An island-shaped MS2@TiO2 heterojunction, its preparation method and application

Abstract

This invention specifically relates to an island-shaped MS2@TiO2 heterojunction, its preparation method, and its applications. First, an island-shaped MS2@TiO2 (M=Fe, Co, Ni, Cu) heterojunction composed of MS2 nanoparticles and TiO2 nanoribbons is prepared through a simple hydrothermal, ion exchange, and sulfidation reaction to capture and catalyze polysulfides. The MS2 nanoparticles are uniformly anchored on the surface of the TiO2 nanoribbons. In the MS2@TiO2 heterojunction, TiO2 acts as an adsorption site, effectively inhibiting lithium polysulfide shuttle, while MS2 acts as an electrocatalytic site, improving the conversion kinetics of polysulfides. Li-S batteries using MS2@TiO2 heterojunction-modified membranes exhibit excellent electrochemical performance, including a 2318 mAh g⁻¹ at 0.1 C. ‑1 It exhibits high initial discharge capacity, a capacity decay rate of 0.046% at 1 C, and excellent long-term cycling stability.

Description

Technical Field

[0001] This invention relates to the field of battery materials, specifically to an island-shaped MS2@TiO2 heterojunction, its preparation method, and its application. Background Technology

[0002] Due to its abundant reserves, environmental friendliness, and large theoretical specific capacity (1675 mAh g), -1 Energy density up to 2500 Wh / kg -1 Lithium-sulfur batteries are considered promising energy storage devices. Despite these advantages, their practical applications are significantly limited by the low cycle durability caused by the dissolution and shuttle effect of lithium polysulfides (LiPSs). Therefore, suppressing the shuttle effect of polysulfides and improving the performance of lithium-sulfur batteries is currently a research hotspot.

[0003] To address the shuttling effect of polysulfides, commonly used methods include designing sulfur host materials, encompassing chemisorption strategies (using polar materials such as transition metal compounds, covalent organic frameworks, metal-organic frameworks, and MXenes) and physical confinement methods (using nanomaterials with various innovative structures). However, limited adsorption sites and sulfur storage space can lead to structural collapse of the host material. Another effective strategy to suppress LiPSs dissolution / shutdown is to establish a shuttle barrier between the cathode and anode, i.e., membrane modification. Commonly used materials for membrane modification include carbon materials and transition metal compounds (oxides, sulfides, phosphides, nitrides, etc.). The physical confinement of nonpolar carbon materials is very limited in adsorbing large amounts of polysulfides. In contrast, polar materials such as transition metal oxides, like TiO2, have a stronger adsorption capacity for LiPSs. While some electrocatalytic materials (such as FeS2, CoS2, Ni2P, and ZnS) can accelerate the conversion of soluble LiPSs to Li2S, they typically have poor conductivity. It is a challenge to simultaneously meet multiple requirements for single-function materials, including high conductivity, strong adsorption capacity, and excellent electrocatalytic properties for LiPSs.

[0004] Due to their distinct interfaces, robust structures, and synergistic effects, heterojunctions typically exhibit higher conductivity. Furthermore, the charge redistribution occurring in heterostructures induces more energy storage active sites, enabling continuous adsorption and conversion, higher reversible capacity, and better cycle stability. Therefore, it is crucial to develop heterojunctions with low development costs, simple processes, and the ability to rapidly adsorb and catalytically convert polysulfides for use in lithium-sulfur batteries. Summary of the Invention

[0005] This invention overcomes the shortcomings of existing technologies, and the technical problem it aims to solve is to provide an island-like MS2@TiO2 heterojunction that is low-cost, simple to process, and enables rapid adsorption and catalytic conversion of polysulfides. From the perspective of heterojunction construction, based on the need to enhance the built-in electric field strength and improve cycle stability, TiO2, which has a wide band structure and adsorption capacity for polysulfides, is selected to construct a heterojunction with catalytically active metal sulfides MS2 (M=Fe, Co, Ni, Cu). This induces the formation of a built-in electric field and realizes a continuous process of polysulfide adsorption, anchoring, and catalytic conversion, thereby improving the cycle stability of lithium-sulfur batteries.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a method for preparing an island-like MS2@TiO2 heterojunction, comprising the following steps:

[0007] (1) Preparation of precursor Na2Ti2O5: Titanium powder was dispersed in NaOH solution, mixed thoroughly, and then poured into a reaction vessel for hydrothermal reaction; after filtration, washing, and drying, precursor Na2Ti2O5 was obtained;

[0008] (2) Ion exchange reaction: Add dry Na2Ti2O5 precursor to the salt solution of metal M, stir magnetically and let stand for 2-6 h to allow the ion exchange reaction to proceed fully; then filter, wash and dry; the metal M is at least one of Fe, Co, Ni and Cu.

[0009] (3) Sulfidation reaction: The dried sample after ion exchange and sulfur powder were placed in a tube furnace for sulfidation and calcination treatment. After cooling, isolated MS2@TiO2 heterojunctions were obtained.

[0010] As a further limitation of the technical solution of the present invention, the temperature of the hydrothermal reaction in step (1) is 160~200 ℃, and the duration is 24~60 h.

[0011] As a further limitation of the technical solution of the present invention, the molar ratio of titanium powder to NaOH solution in step (1) is 1:10 ~ 1:20.

[0012] As a further limitation of the technical solution of the present invention, in step (2), the metal M salt is at least one of ferric nitrate, cobalt nitrate, nickel nitrate, copper nitrate, ferric chloride, cobalt chloride, nickel chloride, and copper chloride; the molar ratio of the metal M salt to the Na2Ti2O5 precursor is 5~10:1; and the concentration of the metal M salt solution is 0.25 mol L. -1 .

[0013] As a further limitation of the technical solution of the present invention, the mass ratio of the dried sample to the sulfur powder in step (3) is 1:3~6.

[0014] As a further limitation of the technical solution of the present invention, the calcination parameters in the tube furnace in step (3) are: heating to 400~600 ℃ under an inert atmosphere and holding for 2~4 h, and then naturally cooling to room temperature.

[0015] First, an island-like MS2@TiO2 (M=Fe,Co,Ni,Cu) heterojunction, composed of MS2 (M=Fe,Co,Ni,Cu) nanoparticles and TiO2 nanoribbons, was prepared via a simple hydrothermal, ion exchange, and sulfidation reaction to capture and catalyze polysulfides. The MS2 nanoparticles were uniformly anchored on the surface of the TiO2 nanoribbons. In the MS2@TiO2 (M=Fe,Co,Ni,Cu) heterojunction, TiO2 acts as an adsorption site, effectively inhibiting lithium polysulfide shuttle, while MS2 acts as an electrocatalytic site, enhancing the conversion kinetics of polysulfides.

[0016] The present invention also provides an island-shaped MS2@TiO2 heterojunction obtained by the above preparation method.

[0017] In addition, the present invention also provides the application of the island-shaped MS2@TiO2 heterojunction obtained by the above preparation method in modifying lithium-sulfur battery separators and improving battery electrochemical performance.

[0018] As a further limitation of the technical solution of the present invention, the method of using island-shaped MS2@TiO2 heterojunction modified lithium-sulfur battery separator is as follows: MS2@TiO2 active material, conductive agent and binder are weighed according to the mass ratio of 6-8:3-1:1, ground and added to solvent to prepare slurry, coated on the surface of separator, and vacuum dried to obtain MS2@TiO2 modified separator.

[0019] As a further limitation of the technical solution of the present invention, the conductive agent is at least one of conductive carbon black, acetylene black, Ketjen black and graphene; the binder is polyvinylidene fluoride; and the solvent is N-methylpyrrolidone.

[0020] Due to the different band gaps of MS2 and TiO2, the heterojunction between these two components generates an internal electric field, thereby accelerating the conversion of polysulfides (especially the reduction of Li2S2 to Li2S). Furthermore, Li-S batteries using MS2@TiO2 (M=Fe, Co, Ni, Cu) heterojunction-modified separators exhibit excellent electrochemical performance, including a 2318 mAh g⁻¹ at 0.1 C. -1 It exhibits high initial discharge capacity, a capacity decay rate of 0.046% at 1 C, and excellent long-term cycling stability.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] This invention utilizes inexpensive and readily available raw materials to prepare island-like MS2@TiO2 (M=Fe, Co, Ni, Cu) heterojunctions through simple hydrothermal reactions, ion exchange, and sulfidation reactions. These heterojunctions possess excellent adsorption properties, efficient catalytic conversion properties, and outstanding electrochemical performance, providing a novel method for preparing lithium-sulfur battery separator modification materials with both excellent adsorption properties and rapid catalytic conversion properties.

[0023] The island-like MS2@TiO2 (M=Fe, Co, Ni, Cu) heterojunction prepared in this invention not only has the ability to rapidly adsorb lithium polysulfides, but also, when coated on a commercial PP separator with a thickness of only 8 μm, it can significantly inhibit the penetration of polysulfides, showing only slight discoloration after 8 hours. When batteries are assembled using the modified separator, extremely high initial capacity, good rate performance, and cycle stability can be achieved.

[0024] The island-like MS2@TiO2 (M=Fe, Co, Ni, Cu) heterojunction prepared by this invention is low-cost, simple to implement, and can be industrially produced. This island-like heterostructure construction can reduce the shuttle effect and promote the catalytic conversion of polysulfides, providing important insights for improving the electrochemical performance of lithium-sulfur batteries. Attached Figure Description

[0025] Figure 1 SEM image and mapping image of Na2Ti2O5, the precursor prepared in Example 1 of this invention.

[0026] Figure 2 The images show SEM, TEM, SAED, and mapping images of FeS2@TiO2 prepared in Example 1 of this invention.

[0027] Figure 3 The images show the XRD patterns of FeS2@TiO2 and TiO2 prepared in Example 1 and Comparative Example 1 of this invention.

[0028] Figure 4 The images show the SEM image and mapping diagram of TiO2 prepared in Comparative Example 1 of this invention.

[0029] Figure 5 The images show FeS2@TiO2 / PP (right) and PP (left) coated in Example 5 of the present invention.

[0030] Figure 6 The figures show a comparison of the permeation experiments of Li2S6 by FeS2@TiO2 / PP, TiO2 / PP, and PP membranes prepared in Example 1 and Comparative Example 1 of this invention.

[0031] Figure 7The graphs show the cycle performance of FeS2@TiO2 / PP, TiO2 / PP, and PP separator-assembled batteries prepared in Example 1 and Comparative Example 1 of this invention.

[0032] Figure 8 The data shows the rate capability of FeS2@TiO2 / PP, TiO2 / PP, and PP separator-assembled batteries prepared in Example 1 and Comparative Example 1 of this invention. Detailed Implementation

[0033] The present invention will be further described below with reference to specific embodiments. Example 1

[0034] A method for preparing island-like FeS2@TiO2 heterojunctions

[0035] (1) Disperse titanium powder (1 g) in 80 mL of 5 mol L -1 The solution was added to a NaOH solution. After thorough mixing, the solution was poured into a 100 mL high-pressure reactor and reacted at 180 °C for 24 hours using a hydrothermal method. After cooling to room temperature, the precipitate was collected by filtration and washed three times with distilled water and ethanol, respectively. Finally, it was dried at 60 °C to obtain the precursor Na₂Ti₂O₅; the corresponding SEM image is shown below. Figure 1 As shown.

[0036] (2) In 30 mL of 0.25 mol L -1 0.2 g of dry Na2Ti2O5 precursor was added to Fe(NO3)3 solution, and the mixture was magnetically stirred for 30 min, then allowed to stand for 2 h to allow the ion exchange reaction to proceed fully. After the reaction was completed, the mixture was filtered and washed three times with deionized water and ethanol, and then dried at 60 °C.

[0037] (3) The dried sample after ion exchange and sulfur powder were placed in a tube furnace for sulfidation treatment and reacted in an argon atmosphere at 500℃ for 2 h. After cooling to room temperature, FeS2@TiO2 heterojunction material was obtained; the corresponding SEM images are shown below. Figure 2 XRD pattern as shown Figure 3 As shown. Example 2

[0038] A method for preparing island-like CoS2@TiO2 heterojunctions:

[0039] (1) Na2Ti2O5 was synthesized according to step (1) of Example 1;

[0040] (2) In 30 mL of 0.25 mol L -10.2 g of dry Na2Ti2O5 precursor was added to a Co(NO3)2 solution, and the mixture was magnetically stirred for 30 min, then allowed to stand for 2 h to allow the ion exchange reaction to proceed fully. After the reaction was complete, the mixture was filtered and washed three times with deionized water and ethanol, and then dried at 60 °C.

[0041] (3) The dried sample after ion exchange and sulfur powder were placed in a tube furnace for sulfidation treatment and reacted in an argon atmosphere at 500°C for 2 h. After cooling to room temperature, CoS2@TiO2 heterojunction material was obtained. Example 3

[0042] A method for preparing island-like NiS2@TiO2 heterojunctions:

[0043] (1) Na2Ti2O5 was synthesized according to step (1) of Example 1;

[0044] (2) In 30 mL of 0.25 mol L -1 0.2 g of dry Na2Ti2O5 precursor was added to the Ni(NO3)2 solution, and the mixture was magnetically stirred for 30 min, then allowed to stand for 2 h to allow the ion exchange reaction to proceed fully. After the reaction was completed, the mixture was filtered and washed three times with deionized water and ethanol, and then dried at 60 °C.

[0045] (3) The dried sample after ion exchange and sulfur powder were placed in a tube furnace for sulfidation treatment and reacted in an argon atmosphere at 500°C for 2 h. After cooling to room temperature, NiS2@TiO2 heterojunction material was obtained. Example 4

[0046] A method for preparing island-like CuS2@TiO2 heterojunctions:

[0047] (1) Na2Ti2O5 was synthesized according to step (1) of Example 1;

[0048] (2) In 30 mL of 0.25 mol L -1 0.2 g of dry Na2Ti2O5 precursor was added to a Cu(NO3)2 solution, and the mixture was magnetically stirred for 30 min, then allowed to stand for 2 h to allow the ion exchange reaction to proceed fully. After the reaction was complete, the mixture was filtered and washed three times with deionized water and ethanol, and then dried at 60 °C.

[0049] (3) The dried sample after ion exchange and sulfur powder were placed in a tube furnace for sulfidation treatment and reacted in an argon atmosphere at 500°C for 2 h. After cooling to room temperature, CuS2@TiO2 heterojunction material was obtained.

[0050] Comparative Example 1

[0051] Preparation method of TiO2:

[0052] The difference from Embodiment 1 above is that:

[0053] The solution for the ion exchange reaction is HCl, which is then directly calcined without adding sulfur powder during the calcination process.

[0054] (1) Na2Ti2O5 was synthesized according to step (1) of Example 1;

[0055] (2) In 1 mol L -1 0.2 g of dry Na₂Ti₂O₅ precursor was added to HCl solution, and the mixture was magnetically stirred for 30 min and then allowed to stand for 2 h. After the reaction was complete, the sample was filtered and washed three times with deionized water and ethanol, and then dried at 60 °C.

[0056] (3) The dried sample after ion exchange was placed in a tube furnace and reacted in an argon atmosphere at 500 °C for 2 h. Then it was cooled to room temperature to obtain TiO2.

[0057] SEM images of the TiO2 prepared in this comparative example are attached. Figure 4 As shown, the nanoribbon structure appears as a flower cluster, with no particles attached to it.

[0058] Using the isolated FeS2@TiO2, CoS2@TiO2, NiS2@TiO2, CuS2@TiO2, and TiO2 prepared in Examples 1, 2, 3, and 4 of this invention, as well as Comparative Example 1, as membrane modification materials, a visualization experiment on lithium polysulfide adsorption was conducted. These materials were then assembled with lithium sheets and S / C cathodes to form CR2025 coin-type Li-S batteries, and their electrochemical performance was tested.

[0059] Li-S battery assembly:

[0060] Step 1: Weigh MS2@TiO2 heterojunction / TiO2 material, graphene, and polyvinylidene fluoride at a mass ratio of 8:1:1, grind them evenly, transfer them to a 5 mL weighing bottle, then add 2 mL of N-methylpyrrolidone, and stir continuously for 4 h to form a slurry. Coat this slurry onto a PP membrane, then dry it in a vacuum oven at 60 ℃ for 12 h. Use a slicer to cut it into 19 mm diameter circular composite membranes, labeled as MS2@TiO2 / PP and TiO2 / PP, respectively. Figure 5 .

[0061] Step 2: Assembly of Li-S batteries; The Li-S battery assembled with MS2@TiO2 / PP is labeled as Battery 1, and the Li-S battery assembled with TiO2 / PP is labeled as Battery 2;

[0062] Lithium polysulfide adsorption visualization:

[0063] Diffusion experiments of polysulfides with different diaphragms were conducted in an H-type electrolytic cell. 67 mL of 0.02 M Li₂S was added to the left side, and 7 mL of a DOL:DME = 1:1 solution was added to the right side. Different diaphragms were used to sandwich the H-type apparatus. For example... Figure 6 After 1 hour, the color of the left chamber using the original PP membrane permeated to the right chamber; while with the FeS2@TiO2 modified membrane, only a slight color change was observed after 8 hours, which confirms the excellent ability of the FeS2@TiO2 heterojunction to suppress polysulfide shuttle.

[0064] Battery performance evaluation:

[0065] Battery 1 and Battery 2 were subjected to cycle stability tests at current densities of 0.1 C and 1 C, and rate performance tests were conducted at 0.1 C, 0.2 C, 0.5 C, 1.0 C, and 2.0 C. For example... Figure 7 and Figure 8 At 0.1C, the initial capacity of the main sample reached 2318 mAh / g, while the control samples were 1937 and 905.2, and the battery reversibility was good.

[0066] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. The application of an island-shaped MS2@TiO2 heterojunction in modifying lithium-sulfur battery separators and improving battery electrochemical performance, characterized in that, The method for preparing the isolated MS2@TiO2 heterojunction includes the following steps: (1) Preparation of precursor Na2Ti2O5: Titanium powder was dispersed in NaOH solution, mixed thoroughly, and then poured into a reaction vessel for hydrothermal reaction; after filtration, washing, and drying, precursor Na2Ti2O5 was obtained; (2) Ion exchange reaction: Add dry Na2Ti2O5 precursor to the salt solution of metal M, stir magnetically and let stand for 2-6 h to allow the ion exchange reaction to proceed fully; then filter, wash and dry; the metal M is at least one of Fe, Co, Ni and Cu. (3) Sulfidation reaction: The dried sample after ion exchange and sulfur powder were placed in a tube furnace for sulfidation and calcination treatment. After cooling, isolated MS2@TiO2 heterojunctions were obtained.

2. The application according to claim 1, characterized in that, The hydrothermal reaction in step (1) is carried out at a temperature of 160~200 ℃ for 24~60 h.

3. The application according to claim 1, characterized in that, The molar ratio of titanium powder to NaOH solution in step (1) is 1:10 ~ 1:

20.

4. The application according to claim 1, characterized in that, In step (2), the metal M salt is at least one of ferric nitrate, cobalt nitrate, nickel nitrate, copper nitrate, ferric chloride, cobalt chloride, nickel chloride, and copper chloride; the molar ratio of the metal M salt to the Na2Ti2O5 precursor is 5~10:1; and the concentration of the metal M salt solution is 0.25 mol L. -1 .

5. The application according to claim 1, characterized in that, In step (3), the mass ratio of the dried sample to sulfur powder is 1:3~6.

6. The application according to claim 1, characterized in that, The calcination parameters in the tube furnace in step (3) are: heating to 400~600 ℃ under an inert atmosphere and holding for 2~4 h, then naturally cooling to room temperature.

7. The application according to claim 1, characterized in that, The method for modifying lithium-sulfur battery separators using island-shaped MS2@TiO2 heterojunctions is as follows: MS2@TiO2 active material, conductive agent and binder are weighed according to a mass ratio of 6-8:3-1:1, ground and added to a solvent to prepare a slurry, which is then coated on the surface of the separator and vacuum dried to obtain the MS2@TiO2 modified separator.

8. The application according to claim 7, characterized in that, The conductive agent is at least one of conductive carbon black, acetylene black, Ketjen black, and graphene; the binder is polyvinylidene fluoride; and the solvent is N-methylpyrrolidone.

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