalt bimetallic phosphide with in-situ grown nitrogen-doped carbon nanotubes prepared by the method according to any one of claims 1-7, characterized in that, Nickel-cobalt bimetallic phosphide nanoparticles are coated in in-situ grown nitrogen-doped carbon nanotubes, with a particle size of 30-60 nm.

9. The application of the nickel-cobalt bimetallic phosphide with in-situ grown nitrogen-doped carbon nanotubes as described in claim 8 as a material for modifying lithium-sulfur battery separators.

10. The application according to claim 9, characterized in that, The specific application is as follows: the nickel-cobalt bimetallic phosphide of in-situ grown nitrogen-doped carbon nanotubes is mixed with carbon nanotubes and polyvinylidene fluoride in N-methylpyrrolidone at a mass ratio of (6-8):(1-3):1 to form a slurry, which is then coated on a polypropylene diaphragm and vacuum dried to obtain a modified diaphragm.

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