A high volume specific capacity sodium ion capacitor carbon positive electrode material and a preparation method and application thereof

Abstract

The application relates to a preparation method of a high-volume specific capacity sodium ion capacitor carbon positive electrode material, which comprises the following steps: mixing rose bengal acid disodium salt and melamine, reacting in a protective gas atmosphere by being heated to a carbonization temperature to obtain a carbonization product; adding dilute hydrochloric acid into the carbonization product to perform acid washing, then performing solid-liquid separation, washing the solid with deionized water until neutral, drying the solid product to obtain the carbon positive electrode material; wherein the mass ratio of the rose bengal acid disodium salt and the melamine is 1:0.3-0.55; by adding melamine in the carbonization process of the carbon source, the specific surface area of the carbon material is reduced, and the activity of the carbon material surface is increased, so that the obtained nitrogen-doped carbon positive electrode material has low specific surface area, low pore volume, high tap density and rich active groups, is applied to a sodium ion capacitor, and exhibits excellent electrochemical performance.

Description

Technical Field

[0001] The present invention relates to the field of sodium ion capacitor positive electrode materials, and more specifically, to a high volume ratio sodium ion capacitor carbon positive electrode material, a preparation method thereof, and applications thereof. Background Art

[0002] Sodium ion capacitors (SICs) are usually composed of a battery-type negative electrode and a capacitor-type positive electrode. They have the characteristics of high energy density of sodium ion batteries (SIBs) and high power density of supercapacitors (SCs), and are a promising technology for the future. At present, in many practical applications, the volumetric energy density (E vol ) has become a key evaluation indicator, which in turn depends on the volume performance of the electrode used in the battery. Due to the differences in energy storage mechanism and material structure between battery-type negative electrode and capacitor-type positive electrode, the volumetric capacity (C vol ) is much higher than that of the capacitor-type positive electrode. In order to match the capacity of the battery-type negative electrode, the carbon positive electrode needs a larger volume to compensate for its lower C vol , which will inevitably lead to an increase in the total volume of SICs, thereby significantly reducing the energy density (E vol ). Therefore, from formula C vol =C wt ×ρ, it can be seen that increasing the mass specific capacity of the carbon cathode (C wt ) and density (ρ), reducing the volumetric capacity (C vol ) gap, it is important to improve the energy density of SICs (E vol ) is crucial.

[0003] The pore structure and surface chemical properties are the factors that affect the carbon material C wt The large specific surface area and pore volume can provide a large number of sites for the reversible adsorption of ions, which is beneficial to improve C wt However, the loose porous structure will reduce the ρ of the material, resulting in C vol Lowering the specific surface area of ​​carbon materials is beneficial for increasing ρ, but it will lead to a decrease in the double-layer specific capacity of the electrode. In recent years, researchers have discovered that some functional groups such as carbonyl and pyrrole can provide additional specific capacity to the carbon cathode through redox reactions during electrochemical processes. Therefore, reducing the specific surface area of ​​porous carbon while increasing its surface active sites is an effective solution to this problem. Summary of the Invention

[0004] Based on the technical problems existing in the prior art, the present invention adds melamine during the carbonization process of the carbon source to reduce the specific surface area of ​​the carbon material and increase the activity of the carbon material surface, so that the obtained nitrogen-doped carbon positive electrode material has a low specific surface area, low pore volume, high tap density and rich active groups.

[0005] In order to achieve the above object, the technical solution of the present invention is as follows:

[0006] A method for preparing a carbon positive electrode material for a sodium ion capacitor with high volumetric capacity comprises the following steps:

[0007] Mixing rhodamine disodium salt and melamine, heating to a carbonization temperature in a protective gas atmosphere to react, to obtain a carbonized product; adding dilute hydrochloric acid to the carbonized product for pickling, then performing solid-liquid separation, washing the solid with deionized water until neutral, and drying the solid product to obtain the carbon positive electrode material;

[0008] Wherein, the mass ratio of the disodium salt of rhodamine to melamine is 1:0.3-0.55.

[0009] In some embodiments, the carbonization temperature is 600-1000°C.

[0010] In some embodiments, the temperature is increased to the carbonization temperature at a rate of 1-10° C. / min.

[0011] In some embodiments, the concentration of dilute hydrochloric acid is 0.1-5 mol / L.

[0012] In some embodiments, the acid washing method is specifically as follows: dripping the dilute hydrochloric acid into the carbonized product, stirring evenly, then separating the solid and the liquid, and washing the solid with deionized water until it is neutral.

[0013] In some embodiments, the carbonization reaction time is 0.5-6 hours.

[0014] The present invention also provides a carbon cathode material obtained by the preparation method of any of the above embodiments, wherein the specific surface area of ​​the carbon cathode material is 20-90 m 2 / g, nitrogen content is 16-20at%, and tap density is 0.4-0.81g / cm 3 .

[0015] The present invention also provides a sodium ion capacitor positive electrode, which includes the above-mentioned carbon positive electrode material.

[0016] The present invention also provides a sodium ion capacitor, which includes the above-mentioned positive electrode.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The preparation method of the present invention uses a specific carbon source and a nitrogen source as raw materials, combined with a specific preparation process, so that the prepared nitrogen-doped carbon material has a low specific surface area, low pore volume, high tap density and abundant active groups. When used as a positive electrode material for sodium ion capacitors, the high tap density is conducive to consuming lower solvents (such as NMP) during the preparation of the positive electrode sheet, thereby reducing the preparation cost of the electrode sheet; the low specific surface area and pore volume reduce the decomposition sites of the electrolyte, which is beneficial to the cycle stability of the carbon positive electrode; and the abundant active sites can provide a large amount of specific capacity for the carbon positive electrode through pseudocapacitive reactions. In addition, compared with physical adsorption, chemical adsorption of ions can produce higher capacity. Therefore, converting the behavior of energy storage mainly through the double layer mechanism to the behavior of energy storage mainly through the pseudocapacitive reaction mechanism is conducive to reducing the capacity of the electrolyte, thereby reducing the preparation cost of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a transmission electron microscope image of the nitrogen-doped carbon material of Example 1;

[0020] Figure 2 This is a transmission electron microscope image of the nitrogen-doped carbon material of Example 2;

[0021] Figure 3 Powder X-ray diffraction spectra of nitrogen-doped carbon materials of Examples 1 and 2;

[0022] Figure 4 The nitrogen adsorption-desorption isotherms of the nitrogen-doped carbon materials of Examples 1 and 2;

[0023] Figure 5 The nitrogen doping amount test results of the nitrogen-doped carbon materials prepared in Examples 1-3;

[0024] Figure 6 is the tap density of the nitrogen-doped carbon materials of Examples 1 and 2;

[0025] Figure 7 High-resolution O1s X-ray photoelectron spectra of the nitrogen-doped carbon materials of Examples 1 and 2;

[0026] Figure 8 The half-cells assembled for Examples 1 and 2 were tested at a current density of 0.1 Ag -1 Cyclic stability diagram after 200 cycles;

[0027] Figure 9 Specific capacity diagram of the half-cells assembled in Examples 1 and 2 at different current densities;

[0028] Figure 10 The half-cells assembled in Example 1 were prepared with 1Ag -1 Stability diagram of current density cycled for 1000 cycles;

[0029] Figure 11 The half-cells assembled for Example 2 were 1Ag -1 Stability diagram of current density cycled for 1000 cycles;

[0030] Figure 12 The half-cell assembled for Example 3 was charged with 1Ag -1 Stability diagram of the current density after 1000 cycles. DETAILED DESCRIPTION

[0031] The following description sets forth numerous specific details to facilitate a thorough understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art may make similar modifications without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific implementations disclosed below.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in this specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0033] Example 1

[0034] A method for preparing a nitrogen-doped carbon material comprises the following steps:

[0035] S1. Grind 5 g of rhodendric acid disodium salt and 1.25 g of melamine in a mortar until uniformly distributed. Then, place the mixture in a tube furnace and heat it to 700° C. at a heating rate of 5° C. / min under argon protection at a gas flow rate of 50 mL / min. Maintain the temperature for 2 h, and cool naturally to obtain product A.

[0036] S2. Grind product A evenly and place it in a 500 mL beaker. Then slowly drop 100 mL of 1 M dilute hydrochloric acid into the beaker and stir for 12 h.

[0037] S3. The stirred solution was filtered with a large amount of deionized water until it became neutral, and then added into a vacuum drying oven and dried at 80° C. for 12 h to obtain a nitrogen-doped carbon material.

[0038] Example 2

[0039] A method for preparing a nitrogen-doped carbon material comprises the following steps:

[0040] S1. Grind 5 g of rose bengal sodium salt and 2.50 g of melamine in a mortar, then place in a tube furnace, and heat to 700°C at a heating rate of 5°C / min under argon protection at a gas flow rate of 50 mL / min, and maintain at this temperature for 2 h. After natural cooling, obtain product A;

[0041] S2. Grind product A evenly and place it in a 500 mL beaker. Then slowly drop 100 mL of 1 M dilute hydrochloric acid into the beaker and stir for 12 h.

[0042] S3. The stirred solution was filtered with a large amount of deionized water until it became neutral, and then placed in a vacuum drying oven and dried at 80° C. for 12 h to obtain a nitrogen-doped carbon material.

[0043] Example 3

[0044] A method for preparing a nitrogen-doped carbon material comprises the following steps:

[0045] S1. Grind 5 g of rose bengal sodium salt and 3 g of melamine in a mortar, then place in a tube furnace, and heat to 700°C at a heating rate of 5°C / min under argon protection at a gas flow rate of 50 mL / min, and maintain at this temperature for 2 h. After natural cooling, obtain product A;

[0046] S2. Grind product A evenly and place it in a 500 mL beaker. Then slowly drop 100 mL of 1 M dilute hydrochloric acid into the beaker and stir for 12 h.

[0047] S3. The stirred solution was filtered with a large amount of deionized water until it became neutral, and then placed in a vacuum drying oven and dried at 80° C. for 12 h to obtain a nitrogen-doped carbon material.

[0048] The morphologies of the samples obtained in Example 1 and Example 2 were characterized using a transmission electron microscope. The characterization results are shown in FIG. Figure 1 and Figure 2 shown.

[0049] like Figure 1 and Figure 2 The carbon materials prepared in Example 1 and Example 2 are both in the form of flakes, but it is obvious that the carbon sheet prepared in Example 2 is thicker and has fewer pores, and has a more compact structure. The compact structure is conducive to increasing the density of the material.

[0050] The microstructure of the samples was further studied by X-ray diffraction (XRD) and N2 adsorption-desorption isotherm (BET). The test results were as follows: Figure 3 and Figure 4 shown.

[0051] like Figure 3The XRD spectra of the samples of Example 1 and Example 2 both show broad peaks centered at 25° and 44°, corresponding to (002) and (100) of graphite, indicating that they are both amorphous carbon materials; while the diffraction peak intensity of Example 2 at low angles is lower, corresponding to less micropore content in the sample; the broad peak shift at 25° may be related to the introduction of nitrogen-containing functional groups, which increases the van der Waals force between carbon sheets and causes stacking between layers, which is consistent with the TEM test results; the increase in the degree of graphitization may be related to the formation of crystalline carbon and nitrogen compounds. The specific surface area and pore structure of the sample were further explored through nitrogen adsorption-desorption isotherms. As Figure 4 The samples of Example 1 and Example 2 all exhibited type IV isotherm characteristics, with adsorption at low pressure (0.0-0.01) and hysteresis loops at medium to high pressure (0.4-0.9), indicating the presence of micropores and mesopores in all samples. The specific surface areas of the samples of Example 1 and Example 2 were 866 m 2 / g、79m 2 / g, and the pore volume is 0.7 cm 3 / g, 0.12cm 3 / g. This indicates that excessive melamine will lead to a sharp decrease in the specific surface area and pore volume of carbon materials.

[0052] The nitrogen doping test results of the nitrogen doped carbon materials prepared in Example 1, Example 2 and Example 3 are as follows: Figure 5 As shown. Figure 5 It can be seen that the nitrogen content in the carbon material increases with the increase of the added amount of melamine.

[0053] Figure 6 The tap density test results of the samples of Example 1 and Example 2 are shown. Thanks to the reduction of specific surface area and pore volume and the stacking of carbon layers, the tap density of the sample of Example 2 (0.55 g / cm 3 ) is significantly higher than the tap density of the sample in Example 1 (0.325 g / cm 3 ) and the tap density of commercial activated carbon YP50F (0.37 g / cm 3 ). In addition, Figure 7 As shown, the carbonyl content of the sample prepared in Example 2 is significantly higher than that of the sample in Example 1, providing sufficient sites for the adsorption of ions.

[0054] The electrochemical performance of the nitrogen-doped carbon materials prepared in Example 1, Example 2, and Example 3 was tested, as follows:

[0055] The nitrogen-doped carbon material, SuperP, and binder PVDF prepared in Example 1, Example 2, and Example 3 were mixed in a mass ratio of 8:1:1, ground evenly, and then 1-methyl-2-pyrrolidone (NMP) was dropped into the mixture and stirred for 12 hours to obtain a slurry. The slurry was evenly coated on an aluminum foil with a scraper thickness of 15 mm. The aluminum foil coated with the slurry was placed in a vacuum oven and dried at 120° C. for 12 hours, and then cut into discs on a microtome for later use.

[0056] The obtained disc was used as the positive electrode, the sodium sheet as the negative electrode, 1 M sodium perchlorate solution as the electrolyte, and glass fiber filter paper as the separator to assemble a sodium ion half-cell in an argon atmosphere glove box.

[0057] At 1.5-4.2V (vs Na + The electrochemical performance of the prepared sodium ion half-cell was tested using a blue battery test system in the voltage range of 1 / Na. The test results are shown in the figure. Figure 8 shown.

[0058] like Figure 8 At a current density of 0.1 A / g, the carbon material prepared in Example 2 has an initial discharge capacity of 56 mAh / cm 3 , while the first discharge specific capacity of the carbon material prepared in Example 1 is 45 mAh / cm 3 As the number of cycles increases, the volumetric capacity of the sample prepared in Example 2 increases to 68 mAh / cm 3 , while the volumetric capacity of the carbon material prepared in Example 1 decays rapidly. This is because the carbon material in Example 2 has a smaller specific surface area and a limited number of groups participating in the initial reaction, which increases the volumetric capacity. The rapid capacity decay of the carbon material in Example 1 may be due to the large specific surface area facilitating the decomposition of the electrolyte. The electrolyte decomposition products clog the pores, hindering the adsorption of ions by the active sites, resulting in a rapid decay of the specific capacity.

[0059] The sodium ion half-cell was cycled at current densities of 0.1, 0.5, 1, 2, 5, and 10 A / g and then returned to a current density of 0.1 A / g for cycling. The results are shown in Figure 2. Figure 9 As shown. Figure 9 The carbon material prepared in Example 2 has a higher volumetric capacity at different current densities.

[0060] Figure 10 and Figure 11 The cycling performance of the carbon materials of Example 1 and Example 2 under different electrolyte contents are shown respectively. Figure 10 and Figure 11For the carbon material of Example 2, the amount of electrolyte used has little effect on cycling stability. Compared with physical adsorption of ions through the double layer, chemical adsorption of ions through pseudocapacitive reactions can provide a higher specific capacity. Therefore, the carbon material prepared in Example 2 requires less electrolyte to maintain its specific capacity.

[0061] Figure 12 The cycling performance of the carbon material prepared in Example 3 under the condition of an electrolyte content of 80 μL is shown in FIG. Figure 12 The initial specific capacity of the carbon material prepared in Example 3 is very low. After 400 cycles, the capacity reaches a stable state, and the maximum is only about 54 mAh / g, indicating that excessive heteroatom doping leads to poor conductivity of the carbon material and a significant reduction in capacity.

[0062] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0063] The above-described embodiments merely illustrate several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that a person skilled in the art would be able to make numerous modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for preparing a carbon positive electrode material for a sodium ion capacitor with high volumetric capacity, characterized in that: The following steps are involved: Mixing rhodamine disodium salt and melamine, heating to a carbonization temperature in a protective gas atmosphere to react and obtain a carbonized product; adding dilute hydrochloric acid to the carbonized product for pickling, then performing solid-liquid separation, washing the solid with deionized water until it is neutral, and drying the solid product to obtain the carbon positive electrode material; Wherein, the mass ratio of the disodium salt of rhodendric acid to melamine is 1:0.3-0.55; The pickling method is specifically as follows: dripping the dilute hydrochloric acid into the carbonized product, stirring evenly, then separating the solid and the liquid, and washing the solid with deionized water until it is neutral.

2. The method for preparing a carbon positive electrode material for a sodium ion capacitor with a high volumetric capacity according to claim 1, wherein: The carbonization temperature is 600-1000℃.

3. The method for preparing a carbon positive electrode material for sodium ion capacitors with high volumetric capacity according to claim 1, wherein: The temperature was raised to the carbonization temperature at a rate of 1-10°C / min.

4. The method for preparing a carbon positive electrode material for a sodium ion capacitor with a high volumetric capacity according to claim 1, wherein: The concentration of dilute hydrochloric acid is 0.1-5 mol / L.

5. The method for preparing a carbon positive electrode material for a sodium ion capacitor with a high volumetric capacity according to claim 1, wherein: The carbonization reaction time is 0.5-6h.

6. The carbon cathode material obtained by the preparation method according to any one of claims 1 to 5, wherein the specific surface area of ​​the carbon cathode material is 20-90 m 2 / g, nitrogen content is 16-20at%.

7. A sodium ion capacitor positive electrode, characterized in that Comprising the carbon positive electrode material according to claim 6.

8. A sodium ion capacitor, characterized in that Comprising the positive electrode according to claim 7.

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