A nitrogen-phosphorus co-doped hollow carbon microsphere and its preparation method and application

Abstract

The present invention discloses a nitrogen-phosphorus co-doped hollow carbon microsphere, a preparation method thereof, and an application thereof. The preparation method of the nitrogen-phosphorus co-doped hollow carbon microsphere of the present invention comprises the following steps: 1) preparing carboxylated polystyrene microspheres; 2) preparing ZIF-8-coated carboxylated polystyrene microspheres; 3) preparing nitrogen-doped hollow carbon microspheres; 4) preparing phosphoric acid-modified nitrogen-doped hollow carbon microspheres; 5) sintering the phosphoric acid-modified nitrogen-doped hollow carbon microspheres. The nitrogen-phosphorus co-doped hollow carbon microspheres of the present invention can well adapt to the volume expansion of sulfur and provide adsorption sites for polysulfides and can promote the rapid conversion of polysulfides. The preparation method thereof is simple and the production cost is low. The room temperature sodium-sulfur battery assembled after the nitrogen-phosphorus co-doped hollow carbon microspheres are composited with sublimated sulfur to prepare a positive electrode material has excellent cycle stability and rate performance, and is suitable for large-scale industrial production and application.

Description

Technical Field

[0001] The present invention relates to the technical field of room-temperature sodium-sulfur batteries, and in particular to a nitrogen-phosphorus co-doped hollow carbon material and a preparation method and application thereof. Background Art

[0002] Room-temperature sodium-sulfur batteries (NSBs) have demonstrated tremendous potential for development due to their high energy density, low cost, abundant raw material reserves, and environmentally friendly raw materials. They have become a highly anticipated chemical energy storage device in recent years. However, due to the insulating and low reactivity of sulfur, the "shuttle effect" of polysulfides, and the significant volume expansion, room-temperature NSBs have significant shortcomings in cycle performance, rate capability, and Coulombic efficiency, significantly limiting their practical application.

[0003] Therefore, it is of great significance to develop a positive electrode carrier material that can effectively solve the "shuttle effect", adapt to the volume expansion of sulfur, and has high conductivity. Summary of the Invention

[0004] The purpose of the present invention is to provide a nitrogen-phosphorus co-doped hollow carbon microsphere and a preparation method and application thereof.

[0005] The technical solution adopted by the present invention is:

[0006] A method for preparing nitrogen and phosphorus co-doped hollow carbon microspheres comprises the following steps:

[0007] 1) dispersing styrene, methyl methacrylate and acrylic acid in a solvent for copolymerization to obtain carboxylated polystyrene microspheres;

[0008] 2) dispersing carboxylated polystyrene microspheres, a soluble zinc salt, and 2-methylimidazole in a solvent for reaction to obtain ZIF-8-coated carboxylated polystyrene microspheres;

[0009] 3) sintering the ZIF-8-coated carboxylated polystyrene microspheres in a protective atmosphere to obtain nitrogen-doped hollow carbon microspheres;

[0010] 4) soaking the nitrogen-doped hollow carbon microspheres in a phosphoric acid solution to obtain phosphoric acid-modified nitrogen-doped hollow carbon microspheres;

[0011] 5) The phosphoric acid-modified nitrogen-doped hollow carbon microspheres are placed in a protective atmosphere for sintering to obtain nitrogen-phosphorus co-doped hollow carbon microspheres.

[0012] Preferably, in step 1), the volume ratio of styrene, methyl methacrylate and acrylic acid is 20-40:0.5-2:1.

[0013] Preferably, the solvent in step 1) is water.

[0014] Preferably, the reaction raw materials in step 1) further include a buffer and an initiator.

[0015] Preferably, the buffer is ammonium bicarbonate.

[0016] Preferably, the initiator is ammonium persulfate.

[0017] Preferably, the copolymerization reaction in step 1) is carried out at a temperature of 70° C. to 90° C., and the reaction time is 10 h to 15 h.

[0018] Preferably, in step 2), the weight ratio of the carboxylated polystyrene microspheres to 2-methylimidazole is 1:5-20.

[0019] Preferably, in step 2), the molar ratio of the soluble zinc salt to 2-methylimidazole is 1:1-5.

[0020] Preferably, the soluble zinc salt in step 2) is at least one of zinc nitrate, zinc sulfate and zinc chloride.

[0021] Preferably, the solvent in step 2) is methanol.

[0022] Preferably, the protective atmosphere in step 3) is a nitrogen atmosphere or an argon atmosphere.

[0023] Preferably, the specific operation of the sintering in step 3) is as follows: heating from room temperature (25°C±5°C) to 800°C-1000°C at a heating rate of 3°C / min-5°C / min, and then keeping the temperature for 1h-3h.

[0024] Preferably, the weight ratio of the solute to the solvent in the phosphoric acid solution in step 4) is 1:20 to 35.

[0025] Preferably, the solvent in the phosphoric acid solution in step 4) is methanol.

[0026] Preferably, the protective atmosphere in step 5) is a nitrogen atmosphere or an argon atmosphere.

[0027] Preferably, the specific operation of the sintering in step 5) is as follows: heating from room temperature (25°C±5°C) to 400°C-800°C at a heating rate of 8°C / min-10°C / min, and then keeping the temperature for 1h-3h.

[0028] A nitrogen and phosphorus co-doped hollow carbon microsphere is prepared by the above preparation method.

[0029] A positive electrode material comprises sublimated sulfur and the above-mentioned nitrogen and phosphorus co-doped hollow carbon microspheres.

[0030] Preferably, the weight ratio of the sublimated sulfur and nitrogen and phosphorus co-doped hollow carbon microspheres is 1:0.80-1.25.

[0031] A method for preparing the positive electrode material as described above comprises the following steps:

[0032] The sublimated sulfur and nitrogen and phosphorus co-doped hollow carbon microspheres are dispersed in a volatile organic solvent, and then ground until the volatile organic solvent is completely volatilized. The microspheres are then kept at 150°C to 160°C for 10 hours to 12 hours, naturally cooled to room temperature, and then placed in a protective atmosphere at 200°C to 300°C for 20 minutes to 30 minutes to obtain the positive electrode material.

[0033] Preferably, the volatile organic solvent is carbon disulfide.

[0034] Preferably, the protective atmosphere is a nitrogen atmosphere or an argon atmosphere.

[0035] A room temperature sodium-sulfur battery comprises the above-mentioned positive electrode material.

[0036] The beneficial effects of the present invention are as follows: the nitrogen-phosphorus co-doped hollow carbon microspheres of the present invention can well adapt to the volume expansion of sulfur, provide adsorption sites for polysulfides, and promote the rapid conversion of polysulfides. The preparation method is simple and the production cost is low. After the microspheres are combined with sublimated sulfur to prepare a positive electrode material and then assembled into a room-temperature sodium-sulfur battery, they have excellent cycle stability and rate performance, and are suitable for large-scale industrial production and application.

[0037] Specifically:

[0038] 1) The hollow structure of the nitrogen-phosphorus co-doped hollow carbon microspheres of the present invention is conducive to the loading of sulfur and can provide sufficient buffer space to accommodate the volume expansion of sulfur;

[0039] 2) The nitrogen-phosphorus co-doped carbon shell in the nitrogen-phosphorus co-doped hollow carbon microspheres of the present invention can provide active sites for the adsorption and conversion of polysulfides;

[0040] 3) The preparation method of the nitrogen and phosphorus co-doped hollow carbon microspheres of the present invention is simple, has low production cost, and is suitable for large-scale industrial production and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 TEM and SEM images of nitrogen and phosphorus co-doped hollow carbon microspheres in Example 1.

[0042] Figure 2 This is the nitrogen adsorption-desorption isotherm curve of the nitrogen and phosphorus co-doped hollow carbon microspheres in Example 1.

[0043] Figure 3 This is the TGA curve of the positive electrode material in Example 1.

[0044] Figure 4 This is a graph showing the electrochemical performance test results of the CR2032 button battery in Example 1.

[0045] Figure 5 This is the SEM image of nitrogen and phosphorus co-doped hollow carbon microspheres in Example 2.

[0046] Figure 6 This is a graph showing the electrochemical performance test results of the CR2032 button battery in Example 2.

[0047] Figure 7 This is the SEM image of nitrogen and phosphorus co-doped hollow carbon microspheres in Example 3.

[0048] Figure 8 This is a graph showing the electrochemical performance test results of the CR2032 button battery in Example 3.

[0049] Figure 9 This is the SEM image of the nitrogen-doped hollow carbon microspheres in the comparative example.

[0050] Figure 10 This is a graph showing the electrochemical performance test results of the CR2032 button battery in the comparative example. DETAILED DESCRIPTION

[0051] The present invention will be further explained and illustrated below with reference to specific embodiments.

[0052] Example 1:

[0053] A nitrogen and phosphorus co-doped hollow carbon microsphere, the preparation method of which is as follows:

[0054] 1) 21 mL of styrene, 1.1 mL of methyl methacrylate, 0.92 mL of acrylic acid, and 0.49 g of ammonium bicarbonate were dispersed in 100 mL of ultrapure water, the temperature was raised to 70°C, 0.53 g of ammonium persulfate was added, the temperature was raised to 80°C, and the mixture was stirred at this temperature for 12 h. The mixture was centrifuged, the solid was washed with water, and then freeze-dried to obtain carboxylated polystyrene microspheres (denoted as PS);

[0055] 2) 0.3 g of carboxylated polystyrene microspheres and 3.284 g of 2-methylimidazole were added to 100 mL of methanol and ultrasonically dispersed for 30 min. 1.487 g of zinc nitrate, pre-dissolved in 100 mL of methanol, was then added dropwise. Stirring was continued for 16 h after the addition was complete, and the solid was collected by centrifugation to obtain ZIF-8-coated carboxylated polystyrene microspheres (denoted as PS@ZIF-8).

[0056] 3) The ZIF-8-coated carboxylated polystyrene microspheres were placed in a tube furnace and filled with argon for protection. The temperature was then increased from room temperature to 910°C at a heating rate of 5°C / min, then kept at this temperature for 2 hours, and cooled to room temperature in the furnace to obtain nitrogen-doped hollow carbon microspheres (denoted as NHC);

[0057] 4) 1.0 g of nitrogen-doped hollow carbon microspheres were added to a phosphoric acid solution consisting of 0.8 g of phosphoric acid and 20 mL of methanol, stirred at room temperature for 24 h, and then heated to 80°C and stirred continuously until the solvent was completely evaporated to obtain phosphoric acid-modified nitrogen-doped hollow carbon microspheres (denoted as H3PO4@NHC);

[0058] 5) The phosphoric acid-modified nitrogen-doped hollow carbon microspheres were placed in a tubular furnace and filled with argon for protection. The temperature was then increased from room temperature to 600°C at a heating rate of 10°C / min, and then kept at this temperature for 2 h. The furnace was cooled to room temperature to obtain nitrogen-phosphorus co-doped hollow carbon microspheres (denoted as P-NHC-600).

[0059] Performance testing:

[0060] 1) The transmission electron microscope (TEM) and scanning electron microscope (SEM) images of the nitrogen and phosphorus co-doped hollow carbon microspheres (P-NHC-600) in this embodiment are as follows: Figure 1 (a, b and c are TEM images at different magnifications, d, e and f are SEM images at different magnifications).

[0061] Depend on Figure 1 It can be seen that the nitrogen and phosphorus co-doped hollow carbon microspheres in this embodiment have a hollow structure, which is conducive to the loading of sulfur and adapting to the volume expansion of sulfur.

[0062] 2) The nitrogen adsorption-desorption isotherm of the nitrogen-phosphorus co-doped hollow carbon microspheres (P-NHC-600) in this embodiment is shown in FIG. Figure 2 (a is the adsorption amount-relative pressure relationship curve, b is the pore volume-pore width relationship curve).

[0063] Depend on Figure 2 It can be seen that the micropores and mesopores coexist in the nitrogen and phosphorus co-doped hollow carbon microspheres in this embodiment, which can provide space for the accommodation of sulfur.

[0064] A positive electrode material, the preparation method of which is as follows:

[0065] 1.1 g of sublimed sulfur and 0.9 g of the above-mentioned nitrogen and phosphorus co-doped hollow carbon microspheres (P-NHC-600) were stirred and dispersed in 15 mL of carbon disulfide, and then ground until the carbon disulfide was completely volatilized. The temperature was then raised to 155°C and kept warm for 12 hours. The mixture was naturally cooled to room temperature and placed in a tubular furnace, filled with argon for protection, and kept warm at 200°C for 25 minutes to obtain the positive electrode material.

[0066] Performance testing:

[0067] The thermal gravimetric analysis (TGA) curve of the positive electrode material in this embodiment is shown in FIG. Figure 3 shown.

[0068] Depend on Figure 3It can be seen that the sulfur content of the positive electrode material in this embodiment is 49 wt %.

[0069] A room temperature sodium-sulfur battery, the preparation method of which is as follows:

[0070] The room-temperature sodium-sulfur battery positive electrode material was made into a positive electrode sheet, metallic sodium was made into a negative electrode sheet, and a 1.0 mol / L sodium perchlorate solution of ethylene carbonate-diethyl carbonate (the volume ratio of ethylene carbonate and diethyl carbonate was 1:1) was used as the electrolyte. CR2032 button batteries were assembled in an argon-filled glove box.

[0071] Performance testing:

[0072] The electrochemical performance test results of the CR2032 button battery in this embodiment are as follows: Figure 4 shown.

[0073] Depend on Figure 4 It can be seen that the CR2032 button battery in this embodiment has excellent rate performance, and the discharge specific capacity is as high as 527.5 mAh / g even at a discharge rate of 3C.

[0074] Example 2:

[0075] A nitrogen and phosphorus co-doped hollow carbon microsphere, the preparation method of which is as follows:

[0076] The phosphoric acid-modified nitrogen-doped hollow carbon microspheres (same as in Example 1) were placed in a tubular furnace and filled with argon for protection. The temperature was then increased from room temperature to 400°C at a heating rate of 10°C / min, and then kept at this temperature for 2 h. The mixture was then cooled to room temperature with the furnace to obtain nitrogen-phosphorus co-doped hollow carbon microspheres (denoted as P-NHC-400).

[0077] Performance testing:

[0078] 1) The SEM image of nitrogen and phosphorus co-doped hollow carbon microspheres (P-NHC-400) in this embodiment is as follows Figure 5 (a, b and c represent different magnifications).

[0079] Depend on Figure 5 It can be seen that the nitrogen and phosphorus co-doped hollow carbon microspheres in this embodiment have a hollow spherical structure, which is conducive to the loading of sulfur and adapting to the volume expansion of sulfur.

[0080] 2) Prepare CR2032 button cell according to Example 1, and then conduct electrochemical performance test. The test results are as follows: Figure 6 shown.

[0081] Depend on Figure 6 It can be seen that the CR2032 button battery in this embodiment has excellent rate performance, and the discharge specific capacity is as high as 496.5 mAh / g even at a discharge rate of 3C.

[0082] Example 3:

[0083] A nitrogen and phosphorus co-doped hollow carbon microsphere, the preparation method of which is as follows:

[0084] The phosphoric acid-modified nitrogen-doped hollow carbon microspheres (same as in Example 1) were placed in a tube furnace and filled with argon for protection. The temperature was then increased from room temperature to 800°C at a heating rate of 10°C / min, and then kept at this temperature for 2 h. The mixture was then cooled to room temperature with the furnace to obtain nitrogen-phosphorus co-doped hollow carbon microspheres (denoted as P-NHC-800).

[0085] Performance testing:

[0086] 1) The SEM image of nitrogen and phosphorus co-doped hollow carbon microspheres (P-NHC-800) in this embodiment is as follows Figure 7 (a, b and c represent different magnifications).

[0087] Depend on Figure 7 It can be seen that the nitrogen and phosphorus co-doped hollow carbon microspheres in this embodiment have a hollow spherical structure, which is conducive to the loading of sulfur and adapting to the volume expansion of sulfur.

[0088] 2) Prepare CR2032 button cell according to Example 1, and then conduct electrochemical performance test. The test results are as follows: Figure 8 shown.

[0089] Depend on Figure 8 It can be seen that the CR2032 button battery in this embodiment has excellent rate performance, and the discharge specific capacity is as high as 436.8 mAh / g even at a discharge rate of 3C.

[0090] Comparative Example:

[0091] Nitrogen-doped hollow carbon microspheres (denoted as NHC; same as Example 1).

[0092] Performance testing:

[0093] 1) The SEM image of nitrogen-doped hollow carbon microspheres (NHC) in this comparative example is as follows Figure 9 (a, b and c represent different magnifications).

[0094] Depend on Figure 9 It can be seen that the nitrogen-doped hollow carbon microspheres in this comparative example have a hollow spherical structure, which is conducive to the loading of sulfur and adapting to the volume expansion of sulfur.

[0095] 2) Prepare CR2032 button cell according to Example 1, and then conduct electrochemical performance test. The test results are as follows: Figure 10 shown.

[0096] Depend on Figure 10It can be seen that the rate performance of the CR2032 button battery in this comparative example is poor, and the discharge specific capacity is only 327.5 mAh / g at a discharge rate of 3C.

[0097] From Examples 1 to 3 and the comparative example, it can be seen that by further introducing phosphorus on the basis of nitrogen-doped hollow carbon microspheres and co-doping nitrogen and phosphorus, the electrochemical performance of the assembled CR2032 button battery can be significantly improved.

[0098] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing nitrogen and phosphorus co-doped hollow carbon microspheres, characterized in that: The following steps are involved: 1) dispersing styrene, methyl methacrylate and acrylic acid in a solvent for copolymerization to obtain carboxylated polystyrene microspheres; 2) dispersing carboxylated polystyrene microspheres, a soluble zinc salt, and 2-methylimidazole in a solvent for reaction to obtain ZIF-8-coated carboxylated polystyrene microspheres; 3) sintering the ZIF-8-coated carboxylated polystyrene microspheres in a protective atmosphere to obtain nitrogen-doped hollow carbon microspheres; 4) soaking the nitrogen-doped hollow carbon microspheres in a phosphoric acid solution to obtain phosphoric acid-modified nitrogen-doped hollow carbon microspheres; 5) The phosphoric acid-modified nitrogen-doped hollow carbon microspheres are placed in a protective atmosphere for sintering to obtain nitrogen-phosphorus co-doped hollow carbon microspheres.

2. The preparation method according to claim 1, wherein: The volume ratio of styrene, methyl methacrylate and acrylic acid in step 1) is 20-40:0.5-2:1; the copolymerization reaction in step 1) is carried out at a temperature of 70° C. to 90° C. and the reaction time is 10 h to 15 h.

3. The preparation method according to claim 1 or 2, characterized in that: The weight ratio of the carboxylated polystyrene microspheres to 2-methylimidazole in step 2) is 1:5-20; the molar ratio of the soluble zinc salt to 2-methylimidazole in step 2) is 1:1-5.

4. The preparation method according to claim 1 or 2, characterized in that: Step 3) The specific operation of the sintering is as follows: heating from room temperature to 800° C. to 1000° C. at a heating rate of 3° C. / min to 5° C. / min, and then keeping the temperature for 1 hour to 3 hours.

5. The preparation method according to claim 1 or 2, characterized in that: Step 5) The specific operation of the sintering is as follows: heating from room temperature to 400° C. to 800° C. at a heating rate of 8° C. / min to 10° C. / min, and then keeping the temperature for 1 hour to 3 hours.

6. A nitrogen-phosphorus co-doped hollow carbon microsphere, characterized in that: Prepared by the preparation method according to any one of claims 1 to 5.

7. A positive electrode material, characterized in that The hollow carbon microspheres comprise sublimed sulfur and the nitrogen and phosphorus co-doped hollow carbon microspheres according to claim 6.

8. The positive electrode material according to claim 7, characterized in that: The weight ratio of the sublimated sulfur and nitrogen and phosphorus co-doped hollow carbon microspheres is 1:0.80-1.

25.

9. A method for preparing a positive electrode material according to claim 7 or 8, characterized in that: The following steps are involved: The sublimated sulfur and nitrogen and phosphorus co-doped hollow carbon microspheres are dispersed in a volatile organic solvent, and then ground until the volatile organic solvent is completely volatilized. The microspheres are then kept at 150°C to 160°C for 10 hours to 12 hours, naturally cooled to room temperature, and then placed in a protective atmosphere at 200°C to 300°C for 20 minutes to 30 minutes to obtain the positive electrode material.

10. A room temperature sodium-sulfur battery, characterized in that: Contains the positive electrode material according to claim 7 or 8.

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