Nitrogen and phosphorus co-doped hollow cubic carbon material as well as preparation method and application thereof

Abstract

The invention discloses a nitrogen-phosphorus co-doped hollow cubic carbon material as well as a preparation method and application thereof, and belongs to the technical field of electrochemical energy storage devices. The preparation method comprises the following steps: dispersing soluble zinc salt, soluble iron salt, 2-methylimidazole and hexadecyl trimethyl ammonium bromide in deionized water, stirring, mixing and reacting to obtain ZnFe-ZIFs; the preparation method comprises the following steps: dispersing phytic acid and ZnFe-ZIFs in methanol, and carrying out an etching reaction to obtain PA / HZnFe-ZIFs; the PA / HZnFe-ZIFs is placed in an inert atmosphere for carbonization treatment, and the ferrous phosphide modified nitrogen and phosphorus co-doped hollow cubic carbon material is obtained. The prepared carbon material is beneficial to adsorption of polysulfide, the shuttle effect can be slowed down, conversion between sulfur and the polysulfide can be accelerated, the preparation method is simple, the production cost is low, and the room-temperature sodium-sulfur battery assembled after the carbon material is compounded with sublimed sulfur to prepare a positive electrode material has excellent cycling stability and rate capability and is suitable for industrial production. The method is suitable for large-scale application.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemical energy storage devices, and particularly to a nitrogen and phosphorus co-doped hollow cubic carbon material, a preparation method thereof and an application thereof. Background Art

[0002] With the rapid development of electric vehicles, the existing energy storage systems have been difficult to meet the growing demands, and there is an urgent need to develop new energy storage technologies with high energy density, stable performance and low cost. Lithium-sulfur batteries were once regarded as promising next-generation high-energy-density energy storage devices due to their high energy density and power density. However, the low crustal abundance and uneven distribution of lithium resources limit their further development and application. Sodium and lithium belong to the same main group elements and have many similar electrochemical properties, and the crustal reserves of sodium are more than 400 times that of lithium. Therefore, developing sodium-ion batteries to replace costly lithium-ion batteries is gradually becoming an important direction of scientific research.

[0003] The room-temperature sodium-sulfur battery is regarded as a promising next-generation battery system due to its theoretical specific capacity of up to 1675 mAh / g However, its practical application still faces the following key technical challenges: 1) Sulfur and its discharge products have intrinsic electron / ion insulation, resulting in slow conversion kinetics between sulfur and polysulfides, severely limiting the utilization rate of sulfur; 2) Soluble higher-order polysulfides (Na2S x , 4 < x < 8) are easily soluble in organic electrolytes and migrate and shuttle between the positive and negative electrodes, causing loss of active materials and self-discharge, significantly reducing the Coulomb efficiency and cycle stability; 3) When discharging to the final product Na2S, the active material undergoes a volume expansion of up to 170%, resulting in electrode structure damage and rapid capacity decay.

[0004] Therefore, developing an efficient catalyst as a sulfur host for room-temperature sodium-sulfur batteries to inhibit polysulfide shuttle and accelerate its conversion kinetics is crucial for improving the overall electrochemical performance of room-temperature sodium-sulfur batteries. Summary of the Invention

[0005] The purpose of the present invention is to provide a nitrogen and phosphorus co-doped hollow cubic carbon material, a preparation method thereof and an application thereof to solve the problems raised in the background art.

[0006] To achieve the above purpose, the present invention provides a preparation method of a nitrogen and phosphorus co-doped hollow cubic carbon material, comprising the following steps: 1) Dissolve cetyltrimethylammonium bromide in deionized water, then add soluble zinc salt and soluble iron salt, and finally add 2-methylimidazole dissolved in deionized water, stir and mix for reaction for 1 h - 3 h to obtain a cubic ZnFe-ZIFs precursor; 2) adding phytic acid to methanol and mixing, then adding ZnFe-ZIFs precursor, stirring and performing etching reaction for 20 min-40 min to obtain PA / HZnFe-ZIFs with a hollow cubic structure; 3) The PA / HZnFe-ZIFs were carbonized in an inert atmosphere, and after cooling, ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon materials were obtained.

[0007] Preferably, in step 1), the molar ratio of the soluble zinc salt to the soluble iron salt is 75:1-50:1; and the molar ratio of the soluble zinc salt to 2-methylimidazole is 1:26-1:78.

[0008] Preferably, in step 1), the soluble zinc salt is at least one of zinc nitrate, zinc chloride, and zinc sulfate; and the soluble iron salt is at least one of iron nitrate, iron sulfate, and iron chloride.

[0009] Preferably, in step 2), the volume ratio of phytic acid to methanol is 1:180-1:280.

[0010] Preferably, in step 3), the specific operation of the carbonization treatment is: heating to 850°C-950°C at a heating rate of 3°C / min-5°C / min, and keeping warm for 1h-3h; the inert atmosphere is one of argon and nitrogen.

[0011] The present invention also provides a nitrogen and phosphorus co-doped hollow cubic carbon material prepared by the above preparation method.

[0012] The present invention also provides the use of the above-mentioned nitrogen and phosphorus co-doped hollow cubic carbon material in preparing a room temperature sodium-sulfur battery positive electrode material.

[0013] Preferably, the preparation process of the room-temperature sodium-sulfur battery positive electrode material is as follows: dispersing nitrogen and phosphorus co-doped hollow cubic carbon material and sublimed sulfur in carbon disulfide, grinding until the carbon disulfide volatilizes, heating the mixture and then keeping it warm to obtain the room-temperature sodium-sulfur battery positive electrode material.

[0014] Preferably, the mass ratio of the nitrogen and phosphorus co-doped hollow cubic carbon material to the sublimated sulfur is 1:1.2-1:2.0; the material is heated to a temperature of 150° C.-160° C. and the holding time is 6 h-12 h.

[0015] The present invention also provides a method for preparing a room temperature sodium-sulfur battery by applying the above-prepared positive electrode material to the room temperature sodium-sulfur battery.

[0016] Therefore, the ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material provided by the present invention not only effectively improves the sulfur loading capacity and polysulfide adsorption performance, but also helps promote the reversible conversion between sulfur and polysulfides. The material preparation process is simple and low-cost. The positive electrode material prepared by combining it with sublimated sulfur can be applied to room-temperature sodium-sulfur batteries, which can significantly improve the battery's cycle stability and rate performance, and has good prospects for large-scale application. Specifically: (1) The ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material of the present invention has a large specific surface area and rich microporous / mesoporous structure, which can achieve high sulfur loading and adapt to volume expansion during charge and discharge; (2) The nitrogen and phosphorus co-doping of the present invention effectively increases the chemical adsorption capacity of the carbon material for polysulfides, effectively inhibiting and slowing down the shuttle effect; (3) The ferrous phosphide nanoparticles of the present invention not only improve the conductivity of the electrode, but also provide abundant active sites for the adsorption and catalytic conversion of polysulfides, thereby accelerating the reaction kinetics; (4) The synergistic effect of the ferrous phosphide nanoparticles and N / P co-doping of the present invention further significantly improves the electrical conductivity of the carbon framework and its ability to adsorb and catalyze polysulfides, thereby achieving excellent electrochemical performance; (5) The ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material prepared by the present invention has a simple process and low production cost, and has good potential for large-scale promotion and application.

[0017] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The SEM and TEM images of Fe2P / NPHC-75 in Example 1; wherein a is a 200nm SEM image; b is a 100nm SEM image; c is a 200nm TEM image; d is a 5nm TEM image; Figure 2 The nitrogen adsorption-desorption curve and pore size distribution diagram of Fe2P / NPHC-75 in Example 1, wherein a is the nitrogen adsorption-desorption curve; b is the pore size distribution diagram; Figure 3 Schematic diagram of the preparation process of the room temperature sodium-sulfur battery positive electrode material in Example 1; Figure 4 This is the TGA curve of the room temperature sodium-sulfur battery cathode material in Example 1; Figure 5 1 is a graph showing the electrochemical performance test results of the CR2032 button battery in Example 1; Figure 6This is the SEM image of Fe2P / NPHC-50 in Example 2; wherein a is 200 nm; b is 100 nm; Figure 7 1 is a graph showing the electrochemical performance test results of the CR2032 button battery in Example 2; Figure 8 This is the SEM image of NPHC in Comparative Example 1; wherein a is 200 nm; b is 100 nm; Figure 9 1 is a graph showing the electrochemical performance test results of the CR2032 button battery in Comparative Example 1; Figure 10 This is the SEM image of NC in Comparative Example 2; wherein a is 200 nm; b is 100 nm; Figure 11 This is a graph showing the electrochemical performance test results of the CR2032 button battery in Comparative Example 2. DETAILED DESCRIPTION

[0019] The technical solution of the present invention is further described below by means of the accompanying drawings and examples. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. Any other changes, modifications, substitutions, combinations, and simplifications made without violating the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the protection scope of the present invention. In addition, it should be understood that after reading the contents of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application and belong to the scope of protection of the present invention.

[0020] References to "embodiments" herein mean that the specific features, structures, or characteristics described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the word "embodiment" in various places in the specification does not necessarily refer to the same embodiment, nor does it particularly limit its independence or relevance to other embodiments. In principle, in this application, as long as there are no technical contradictions or conflicts, the various technical features mentioned in the embodiments can be combined in any manner to form a corresponding implementable technical solution.

[0021] Unless otherwise defined, the technical terms used herein have the same meanings as those generally understood by those skilled in the art to which this application belongs; the use of relevant terms herein is only for describing specific embodiments and is not intended to limit this application.

[0022] Unless otherwise specified in the present invention, the reagents, instruments, equipment and performance testing methods used are those commonly used by those skilled in the art.

[0023] Example 1 A method for preparing a ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material comprises the following steps: 1) Add 16 mg of hexadecyltrimethylammonium bromide (CTAB) to 32 mL of deionized water. After thorough dissolution, add 0.98 g of zinc nitrate hexahydrate and 0.0173 g of ferric nitrate nonahydrate. Subsequently, dissolve 13.14 g of 2-methylimidazole in 224 mL of deionized water and quickly add this solution. Stir rapidly for 2 hours. After the reaction, centrifuge, wash, and finally dry to obtain cubic ZnFe-ZIFs-75.

[0024] 2) Add 450 μL of phytic acid (PA) to 100 mL of methanol and mix thoroughly. Then, add the ZnFe-ZIFs-75 precursor to the solution and stir for 30 minutes. After the reaction, centrifuge and wash with methanol and dry at 80°C to obtain PA / HZnFe-ZIFs-75 with a hollow cubic structure.

[0025] 3) PA / HZnFe-ZIFs-75 was placed in a tube furnace and heated to 900°C at a heating rate of 3°C / min under an argon atmosphere. The mixture was kept at this temperature for 2 h and then naturally cooled to room temperature to obtain ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material (denoted as Fe2P / NPHC-75).

[0026] The scanning electron microscope (SEM) and transmission electron microscope (TEM) images of Fe2P / NPHC-75 in this embodiment are as follows: Figure 1 As shown in the figure, the nitrogen adsorption-desorption curve is as follows Figure 2 As shown. Figure 1 It can be seen that the Fe2P / NPHC-75 in this embodiment presents a hollow cubic structure, which is beneficial to enhance the sulfur loading. Figure 2 It can be seen that the Fe2P / NPHC-75 in this embodiment has a large specific surface area and rich microporous / mesoporous structure, which is conducive to providing space for the accommodation of sulfur and sufficient contact between the electrolyte.

[0027] like Figure 3 As shown, the preparation process of a room-temperature sodium-sulfur battery positive electrode material is as follows: 0.12 g of the above-mentioned Fe2P / NPHC-75 and 0.15 g of sublimed sulfur are dispersed in 15 mL of carbon disulfide, ground in a fume hood until the carbon disulfide is completely volatilized, and then transferred to a hydrothermal reactor, heated to 155°C, kept warm for 12 hours, and naturally cooled to room temperature to obtain a room-temperature sodium-sulfur battery positive electrode material.

[0028] The thermal gravimetric analysis (TGA) curve of the room temperature sodium-sulfur battery cathode material prepared in this embodiment is as follows: Figure 4 As shown. Figure 4It can be seen that the sulfur content in the room temperature sodium-sulfur battery positive electrode material is 52wt%.

[0029] A method for preparing a room-temperature sodium-sulfur battery comprises the following steps: preparing a positive electrode sheet from the above-mentioned room-temperature sodium-sulfur battery positive electrode material, preparing a negative electrode sheet from metallic sodium, using 1.0 mol / L sodium perchlorate dissolved in a mixed solvent of ethylene carbonate / diethyl carbonate (volume ratio of 1:1) as an electrolyte, and assembling the resulting battery into a CR2032 button cell (i.e., a room-temperature sodium-sulfur battery) in an argon-filled glove box.

[0030] The electrochemical performance test results of the CR2032 button battery in this embodiment are shown in the figure Figure 5 As shown. Figure 5 It can be seen that the CR2032 button battery in this embodiment shows good rate performance. Even at a high discharge rate of 10C, it can still achieve a high capacity of 370.8mAh / g. -1 discharge capacity.

[0031] Example 2 A method for preparing a ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material comprises the following steps: 1) Add 16 mg of hexadecyltrimethylammonium bromide (CTAB) to 32 mL of deionized water. After thorough dissolution, add 0.98 g of zinc nitrate hexahydrate and 0.0259 g of ferric nitrate nonahydrate. Subsequently, dissolve 13.14 g of 2-methylimidazole in 224 mL of deionized water and quickly add this solution. Stir rapidly for 2 hours. After the reaction, centrifuge and wash several times, then dry the mixture to obtain cubic ZnFe-ZIFs-50.

[0032] 2) Add 450 μL of phytic acid (PA) to 100 mL of methanol and mix thoroughly. Then, add the ZnFe-ZIFs-50 precursor to the solution and stir for 30 minutes. After the reaction, centrifuge and wash with methanol and dry at 80°C to obtain PA / HZnFe-ZIFs-50 with a hollow cubic structure.

[0033] 3) PA / HZnFe-ZIFs-50 was placed in a tube furnace and heated to 900°C at a heating rate of 3°C / min under an argon atmosphere. The mixture was kept at this temperature for 2 h and then naturally cooled to room temperature to obtain ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material (denoted as Fe2P / NPHC-50).

[0034] The SEM image of Fe2P / NPHC-50 in this embodiment is as follows: Figure 6 As shown. Figure 6 It can be seen that the Fe2P / NPHC-50 in this embodiment has a hollow cubic structure.

[0035] The positive electrode material of room temperature sodium-sulfur battery was prepared and CR2032 button cell (i.e. room temperature sodium-sulfur battery) was assembled according to the method of Example 1. The electrochemical performance test results of CR2032 button cell in this example are shown in FIG. Figure 7 As shown. Figure 7 It can be seen that the CR2032 button battery in this embodiment has good rate performance and can release 292.1mAh / g at a discharge rate of 10C. -1 High discharge capacity.

[0036] Example 3 The only difference between this example and Example 1 is that in preparing the ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material, the amount of 2-methylimidazole used in step 1) is 6.57 g. All other steps are the same as in Example 1 and are not repeated here. The carbon material prepared in this example also exhibits a hollow cubic structure, similar to that in Example 1.

[0037] A room temperature sodium-sulfur battery cathode material and a CR2032 button cell (i.e., a room temperature sodium-sulfur battery) were prepared by referring to the method of Example 1. Testing showed that the performance of the CR2032 button cell assembled in this example was similar to that of the CR2032 button cell assembled in Example 1.

[0038] Example 4 The only difference between this example and Example 2 is that in preparing the ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material, the amount of 2-methylimidazole used in step 1) is 6.57 g. All other steps are the same as in Example 2 and are not repeated here. The carbon material prepared in this example also exhibits a hollow cubic structure, similar to that in Example 2.

[0039] A room temperature sodium-sulfur battery cathode material and a CR2032 button cell (i.e., a room temperature sodium-sulfur battery) were prepared by referring to the method of Example 1. Testing showed that the performance of the CR2032 button cell assembled in this example was similar to that of the CR2032 button cell assembled in Example 2.

[0040] Example 5 This Example differs from Example 1 only in that, in preparing the ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material, the amount of 2-methylimidazole used in step 1) is 19.71 g. All other steps are the same as in Example 1 and are not repeated here. The carbon material prepared in this Example also exhibits a hollow cubic structure, similar to that in Example 1.

[0041] A room temperature sodium-sulfur battery cathode material and a CR2032 button cell (i.e., a room temperature sodium-sulfur battery) were prepared by referring to the method of Example 1. Testing showed that the performance of the CR2032 button cell assembled in this example was similar to that of the CR2032 button cell assembled in Example 1.

[0042] Example 6 The only difference between this example and Example 2 is that in preparing the ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material, the amount of 2-methylimidazole used in step 1) is 19.71 g. All other steps are the same as in Example 2 and are not repeated here. The carbon material prepared in this example also exhibits a hollow cubic structure, similar to that of Example 2.

[0043] A room temperature sodium-sulfur battery cathode material and a CR2032 button cell (i.e., a room temperature sodium-sulfur battery) were prepared by referring to the method of Example 1. Testing showed that the performance of the CR2032 button cell assembled in this example was similar to that of the CR2032 button cell assembled in Example 2.

[0044] Example 7 This Example differs from Example 1 only in that, in preparing the ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material, the reaction time in step 1) is 1 hour. All other steps are the same as in Example 1 and are not repeated here. The carbon material prepared in this Example also exhibits a hollow cubic structure, similar to that in Example 1.

[0045] A room temperature sodium-sulfur battery cathode material and a CR2032 button cell (i.e., a room temperature sodium-sulfur battery) were prepared by referring to the method of Example 1. Testing showed that the performance of the CR2032 button cell assembled in this example was similar to that of the CR2032 button cell assembled in Example 1.

[0046] Example 8 The only difference between this example and Example 2 is that the reaction time in step 1) of preparing the ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material is 1 hour. All other steps are the same as in Example 2 and are not repeated here. The carbon material prepared in this example also exhibits a hollow cubic structure, similar to that of Example 2.

[0047] A room temperature sodium-sulfur battery cathode material and a CR2032 button cell (i.e., a room temperature sodium-sulfur battery) were prepared by referring to the method of Example 1. Testing showed that the performance of the CR2032 button cell assembled in this example was similar to that of the CR2032 button cell assembled in Example 2.

[0048] Example 9 This Example differs from Example 1 only in that, in preparing the ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material, the reaction time in step 1) is 3 hours. All other steps are the same as in Example 1 and are not repeated here. The carbon material prepared in this Example also exhibits a hollow cubic structure, similar to that in Example 1.

[0049] A room temperature sodium-sulfur battery cathode material and a CR2032 button cell (i.e., a room temperature sodium-sulfur battery) were prepared by referring to the method of Example 1. Testing showed that the performance of the CR2032 button cell assembled in this example was similar to that of the CR2032 button cell assembled in Example 1.

[0050] Example 10 The only difference between this example and Example 2 is that the reaction time in step 1) of preparing the ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material is 3 hours. All other steps are the same as in Example 2 and are not repeated here. The carbon material prepared in this example also exhibits a hollow cubic structure, similar to that of Example 2.

[0051] A room temperature sodium-sulfur battery cathode material and a CR2032 button cell (i.e., a room temperature sodium-sulfur battery) were prepared by referring to the method of Example 1. Testing showed that the performance of the CR2032 button cell assembled in this example was similar to that of the CR2032 button cell assembled in Example 2.

[0052] Example 11 This Example differs from Example 1 only in that, in preparing the ferrous phosphide-modified, nitrogen-phosphorus co-doped hollow cubic carbon material, 0.4362 g of zinc chloride is used in place of 0.98 g of zinc nitrate hexahydrate in step 1). All other steps are the same as in Example 1 and are not repeated here. The carbon material prepared in this Example also exhibits a hollow cubic structure, similar to that of Example 1.

[0053] A room temperature sodium-sulfur battery cathode material and a CR2032 button cell (i.e., a room temperature sodium-sulfur battery) were prepared by referring to the method of Example 1. Testing showed that the performance of the CR2032 button cell assembled in this example was similar to that of the CR2032 button cell assembled in Example 1.

[0054] Example 12 This Example differs from Example 2 only in that, in preparing the ferrous phosphide-modified, nitrogen-phosphorus co-doped hollow cubic carbon material, 0.4362 g of zinc chloride is used in place of 0.98 g of zinc nitrate hexahydrate in step 1). All other steps are the same as in Example 2 and are not repeated here. The carbon material prepared in this Example also exhibits a hollow cubic structure, similar to that of Example 2.

[0055] A room temperature sodium-sulfur battery cathode material and a CR2032 button cell (i.e., a room temperature sodium-sulfur battery) were prepared by referring to the method of Example 1. Testing showed that the performance of the CR2032 button cell assembled in this example was similar to that of the CR2032 button cell assembled in Example 2.

[0056] Example 13 This Example differs from Example 1 only in that, in preparing the ferrous phosphide-modified, nitrogen-phosphorus co-doped hollow cubic carbon material, 0.5166 g of zinc sulfate was used in place of 0.98 g of zinc nitrate hexahydrate in step 1). All other steps are the same as in Example 1 and are not repeated here. The carbon material prepared in this Example also exhibits a hollow cubic structure, similar to that of Example 1.

[0057] A room temperature sodium-sulfur battery cathode material and a CR2032 button cell (i.e., a room temperature sodium-sulfur battery) were prepared by referring to the method of Example 1. Testing showed that the performance of the CR2032 button cell assembled in this example was similar to that of the CR2032 button cell assembled in Example 1.

[0058] Example 14 This Example differs from Example 2 only in that, in preparing the ferrous phosphide-modified, nitrogen-phosphorus co-doped hollow cubic carbon material, 0.5166 g of zinc sulfate was used in place of 0.98 g of zinc nitrate hexahydrate in step 1). All other steps are the same as in Example 2 and are not repeated here. The carbon material prepared in this Example also exhibits a hollow cubic structure, similar to that of Example 2.

[0059] A room temperature sodium-sulfur battery cathode material and a CR2032 button cell (i.e., a room temperature sodium-sulfur battery) were prepared by referring to the method of Example 1. Testing showed that the performance of the CR2032 button cell assembled in this example was similar to that of the CR2032 button cell assembled in Example 2.

[0060] Example 15 The only difference between this example and Example 1 is that, in step 1), 0.0116 g of ferric chloride hexahydrate was used instead of 0.0173 g of ferric nitrate nonahydrate in preparing the ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material. The remaining steps are the same as in Example 1 and are not repeated here. The carbon material prepared in this example also exhibits a hollow cubic structure, similar to that of Example 1.

[0061] A room temperature sodium-sulfur battery cathode material and a CR2032 button cell (i.e., a room temperature sodium-sulfur battery) were prepared by referring to the method of Example 1. Testing showed that the performance of the CR2032 button cell assembled in this example was similar to that of the CR2032 button cell assembled in Example 1.

[0062] Example 16 The only difference between this example and Example 2 is that, in step 1), 0.0173 g of ferric chloride hexahydrate was used instead of 0.0259 g of ferric nitrate nonahydrate in preparing the ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material. The remaining steps are the same as in Example 2 and are not repeated here. The carbon material prepared in this example also exhibits a hollow cubic structure, similar to that of Example 2.

[0063] A room temperature sodium-sulfur battery cathode material and a CR2032 button cell (i.e., a room temperature sodium-sulfur battery) were prepared by referring to the method of Example 1. Testing showed that the performance of the CR2032 button cell assembled in this example was similar to that of the CR2032 button cell assembled in Example 2.

[0064] Example 17 This Example differs from Example 1 only in that, in preparing the ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material, 0.0073 g of ferric sulfate hydrate is used in place of 0.0173 g of ferric nitrate nonahydrate in step 1). The remaining steps are the same as in Example 1 and are not repeated here. The carbon material prepared in this Example also exhibits a hollow cubic structure, similar to that of Example 1.

[0065] A room temperature sodium-sulfur battery cathode material and a CR2032 button cell (i.e., a room temperature sodium-sulfur battery) were prepared by referring to the method of Example 1. Testing showed that the performance of the CR2032 button cell assembled in this example was similar to that of the CR2032 button cell assembled in Example 1.

[0066] Example 18 The only difference between this example and Example 2 is that, in step 1), 0.0109 g of ferric sulfate hydrate was used instead of 0.0259 g of ferric nitrate nonahydrate in preparing the ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material. The remaining steps are the same as in Example 2 and are not repeated here. The carbon material prepared in this example also exhibits a hollow cubic structure, similar to that of Example 2.

[0067] A room temperature sodium-sulfur battery cathode material and a CR2032 button cell (i.e., a room temperature sodium-sulfur battery) were prepared by referring to the method of Example 1. Testing showed that the performance of the CR2032 button cell assembled in this example was similar to that of the CR2032 button cell assembled in Example 2.

[0068] Example 19 This Example differs from Example 1 only in that, in preparing the ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material, the amount of acid used in step 2) is 350 μL. All other steps are the same as in Example 1 and are not repeated here. The carbon material prepared in this Example also exhibits a hollow cubic structure, similar to that of Example 1.

[0069] A room temperature sodium-sulfur battery cathode material and a CR2032 button cell (i.e., a room temperature sodium-sulfur battery) were prepared by referring to the method of Example 1. Testing showed that the performance of the CR2032 button cell assembled in this example was similar to that of the CR2032 button cell assembled in Example 1.

[0070] Example 20 The only difference between this example and Example 2 is that in preparing the ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material, the amount of acid used in step 2) is 350 μL. All other steps are the same as in Example 2 and are not repeated here. The carbon material prepared in this example also exhibits a hollow cubic structure, similar to that of Example 2.

[0071] A room temperature sodium-sulfur battery cathode material and a CR2032 button cell (i.e., a room temperature sodium-sulfur battery) were prepared by referring to the method of Example 1. Testing showed that the performance of the CR2032 button cell assembled in this example was similar to that of the CR2032 button cell assembled in Example 2.

[0072] Example 21 This Example differs from Example 1 only in that, in preparing the ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material, the amount of acid used in step 2) is 550 μL. All other steps are the same as in Example 1 and are not repeated here. The carbon material prepared in this Example also exhibits a hollow cubic structure, similar to that of Example 1.

[0073] A room temperature sodium-sulfur battery cathode material and a CR2032 button cell (i.e., a room temperature sodium-sulfur battery) were prepared by referring to the method of Example 1. Testing showed that the performance of the CR2032 button cell assembled in this example was similar to that of the CR2032 button cell assembled in Example 1.

[0074] Example 22 The only difference between this example and Example 2 is that in preparing the ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material, the amount of acid used in step 2) is 550 μL. All other steps are the same as in Example 2 and are not repeated here. The carbon material prepared in this example also exhibits a hollow cubic structure, similar to that of Example 2.

[0075] A room temperature sodium-sulfur battery cathode material and a CR2032 button cell (i.e., a room temperature sodium-sulfur battery) were prepared by referring to the method of Example 1. Testing showed that the performance of the CR2032 button cell assembled in this example was similar to that of the CR2032 button cell assembled in Example 2.

[0076] Example 23 The only difference between this example and Example 1 is that, in preparing the ferrous phosphide-modified, nitrogen-phosphorus co-doped hollow cubic carbon material, the etching time in step 2) is 20 minutes. All other steps are the same as in Example 1 and are not repeated here. The carbon material prepared in this example also exhibits a hollow cubic structure, similar to that in Example 1.

[0077] A room temperature sodium-sulfur battery cathode material and a CR2032 button cell (i.e., a room temperature sodium-sulfur battery) were prepared by referring to the method of Example 1. Testing showed that the performance of the CR2032 button cell assembled in this example was similar to that of the CR2032 button cell assembled in Example 1.

[0078] Example 24 The only difference between this example and Example 2 is that, in preparing the ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material, the etching time in step 2) is 20 minutes. All other steps are the same as in Example 2 and are not repeated here. The carbon material prepared in this example also exhibits a hollow cubic structure, similar to that in Example 2.

[0079] A room temperature sodium-sulfur battery cathode material and a CR2032 button cell (i.e., a room temperature sodium-sulfur battery) were prepared by referring to the method of Example 1. Testing showed that the performance of the CR2032 button cell assembled in this example was similar to that of the CR2032 button cell assembled in Example 2.

[0080] Example 25 The only difference between this example and Example 1 is that, in preparing the ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material, the etching time in step 2) is 40 minutes. All other steps are the same as in Example 1 and are not repeated here. The carbon material prepared in this example also exhibits a hollow cubic structure, similar to that in Example 1.

[0081] A room temperature sodium-sulfur battery cathode material and a CR2032 button cell (i.e., a room temperature sodium-sulfur battery) were prepared by referring to the method of Example 1. Testing showed that the performance of the CR2032 button cell assembled in this example was similar to that of the CR2032 button cell assembled in Example 1.

[0082] Example 26 The only difference between this example and Example 2 is that, in preparing the ferrous phosphide-modified, nitrogen-phosphorus co-doped hollow cubic carbon material, the etching time in step 2) is 40 minutes. All other steps are the same as in Example 2 and are not repeated here. The carbon material prepared in this example also exhibits a hollow cubic structure, similar to that in Example 2.

[0083] A room temperature sodium-sulfur battery cathode material and a CR2032 button cell (i.e., a room temperature sodium-sulfur battery) were prepared by referring to the method of Example 1. Testing showed that the performance of the CR2032 button cell assembled in this example was similar to that of the CR2032 button cell assembled in Example 2.

[0084] Example 27 This Example differs from Example 1 only in that, in preparing the ferrous phosphide-modified, nitrogen-phosphorus co-doped hollow cubic carbon material, nitrogen is used instead of argon as the inert atmosphere in step 3). The remaining steps are the same as in Example 1 and are not repeated here. The carbon material prepared in this Example also exhibits a hollow cubic structure, similar to that of Example 1.

[0085] A room temperature sodium-sulfur battery cathode material and a CR2032 button cell (i.e., a room temperature sodium-sulfur battery) were prepared by referring to the method of Example 1. Testing showed that the performance of the CR2032 button cell assembled in this example was similar to that of the CR2032 button cell assembled in Example 1.

[0086] Example 28 This Example differs from Example 2 only in that, in preparing the ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material, nitrogen is used instead of argon as the inert atmosphere in step 3). The remaining steps are the same as in Example 2 and are not repeated here. The carbon material prepared in this Example also exhibits a hollow cubic structure, similar to that of Example 2.

[0087] A room temperature sodium-sulfur battery cathode material and a CR2032 button cell (i.e., a room temperature sodium-sulfur battery) were prepared by referring to the method of Example 1. Testing showed that the performance of the CR2032 button cell assembled in this example was similar to that of the CR2032 button cell assembled in Example 2.

[0088] Example 29 This Example differs from Example 1 only in that, in preparing the ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material, the carbonization temperature in step 3) is 850°C. All other steps are the same as in Example 1 and are not repeated here. The carbon material prepared in this Example also exhibits a hollow cubic structure, similar to that of Example 1.

[0089] A room temperature sodium-sulfur battery cathode material and a CR2032 button cell (i.e., a room temperature sodium-sulfur battery) were prepared by referring to the method of Example 1. Testing showed that the performance of the CR2032 button cell assembled in this example was similar to that of the CR2032 button cell assembled in Example 1.

[0090] Example 30 The only difference between this example and Example 2 is that the carbonization temperature in step 3) is 850°C when preparing the ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material. All other steps are the same as in Example 2 and are not repeated here. The carbon material prepared in this example also exhibits a hollow cubic structure, similar to that of Example 2.

[0091] A room temperature sodium-sulfur battery cathode material and a CR2032 button cell (i.e., a room temperature sodium-sulfur battery) were prepared by referring to the method of Example 1. Testing showed that the performance of the CR2032 button cell assembled in this example was similar to that of the CR2032 button cell assembled in Example 2.

[0092] Example 31 This Example differs from Example 1 only in that, in preparing the ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material, the carbonization temperature in step 3) is 950°C. All other steps are the same as in Example 1 and are not repeated here. The carbon material prepared in this Example also exhibits a hollow cubic structure, similar to that of Example 1.

[0093] A room temperature sodium-sulfur battery cathode material and a CR2032 button cell (i.e., a room temperature sodium-sulfur battery) were prepared by referring to the method of Example 1. Testing showed that the performance of the CR2032 button cell assembled in this example was similar to that of the CR2032 button cell assembled in Example 1.

[0094] Example 32 The only difference between this example and Example 2 is that the carbonization temperature in step 3) is 950°C when preparing the ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material. All other steps are the same as those in Example 2 and are not repeated here. The carbon material prepared in this example also exhibits a hollow cubic structure, similar to that in Example 2.

[0095] A room temperature sodium-sulfur battery cathode material and a CR2032 button cell (i.e., a room temperature sodium-sulfur battery) were prepared by referring to the method of Example 1. Testing showed that the performance of the CR2032 button cell assembled in this example was similar to that of the CR2032 button cell assembled in Example 2.

[0096] Example 33 The only difference between this example and Example 1 is that, in preparing the ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material, the holding time in step 3) is 1 hour. All other steps are the same as in Example 1 and are not repeated here. The carbon material prepared in this example also exhibits a hollow cubic structure, similar to that of Example 1.

[0097] A room temperature sodium-sulfur battery cathode material and a CR2032 button cell (i.e., a room temperature sodium-sulfur battery) were prepared by referring to the method of Example 1. Testing showed that the performance of the CR2032 button cell assembled in this example was similar to that of the CR2032 button cell assembled in Example 1.

[0098] Example 34 The only difference between this example and Example 2 is that, in preparing the ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material, the holding time in step 3) is 1 hour. All other steps are the same as in Example 2 and are not repeated here. The carbon material prepared in this example also exhibits a hollow cubic structure, similar to that of Example 2.

[0099] A room temperature sodium-sulfur battery cathode material and a CR2032 button cell (i.e., a room temperature sodium-sulfur battery) were prepared by referring to the method of Example 1. Testing showed that the performance of the CR2032 button cell assembled in this example was similar to that of the CR2032 button cell assembled in Example 2.

[0100] Example 35 The only difference between this example and Example 1 is that, in preparing the ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material, the holding time in step 3) is 3 hours. All other steps are the same as in Example 1 and are not repeated here. The carbon material prepared in this example also exhibits a hollow cubic structure, similar to that of Example 1.

[0101] A room temperature sodium-sulfur battery cathode material and a CR2032 button cell (i.e., a room temperature sodium-sulfur battery) were prepared by referring to the method of Example 1. Testing showed that the performance of the CR2032 button cell assembled in this example was similar to that of the CR2032 button cell assembled in Example 1.

[0102] Example 36 The only difference between this example and Example 2 is that, in preparing the ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material, the holding time in step 3) is 3 hours. All other steps are the same as in Example 2 and are not repeated here. The carbon material prepared in this example also exhibits a hollow cubic structure, similar to that of Example 2.

[0103] A room temperature sodium-sulfur battery cathode material and a CR2032 button cell (i.e., a room temperature sodium-sulfur battery) were prepared by referring to the method of Example 1. Testing showed that the performance of the CR2032 button cell assembled in this example was similar to that of the CR2032 button cell assembled in Example 2.

[0104] Example 37 The only difference between this example and Example 1 is that in preparing the ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material, the heating rate in step 3) is 5°C / min. All other steps are the same as in Example 1 and are not repeated here. The carbon material prepared in this example also exhibits a hollow cubic structure, similar to that in Example 1.

[0105] A room temperature sodium-sulfur battery cathode material and a CR2032 button cell (i.e., a room temperature sodium-sulfur battery) were prepared by referring to the method of Example 1. Testing showed that the performance of the CR2032 button cell assembled in this example was similar to that of the CR2032 button cell assembled in Example 1.

[0106] Example 38 The only difference between this example and Example 2 is that, in preparing the ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material, the heating rate in step 3) is 5°C / min. All other steps are the same as in Example 2 and are not repeated here. The carbon material prepared in this example also exhibits a hollow cubic structure, similar to that in Example 2.

[0107] A room temperature sodium-sulfur battery cathode material and a CR2032 button cell (i.e., a room temperature sodium-sulfur battery) were prepared by referring to the method of Example 1. Testing showed that the performance of the CR2032 button cell assembled in this example was similar to that of the CR2032 button cell assembled in Example 2.

[0108] Comparative Example 1 A method for preparing a nitrogen-phosphorus co-doped hollow cubic carbon material comprises the following steps: 1) Add 16 mg of cetyltrimethylammonium bromide (CTAB) to 32 mL of deionized water. Dissolve thoroughly, then add 0.98 g of zinc nitrate hexahydrate. Subsequently, dissolve 13.14 g of 2-methylimidazole in 224 mL of deionized water as described above. Rapidly add this solution and stir for 2 hours. After several centrifugations, washing, and drying, a cubic Zn-ZIF is obtained.

[0109] 2) Add 450 μL of phytic acid (PA) to 100 mL of methanol and mix thoroughly. Then, add the ZnFe-ZIFs-75 precursor to the solution and stir for 30 minutes. After the reaction, wash the mixture with methanol by centrifugation and dry it at 80°C to obtain PA / HZn-ZIFs with a hollow cubic structure.

[0110] 3) The PA / HZn-ZIFs were placed in a tube furnace and heated to 900°C at a heating rate of 3°C / min under an argon atmosphere. The temperature was kept at this temperature for 2 h and then naturally cooled to room temperature to obtain ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon materials (denoted as NPHC).

[0111] The SEM image of NPHC in this comparative example is as follows: Figure 8 As shown. Figure 8 It can be seen that the NPHC in this comparative example presents a hollow cubic structure.

[0112] The room temperature sodium sulfur battery cathode material and CR2032 button cell (i.e. room temperature sodium sulfur battery) were prepared by referring to the method of Example 1. The electrochemical performance test results of CR2032 button cell are shown in the figure below. Figure 9 As shown. Figure 9 It can be seen that the rate performance of room temperature sodium sulfur battery is poor. When the discharge rate is 10C, the discharge capacity is only 207.2mAh / g. -1 .

[0113] Comparative Example 2 A method for preparing a nitrogen-doped porous carbon material comprises the following steps: 1) Add 16 mg of cetyltrimethylammonium bromide (CTAB) to 32 mL of deionized water. Dissolve thoroughly, then add 0.98 g of zinc nitrate hexahydrate. Subsequently, dissolve 13.14 g of 2-methylimidazole in 224 mL of deionized water as described above. Rapidly add this solution and stir for 2 hours. After several centrifugations, washing, and drying, a cubic Zn-ZIF is obtained.

[0114] 2) The Zn-ZIF was placed in a tube furnace and heated to 900°C at a heating rate of 3°C / min under an argon atmosphere. The temperature was kept at this temperature for 2 hours and then naturally cooled to room temperature to obtain a ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material (denoted as NC).

[0115] The SEM image of NC in this comparative example is as follows Figure 10 As shown. Figure 10 It can be seen that the NC in this comparative example presents a cubic structure and has a smooth surface.

[0116] The room temperature sodium sulfur battery cathode material and CR2032 button cell (i.e. room temperature sodium sulfur battery) were prepared by referring to the method of Example 1. The electrochemical performance test results of CR2032 button cell are shown in the figure below. Figure 11 As shown. Figure 11 It can be seen that the rate performance of room temperature sodium sulfur battery is poor. When the discharge rate is 10C, the discharge capacity is only 78mAh / g. -1 .

[0117] From the SEM images of Examples 1 and 2 and Comparative Examples 1 and 2, it can be seen that the Fe2P / NPHC material exhibits a hollow cubic structure, while the NC material of Comparative Example 2 has a solid cubic structure. This hollow structure provides more space for sulfur loading and can accommodate volume expansion during charge and discharge, thereby improving battery performance. For example, the Fe2P / NPHC-75 of Example 1 can still achieve 370.8 mAh / g at a high discharge rate of 10C. -1 The discharge capacity of the NC material in comparative example 2 is only 78 mAh / g at 10C.-1 , which fully illustrates the positive impact of the hollow structure on performance.

[0118] The nitrogen adsorption-desorption curves of Example 1 demonstrate that Fe2P / NPHC-75 possesses a large specific surface area and a rich microporous / mesoporous structure. This allows for sufficient contact with the electrolyte, promoting ion and electron transport, thereby improving sulfur utilization and battery reaction kinetics. In contrast, the NC material of Comparative Example 2 exhibits a smooth surface and a less porous structure, resulting in poor electrochemical performance.

[0119] NPHC material of Comparative Example 1 (without Fe 2+ doping, only N / P co-doping) at 10C discharge capacity of 207.2mAh / g -1 , while the specific capacity of Fe2P / NPHC-75 (N / P co-doped and Fe2P modified) in Example 1 reached 370.8mAh / g -1 . This shows that nitrogen and phosphorus co-doping can effectively increase the chemical adsorption capacity of carbon materials for polysulfides, inhibit the shuttle effect, and thus improve the cycle stability and rate performance of the battery. The introduction of ferrous phosphide nanoparticles not only improves the conductivity of the electrode, but also provides abundant active sites for the adsorption and catalytic conversion of polysulfides, accelerating the reaction kinetics. The comparison between Example 1 and Comparative Example 1 fully demonstrates this point. The modification of Fe2P significantly improves the electrochemical performance of the material.

[0120] In summary, the hollow cubic structure of Fe2P / NPHC material, the synergistic effect of nitrogen and phosphorus co-doping and ferrous phosphide modification, and the optimized preparation process parameters together enable this material to exhibit excellent performance in room-temperature sodium-sulfur batteries and have good application prospects.

[0121] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a nitrogen-phosphorus co-doped hollow cubic carbon material, characterized in that: The following steps are involved: 1) dispersing hexadecyltrimethylammonium bromide in deionized water and dissolving it, then adding a soluble zinc salt and a soluble iron salt, and finally adding 2-methylimidazole dissolved in deionized water, stirring and reacting for 1 h to 3 h to obtain a cubic ZnFe-ZIFs precursor; 2) adding phytic acid to methanol and mixing, then adding ZnFe-ZIFs precursor, stirring and performing etching reaction for 20 min-40 min to obtain PA / HZnFe-ZIFs with a hollow cubic structure; 3) The PA / HZnFe-ZIFs were carbonized in an inert atmosphere, and after cooling, ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon materials were obtained.

2. The method for preparing a nitrogen-phosphorus co-doped hollow cubic carbon material according to claim 1, characterized in that: In step 1), the molar ratio of the soluble zinc salt to the soluble iron salt is 75:1-50:1; and the molar ratio of the soluble zinc salt to 2-methylimidazole is 1:26-1:

78.

3. The method for preparing a nitrogen-phosphorus co-doped hollow cubic carbon material according to claim 1, characterized in that: In step 1), the soluble zinc salt is at least one of zinc nitrate, zinc chloride, and zinc sulfate; and the soluble iron salt is at least one of iron nitrate, iron sulfate, and iron chloride.

4. The method for preparing a nitrogen-phosphorus co-doped hollow cubic carbon material according to claim 1, characterized in that: In step 2), the volume ratio of phytic acid to methanol is 1:180-1:

280.

5. The method for preparing a nitrogen-phosphorus co-doped hollow cubic carbon material according to claim 1, characterized in that: In step 3), the specific operation of the carbonization treatment is: heating to 850°C-950°C at a heating rate of 3°C / min-5°C / min, and keeping warm for 1h-3h; the inert atmosphere is one of argon and nitrogen.

6. A nitrogen-phosphorus co-doped hollow cubic carbon material, characterized in that: The nitrogen and phosphorus co-doped hollow cubic carbon material is prepared by the preparation method according to any one of claims 1 to 5.

7. The use of a nitrogen and phosphorus co-doped hollow cubic carbon material according to claim 6, characterized in that: The nitrogen and phosphorus co-doped hollow cubic carbon material is used to prepare a room temperature sodium-sulfur battery positive electrode material.

8. The use of a nitrogen and phosphorus co-doped hollow cubic carbon material according to claim 7, characterized in that: The preparation process of the room-temperature sodium-sulfur battery positive electrode material is as follows: disperse nitrogen and phosphorus co-doped hollow cubic carbon material and sublimated sulfur in carbon disulfide, grind until the carbon disulfide volatilizes, heat the mixture and keep it warm to obtain the room-temperature sodium-sulfur battery positive electrode material.

9. The use of a nitrogen and phosphorus co-doped hollow cubic carbon material according to claim 7, characterized in that: The mass ratio of the nitrogen and phosphorus co-doped hollow cubic carbon material to the sublimated sulfur is 1:1.2-1:2.0; the material is heated to a temperature of 150° C.-160° C. and the holding time is 6 h-12 h.

10. A room temperature sodium-sulfur battery, characterized in that: The positive electrode composition of the battery comprises the room temperature sodium-sulfur battery positive electrode material described in claims 7-9.

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