Preparation method and application of PSN-TiO2 heterostructure composite material

Abstract

A preparation method of a PSN-TiO2 heterostructure composite material and application thereof, comprising the following steps: (1) adding Ti(SO4)2 into deionized water, stirring and dispersing to obtain a titanium precursor solution; (2) adding two-dimensional porous silicon-oxygen nanosheets into deionized water, ultrasonic dispersing to obtain a two-dimensional porous silicon-oxygen nanosheet dispersion liquid; (3) mixing and stirring the titanium precursor solution and the two-dimensional porous silicon-oxygen nanosheet dispersion liquid, and hydrothermally in-situ compositing to obtain the PSN-TiO2 heterostructure composite material. The PSN-TiO2 heterostructure composite material is used as a functional barrier layer active component to prepare a modified diaphragm of a lithium-sulfur battery. The present application has the advantages of low raw material cost, simple preparation method, effective inhibition of TiO2 agglomeration, promotion of ion / electron cooperative supply in the polysulfide conversion process, mitigation of the shuttle effect, facilitation of uniform lithium nucleation and inhibition of lithium dendrite growth, lower shuttle current, higher lithium ion migration number and good high-sulfur load cycle stability.

Description

Technical Field

[0001] This invention relates to a heterogeneous composite material, and more particularly to a method for preparing a PSN-TiO2 heterogeneous composite material and its application. Background Technology

[0002] Lithium-sulfur batteries still face limitations in practical applications due to severe polysulfide shuttle effects, slow sulfur species conversion kinetics, and instability at the lithium metal anode interface. In particular, the migration of soluble polysulfides generated during charge and discharge between the positive and negative electrodes leads to loss of active material, decreased coulombic efficiency, increased polarization, and rapid capacity decay.

[0003] Functional modification of commercial polypropylene separators is a simple and effective strategy to alleviate the aforementioned problems. By constructing a barrier layer with adsorption, catalysis, and transport regulation functions on the separator surface, polysulfides can be intercepted on the positive electrode side and their rapid conversion can be promoted, while improving the separator / electrolyte interface environment. However, single-component separator modification materials usually cannot simultaneously achieve polysulfide adsorption, sulfur redox catalysis, lithium ion migration, and lithium anode interface stability.

[0004] Therefore, in view of the shortcomings of the prior art, the present invention provides a method for preparing PSN-TiO2 heterostructure composite material and its application. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing PSN-TiO2 heterostructure composite materials and their applications. This invention features low raw material cost, a simple preparation method, and the ability of the prepared PSN-TiO2 heterostructure composite material to effectively inhibit TiO2 agglomeration, promote ion / electron synergistic supply during polysulfide conversion, effectively confine and continuously convert polysulfides, alleviate the shuttle effect, facilitate uniform lithium nucleation and inhibit lithium dendrite growth, and exhibit low shuttle current, high lithium ion transference number, and good high sulfur loading cycle stability.

[0006] The technical solution of this invention: A method for preparing a PSN-TiO2 heterostructure composite material, comprising the following steps: (1) Add Ti(SO4)2 to deionized water and stir to disperse to obtain a titanium precursor solution; (2) Two-dimensional porous silica nanosheets were added to deionized water and ultrasonically dispersed to obtain a dispersion of two-dimensional porous silica nanosheets. (3) The titanium precursor solution and the two-dimensional porous silica nanosheet dispersion were mixed and stirred, and the in-situ composite reaction was carried out in a hydrothermal environment of 90-110℃ for 4-8 h. The precipitate was collected by centrifugation, washed with deionized water, and freeze-dried to obtain the PSN-TiO2 heterostructure composite material.

[0007] In the aforementioned method for preparing PSN-TiO2 heterostructure composite material, in step (1), 0.5-2.5g Ti(SO4)2 is added to 30-40mL of deionized water and stirred and dispersed for 1-4 hours to obtain a titanium precursor solution.

[0008] In the aforementioned method for preparing PSN-TiO2 heterostructure composite material, in step (2), 0.2-0.8 g of two-dimensional porous silica nanosheets are added to 40-80 mL of deionized water and ultrasonically dispersed for 0.5-2 h to obtain a two-dimensional porous silica nanosheet dispersion.

[0009] In the aforementioned method for preparing PSN-TiO2 heterostructure composite materials, in step (3), the in-situ composite reaction is carried out for 4-8 h under a hydrothermal environment of 90-110℃. The -OH functional groups on the surface of the two-dimensional porous silica nanosheets serve as heterogeneous nucleation active sites, inducing the TiO2 in the system to undergo a composite reaction. 4+ TiO2 nanoparticles are uniformly loaded onto the surface of two-dimensional porous silica nanosheets by directional nucleation and in-situ growth, forming a PSN-TiO2 heterostructure composite material with amorphous porous silica phase and crystalline titanium dioxide phase coupling.

[0010] In the aforementioned method for preparing PSN-TiO2 heterostructure composite material, in step (3), the titanium precursor solution and the two-dimensional porous silica nanosheet dispersion are mixed and stirred for 1-2 h, and then in situ composite reaction is carried out for 4-8 h under hydrothermal environment at 90-110℃. The precipitate is collected by centrifugation, washed with deionized water 4-8 times, and then freeze-dried at -70 to -30℃ for 20-28 h to obtain PSN-TiO2 heterostructure composite material.

[0011] In the aforementioned method for preparing PSN-TiO2 heterostructure composite material, the two-dimensional porous silica nanosheets are prepared by using layered vermiculite crystals as raw materials, followed by sodium ion exchange, lithium ion exchange, two-step acid etching, centrifugation to obtain the supernatant, and freeze drying.

[0012] In the aforementioned method for preparing the PSN-TiO2 heterostructure composite material, the two-dimensional porous silica nanosheets are prepared by the following method: 5–15 g of vermiculite crystals are added to 150–350 mL of saturated sodium chloride solution, stirred at 70–90 °C for 18–30 h, and washed until no white precipitate is detected by 0.1–1 mol / L silver nitrate solution; the resulting sample is then placed in 1–3 mol / L lithium chloride solution, stirred at 70–90 °C for another 18–30 h, and dialyzed until no white precipitate is detected by 0.1–1 mol / L silver nitrate solution; subsequently, the product is placed in 100–200 mL of 30–38 wt.% hydrochloric acid solution, stirred at 70–90 °C for 18–30 h, and washed until the pH value is 6.5–7; then, a second etching is performed under the same hydrochloric acid conditions; finally, the resulting suspension is centrifuged at 800–1500 r / min for 5–20 minutes. After min, the supernatant was collected and freeze-dried at -70 to -50°C for 20 to 28 h to obtain two-dimensional porous silica nanosheets.

[0013] The PSN-TiO2 heterostructure composite material is used as a functional barrier layer active component in the preparation of modified separators for lithium-sulfur batteries, which is used to suppress polysulfide shuttle and promote sulfur oxidation-reduction conversion.

[0014] In the aforementioned application of the PSN-TiO2 heterostructure composite material, the preparation of the lithium-sulfur battery modified separator involves: mixing 3-5 parts by weight of the PSN-TiO2 heterostructure composite material, 4-6 parts by weight of carbon nanotubes, and 0.5-1.5 parts by weight of polyvinylidene fluoride to obtain a mixture; adding 8-12 g of the mixture to 240-280 mL of N-methylpyrrolidone in a certain proportion, and stirring to form a uniform slurry; coating the slurry onto the surface of a polypropylene separator, and vacuum drying at 50-70°C for 8-16 h to form a barrier layer on the surface of the polypropylene separator, thereby obtaining the PSN-TiO2 modified separator.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention uses vermiculite crystals as raw material to obtain two-dimensional porous silicon oxide nanosheets (PSN) through ion exchange exfoliation, two-step acid etching, and centrifugation. Using Ti(SO4)2 as the titanium source and PSN as the substrate, a PSN-TiO2 heterostructure composite material is prepared through titanium precursor solution preparation, PSN dispersion preparation, mixing and stirring, hydrothermal in-situ composite, centrifugal washing, and freeze-drying. This method features mild reaction conditions, a simple process flow, widely available raw materials, and low cost. It can effectively combine two-dimensional porous silicon oxide nanosheets with TiO2 nanoparticles to form a heterostructure composite material coupling an amorphous porous silicon oxide phase and a crystalline titanium dioxide phase, providing a foundation for the preparation of functional barrier layer materials for lithium-sulfur battery separators.

[0016] 2. In this invention, 5–15 g of vermiculite crystals are dispersed in 150–350 mL of saturated sodium chloride solution and stirred in an oil bath at 70–90 °C for 18–30 h. After washing, the resulting sample is placed in a 1–3 mol / L lithium chloride solution and stirred for another 18–30 h at 70–90 °C. + and Li + It can gradually penetrate the vermiculite interlayer, weakening the electrostatic interactions and interlayer bonding forces between vermiculite layers, causing the massive, layered vermiculite crystals to gradually peel off into a thin-layer structure. After two ion exchange treatments, dialysis or washing was performed until no white precipitate was detected with 0.1–1 mol / L silver nitrate solution, indicating that residual Cl in the system was present. - Effective removal of impurity ions reduces the adverse effects of impurity ions on the structural stability and electrochemical performance of the material. The product is then subjected to a two-step acid etching process in 100–200 mL of 30–38 wt.% hydrochloric acid solution, followed by washing to a pH of 6.5–7. After centrifugation at 800–1500 r / min for 5–20 min, the supernatant is freeze-dried at -70–-50℃ for 20–28 h to obtain a PSN with good dispersibility, thinner layers, and a richer pore structure. This PSN can improve electrolyte wettability and shorten the Li... + This facilitates transport pathways and provides more interfacial sites for polysulfide adsorption and in-situ TiO2 loading.

[0017] 3. The PSN prepared by this invention has an ultrathin two-dimensional sheet structure and a high specific surface area, with a thickness of 0.5–0.7 nm and a specific surface area of ​​185–215 m². 2 / g. The ultrathin lamellar structure is beneficial for shortening the Li... + The transport path at the material interface reduces ion migration resistance; the higher specific surface area increases the contact area between the material and the electrolyte, providing more interfacial interaction sites, thereby improving the electrolyte adsorption capacity and wetting performance of the membrane. Simultaneously, the abundant -OH groups on the PSN surface can interact with polar electrolyte components, which is beneficial for improving the membrane / electrolyte interfacial environment and promoting Li... + Uniform transmission.

[0018] 4. In this invention, 0.2–0.8 g of PSN is added to 40–80 mL of deionized water and ultrasonically dispersed for 0.5–2 h to obtain a two-dimensional porous silica nanosheet dispersion (PSN dispersion). Ultrasonic dispersion can promote the full dispersion of PSN sheets, reduce the stacking and agglomeration between sheets, and make PSN form a relatively uniform dispersion in the aqueous system. PSN has a two-dimensional sheet structure, porous channels, and abundant surface -OH functional groups, which can provide sufficient active sites for the heterogeneous nucleation and in-situ growth of TiO2, and at the same time provide suitable electrolyte wetting and Li-sulfur battery.+ The transmission provides a favorable structural foundation.

[0019] 5. In this invention, 0.5–2.5 g of Ti(SO4)2 is added to 30–40 mL of deionized water and stirred and dispersed for 1–4 h to obtain a titanium precursor solution. By thoroughly stirring and dispersing Ti(SO4)2 in the aqueous system, the titanium source can be uniformly distributed, reducing rapid hydrolysis and particle agglomeration caused by excessively high local concentrations of titanium species, which is beneficial for subsequent Ti… 4+ It allows for full contact with the active sites on the PSN surface, thereby improving the uniformity of in-situ nucleation of TiO2 on the PSN surface and the stability of the load.

[0020] 6. In this invention, a titanium precursor solution and a PSN dispersion are mixed and stirred for 1–2 h, followed by a hydrothermal in-situ composite reaction. The mixture is then collected by centrifugation, washed 4–8 times with deionized water, and freeze-dried at -70 to -30°C for 20–28 h to obtain a PSN-TiO2 heterostructure composite material. Appropriate mixing and stirring time improves the contact uniformity between the titanium precursor and PSN. The hydrothermal reaction promotes the stable growth of TiO2 on the PSN surface. Multiple washings remove residual ions and unreacted precursors. Freeze-drying helps reduce PSN layer recombination and pore structure collapse, thereby maintaining the two-dimensional porous structure and heterostructure activity of the composite material.

[0021] 7. In this invention, 3-5 parts of PSN-TiO2 heterostructure composite material, 4-6 parts of carbon nanotubes, and 0.5-1.5 parts of polyvinylidene fluoride are mixed and then added to N-methylpyrrolidone in a specific ratio and stirred to form a uniform slurry. The slurry is then coated onto the surface of a polypropylene membrane and vacuum dried at 50-70°C for 8-16 hours to form a barrier layer on the surface of the polypropylene membrane, thus obtaining a PSN-TiO2 modified membrane. The PSN-TiO2 heterostructure composite material provides active sites for polysulfide adsorption and catalytic conversion, the carbon nanotubes construct a continuous conductive network, and the polyvinylidene fluoride enhances the film-forming properties of the barrier layer and the bonding stability between the barrier layer and the polypropylene membrane.

[0022] 8. The material preparation and membrane modification processes of this invention possess excellent scalability and practical application value. On the raw material side, natural vermiculite minerals are used as precursors to prepare the PSN substrate. These minerals are abundant and inexpensive, effectively controlling the overall material cost. The preparation process employs conventional hydrothermal, centrifugal, and drying chemical unit operations, with mild reaction conditions and no need for extreme equipment or complex procedures. The membrane coating process is highly compatible with existing commercial lithium-ion battery membrane coating production lines, requiring no large-scale modifications to existing production lines. It has promising prospects for industrial application.

[0023] 9. The PSN-TiO2 heterostructure composite material prepared by this invention can effectively inhibit the aggregation and growth of TiO2 nanoparticles, while optimizing the catalytic activity of the material through the electronic interaction at the two-phase interface. The PSN two-dimensional sheets serve as a supporting substrate, and Ti can be anchored through surface hydroxyl sites. 4+ The precursor can preferentially nucleate and grow TiO2, avoiding excessive aggregation and size coarsening of TiO2 particles during hydrothermal processes, and ensuring full exposure of catalytic active sites.

[0024] 10. The PSN-TiO2 heterostructure composite material prepared in this invention can achieve effective confinement and continuous conversion of polysulfides through a triple action of physical confinement, chemical anchoring, and catalytic conversion, significantly alleviating the shuttle effect of lithium-sulfur batteries. Specifically, the two-dimensional mesoporous structure of PSN can exert a spatial sieving effect, physically preventing the diffusion of soluble long-chain polysulfides to the negative electrode side; the polar hydroxyl and oxygen sites on the PSN surface and the metal active sites of TiO2 can form strong chemical interactions with polysulfides from the lithium and sulfur ends, respectively, achieving firm anchoring of polysulfides; simultaneously, the abundant catalytic sites provided by the heterostructure can accelerate the redox conversion rate of polysulfides, enabling the adsorbed and captured polysulfides to be rapidly converted into short-chain sulfides, avoiding the accumulation of polysulfides at the interface, thus achieving the adsorption and rapid catalytic conversion of polysulfides.

[0025] 11. The PSN-TiO2 modified membrane of this invention can achieve ion / electron synergistic supply in the polysulfide conversion process, significantly accelerating the kinetics of sulfur oxidation-reduction reaction. At the ion transport level, the two-dimensional porous channels and abundant polar sites on the surface of PSN can provide Li... + By constructing a continuous, low-resistance transport path, the ion diffusion distance is effectively shortened, improving the lithium-ion diffusion coefficient. At the electron transport level, carbon nanotubes can construct a through-type conductive network within the barrier layer. The charge conductivity of TiO2 and the efficient charge transfer characteristics of the heterojunction provide a continuous and rapid electron supply for the polysulfide conversion reaction. Simultaneously, the difference in work function between PSN and TiO2 drives a spontaneous charge redistribution at the heterojunction, regulating the local electronic structure of TiO2 and inducing the generation of more oxygen vacancy defect active sites. This further enhances the intrinsic catalytic activity of the material for sulfur redox reactions, lowers the reaction energy barrier for polysulfide conversion, and promotes synergistic ion / electron supply during the polysulfide conversion process. The synergistic matching of the ion transport channel and the electron conduction network can significantly reduce the interfacial charge transfer impedance of the battery, reduce voltage polarization during charging and discharging, and effectively improve the utilization efficiency of sulfur-active materials.

[0026] 12. The PSN-TiO2 modified separator of this invention can precisely control lithium-ion deposition behavior, achieving uniform lithium nucleation and effectively suppressing lithium dendrite growth, significantly improving the cycle stability and operational safety of the lithium metal anode. The Li||Li symmetric battery assembled using the PSN-TiO2 modified separator can achieve a lithium-ion transference number of 0.67 and a lithium-ion diffusion coefficient of 9.7 × 10⁻⁶. -12 cm²s -1 Both are superior to pure PP membranes and single-component modified membranes, exhibiting better ion transport and flux uniformity control capabilities. At 2 mA·cm⁻¹ -2 At the specified current density, symmetric cells with pure PP, PSN, and TiO2 modified separators exhibited continuously increasing voltage polarization and drastic voltage fluctuations with cycling, resulting in poor cycle stability. In contrast, the symmetric cell with the PSN-TiO2 modified separator could cycle stably for up to 1200 hours, maintaining low and stable voltage polarization throughout, demonstrating excellent lithium deposition / stripping reversibility and long-term cycle stability. This is partly due to the PSN-TiO2 modified separator's uniformly distributed porous channels and abundant polar active sites, which can homogenize the transmembrane Li... + The modified separator improves flux, preventing uneven lithium deposition caused by excessively high local current density and guiding lithium metal to nucleate and grow smoothly and uniformly on the anode surface. Furthermore, its effective blocking of the polysulfide shuttle effect significantly reduces side reactions between soluble polysulfides and the lithium anode, facilitating the formation of a thin, uniform, stable, and dense interface layer. This further suppresses the initiation and extension of lithium dendrites at the interface environment level. Optical microscopy observations further validated these effects: with prolonged cycling time, the lithium anode using a pure PP separator gradually developed obvious lithium dendrite protrusions and irregular deposition morphology; while the lithium anode using a PSN-TiO2 modified separator maintained a smooth and dense surface after cycling, without significant dendrite formation. This directly demonstrates the significant inhibitory effect of the modified separator on lithium dendrite growth, effectively extending the cycle life of the lithium metal anode and improving battery safety.

[0027] 13. The PSN-TiO2 modified separator prepared in this invention can significantly improve the rate performance and cycle life of lithium-sulfur batteries, while exhibiting lower shuttle current and maintaining excellent electrochemical performance under high sulfur loading conditions. Because this functional separator combines multiple functions of polysulfide physical confinement, chemical anchoring, and catalytic conversion, and possesses good electrolyte wettability, efficient ion transport channels, and uniform lithium-ion flux, it can effectively suppress the polysulfide shuttle effect, reduce the charge transfer impedance at the battery interface, and improve the kinetics of sulfur redox reactions and the stability of the lithium anode interface. In lithium-sulfur battery systems, batteries using PSN-TiO2 modified separators exhibit superior rate capacity, lower shuttle current, and better long-cycle capacity retention. Even under high sulfur loading conditions, the batteries can still maintain high discharge specific capacity and stable cycle performance, indicating that the modified separator can not only efficiently block polysulfides and accelerate sulfur species conversion, but also stabilize the lithium metal anode interface, comprehensively improving the overall electrochemical performance of the battery under different rate, long-cycle, and high sulfur loading conditions.

[0028] In summary, this invention has the advantages of low raw material cost, simple preparation method, and the ability of the prepared PSN-TiO2 heterostructure composite material to effectively inhibit TiO2 agglomeration, promote ion / electron synergistic supply during polysulfide conversion, effectively confine and continuously convert polysulfides, alleviate shuttle effect, facilitate uniform lithium nucleation and inhibit lithium dendrite growth, and provide benefits such as lower shuttle current, higher lithium ion transference number and good high sulfur loading cycle stability. Attached Figure Description

[0029] Figure 1 These are morphology and pore structure characterization images of the PSN two-dimensional material prepared according to embodiments of the present invention; wherein Figure 1 a is the AFM image of the PSN material. Figure 2 b is the AFM height line scan curve corresponding to the PSN material. Figure 1 c represents the N2 adsorption-desorption isotherm of the PSN material. Figure 2 d represents the pore size distribution curve of the PSN material.

[0030] Figure 2 The morphology and elemental distribution diagrams of the PSN-TiO2 heterostructure composite material prepared in the embodiments of the present invention are shown below; wherein, Figure 2 a is a scanning electron microscope image of the PSN material. Figure 2 b is a scanning electron microscope image of the TiO2 material. Figure 2 c is a scanning electron microscope image of the PSN-TiO2 composite material. Figure 2 d is a transmission electron microscope image of the PSN-TiO2 composite material. Figure 2 e represents a high-resolution projection electron micrograph of the PSN-TiO2 composite material; Figure 2 fh is a distribution diagram of Si, Ti and O elements in the PSN-TiO2 composite material.

[0031] Figure 3 The structural and chemical characterization diagrams of the PSN-TiO2 heterostructure composite material prepared in the embodiments of the present invention and the PSN and TiO2 materials in the comparative examples are shown; wherein, Figure 3 a represents the XRD pattern. Figure 3 b is the FTIR spectrum. Figure 3 c is the XPS full spectrum. Figure 3 d is the high-resolution XPS spectrum of Ti 2p. Figure 3 e represents the high-resolution XPS spectrum of Si 2p. Figure 3 f is the O 1s high-resolution XPS spectrum. Figure 3 g represents the EPR spectrum.

[0032] Figure 4 The work function and density of states of the PSN-TiO2 heterostructure composite material prepared in the embodiments of the present invention and the comparative examples of PSN and TiO2 materials; wherein, Figure 4 a is the work function graph of PSN. Figure 4 b is the work function graph of TiO2. Figure 4 c is the work function graph of PSN-TiO2. Figure 4 b is the density of states plot of the PSN. Figure 4 e represents the density of states diagram of TiO2. Figure 4 f is the density of states diagram of PSN-TiO2.

[0033] Figure 5 Characterization diagrams of the adsorption and interfacial chemical interactions of PSN and TiO2 materials on Li2S6 in the PSN-TiO2 heterostructure composite materials prepared in the embodiments of the present invention and in the comparative examples; wherein, Figure 5 a shows the UV-Vis absorption spectrum of the solution after adsorption (the inset is a visualization of the adsorption of PSN, TiO2, and PSN-TiO2 after 12 hours of addition to Li2S6 solution). Figure 5 b is the high-resolution XPS spectrum of Ti2p after adsorption. Figure 5 c is the high-resolution XPS spectrum of S 2p after adsorption. Figure 5 d is the high-resolution XPS spectrum of Li 1s after adsorption.

[0034] Figure 6 The images show the interface morphology and wettability characterization of the PSN-TiO2 heterostructure composite material prepared in the embodiments of the present invention and the PSN and TiO2 materials in the comparative examples; wherein, Figure 6 a, 6b, and 6c are scanning electron microscope (SEM) images of the surfaces of PSN, TiO2, and PSN-TiO2 modified membranes, respectively. Figure 6Images d, 6e, and 6f are cross-sectional scanning electron microscope (SEM) images of PSN, TiO2, and PSN-TiO2 modified membranes, respectively. Figure 6 g, 6h, and 6i are PSN, TiO2, and PSN-TiO2 modified membranes, respectively.

[0035] Figure 7 The performance diagrams of the PSN-TiO2 heterostructure composite material prepared in the embodiments of the present invention and the Li||Li symmetric cells assembled from PSN, TiO2 and PP materials in the comparative examples are shown; wherein, Figure 7 Figure a shows the lithium-ion transference number measurements of Li||Li symmetric batteries assembled with PP, PSN, TiO2, and PSN-TiO2 separators. Figure 7 b is the lithium-ion diffusion coefficient of PP, PSN, TiO2, and PSN-TiO2 separators. Figure 7 c is the cycle stability diagram of Li||Li symmetric cells assembled with PP, PSN, TiO2 and PSN-TiO2 separators under the condition of 2 mA cm⁻². Figure 7 d is an optical microscope image of a Li||Li symmetric cell assembled with PP and PSN-TiO2 separator.

[0036] Figure 8 Electrochemical performance diagram of a lithium-sulfur battery assembled with a PSN-TiO2 modified separator prepared in an embodiment of the present invention; wherein, Figure 8 Figure a shows the 0.1C charge-discharge curves of lithium-sulfur batteries assembled with PP, PSN, TiO2, and PSN-TiO2 separators. Figure 8 b represents the Q of PP, PSN, TiO2, and PSN-TiO2. L / Q H The ratio, Figure 8 c shows the rate performance of lithium-sulfur batteries assembled with PP, PSN, TiO2, and PSN-TiO2 separators. Figure 8 d is the electrochemical impedance spectroscopy diagram of lithium-sulfur batteries assembled with PP, PSN, TiO2 and PSN-TiO2 separators. Figure 8 e represents the 2C cycle performance of lithium-sulfur batteries assembled with PP, PSN, TiO2, and PSN-TiO2 separators. Figure 8 f shows the shuttle current test results for lithium-sulfur batteries assembled with PP, PSN, TiO2, and PSN-TiO2 separators. Figure 8 g represents the cycle performance of a lithium-sulfur battery assembled with a PSN-TiO2 modified separator under high sulfur loading conditions. Detailed Implementation

[0037] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this should not be construed as limiting the present invention.

[0038] Example 1: A method for preparing a PSN-TiO2 heterostructure composite material, comprising the following steps: (1) Add 0.5g Ti(SO4)2 to 30mL of deionized water and stir to disperse for 1 h to obtain a titanium precursor solution; (2) Add 0.2g of two-dimensional porous silica nanosheets (PSN) to 40mL of deionized water and ultrasonically disperse for 0.5h to obtain a two-dimensional porous silica nanosheet dispersion (PSN dispersion). (3) Mix the titanium precursor solution and PSN dispersion for 1 hour, and then perform in-situ composite reaction for 4 hours under hydrothermal conditions at 90°C. Collect the precipitate by centrifugation, wash it 4 times with deionized water, and freeze-dry it at -70°C for 20 hours to obtain the PSN-TiO2 heterostructure composite material.

[0039] The PSN was prepared by the following method: 5 g of vermiculite crystals were added to 150 mL of saturated sodium chloride solution and stirred at 70 °C for 18 h. The solution was washed until no white precipitate was detected by 0.1 mol / L silver nitrate solution. The resulting sample was then placed in 1 mol / L lithium chloride solution and stirred at 70 °C for another 18 h. The solution was dialyzed until no white precipitate was detected by 0.1 mol / L silver nitrate solution. The product was then placed in 100 mL of 30 wt.% hydrochloric acid solution and stirred at 70 °C for 18 h. The solution was washed until the pH value was 6.5. The product was then etched a second time under the same hydrochloric acid conditions. Finally, the resulting suspension was centrifuged at 800 r / min for 5 min, the supernatant was collected, and the solution was freeze-dried at -70 °C for 20 h to obtain PSN.

[0040] Example 2: A method for preparing a PSN-TiO2 heterostructure composite material, comprising the following steps: (1) Add 1g Ti(SO4)2 to 32mL of deionized water and stir to disperse for 1.5 h to obtain a titanium precursor solution; (2) Add 0.4 g PSN to 50 mL of deionized water and sonicate for 0.8 h to obtain PSN dispersion; (3) The titanium precursor solution and PSN dispersion were mixed and stirred for 1.3 h. The in-situ composite reaction was carried out for 5 h under hydrothermal environment at 95℃. The precipitate was collected by centrifugation, washed 5 times with deionized water, and freeze-dried at -30℃ for 22 h to obtain PSN-TiO2 heterostructure composite material.

[0041] The PSN was prepared by the following method: 8 g of vermiculite crystals were added to 200 mL of saturated sodium chloride solution and stirred at 75 °C for 22 h. The mixture was washed until no white precipitate was detected by 0.3 mol / L silver nitrate solution. The resulting sample was then placed in 1.5 mol / L lithium chloride solution and stirred at 75 °C for another 22 h. The mixture was dialyzed until no white precipitate was detected by 0.3 mol / L silver nitrate solution. The product was then placed in 125 mL of 34 wt.% hydrochloric acid solution and stirred at 75 °C for 22 h. The mixture was washed until the pH value was 6.6. The product was then etched a second time under the same hydrochloric acid conditions. Finally, the resulting suspension was centrifuged at 900 r / min for 8 min, the supernatant was collected, and the supernatant was freeze-dried at -55 °C for 22 h to obtain PSN.

[0042] Example 3: A method for preparing a PSN-TiO2 heterostructure composite material, comprising the following steps: (1) Add 1.5g Ti(SO4)2 to 35 mL of deionized water and stir to disperse for 2h to obtain a titanium precursor solution; (2) Add 0.5g PSN to 60 mL of deionized water and sonicate for 1 h to obtain PSN dispersion; (3) Mix the titanium precursor solution and PSN dispersion for 1.5 h, and perform in-situ composite reaction for 6 h under hydrothermal environment at 100℃. Collect the precipitate by centrifugation, wash it 6 times with deionized water, and freeze dry it at -50℃ for 24 h to obtain PSN-TiO2 heterostructure composite material.

[0043] The PSN was prepared by the following method: 10 g of vermiculite crystals were added to 250 mL of saturated sodium chloride solution and stirred at 80 °C for 24 h. The solution was washed until no white precipitate was detected by 0.5 mol / L silver nitrate solution. The resulting sample was then placed in 2 mol / L lithium chloride solution and stirred at 80 °C for 18–30 h. The solution was dialyzed until no white precipitate was detected by 0.5 mol / L silver nitrate solution. The product was then placed in 150 mL of 36 wt.% hydrochloric acid solution and stirred at 80 °C for 24 h. The solution was washed until the pH value was 6.8. The solution was then etched a second time under the same hydrochloric acid conditions. Finally, the resulting suspension was centrifuged at 1000 r / min for 10 min, the supernatant was collected, and the solution was freeze-dried at -60 °C for 24 h to obtain PSN.

[0044] Example 4: A method for preparing a PSN-TiO2 heterostructure composite material, comprising the following steps: (1) Add 2.0g Ti(SO4)2 to 38mL of deionized water and stir to disperse for 3h to obtain a titanium precursor solution; (2) Add 0.6 g PSN to 70 mL of deionized water and sonicate for 1.5 h to obtain PSN dispersion; (3) The titanium precursor solution and PSN dispersion were mixed and stirred for 1.8 h. The in-situ composite reaction was carried out for 7 h under hydrothermal environment at 105℃. The precipitate was collected by centrifugation, washed 7 times with deionized water, and freeze-dried at -60℃ for 26 h to obtain PSN-TiO2 heterostructure composite material.

[0045] The PSN was prepared by the following method: 13 g of vermiculite crystals were added to 300 mL of saturated sodium chloride solution and stirred at 85 °C for 26 h. The solution was washed until no white precipitate was detected by 0.7 mol / L silver nitrate solution. The resulting sample was then placed in 2.5 mol / L lithium chloride solution and stirred at 95 °C for 26 h. The solution was dialyzed until no white precipitate was detected by 0.7 mol / L silver nitrate solution. The product was then placed in 175 mL of 37 wt.% hydrochloric acid solution and stirred at 95 °C for 26 h. The solution was washed until the pH value was 6.9. The product was then etched a second time under the same hydrochloric acid conditions. Finally, the resulting suspension was centrifuged at 1300 r / min for 15 min, the supernatant was collected, and the solution was freeze-dried at -60 °C for 26 h to obtain PSN.

[0046] Example 5: A method for preparing a PSN-TiO2 heterostructure composite material, comprising the following steps: (1) Add 2.5g Ti(SO4)2 to 40mL of deionized water and stir to disperse for 4 h to obtain a titanium precursor solution; (2) Add 0.8 g PSN to 80 mL of deionized water and sonicate for 2 h to obtain PSN dispersion; (3) Mix the titanium precursor solution and PSN dispersion for 2 h, and then perform in-situ composite reaction for 8 h under hydrothermal environment at 110℃. Collect the precipitate by centrifugation, wash it 8 times with deionized water, and freeze dry it at -30℃ for 28 h to obtain PSN-TiO2 heterostructure composite material.

[0047] The PSN was prepared by the following method: 15 g of vermiculite crystals were added to 350 mL of saturated sodium chloride solution and stirred at 90 °C for 30 h. The solution was washed until no white precipitate was detected by 1 mol / L silver nitrate solution. The resulting sample was then placed in 3 mol / L lithium chloride solution and stirred at 90 °C for another 30 h. The solution was dialyzed until no white precipitate was detected by 1 mol / L silver nitrate solution. The product was then placed in 200 mL of 38 wt.% hydrochloric acid solution and stirred at 90 °C for 30 h. The solution was washed until the pH value was 7. The product was then etched a second time under the same hydrochloric acid conditions. Finally, the resulting suspension was centrifuged at 1500 r / min for 20 min, the supernatant was collected, and the solution was freeze-dried at -50 °C for 28 h to obtain PSN.

[0048] Comparative Example 1: Preparation of TiO2 material, including the following steps: (1) Add 1.5g Ti(SO4)2 to 35mL of deionized water and stir to disperse for 2 h to obtain a titanium precursor solution; (2) The titanium precursor solution was subjected to in-situ composite reaction at 100℃ hydrothermal environment for 6 h. The precipitate was collected by centrifugation, washed 6 times with deionized water, and freeze-dried at -50℃ for 26 h to obtain TiO2 material.

[0049] Comparative Example 2: Preparation of PSN material, including the following steps: 10 g of vermiculite crystals were added to 250 mL of saturated sodium chloride solution and stirred at 80 °C for 24 h. The mixture was washed until no white precipitate was detected by 0.5 mol / L silver nitrate solution. The resulting sample was then placed in 2 mol / L lithium chloride solution and stirred at 80 °C for another 24 h. The mixture was dialyzed until no white precipitate was detected by 0.5 mol / L silver nitrate solution. The product was then placed in 150 mL of 36 wt.% hydrochloric acid solution and stirred at 80 °C for 24 h. The mixture was washed until the pH value was 6.7. A second etching was performed under the same hydrochloric acid conditions. Finally, the resulting suspension was centrifuged at 1000 r / min for 10 min, the supernatant was collected, and freeze-dried at -60 °C for 24 h to obtain PSN.

[0050] Application Example 1: Preparation of PSN-TiO2 modified separator and assembly of lithium-sulfur battery A mixture of 3-5 parts PSN-TiO2 heterostructure composite material, 4-6 parts carbon nanotubes, and 0.5-1.5 parts polyvinylidene fluoride was prepared. 8-12 g of the mixture was added to 240-280 mL of N-methylpyrrolidone and stirred to form a uniform slurry. The slurry was coated onto the surface of a Celgard 2500 polypropylene separator and vacuum dried at 50-70°C for 8-16 h to form a barrier layer on the polypropylene separator surface, resulting in a PSN-TiO2 modified separator. The dried PSN-TiO2 lithium-sulfur battery modified separator was cut to obtain a circular sample with a diameter of 16 mm, denoted as PSN-TiO2-PP.

[0051] For comparative studies, the same PSN-TiO2-PP preparation process was used, but the PSN-TiO2 heterostructure composite material was replaced with comparative TiO2 material and comparative PSN material respectively to prepare PSN-PP and TiO2-PP modified diaphragms; the uncoated Celgard 2500 polypropylene diaphragm was denoted as PP.

[0052] Experiments have shown that: 1. Figure 1 These are morphology and pore structure characterization images of the PSN two-dimensional material prepared according to embodiments of the present invention; wherein Figure 1 a is the AFM image of the PSN material. Figure 2 b is the AFM height line scan curve corresponding to the PSN material. Figure 1 c represents the N2 adsorption-desorption isotherm of the PSN material. Figure 2 d represents the pore size distribution curve of the PSN material. For example... Figure 1 As shown in Figure a, the PSN material exhibits a distinct two-dimensional lamellar morphology with abundant porous structures on the lamellar surface, indicating that after ion exchange and acid etching, the vermiculite layered structure was effectively exfoliated and transformed into two-dimensional porous silicon-oxygen nanosheets. Figure 1 The thickness distribution diagram (b) shows that the PSN sheet thickness is approximately 0.6 nm, proving that the obtained PSN has a two-dimensional thin-layer structure. For example... Figure 1 As shown in Figure c, the PSN material exhibits obvious porous adsorption characteristics, with a specific surface area of ​​193.82 m² / g, indicating that the material possesses a high specific surface area and abundant pore structure. Figure 1 As shown in d, the pore size of the PSN material is mainly distributed in the mesopore range, indicating that the acid etching process has constructed abundant mesopore channels in the PSN sheets.

[0053] 2. Figure 2 These are characterization diagrams of the morphology, crystal structure, and elemental distribution of the PSN-TiO2 heterostructure composite material prepared in this invention and its comparative examples; wherein... Figure 2 a is the SEM image of the PSN material. Figure 2b is the SEM image of TiO2 material. Figure 2 c is the SEM image of the PSN-TiO2 composite material. Figure 2 d is a TEM image of the PSN-TiO2 heterostructure composite material. Figure 2 e is the selected area electron diffraction pattern of the PSN-TiO2 composite material. Figure 2 fh are mapping diagrams of Ti, Si, and O elements in the PSN-TiO2 heterostructure composite material, respectively. Figure 2 As shown in Figure a, the PSN material exhibits a distinct two-dimensional layered stacked structure with a relatively rough surface, indicating that after ion exchange and acid etching, the vermiculite-derived material formed a two-dimensional porous silicon-oxygen layered structure. Figure 2 As shown in b, the TiO2 material prepared alone mainly exhibits particulate aggregates, with obvious aggregation between particles. This indicates that TiO2 alone is prone to aggregation during hydrothermal processes, which may lead to the masking of some active sites. Figure 2 As shown in Figure c, TiO2 nanoparticles are uniformly distributed on the surface of the PSN two-dimensional sheets in the PSN-TiO2 heterostructure composite material, forming a sheet-particle coupled structure. This indicates that the PSN sheets can serve as a carrier for in-situ growth of TiO2, effectively limiting the excessive aggregation of TiO2 particles and increasing the exposure of active sites. Figure 2 As shown in d, the TEM image of the PSN-TiO2 heterostructure composite material further reveals that TiO2 particles are loaded on the surface of the PSN sheets, indicating a relatively tight interfacial contact between TiO2 and PSN. Figure 2 As shown in Figure e, the selected area electron diffraction pattern of the PSN-TiO2 heterostructure composite material shows obvious diffraction rings, corresponding to the (101), (200), and (004) crystal planes of the anatase phase TiO2, indicating that TiO2 in the composite material has a good crystal structure. Figure 2 As shown in fh, Ti, Si, and O elements are uniformly distributed in the PSN-TiO2 heterostructure composite material. The results indicate that the PSN-TiO2 heterostructure composite material was successfully synthesized.

[0054] 3. Figure 3 These are the XRD, FTIR, XPS, and EPR characterization images of the PSN-TiO2 heterostructure composite material prepared in this invention and the PSN and TiO2 materials in the comparative examples; wherein Figure 3 a represents the XRD pattern. Figure 3 b is the FTIR spectrum. Figure 3 c is the XPS full spectrum. Figure 3 d is the high-resolution XPS spectrum of Ti 2p. Figure 3 e represents the O 1s high-resolution XPS spectrum. Figure 3 f is the high-resolution XPS spectrum of Si 2p. Figure 3 g represents the EPR spectrum. For example... Figure 3 As shown in Figure a, PSN exhibits a broad diffraction peak at approximately 22.5°, indicating that it is primarily an amorphous silicon-oxygen structure. TiO2 shows characteristic diffraction peaks near 25.3°, 37.8°, 48.0°, 53.9°, and 62.7°, corresponding to the (101), (004), (200), (105), and (204) crystal planes of the anatase phase TiO2, respectively. The simultaneous display of characteristic peaks from both PSN and TiO2 in PSN-TiO2 indicates that TiO2 was successfully loaded onto the PSN surface. Figure 3 As shown in b, PSN is at approximately 1083 cm. -1 and 460 cm -1 The absorption peaks at these locations are attributed to Si-O-Si and Si-O vibrations, respectively; the absorption peaks of TiO2 at 460–800 cm⁻¹ are at 460–800 cm⁻¹. -1 The absorption peaks within the range are attributed to the Ti-O-Ti / Ti-O vibration. PSN-TiO2 retains the main characteristic absorption peaks of both, further proving the successful recombination of PSN and TiO2. Figure 3 As shown in Figure c, the XPS full spectrum of PSN-TiO2 simultaneously contains Si, Ti, and O elements, indicating that TiO2 has been introduced into the PSN system. Figure 3 As shown in df, the peak positions of Ti2p, O 1s, and Si 2p in PSN-TiO2 change compared to the single component, indicating that the local chemical environment of Ti-O and Si-O is regulated after compositing, and there is interfacial electronic interaction between PSN and TiO2. Figure 3 As shown in g, both TiO2 and PSN-TiO2 exhibit oxygen vacancy-related EPR signals near g=2.003, with PSN-TiO2 showing a stronger signal, indicating that the construction of the PSN-TiO2 heterointerface is beneficial for inducing the generation of more oxygen vacancy defects. In summary, Figure 3 The results show that the PSN-TiO2 composite material prepared by this invention has both the amorphous silicon-oxygen structure of PSN and the anatase crystal phase structure of TiO2, and a heterogeneous interface with interfacial electronic interaction and oxygen vacancy defects is formed between the two, which is beneficial to improving the adsorption of polysulfides and the catalytic conversion of sulfur oxidation-reduction.

[0055] 4. Figure 4 The work function and density of states of the PSN-TiO2 heterostructure composite material prepared in the embodiments of the present invention and the comparative examples of PSN and TiO2 materials; wherein, Figure 4 a is the work function graph of PSN. Figure 4 b is the work function graph of TiO2. Figure 4 c is the work function graph of PSN-TiO2. Figure 4 b is the density of states plot of the PSN. Figure 4 e represents the density of states diagram of TiO2. Figure 4 e is the density of states diagram of PSN-TiO2. For example... Figure 4 As shown in Figure ac, the work functions of PSN, TiO2, and PSN-TiO2 are 7.557, 6.406, and 7.449, respectively. The difference in work function between PSN and TiO2 indicates a driving force for interfacial charge redistribution after their contact. The work function state of the PSN-TiO2 heterostructure composite material changes compared to PSN and TiO2 alone, indicating that a new interfacial electronic structure is formed after PSN and TiO2 are combined. Figure 4 As shown in df, the density of states distributions of PSN, TiO2, and PSN-TiO2 differ. The electronic state distributions of individual PSN and TiO2 are relatively independent, while the electronic state distribution near the Fermi level is modulated after PSN-TiO2 recombination, indicating that the construction of heterojunctions can improve the local electronic structure and promote interfacial electron transport. Figure 4 It can be seen that the work function difference between PSN and TiO2 can induce charge redistribution at the PSN-TiO2 heterostructure interface and regulate its density of states distribution. This modulation of the interface's electronic structure helps reduce charge transfer resistance, promotes electron supply during polysulfide conversion, and thus improves the kinetics of sulfur redox reactions in lithium-sulfur batteries.

[0056] 5. Figure 5 This invention presents the PSN-TiO2 heterostructure composite material prepared in the embodiments of the present invention, and the comparative examples of PSN and TiO2 materials for Li2S6, including visualization adsorption experiments, UV-vis spectra, and XPS characterization diagrams after adsorption. Figure 5 a shows the visualization of the adsorption experiments and UV-vis spectra of PSN, TiO2, and PSN-TiO2 materials after standing for 6 h following the addition of Li2S6 solution; after the Li2S6 adsorption experiment... Figure 5 b is the Ti 2p high-resolution XPS image of TiO2 and PSN-TiO2 materials; Figure 5 c is the high-resolution XPS image of S 2p after adsorption of Li2S6, PSN, TiO2 and PSN-TiO2 materials; Figure 5 d is a high-resolution XPS image of Li 1s after adsorption in Li2S6, PSN, TiO2, and PSN-TiO2 materials. (See image for reference.) Figure 5As shown in Figure a, after 12 h of static adsorption, the PSN-TiO2 and TiO2 systems were nearly colorless, while the PSN system remained pale yellow, indicating that both PSN-TiO2 and TiO2 possessed strong adsorption capacity for Li2S6. The superior adsorption performance of PSN-TiO2 was mainly attributed to the physical confinement effect of the two-dimensional porous structure of PSN and the strong chemisorption effect of the polar sites of TiO2 on Li2S6. The UV-vis spectral results were consistent with the visualized adsorption phenomenon; the PSN-TiO2 system exhibited the lowest absorbance at the characteristic absorption peak of LiPSs, indicating that it could effectively reduce the concentration of soluble Li2S6 in the solution, thereby inhibiting the diffusion of polysulfides in the electrolyte. Figure 5 As shown in b, after Li₂S₆ adsorption, new peaks appear near 459.2 eV and 457.5 eV in the Ti 2p high-resolution XPS spectrum of PSN-TiO₂, which can be attributed to Ti-S bonds. This indicates that the Ti active sites in TiO₂ can chemically interact with the S atoms in LiPSs, thereby achieving effective anchoring of polysulfides. Figure 5 As shown in c, in the high-resolution XPS spectrum of S 2p after adsorption, the peaks at 170.5 eV and 169.2 eV belong to polythionates, the peaks at 167.9 eV and 166.6 eV belong to thiosulfates, the peaks at 165.4 eV and 164.1 eV correspond to bridged sulfur S0B, the peaks at 163.2 eV and 162.2 eV correspond to terminal sulfur S-1T, and the peak near 161.1 eV belongs to Ti-S bonds. Figure 5 As shown in Figure d, Li-O and Li-S correlation signals can be observed in the high-resolution XPS spectrum of Li 1s. Compared with the blank Li2S6 sample, the samples after adsorption by PSN, TiO2, and PSN-TiO2 all showed Li-O interaction signals, indicating that the hydroxyl / oxygen sites on the PSN surface and the oxygen sites on the TiO2 surface can chemically interact with lithium species in Li2S6. Among them, the PSN-TiO2 heterostructure composite material showed a more obvious Li-O characteristic peak and retained the Li-S signal, indicating that it has both lithium-end adsorption and sulfur-end anchoring effects during LiPSs adsorption. Figure 5 It can be seen that the PSN-TiO2 heterostructure composite material prepared in this invention has excellent adsorption capacity and strong chemical affinity for Li2S6.

[0057] 6. Figure 6 The images show the interface morphology and wettability of the PSN-TiO2 heterostructure composite material prepared in the embodiments of the present invention and the PSN and TiO2 materials used as membrane barrier layers in the comparative examples; wherein, Figure 6 Images a and c are scanning electron microscope (SEM) images of the surfaces of PSN, TiO2, and PSN-TiO2 modified membranes, respectively. Figure 6 df are cross-sectional scanning electron microscope images of PSN, TiO2, and PSN-TiO2 modified membranes, respectively. Figure 6 gi represents the electrolyte contact angle test results for PSN, TiO2, and PSN-TiO2 modified separators, respectively. Figure 6 As shown in Figure ac, the PSN membrane surface mainly exhibits a layered stacked structure, while the TiO2 membrane surface shows a granular distribution with some agglomeration. The PSN-TiO2 modified membrane, however, forms a more uniform layer-particle composite structure, indicating that PSN can act as a carrier to improve the dispersion of TiO2 particles and form a continuous barrier layer. Figure 6 As shown in df, the PSN, TiO2, and PSN-TiO2 modified separators all formed distinct coatings with thicknesses of approximately 6.52 µm, 5.74 µm, and 5.34 µm, respectively. This indicates that the PSN-TiO2 coating is thinner and more compact, which is beneficial for reducing ion transport resistance. Figure 6 As shown in Figure gi, the electrolyte contact angles of the PSN, TiO2, and PSN-TiO2 modified separators are 24.5°, 30.3°, and 18.5°, respectively. The PSN-TiO2 modified separator has the smallest contact angle, indicating that it has the best electrolyte wettability. Figure 6 It can be seen that the PSN-TiO2 composite material can form a uniform, dense, and well-wetting functional barrier layer on the surface of the polypropylene membrane, which is beneficial for promoting Li + It transports and enhances the barrier and adsorption of polysulfides.

[0058] 7. Figure 7 The performance diagrams of the PSN-TiO2 heterostructure composite material prepared in the embodiments of the present invention and the Li||Li symmetric cells assembled with PP, PSN and TiO2 separators in the comparative examples are shown; wherein, Figure 7 Figure a shows the lithium-ion transference number measurements of Li||Li symmetric batteries assembled with PP, PSN, TiO2, and PSN-TiO2 separators. Figure 7 b is a graph showing the lithium-ion diffusion coefficients for PP, PSN, TiO2, and PSN-TiO2 separators. Figure 7 c represents a Li||Li symmetric cell assembled with PP, PSN, TiO2, and PSN-TiO2 separators at 2 mA cm⁻¹. -2 Cyclic stability plot under given conditions. For example... Figure 7 As shown in Figure a, the lithium-ion transference numbers corresponding to PP, PSN, TiO2, and PSN-TiO2 membranes are 0.50, 0.52, 0.61, and 0.71, respectively. Among them, the PSN-TiO2 modified membrane has the highest lithium-ion transference number, indicating that the PSN-TiO2 heterostructure can promote the selective migration of Li⁺ and improve the ion transport capacity of the membrane interface. Figure 7As shown in b, the lithium-ion diffusion coefficient of the PSN-TiO2 modified separator is higher than that of the PP, PSN, and TiO2 separators, indicating that the PSN-TiO2 modified separator can provide a more favorable lithium diffusion coefficient. + Diffusion channels reduce obstacles to ion migration. For example... Figure 7 As shown in c, at 2 mA cm -2 Under the specified conditions, the Li||Li symmetric cell assembled with a PSN-TiO2 modified separator exhibited a more stable voltage plateau and lower polarization, and could cycle stably for 1200 h, significantly outperforming PP, PSN, and TiO2 separators. This indicates that the PSN-TiO2 modified separator can homogenize the Li⁺ flux, improve lithium deposition / stripping stability, and suppress lithium dendrite growth. Figure 7 The optical microscopy characterization results of d show that the above-mentioned regulation effect was directly verified: with the extension of cycling time, the lithium anode using a pure PP membrane gradually developed obvious lithium dendrite protrusions and irregular deposition morphology on its surface; while the lithium anode using a PSN-TiO2 modified membrane maintained a smooth and dense surface after cycling, with no obvious dendrite formation, directly confirming the significant inhibitory effect of the modified membrane on lithium dendrite growth. A stable lithium anode interface can not only effectively extend the cycle life of the lithium metal anode, but also provide a stable and efficient ion transport channel for the continuous conversion of polysulfides, further improving the safety and stability of battery operation. In summary, by Figure 7 Overall, the results show that the PSN-TiO2 heterostructure composite material prepared in this invention, as a modified membrane, can significantly improve the performance of Li... + It enhances the migration and diffusion capabilities of lithium and effectively improves the interface stability of lithium anodes.

[0059] 8. Figure 8 Electrochemical performance diagram of a lithium-sulfur battery assembled with a PSN-TiO2 modified separator prepared in an embodiment of the present invention; wherein, Figure 8 Figure a shows the charge-discharge curves of lithium-sulfur batteries assembled with PP, PSN, TiO2, and PSN-TiO2 separators at 0.1 C. Figure 8 b represents the Q of the battery corresponding to PP, PSN, TiO2, and PSN-TiO2 separators. I / Q H Ratio chart Figure 8 c shows the rate performance of lithium-sulfur batteries assembled with PP, PSN, TiO2, and PSN-TiO2 separators. Figure 8 d represents the electrochemical impedance spectroscopy (EIS) of lithium-sulfur batteries assembled with PP, PSN, TiO2, and PSN-TiO2 separators. Figure 8 e represents the cycle performance of lithium-sulfur batteries assembled with PP, PSN, TiO2, and PSN-TiO2 separators under 2C conditions. Figure 8 f shows the shuttle current test results for lithium-sulfur batteries assembled with PP, PSN, TiO2, and PSN-TiO2 separators. Figure 8 g represents the cycle performance of a lithium-sulfur battery assembled with a PSN-TiO2 modified separator under high sulfur loading conditions. (See figure.) Figure 8 As shown in Figure a, under 0.1 C conditions, the lithium-sulfur battery assembled with the PSN-TiO2 modified separator exhibits higher discharge specific capacity and lower voltage polarization, indicating that the PSN-TiO2 modified separator can promote the redox conversion of sulfur species and improve the utilization rate of active sulfur. Figure 8 As shown in b, the PSN-TiO2 battery has a higher Q. L / Q H The ratio indicates that it can promote the deep conversion of long-chain polysulfides to low-valent sulfur species such as Li2S2 / Li2S. Figure 8 As shown in Figure c, the lithium-sulfur battery assembled with the PSN-TiO2 separator exhibits high capacity at different rates and maintains good capacity recovery capability after rate recovery, indicating that the PSN-TiO2 modified separator can improve the rate performance and reaction reversibility of the battery. Figure 8 As shown in Figure d, the PSN-TiO2 modified separator exhibits lower charge transfer impedance in the battery, indicating that this heterostructure is beneficial for reducing interfacial charge transport resistance and promoting ion / electron co-transport. Figure 8 As shown in Figure e, under 2C conditions, the lithium-sulfur battery assembled with the PSN-TiO2 modified separator exhibits better cycle stability than the PP, PSN, and TiO2 modified separators, indicating that PSN-TiO2 can effectively mitigate polysulfide shuttle and slow down capacity decay. Figure 8 As shown in f, the PSN-TiO2 modified membrane has the lowest shuttle current, indicating that it has a stronger blocking and adsorption effect on soluble polysulfides. Figure 8 As shown in g, under high sulfur loading conditions, the lithium-sulfur battery assembled with the PSN-TiO2 modified separator can still maintain stable cycling, indicating that the modified separator has good adaptability to high sulfur loading. Figure 8 It can be seen that the PSN-TiO2 heterostructure composite material prepared in this invention can comprehensively improve the overall electrochemical performance of lithium-sulfur batteries when used as a separator. Benefiting from the interfacial charge rearrangement effect induced by the difference in work function between PSN and TiO2, the charge transfer efficiency at the heterostructure interface is significantly enhanced. Combined with the ion transport pathways provided by the two-dimensional porous channels of PSN, synergistic transport of electrons and ions during polysulfide conversion can be achieved. This synergistic effect can effectively improve the utilization rate of active sulfur, promote the deep conversion of long-chain polysulfides to low-valence sulfur species, reduce the charge transfer impedance at the battery interface, and effectively suppress the polysulfide shuttle effect, ultimately significantly improving the rate performance, long-cycle stability, and high sulfur loading adaptability of lithium-sulfur batteries.

Claims

1. A method for preparing a PSN-TiO2 heterostructure composite material, characterized in that: Includes the following steps: (1) Add Ti(SO4)2 to deionized water and stir to disperse to obtain a titanium precursor solution; (2) Two-dimensional porous silica nanosheets were added to deionized water and ultrasonically dispersed to obtain a dispersion of two-dimensional porous silica nanosheets. (3) The titanium precursor solution and the two-dimensional porous silica nanosheet dispersion were mixed and stirred, and the in-situ composite reaction was carried out in a hydrothermal environment of 90-110℃ for 4-8 h. The precipitate was collected by centrifugation, washed with deionized water, and freeze-dried to obtain the PSN-TiO2 heterostructure composite material.

2. The method for preparing the PSN-TiO2 heterostructure composite material according to claim 1, characterized in that: In step (1), 0.5-2.5g Ti(SO4)2 is added to 30-40mL of deionized water and stirred and dispersed for 1-4 hours to obtain a titanium precursor solution.

3. The method for preparing the PSN-TiO2 heterostructure composite material according to claim 2, characterized in that: In step (2), 0.2 to 0.8 g of two-dimensional porous silica nanosheets are added to 40 to 80 mL of deionized water and ultrasonically dispersed for 0.5 to 2 h to obtain a two-dimensional porous silica nanosheet dispersion.

4. The method for preparing the PSN-TiO2 heterostructure composite material according to claim 1, characterized in that: In step (3), the in-situ composite reaction is carried out for 4-8 hours under a hydrothermal environment of 90-110℃. The -OH functional groups on the surface of the two-dimensional porous silica nanosheets serve as heterogeneous nucleation active sites, inducing the Ti in the system. 4+ TiO2 nanoparticles are uniformly loaded onto the surface of two-dimensional porous silica nanosheets by directional nucleation and in-situ growth, forming a PSN-TiO2 heterostructure composite material with amorphous porous silica phase and crystalline titanium dioxide phase coupling.

5. The method for preparing the PSN-TiO2 heterostructure composite material according to claim 1, characterized in that: In step (3), the titanium precursor solution and the two-dimensional porous silica nanosheet dispersion are mixed and stirred for 1-2 h, and then in situ composite reaction is carried out for 4-8 h under hydrothermal environment at 90-110℃. The precipitate is collected by centrifugation, washed with deionized water 4-8 times, and then freeze-dried at -70 to -30℃ for 20-28 h to obtain PSN-TiO2 heterostructure composite material.

6. The method for preparing the PSN-TiO2 heterostructure composite material according to claim 1, characterized in that: The two-dimensional porous silica nanosheets are prepared by using layered vermiculite crystals as raw material, through sodium ion exchange, lithium ion exchange, two-step acid etching, centrifugation to obtain the supernatant, and freeze drying.

7. The method for preparing the PSN-TiO2 heterostructure composite material according to claim 6, characterized in that: The two-dimensional porous silica nanosheets were prepared by the following method: 5–15 g of vermiculite crystals were added to 150–350 mL of saturated sodium chloride solution and stirred at 70–90 °C for 18–30 h. The mixture was washed until no white precipitate was detected by 0.1–1 mol / L silver nitrate solution. The resulting sample was then placed in 1–3 mol / L lithium chloride solution and stirred at 70–90 °C for another 18–30 h. The mixture was dialyzed until no white precipitate was detected by 0.1–1 mol / L silver nitrate solution. Subsequently, the product was placed in 100–200 mL of 30–38 wt.% hydrochloric acid solution and stirred at 70–90 °C for 18–30 h. The mixture was washed until the pH value was 6.5–7. A second etching was performed under the same hydrochloric acid conditions. Finally, the resulting suspension was centrifuged at 800–1500 r / min for 5–20 minutes. After min, the supernatant was collected and freeze-dried at -70 to -50°C for 20 to 28 h to obtain two-dimensional porous silica nanosheets.

8. The application of the PSN-TiO2 heterostructure composite material according to any one of claims 1-7, characterized in that: The PSN-TiO2 heterostructure composite material is used as the active component of the functional barrier layer to prepare a modified separator for lithium-sulfur batteries, which is used to suppress polysulfide shuttle and promote sulfur oxidation-reduction conversion.

9. The application of the PSN-TiO2 heterostructure composite material according to claim 8, characterized in that: The modified lithium-sulfur battery separator was prepared as follows: 3-5 parts by weight of PSN-TiO2 heterostructure composite material, 4-6 parts by weight of carbon nanotubes and 0.5-1.5 parts by weight of polyvinylidene fluoride were mixed to obtain a mixture; 8-12g of the mixture was added to 240-280 mL of N-methylpyrrolidone and stirred to form a uniform slurry; the slurry was coated on the surface of a polypropylene separator and vacuum dried at 50-70℃ for 8-16 h to form a barrier layer on the surface of the polypropylene separator, thus obtaining the PSN-TiO2 modified separator.

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