A modified separator for lithium-sulfur batteries and a preparation method and application thereof

Abstract

This invention discloses a modified separator for lithium-sulfur batteries, its preparation method, and its application. The modified separator comprises a base film and a modified layer disposed on one side of the base film. The modified layer comprises a dual rare-earth metal selenide-boron-nitrogen co-doped functionalized carbon nanotube hybrid material. The preparation method is as follows: S1, functionalized carbon nanotubes, a boron source, a nitrogen source, and a solvent are mixed, and then ultrasonically dispersed and stirred until the boron and nitrogen sources are completely dissolved to obtain a carbon nanotube solution; a selenium source, a reducing agent, and a nucleating agent are mixed to obtain a mixed solution; S2, the carbon nanotube solution is mixed with the mixed solution, cerium salt, and lanthanum salt, and a solvothermal reaction is performed. The solid is then separated to obtain the hybrid material. This invention, by modifying the separator towards the sulfur cathode with a specific hybrid material, provides a large number of adsorption sites and effectively anchors and catalyzes the conversion of lithium polysulfides, effectively improving the deposition kinetics of Li2S and increasing sulfur utilization, thereby enhancing the long-cycle stability of lithium-sulfur batteries.

Description

Technical Field

[0001] This invention relates to the field of lithium-sulfur battery technology, specifically to a modified separator for lithium-sulfur batteries, its preparation method, and its application. Background Technology

[0002] Lithium-sulfur batteries are considered one of the most promising next-generation high-energy-density energy storage systems due to their ultra-high theoretical energy density and the advantages of abundant sulfur resources, low cost, and environmental friendliness. However, the sulfur cathode involves multi-step, multi-phase electrochemical reactions during charging and discharging. The soluble intermediates produced—lithium polysulfides (LiPSs)—easily diffuse through traditional separators to the lithium anode, causing a severe "shuttle effect." This not only leads to irreversible loss of active materials and reduced coulombic efficiency but also causes corrosion and dendrite growth in the metallic lithium anode, resulting in rapid capacity decay, poor cycle stability, and safety issues, severely hindering the commercialization of lithium-sulfur batteries.

[0003] As a crucial barrier between the positive and negative electrodes in lithium-sulfur batteries, the separator not only needs to ensure rapid lithium-ion transport but also effectively suppress LiPSs shuttle. Currently widely used polyolefin separators (such as polypropylene (PP) and polyethylene (PE) are chemically inert, have a simple pore structure, and large pore size, offering almost no barrier or adsorption capacity for polar LiPSs. This fails to mitigate the shuttle effect, leading to severe capacity decay during long-cycle periods. Therefore, developing novel high-performance separators with chemical anchoring or catalytic conversion capabilities for LiPSs has become a key research focus for improving the cycle life of lithium-sulfur batteries.

[0004] In recent years, researchers have introduced polar inorganic materials with strong adsorption or catalytic conversion capabilities for LiPSs by coating the surface of traditional separators with functional modification layers, aiming to suppress the shuttle effect and improve sulfur reaction kinetics. Reported modification materials mainly include oxides, sulfides, nitrides, and selenides of transition metals (such as Ni and Co), and oxides of rare earth metals (such as Ce, Nd, and Sm). Among these, rare earth metals, due to their unique structure, can catalyze LiPS conversion more efficiently than transition metals. However, existing modified separators still have the following significant drawbacks, making it difficult to meet the practical application requirements of ultra-long cycling (>800 cycles) in lithium-sulfur batteries: (1) Adsorption and catalytic sites gradually become depleted with cycling: Although single-component or simple composite rare earth metal oxide modification layers have certain anchoring and catalytic effects on LiPSs in the initial stage, during long-term charge and discharge, the limited active sites are easily saturated or poisoned by the continuous adsorption of LiPSs, resulting in the gradual failure of the modification layer and the re-intensification of the shuttle effect.

[0005] (2) Catalytic activity decay and poor structural stability: Existing rare earth-based modification materials (such as CeO2, Sm2O3, etc.) are prone to particle agglomeration, structural pulverization and detachment from the membrane surface under the volume stress change and electrochemical corrosion in the later stage of battery cycling, resulting in cracks or peeling of the modification layer, which greatly reduces its catalytic durability and barrier effect, and cannot achieve continuous and efficient LiPSs conversion.

[0006] (3) Limited improvement in sulfur utilization and long-cycle stability: Due to the above-mentioned insufficient adsorption sites and structural damage, existing modified separators often exhibit a significant capacity drop after more than 800 cycles, with a substantial decrease in the utilization rate of sulfur active materials. The battery life is far from meeting the cycle stability requirements of commercial energy storage systems (usually more than 1,000 cycles and a capacity retention rate of >80%). In particular, for sulfur cathodes with high sulfur loading, the shuttle effect is more prominent, and existing technologies cannot achieve both high sulfur utilization and ultra-long cycle life.

[0007] Therefore, there is an urgent need to develop a modified separator for lithium-sulfur batteries that can provide abundant and stable LiPSs adsorption / catalytic sites, has excellent structural durability, and maintains high catalytic activity during ultra-long cycles, so as to simultaneously solve core problems such as shuttle effect, slow reaction kinetics and insufficient cycle stability, thereby promoting the practical application of lithium-sulfur batteries. Summary of the Invention

[0008] Existing modified separators suffer from insufficient adsorption sites in the modification layer, decreased catalytic activity, and easy pulverization of the material structure in the later stages of long-term cycling, making it difficult to continuously suppress lithium polysulfide shuttle and leading to rapid capacity decay. To solve the above problems, this invention provides a modified separator for lithium-sulfur batteries, its preparation method, and its application. By modifying the side of the separator facing the sulfur cathode with a dual rare-earth metal selenide-boron-nitrogen co-doped functionalized carbon nanotube hybrid material, a large number of adsorption sites are provided, effectively anchoring and catalytically converting lithium polysulfides. This effectively improves the deposition kinetics of Li2S and increases sulfur utilization, thereby enhancing the long-term cycling stability of lithium-sulfur batteries.

[0009] Specifically, the following technical solutions are provided: The first aspect of the present invention provides a modified separator for lithium-sulfur batteries, the modified separator comprising a base film and a modified layer disposed on one side of the base film along the thickness direction, the modified layer comprising a dual rare earth metal selenide-boron nitrogen co-doped functionalized carbon nanotube hybrid material. The preparation method of the dual rare earth metal selenide-boron nitrogen co-doped functionalized carbon nanotube hybrid material includes the following steps: S1. Functionalized carbon nanotubes, boron source, nitrogen source and solvent are mixed, and ultrasonically dispersed and stirred until the boron source and nitrogen source are completely dissolved to obtain carbon nanotube solution; Selenium source, reducing agent and nucleating agent are mixed to obtain mixed solution; S2. The carbon nanotube solution is mixed with the mixed liquid, cerium salt, and lanthanum salt, and a solvothermal reaction is carried out to separate the solid, thereby obtaining the dual rare earth metal selenide-boron nitrogen co-doped functionalized carbon nanotube hybrid material.

[0010] This invention prepares a hybrid material of cerium (Ce)-lanthanum (La) dual rare earth metal selenide and boron-nitrogen co-doped functionalized carbon nanotubes (B,N-CNTs-OH) via a one-step solvothermal method, and coats this hybrid material onto the side of a base film facing the sulfur cathode to form a bilayer composite membrane. The core of this invention lies in utilizing the synergistic effect of the dual rare earth metal selenide and functionalized carbon nanotubes: on the one hand, boron-nitrogen co-doping and functionalization endow the carbon nanotubes with abundant Li... + The Ce / La dual rare-earth metal selenide possesses a unique electronic structure, forming multiple chemical bonds with lithium polysulfides (La-S-Se, Ce-S-Se, and Se-Li ionic bonds). Simultaneously, the orbital hybridization of rare-earth metals and selenium (La 5d, Ce 4f, and Se 3p) significantly lowers the redox reaction energy barrier of lithium polysulfides, thus achieving an integrated function of irreversible capture, rapid catalytic conversion, and efficient ion transport. Ultimately, it maintains excellent electrochemical stability even under ultra-high sulfur loading and long cycling conditions. Specifically: Multiple chemical bonds achieve irreversible anchoring: In hybrid materials, La 3+ / La 2+ and Ce 3+ / Ce 4+ Ion pairs can react with S in lithium polysulfides 2- / S n 2- Formation of La-S-Se and Ce-S-Se coordination bonds; simultaneously, Se in the selenide 2- With Li + Se-Li ionic bonds are formed between them. This "double mutual bonding" effect allows lithium polysulfides to be strongly and irreversibly captured on the surface of the membrane modification layer, effectively suppressing their shuttle to the lithium anode, thereby greatly reducing the shuttle effect.

[0011] Orbital hybridization lowers the reaction energy barrier and accelerates the catalytic conversion of LiPSs: The 5d orbital of lanthanum, the 4f orbital of cerium, and the 3p orbital of selenium hybridize to form a new electronic state. This electronic state significantly lowers the redox reaction energy barrier (E0) for the liquid-solid conversion of lithium polysulfides and subsequent solid-phase deposition. barrier This enables rapid solid-liquid-solid conversion of LiPSs. This avoids the accumulation of lithium polysulfides on the membrane surface and the poisoning of active sites, improves sulfur utilization and reaction kinetics, and maintains a low decay rate even at ultra-high rates of 5C.

[0012] Functionalized carbon nanotubes provide a stable framework and ion transport channels: boron-nitrogen co-doping introduces defects and polar sites into the carbon nanotubes, enhancing their chemisorption capacity for LiPSs; functionalized (e.g., hydroxylated) groups (e.g., -OH) form covalent bonds with Ce / La metals, enabling Ce / La dual rare earth metal selenides to firmly adhere to the carbon nanotube surface, ensuring continuous exposure of adsorption active sites during long-term cycling without pulverization or delamination. Simultaneously, the carbon nanotubes themselves construct a three-dimensional conductive network and Li... + The fast migration channel reduces interface impedance, thus maintaining a high capacity retention rate even under high sulfur loading.

[0013] Synergistic effect of dual rare earth metals: The catalytic activity of a single rare earth metal is limited, while the combination of Ce and La utilizes their different electronic structures and variable valence states (Ce... 3+ / Ce 4+ La 3+ / La 2+ This provides a richer array of redox pairs, enabling synergistic adsorption and catalysis of lithium polysulfide intermediates with varying chain lengths. This synergistic effect significantly extends the catalytic lifetime, far surpassing existing membranes modified with a single rare earth or transition metal.

[0014] Furthermore, the base film includes one or more of polyolefin film, polyester film, cellulose film, polyimide film, polyamide film, spandex film, and aramid film; the modified layer also includes a conductive agent and a binder, the conductive agent including acetylene black, and the binder including polyvinylidene fluoride.

[0015] Furthermore, the thickness of the base film is 25-30 μm; the thickness of the modified layer is 37-40 μm.

[0016] Furthermore, the mass ratio of the dual rare earth metal selenide-boron nitrogen co-doped functionalized carbon nanotube hybrid material to the conductive agent and binder in the modified layer is (7-8):(1-2):(1-1.5), for example, 7:2:1, etc.

[0017] Furthermore, in step S1, the functionalized carbon nanotubes include, but are not limited to, hydroxylated carbon nanotubes, with an -OH content of 3%-8%, for example 5.58 wt%, and an outer diameter of 5-15 nm.

[0018] Further, in step S1, the boron source includes, but is not limited to, boric acid and / or boron oxide, the nitrogen source includes, but is not limited to, urea and / or melamine, and the solvent is a mixed solvent of ethanol and water, such as a mixed solvent obtained by mixing ethanol and water in a volume ratio of 1:2.

[0019] Further, in step S1, the ultrasonic dispersion time is preferably 20-40 min, the stirring temperature is preferably 30-50 ℃, and the time is preferably 8-12 h.

[0020] Further, in step S1, the selenium source includes, but is not limited to, selenium powder and / or selenium dioxide, the reducing agent includes, but is not limited to, hydrazine hydrate and / or sodium borohydride, and the nucleating agent includes, but is not limited to, hexadecyltrimethylammonium bromide and / or hexadecyltrimethylammonium chloride.

[0021] Further, in step S1, the preferred mass ratio of the functionalized carbon nanotubes to the boron source, nitrogen source, selenium source, reducing agent, and nucleating agent is (0.30-0.60):(0.62-3.71):(1.20-4.80):(0.48-0.95):(15.45-20.03):(0.20-0.30), for example, 0.40:1.24:1.80:0.48:15.45:0.20.

[0022] Further, in step S2, the cerium salt includes, but is not limited to, one or more of cerium nitrate and its hydrate, and the lanthanum salt includes, but is not limited to, one or more of lanthanum nitrate and its hydrate; preferably, the mass ratio of functionalized carbon nanotubes to cerium salt and lanthanum salt in the carbon nanotube solution is (0.30-0.60):(0.87-1.74):(0.86-1.73), for example, 0.40:0.87:0.86.

[0023] Further, in step S2, the temperature of the solvothermal reaction is preferably 170-200 °C, and the time is preferably 20-30 h. Preferably, the carbon nanotube solution is first mixed with the mixture, then cerium salt and lanthanum salt are added, and the mixture is stirred at 30-50 °C for 1-3 h, and then heated to 170-200 °C for 20-30 h.

[0024] Further, in step S2, the solid separation step involves centrifuging the solvothermal reaction product at a rate of 5000-20000 r / min and washing it alternately with deionized water / ethanol to obtain a reddish-brown precipitate.

[0025] The second aspect of this invention provides a method for preparing the modified lithium-sulfur battery separator described in the first aspect, comprising the following steps: A modified slurry was obtained by mixing a dual rare earth metal selenide-boron nitrogen co-doped functionalized carbon nanotube hybrid material with a conductive agent, a binder, and a solvent. The modified slurry is coated onto one side of the base film along the thickness direction and vacuum dried to form a modified layer, thus obtaining the modified separator for lithium-sulfur batteries.

[0026] Furthermore, the mass ratio of the dual rare earth metal selenide-boron nitrogen co-doped functionalized carbon nanotube hybrid material to the conductive agent, binder, and solvent is (7-8):(1-2):1:(4-6); the solvent is preferably N-methylpyrrolidone.

[0027] Furthermore, the vacuum drying temperature is 60-70 °C, and the time is 12-24 h.

[0028] A third aspect of the present invention provides a lithium-sulfur battery, the lithium-sulfur battery comprising a positive electrode, a lithium-sulfur battery modified separator as described in the first aspect, and a negative electrode stacked sequentially, wherein the modified layer of the lithium-sulfur battery modified separator is bonded to the positive electrode.

[0029] The fourth aspect of this invention provides a method for preparing a dual rare-earth metal selenide-boron-nitrogen co-doped functionalized carbon nanotube hybrid material for use in lithium-sulfur battery modified separators, comprising the following steps: S1. Functionalized carbon nanotubes, boron source, and nitrogen source are dispersed in a solvent to obtain a dispersion; selenium source, reducing agent, and nucleating agent are mixed to obtain a mixture. S2. The dispersion is mixed with the mixture, cerium salt, and lanthanum salt, and a solvothermal reaction is carried out to separate the solid, thereby obtaining the dual rare earth metal selenide-boron nitrogen co-doped functionalized carbon nanotube hybrid material.

[0030] The beneficial effects of this invention are: This invention provides a modified separator for lithium-sulfur batteries. A hybrid material consisting of cerium / lanthanum dual rare-earth metal selenide and boron / nitrogen co-doped functionalized carbon nanotubes is prepared via a one-step solvothermal method. This hybrid material is then coated onto the side of a base film facing the sulfur cathode to form the modified separator. The synergistic effect of the dual rare-earth metal selenide and the boron / nitrogen co-doped functionalized carbon nanotubes not only firmly fixes the Ce / La dual rare-earth metal selenide onto the base film surface but also provides abundant Li₂. + It integrates transport channels and lithium polysulfide adsorption sites, and can significantly reduce the energy barrier of lithium polysulfide redox reactions, thereby achieving an integrated function of irreversible capture, rapid catalytic conversion and efficient ion transport.

[0031] The lithium-sulfur battery constructed from the modified lithium-sulfur battery separator has high specific capacity and excellent long-cycle stability. At 1 C rate, the capacity decay rate per cycle after 1000 cycles is only 0.046%; at 5 C ultra-high rate, the capacity decay rate per cycle after 400 cycles is 0.092%. Attached Figure Description

[0032] Figure 1This is a flowchart illustrating the preparation process of the cerium-lanthanum dual rare earth metal selenide / boron-nitrogen co-doped hydroxylated carbon nanotube hybrid material (Ce2Se3 / La2Se3-BNCNTOH) in Example 1 of this invention.

[0033] Figure 2 This is a scanning electron microscope (SEM) image of the Ce2Se3 / La2Se3-BNCNTOH material prepared in Example 1 of this invention.

[0034] Figure 3 This is the elemental distribution mapping (EDS) diagram of the Ce2Se3 / La2Se3-BNCNTOH material prepared in Example 1 of this invention.

[0035] Figure 4 This is a transmission electron microscope (TEM) image of the Ce2Se3 / La2Se3-BNCNTOH material prepared in Example 1 of this invention.

[0036] Figure 5 These are X-ray diffraction (XRD) patterns of the Ce2Se3 / La2Se3-BNCNTOH material prepared in Example 1, the Ce2Se3-BNCNTOH material prepared in Comparative Example 1, and the BNCNTOH material prepared in Comparative Example 2.

[0037] Figure 6 These are the Raman spectra of the Ce2Se3 / La2Se3-BNCNTOH material prepared in Example 1, the Ce2Se3-BNCNTOH material prepared in Comparative Example 1, and the BNCNTOH material prepared in Comparative Example 2.

[0038] Figure 7 These are the adsorption-desorption isotherms (BET) and particle size distribution diagrams of the Ce2Se3 / La2Se3-BNCNTOH material prepared in Example 1 of this invention.

[0039] Figure 8 This is the X-ray photoelectron spectroscopy (XPS) spectrum of the Ce2Se3 / La2Se3-BNCNTOH material prepared in Example 1 of this invention.

[0040] Figure 9 This is a SEM image of the Ce2Se3-BNCNTOH material prepared in Comparative Example 1 of this invention.

[0041] Figure 10 This is a SEM image of the BNCNTOH material prepared in Comparative Example 2 of this invention.

[0042] Figure 11 These are visual experimental images of the adsorption of polysulfides by the materials prepared in Examples 1, 7, 8 and Comparative Examples 1-5 of this invention.

[0043] Figure 12 This is an X-ray photoelectron spectroscopy (XPS) image of the Ce2Se3 / La2Se3-BNCNTOH material prepared in Example 1 of this invention before and after adsorption of polysulfides.

[0044] Figure 13 These are experimental images of H-type electrolytic cells of the diaphragms prepared in Examples 1, 3, 4, 6-8 and Comparative Examples 1-5 of the present invention.

[0045] Figure 14 This is the electrochemical impedance spectroscopy (EIS) diagram of the membrane-assembled batteries prepared by material modification according to Examples 1, 1, and 2 of this invention.

[0046] Figure 15 These are rate performance graphs of button batteries assembled with separators prepared by material modification according to Examples 1, 1, and 2 of the present invention at different current densities.

[0047] Figure 16 This is a charge / discharge curve (GCD) graph of a battery assembled from Ce2Se3 / La2Se3-BNCNTOH‖PP at different rates.

[0048] Figure 17 This is a graph showing the long-cycle performance of button batteries assembled with separators prepared by material modification according to Embodiment 1, Comparative Example 1 and Comparative Example 2 of the present invention under 1C high-rate charge and discharge.

[0049] Figure 18 This is a graph showing the long-cycle performance of a Ce2Se3 / La2Se3-BNCNTOH‖PP assembled battery at an ultra-high rate of 5 C.

[0050] Figure 19 This is a graph showing the cycle performance of a battery assembled from Ce2Se3 / La2Se3-BNCNTOH‖PP under high sulfur load. Detailed Implementation

[0051] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0052] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The terms “comprising” or “including” used in this invention may also be replaced with the closed form “is” or “consisting of”.

[0053] Unless otherwise specified, all raw materials used in the following examples are commercially available, and the specific preparation operations and testing methods involved are conventional methods in the art. Among them: The surface morphology of the nanofiller was observed using a scanning electron microscope (S-4700).

[0054] The structure of the nanomaterials was observed using a field emission transmission electron microscope (Talos F200X G2).

[0055] The phase structure of the material was tested using an X-ray diffractometer (D8 Advance).

[0056] X-ray photoelectron spectroscopy (XPS) was used to test information such as the type, content and valence state of elements on the surface of nanofillers.

[0057] The rate capability and cycle performance of lithium-sulfur batteries were tested using a battery testing system (CT3002A, Blue Electric).

[0058] The reaction kinetics of lithium-sulfur batteries were analyzed using an electrochemical workstation (Zana).

[0059] Example 1 This embodiment relates to the preparation of a cerium-lanthanum dual rare earth metal selenide / boron-nitrogen co-doped hydroxylated carbon nanotube hybrid material (Ce2Se3 / La2Se3-BNCNTOH), such as... Figure 1 As shown, the specific operation is as follows: (1) 0.40 g of hydroxylated carbon nanotubes (CNTOH, Jiangsu Argon Krypton Xenon Materials Technology Co., Ltd., CAS: 308068-56-6, -OH content of 5.58 wt%, outer diameter of 5-15 nm) were added to 60 mL of mixed solvent (water to ethanol volume ratio 2:1), sonicated at room temperature for 20 min, and then 1.24 g of boric acid and 1.80 g of urea were added. The mixture was then stirred at 30 °C for 12 h until it was completely dissolved to obtain a carbon nanotube mixture. (2) Dissolve 0.48 g selenium powder and 0.20 g CTAB in 15.45 g hydrazine hydrate solution (15 mL, 1.03 g / mL), stir at room temperature for 24 h to obtain a dark red selenium powder mixture; (3) The carbon nanotube mixture prepared in steps (1) and (2) and the selenium powder mixture were mixed, and 0.87 g Ce(NO3)3·6H2O and 0.86 g La(NO3)3·6H2O were added. The mixture was stirred at 30 °C for 3 h, and then transferred to a hydrothermal reactor and reacted at 180 °C for 24 h under hydrothermal conditions. After the reaction was completed, the reaction product was centrifuged at 11000 r / min for 10 minutes to obtain a reddish-brown precipitate. The precipitate was washed 6 times with deionized water / ethanol, and then dried in a vacuum oven (80 °C, 4 h). Finally, the product was obtained by grinding: cerium lanthanum double rare earth metal selenide / boron nitrogen co-doped hydroxylated carbon nanotube hybrid material (Ce2Se3 / La2Se3-BNCNTOH).

[0060] The surface morphology, surface elemental distribution, material structure, phase and crystal structure, degree of graphitization, specific surface area and pore size distribution, elemental composition and chemical bond energy state of the prepared product Ce2Se3 / La2Se3-BNCNTOH were characterized by corresponding tests, and the results are as follows: The SEM image of Ce2Se3 / La2Se3-BNCNTOH prepared in this embodiment is shown below. Figure 2 As shown in the figure, Ce2Se3 and La2Se3 selenides are uniformly distributed with hybrid multi-walled carbon nanotubes, forming short rods with a length of approximately 0.2 μm.

[0061] The EDS curve of Ce2Se3 / La2Se3-BNCNTOH prepared in this embodiment is shown below. Figure 3 As shown in the figure, N, B, Ce, La and Se elements are uniformly distributed on the surface of Ce2Se3 / La2Se3-BNCNTOH material.

[0062] The TEM image of Ce2Se3 / La2Se3-BNCNTOH prepared in this embodiment is shown below. Figure 4 As shown in the figure, rare earth metal selenides are attached and grown on carbon nanotubes. Meanwhile, high-resolution TEM images further show that the interplanar spacing of the Ce2Se3 characteristic crystal plane (011) is 0.377 nm, and the interplanar spacing of the La2Se3 characteristic crystal plane (310) is 0.286 nm.

[0063] The XRD pattern of Ce2Se3 / La2Se3-BNCNTOH prepared in this embodiment is shown below. Figure 5As shown in the figure, the diffraction peaks of Ce2Se3 / La2Se3-BNCNTOH are relatively sharp, indicating that the material has good crystallinity. In addition, Ce2Se3 / La2Se3-BNCNTOH exhibits characteristic diffraction peaks at 20.9°, 23.8°, 30.4°, and 38.3°, which correspond to the (002), (011), (210), and (013) crystal planes of Ce2Se3 (PDF#74-1279), respectively. At 27.8°, 31.2°, 47.1°, and 57.5°, they correspond to the (220), (310), (332), and (440) crystal planes of La2Se3 (PDF#77-2018), respectively, further demonstrating the successful synthesis of Ce2Se3 and La2Se3.

[0064] The Raman spectrum of Ce2Se3 / La2Se3-BNCNTOH prepared in this embodiment is as follows: Figure 6 As shown in the figure, the I of Ce2Se3 / La2Se3-BNCNTOH is... D / I G The lowest value is 1.004, indicating that Ce2Se3 / La2Se3-BNCNTOH has a high degree of graphitization and excellent electrical conductivity.

[0065] The BET diagram and particle size distribution diagram of Ce2Se3 / La2Se3-BNCNTOH prepared in this embodiment are as follows: Figure 7 As shown in the figure, Ce₂Se₃ / La₂Se₃-BNCNTOH exhibits a type IV isotherm, indicating that it has a mesoporous structure and a specific surface area of ​​128.473 m². 2 g -1 The pore size is mainly concentrated at 24.11 nm.

[0066] The XPS plot of Ce2Se3 / La2Se3-BNCNTOH prepared in this embodiment is shown below. Figure 8 As shown, XPS test results demonstrate the successful doping of B and N into multi-walled carbon nanotubes, while Ce and La rare earth elements modify their surface.

[0067] In summary, this embodiment successfully prepared a cerium-lanthanum dual rare earth metal selenide / boron-nitrogen co-doped hydroxylated carbon nanotube hybrid material. Boron and nitrogen atoms were doped into the carbon nanotubes to form corresponding chemical bonds. Ce2Se3 and La2Se3 grew in situ on the carbon nanotubes and bonded with hydroxyl groups and hybrid atoms on the surface of the carbon nanotubes to form metal-OC, metal-NC, metal-Se-C bonds, etc.

[0068] Example 2 This embodiment relates to the preparation of a cerium-lanthanum dual rare earth metal selenide / boron-nitrogen co-doped hydroxylated carbon nanotube hybrid material, which differs from Example 1 only in that: In step (1), the amount of boric acid added is 1.86 g, and the amount of urea added is 2.40 g; The hydrothermal reaction time in step (3) is 20 h.

[0069] With all other conditions being equal, a cerium-lanthanum dual rare earth metal selenide / boron-nitrogen co-doped hydroxylated carbon nanotube hybrid material was successfully prepared.

[0070] Example 3 This embodiment relates to the preparation of a cerium-lanthanum dual rare earth metal selenide / boron-nitrogen co-doped hydroxylated carbon nanotube hybrid material, which differs from Example 1 only in that: In step (1), the amount of hydroxylated carbon nanotubes added was 0.30 g, the amount of boric acid added was 1.86 g, the amount of urea added was 2.40 g, and the stirring time was 10 h. In step (2), the amount of selenium powder added is 0.63 g; In step (3), the hydrothermal reaction temperature is 200 °C and the drying time is 5 h.

[0071] With all other conditions being equal, a cerium-lanthanum dual rare earth metal selenide / boron-nitrogen co-doped hydroxylated carbon nanotube hybrid material was successfully prepared.

[0072] Example 4 This embodiment relates to the preparation of a cerium-lanthanum dual rare earth metal selenide / boron-nitrogen co-doped hydroxylated carbon nanotube hybrid material, which differs from Example 1 only in that: The stirring time in step (1) is 10 h; In step (2), the amount of selenium powder added is 0.95 g, the amount of CTAB added is 0.3 g, and the volume of hydrazine hydrate solution is 20 mL. In step (3), the amount of Ce(NO3)3·6H2O added was 1.74 g, the amount of La(NO3)3·6H2O added was 1.73 g, the hydrothermal reaction temperature was 200 ℃, and the drying time was 5 h.

[0073] With all other conditions being equal, a cerium-lanthanum dual rare earth metal selenide / boron-nitrogen co-doped hydroxylated carbon nanotube hybrid material was successfully prepared.

[0074] Example 5 This embodiment relates to the preparation of a cerium-lanthanum dual rare earth metal selenide / boron-nitrogen co-doped hydroxylated carbon nanotube hybrid material, which differs from Example 1 only in that: In step (1), the amount of hydroxylated carbon nanotubes added is 0.50 g, the amount of boric acid added is 0.62 g, and the amount of urea added is 1.20 g; In step (3), the hydrothermal reaction temperature is 190 °C and the drying time is 5 h.

[0075] With all other conditions being equal, a cerium-lanthanum dual rare earth metal selenide / boron-nitrogen co-doped hydroxylated carbon nanotube hybrid material was successfully prepared.

[0076] Example 6 This embodiment relates to the preparation of a cerium-lanthanum dual rare earth metal selenide / boron-nitrogen co-doped hydroxylated carbon nanotube hybrid material, which differs from Example 1 only in that: In step (1), the amount of hydroxylated carbon nanotubes added is 0.60 g, the amount of boric acid added is 3.71 g, and the amount of urea added is 4.80 g; In step (2), the amount of selenium powder added is 0.63 g, and the volume of hydrazine hydrate solution is 20 mL; In step (3), the hydrothermal reaction temperature is 200 °C, the centrifugation time is 15 min, and the drying time is 5 h.

[0077] With all other conditions being equal, a cerium-lanthanum dual rare earth metal selenide / boron-nitrogen co-doped hydroxylated carbon nanotube hybrid material was successfully prepared.

[0078] Example 7 This embodiment relates to the preparation of a cerium-lanthanum dual rare earth metal selenide / boron-nitrogen co-doped hydroxylated carbon nanotube hybrid material (Ce2Se3 / La2Se3-BNCNTOH (2:1)). The only difference from Example 1 is that the amount of Ce(NO3)3·6H2O added is 1.74 g, and the molar ratio of Ce(NO3)3·6H2O to La(NO3)3·6H2O is 2:1. All other conditions are the same, and the corresponding cerium-lanthanum dual rare earth metal selenide / boron-nitrogen co-doped hydroxylated carbon nanotube hybrid material is prepared.

[0079] Example 8 This embodiment relates to the preparation of a cerium-lanthanum dual rare earth metal selenide / boron-nitrogen co-doped hydroxylated carbon nanotube hybrid material (Ce2Se3 / La2Se3-BNCNTOH (1:2)). The only difference from Example 1 is that the amount of La(NO3)3·6H2O added is 1.73 g, and the molar ratio of Ce(NO3)3·6H2O to La(NO3)3·6H2O is 1:2. All other conditions are the same, and the corresponding cerium-lanthanum dual rare earth metal selenide / boron-nitrogen co-doped hydroxylated carbon nanotube hybrid material is prepared.

[0080] Comparative Example 1 This comparative example relates to the preparation of cerium selenide / boron nitrogen co-doped hydroxylated carbon nanotube hybrid material (Ce2Se3-BNCNTOH). The only difference from Example 1 is that an equimolar amount of Ce(NO3)3·6H2O is used to replace La(NO3)3·6H2O, while all other conditions are the same, and the corresponding cerium selenide / boron nitrogen co-doped hydroxylated carbon nanotube hybrid material is prepared.

[0081] The surface morphology, phase composition, crystal structure, and degree of graphitization of the Ce2Se3-BNCNTOH product prepared in this comparative example are as follows: The SEM image of the product Ce2Se3-BNCNTOH prepared in this comparative example is shown below. Figure 9 As shown in the figure, Ce2Se3 is interspersed in the middle of the hybrid functionalized carbon nanotubes.

[0082] The XRD pattern of the product Ce2Se3-BNCNTOH prepared in this comparative example is shown below. Figure 5 As shown in the figure, the diffraction peaks of Ce2Se3-BNCNTOH are also quite sharp, indicating that the material has good crystallinity. In addition, Ce2Se3-BNCNTOH exhibits characteristic diffraction peaks at 20.9°, 23.8°, 30.4°, and 38.3°, which correspond to the (002), (011), (210), and (013) crystal planes of Ce2Se3 (PDF#74-1279), respectively, proving that Ce2Se3 has been successfully synthesized.

[0083] The Raman spectrum of the product Ce2Se3-BNCNTOH prepared in this comparative example is shown below. Figure 6 As shown in the figure, the I of Ce2Se3-BNCNTOH D / I G The value is 1.021, slightly higher than Ce2Se3 / La2Se3-BNCNTOH. This structure indicates that they have a low degree of graphitization and certain surface defects.

[0084] Comparative Example 2 This comparative example relates to the preparation of boron-nitrogen co-doped hydroxylated carbon nanotube hybrid material (BNCNTOH), and differs from Example 1 only in that: The carbon nanotube mixture was prepared according to step (1) of Example 1 and directly transferred to a hydrothermal reactor. It was reacted under hydrothermal conditions at 180 °C for 24 h. After the reaction, the reaction product was centrifuged at 11000 r / min for 10 minutes to obtain a dark brown precipitate. The precipitate was washed 6 times with deionized water / ethanol, and then dried in a vacuum oven (80 °C, 4 h). Finally, the product was obtained by grinding: boron-nitrogen co-doped hydroxylated carbon nanotube hybrid material.

[0085] The surface morphology, phase composition, crystal structure, and degree of graphitization of the BNCNTOH product prepared in this comparative example are as follows: The SEM image of the product BNCNTOH prepared in this comparative example is shown below. Figure 10 As shown in the figure, the product is a randomly distributed carbon nanotube.

[0086] The XRD pattern of the product BNCNTOH prepared in this comparative example is shown below. Figure 5 As shown in the figure, a broad diffraction peak appears at position 26°, corresponding to the (002) characteristic peak of graphitic carbon (PDF#41-1478). A slight shift to the left of the diffraction peak can be observed, mainly due to the increased interplanar spacing induced by B and N heteroatom doped carbon nanotubes.

[0087] The Raman spectrum of the product BNCNTOH prepared in this comparative example is shown below. Figure 6 As shown in the figure, BNCNTOH's I D / I G The value is 1.244, which is higher than Ce2Se3 / La2Se3-BNCNTOH. This indicates that its graphitization degree is low and there are certain defects on the surface.

[0088] Comparative Example 3 This comparative example relates to the preparation of a cerium-lutetium dual rare earth metal selenide / boron-nitrogen co-doped hydroxylated carbon nanotube hybrid material (Ce2Se3 / Lu2Se3-BNCNTOH). The only difference from Example 1 is that an equimolar amount of Lu(NO3)3·6H2O (0.94 g) was used to replace La(NO3)3·6H2O. All other conditions were the same, and the corresponding cerium-lutetium dual rare earth metal selenide / boron-nitrogen co-doped hydroxylated carbon nanotube hybrid material was prepared.

[0089] Comparative Example 4 This comparative example relates to the preparation of a cerium-lanthanum dual rare earth metal oxide / boron-nitrogen co-doped hydroxylated carbon nanotube hybrid material (CeO2 / La2O3-BNCNTOH). The only difference from Example 1 is that selenium powder was not added, while all other conditions were the same, and the corresponding cerium-lanthanum dual rare earth metal oxide / boron-nitrogen co-doped hydroxylated carbon nanotube hybrid material was prepared.

[0090] Comparative Example 5 This comparative example provides a method for preparing a cerium-lanthanum dual rare earth metal selenide / boron-nitrogen co-doped hydroxylated carbon nanotube composite material (Ce2Se3 / La2Se3-BNCNTOH (physical mixture)), and the specific operation is as follows: (1) Preparation of cerium selenide: 0.24 g of selenium powder was dissolved in hydrazine hydrate solution (7.5 mL, 1.03 g / mL), stirred at room temperature for 24 h to obtain a dark red selenium powder mixture; then 0.87 g Ce(NO3)3·6H2O was added, stirred at 30 ℃ for 3 h, and then transferred to a hydrothermal reactor and reacted at 180 ℃ under hydrothermal conditions for 24 h; after the reaction was completed, the reaction product was centrifuged at 11000 r / min for 10 minutes to obtain a dark brown precipitate, washed 6 times with deionized water / ethanol alternately, and then dried in a vacuum oven (80 ℃, 4 h), and finally ground to obtain the product cerium selenide (Ce2Se3).

[0091] (2) Preparation of lanthanum selenide: 0.24 g of selenium powder was dissolved in hydrazine hydrate solution (7.5 mL, 1.03 g / mL) and stirred at room temperature for 24 h to obtain a dark red selenium powder mixture; then 0.86 g of La(NO3)3·6H2O was added and stirred at 30 °C for 3 h, and then transferred to a hydrothermal reactor and reacted at 180 °C for 24 h under hydrothermal conditions; after the reaction was completed, the reaction product was centrifuged at 11000 r / min for 10 minutes to obtain a dark brown precipitate, which was washed 6 times with deionized water / ethanol alternately, and then dried in a vacuum oven (80 °C, 4 h), and finally ground to obtain the product cerium selenide (La2Se3).

[0092] (3) 0.40 g of hydroxylated carbon nanotubes (CNTOH, the same as in Example 1) were added to 30 mL of mixed solution (water to ethanol volume ratio 2:1), sonicated at room temperature for 20 min, and then 1.24 g of boric acid and 1.80 g of urea were added. The mixture was then stirred at 30 °C for 12 h until a complete solution was obtained, and the carbon nanotube mixture was transferred to a hydrothermal reactor and reacted at 180 °C for 12 h under hydrothermal conditions. After the reaction was completed, the reaction product was centrifuged at 11000 r / min for 8 min to obtain a black product. The product was washed 6 times with deionized water / ethanol alternately, and then dried in a vacuum oven (80 °C, 4 h) to obtain boron nitrogen doped hydroxylated carbon nanotubes (BNCNTOH).

[0093] (4) The Ce2Se3 and La2Se3 prepared above are mixed together with BNCNTOH and ground in a mortar until fully ground to obtain a cerium-lanthanum dual rare earth metal selenide / boron-nitrogen co-doped hydroxylated carbon nanotube composite material.

[0094] Test Example 1 The materials prepared in Examples 1, 7, 8 and Comparative Examples 1-5 were subjected to polysulfide adsorption tests, and the specific procedures are as follows: In an argon-filled glove box, 0.30 g of Li₂S and 1.04 g of S were dissolved in 130 mL of dimethyl ethylene glycol (DME) solution and stirred at 60 °C for 24 h to prepare Li₂S₆ solution. 0.20 g of sample and 13 mL of Li₂S₆ solution were added to each sample vial, and the solution was allowed to stand for 12 h. The supernatant was then used for spectral analysis. The results are shown below. Figure 11 As shown, the wavelength ranges of 400-450 nm and 480-500 nm are respectively S4 2- S6 2- Characteristic peak positions, as shown in the figure, indicate that the adsorption capacity of different materials for polysulfides is in the following order: Example 1 (Ce2Se3 / La2Se3-BNCNTOH) > Example 8 (Ce2Se3 / La2Se3-BNCNTOH(1:2)) > Example 7 (Ce2Se3 / La2Se3-BNCNTOH(2:1)) > Comparative Example 3 (Ce2Se3 / Lu2Se3-BNCNTOH) > Comparative Example 4 (CeO2 / La2O3-BNCNTOH) > Comparative Example 5 (Ce2Se3 / La2Se3-BNCNTOH (physical blend)) > Comparative Example 1 (Ce2Se3-BNCNTOH) > Comparative Example 2 (BNCNTOH). Therefore, it can be seen that the cerium-lanthanum dual rare earth metal selenide / boron-nitrogen co-doped hydroxylated carbon nanotube hybrid material prepared in Example 1 has the best adsorption effect on Li2S6. The type of rare earth element and the content of the two rare earth elements added will affect the adsorption of Li2S6 by the material.

[0095] To further investigate the adsorption mechanism of polysulfides by cerium-lanthanum dual rare earth metal selenide / boron-nitrogen co-doped hydroxylated carbon nanotube hybrid materials, the Ce₂Se₃ / La₂Se₃-BNCNTOH prepared in Example 1 was used as an example. XPS characterization was performed on the materials before and after adsorption. The characterization results are as follows: Figure 12 As shown in the figure, Ce 3d 3 / 2 Fitting peaks (904.7 eV and 900.9 eV) and Ce3d 5 / 2 The fitted peaks (886.5 eV and 883.0 eV) shifted towards lower binding energies by 1.25 eV, 1.15 eV, 1.01 eV, and 0.91 eV, respectively. Meanwhile, La 3d... 3 / 2 Fitting peak (853.3 eV) and La 3d 5 / 2 The fitted peak (836.4 eV) shifted towards lower binding energies by 0.31 eV and 0.38 eV, while Se 3d 3 / 2 Fitting peak (56.0 eV) and Se 3d 5 / 2The fitting peak (54.9 eV) shifted towards higher binding energy by 0.32 eV and 0.22 eV. The above results indicate that Ce2Se3 / La2Se3-BNCNTOH has a strong adsorption capacity for polysulfides (LiPSs), which can effectively anchor LiPSs and inhibit their shuttle.

[0096] Test Example 2 The materials prepared in Examples 1, 3, 4, 6-8 and Comparative Examples 1-5 were used to prepare modified membranes, and the inhibitory effect of each membrane on the migration of polysulfides was tested. The specific operations are as follows: Membrane preparation: (1) Weigh 0.14 g of sample, 0.04 g of acetylene black (AB) and 0.40 g (5 wt%) of polyvinylidene fluoride (PVDF) in a mortar and grind them to obtain mixture A; (2) Add 2 mL of N-methylpyrrolidone (NMP) to the above mixture A and stir on a slurry mixer (8000 r / min, 30 min) to make a black slurry. Use a scraper to evenly coat the slurry onto a commercially available polyolefin membrane with a coating thickness of 100 μm. Coat one side only to obtain an undried double-layer composite membrane. (3) The undried double-layer diaphragm prepared in step (2) is dried in a vacuum oven (60 °C, 24 h) to obtain a double-layer composite diaphragm; it is cut into circular pieces with a diameter of 16 mm using a slicer to obtain diaphragms prepared from different samples.

[0097] The membranes prepared from the above-mentioned different samples were subjected to H-type electrolytic cell experiments, such as... Figure 13As shown, the left side contains a 4.0 mM Li₂S₆ solution (solvent: ethylene glycol dimethyl ether), and the right side contains a clear, transparent ethylene glycol dimethyl ether (DME) solution, separated by a membrane. The solutions were allowed to stand for 24 hours to observe the diffusion of polysulfides. The figure shows that after 24 hours of standing, the solution on the right in the experimental group corresponding to Example 1 was the clearest and most transparent. In contrast, in the experimental groups corresponding to Comparative Examples 1-5, the solution on the right gradually changed color and became cloudy with increasing diffusion time. The order of the inhibitory effects of membranes modified with different materials on the diffusion and shuttle of polysulfides is as follows: Example 1 (Ce2Se3 / La2Se3-BNCNTOH) > Example 4 (Ce2Se3 / La2Se3-BNCNTOH) > Example 3 (Ce2Se3 / La2Se3-BNCNTOH) > Example 6 (Ce2Se3 / La2Se3-BNCNTOH) > Example 8 (Ce2Se3 / La2Se3-BNCNTOH (1:2)) > Example 7 (Ce2Se3 / La2Se3-BNCNTOH (2:1)) > Comparative Example 3 (Ce2Se3 / Lu2Se3-BNCNTOH) > Comparative Example 4 (CeO2 / La2O3-BNCNTOH) > Comparative Example 5 (Ce2Se3 / La2Se3-BNCNTOH (physical blend)) > Comparative Example 1 (Ce2Se3-BNCNTOH) Comparative Example 2 (BNCNTOH). It can be seen that the membrane modified with Ce2Se3 / La2Se3-BNCNTOH material prepared in this invention can effectively inhibit polysulfide migration.

[0098] Application examples and performance tests The separators prepared using the materials from Example 1 and Comparative Examples 1 and 2 in Test Example 2 (named Ce2Se3 / La2Se3-BNCNTOH‖PP, Ce2Se3-BNCNTOH‖PP, and BNCNTOH‖P, respectively) were used to assemble standard CR2032 button cells, and the electrochemical performance of each cell was tested, as follows: Assemble lithium-sulfur batteries in an argon-atmosphere glove box: a standard CR2032 coin cell consisting of a lithium metal anode, a sulfur cathode, a separator (coated side facing the sulfur cathode), and an electrolyte; wherein the electrolyte composition is dioxolane (DOL): ethylene glycol dimethyl ether (DME) = 1:1 (v / v), 2 wt% LiNO3, and 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0099] The assembled coin cells were placed in a 28 ℃ constant temperature chamber, and their electrochemical performance was tested using a battery testing system and an electrochemical workstation. The test results are as follows: The electrochemical impedance of coin cells assembled with different separators is as follows: Figure 14As shown in the figure, the battery constructed with the separator prepared by Example 1 has the minimum impedance value of 56.7 Ω. This further illustrates that the separator prepared by modification with Ce2Se3 / La2Se3-BNCNTOH material has high ion transport efficiency and can effectively reduce the impedance value of the battery.

[0100] Figure 15 The graph shows the rate performance of button cells assembled with different separators at different current densities. As can be seen from the graph, at 8C rate, the cell assembled with Ce₂Se₃ / La₂Se₃-BNCNTOH‖PP exhibits a rate performance of 470.9 mAh g⁻¹. -1 The specific capacity is higher than that of Comparative Example 1 (378.8 mAh g). -1 Comparative Example 2 (298.4 mAh g) -1 This is because Ce2Se3 / La2Se3-BNCNTOH materials are beneficial to Li + In addition to preventing the transport and diffusion of LiPSs, it can also act as a physical barrier to effectively block the back-and-forth movement of LiPSs. At the same time, it can also achieve efficient anchoring of LiPSs through chemical adsorption. More importantly, the unique electronic structure and highly active sites of the Ce and La rare earth bimetals can rapidly catalyze the conversion of adsorbed LiPSs, thereby achieving higher sulfur utilization and enabling the assembled lithium-sulfur battery to have superior rate performance.

[0101] Figure 16 The charge / discharge curve (GCD) of the battery assembled by Ce2Se3 / La2Se3-BNCNTOH‖PP is shown in the figure. As can be seen from the figure, under the high-rate charge and discharge conditions of 8 C, the battery still maintains a certain degree of the charge / discharge plateau of lithium-sulfur batteries, indicating that the separator modified by Ce2Se3 / La2Se3-BNCNTOH material has little impact on the polarization of the battery.

[0102] Figure 17 The graph shows the long-cycle performance of button cells assembled with different separators. As can be seen from the graph, the sulfur loading is 1.5 mg / cm³. -2 The battery assembled from Ce2Se3 / La2Se3-BNCNTOH‖PP exhibited an initial discharge specific capacity of 900.4 mAh g⁻¹ at 1 C after three activation cycles at 0.1 C. -1 After 1000 cycles at a high rate of 1 C, the capacity remained at 484.3 mAh g. -1The capacity decay rate is only 0.046% per cycle, far lower than Comparative Example 1 (0.058%) and Comparative Example 2 (0.072%). This is because the cerium-lanthanum dual rare earth metal selenide / boron-nitrogen co-doped hydroxylated carbon nanotube hybrid material combines physical adsorption, chemical anchoring, and rare earth dual metal selenide catalysis, which can effectively suppress polysulfide shuttle and catalyze the conversion of lithium polysulfides. Therefore, the lithium-sulfur battery assembled with the Ce2Se3 / La2Se3-BNCNTOH‖PP separator provided by this invention has excellent long-cycle stability.

[0103] Figure 18 The battery assembled with Ce2Se3 / La2Se3-BNCNTOH‖PP exhibits long-cycle performance at an ultra-high rate of 5 C. The sulfur loading is 1.5 mg cm⁻¹. -2 After activation, at a 5C ultra-high rate, the first discharge specific capacity is 484.6 mAh g⁻¹. -1 After 400 cycles at a 5C high-rate, the capacity remained at 306.5 mAh g. -1 The capacity decay rate is only 0.092% per revolution.

[0104] Figure 19 Cyclic performance of Ce2Se3 / La2Se3-BNCNTOH‖PP assembled batteries under high sulfur loading. The sulfur loading is 4.2 mg cm⁻¹. -2 After three cycles of activation at 0.1 C, the first discharge specific capacity at a rate of 0.3 C is 741.3 mAh g⁻¹. -1 Meanwhile, after 100 cycles at 0.3 C, the capacity remained at 682 mAh g. -1 This indicates that the Ce2Se3 / La2Se3-BNCNTOH‖PP assembled battery has high energy density and excellent cycle stability.

[0105] In summary, this invention prepares a cerium-lanthanum dual rare earth metal selenide / boron-nitrogen co-doped hydroxylated carbon nanotube hybrid material (Ce2Se3 / La2Se3-BNCNTOH) via a one-pot hydrothermal method. Ce2Se3 / La2Se3-BNCNTOH can be used as a modification material for lithium-sulfur battery separators. The modified separator prepared from it can not only catalyze the conversion of polysulfides but also suppress the shuttle effect of polysulfides, resulting in lower capacity decay rates in high-rate long-cycle tests and higher capacity retention rates in high-sulfur load tests.

[0106] The above-described embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A modified separator for lithium-sulfur batteries, characterized in that, The modified separator for lithium-sulfur batteries includes a base film and a modified layer disposed on one side of the base film along the thickness direction. The modified layer includes a dual rare earth metal selenide-boron nitrogen co-doped functionalized carbon nanotube hybrid material. The preparation method of the dual rare earth metal selenide-boron nitrogen co-doped functionalized carbon nanotube hybrid material includes the following steps: S1. Functionalized carbon nanotubes, boron source, nitrogen source and solvent are mixed, and ultrasonically dispersed and stirred until the boron source and nitrogen source are completely dissolved to obtain carbon nanotube solution; Selenium source, reducing agent and nucleating agent are mixed to obtain mixed solution; S2. The carbon nanotube solution is mixed with the mixed liquid, cerium salt, and lanthanum salt, and a solvothermal reaction is carried out to separate the solid, thereby obtaining the dual rare earth metal selenide-boron nitrogen co-doped functionalized carbon nanotube hybrid material.

2. The lithium-sulfur battery modified separator according to claim 1, characterized in that, The base film includes one or more of the following: polyolefin film, polyester film, cellulose film, polyimide film, polyamide film, spandex film, and aramid film. And / or, the modified layer further comprises a conductive agent and a binder, the conductive agent comprising acetylene black, and the binder comprising polyvinylidene fluoride.

3. The lithium-sulfur battery modified separator according to claim 1 or 2, characterized in that, The thickness of the base film is 25-30 μm; And / or, the thickness of the modified layer is 37-40 μm; And / or, the mass ratio of the dual rare earth metal selenide-boron nitrogen co-doped functionalized carbon nanotube hybrid material to the conductive agent and binder in the modified layer is (7-8):(1-2):(1-1.5).

4. The lithium-sulfur battery modified separator according to claim 1, characterized in that, In step S1, the functionalized carbon nanotubes include hydroxylated carbon nanotubes; And / or, the boron source includes boric acid and / or boron oxide; And / or, the nitrogen source includes urea and / or melamine; And / or, the solvent is a mixture of ethanol and water; And / or, the selenium source includes selenium powder and / or selenium dioxide; And / or, the reducing agent includes hydrazine hydrate and / or sodium borohydride; And / or, the nucleating agent comprises hexadecyltrimethylammonium bromide and / or hexadecyltrimethylammonium chloride; And / or, the mass ratio of the functionalized carbon nanotubes to the boron source, nitrogen source, selenium source, reducing agent, and nucleating agent is (0.30-0.60): (0.62-3.71): (1.20-4.80): (0.48-0.95): (15.45-20.03): (0.20-0.30).

5. The lithium-sulfur battery modified separator according to claim 1 or 4, characterized in that, In step S1, the ultrasonic dispersion time is 20-40 min; And / or, the stirring treatment is carried out at a temperature of 30-50 °C for 8-12 h.

6. The lithium-sulfur battery modified separator according to claim 1, characterized in that, In step S2, the cerium salt includes one or more of cerium nitrate and its hydrates; And / or, the lanthanum salt includes one or more of lanthanum nitrate and its hydrates; And / or, the mass ratio of functionalized carbon nanotubes to cerium salt and lanthanum salt in the carbon nanotube solution is (0.30-0.60):(0.87-1.74):(0.86-1.73).

7. The lithium-sulfur battery modified separator according to claim 1, characterized in that, In step S2, the temperature of the solvothermal reaction is 170-200 °C, and the time is 20-30 h.

8. A method for preparing a modified lithium-sulfur battery separator as described in any one of claims 1-7, characterized in that, Includes the following steps: A modified slurry was obtained by mixing a dual rare earth metal selenide-boron nitrogen co-doped functionalized carbon nanotube hybrid material with a conductive agent, a binder, and a solvent. The modified slurry is coated onto one side of the base film along the thickness direction and vacuum dried to form a modified layer, thus obtaining the modified separator for lithium-sulfur batteries.

9. A lithium-sulfur battery, characterized in that, The lithium-sulfur battery includes a positive electrode, a lithium-sulfur battery modified separator according to any one of claims 1-7, and a negative electrode, which are stacked sequentially, and the modified layer of the lithium-sulfur battery modified separator is attached to the positive electrode.

10. A method for preparing a dual rare-earth metal selenide-boron-nitrogen co-doped functionalized carbon nanotube hybrid material for use in lithium-sulfur battery modified separators, characterized in that, Includes the following steps: S1. Functionalized carbon nanotubes, boron source, and nitrogen source are dispersed in a solvent to obtain a dispersion; selenium source, reducing agent, and nucleating agent are mixed to obtain a mixture. S2. The dispersion is mixed with the mixture, cerium salt, and lanthanum salt, and a solvothermal reaction is carried out to separate the solid, thereby obtaining the dual rare earth metal selenide-boron nitrogen co-doped functionalized carbon nanotube hybrid material.

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