All-carbon sodium-based double-ion capacitor and preparation method thereof

Abstract

The invention belongs to the technical field of new energy science, discloses an all-carbon sodium-based double-ion capacitor and a preparation method thereof, and aims to solve the technical problems of contradiction between reversible capacity and rate capability and short cycle life. An all-carbon sodium-based double-ion capacitor comprises a negative pole piece, a diaphragm, an electrolyte and a positive pole piece, the positive pole piece comprises nitrogen-doped porous carbon, zinc citrate, a dispersing agent and dopamine hydrochloride are added into deionized water, then absolute ethyl alcohol is added, and a precursor is obtained after room-temperature stirring, suction filtration, washing and drying; annealing the precursor under the protection of inert gas to obtain a pyrolysis product, and then soaking the pyrolysis product in acid, washing and drying to obtain the nitrogen-doped porous carbon. The full-carbon sodium-based double-ion capacitor positive electrode material has a rich pore structure and a specific surface area, can provide rich active sites for storage of anions, and ensures the electrochemical kinetics and long-cycle reversibility of the positive electrode material in the repeated storage process of the anions.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of new energy science and technology, and particularly relates to a capacitor. BACKGROUND

[0002] Energy crisis is increasingly serious, and the demand for new energy is increasingly urgent. It is of great strategic significance to develop new alternative energy and energy saving and emission reduction. Sodium-based dual-ion capacitors have the advantages of sodium-ion batteries and supercapacitors, and can provide high power at relatively high energy density, showing wide application prospects. At present, graphite is generally used as a positive electrode in dual-ion batteries to realize anion reversible storage (>4.5 V vs. Li + / Li), and the diffusion energy barrier of anions between graphite layers is as low as approximately 0.2 eV, which enables sodium-based dual-ion capacitors to generally exhibit high working voltage and fast insertion kinetics, which is beneficial to realize high energy density and good rate performance. However, for the layered graphite positive electrode material, repeated intercalation of anions will cause a series of problems: firstly, the reversible intercalation potential is about 5.4 V, however, during the charging process, when the voltage reaches 5 V or more, the commonly used organic solvent of dual-ion batteries will be oxidized and decomposed, so the capacity and cycle performance are poor, and therefore the working voltage of many related researches is low; secondly, the intercalation of anions is always accompanied by the intercalation of solvated solvent molecules, which results in that the intercalation capacity is much larger than the extraction capacity, causing low initial efficiency, and there are problems such as poor cycle performance and structural instability. In view of the great application advantages and high safety of dual-ion batteries, it is of great significance to develop new anion intercalation positive electrode materials.

[0003] Sodium-based dual-ion hybrid capacitors have attracted much attention due to their combination of high energy density of batteries and high power density of supercapacitors, but their performance is largely limited by the structure of electrode materials, especially the storage and transmission efficiency of sodium ions in carbon materials. In the prior art, in order to improve the intercalation and diffusion capacity of sodium ions, researchers mainly adopt the following strategies, but all face corresponding challenges. Firstly, expanding the interlayer spacing of carbon materials is a direct idea, for example, carbon thermal shock treatment can expand the interlayer spacing (d 002) or by using chemical reagents such as potassium carbonate to produce potassium vapor intercalation at high temperatures to expand the carbon layer spacing. However, although the interlayer spacing has increased, repeated intercalation / deintercalation of sodium ions (Na+) and larger anions (such as PF6-) can still cause irreversible expansion or collapse of the highly ordered layered structure of the graphite-based material, restricting its long-term cycle stability. Second, building a porous structure to increase the specific surface area and ion transport channels is another commonly used method. For example, using strong corrosive reagents such as KOH, ZnCl2 for severe activation can create a large number of pores in hard carbon, or by thermal etching method to make pores on graphene sheets to improve the longitudinal diffusion speed of ions. However, excessive pursuit of high specific surface area often leads to too high a proportion of micropores (<2 nm), which can hinder the rapid diffusion of ions during high-speed charging and discharging, causing capacitance decay and rate performance decline. In addition, such strong corrosive activators are prone to cause equipment corrosion, wastewater treatment problems, and excessive activation can damage the carbon skeleton, reduce the mechanical strength of the material, and bring cost and environmental pressure. It is worth noting that a reasonable multi-level pore structure (micropores, mesopores, macropores) design has been proven to be more effective, which can better balance the sodium storage sites and ion transport kinetics. In terms of electrode structure, studies have shown that electrodes with low-curvature finger-like pores can significantly shorten the sodium ion transport path and improve the ion diffusion kinetics under high surface load. Therefore, developing carbon materials that can accurately regulate the interlayer spacing and pore structure of the material, while also considering the environmental friendliness and equipment friendliness of the process, is still the key to improving the performance of sodium-based dual-ion hybrid capacitors. SUMMARY

[0004] In view of the imbalance between reversible capacity, rate performance and cycle stability, the present application provides a full-carbon sodium-based dual-ion capacitor and a preparation method thereof.

[0005] To achieve the above object, the technical scheme of the present application is as follows: A full-carbon sodium-based dual-ion capacitor, comprising a negative electrode sheet, a separator, an electrolyte and a positive electrode sheet; wherein the positive electrode sheet comprises nitrogen-doped porous carbon, and during charging and discharging, the positive electrode is anion adsorption / desorption at medium-low potential and anion intercalation and deintercalation at high potential.

[0006] The preparation method of the above-mentioned nitrogen-doped porous carbon is as follows: (1) Zinc citrate, dispersant and dopamine hydrochloride are added to deionized water, and then anhydrous ethanol is added. After stirring at room temperature for 18-24 h, suction filtration, washing and drying, the precursor is obtained. Dopamine hydrochloride is used as a nitrogen source, and zinc citrate is used as a self-template carbon source. The zinc citrate produces a multi-level pore structure through the synergistic effect of the impurities and CO / CO2 gas produced during the pyrolysis process. The anhydrous ethanol and the aqueous buffer (such as tris) are mixed to affect the solubility of dopamine monomers and the polymerization rate.

[0007] (2) The precursor obtained in step (1) is annealed under the protection of an inert gas (such as argon) to obtain a pyrolysis product. Then the pyrolysis product is soaked in acid, washed with deionized water until neutral, and vacuum dried to obtain nitrogen-doped porous carbon. The specific surface area of the nitrogen-doped porous carbon prepared by the above method is 942.80-1286.78 cm 3 g -1 , the pore size distribution is 2-20 nm, there are a large number of mesoporous structures, and the nitrogen content is 1.87-5.29 %.

[0008] The molar ratio of the above zinc citrate, dispersant and dopamine hydrochloride is (1-3):2:1.

[0009] The above dispersant is tris.

[0010] 0.05 moL-0.2 moL zinc citrate is added to each L deionized water; the volume ratio of anhydrous ethanol to deionized water is 1-2:1.

[0011] The temperature of the above annealing treatment is 700-1200℃, and the time is 1-10 h.

[0012] Further, the above positive electrode sheet further comprises a conductive agent and a binder, and the mass ratio of the nitrogen-doped porous carbon, the conductive agent and the binder is (8-9):1:1; the negative electrode sheet comprises hard carbon powder, a conductive agent and a binder, and the mass ratio of the three is (8-9):1:1.

[0013] The preparation method of the above all-carbon sodium-based dual-ion capacitor comprises the following steps: S1. Prepare nitrogen-doped porous carbon according to the above preparation method; S2. Mix the nitrogen-doped porous carbon prepared in step S1 with Ketjen black and polyvinylidene fluoride according to (8-9):1:1 to obtain a positive electrode slurry, and coat the positive electrode slurry on a copper foil according to a loading of 0.7-1.2 mg cm -2 ; then dry the copper foil in a vacuum drying oven to remove water, and cut it to obtain a positive electrode sheet. S3. Hard carbon powder is mixed with Ketjen black and polyvinylidene fluoride at a ratio of (8-9):1:1 to obtain a negative electrode slurry, and then mixed at a concentration of 0.5-0.8 mg / cm³. -2 The loading amount is coated on aluminum foil, and then the aluminum foil is placed in a vacuum drying oven to dry and remove moisture before being cut to obtain the negative electrode sheet.

[0014] S4. The positive electrode, separator, and negative electrode are stacked in sequence, and the electrolyte is added to assemble the electrode.

[0015] The beneficial effects of this invention are: (1) This invention provides a nitrogen-doped porous carbon-sodium-based dual-ion capacitor and its preparation method; the nitrogen-doped porous carbon of this invention has a hierarchical porous structure and a rich specific surface area (942.80-1286.78 cm²). 3 g -1 Nitrogen-doped porous carbon can stably and reversibly store anions, providing energy. The storage of anions in nitrogen-doped porous carbon primarily relies on pseudocapacitive reactions, ensuring efficient anion storage and resulting in excellent electrochemical performance.

[0016] (2) The sodium-based dual-ion capacitor provided by the present invention includes a positive electrode, a negative electrode, a separator between the positive and negative electrodes, and an electrolyte; the active material of the negative electrode is a hard carbon material that can reversibly store sodium ions; the active material of the positive electrode is a novel nitrogen-doped porous carbon, which can reversibly store anions and provide energy; the electrolyte includes sodium salt and non-aqueous solvent; the sodium-based dual-ion capacitor has high specific capacitance, long cycle life, low cost, and good safety performance.

[0017] (3) The reversible capacity of the full cell of the all-carbon sodium-based dual-ion capacitor prepared in this invention after 16,000 cycles is 75.1 mAh g. -1 The capacity retention rate and coulombic efficiency are as high as 80.8% and 92%, respectively. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 These are TEM images of nitrogen-doped porous carbon prepared in Examples 1-3 of the present invention and porous carbon materials prepared in Comparative Example 1.

[0020] Figure 2HRTEM images of the nitrogen-doped porous carbons prepared in Examples 1-3 of the present application and the porous carbon material prepared in Comparative Example 1.

[0021] Figure 3 XRD images of the nitrogen-doped porous carbons prepared in Examples 1-3 of the present application and the porous carbon material prepared in Comparative Example 1.

[0022] Figure 4 XPS survey spectra of the nitrogen-doped porous carbons prepared in Examples 1-3 of the present application and nitrogen adsorption / desorption and pore size distribution of the nitrogen-doped porous carbon prepared in Example 1.

[0023] Figure 5 Ex-situ XPS of the nitrogen-doped porous carbon prepared in Example 1 of the present application.

[0024] Figure 6 Ex-situ XRD of the nitrogen-doped porous carbon prepared in Example 1 of the present application.

[0025] Figure 7 Ex-situ FTIR of the nitrogen-doped porous carbon prepared in Example 1 of the present application.

[0026] Figure 8 Ex-situ Raman of the nitrogen-doped porous carbon prepared in Example 1 of the present application.

[0027] Figure 9 Rate capability graphs and capacity retention comparison graphs of half-cells assembled with the carbon materials prepared in Examples 1-3 and Comparative Example 1 of the present application.

[0028] Figure 10 Long cycle stability graphs of half-cells assembled with the carbon materials prepared in Examples 1-3 and Comparative Example 1 of the present application.

[0029] Figure 11 Rate capability graphs of sodium-based dual-ion capacitors assembled with the carbon materials prepared in Example 1 and Comparative Example 1 of the present application.

[0030] Figure 12 Long cycle stability graphs of sodium-based dual-ion capacitors assembled with the carbon materials prepared in Example 1 and Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort belong to the scope of protection of the present application.

[0032] Example 1 The preparation method of the nitrogen-doped porous carbon of the embodiment is as follows: Step 1: 6.1 g of zinc citrate, 2.42 g of trishydroxymethyl aminomethane, and 1.89 g of dopamine hydrochloride were uniformly dispersed in 200 mL of deionized water, and after stirring for 2 min, 200 mL of anhydrous ethanol was added to obtain a precursor solution; the precursor solution was stirred at room temperature for 24 h; Step 2: The obtained solution was centrifuged, washed, and dried to obtain a powder, which was washed with deionized water and anhydrous ethanol for several times and then freeze-dried for 12 h; Step 3: The powder obtained in step 2 was heated to 900 DEG C at a heating rate of 5 DEG C min -1 -1 under Ar atmosphere and kept for 5 h, the obtained powder was soaked in 1 M HCl for 24 h to remove impurities, and then washed with deionized water and dried to obtain a nitrogen-doped porous carbon material.

[0033] Application Example 1 A preparation method of a sodium ion battery, the steps are as follows: (1) The nitrogen-doped porous carbon prepared in the embodiment, ketchen black and polyvinylidene fluoride were placed in a marver mortar in a ratio of 8:1:1 and ground uniformly to obtain a positive electrode slurry; and the positive electrode slurry was coated on a copper foil at a loading of 1 mg cm -2 -2, and then the copper foil was placed in a vacuum drying oven to dry the water, and then cut to obtain a positive electrode sheet; (2) In a glove box, a sodium sheet was cut into a circular electrode sheet with a diameter of 8 mm as a negative electrode sheet; (3) The positive electrode sheet, glass fiber separator, and negative electrode sheet were stacked in sequence, and then a 1 M NaPF6-based electrolyte was added to assemble the sodium ion battery.

[0034] Application Example 2 A preparation method of an all-carbon sodium-based dual-ion capacitor, the steps are as follows: (1) The nitrogen-doped porous carbon prepared in the embodiment, ketchen black and polyvinylidene fluoride were placed in a marver mortar in a ratio of 8:1:1 and ground uniformly to obtain a positive electrode slurry; and the positive electrode slurry was coated on a copper foil at a loading of 1 mg cm -2 -2, and then the copper foil was placed in a vacuum drying oven to dry the water, and then cut to obtain a positive electrode sheet; (2) Commercial hard carbon powder (Hefei Kexin Material Technology Co., Ltd.) was placed in a marver mortar in a ratio of 8:1:1 with ketchen black and polyvinylidene fluoride to obtain a negative electrode slurry; and the negative electrode slurry was coated on an aluminum foil at a loading of 0.8 mg cm -2 -2, and then the aluminum foil was placed in a vacuum drying oven to dry the water, and then cut to obtain a negative electrode sheet.

[0035] (3) The positive electrode sheet, glass fiber separator, and negative electrode sheet are sequentially stacked, and a 1 M NaPF6-based electrolyte is added to assemble the sodium ion battery.

[0036] Example 2 The preparation method of the nitrogen-doped porous carbon in this example is as follows: Step 1: 6.1 g of zinc citrate, 2.42 g of tris-hydroxymethyl aminomethane, and 1.89 g of dopamine hydrochloride were uniformly dispersed in 200 mL of deionized water, and 200 mL of anhydrous ethanol was added after stirring for 2 min to obtain a precursor solution; the precursor solution was stirred at room temperature for 24 h; Step 2: The obtained solution was centrifuged, washed, and dried to obtain a powder, which was washed with deionized water and anhydrous ethanol several times and then freeze-dried for 12 h; Step 3: The powder obtained in Step 2 was heated to 800℃ at a heating rate of 5℃ / min in an Ar atmosphere and kept for 5 h, the obtained powder was soaked in 1 M HCl for 24 h to remove impurities, and then washed with deionized water and dried to obtain a nitrogen-doped porous carbon material. -1

[0037] Application Example 3 A preparation method of a sodium ion battery, the steps are as follows: (1) The nitrogen-doped porous carbon prepared in this example, Ketjen black, and polyvinylidene fluoride were placed in a marcasite mortar and ground uniformly at a ratio of 8:1:1 to obtain a positive electrode slurry; and the positive electrode slurry was coated on a copper foil at a loading of 1 mg / cm -2 , and then the copper foil was placed in a vacuum drying box to remove water, and then cut to obtain a positive electrode sheet; (2) In a glove box, a sodium sheet was cut into a circular electrode sheet with a diameter of 8 mm as a negative electrode sheet; (3) The positive electrode sheet, glass fiber separator, and negative electrode sheet were sequentially stacked, and a 1 M NaPF6-based electrolyte was added to assemble the sodium ion battery.

[0038] Example 3 The preparation method of the nitrogen-doped porous carbon in this example is as follows: Step 1: 6.1 g of zinc citrate, 2.42 g of tris-hydroxymethyl aminomethane, and 1.89 g of dopamine hydrochloride were uniformly dispersed in 200 mL of deionized water, and 200 mL of anhydrous ethanol was added after stirring for 2 min to obtain a precursor solution; the precursor solution was stirred at room temperature for 24 h; Step 2: The obtained solution was centrifuged, washed, and dried to obtain a powder, which was washed with deionized water and anhydrous ethanol several times and then freeze-dried for 12 h; Step 3: The powder obtained in Step 2 was heated to 800℃ at a heating rate of 5℃ / min in an Ar atmosphere and kept for 5 h, the obtained powder was soaked in 1 M HCl for 24 h to remove impurities, and then washed with deionized water and dried to obtain a nitrogen-doped porous carbon material.​-1 The obtained powder is soaked in 1 M HCl for 24 h to remove impurities, and then washed with deionized water and dried to obtain the nitrogen-doped porous carbon material.

[0039] Application Example 4 A preparation method of a sodium ion battery, comprising the following steps: (1) The nitrogen-doped porous carbon prepared in this embodiment is uniformly ground with Ketjen black and polyvinylidene fluoride in a ratio of 8:1:1 in a agate mortar to obtain a positive electrode slurry; and the positive electrode slurry is coated on a copper foil at a loading of 1 mg cm -2 , and then the copper foil is dried in a vacuum drying box to remove water, and then cut to obtain a positive electrode sheet; (2) In a glove box, a sodium sheet is cut into a circular electrode sheet with a diameter of 8 mm as a negative electrode sheet; (3) The positive electrode sheet, a glass fiber separator, and the negative electrode sheet are sequentially stacked, and then a 1 M NaPF6-based electrolyte is added to assemble the sodium ion battery.

[0040] Example 4 A preparation method of the nitrogen-doped porous carbon in this embodiment, comprising the following steps: Step 1: 12.2 g of zinc citrate, 2.42 g of tris-hydroxymethyl aminomethane, and 1.89 g of dopamine hydrochloride are uniformly dispersed in 200 mL of deionized water, and then 300 mL of anhydrous ethanol is added after stirring for 2 min to obtain a precursor solution; and the precursor solution is stirred at room temperature for 18 h; Step 2: The solution obtained in the above step is centrifuged, washed, and dried to obtain a powder, which is washed with deionized water and anhydrous ethanol for several times and then freeze-dried for 12 h; Step 3: The powder obtained in Step 2 is heated to 700°C at a heating rate of 5°C / min -1 in an Ar atmosphere and kept for 10 h, and then the obtained powder is soaked in 1 M HCl for 24 h to remove impurities, and then washed with deionized water and dried to obtain the nitrogen-doped porous carbon material.

[0041] Application Example 5 A preparation method of a full-carbon sodium-based dual-ion capacitor, comprising the following steps: (1) The nitrogen-doped porous carbon prepared in this embodiment is uniformly ground with Ketjen black and polyvinylidene fluoride in a ratio of 9:1:1 in a agate mortar to obtain a positive electrode slurry; and the positive electrode slurry is coated on a copper foil at a loading of 1.2 mg cm -2 , and then the copper foil is dried in a vacuum drying box to remove water, and then cut to obtain a positive electrode sheet; (2) The commercially available hard carbon powder (Hefei Kexing Material Technology Co., Ltd.) is uniformly ground with Ketjen black and polyvinylidene fluoride in a ratio of 9:1:1 in an agate mortar to obtain a negative electrode slurry; and the negative electrode slurry is coated on an aluminum foil at a loading of 0.5 mg cm -2 , and then the aluminum foil is dried in a vacuum drying oven to remove water, and then cut to obtain a negative electrode sheet.

[0042] (3) The positive electrode sheet, glass fiber separator, and negative electrode sheet are sequentially stacked, and then a 1 M NaPF6-based electrolyte is added to assemble the sodium-based full-carbon dual-ion capacitor.

[0043] Example 5 The preparation method of the nitrogen-doped porous carbon in this example is as follows: Step ①: 18.3 g of zinc citrate, 2.42 g of tris-hydroxymethyl aminomethane, and 1.89 g of dopamine hydrochloride are uniformly dispersed in 150 mL of deionized water, and then 300 mL of anhydrous ethanol is added after stirring for 2 min to obtain a precursor solution; the precursor solution is stirred at room temperature for 22 h; Step ②: The obtained solution is centrifuged, washed, and dried to obtain a powder, which is washed several times with deionized water and anhydrous ethanol and then freeze-dried for 12 h; Step ③: The powder obtained in step ② is heated to 1200℃ at a heating rate of 5℃ / min in an Ar atmosphere and kept for 1 h, and the obtained powder is soaked in 1 M HCl for 24 h to remove impurities, and then washed with deionized water and dried to obtain a nitrogen-doped porous carbon material. -1

[0044] Application Example 6 A preparation method of a full-carbon sodium-based dual-ion capacitor is as follows: (1) The nitrogen-doped porous carbon prepared in this example is uniformly ground with Ketjen black and polyvinylidene fluoride in a ratio of 8:1:1 in an agate mortar to obtain a positive electrode slurry; and the positive electrode slurry is coated on a copper foil at a loading of 0.7 mg cm -2 , and then the copper foil is dried in a vacuum drying oven to remove water, and then cut to obtain a positive electrode sheet; (2) The commercially available hard carbon powder (Hefei Kexing Material Technology Co., Ltd.) is uniformly ground with Ketjen black and polyvinylidene fluoride in a ratio of 8:1:1 in an agate mortar to obtain a negative electrode slurry; and the negative electrode slurry is coated on an aluminum foil at a loading of 0.7 mg cm -2 , and then the aluminum foil is dried in a vacuum drying oven to remove water, and then cut to obtain a negative electrode sheet.

[0045] (3) The positive electrode sheet, glass fiber separator, and negative electrode sheet are sequentially stacked, and then a 1 M NaPF6-based electrolyte is added to assemble the sodium-based full-carbon dual-ion capacitor.​

[0046] Comparative Example 1 The preparation method of the porous carbon of the present comparative example is different from that of Example 1 in that it does not contain trimethylol aminomethane and dopamine hydrochloride, and the specific steps are as follows: 6.1 g of zinc citrate was heated to 900℃ at a heating rate of 5℃ min -1 -1 under Ar atmosphere and kept for 5 h. The obtained powder was immersed in 1 M HCl for 24 h to remove impurities, and then washed with deionized water and dried to obtain a nitrogen-doped porous carbon material.

[0047] Application Example 7 A preparation method of a sodium ion battery, the steps are as follows: (1) The porous carbon prepared in the present comparative example, ketjen black and polyvinylidene fluoride were placed in a agate mortar in a ratio of 8:1:1 and ground uniformly to obtain a positive electrode slurry; and the positive electrode slurry was coated on a copper foil at a loading of 1 mg cm -2 -2, and then the copper foil was placed in a vacuum drying oven to dry and remove water, and then cut to obtain a positive electrode sheet; (2) In a glove box, a sodium sheet was cut into a circular electrode sheet with a diameter of 8 mm as a negative electrode sheet; (3) The positive electrode sheet, glass fiber separator and negative electrode sheet were stacked in order, and then a NaPF6-based electrolyte with a concentration of 1 M was added to assemble it.

[0048] Application Example 8 A preparation method of a full-carbon sodium-based dual-ion capacitor, the steps are as follows: (1) The porous carbon prepared in the present comparative example, ketjen black and polyvinylidene fluoride were placed in a agate mortar in a ratio of 8:1:1 and ground uniformly to obtain a positive electrode slurry; and the positive electrode slurry was coated on a copper foil at a loading of 1 mg cm -2 -2, and then the copper foil was placed in a vacuum drying oven to dry and remove water, and then cut to obtain a positive electrode sheet; (2) Commercial hard carbon powder (Hefei Kexing Material Technology Co., Ltd.), ketjen black and polyvinylidene fluoride were placed in a agate mortar in a ratio of 8:1:1 and ground uniformly to obtain a negative electrode slurry; and the negative electrode slurry was coated on an aluminum foil at a loading of 0.8 mg cm -2 -2, and then the aluminum foil was placed in a vacuum drying oven to dry and remove water, and then cut to obtain a negative electrode sheet.

[0049] (3) The positive electrode sheet, glass fiber separator and negative electrode sheet were stacked in order, and then a NaPF6-based electrolyte with a concentration of 1 M was added to assemble it.

[0050] Implementation Effect Example Figure 1The TEM images of the nitrogen-doped porous carbon prepared in Examples 1-3 of the present application and the porous carbon material prepared in Comparative Example 1 show that the nitrogen-doped porous carbon prepared in the present application has a loose porous structure.

[0051] Figure 2 The HRTEM images of the nitrogen-doped porous carbon prepared in Examples 1-3 of the present application and the porous carbon material prepared in Comparative Example 1 show that the interlayer spacing of the nitrogen-doped porous carbon prepared in the present application is about 0.384-0.406 nm. The interlayer spacing of Example 2 is the largest, about 0.406 nm, and the annealing temperature is 900°C. The larger interlayer spacing is beneficial to the improvement of the cycle stability. The interlayer spacing of Comparative Example 1 is only about 0.390 nm at the same annealing temperature.

[0052] Figure 3 The XRD images of the nitrogen-doped porous carbon prepared in Examples 1-3 of the present application and the porous carbon material prepared in Comparative Example 1 show that each sample shows two diffraction peaks corresponding to the broad peaks of the (002) and (100) diffraction peaks of hard carbon, and the XRD diffraction peak positions of the (002) crystal plane are close, which side confirms that the interlayer spacing is close, which is consistent with the HRTEM results. At the same time, it can be seen from the XRD spectrum that there is a wide peak at low angle, which is formed by the pore structure or disordered stacking of carbon layers in the material.

[0053] From Figure 4 It can be seen from a that the nitrogen content of the nitrogen-doped porous carbon prepared in Examples 1-3 of the present application is 1.87-5.29%. Figure 4 b is the nitrogen adsorption and desorption and pore size distribution of the nitrogen-doped porous carbon prepared in Example 1 of the present application. It can be seen from the figure that it is a typical type IV adsorption and desorption isotherm with a clear hysteresis loop, which means that Example 1 has both microporous structure and mesoporous structure. In addition, it can be confirmed from the pore size distribution graph that it has a rich pore size distribution, mainly concentrated in the mesoporous structure around 3.75 nm, but there are also rich pore structures in the larger pore size range, which also has a hierarchical pore structure.

[0054] Figure 5 The non-in-situ XPS of the nitrogen-doped porous carbon prepared in Example 1 of the present application shows that the atomic percentage of F and P in the full spectrum and the appearance and shift of the PF6 - peak in the fine spectrum at different potentials prove that the nitrogen-doped porous carbon can reversibly store PF6 - .

[0055] Figure 6 The non-in-situ XRD of the nitrogen-doped porous carbon prepared in Example 1 of the present application shows that the (002) crystal plane shifts at different potentials, which proves that the nitrogen-doped porous carbon stores PF6 - between carbon layers.

[0056] Figure 7 The non-in-situ FTIR of the nitrogen-doped porous carbon prepared in Example 1 shows the change of P-F stretching vibration signal peaks at different potentials, which proves that the nitrogen-doped porous carbon can reversibly store PF6 - .

[0057] Figure 8 The non-in-situ Raman of the nitrogen-doped porous carbon prepared in Example 1 shows the change of I D / I G values at different potentials, which proves that the nitrogen-doped porous carbon stores PF6 - by adsorption behavior at low potential and by intercalation behavior at high potential - .

[0058] Figure 9 The rate performance of the half-cells assembled with the carbon materials prepared in Examples 1-3 and Comparative Example 1 is shown in the figure. As can be seen from the figure, Figure 9 the half-cell assembled with the carbon material of Example 1 (Application Example 1) and the half-cell assembled with the carbon material of Example 2 (Application Example 3) have discharge capacities of 210.1 / 70 mAh g -1 and 135.1 / 62.1 mAh g -1 at a current density of 0.1 / 20 A g -1 , respectively. The half-cell assembled with the carbon material of Comparative Example 1 (Application Example 5) has discharge capacities of 113.0 mAh g -1 / 68.3 mAh g -1 at a current density of 0.1 / 5 A g -1 . The comparative example cannot be cycled at a large current density, and the capacity is very different from that of the examples.

[0059] Figure 10 The long cycle stability of the half-cells assembled with the carbon materials prepared in Examples 1-3 and Comparative Example 1 is shown in the figure. As can be seen from the figure, Figure 10 the half-cell assembled with the carbon material of Example 1 (Application Example 1) has a discharge capacity of 202.7 mAh g -1 after 1000 cycles at a current density of 0.5 A g -1 , and the coulombic efficiency is always maintained at about 95%; the half-cell assembled with the carbon material of Example 2 (Application Example 3) has a discharge capacity of 136.1 mAh g -1 after 1000 cycles at a current density of 0.5 A g -1 ; the half-cell assembled with the carbon material of Example 3 (Application Example 4) has a discharge capacity of 135.1 mAh g -1after 1000 cycles at a current density of 0.5 A g -1 has a discharge capacity of 154.2 mAh g -1 after 1000 cycles at a current density of 0.5 A g -1 .

[0060] Figure 11 Figure 2 is a graph of the rate performance of sodium-based dual-ion capacitors assembled with the carbon material prepared in Example 1 and Comparative Example 1, and a comparison graph of the capacity retention rate. As can be seen from the graph, the sodium-based dual-ion capacitor (Application Example 2) assembled with the carbon material of Example 1 has reversible capacities of 161.6, 145.3, 125.7, 108.4, 91.7, 65.1, and 40.1 mAh g -1 at current densities of 0.1, 0.2, 0.5, 1.0, 2.0, 5.0, and 10.0 A g -1 , respectively, and the corresponding capacity retention rates at different current densities are 90.0%, 77.8%, 67.1%, 56.7%, 40.3%, and 24.8%, respectively. When the current density is reduced from 10.0 A g -1 to 0.1 A g -1 , the reversible capacity of the sodium-based dual-ion capacitor increases to 140.7 mAh g -1 . The corresponding capacity retention rate is 87.1%. The sodium-based dual-ion capacitor (Application Example 8) assembled with the carbon material of Comparative Example 1 has reversible capacities of 135.7, 88.4, 72.5, 57.4, and 42.3 mAh g -1 at current densities of 0.1, 0.2, 0.5, 1.0, and 2.0 A g -1 , respectively, and the corresponding capacity retention rates at different current densities are 65.1%, 53.4%, 42.3%, and 31.2%, respectively. When the current density is reduced from 2.0 A g -1 to 0.1 A g -1 , the reversible capacity of the sodium-based dual-ion capacitor increases to 84.1 mAh g -1 . The corresponding capacity retention rate is 62.2%. It can be seen that the reversible capacity and retention rate of Application Example 2 are higher than those of Application Example 8 at different current densities, indicating that the sodium-based dual-ion capacitor assembled with the carbon material of Example 1 has excellent rate performance.

[0061] Figure 12 Figure 3 is a graph of the long cycle stability performance of sodium-based dual-ion capacitors assembled with the carbon material prepared in Example 1 and Comparative Example 1. It can be seen that the sodium-based dual-ion capacitor (Application Example 2) assembled with the carbon material of Example 1 has first cycle discharge / charge capacities of 93.1 mAh g-1 and 75.1 mAh g -1 The capacity retention was 80.8% and the coulombic efficiency was 92% after 16000 cycles. The sodium-based dual-ion capacitor assembled by the carbon material of Comparative Example 1 (Application Example 8) had a first week discharge / charge capacity of 60.2 mAh g -1 and 48.9 mAh g -1 The coulombic efficiency was 81% in the first week, and the capacity retention was 96.1% after 10000 cycles. The performance difference between Example 1 and Comparative Example 1 was due to: Example 1 introduced more abundant reaction active sites by nitrogen doping, and expanded the interlayer spacing of the pseudo-graphite structure, thereby significantly improving the reversible capacity and rate performance. At the same time, nitrogen doping would cause certain damage to the microstructure of the porous carbon material, thereby weakening the cycle stability. The comprehensive performance trade-off showed that although the cycle stability of Example 1 was slightly lower than that of Comparative Example 1, the reversible capacity and rate performance were significantly improved, and the cycle stability was still excellent compared with the same type of material.

[0062] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An all-carbon sodium-based bi-ion capacitor comprising a negative electrode sheet, a separator, an electrolyte, and a positive electrode sheet, characterized by, The positive electrode plate comprises nitrogen-doped porous carbon, wherein the nitrogen-doped porous carbon is prepared by the following steps: (1) zinc citrate, dispersant and dopamine hydrochloride are added into deionized water, then anhydrous ethanol is added, and the mixture is stirred at room temperature, filtered, washed and dried to obtain a precursor; (2) the precursor obtained in step (1) is annealed under the protection of inert gas to obtain a pyrolysis product, and then the pyrolysis product is soaked in acid, washed and dried to obtain nitrogen-doped porous carbon.

2. The all-carbon sodium-based bi-ion capacitor of claim 1, wherein, The molar ratio of zinc citrate, dispersant and dopamine hydrochloride is (1-3):2:

1.

3. The all-carbon sodium-based bi-ion capacitor of claim 1 or 2, wherein, The dispersant is tris(hydroxymethyl) aminomethane.

4. The all-carbon sodium-based bi-ion capacitor of claim 3, wherein, 0.05-0.2 moL zinc citrate is added per L deionized water; the volume ratio of anhydrous ethanol to deionized water is (1-2):

1.

5. The all-carbon sodium-based bi-ion capacitor of claim 3, wherein, The stirring time at room temperature is 18-24 h.

6. The all-carbon sodium-based bi-ion capacitor of claim 5, wherein, The annealing temperature is 700-1200℃, and the annealing time is 1-10 h.

7. The all-carbon sodium-based bi-ion capacitor of claim 6, wherein, The positive electrode plate further comprises a conductive agent and a binder; the negative electrode plate comprises hard carbon powder, a conductive agent and a binder.

8. The all-carbon sodium-based bi-ion capacitor of claim 7, wherein, The mass ratio of the nitrogen-doped porous carbon, the conductive agent and the binder is (8-9):1:

1.

9. The all-carbon sodium-based bi-ion capacitor of claim 8, wherein, The mass ratio of the hard carbon powder, the conductive agent and the binder is (8-9):1:

1.

10. The method of making an all-carbon sodium-based bi-ion capacitor of claim 1, wherein, The steps are as follows: the positive electrode plate, the separator and the negative electrode plate are stacked in sequence, electrolyte is added, and then the battery is assembled.

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