Preparation method of high-yield nickel disulfide or nickel disulfide / sulfur compound and application of high-yield nickel disulfide or nickel disulfide / sulfur compound in electrode material

Abstract

The invention belongs to the technical field of new materials, and provides a preparation method of high-yield nickel disulfide (NiS2) or a nickel disulfide / sulfur compound (NiS2 / (x-2) S, 3 < = x < = 8) and an application of NiS2 or NiS2 / S in an electrode material. The preparation method comprises the following steps: mixing a nickel ion (Ni < 2 + >) solution with a sodium disulfide (Na2S2) solution or a sodium polysulfide (Na2Sx, x is greater than or equal to 3 and less than or equal to 8) solution, stirring and reacting for 0.5-12 hours, collecting precipitates obtained by reaction, washing and drying to obtain a NiS2 or NiS2 / (x-2) S (x is greater than or equal to 3 and less than or equal to 8) product. The preparation method is simple and easy to operate, low in cost, high in atom utilization rate, green and environment-friendly, high in safety and capable of realizing large-scale industrial production. And when used as an electrode material for a sodium ion battery, the composite material shows good electrochemical performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of new materials, and particularly relates to a method for preparing high-yield nickel disulfide or nickel disulfide / sulfur composite and its application in electrode materials. Further, it relates to a method for preparing high-yield nickel disulfide (NiS2) or nickel disulfide / sulfur composite (NiS2 / (x - 2)S, 3 ≤ x ≤ 8) and the application of NiS2 or NiS2 / S in electrode materials. Background Art

[0002] Transition metal sulfides are widely used in electrochemical ion storage, including Li + , Na + , K + , Mg 2+ , Al 3+ , Cu 2+ and OH −(eScience 3 (2023) 100138; Energy Storage Materials 54 (2023) 323-329; Advanced Functional Materials 31 (2021) 2010832; Journal of Alloys and Compounds 1012 (2025) 178541; Nature Communications 15 (2024) 492; Nature Communications 15 (2024) 1005; Inorganic Chemistry Frontiers 10 (2023) 3406-3414; National Science Review 10 (2023) nwac268; Journal of Alloys and Compounds 891 (2021) 161935; Nature Communications 12 (2021) 5714; Science Advances 7 (2021) eabg6314; Science 192 (4244) 1126-1127; ACS Sustainable Chemistry & Engineering 11 (2023) 7012-7020; ACS Sustainable Chemistry & Engineering 11 (2023) 3260−3269). Among them, nickel disulfide (NiS2) is a sulfide with high specific capacity and low cost characteristics. In recent years, great progress has been made in the research on the ion storage properties of NiS2. The preparation methods of nickel disulfide are divided into solid-phase method and liquid-phase method. They all have problems such as complex production methods, high costs, or low safety levels.

[0003] The previous solid-state sulfidation method for preparing NiS2 (Advanced Functional Materials 34 (2024) 2403166; Applied Surface Science 669 (2024) 160524; Journal of Colloid and Interface Science 638 (2023) 274-280; Journal of Materials Chemistry A 6 (2018) 6595-6605; Journal of Materials Chemistry A 8 (2020) 8612-8619; Journal of Materials Chemistry A 5 (2017) 10173-10181) and hydrothermal / solvothermal method (Advanced Functional Materials 31 (2021) 2010832; Chemical Engineering Journal 409 (2021) 127237; Journal of Alloys and Compounds 937 (2023) 168379; Nanoscale 15 (2023) 1702-1708; Small 13 (2017) 1701744) have the same disadvantages, namely low atomic utilization rate and the generation of harmful by-product SO2.

[0004] A typical solid-state sulfidation strategy is to react Ni(OH)2 or Ni-MOF with an excessive sulfur precursor at high temperature. For example, Ni-MOFs powder and thiourea are mixed in a mass ratio of 1:20 and then heat-treated at 350 °C to obtain NiS2 (Journal of Materials Chemistry A 6 (2018) 14077-14082). This reaction is equivalent to only 10% of S atoms being effectively utilized to form NiS2 crystals together with nickel atoms. In addition, for the chemical reaction between Ni(OH)2 powder and sulfur powder, an excessive amount of sulfur powder is also used, and the reaction equation is 2Ni(OH)2 + 5S → 2NiS2 + SO2 + 2H2O (RSC Advances 12 (2022) 10401-10408). Most of the sulfur powder used sublimes at high temperature and is wasted. For the small amount of sulfur powder participating in the chemical reaction, 80% enters the NiS2 lattice, and the other 20% is generated in the form of harmful gas SO2, which is not only a waste of sulfur raw materials but also causes environmental pollution.

[0005] A typical solvothermal method synthesizes NiS2 nanospheres (Small 13 (2017) 1701744) through the chemical reaction between C4H6O4Ni·4H2O and Na2S2O3·5H2O with a molar ratio of 1:3, that is, the molar ratio of Ni and S atoms is 1:6. The chemical equation of this reaction is Ni 2+ + 2S2O3 2− → NiS2+ SO4 2− + SO2. It can be seen that among the added sulfur sources, 2 / 3 participated in this chemical reaction, and the other 1 / 3 was decomposed and consumed in the high-temperature and high-pressure environment. Among the 2 / 3 sulfur sources that participated, 50% entered the lattice of NiS2, 25% formed the harmful by-product SO2, and the other 25% formed the by-product SO4 2− . Generally speaking, under the condition that the molar ratio of Ni and S atoms in the feed is 1:6, only 1 / 3 of the S atoms are effectively utilized and form NiS2 crystals together with nickel, and the other 2 / 3 of the S atoms are wasted in various forms.

[0006] Based on the above research and development status of the preparation of nickel disulfide, it is urgent to develop a more simple, environmentally friendly and higher atomic utilization innovative synthesis method. Summary of the Invention

[0007] To solve the above existing technical problems, the present invention provides a method for preparing high-yield nickel disulfide or nickel disulfide / sulfur composite and its application in electrode materials. Further, it provides a method for preparing high-yield nickel disulfide (NiS2) or nickel disulfide / sulfur composite (NiS2 / (x - 2)S, 3 ≤ x ≤ 8) and its application in electrode materials. This method is simple, low-cost, high-yield and suitable for mass production. The nickel disulfide prepared above is used as the electrode material of sodium-ion batteries.

[0008] The present invention is realized by the following technical solutions: A method for preparing high-yield nickel disulfide NiS2, comprising the following steps: (1) Preparation of sodium disulfide Na2S2 solution: Sodium sulfide nonahydrate Na2S·9H2O or sodium sulfide Na2S and sulfur powder with a molar ratio of 1:1 are added to a solvent and stirred until completely dissolved to obtain a Na2S2 solution with a concentration of a mol / L; where 0.01 ≤ a ≤ 1; (2) Preparation of nickel ion Ni 2+ solution: A soluble nickel salt is added to a solvent and stirred until completely dissolved to obtain a nickel ion Ni 2+ solution with a concentration of b mol / L; where: 0.01 ≤ b ≤ 1; (3) Preparation of NiS₂ product: Mix the Na₂S₂ solution obtained in step (1) with a volume of c L and the nickel ion Ni solution obtained in step (2) with a volume of d L, stir and react for 0.5 - 12 h, collect the precipitate obtained from the reaction, wash, and dry to obtain the NiS₂ product. 2+ The solvents described in steps (1) and (2) are deionized water or ethylene glycol EG.

[0009] The soluble nickel salt described in step (2) is any one of nickel chloride hexahydrate, nickel chloride, nickel sulfate hexahydrate, or nickel sulfate.

[0010] In step (3), control the reaction temperature below the boiling point of the solvent.

[0011] Furthermore, 0.5ac ≤ bd ≤ 2ac. More preferably, ac = bd.

[0012] The present invention also provides a method for preparing nickel disulfide / sulfur composite NiS₂ / (x - 2)S, 3 ≤ x ≤ 8, comprising the following steps:

[0013] (1) Preparation of sodium polysulfide Na₂Sₓ, 3 ≤ x ≤ 8 solution: Add Na₂S·9H₂O or Na₂S and sulfur powder with a molar ratio of 1:x - 1 to the solvent, stir until completely dissolved to obtain a Na₂Sₓ solution with a concentration of y mol / L; wherein the solvent is any one of diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, or tetraethylene glycol dimethyl ether; (1) Sodium polysulfide Na₂Sₓ x , 3 ≤ x ≤ 8 solution preparation: Add Na₂S·9H₂O or Na₂S and sulfur powder with a molar ratio of 1:x - 1 to the solvent, stir until completely dissolved to obtain a Na₂Sₓ solution, with a concentration of y mol / L; where the solvent is any one of diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, or tetraethylene glycol dimethyl ether; x The solvents described in steps (1) and (2) are deionized water or ethylene glycol EG. (2) Preparation of nickel ion Ni solution: Add the soluble nickel salt to ethylene glycol EG or deionized water, stir until completely dissolved to obtain a nickel ion Ni solution with a concentration of z mol / L, and the soluble nickel salt is any one of nickel chloride hexahydrate, nickel chloride, nickel sulfate hexahydrate, or nickel sulfate; 2+ Solution preparation: Add the soluble nickel salt to ethylene glycol EG or deionized water, stir until completely dissolved to obtain a nickel ion Ni solution, with a concentration of z mol / L, and the soluble nickel salt is any one of nickel chloride hexahydrate, nickel chloride, nickel sulfate hexahydrate, or nickel sulfate; 2+ The soluble nickel salt described in step (2) is any one of nickel chloride hexahydrate, nickel chloride, nickel sulfate hexahydrate, or nickel sulfate. (3) Preparation of NiS₂ / (x - 2)S (3 ≤ x ≤ 8) product: Mix the Na₂Sₓ solution obtained in step (1) with a volume of m L and the nickel ion Ni solution obtained in step (2) with a volume of n L, stir and react at 0 - 190 °C for 0.5 - 12 h, collect the precipitate obtained from the reaction, wash, and dry to obtain the NiS₂ / (x - 2)S (3 ≤ x ≤ 8) product; wherein: 0.5ym ≤ zn ≤ 2ym. x Solution and the nickel ion Ni solution obtained in step (2) with a volume of n L 2+ Mix the solution, stir and react at 0 - 190 °C for 0.5 - 12 h, collect the precipitate obtained from the reaction, wash, and dry to obtain the NiS₂ / (x - 2)S (3 ≤ x ≤ 8) product; where: 0.5ym ≤ zn ≤ 2ym.

[0014] Furthermore, ym = zn.

[0015] The present invention also provides the use of NiS2 prepared by the described method or NiS2 / (x-2)S (3 ≤ x ≤ 8) prepared by the described method as an active material in an electrode material.

[0016] The reaction principle of the present invention is as follows: Based on the fact that the NiS2 crystal is composed of Ni 2+ cations and S2 2- anions, Ni 2+ and S2 2- undergo a precipitation reaction to form NiS2 (Ni 2+ + S2 2− → NiS2), and Ni 2+ and S x 2- (3 ≤ x ≤ 8) in-situ undergo a coprecipitation reaction to form a NiS2 / (x-2)S composite material (Ni 2+ + S x 2− → NiS2+(x-2)S). The prepared NiS2 and NiS2 / (x-2)S are used for ion storage applications taking sodium batteries as an example.

[0017] The core of the present invention is that disulfide ions (S2 2- ) and nickel ions (Ni 2+ ) can undergo a precipitation reaction to form nickel disulfide. The internal mechanism is that the cations in the nickel disulfide solid are divalent nickel ions and the anions are disulfide ions. Therefore, when disulfide ions and nickel ions meet in solution, a precipitation reaction can occur to generate nickel disulfide. The nickel disulfide and the corresponding composite materials formed based on this mechanism are all within the protection scope of the present invention.

[0018] Another core of the present invention is that polysulfide ions (S x 2- , 3 ≤ x ≤ 8) and nickel ions (Ni 2+ ) can undergo a coprecipitation reaction to form a composite of nickel disulfide and elemental sulfur. The internal mechanism is that the cations in the nickel disulfide solid are divalent nickel ions and the anions are disulfide ions. Therefore, when polysulfide ions and nickel ions meet in solution, a coprecipitation reaction can occur to generate a composite of nickel disulfide and elemental sulfur. The composite materials of nickel disulfide and sulfur formed based on this mechanism are all within the protection scope of the present invention.

[0019] The function of the solvent used in the present invention is to dissolve the corresponding nickel salts, sodium sulfide, sodium disulfide or polysodium sulfide, and it is required not to chemically react with the nickel salts, sodium sulfide, sodium disulfide or polysodium sulfide. The solvent systems based on this mechanism are all within the protection scope of the present invention.

[0020] The nickel salt used in the present invention is to dissolve in the corresponding solvent system to provide solvated nickel ions (Ni 2+ ). Nickel salt systems based on this mechanism are all within the protection scope of the present invention.

[0021] The sodium sulfide used in the present invention is to react with elemental sulfur in the corresponding solvent system to form disulfide ions or polysulfide ions. Sulfide systems based on this mechanism are all within the protection scope of the present invention.

[0022] The preparation process of the present invention is simple and easy to operate, and large-scale industrial production can be realized. The prepared nickel disulfide material can be widely used in many fields such as catalysis, energy storage, and electronic devices. As an example, the present invention uses nickel disulfide in sodium-ion batteries and obtains good electrochemical performance. Description of the Drawings

[0023] Figure 1 Optical photographs of solubility tests of Na2S2 and Na2S8 in different solvents respectively. √ represents that a 0.5 M concentration solution can be formed at room temperature. No mark represents that a 0.5 M solution cannot be formed, and the added sulfur powder cannot be completely dissolved, and there is solid precipitation; Figure 2 XRD patterns of NiS2 prepared in deionized aqueous solution at 10, 25, 50 and 80 °C in Example 1; Figure 3 XRD patterns of NiS2 prepared in ethylene glycol (EG) solution at 10 °C and 25 °C in Example 2; Figure 4 XRD patterns of NiS2 prepared in ethylene glycol (EG) solution at 150 °C in Example 3; Figure 5 XRD patterns of NiS2 / 6S prepared in water / diethylene glycol dimethyl ether solution at 25 °C in Example 4; Figure 6 XRD patterns of NiS2 / 6S prepared in ethylene glycol / diethylene glycol dimethyl ether solution at 25 °C in Example 5; Figure 7 XRD patterns of NiS2 / 2S, NiS2 / 4S and NiS2 / 6S prepared in ethylene glycol / diethylene glycol dimethyl ether solution at 150 °C in Example 6; Figure 8Thermogravimetric curves of NiS2 and NiS2 / 6S prepared for Example 3 and Example 6 respectively. Calculation of sulfur content in NiS2 / 6S: Under N2 atmosphere, when heated to 500 °C, the residual contents of NiS2 and NiS2 / 6S are 83.34% and 39.20% respectively. We assume that the molar ratio of S to NiS2 in the NiS2 / S composite is x, and the molar masses of NiS2 and NiS2 / 6S are 122.81 and 122.81 + 32.06x g / mol respectively. Therefore, according to (122.81 + 32.06x) × 39.20% = 122.81 × 83.34%, x = 4.31 is calculated. Then the sulfur content in NiS2 / 6S is 32.06 × 4.31 / (122.81 + 32.06 × 4.31) = 52.94%. Theoretically, the S:NiS2 molar ratio of the NiS2 / 6S composite is 6:1, and the sulfur content is 32.06 × 6 / (122.81 + 32.06 × 6) = 61.03%. Based on these data, the contents of NiS2 and S in NiS2 / 6S are 47.06% and 52.94% respectively. This actual sulfur content is slightly lower than the theoretical value of 61.03%. This lower sulfur content may be due to the dissolution of sulfur in the non-aqueous solvent at high temperature.

[0024] Figure 9 Scanning electron microscope (SEM) images of NiS2 (a) and NiS2 / 6S (b) prepared for Example 3 and Example 6; It shows that the particle size of NiS2 in Example 3 is about 25 nm, and the particle size of NiS2 / 6S in Example 6 is about 170 nm, indicating that the in-situ formation of the NiS2 / 6S composite results in a larger particle size than the original NiS2.

[0025] Figure 10 Sodium ion storage performance of NiS2 and NiS2 / 6S prepared for Example 3 and Example 6; In the figure: (a) is the rate performance of NiS2 and NiS2 / 6S; (b) is the charge-discharge curves of NiS2 and NiS2 / 6S at 2.0 A g -1 -1; (c) is the cycling performance of NiS2 and NiS2 / 6S at 0.5 A g -1 -1; (d) is the charge-discharge curves of NiS2 and NiS2 / 6S when cycling 50 times at 0.5 A g -1 -1. The initial discharge capacity of NiS2 / 6S at 0.1 A g -1 -1 is significantly higher than that of NiS2 (1074.8 vs. 539.4 mAh g -1 -1) ( Figure 10 a). The rate performance of NiS2 / 6S is better. At 2.0 A g -1At this time, the specific capacity of NiS2 / 6S doubles (507.2 vs. 251.5 mAh g -1 ). ( Figure 10 b). After cycling at different rates, the capacity of NiS2 / 6S recovers to 512.5 mAh g -1 at 1.0 A g -1 ; in contrast, the capacity of NiS2 recovers to 253.9 mAh g -1 , less than half of the corresponding value of NiS2 / S. NiS2 / 6S not only has better rate performance than NiS2 but also better cycling performance than NiS2. At 0.5 A g -1 , after 190 cycles, the remaining capacity of NiS2 / 6S is significantly higher than that of NiS2 (672.3 vs. 167.5 mAh g -1 ) ( Figure 10 c). NiS2 / 6S has stable cycling, while the capacity of NiS2 drops rapidly in the first 70 cycles. For example, at the 50th cycle, the charge-discharge capacity of NiS2 / 6S is 639.1 / 640.7 mAh g -1 ( Figure 10 d). Detailed implementation manners

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some but not all of the embodiments of the present invention; based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs. The materials cited herein and their cited materials will be incorporated by reference.

[0028] Equivalent technologies of the specific embodiments described that can be understood by those skilled in the art through routine experiments will be included in this application.

[0029] The experimental methods in the following embodiments are all conventional methods unless otherwise specified. The instruments and equipment used in the following embodiments are all conventional laboratory instruments and equipment unless otherwise specified; the experimental materials used in the following embodiments are all obtained from conventional biochemical reagent stores unless otherwise specified.

[0030] Example 1: NiS2 was prepared in deionized water at 10, 25, 50 or 80 °C. The specific preparation method was as follows: Weigh 3 mmol of Na2S·9H2O and 3 mmol of sulfur powder and pour them into 10 mL of deionized water, stir until completely dissolved to obtain a Na2S2 solution; Weigh 3 mmol of NiCl2·6H2O and pour it into 10 mL of deionized water, stir until completely dissolved to obtain a NiCl2 solution; Drop the NiCl2 solution into the Na2S2 solution, and stir and react at 10, 25, 50, 80 °C for 3 h respectively. Centrifuge and wash the resulting solution with deionized water and absolute ethanol. Among them, the centrifuge speed is 8000 r / min and the time is 5 min; Then dry the obtained precipitate in a vacuum oven at 80 °C for 12 h to obtain NiS2 products prepared under different temperature conditions. The XRD pattern of the obtained product is as Figure 2 shown.

[0031] Example 2: NiS2 was prepared in ethylene glycol at 10 °C or 25 °C. The specific preparation method was as follows: Weigh 3 mmol of Na2S·9H2O and 3 mmol of sulfur powder and pour them into 10 mL of EG (ethylene glycol), stir until completely dissolved to obtain a Na2S2 solution; Weigh 3 mmol of NiCl2·6H2O and pour it into 10 mL of EG, stir until completely dissolved to obtain a NiCl2 solution; Drop the NiCl2 solution into the Na2S2 solution, and stir and react at 10, 25 °C for 3 h respectively. Centrifuge and wash the resulting solution with deionized water and absolute ethanol. Among them, the centrifuge speed is 8000 r / min and the time is 5 min; Then dry the obtained precipitate in a vacuum oven at 80 °C for 12 h to obtain NiS2 / S products. The XRD pattern of the obtained product is as Figure 3 shown.

[0032] Example 3: NiS2 was prepared at 150 °C in ethylene glycol (EG). The specific preparation method was as follows: Weigh 9 mmol of Na2S·9H2O and 9 mmol of sulfur powder, pour them into 30 mL of ethylene glycol, and stir until completely dissolved to obtain a Na2S2 solution; Weigh 9 mmol of NiCl2·6H2O and pour it into 30 mL of EG, and stir until completely dissolved to obtain a NiCl2 solution; Transfer the Na2S2 solution and the NiCl2 solution to a round-bottom flask and a separatory funnel respectively, pass N2 into the device for 30 min to exhaust the air, and seal it; When the Na2S2 solution in the round-bottom flask is heated to 150 °C, gradually add the NiCl2 solution in the separatory funnel dropwise to the Na2S2 solution, stir and react at 150 °C for 3 h, and centrifuge and wash the resulting solution with deionized water and absolute ethanol. Among them, the centrifuge speed is 8000 r / min and the time is 5 min; Then dry the obtained precipitate in a vacuum oven at 80 °C for 12 h to obtain the NiS2 product. The XRD pattern of the obtained product is as shown in Figure 4 shown.

[0033] Example 4: NiS2 / 6S was prepared at 25 °C in water / diethylene glycol dimethyl ether. The specific preparation method was as follows: Pour 3 mmol of Na2S·9H2O and 21 mmol of sulfur powder into 10 mL of DEGDME (diethylene glycol dimethyl ether), and stir until completely dissolved to obtain a Na2S2 solution; Weigh 3 mmol of NiCl2·6H2O and pour it into 10 mL of deionized water, and stir until completely dissolved to obtain a NiCl2 solution; Add the NiCl2 solution dropwise to the Na2S2 solution, stir and react at 25 °C for 3 h respectively, and centrifuge and wash the resulting solution with deionized water and absolute ethanol. Among them, the centrifuge speed is 8000 r / min and the time is 5 min; Then dry the obtained precipitate in a vacuum oven at 80 °C for 12 h to obtain the NiS2 / 6S product. The XRD pattern of the obtained product is as shown in Figure 5 shown.

[0034] Example 5: Preparation of NiS2 / 6S at 25 °C in ethylene glycol / diglyme. The specific preparation method is as follows: 3 mmol of Na2S·9H2O and 21 mmol of sulfur powder are poured into 10 mL of DEGDME (diglyme), and stirred until completely dissolved to obtain a Na2S2 solution; 3 mmol of NiCl2·6H2O is weighed and poured into 10 mL of EG, and stirred until completely dissolved to obtain a NiCl2 solution; the NiCl2 solution is added dropwise to the Na2S2 solution, and the mixture is stirred and reacted at 25 °C for 3 h. The resulting solution is centrifuged and washed with deionized water and absolute ethanol. The centrifuge speed is 8000 r / min, and the time is 5 min; then the obtained precipitate is dried in a vacuum oven at 80 °C for 12 h to obtain the NiS2 / 6S product. The XRD of the obtained product is as shown in Figure 6 shown.

[0035] Example 6: Preparation of NiS2 / (x-2)S at 150 °C in ethylene glycol / diglyme. The specific preparation method is as follows: 9 mmol of Na2S·9H2O and 27 mmol, 45 mmol or 63 mmol of sulfur powder are weighed and poured into 30 mL of DEGDME (diglyme), and stirred until completely dissolved to obtain a Na2S4, Na2S6 or Na2S8 solution; 9 mmol of NiCl2·6H2O is weighed and poured into 30 mL of EG, and stirred until completely dissolved to obtain a NiCl2 solution; the Na2S4, Na2S6 or Na2S8 solution and the NiCl2 solution are transferred to a round-bottom flask and a separatory funnel respectively. The air in the device is exhausted by introducing N2 for 30 min, and then sealed; when the Na2S4, Na2S6 or Na2S8 solution in the round-bottom flask is heated to 150 °C, the NiCl2 solution in the separatory funnel is added dropwise to the Na2S4, Na2S6 or Na2S8 solution, and the mixture is stirred and reacted at 150 °C for 3 h. The resulting solution is centrifuged and washed with deionized water and absolute ethanol. The centrifuge speed is 8000 r / min, and the time is 5 min; then the obtained precipitate is dried in a vacuum oven at 80 °C for 12 h to obtain the NiS2 / 2S, NiS2 / 4S, NiS2 / 6S products. The XRD patterns of the obtained products are as shown in Figure 7 shown.

[0036] Electrochemical performance test of sodium-ion battery: The NiS2 and NiS2 / 6S products prepared in Example 3 and Example 6 were used as active materials respectively. The active material (i.e., NiS2 or NiS2 / 6S), conductive carbon black (Super-P) and polyvinylidene fluoride (PVDF) were uniformly mixed according to a mass ratio of 75:10:15, and then N-methylpyrrolidone (NMP) was added for grinding. Then it was coated on a copper foil current collector and dried in a vacuum oven at 80 °C for 12 h, and then stamped into a circular pole piece with a diameter of 12 mm. A sodium sheet was used as the negative electrode, the separator was a glass fiber separator (GF / D), the electrolyte was DEGDME containing 1 M NaCF3SO3, and the addition amount of the electrolyte was 100 μL. A CR2025 button battery was assembled in a glove box filled with argon (O2 < 0.01 ppm, H2O < 0.01 ppm). The cycle and rate performance of the battery were tested on a Neware battery test system (BTSDA7.6.0.404), and the voltage window was 0.2 - 3V. Cyclic voltammetry (CV) test was carried out on an electrochemical workstation (CHI660E).

[0037] The thermogravimetric curves of NiS2 and NiS2 / 6S prepared in Example 3 and Example 6 respectively are as Figure 8 shown. Calculation of sulfur content in NiS2 / 6S: Under N2 atmosphere, when heated to 500 °C, the residual contents of NiS2 and NiS2 / 6S are 83.34% and 39.20% respectively. Assuming that the molar ratio of S to NiS2 in the NiS2 / S composite is x, the molar masses of NiS2 and NiS2 / 6S are 122.81 and 122.81 + 32.06x g / mol respectively. Therefore, according to (122.81 + 32.06x) × 39.20% = 122.81× 83.34%, x = 4.31 is calculated. Then the sulfur content in NiS2 / 6S is 32.06 × 4.31 / (122.81 + 32.06 ×4.31) = 52.94%. Theoretically, the S:NiS2 molar ratio of the NiS2 / 6S composite is 6:1, and the sulfur content is 32.06 × 6 / (122.81 + 32.06 × 6) = 61.03%. Based on these data, the contents of NiS2 and S in NiS2 / 6S are 47.06% and 52.94% respectively. This actual sulfur content is slightly lower than the theoretical value of 61.03%. This lower sulfur content may be due to the dissolution of sulfur in non-aqueous solvents at high temperatures.

[0038] The scanning electron microscope (SEM) images of NiS2(a) and NiS2 / 6S(b) prepared in Example 3 and Example 6 are as Figure 9As shown; in the figure, the particle size of NiS2 in Example 3 is about 25 nm, and the particle size of NiS2 / 6S in Example 6 is about 170 nm, indicating that the in-situ formation of the NiS2 / 6S composite results in a larger particle size than the original NiS2.

[0039] The sodium-ion storage performances of NiS2 and NiS2 / 6S prepared in Example 3 and Example 6 are as Figure 10 shown. The initial discharge capacity of NiS2 / 6S at 0.1 A g -1 is significantly higher than that of NiS2 (1074.8 vs. 539.4 mAh g -1 ) ( Figure 10 a). The rate performance of NiS2 / 6S is better. At 2.0 A g -1 , the specific capacity of NiS2 / 6S doubles (507.2 vs. 251.5 mAh g -1 ) ( Figure 10 b). After cycling at different rates, the capacity of NiS2 / 6S recovers to 512.5 mAh g -1 at 1.0 A g -1 ; in contrast, the capacity of NiS2 recovers to 253.9 mAh g -1 , less than half of the corresponding value of NiS2 / S. NiS2 / 6S not only has better rate performance than NiS2 but also better cycling performance than NiS2. At 0.5 A g -1 , after 190 cycles, the remaining capacity of NiS2 / 6S is significantly higher than that of NiS2 (672.3 vs. 167.5 mAh g -1 ) ( Figure 10 c). NiS2 / 6S has stable cycling, while the capacity of NiS2 drops rapidly in the first 70 cycles. For example, at the 50th cycle, the charge-discharge capacity of NiS2 / 6S is 639.1 / 640.7 mAh g -1 ( Figure 10 d).

[0040] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A preparation method of high-yield nickel disulfide NiS2, characterized in that: It includes the following steps: (1) Preparation of sodium disulfide Na2S2 solution: Sodium sulfide nonahydrate Na2S·9H2O or sodium sulfide Na2S and sulfur powder with a molar ratio of 1:1 are added to a solvent, and stirred until completely dissolved to obtain a Na2S2 solution with a concentration of a mol / L; where 0.01 ≤ a ≤ 1; (2) Nickel ion Ni 2+ Preparation of the solution: Add soluble nickel salt into a solvent and stir until it is completely dissolved to obtain a nickel ion Ni 2+ solution with a concentration of b mol / L; where: 0.01 ≤ b ≤ 1; (3)Preparation of NiS2 product: Mix the Na2S2 solution obtained in step (1) with a volume of c L and the nickel ion Ni 2+ solution obtained in step (2) with a volume of d L, stir and react for 0.5 - 12 h, collect the precipitate obtained from the reaction, wash and dry it to obtain the NiS2 product.

2. The preparation method according to claim 1, characterized in that: The solvent described in step (1) and step (2) is deionized water or ethylene glycol EG.

3. The preparation method according to claim 1, characterized in that: The soluble nickel salt described in step (2) is any one of nickel chloride hexahydrate, nickel chloride, nickel sulfate hexahydrate or nickel sulfate.

4. The preparation method according to claim 1, characterized in that: In step (3), the reaction temperature is controlled to be lower than the boiling point of the solvent.

5. The preparation method according to claim 1, characterized in that: 0.5ac ≤ bd ≤ 2ac.

6. The preparation method according to claim 1 or 5, characterized in that: The ac = bd.

7. A method for preparing a high-yield nickel disulfide / sulfur composite NiS2 / (x - 2)S, where 3 ≤ x ≤ 8, characterized in that: It includes the following steps: (1) Sodium polysulfide Na₂S x , Preparation of solution with 3 ≤ x ≤ 8: Add Na₂S·9H₂O or Na₂S and sulfur powder with a molar ratio of 1:x - 1 into a solvent, stir until completely dissolved to obtain Na₂S x solution with a concentration of y mol / L; wherein the solvent is any one of diethylene glycol dimethyl ether, triethylene glycol dimethyl ether or tetraethylene glycol dimethyl ether; (2)Nickel ion Ni 2+ Preparation of the solution: Add a soluble nickel salt to ethylene glycol EG or deionized water, and stir until completely dissolved to obtain a nickel ion Ni 2+ solution with a concentration of z mol / L. The soluble nickel salt is any one of nickel chloride hexahydrate, nickel chloride, nickel sulfate hexahydrate or nickel sulfate; (3) Preparation of NiS2 / (x - 2)S (3 ≤ x ≤ 8) product: Mix the Na2S solution obtained in step (1) with a volume of m L and the nickel ion Ni solution obtained in step (2) with a volume of n L, stir and react at 0 - 190 °C for 0.5 - 12 h, collect the precipitate obtained from the reaction, wash and dry it to obtain the NiS2 / (x - 2)S (3 ≤ x ≤ 8) product; where: 0.5ym ≤ zn ≤ 2ym. x solution and the nickel ion Ni 2+ solution obtained in step (2) with a volume of n L are mixed, stirred and reacted at 0 - 190 °C for 0.5 - 12 h, the precipitate obtained from the reaction is collected, washed and dried to obtain the NiS2 / (x - 2)S (3 ≤ x ≤ 8) product; where: 0.5ym ≤ zn ≤ 2ym.

8. The preparation method according to claim 7, characterized in that: The ym = zn.

9. Application of NiS2 prepared by the method described in claim 1 or NiS2 / (x - 2)S (3 ≤ x ≤ 8) prepared by the method described in claim 7 as an active substance in an electrode material.

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