Nickel-sulfur-selenium selenide / nitrogen-doped carbon composite material, preparation method thereof and energy storage device

Abstract

The application belongs to the field of electrochemical energy storage, and discloses a nickel-sulfur-selenium compound / nitrogen-doped carbon composite material, a preparation method thereof and an energy storage device. The preparation method comprises the following steps: dissolving nickel ammonium sulfate, citric acid and sodium chloride in water to obtain a mixed solution, and then evaporating the mixed solution to obtain a solid precursor; the mass ratio of nickel ammonium sulfate, citric acid and sodium chloride is 1:(0.8-1.2):(8-15); the solid precursor is placed in a reducing atmosphere, calcined at 500-800 DEG C for 2-4 h to obtain a triniickel disulfide / nickel / nitrogen-doped carbon composite material; the triniickel disulfide / nickel / nitrogen-doped carbon composite material is uniformly mixed with selenium powder, and then placed in an inert atmosphere, calcined at 400-500 DEG C for 2-4 h to obtain the final nickel-sulfur-selenium compound / nitrogen-doped carbon composite material; the mass ratio of the triniickel disulfide / nickel / nitrogen-doped carbon composite material and the selenium powder is 1:(2-5). The application can improve the stability of the potassium ion hybrid capacitor electrode material.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage, specifically relating to nickel sulfide selenide / nitrogen-doped carbon composite materials, their preparation methods, and energy storage devices. Background Technology

[0002] Potassium-ion hybrid capacitors, as novel asymmetric energy storage devices, combine a potassium-ion battery-type negative electrode with a capacitor-type positive electrode, integrating the core electrochemical advantages of both types of devices. During charging, potassium ions in the electrolyte are embedded into the lattice of the negative electrode material to store charge, while anions in the electrolyte are adsorbed onto the surface of the porous carbon material of the positive electrode to form an electric double layer. During discharging, potassium ions are de-intercalated from the negative electrode, and anions are desorbed from the surface of the positive electrode, jointly achieving a stable release of electrical energy. This unique energy storage mechanism not only enables potassium-ion hybrid capacitors to achieve breakthroughs in energy density, cycle stability, and operating voltage, but also inherits the advantages of low-cost and high conductivity of potassium resources, effectively compensating for the resource limitations of lithium-ion batteries and the insufficient energy density of traditional capacitors. However, potassium-ion hybrid capacitors experience particle agglomeration and volume expansion during charging and discharging, which generates continuous internal stress within the electrode material, ultimately leading to microcracks or even overall fragmentation and pulverization of the electrode material. Therefore, the stability of the electrode material in potassium-ion hybrid capacitors needs to be improved. Summary of the Invention

[0003] To address the problems existing in the prior art, the present invention aims to provide a nickel sulfide selenide / nitrogen-doped carbon composite material, its preparation method, and an energy storage device. The present invention can improve the stability of potassium ion hybrid capacitor electrode materials.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The preparation method of nickel sulfide selenide / nitrogen-doped carbon composite material includes the following steps: Nickel ammonium sulfate, citric acid, and sodium chloride are dissolved in water to obtain a mixed solution, which is then evaporated to dryness to obtain a solid precursor; wherein the mass ratio of nickel ammonium sulfate, citric acid, and sodium chloride is 1:(0.8-1.2):(8-15). The solid precursor was placed in a reducing atmosphere and calcined at 500-800℃ for 2-4 hours to obtain a nickel disulfide / nickel / nitrogen-doped carbon composite material. The nickel disulfide / nickel / nitrogen-doped carbon composite material is mixed with selenium powder, and then placed in an inert atmosphere and calcined at 400-500 °C for 2-4 h to obtain the final nickel sulfide selenide / nitrogen-doped carbon composite material; wherein the mass ratio of the nickel disulfide / nickel / nitrogen-doped carbon composite material to selenium powder is 1:(2-5).

[0005] Preferably, when evaporating the mixed solution to dryness, the mixed solution is stirred while evaporating at 60-90°C.

[0006] Preferably, the reducing atmosphere is a mixture of argon and hydrogen; in the mixed atmosphere, the volume fraction of argon is 90%-95%, and the remainder is hydrogen.

[0007] Preferably, when the solid precursor is placed in a mixed atmosphere and calcined at 500-800°C, a mixed gas consisting of argon and hydrogen is introduced into the calcination furnace at a flow rate of 50-90 SCCM, where SCCM refers to standard cubic centimeters per minute.

[0008] Preferably, the solid precursor is placed in a reducing atmosphere and calcined at 500-800°C, and heated to the calcination temperature at a heating rate of 3-5°C / min.

[0009] Preferably, the inert atmosphere is argon; The nickel disulfide / nickel / nitrogen-doped carbon composite material is mixed with selenium powder and then placed in an inert atmosphere. When calcined at 400-500 °C, the flow rate of argon gas is 30-60 SCCM.

[0010] Preferably, the nickel disulfide / nickel / nitrogen-doped carbon composite material is mixed with selenium powder, and then placed in an inert atmosphere and calcined at 400-500 °C, and heated to the calcination temperature at a heating rate of 1-3 °C / min.

[0011] The present invention also provides a nickel sulfide selenide / nitrogen-doped carbon composite material, which is prepared by the method for preparing nickel sulfide selenide / nitrogen-doped carbon composite material as described above.

[0012] The present invention also provides an energy storage device, wherein the negative electrode of the energy storage device is made of the nickel sulfide selenide / nitrogen-doped carbon composite material described above.

[0013] Preferably, the energy storage device is a potassium-ion battery or a potassium-ion hybrid capacitor.

[0014] The present invention has the following beneficial effects: This invention involves preparing a mixed solution of nickel ammonium sulfate, citric acid, and sodium chloride in a specific mass ratio of 1:(0.8-1.2):(8-15) and evaporating it to dryness to form a solid precursor. Citric acid acts as a carbon source and complexing agent to ensure uniform dispersion of nickel, while sodium chloride acts as a pore-forming agent, volatilizing during subsequent calcination to create abundant pores. After calcination at 500-800℃ in a reducing atmosphere for 2-4 hours, the citric acid carbonizes to form nitrogen-doped carbon (NC), while simultaneously, nickel ions in the nickel ammonium sulfate are reduced and combine with sulfur to form... Nickel disulfide / nickel composite particles were formed, and these particles (i.e., nickel disulfide / nickel composite particles) were grown in situ in the NC sheet structure, thus forming a nickel disulfide / nickel / nitrogen-doped carbon composite material. The nickel disulfide / nickel / nitrogen-doped carbon composite material was mixed with selenium powder at a mass ratio of 1:(2-5) and calcined at 400-500℃ in an inert atmosphere for 2-4 hours to form nickel sulfide selenide nanoparticles. Finally, a three-dimensional porous composite structure of nickel sulfide selenide composite nanoparticles in situ loaded on two-dimensional NC sheets was constructed. In this three-dimensional porous composite structure, the NC framework can suppress the aggregation of nanoparticles during the charging and discharging process through the steric hindrance effect. At the same time, the buffer space of the porous structure can alleviate the volume expansion caused by potassium ion insertion or extraction, thereby reducing the internal stress of the material to avoid fragmentation and pulverization, effectively improving the stability of the nickel sulfide selenide / nitrogen-doped carbon composite material of the present invention. Furthermore, the three-dimensional porous network constructed by NC can serve as a conductive pathway to reduce electron transport resistance. Combined with the Ni3S2 and NiSe2 heterostructure formed by two-step calcination, it increases potassium storage active sites and optimizes potassium ion diffusion kinetics, thereby improving the electrochemical performance of the nickel sulfide selenide / nitrogen-doped carbon composite material of the present invention. Attached Figure Description

[0015] Figure 1 The images show the XRD patterns of the nickel sulfide selenide / nitrogen-doped carbon composite material (denoted as Ni3S2 / NiSe2 / NC composite material) and the Ni3S2 / Ni / NC composite material prepared in Example 1 of this invention.

[0016] Figure 2 This is a SEM image of the Ni3S2 / NiSe2 / NC composite material prepared in Example 1 of this invention.

[0017] Figure 3 This is a TEM image of the Ni3S2 / NiSe2 / NC composite material prepared in Example 1 of this invention.

[0018] Figure 4 This is a SEM image of the porous C composite material prepared in Comparative Example 1 of this invention. Figure 5 The graph shows the potassium storage cycling performance of the Ni3S2 / NiSe2 / NC composite material, Ni3S2 / Ni / NC composite material, and porous C composite material prepared in Example 1 of the present invention at 0.1 A / g.

[0019] Figure 6 These are the charging and discharging curves of a potassium ion hybrid capacitor assembled from the Ni3S2 / NiSe2 / NC composite material prepared in Example 1 of this invention and activated carbon (AC) at different current densities.

[0020] Figure 7 Potassium ion rate performance of the potassium ion mixed capacitor assembled with activated carbon using the Ni3S2 / NiSe2 / NC composite material prepared in Example 1 of this invention.

[0021] Figure 8 This is a graph showing the potassium storage cycling performance of the Ni3S2 / NiSe2 / NC composite material prepared in Example 2 of this invention at 0.1 A / g. Detailed Implementation

[0022] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] The preparation method of the nickel sulfide selenide / nitrogen-doped carbon composite material of the present invention includes the following steps: Step (1): Dissolve nickel ammonium sulfate, citric acid and sodium chloride in water to obtain a mixed solution. Then, stir and evaporate the mixed solution at 60-90℃ to obtain a solid precursor. The mass ratio of nickel ammonium sulfate, citric acid and sodium chloride is 1:(0.8-1.2):(8-15).

[0024] Step (2): The solid precursor obtained in step (1) is placed in a reducing atmosphere and heated to 500-800 °C at a heating rate of 3-5 °C / min for calcination for 2-4 h to obtain a nickel disulfide / nickel / nitrogen-doped carbon composite material (denoted as Ni3S2 / Ni / NC composite material); wherein, the reducing atmosphere can be a mixture of argon and hydrogen, in which the volume fraction of argon is 90%-95% and the remainder is hydrogen; during the calcination process, a mixture of argon and hydrogen is introduced into the calcination furnace at a flow rate of 50-90 SCCM.

[0025] Step (3): Mix the nickel disulfide / nickel / nitrogen-doped carbon composite material obtained in step (2) with selenium powder to obtain a mixture. The mass ratio of the nickel disulfide / nickel / nitrogen-doped carbon composite material to selenium powder in the mixture is 1:(2-5). Place the mixture in an inert atmosphere (such as argon) and heat it to 400-600 ℃ at a heating rate of 1-3 ℃ / min for calcination. The calcination time is 1-4h to obtain the final nickel sulfide selenide / nitrogen-doped carbon composite material (denoted as Ni3S2 / NiSe2 / NC composite material). During the calcination process, the flow rate of the inert gas is 30-60 SCCM.

[0026] The Ni3S2 / NiSe2 / NC composite material obtained by this invention can be applied to potassium-ion energy storage devices (such as potassium-ion batteries or potassium-ion hybrid capacitors). The Ni3S2 / NiSe2 / NC composite material of this invention can alleviate the volume expansion effect of electrode materials during charging and discharging and effectively improve the conductivity of electrode materials, thereby achieving the goal of improving the electrochemical performance of potassium-ion batteries and potassium-ion hybrid capacitors.

[0027] Example 1 The preparation method of the Ni3S2 / NiSe2 / NC composite material in this embodiment includes the following steps: Step (1): Dissolve 1.0 g nickel ammonium sulfate, 1.1 g citric acid and 10.0 g sodium chloride in water to obtain a mixed solution. Then, stir and evaporate the mixed solution at 80 °C to obtain a solid precursor.

[0028] Step (2): The solid precursor obtained in step (1) is placed in a calcining furnace, and a mixed gas consisting of argon and hydrogen is introduced into the calcining furnace at a flow rate of 80 SCCM. Then, it is heated to 700 ℃ at a heating rate of 3 ℃ / min for calcination for 3 h to obtain Ni3S2 / Ni / NC composite material. The volume fraction of argon in the mixed gas is 90%, and the volume fraction of hydrogen is 10%.

[0029] Step (3): Mix the Ni3S2 / Ni / NC composite material obtained in step (2) with selenium powder to obtain a mixture. The mass ratio of Ni3S2 / Ni / NC composite material to selenium powder in the mixture is 1:3. Place the mixture in an inert atmosphere and heat it to 500 ℃ at a heating rate of 3 ℃ / min for calcination for 2 h to obtain the final nickel sulfide selenide / nitrogen-doped carbon composite material. The inert atmosphere is argon gas, and the argon gas flow rate is 50 SCCM.

[0030] The Ni3S2 / NiSe2 / NC composite material and the Ni3S2 / Ni / NC composite material obtained in this embodiment were characterized by X-ray diffraction, and the XRD patterns of the Ni3S2 / NiSe2 / NC composite material and the Ni3S2 / Ni / NC composite material were obtained. The results are as follows. Figure 1 As shown, Figure 1 In the diagram, the curve below Ni3S2 / NiSe2 / NC is the XRD pattern of the Ni3S2 / NiSe2 / NC composite material, the curve below Ni3S2 / Ni / NC is the XRD pattern of the Ni3S2 / Ni / NC composite material, PDF#44-1418 is the XRD pattern of Ni3S2 in the standard PDF card for Ni3S2, and PDF#41-1495 is the XRD pattern of NiSe2 in the standard PDF card for NiSe2.

[0031] from Figure 1 It can be seen that the XRD diffraction peaks of the Ni3S2 / NiSe2 / NC composite material and the Ni3S2 / Ni / NC composite material correspond to the XRD diffraction peaks in the standard PDF card of Ni3S2, and the XRD diffraction peaks of the Ni3S2 / NiSe2 / NC composite material correspond to the XRD diffraction peaks in the standard PDF card of NiSe2, proving that the Ni3S2 / NiSe2 / NC composite material was successfully prepared in this embodiment.

[0032] The morphology of the Ni3S2 / NiSe2 / NC composite material obtained in this embodiment was characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the results are as follows. Figure 2 and Figure 3 As shown, the Ni3S2 / NiSe2 nanoparticles in the Ni3S2 / NiSe2 / NC composite material are uniformly loaded on the two-dimensional NC substrate, forming a structurally stable three-dimensional hierarchical composite material. Figure 3 Two-dimensional materials (i.e., NC substrates, which have a layered structure) can be clearly observed. In the Ni3S2 / NiSe2 / NC composite structure, the three-dimensional porous NC can effectively suppress the agglomeration and volume expansion of Ni3S2 / NiSe2 nanoparticles during charging and discharging, and can also act as a three-dimensional conductor, effectively improving the electronic conductivity of Ni3S2 / NiSe2. Ni3S2 / NiSe2 has a high theoretical specific capacity as a conversion-type anode, and the heterojunction between Ni3S2 and NiSe2 can provide more potassium storage active sites. The synergistic effect of the two (i.e., Ni3S2 and NiSe2) can effectively improve the electrochemical performance of potassium-ion batteries and potassium-ion hybrid capacitors.

[0033] Comparative Example 1 The preparation method of the composite material in this comparative example includes the following steps: Step (1): Dissolve 1.1 g of citric acid and 10.0 g of sodium chloride in water to obtain a mixed solution. Then, stir and evaporate the mixed solution at 80 °C to obtain a solid precursor.

[0034] Step (2): The solid precursor obtained in step (1) is placed in a calcining furnace. A mixed gas consisting of argon and hydrogen is introduced into the calcining furnace at a flow rate of 80 SCCM. Then, it is heated to 700 ℃ at a heating rate of 3 ℃ / min for calcination for 3 h to obtain a porous C composite material. The volume fraction of argon in the mixed gas is 90%, and the volume fraction of hydrogen is 10%.

[0035] The morphology of the porous C composite material obtained in this comparative example was characterized by scanning electron microscopy, and the results are as follows: Figure 4 As shown in the figure, the porous C composite material obtained in this comparative example exhibits a three-dimensional porous structure.

[0036] In Example 1 and Comparative Example 1 above, the Ni3S2 / Ni / NC composite material, the Ni3S2 / NiSe2 / NC composite material, and the porous C composite material (denoted as C) were all powdered composite materials. The composite materials obtained in Example 1 and Comparative Example 1 were respectively used to prepare working electrodes, and then assembled into potassium-ion batteries and potassium-ion hybrid capacitors, respectively. The electrochemical performance of the potassium-ion batteries and potassium-ion hybrid capacitors was tested, and the specific experimental conditions are as follows: (1) Preparation of working electrode The powdered composite material prepared in Example 1 was mixed uniformly with acetylene black and polyvinylidene fluoride at a mass ratio of 7:2:1. Then, an appropriate amount of N-methylpyrrolidone was added dropwise and the mixture was stirred until homogeneous. The homogeneous slurry was uniformly coated onto copper foil and dried in a vacuum drying oven at 80 °C. Finally, it was punched into a disc with a diameter of 12 mm, which was used as the working electrode. The disc was weighed, and the mass of the active material in the electrode was found to be 1.6 ± 0.1 mg cm⁻¹ according to the feeding ratio. -2 .

[0037] (2) Potassium-ion battery assembly Using the aforementioned disc as the working electrode, pure potassium metal as the counter electrode and reference electrode, and glass fiber as the diaphragm, the electrolyte is a 1 mol / L potassium hexafluorophosphate (KPF6) electrolyte, and its solvent system is a mixture of ethylene carbonate (EC) and propylene carbonate (PC) in a volume ratio of 1:1.

[0038] (3) Assembly of potassium ion mixed capacitors Using the aforementioned disc as the negative electrode, activated carbon as the positive electrode, and glass fiber as the separator, and with the same electrolyte as used in the potassium-ion battery assembly described above, and a negative-to-positive electrode mass ratio of 3:1, a Ni3S2 / NiSe2 / NC||AC potassium-ion hybrid capacitor was assembled. Before assembling the potassium-ion hybrid capacitor, the Ni3S2 / NiSe2 / NC loaded electrode (i.e., the aforementioned disc) was tightly bonded to the potassium metal sheet, and then placed in the electrolyte and allowed to stand for 2 hours for activation.

[0039] The entire assembly process was completed in a glove box filled with Ar atmosphere, and the glove was sealed using a sealing machine.

[0040] Similarly, the porous C composite material obtained in Comparative Example 1 was also assembled into a potassium-ion battery and a potassium-ion hybrid capacitor according to the same process described above.

[0041] (4) Electrochemical performance testing The electrochemical performance of potassium-ion batteries and potassium-ion hybrid capacitors was tested using assembled button cells as test devices. The specific charge capacity, cycle stability, and rate performance of these devices were tested using a battery tester. The test results are shown below. Figures 5-7 .

[0042] Figure 5 The Ni3S2 / NiSe2 / NC composite material prepared in Example 1 is shown in a comparative manner (in... Figure 5 The abbreviation is Ni3S2 / NiSe2 / NC, and the composite material is Ni3S2 / Ni / NC. Figure 5 The porous C composite material prepared in Comparative Example 1 (abbreviated as Ni3S2 / Ni / NC) is compared with that prepared in Comparative Example 1. Figure 5 (C) Potassium storage cycle performance at a current density of 0.1 A / g. From... Figure 5 As observed, the Ni3S2 / NiSe2 / NC composite material prepared in Example 1 exhibits a charge specific capacity of 382 mAh / g and a coulombic efficiency of 98.7% after 150 cycles. The Ni3S2 / Ni / NC composite material prepared in Example 1 also exhibits a charge specific capacity of 233 mAh / g and a coulombic efficiency of 97.3% after 150 cycles. In contrast, the porous C composite material prepared in Comparative Example 1 has a charge specific capacity of only 192 mAh / g and a coulombic efficiency of 96.1% after 60 cycles at the same current density (0.1 A / g). These experimental results demonstrate that the Ni3S2 / NiSe2 / NC composite material prepared in this example exhibits high charge specific capacity and good cycling stability, proving the effectiveness of the synthesis method of this invention.

[0043] Figure 6The figures show the charging and discharging curves of a potassium-ion hybrid capacitor (denoted as Ni3S2 / NiSe2 / NC ||AC) assembled using the Ni3S2 / NiSe2 / NC composite material prepared in Example 1, under current densities of 0.1 A / g, 1 A / g, and 4 A / g, with a voltage range of 0.01-4.0 V. It can be seen that the charging and discharging curves of this potassium-ion hybrid capacitor are not ideally linear, indicating that the "coupling effect" between two different forms of energy storage (i.e., battery and capacitor) is the cause. Furthermore, the shapes of the charging and discharging curves are maintained as the charging and discharging current densities increase.

[0044] Figure 7 This is a rate performance graph of a potassium-ion hybrid capacitor assembled using the Ni3S2 / NiSe2 / NC composite material prepared in Example 1. The specific capacity of this potassium-ion hybrid capacitor is 80 mAh / g at a current density of 0.1 A / g, 72 mAh / g at 0.2 A / g, 64 mAh / g at 0.5 A / g, 53 mAh / g at 1 A / g, 47 mAh / g at 2 A / g, 38 mAh / g at 3 A / g, and 32 mAh / g at 4 A / g. When the current density returns to 0.1 A / g, the specific capacity recovers to 68 mAh / g. These experimental data further demonstrate that the Ni3S2 / NiSe2 / NC composite material prepared in this example also exhibits excellent rate performance when used as the negative electrode material of the potassium-ion hybrid capacitor.

[0045] Example 2 The preparation method of the Ni3S2 / NiSe2 / NC composite material in this embodiment includes the following steps: Step (1): Dissolve 1.0 g nickel ammonium sulfate, 1.2 g citric acid and 15.0 g sodium chloride in water to obtain a mixed solution. Then, stir and evaporate the mixed solution at 90 °C to obtain a solid precursor.

[0046] Step (2): The solid precursor obtained in step (1) is placed in a calcining furnace, and a mixed gas consisting of argon and hydrogen is introduced into the calcining furnace at a flow rate of 90 SCCM. Then, it is heated to 800 ℃ at a heating rate of 5 ℃ / min for calcination for 4 h to obtain Ni3S2 / Ni / NC composite material. The volume fraction of argon in the mixed gas is 93%, and the volume fraction of hydrogen is 7%.

[0047] Step (3): Mix the Ni3S2 / Ni / NC composite material obtained in step (2) with selenium powder to obtain a mixture. The mass ratio of Ni3S2 / Ni / NC composite material to selenium powder in the mixture is 1:5. Place the mixture in an inert atmosphere and heat it to 500 ℃ at a heating rate of 3 ℃ / min for calcination for 2 h to obtain the final nickel sulfide selenide / nitrogen-doped carbon composite material. The inert atmosphere is argon gas, and the argon gas flow rate is 60 SCCM.

[0048] Following the same method as assembling the Ni3S2 / NiSe2 / NC composite material obtained in Example 1 into a potassium-ion battery, the Ni3S2 / NiSe2 / NC composite material prepared in Example 2 was assembled into a potassium-ion battery. After testing, as... Figure 8 As shown, the specific charge capacity of this potassium-ion battery after 150 cycles is 358 mAh / g, and the coulombic efficiency is 98.1%. These experimental results demonstrate that the Ni3S2 / NiSe2 / NC composite material prepared in this embodiment exhibits high specific charge capacity and good cycle stability.

[0049] Example 3 The preparation method of the Ni3S2 / NiSe2 / NC composite material in this embodiment includes the following steps: Step (1): Dissolve 1.0 g nickel ammonium sulfate, 0.8 g citric acid and 8.0 g sodium chloride in water to obtain a mixed solution. Then, stir and evaporate the mixed solution at 60 °C to obtain a solid precursor.

[0050] Step (2): The solid precursor obtained in step (1) is placed in a calcining furnace. A mixed gas consisting of argon and hydrogen is introduced into the calcining furnace at a flow rate of 50 SCCM. Then, it is heated to 500 ℃ at a heating rate of 5 ℃ / min for calcination for 2 h to obtain Ni3S2 / Ni / NC composite material. The volume fraction of argon in the mixed gas is 95%, and the volume fraction of hydrogen is 5%.

[0051] Step (3): The Ni3S2 / Ni / NC composite material obtained in step (2) is mixed with selenium powder to obtain a mixture. The mass ratio of Ni3S2 / Ni / NC composite material to selenium powder in the mixture is 1:2. The mixture is then placed in an inert atmosphere and heated to 400 ℃ at a heating rate of 1 ℃ / min for calcination for 4 h to obtain the final nickel sulfide selenide / nitrogen-doped carbon composite material. The inert atmosphere is argon gas, and the argon gas flow rate is 30 SCCM.

[0052] Following the same method as assembling the Ni3S2 / NiSe2 / NC composite material obtained in Example 1 into a potassium-ion battery, the Ni3S2 / NiSe2 / NC composite material prepared in Example 3 was assembled into a potassium-ion battery. The battery was tested and found to have a specific charge capacity of 341 mAh / g and a coulombic efficiency of 98% after 150 cycles. These experimental results demonstrate that the Ni3S2 / NiSe2 / NC composite material prepared in this example exhibits high specific charge capacity and good cycle stability.

[0053] Example 4 The preparation method of the Ni3S2 / NiSe2 / NC composite material in this embodiment includes the following steps: Step (1): Dissolve 1.0 g nickel ammonium sulfate, 1.0 g citric acid and 9.0 g sodium chloride in water to obtain a mixed solution. Then, stir and evaporate the mixed solution at 70 °C to obtain a solid precursor.

[0054] Step (2): The solid precursor obtained in step (1) is placed in a calcining furnace, and a mixed gas consisting of argon and hydrogen is introduced into the calcining furnace at a flow rate of 60 SCCM. Then, it is heated to 600 ℃ at a heating rate of 4 ℃ / min for calcination for 2 h to obtain Ni3S2 / Ni / NC composite material. The volume fraction of argon in the mixed gas is 95%, and the volume fraction of hydrogen is 5%.

[0055] Step (3): The Ni3S2 / Ni / NC composite material obtained in step (2) is mixed with selenium powder to obtain a mixture. The mass ratio of Ni3S2 / Ni / NC composite material to selenium powder in the mixture is 1:2.5. The mixture is then placed in an inert atmosphere and heated to 450 ℃ at a heating rate of 2 ℃ / min for calcination for 3 h to obtain the final nickel sulfide selenide / nitrogen-doped carbon composite material. The inert atmosphere is argon gas, and the argon gas flow rate is 40 SCCM.

[0056] Following the same method as assembling the Ni3S2 / NiSe2 / NC composite material obtained in Example 1 into a potassium-ion battery, the Ni3S2 / NiSe2 / NC composite material prepared in Example 4 was assembled into a potassium-ion battery. The battery was tested and found to have a specific charge capacity of 339 mAh / g and a coulombic efficiency of 97.8% after 150 cycles. These experimental results demonstrate that the Ni3S2 / NiSe2 / NC composite material prepared in this example exhibits high specific charge capacity and good cycle stability.

[0057] The experimental results above show that the specific charge capacity and coulombic efficiency of the Ni3S2 / NiSe2 / NC composite materials prepared in Examples 1-4 are different. Among them, the Ni3S2 / NiSe2 / NC composite material prepared in Example 1 has the best cycle performance and specific charge capacity.

[0058] Furthermore, the experimental results above show that the Ni3S2 / NiSe2 / NC composite material provided by this invention can significantly improve capacity and cycle stability when used as a negative electrode material for potassium-ion batteries or capacitors.

[0059] As can be seen from the above scheme, the method of the present invention is simple and low in cost. The prepared nickel sulfide selenide Ni3S2 / NiSe2 nanoparticles are loaded in a three-dimensional hierarchical structure of nitrogen-doped carbon, which can effectively improve the conductivity of the electrode material and alleviate the volume expansion effect of the electrode material during charging and discharging. This can achieve the goal of improving the electrochemical performance of potassium-ion batteries and potassium-ion hybrid capacitors.

[0060] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing nickel sulfide selenide / nitrogen-doped carbon composite material, characterized in that, The process includes the following: Nickel ammonium sulfate, citric acid, and sodium chloride are dissolved in water to obtain a mixed solution, which is then evaporated to dryness to obtain a solid precursor; wherein the mass ratio of nickel ammonium sulfate, citric acid, and sodium chloride is 1:(0.8-1.2):(8-15). The solid precursor was placed in a reducing atmosphere and calcined at 500-800℃ for 2-4 hours to obtain a nickel disulfide / nickel / nitrogen-doped carbon composite material. The nickel disulfide / nickel / nitrogen-doped carbon composite material is mixed with selenium powder, and then placed in an inert atmosphere and calcined at 400-500℃ for 2-4 hours to obtain the final nickel sulfide selenide / nitrogen-doped carbon composite material; wherein the mass ratio of the nickel disulfide / nickel / nitrogen-doped carbon composite material to selenium powder is 1:(2-5).

2. The method for preparing the nickel sulfide selenide / nitrogen-doped carbon composite material according to claim 1, characterized in that, When evaporating the mixed solution to dryness, the solution is stirred while evaporating at 60–90°C.

3. The method for preparing the nickel sulfide selenide / nitrogen-doped carbon composite material according to claim 1, characterized in that, The reducing atmosphere is a mixture of argon and hydrogen; in the mixed atmosphere, the volume fraction of argon is 90%-95%, and the remainder is hydrogen.

4. The method for preparing the nickel sulfide selenide / nitrogen-doped carbon composite material according to claim 3, characterized in that, When the solid precursor is placed in a mixed atmosphere and calcined at 500-800°C, a mixed gas consisting of argon and hydrogen is introduced into the calcination furnace at a flow rate of 50-90 SCCM.

5. The method for preparing the nickel sulfide selenide / nitrogen-doped carbon composite material according to claim 1, 3, or 4, characterized in that, The solid precursor is placed in a reducing atmosphere and calcined at 500-800°C, and heated to the calcination temperature at a heating rate of 3-5°C / min.

6. The method for preparing the nickel sulfide selenide / nitrogen-doped carbon composite material according to claim 1, characterized in that, The inert atmosphere is argon; The nickel disulfide / nickel / nitrogen-doped carbon composite material is mixed with selenium powder and then placed in an inert atmosphere. When calcined at 400-500℃, the flow rate of argon gas is 30-60 SCCM.

7. The method for preparing the nickel sulfide selenide / nitrogen-doped carbon composite material according to claim 1 or 6, characterized in that, The nickel disulfide / nickel / nitrogen-doped carbon composite material is mixed with selenium powder, and then placed in an inert atmosphere and calcined at 400-500 °C, with a heating rate of 1-3 °C / min to the calcination temperature.

8. A nickel sulfide selenide / nitrogen-doped carbon composite material, characterized in that, The nickel sulfide selenide / nitrogen-doped carbon composite material is prepared by the method for preparing the nickel sulfide selenide / nitrogen-doped carbon composite material according to any one of claims 1-7.

9. An energy storage device, characterized in that, The negative electrode of the energy storage device is made of the nickel sulfide selenide / nitrogen-doped carbon composite material as described in claim 8.

10. The energy storage device according to claim 9, characterized in that, The energy storage device is a potassium-ion battery or a potassium-ion hybrid capacitor.

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