A nitrogen and phosphorus co-doped hollow cubic carbon material, a preparation method and application thereof

Abstract

The application discloses a nitrogen and phosphorus co-doped hollow cubic carbon material and a preparation method and application thereof, and belongs to the technical field of electrochemical energy storage devices. A soluble zinc salt, a soluble iron salt, 2-methyl imidazole and cetyltrimethylammonium bromide are dispersed in deionized water and stirred and mixed to obtain ZnFe-ZIFs; phytic acid and the ZnFe-ZIFs are dispersed in methanol to perform etching reaction and obtain PA / HZnFe-ZIFs; the PA / HZnFe-ZIFs are placed in an inert atmosphere for carbonization treatment, and a ferrophosphorus modified nitrogen and phosphorus co-doped hollow cubic carbon material is obtained. The carbon material prepared by the application is beneficial to adsorption of polysulfides, can slow down the shuttle effect and accelerate the conversion between sulfur and polysulfides, and has the advantages of simple preparation method and low production cost. After the carbon material is compounded with sublimed sulfur to form a positive electrode material and then assembled into a room-temperature sodium-sulfur battery, the room-temperature sodium-sulfur battery has excellent cycle stability and rate performance, and is suitable for large-scale application.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemical energy storage devices, and in particular 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 demand, and there is an urgent need to develop new energy storage technologies with high energy density, stable performance, and low cost. Lithium-sulfur batteries, with their high energy density and power density, were once regarded as promising next-generation high-energy-density energy storage devices. 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] Room temperature sodium-sulfur batteries are regarded as a potential next-generation battery system due to their theoretical specific capacity of up to 1675 mAh / g -1 . However, their practical applications still face 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 the sulfur host of room temperature sodium-sulfur batteries to inhibit polysulfide shuttling 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. [[ID=二十四]]

[0006] To achieve the above purpose, the present invention provides a preparation method of a nitrogen and phosphorus co-doped hollow cubic carbon material, including the following steps:

[0007] 1) Disperse cetyltrimethylammonium bromide in deionized water and dissolve it, 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;

[0008] 2) Add phytic acid into methanol, then add ZnFe-ZIFs precursor, stir and carry out etching reaction for 20-40 min to obtain PA / HZnFe-ZIFs with hollow cubic structure;

[0009] 3) Place the PA / HZnFe-ZIFs in an inert atmosphere for carbonization treatment, and obtain the ferrous phosphide modified nitrogen and phosphorus co-doped hollow cubic carbon material after cooling.

[0010] Preferably, in step 1), the molar ratio of the soluble zinc salt and the soluble iron salt is 75:1-50:1; and the molar ratio of the soluble zinc salt and 2-methylimidazole is 1:26-1:78.

[0011] 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 ferric nitrate, ferric sulfate and ferric chloride.

[0012] Preferably, in step 2), the volume ratio of phytic acid and methanol is 1:180-1:280.

[0013] Preferably, in step 3), the specific operation of the carbonization treatment is: heating to 850-950℃ at a heating rate of 3-5℃ / min, and keeping the temperature for 1-3h; and the inert atmosphere is one of argon and nitrogen.

[0014] The application further provides a nitrogen and phosphorus co-doped hollow cubic carbon material prepared by the above preparation method.

[0015] The application further provides an application of the above nitrogen and phosphorus co-doped hollow cubic carbon material in preparing a room-temperature sodium-sulfur battery positive electrode material.

[0016] Preferably, the preparation process of the room-temperature sodium-sulfur battery positive electrode material is: dispersing the nitrogen and phosphorus co-doped hollow cubic carbon material and sublimed sulfur in carbon disulfide, grinding until the carbon disulfide volatilizes, and then heating and keeping the temperature of the mixture to obtain the room-temperature sodium-sulfur battery positive electrode material.

[0017] Preferably, the mass ratio of the nitrogen and phosphorus co-doped hollow cubic carbon material and the sublimed sulfur is 1:1.2-1:2.0; the heating temperature is 150-160℃, and the keeping time is 6-12h.

[0018] The application further provides an application of the above prepared room-temperature sodium-sulfur battery positive electrode material in preparing a room-temperature sodium-sulfur battery.

[0019] Therefore, the ferrous phosphide modified nitrogen and phosphorus co-doped hollow cubic carbon material provided by the application not only effectively improves the sulfur loading capacity and the adsorption performance of polysulfides, but also helps to promote the reversible conversion between sulfur and polysulfides. The material has a simple preparation process and low cost. When the positive electrode material prepared by compounding the material with sublimed sulfur is applied to a room temperature sodium-sulfur battery, the cycle stability and rate performance of the battery can be significantly improved, and the material has good prospects for large-scale application. Specifically,

[0020] (1) The ferrous phosphide modified nitrogen and phosphorus co-doped hollow cubic carbon material has a large specific surface area and a rich microporous / mesoporous structure, which can realize high sulfur loading and adapt to the volume expansion in the charging and discharging process;

[0021] (2) The nitrogen and phosphorus co-doping effectively increases the chemical adsorption capacity of the carbon material to polysulfides, effectively inhibits and slows down the shuttle effect;

[0022] (3) The ferrous phosphide nanoparticles not only improve the conductivity of the electrode, but also provide rich active sites for the adsorption and catalytic conversion of polysulfides, thereby accelerating the reaction kinetics process;

[0023] (4) The synergistic effect of the ferrous phosphide nanoparticles and the N / P co-doping further significantly improves the conductivity of the carbon framework and the adsorption and catalytic conversion capacity of polysulfides, thereby obtaining excellent electrochemical performance;

[0024] (5) The ferrous phosphide modified nitrogen and phosphorus co-doped hollow cubic carbon material prepared by the application has a simple preparation process, low production cost, and good potential for large-scale popularization and application.

[0025] The technical solutions of the application will be further described in detail below with reference to the accompanying drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The SEM and TEM images of Fe2P / NPHC-75 in Example 1 are shown in the figure, wherein a is a SEM image of 200 nm; b is a SEM image of 100 nm; c is a TEM image of 200 nm; d is a TEM image of 5 nm;

[0027] Figure 2 The nitrogen adsorption-desorption curve and the pore size distribution graph of Fe2P / NPHC-75 in Example 1 are shown in the figure, wherein a is the nitrogen adsorption-desorption curve; b is the pore size distribution graph;

[0028] Figure 3 The preparation process schematic diagram of the room temperature sodium-sulfur battery positive electrode material in Example 1 is shown in the figure;

[0029] Figure 4TGA curve of the room temperature sodium-sulfur battery cathode material in Example 1;

[0030] Figure 5 Electrochemical performance test result graph of the CR2032 button cell in Example 1;

[0031] Figure 6 SEM image of Fe2P / NPHC-50 in Example 2; wherein, a is 200 nm; b is 100 nm;

[0032] Figure 7 Electrochemical performance test result graph of the CR2032 button cell in Example 2;

[0033] Figure 8 SEM image of NPHC in Comparative Example 1; wherein, a is 200 nm; b is 100 nm;

[0034] Figure 9 Electrochemical performance test result graph of the CR2032 button cell in Comparative Example 1;

[0035] Figure 10 SEM image of NC in Comparative Example 2; wherein, a is 200 nm; b is 100 nm;

[0036] Figure 11 Electrochemical performance test result graph of the CR2032 button cell in Comparative Example 2. DETAILED DESCRIPTION

[0037] The technical solutions of the present application are 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 application and are not used to limit the scope of the present application, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application are equivalent replacement ways, and are all included in the protection scope of the present application. In addition, it should be understood that after reading the content of the present application, those skilled in the art can make various modifications or modifications to the present application, and these equivalent forms also fall within the scope defined by the claims attached to the present application, and are within the protection scope of the present application.

[0038] In this paper, the term "example" means that the specific features, structures or characteristics described in conjunction with the example can be included in at least one example of the present application. The term "example" appearing at various places in the specification does not necessarily refer to the same example, nor does it particularly limit its independence or association with other examples. In principle, in the present application, as long as there is no technical contradiction or conflict, each technical feature mentioned in each example can be combined in any way to form a corresponding implementable technical solution.

[0039] Unless otherwise defined, the meanings of technical terms used in the present application are the same as commonly understood by one of ordinary skill in the art to which the present application belongs; the use of related terms herein is merely to describe specific embodiments and is not intended to limit the present application.

[0040] Unless otherwise specified, the reagents, instruments, equipment and performance test methods used in the present application are the reagents, instruments, equipment and methods commonly used by those skilled in the art.

[0041] Example 1

[0042] A preparation method of a ferrophosphorus modified nitrogen and phosphorus co-doped hollow cubic carbon material includes the following steps:

[0043] 1) 16 mg of cetyltrimethylammonium bromide (CTAB) is added to 32 mL of deionized water, thoroughly dissolved, and then 0.98 g of zinc nitrate hexahydrate and 0.0173 g of ferric nitrate nonahydrate are added. Subsequently, 13.14 g of 2-methylimidazole is dissolved in 224 mL of deionized water, quickly poured into the above solution, and stirred quickly for 2 hours. After the reaction is completed, centrifugation and washing are performed, and finally drying is performed to obtain ZnFe-ZIFs-75 with a cubic structure.

[0044] 2) 450 uL of phytic acid (PA) is added to 100 mL of methanol, mixed thoroughly, and then the ZnFe-ZIFs-75 precursor is added to the solution and stirred for 30 min. After the reaction is completed, centrifugation and washing are performed with methanol and drying is performed at 80°C to obtain PA / HZnFe-ZIFs-75 with a hollow cubic structure.

[0045] 3) The PA / HZnFe-ZIFs-75 is placed in a tube furnace, heated to 900°C at a heating rate of 3°C / min under an argon atmosphere, and held for 2 h, and then naturally cooled to room temperature to obtain the ferrophosphorus modified nitrogen and phosphorus co-doped hollow cubic carbon material (denoted as Fe2P / NPHC-75).

[0046] The scanning electron microscope (SEM) image and the transmission electron microscope (TEM) image of the Fe2P / NPHC-75 in the present embodiment are as shown in Figure 1 , and the nitrogen adsorption-desorption curve is as shown in Figure 2 . As can be seen from Figure 1 , the Fe2P / NPHC-75 in the present embodiment has a hollow cubic structure, which is beneficial to enhance the loading of sulfur. As can be seen from Figure 2 , the Fe2P / NPHC-75 in the present embodiment has a large specific surface area and a rich microporous / mesoporous structure, which is beneficial to provide space for the accommodation of sulfur and sufficient contact between the electrolyte.

[0047] As Figure 3As shown, a preparation process of a room temperature sodium-sulfur battery positive electrode material is as follows: 0.12 g of the above 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, then transferred to a hydrothermal reaction kettle, heated to 155℃, and kept for 12 h, and then naturally cooled to room temperature to obtain the room temperature sodium-sulfur battery positive electrode material.

[0048] The thermogravimetric analysis (TGA) curve of the room temperature sodium-sulfur battery positive electrode material prepared in this example is shown in Figure 4 Figure 4 It can be known that the sulfur content in the room temperature sodium-sulfur battery positive electrode material is 52wt%.

[0049] A preparation method of a room temperature sodium-sulfur battery is as follows: the above room temperature sodium-sulfur battery positive electrode material is made into a positive electrode sheet, a metal sodium is made into a negative electrode sheet, a sodium perchlorate with a concentration of 1.0 mol / L is dissolved in a mixed solvent of ethylene carbonate / diethyl carbonate (volume ratio 1:1) as an electrolyte, and a CR2032 button cell (i.e. a room temperature sodium-sulfur battery) is assembled in an argon-filled glove box.

[0050] The electrochemical performance test result graph of the CR2032 button cell in this example is shown in Figure 5 Figure 5 It can be known that the CR2032 button cell in this example exhibits good rate performance, and even at a high discharge rate of 10C, a discharge specific capacity as high as 370.8mAh / g -1 can still be achieved.

[0051] Example 2

[0052] A preparation method of a ferrous phosphide modified nitrogen and phosphorus co-doped hollow cubic carbon material includes the following steps:

[0053] 1) 16 mg of cetyltrimethylammonium bromide (CTAB) is added to 32 mL of deionized water, thoroughly dissolved, and then 0.98 g of zinc nitrate hexahydrate and 0.0259 g of ferric nitrate nonahydrate are added. Subsequently, 13.14 g of 2-methylimidazole is dissolved in 224 mL of deionized water, quickly poured into the above solution, and quickly stirred for 2 hours. After the reaction is completed, several centrifugations and washings are performed, and finally the cubic structure ZnFe-ZIFs-50 is obtained by drying.

[0054] 2) 450 uL of phytic acid (PA) is added to 100 mL of methanol, mixed thoroughly, and then the ZnFe-ZIFs-50 precursor is added to the solution and stirred for 30 min. After the reaction is completed, the PA / HZnFe-ZIFs-50 with a hollow cubic structure is obtained by centrifugal washing with methanol and drying at 80℃. ​​

[0055] 3) Put PA / HZnFe-ZIFs-50 into a tube furnace, and heat to 900℃ at a heating rate of 3℃ / min under argon atmosphere, keep for 2h, and then cool to room temperature naturally to obtain phosphorous ferrous modified nitrogen and phosphorous co-doped hollow cubic carbon material (denoted as Fe2P / NPHC-50).

[0056] The SEM image of Fe2P / NPHC-50 in this example is shown in Figure 6 It can be seen from Figure 6 that the Fe2P / NPHC-50 in this example has a hollow cubic structure.

[0057] The room temperature sodium-sulfur battery positive electrode material was prepared according to the method of Example 1, and a CR2032 button cell (i.e. room temperature sodium-sulfur battery) was assembled. The electrochemical performance test results of the CR2032 button cell in this example are shown in Figure 7 It can be seen from Figure 7 that the CR2032 button cell in this example has good rate performance, and can release a high discharge specific capacity of 292.1 mAh / g at a discharge rate of 10C. -1

[0058] Example 3

[0059] The difference between this example and Example 1 is only that the amount of 2-methylimidazole used in the preparation of phosphorous ferrous modified nitrogen and phosphorous co-doped hollow cubic carbon material is 6.57g in step 1), and the rest is the same as Example 1, which is not repeated here. The carbon material prepared in this example also has a hollow cubic structure, similar to Example 1.

[0060] The room temperature sodium-sulfur battery positive electrode material was prepared according to the method of Example 1, and a CR2032 button cell (i.e. room temperature sodium-sulfur battery) was assembled. The performance of the CR2032 button cell assembled in this example is close to that of the CR2032 button cell assembled in Example 1 after testing.

[0061] Example 4

[0062] The difference between this example and Example 2 is only that the amount of 2-methylimidazole used in the preparation of phosphorous ferrous modified nitrogen and phosphorous co-doped hollow cubic carbon material is 6.57g in step 1), and the rest is the same as Example 2, which is not repeated here. The carbon material prepared in this example also has a hollow cubic structure, similar to Example 2.

[0063] The room temperature sodium-sulfur battery positive electrode material was prepared according to the method of Example 1, and a CR2032 button cell (i.e. room temperature sodium-sulfur battery) was assembled. The performance of the CR2032 button cell assembled in this example is close to that of the CR2032 button cell assembled in Example 2 after testing.​

[0064] Example 5

[0065] The difference between this example and Example 1 is only that in the preparation of ferrous phosphide modified nitrogen and phosphorus co-doped hollow cubic carbon material, the amount of 2-methylimidazole in step 1) is 19.71 g, and the rest is the same as Example 1, which is not repeated here. The carbon material prepared in this example also presents a hollow cubic structure, similar to Example 1.

[0066] The positive electrode material of the room temperature sodium-sulfur battery was prepared according to the method of Example 1, and the CR2032 button cell (i.e. room temperature sodium-sulfur battery) was assembled. After testing, the performance of the CR2032 button cell assembled in this example is close to that of the CR2032 button cell assembled in Example 1.

[0067] Example 6

[0068] The difference between this example and Example 2 is only that in the preparation of ferrous phosphide modified nitrogen and phosphorus co-doped hollow cubic carbon material, the amount of 2-methylimidazole in step 1) is 19.71 g, and the rest is the same as Example 2, which is not repeated here. The carbon material prepared in this example also presents a hollow cubic structure, similar to Example 2.

[0069] The positive electrode material of the room temperature sodium-sulfur battery was prepared according to the method of Example 1, and the CR2032 button cell (i.e. room temperature sodium-sulfur battery) was assembled. After testing, the performance of the CR2032 button cell assembled in this example is close to that of the CR2032 button cell assembled in Example 2.

[0070] Example 7

[0071] The difference between this example and Example 1 is only that in the preparation of ferrous phosphide modified nitrogen and phosphorus co-doped hollow cubic carbon material, the reaction time in step 1) is 1 hour, and the rest is the same as Example 1, which is not repeated here. The carbon material prepared in this example also presents a hollow cubic structure, similar to Example 1.

[0072] The positive electrode material of the room temperature sodium-sulfur battery was prepared according to the method of Example 1, and the CR2032 button cell (i.e. room temperature sodium-sulfur battery) was assembled. After testing, the performance of the CR2032 button cell assembled in this example is close to that of the CR2032 button cell assembled in Example 1.

[0073] Example 8

[0074] The difference between this example and Example 2 is only that, in the preparation of ferrous phosphide modified nitrogen and phosphorus co-doped hollow cubic carbon material, the reaction time in step 1) is 1 hour, and the rest is the same as Example 2, which is not repeated here. The carbon material prepared in this example also presents a hollow cubic structure, similar to Example 2.

[0075] The room temperature sodium-sulfur battery positive electrode material was prepared and CR2032 button cell (i.e. room temperature sodium-sulfur battery) was assembled according to the method of Example 1. After testing, the performance of the CR2032 button cell assembled in this example is close to that of the CR2032 button cell assembled in Example 2.

[0076] Example 9

[0077] The difference between this example and Example 1 is only that, in the preparation of ferrous phosphide modified nitrogen and phosphorus co-doped hollow cubic carbon material, the reaction time in step 1) is 3 hours, and the rest is the same as Example 1, which is not repeated here. The carbon material prepared in this example also presents a hollow cubic structure, similar to Example 1.

[0078] The room temperature sodium-sulfur battery positive electrode material was prepared and CR2032 button cell (i.e. room temperature sodium-sulfur battery) was assembled according to the method of Example 1. After testing, the performance of the CR2032 button cell assembled in this example is close to that of the CR2032 button cell assembled in Example 1.

[0079] Example 10

[0080] The difference between this example and Example 2 is only that, in the preparation of ferrous phosphide modified nitrogen and phosphorus co-doped hollow cubic carbon material, the reaction time in step 1) is 3 hours, and the rest is the same as Example 2, which is not repeated here. The carbon material prepared in this example also presents a hollow cubic structure, similar to Example 2.

[0081] The room temperature sodium-sulfur battery positive electrode material was prepared and CR2032 button cell (i.e. room temperature sodium-sulfur battery) was assembled according to the method of Example 1. After testing, the performance of the CR2032 button cell assembled in this example is close to that of the CR2032 button cell assembled in Example 2.

[0082] Example 11

[0083] The difference between this example and Example 1 is only that, in the preparation of ferrous phosphide modified nitrogen and phosphorus co-doped hollow cubic carbon material, 0.4362 g of zinc chloride is used instead of 0.98 g of zinc nitrate hexahydrate in step 1), and the rest is the same as Example 1, which is not repeated here. The carbon material prepared in this example also presents a hollow cubic structure, similar to Example 1.

[0084] A positive electrode material for a room-temperature sodium-sulfur battery and a CR2032 button cell (i.e., a room-temperature sodium-sulfur battery) were prepared according to the method of Example 1. The performance of the CR2032 button cell assembled in this example was close to that of the CR2032 button cell assembled in Example 1.

[0085] Example 12

[0086] The difference between this example and Example 2 is only that 0.4362 g of zinc chloride was used instead of 0.98 g of zinc nitrate hexahydrate in step 1) when preparing the ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material, and the rest was the same as in Example 2, which is not repeated here. The carbon material prepared in this example also exhibited a hollow cubic structure, similar to Example 2.

[0087] A positive electrode material for a room-temperature sodium-sulfur battery and a CR2032 button cell (i.e., a room-temperature sodium-sulfur battery) were prepared according to the method of Example 1. The performance of the CR2032 button cell assembled in this example was close to that of the CR2032 button cell assembled in Example 2.

[0088] Example 13

[0089] The difference between this example and Example 1 is only that 0.5166 g of zinc sulfate was used instead of 0.98 g of zinc nitrate hexahydrate in step 1) when preparing the ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material, and the rest was the same as in Example 1, which is not repeated here. The carbon material prepared in this example also exhibited a hollow cubic structure, similar to Example 1.

[0090] A positive electrode material for a room-temperature sodium-sulfur battery and a CR2032 button cell (i.e., a room-temperature sodium-sulfur battery) were prepared according to the method of Example 1. The performance of the CR2032 button cell assembled in this example was close to that of the CR2032 button cell assembled in Example 1.

[0091] Example 14

[0092] The difference between this example and Example 2 is only that 0.5166 g of zinc sulfate was used instead of 0.98 g of zinc nitrate hexahydrate in step 1) when preparing the ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material, and the rest was the same as in Example 2, which is not repeated here. The carbon material prepared in this example also exhibited a hollow cubic structure, similar to Example 2.

[0093] A positive electrode material for a room-temperature sodium-sulfur battery and a CR2032 button cell (i.e., a room-temperature sodium-sulfur battery) were prepared according to the method of Example 1. The performance of the CR2032 button cell assembled in this example was close to that of the CR2032 button cell assembled in Example 2.

[0094] Example 15

[0095] The difference between this example and Example 1 is only that, in the preparation of ferrous phosphide modified nitrogen and phosphorus co-doped hollow cubic carbon material, 0.0116 g of ferric chloride hexahydrate is used instead of 0.0173 g of ferric nitrate nonahydrate in step 1), and the rest is the same as Example 1, which is not repeated here. The carbon material prepared in this example also presents a hollow cubic structure, similar to Example 1.

[0096] The room temperature sodium-sulfur battery positive electrode material is prepared and the CR2032 button cell (i.e. room temperature sodium-sulfur battery) is assembled according to the method of Example 1. After testing, the performance of the CR2032 button cell assembled in this example is close to that of the CR2032 button cell assembled in Example 1.

[0097] Example 16

[0098] The difference between this example and Example 2 is only that, in the preparation of ferrous phosphide modified nitrogen and phosphorus co-doped hollow cubic carbon material, 0.0173 g of ferric chloride hexahydrate is used instead of 0.0259 g of ferric nitrate nonahydrate in step 1), and the rest is the same as Example 2, which is not repeated here. The carbon material prepared in this example also presents a hollow cubic structure, similar to Example 2.

[0099] The room temperature sodium-sulfur battery positive electrode material is prepared and the CR2032 button cell (i.e. room temperature sodium-sulfur battery) is assembled according to the method of Example 1. After testing, the performance of the CR2032 button cell assembled in this example is close to that of the CR2032 button cell assembled in Example 2.

[0100] Example 17

[0101] The difference between this example and Example 1 is only that, in the preparation of ferrous phosphide modified nitrogen and phosphorus co-doped hollow cubic carbon material, 0.0073 g of ferric sulfate hydrate is used instead of 0.0173 g of ferric nitrate nonahydrate in step 1), and the rest is the same as Example 1, which is not repeated here. The carbon material prepared in this example also presents a hollow cubic structure, similar to Example 1.

[0102] The room temperature sodium-sulfur battery positive electrode material is prepared and the CR2032 button cell (i.e. room temperature sodium-sulfur battery) is assembled according to the method of Example 1. After testing, the performance of the CR2032 button cell assembled in this example is close to that of the CR2032 button cell assembled in Example 1.

[0103] Example 18

[0104] The difference between this example and Example 2 is only that, in the preparation of the ferrous phosphide modified nitrogen and phosphorus co-doped hollow cubic carbon material, 0.0109 g of iron sulfate hydrate is used instead of 0.0259 g of iron nitrate nonahydrate in step 1), and the rest is the same as Example 2, which is not repeated here. The carbon material prepared in this example also presents a hollow cubic structure, similar to Example 2.

[0105] The room temperature sodium-sulfur battery positive electrode material is prepared and the CR2032 button cell (i.e. room temperature sodium-sulfur battery) is assembled according to the method of Example 1. After testing, the performance of the CR2032 button cell assembled in this example is close to that of the CR2032 button cell assembled in Example 2.

[0106] Example 19

[0107] The difference between this example and Example 1 is only that, in the preparation of the ferrous phosphide modified nitrogen and phosphorus co-doped hollow cubic carbon material, the acid amount is 350 μL in step 2), and the rest is the same as Example 1, which is not repeated here. The carbon material prepared in this example also presents a hollow cubic structure, similar to Example 1.

[0108] The room temperature sodium-sulfur battery positive electrode material is prepared and the CR2032 button cell (i.e. room temperature sodium-sulfur battery) is assembled according to the method of Example 1. After testing, the performance of the CR2032 button cell assembled in this example is close to that of the CR2032 button cell assembled in Example 1.

[0109] Example 20

[0110] The difference between this example and Example 2 is only that, in the preparation of the ferrous phosphide modified nitrogen and phosphorus co-doped hollow cubic carbon material, the acid amount is 350 μL in step 2), and the rest is the same as Example 2, which is not repeated here. The carbon material prepared in this example also presents a hollow cubic structure, similar to Example 2.

[0111] The room temperature sodium-sulfur battery positive electrode material is prepared and the CR2032 button cell (i.e. room temperature sodium-sulfur battery) is assembled according to the method of Example 1. After testing, the performance of the CR2032 button cell assembled in this example is close to that of the CR2032 button cell assembled in Example 2.

[0112] Example 21

[0113] The difference between this example and Example 1 is only that, in the preparation of the ferrous phosphide modified nitrogen and phosphorus co-doped hollow cubic carbon material, the acid amount is 550 μL in step 2), and the rest is the same as Example 1, which is not repeated here. The carbon material prepared in this example also presents a hollow cubic structure, similar to Example 1.

[0114] A positive electrode material for a room-temperature sodium-sulfur battery and a CR2032 button cell (i.e., a room-temperature sodium-sulfur battery) were prepared according to the method of Example 1. The performance of the CR2032 button cell assembled in this example was close to that of the CR2032 button cell assembled in Example 1.

[0115] Example 22

[0116] The difference between this example and Example 2 is only that, in the preparation of the ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material, the acid dosage in step 2) is 550 μL, and the rest is the same as Example 2, which is not repeated here. The carbon material prepared in this example also presents a hollow cubic structure, similar to Example 2.

[0117] A positive electrode material for a room-temperature sodium-sulfur battery and a CR2032 button cell (i.e., a room-temperature sodium-sulfur battery) were prepared according to the method of Example 1. The performance of the CR2032 button cell assembled in this example was close to that of the CR2032 button cell assembled in Example 2.

[0118] Example 23

[0119] The difference between this example and Example 1 is only that, in the preparation of the ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material, the etching time in step 2) is 20 min, and the rest is the same as Example 1, which is not repeated here. The carbon material prepared in this example also presents a hollow cubic structure, similar to Example 1.

[0120] A positive electrode material for a room-temperature sodium-sulfur battery and a CR2032 button cell (i.e., a room-temperature sodium-sulfur battery) were prepared according to the method of Example 1. The performance of the CR2032 button cell assembled in this example was close to that of the CR2032 button cell assembled in Example 1.

[0121] Example 24

[0122] The difference between this example and Example 2 is only that, in the preparation of the ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material, the etching time in step 2) is 20 min, and the rest is the same as Example 2, which is not repeated here. The carbon material prepared in this example also presents a hollow cubic structure, similar to Example 2.

[0123] A positive electrode material for a room-temperature sodium-sulfur battery and a CR2032 button cell (i.e., a room-temperature sodium-sulfur battery) were prepared according to the method of Example 1. The performance of the CR2032 button cell assembled in this example was close to that of the CR2032 button cell assembled in Example 2.

[0124] Example 25

[0125] The difference between this example and Example 1 is only that, in the preparation of ferrous phosphide modified nitrogen and phosphorus co-doped hollow cubic carbon material, the etching time in step 2) is 40 min, and the rest is the same as Example 1, which is not repeated here. The carbon material prepared in this example also presents a hollow cubic structure, similar to Example 1.

[0126] The positive electrode material of the room temperature sodium-sulfur battery and the CR2032 button cell (i.e. room temperature sodium-sulfur battery) were prepared according to the method of Example 1. After testing, the performance of the CR2032 button cell assembled in this example was close to that of the CR2032 button cell assembled in Example 1.

[0127] Example 26

[0128] The difference between this example and Example 2 is only that, in the preparation of ferrous phosphide modified nitrogen and phosphorus co-doped hollow cubic carbon material, the etching time in step 2) is 40 min, and the rest is the same as Example 2, which is not repeated here. The carbon material prepared in this example also presents a hollow cubic structure, similar to Example 2.

[0129] The positive electrode material of the room temperature sodium-sulfur battery and the CR2032 button cell (i.e. room temperature sodium-sulfur battery) were prepared according to the method of Example 1. After testing, the performance of the CR2032 button cell assembled in this example was close to that of the CR2032 button cell assembled in Example 2.

[0130] Example 27

[0131] The difference between this example and Example 1 is only that, in the preparation of ferrous phosphide modified nitrogen and phosphorus co-doped hollow cubic carbon material, nitrogen gas is used instead of argon gas as inert atmosphere in step 3), and the rest is the same as Example 1, which is not repeated here. The carbon material prepared in this example also presents a hollow cubic structure, similar to Example 1.

[0132] The positive electrode material of the room temperature sodium-sulfur battery and the CR2032 button cell (i.e. room temperature sodium-sulfur battery) were prepared according to the method of Example 1. After testing, the performance of the CR2032 button cell assembled in this example was close to that of the CR2032 button cell assembled in Example 1.

[0133] Example 28

[0134] The difference between this example and Example 2 is only that, in the preparation of ferrous phosphide modified nitrogen and phosphorus co-doped hollow cubic carbon material, nitrogen gas is used instead of argon gas as inert atmosphere in step 3), and the rest is the same as Example 2, which is not repeated here. The carbon material prepared in this example also presents a hollow cubic structure, similar to Example 2.

[0135] A room-temperature sodium-sulfur battery cathode material was prepared and a CR2032 button cell (i.e., a room-temperature sodium-sulfur battery) was assembled according to the method of Example 1. The performance of the CR2032 button cell assembled in this example was close to that of the CR2032 button cell assembled in Example 1.

[0136] Example 29

[0137] The difference between this example and Example 1 is only that, in the preparation of ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material, the carbonization temperature in step 3) is 850°C, and the rest is the same as Example 1, which is not repeated here. The carbon material prepared in this example also presents a hollow cubic structure, similar to Example 1.

[0138] A room-temperature sodium-sulfur battery cathode material was prepared and a CR2032 button cell (i.e., a room-temperature sodium-sulfur battery) was assembled according to the method of Example 1. The performance of the CR2032 button cell assembled in this example was close to that of the CR2032 button cell assembled in Example 1.

[0139] Example 30

[0140] The difference between this example and Example 2 is only that, in the preparation of ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material, the carbonization temperature in step 3) is 850°C, and the rest is the same as Example 2, which is not repeated here. The carbon material prepared in this example also presents a hollow cubic structure, similar to Example 2.

[0141] A room-temperature sodium-sulfur battery cathode material was prepared and a CR2032 button cell (i.e., a room-temperature sodium-sulfur battery) was assembled according to the method of Example 1. The performance of the CR2032 button cell assembled in this example was close to that of the CR2032 button cell assembled in Example 1.

[0142] Example 31

[0143] The difference between this example and Example 1 is only that, in the preparation of ferrous phosphide-modified nitrogen-phosphorus co-doped hollow cubic carbon material, the carbonization temperature in step 3) is 950°C, and the rest is the same as Example 1, which is not repeated here. The carbon material prepared in this example also presents a hollow cubic structure, similar to Example 1.

[0144] A room-temperature sodium-sulfur battery cathode material was prepared and a CR2032 button cell (i.e., a room-temperature sodium-sulfur battery) was assembled according to the method of Example 1. The performance of the CR2032 button cell assembled in this example was close to that of the CR2032 button cell assembled in Example 1.

[0145] Example 32

[0146] The difference between this embodiment and embodiment 2 is only that, in the preparation of ferrous phosphide modified nitrogen and phosphorus co-doped hollow cubic carbon material, the carbonization temperature in step 3) is 950℃, and the rest is the same as embodiment 2, which is not repeated here. The carbon material prepared in this embodiment also presents a hollow cubic structure, similar to embodiment 2.

[0147] The room temperature sodium-sulfur battery positive electrode material was prepared and CR2032 button cell (i.e. room temperature sodium-sulfur battery) was assembled according to the method of embodiment 1. After testing, the performance of the CR2032 button cell assembled in this embodiment was close to that of the CR2032 button cell assembled in embodiment 1.

[0148] Embodiment 33

[0149] The difference between this embodiment and embodiment 1 is only that, in the preparation of ferrous phosphide modified nitrogen and phosphorus co-doped hollow cubic carbon material, the holding time in step 3) is 1 hour, and the rest is the same as embodiment 1, which is not repeated here. The carbon material prepared in this embodiment also presents a hollow cubic structure, similar to embodiment 1.

[0150] The room temperature sodium-sulfur battery positive electrode material was prepared and CR2032 button cell (i.e. room temperature sodium-sulfur battery) was assembled according to the method of embodiment 1. After testing, the performance of the CR2032 button cell assembled in this embodiment was close to that of the CR2032 button cell assembled in embodiment 1.

[0151] Embodiment 34

[0152] The difference between this embodiment and embodiment 2 is only that, in the preparation of ferrous phosphide modified nitrogen and phosphorus co-doped hollow cubic carbon material, the holding time in step 3) is 1 hour, and the rest is the same as embodiment 2, which is not repeated here. The carbon material prepared in this embodiment also presents a hollow cubic structure, similar to embodiment 2.

[0153] The room temperature sodium-sulfur battery positive electrode material was prepared and CR2032 button cell (i.e. room temperature sodium-sulfur battery) was assembled according to the method of embodiment 1. After testing, the performance of the CR2032 button cell assembled in this embodiment was close to that of the CR2032 button cell assembled in embodiment 2.

[0154] Embodiment 35

[0155] The difference between this embodiment and embodiment 1 is only that, in the preparation of ferrous phosphide modified nitrogen and phosphorus co-doped hollow cubic carbon material, the holding time in step 3) is 3 hours, and the rest is the same as embodiment 1, which is not repeated here. The carbon material prepared in this embodiment also presents a hollow cubic structure, similar to embodiment 1.

[0156] The positive electrode material of the 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. It was tested that the performance of the CR2032 button cell assembled in this example was close to that of the CR2032 button cell assembled in Example 1.

[0157] Example 36

[0158] The difference between this example and Example 2 is only that the holding time in step 3) is 3 hours when preparing the ferrous phosphide modified nitrogen and phosphorus co-doped hollow cubic carbon material, and the rest is the same as Example 2, which is not repeated here. The carbon material prepared in this example also presents a hollow cubic structure, similar to Example 2.

[0159] The positive electrode material of the 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. It was tested that the performance of the CR2032 button cell assembled in this example was close to that of the CR2032 button cell assembled in Example 2.

[0160] Example 37

[0161] The difference between this example and Example 1 is only that the heating rate in step 3) is 5℃ / min when preparing the ferrous phosphide modified nitrogen and phosphorus co-doped hollow cubic carbon material, and the rest is the same as Example 1, which is not repeated here. The carbon material prepared in this example also presents a hollow cubic structure, similar to Example 1.

[0162] The positive electrode material of the 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. It was tested that the performance of the CR2032 button cell assembled in this example was close to that of the CR2032 button cell assembled in Example 1.

[0163] Example 38

[0164] The difference between this example and Example 2 is only that the heating rate in step 3) is 5℃ / min when preparing the ferrous phosphide modified nitrogen and phosphorus co-doped hollow cubic carbon material, and the rest is the same as Example 2, which is not repeated here. The carbon material prepared in this example also presents a hollow cubic structure, similar to Example 2.

[0165] The positive electrode material of the 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. It was tested that the performance of the CR2032 button cell assembled in this example was close to that of the CR2032 button cell assembled in Example 2.

[0166] Comparative Example 1

[0167] A preparation method of a nitrogen and phosphorus co-doped hollow cubic carbon material comprises the following steps:

[0168] 1) 16 mg of cetyltrimethylammonium bromide (CTAB) was added to 32 mL of deionized water, and after complete dissolution, 0.98 g of zinc nitrate hexahydrate was added. Subsequently, 13.14 g of 2-methylimidazole was dissolved in 224 mL of deionized water, and the above solution was quickly mixed and stirred for 2 hours. After several centrifugations, washings and drying, a cubic structure of Zn-ZIF was obtained.

[0169] 2) 450 uL of phytic acid (PA) was added to 100 mL of methanol and mixed thoroughly. Subsequently, the ZnFe-ZIFs-75 precursor was added to the solution and stirred for 30 min. After the reaction was completed, the PA / HZn-ZIFs with a hollow cubic structure were obtained by centrifugal washing with methanol and drying at 80°C.

[0170] 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, and then naturally cooled to room temperature to obtain the ferrous phosphide modified nitrogen and phosphorus co-doped hollow cubic carbon material (denoted as NPHC).

[0171] The SEM image of the NPHC in the present comparative example is shown in Figure 8 . It can be seen from Figure 8 that the NPHC in the present comparative example has a hollow cubic structure.

[0172] A room-temperature sodium-sulfur battery positive electrode material was prepared by the method of Reference Example 1, and a CR2032 button cell (i.e., a room-temperature sodium-sulfur battery) was assembled. The test result graph of the electrochemical performance of the CR2032 button cell is shown in Figure 9 . It can be seen from Figure 9 that the rate performance of the room-temperature sodium-sulfur battery is poor, and the specific discharge capacity is only 207.2 mAh / g -1 at a discharge rate of 10C.

[0173] Comparative Example 2

[0174] A preparation method of a nitrogen-doped porous carbon material comprises the following steps:

[0175] 1) 16 mg of cetyltrimethylammonium bromide (CTAB) was added to 32 mL of deionized water, and after complete dissolution, 0.98 g of zinc nitrate hexahydrate was added. Subsequently, 13.14 g of 2-methylimidazole was dissolved in 224 mL of deionized water, and the above solution was quickly mixed and stirred for 2 hours. After several centrifugations, washings and drying, a cubic structure of Zn-ZIF was obtained.

[0176] 2) The Zn-ZIF was placed in a tube furnace and heated to 900℃ at a heating rate of 3℃ / min under argon atmosphere, and kept for 2h, and then naturally cooled to room temperature to obtain phosphorous iron modified nitrogen and phosphorous co-doped hollow cubic carbon material (denoted as NC).

[0177] The SEM image of NC in the present comparative example is shown in Figure 10 It can be seen from Figure 10 that the NC in the present comparative example presents a cubic structure with smooth surface.

[0178] The room temperature sodium-sulfur battery cathode material was prepared by the method of Example 1 and CR2032 button cell (i.e. room temperature sodium-sulfur battery) was assembled. The results of electrochemical performance test of CR2032 button cell are shown in Figure 11 It can be seen from Figure 11 that the room temperature sodium-sulfur battery has poor rate performance, and the discharge specific capacity is only 78mAh / g -1 at a discharge rate of 10C.

[0179] It can be seen from the SEM images of Example 1, 2 and Comparative Example 1, 2 that the Fe2P / NPHC material presents a hollow cubic structure, while the NC material of Comparative Example 2 is a solid cubic structure. This hollow structure provides more space for the loading of sulfur and can adapt to the volume expansion during charge and discharge, thus being beneficial to improve the performance of the battery. For example, the Fe2P / NPHC-75 of Example 1 can still achieve a discharge specific capacity of 370.8mAh / g -1 at a high discharge rate of 10C, while the discharge specific capacity of the NC material of Comparative Example 2 is only 78mAh / g -1 at 10C, which fully demonstrates the positive effect of the hollow structure on the performance.

[0180] The nitrogen adsorption-desorption curve of Example 1 shows that the Fe2P / NPHC-75 has a large specific surface area and rich microporous / mesoporous structure. This enables the material to be in full contact with the electrolyte, promotes the transmission of ions and electrons, and thus improves the utilization of sulfur and the reaction kinetics of the battery. By contrast, the surface of the NC material of Comparative Example 2 is smooth and has less pore structure, resulting in poor electrochemical performance.

[0181] The NPHC material of Comparative Example 1 (without Fe 2+ doping, only N / P co-doping) has a discharge specific capacity of 207.2mAh / g -1 at 10C, while the Fe2P / NPHC-75 of Example 1 (N / P co-doping and Fe2P modification) has a specific capacity of 370.8mAh / g -1This indicates that nitrogen and phosphorus co-doping can effectively increase the chemical adsorption capacity of the carbon material to 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 rich active sites for the adsorption and catalytic conversion of polysulfides, accelerating the reaction kinetics process. The comparison of Example 1 and Comparative Example 1 fully proves this point, and the modification of Fe2P makes the electrochemical performance of the material significantly improved.

[0182] In summary, the synergistic effect of the hollow cubic structure of the Fe2P / NPHC material, nitrogen and phosphorus co-doping, and ferrous phosphide modification, as well as the optimized preparation process parameters, together make the material exhibit excellent performance in room temperature sodium-sulfur batteries, and have good application prospects.

[0183] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application but not to limit it, although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that: it can still modify or equivalently replace the technical solutions of the present application, and these modifications or equivalent replacements also cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present application.

Claims

1. Use of nitrogen and phosphorus co-doped hollow cubic carbon material in the preparation of a positive electrode material for a room-temperature sodium-sulfur battery, characterized in that, The preparation of the nitrogen and phosphorus co-doped hollow cubic carbon material comprises 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 1-3 hours to obtain ZnFe-ZIFs precursor with a cubic structure; 2) Mix phytic acid in methanol, then add ZnFe-ZIFs precursor, and stir to carry out etching reaction for 20-40 minutes to obtain PA / HZnFe-ZIFs with a hollow cubic structure; 3) Place the PA / HZnFe-ZIFs in an inert atmosphere for carbonization treatment, and obtain the nitrogen and phosphorus co-doped hollow cubic carbon material modified by ferrous phosphide after cooling. 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. In step 2), the volume ratio of phytic acid to methanol is 1:180-1:

280. 2.The use of the nitrogen and phosphorus co-doped hollow cubic carbon material according to claim 1 in the preparation of a positive electrode material for a room-temperature sodium-sulfur battery, 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 ferric nitrate, ferric sulfate and ferric chloride. 3.The application of the nitrogen and phosphorus co-doped hollow cubic carbon material in the preparation of a cathode material for a room-temperature sodium-sulfur battery according to claim 1, characterized in that: In step 3), the specific operation of the carbonization treatment is to heat to 850-950℃ at a heating rate of 3-5℃ / min, and keep the temperature for 1-3 hours; and the inert atmosphere is one of argon and nitrogen. 4.The application of the nitrogen and phosphorus co-doped hollow cubic carbon material in the preparation of a cathode material for a room-temperature sodium-sulfur battery according to claim 1, characterized in that, The preparation process of the room-temperature sodium-sulfur battery positive electrode material is as follows: disperse the nitrogen and phosphorus co-doped hollow cubic carbon material and sublimed sulfur in carbon disulfide, grind until the carbon disulfide volatilizes, then heat the mixture and keep the temperature to obtain the room-temperature sodium-sulfur battery positive electrode material.

5. The use of the nitrogen and phosphorus co-doped hollow cubic carbon material according to claim 4 in the preparation of a positive electrode material for a room-temperature sodium-sulfur battery, characterized in that: The mass ratio of the nitrogen and phosphorus co-doped hollow cubic carbon material to sublimed sulfur is 1:1.2-1:2.0; the heating temperature is 150-160℃, and the holding time is 6-12 hours.

6. A room temperature sodium-sulfur battery characterized by The positive electrode of the battery comprises the room-temperature sodium-sulfur battery positive electrode material according to any one of claims 1-5.

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