Metal-Salen complex functionalized graphene-based composite material as well as preparation method and application thereof

Abstract

The invention discloses a metal-Salen complex functionalized graphene-based composite material as well as a preparation method and application thereof, and belongs to the technical field of energy storage materials. The composite material takes graphene oxide as a substrate, a Salen type ligand skeleton is grafted through a covalent bond, and a metal active center with an M-N2O2 structure is coordinated on the Salen type ligand skeleton. The preparation method comprises the following steps: carrying out amination on graphene oxide, carrying out Schiff base condensation on graphene oxide and salicylaldehyde to form a ligand, and carrying out coordination reaction on the ligand and metal salt. The composite material disclosed by the invention is coated on a commercial diaphragm and can be used for a lithium-sulfur battery. Through atomic-scale dispersed catalytic sites, effective interception and efficient bidirectional catalytic conversion of polysulfide are synergistically realized, uniform deposition of lithium ions can be guided to inhibit dendritic crystal growth, and the key problems of shuttling of polysulfide, slow reaction kinetics, negative electrode instability and the like in a lithium-sulfur battery are solved; and the rate capability, the cycle life and the safety of the lithium-sulfur battery are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of energy storage materials technology, and in particular to a graphene-based composite material functionalized with metal-Salen complexes, its preparation method, and its application. Background Technology

[0002] Lithium-sulfur (Li-S) batteries are considered a promising next-generation high-energy-density energy storage system due to their extremely high theoretical energy density, abundant sulfur resources, and low cost. However, the commercial application of lithium-sulfur batteries still faces severe challenges. First, during battery charge-discharge cycles, soluble lithium polysulfides (LiPSs) intermediates are generated at the sulfur cathode. These substances are easily soluble in the electrolyte and shuttle between the positive and negative electrodes, leading to irreversible loss of the positive electrode active material, a significant decrease in coulombic efficiency, and directly causing rapid capacity decay and severely shortening cycle life. Second, the conversion kinetics of polysulfides have significant shortcomings, especially the extremely slow conversion rate from liquid polysulfides to solid lithium sulfide (Li2S). This problem causes an increase in battery polarization voltage, resulting in a sharp drop in battery output performance under high-rate charge-discharge scenarios, making it difficult to meet the power density requirements of practical applications. Finally, the stability of the lithium metal anode constitutes a core safety hazard. During cycling, lithium dendrites are prone to grow randomly, which on the one hand continuously consumes electrolyte and active lithium, exacerbating capacity decay; on the other hand, the growing lithium dendrites may puncture the battery separator, causing internal short circuits, and leading to serious safety risks such as thermal runaway.

[0003] To address these issues, existing technologies typically employ a strategy of functionalizing the membrane. For example, porous carbon materials are used for physical adsorption of polysulfides, but their interaction with polar polysulfides is weak, resulting in poor long-term performance. Chemical adsorption using polar materials such as metal oxides can effectively immobilize polysulfides, but often insufficient catalytic activity prevents the adsorbed polysulfides from converting in time, forming "dead sulfur" that clogs active sites. Introducing nanoparticle catalysts can accelerate polysulfide conversion, but their active sites are unclear, they are prone to aggregation, and there may be issues of excessively strong or weak adsorption of polysulfides during the catalytic process, making it difficult to achieve the optimal balance between adsorption and catalysis.

[0004] Therefore, developing a novel membrane modification material that can effectively suppress polysulfide shuttle, efficiently catalyze its bidirectional conversion, and synergistically stabilize the lithium metal anode is of great significance for promoting the practical application of high-performance lithium-sulfur batteries. Summary of the Invention

[0005] This invention provides a graphene-based composite material functionalized with metal-Salen complexes, its preparation method, and its application. The graphene-based composite material has well-defined catalytic active sites, can synergistically inhibit polysulfide shuttle, accelerate sulfur oxidation-reduction kinetics, and stabilize lithium metal anodes.

[0006] To achieve the above objectives, the technical solution of this invention is as follows: A first aspect of the present invention provides a graphene-based composite material functionalized with a metal-Salen complex, the graphene-based composite material having the structural formula M-Salen-GO; wherein GO is a graphene oxide substrate; Salen is a Salen-type ligand framework grafted onto the graphene oxide substrate via covalent bonds; M is a metal active center formed by coordination with nitrogen and oxygen atoms on the Salen-type ligand framework, the metal active center M having an M-N2O2 coordination structure.

[0007] Preferably, in conjunction with the first aspect, the metal active center M is Cu. 2+ Zn 2+ Co 2+ Ni 2+ Fe 2+ At least one of them.

[0008] Preferably, in conjunction with the first aspect, the metal active center M is Cu. 2+ .

[0009] A second aspect of the present invention provides a method for preparing a graphene-based composite material functionalized with a metal-Salen complex as described in any of the first aspects, comprising: Amination reaction of graphene oxide with an amino-containing silane coupling agent was carried out in the first solvent to obtain amino-functionalized graphene oxide. The amino-functionalized graphene oxide was subjected to a Schiff base condensation reaction with salicylaldehyde in a second solvent to obtain graphene oxide grafted with Salen-type ligands. The graphene oxide grafted with Salen-type ligands was reacted with a metal ion salt in a third solvent to obtain a graphene-based composite material.

[0010] Preferably, in conjunction with the second aspect, the amino-containing silane coupling agent is 3-aminopropyltriethoxysilane.

[0011] A third aspect of the present invention provides a functional separator for a lithium-sulfur battery, comprising a porous separator substrate and a functional coating disposed on at least one side of the porous separator substrate; the functional coating comprises a graphene-based composite material functionalized with a metal-Salen complex as described in any of the first aspects or a graphene-based composite material functionalized with a metal-Salen complex prepared by any of the methods described in the second aspect.

[0012] In conjunction with the third aspect, preferably, the porous membrane substrate is a polyolefin membrane.

[0013] A fourth aspect of the present invention provides a lithium-sulfur battery, comprising a positive electrode, a negative electrode, an electrolyte, and a lithium-sulfur battery functional separator as described in any of the third aspects.

[0014] The fifth aspect of the present invention provides the use of a graphene-based composite material functionalized with a metal-Salen complex according to any of the first aspects or a graphene-based composite material functionalized with a metal-Salen complex prepared according to any of the methods of the second aspect in the preparation of a functional separator for lithium-sulfur batteries according to the fourth aspect.

[0015] In conjunction with the fifth aspect, preferably, the application is used for synergistic catalysis of polysulfide redox conversion and guiding uniform lithium deposition.

[0016] Compared with the prior art, the advantages or beneficial effects of the embodiments of the present invention include at least the following: Synergistic polysulfide management: The composite material provided by this invention achieves physical interception and preliminary adsorption of polysulfides through a graphene oxide substrate, while achieving efficient chemical anchoring and catalytic conversion of polysulfides through atomically dispersed M-N2O2 active centers, synergistically suppressing the "shuttle effect".

[0017] Highly efficient bidirectional catalytic activity: By modulating the d-orbital electronic configuration of the central metal (e.g., using d... 9 Cu configuration 2 + The composite material of the present invention exhibits highly efficient bidirectional catalytic activity for the redox reaction of sulfur, especially for the kineticly sluggish liquid-solid conversion (LiPSs→Li2S) and solid-liquid conversion (Li2S→LiPSs) processes, which significantly reduces battery polarization and improves rate performance.

[0018] Synergistic negative electrode stabilization effect: The composite material coating of this invention possesses excellent electrolyte affinity and lithiophilic sites, which can homogenize the lithium-ion flow, guide uniform lithium deposition, and fundamentally inhibit the growth of lithium dendrites. Simultaneously, its highly efficient catalytic effect also prevents polysulfides from corroding the negative electrode, promotes the formation of a stable, LiF-rich SEI film, and greatly enhances the cycle stability of the lithium metal negative electrode.

[0019] Excellent electrochemical performance: The lithium-sulfur battery with the functional separator of this invention exhibits extremely high specific capacity, excellent rate performance, ultra-long cycle life (capacity retention rate is still above 60% after 2000 cycles at 0.5C), extremely low self-discharge rate, and can still cycle stably under high sulfur loading and lean electrolyte conditions close to actual application conditions. Attached Figure Description

[0020] Figure 1 A schematic diagram of the preparation route for the metal-Salen complex functionalized graphene-based composite material provided by the present invention; Figure 2 This is a scanning electron microscope image of the Cu-Salen-GO@PP membrane prepared in Example 3 of the present invention; Figure 3 The diagram shows a comparison of the adsorption effects of different materials on lithium polysulfide solution in the embodiments and comparative examples of the present invention; (a) is a photograph of the adsorbed material, and (b) is the ultraviolet-visible absorption spectrum of the supernatant. Figure 4 These are photographs of polysulfide diffusion experiments in H-type electrolytic cells with different diaphragms in the embodiments and comparative examples of the present invention; Figure 5 This is a comparison of the cyclic voltammetry (CV) curves of symmetrical cells with different catalytic electrodes in Example 3 and the comparative example of the present invention; Figure 6 This is a comparison chart of the Tafel curves of symmetrical cells with different catalytic electrodes in Example 3 and the comparative example of the present invention; Figure 7 The graph shows the long-cycle performance of a lithium-lithium symmetric battery using the Cu-Salen-GO@PP functional separator in Example 3 of this invention. Figure 8 The images show 3D laser confocal microscopy (LSCM) images of the surface morphology of the lithium metal anode after cycling; (a) shows the anode using the Salen-GO@PP separator, and (b) shows the anode using the Cu-Salen-GO@PP separator of this invention. Figure 9 A comparison chart showing the rate performance of lithium-sulfur full batteries with different functional separators in the embodiments and comparative examples of the present invention. Figure 10 A comparison chart showing the long-cycle performance of lithium-sulfur full cells with different functional separators in the embodiments and comparative examples of the present invention at a rate of 0.5 C. Figure 11 The graph shows the long-cycle performance of the lithium-sulfur full cell using the Cu-Salen-GO@PP functional separator in the embodiments of the present invention under high sulfur loading and low electrolyte conditions. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings. The described embodiments should not be regarded as limitations on the present invention. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] In the following description, references to "some embodiments" refer to a subset of all possible embodiments; however, it is understood that "some embodiments" may be the same or different subsets of all possible embodiments and may be combined with each other without conflict. Unless otherwise defined, all technical and scientific terms used in the embodiments of the invention have the same meaning as commonly understood by one of ordinary skill in the art to which the embodiments of the invention pertain. The terminology used in the embodiments of the invention is for the purpose of describing the embodiments of the invention only and is not intended to limit the invention.

[0023] In the following description of this embodiment, the terms "including", "comprising", "having", and "containing" are all open-ended terms, meaning that they include but are not limited to.

[0024] It should be noted that all raw materials / reagents in the embodiments of the present invention can be purchased on the market or prepared according to conventional methods known to those skilled in the art; the term "and / or" in the embodiments of the present invention is only used to describe the relationship between related objects, indicating that there can be three relationships. For example, A and / or B means three cases: A exists alone, B exists alone, and A and B exist simultaneously. A and B can be singular or plural. The character " / " generally indicates that the related objects before and after are in an "or" relationship.

[0025] In the following description of this embodiment, the term "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0026] Those skilled in the art should understand that, in the following description of the embodiments of the present invention, the sequence of numbers does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0027] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0028] Those skilled in the art will understand that the numerical ranges in the embodiments of the present invention should be understood to specifically disclose each intermediate value between the upper and lower limits of the range. Each smaller range between any stated value and an intermediate value within the stated range, as well as any other stated value or an intermediate value within the stated range, is also included within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0029] Unless otherwise stated, the technical / scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may be used in embodiments or test cases of the invention. All references to this specification are generally incorporated herein by reference to disclose and describe methods and / or materials associated with said references. In the event of any conflict with any incorporated reference, the contents of this specification shall prevail.

[0030] It should be noted that all raw materials and / or reagents in the embodiments of the present invention were purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0031] In a first aspect, the present invention provides a graphene-based composite material functionalized with a metal-Salen complex, the graphene-based composite material having the structural formula M-Salen-GO; wherein GO is a graphene oxide substrate; Salen is a Salen-type ligand framework grafted onto the graphene oxide substrate via covalent bonds; M is a metal active center formed by coordination with nitrogen and oxygen atoms on the Salen-type ligand framework, the metal active center M having an M-N2O2 coordination structure.

[0032] In one embodiment of the present invention, the composite material uses graphene oxide (GO) as a two-dimensional substrate. The GO can be a single-layer or few-layer graphene oxide sheet. This GO substrate not only provides a huge specific surface area for active sites, but also has oxygen-containing functional groups and a flexible sheet structure, which can play a preliminary role in the physical interception and chemical adsorption of polysulfides in lithium-sulfur batteries.

[0033] A Salen-type ligand framework is covalently grafted onto the GO substrate. The covalent bonds are preferably formed by the reaction of a silane coupling agent with oxygen-containing functional groups (such as hydroxyl and carboxyl groups) on the GO surface. This covalent grafting method ensures that the Salen ligands are stably anchored on the GO substrate, preventing detachment during long-term battery cycling and electrolyte immersion.

[0034] The core of this invention lies in the introduction of a metal active center M into the Salen-type ligand framework through coordination. The metal active center M forms a stable M-N₂O₂ four-coordinate structure with the two imine nitrogen atoms and two phenolic oxygen atoms on the Salen ligand. This structure allows the metal center to be highly dispersed on the GO substrate at the atomic or molecular level, greatly improving the utilization rate of metal atoms and forming uniform and well-defined catalytic active sites. The metal M is preferably a transition metal ion capable of effectively catalyzing polysulfide redox reactions, such as, but not limited to, Cu. 2+ Zn 2+ Co 2+ Ni 2+ or Fe 2+ .

[0035] In a preferred embodiment, the metal M is having d 9 Cu with electronic configuration 2+ Because its unfilled d orbitals can interact strongly with polysulfides, it exhibits optimal catalytic activity.

[0036] Secondly, embodiments of the present invention provide a method for preparing a metal-Salen complex functionalized graphene-based composite material, the method comprising: Amination reaction of graphene oxide with an amino-containing silane coupling agent was carried out in the first solvent to obtain amino-functionalized graphene oxide. The amino-functionalized graphene oxide was subjected to a Schiff base condensation reaction with salicylaldehyde in a second solvent to obtain graphene oxide grafted with Salen-type ligands. The graphene oxide grafted with Salen-type ligands was reacted with a metal ion salt in a third solvent to obtain a graphene-based composite material.

[0037] In one embodiment, the method first performs an amination step. This step preferably uses an aminosilane coupling agent, such as, but not limited to, 3-aminopropyltriethoxysilane (APTES), 3-aminopropyltrimethoxysilane, or N-(2-aminoethyl)-3-aminopropyltrimethoxysilane. The reaction is carried out in a suitable organic solvent (such as toluene or xylene), preferably at a temperature of 80-140 °C, and preferably for 12-48 hours.

[0038] The ligand synthesis step is then carried out. This step is a Schiff base condensation reaction, in which the above-obtained amino-functionalized graphene oxide is reacted with salicylaldehyde or its derivatives in an alcohol solvent (such as ethanol or methanol). The preferred reaction temperature is 60-100 °C, and the preferred reaction time is 4-12 hours.

[0039] Finally, a metal coordination step is performed. The obtained Salen-functionalized graphene oxide is complexed with a metal ion-containing salt in a solvent. The metal ion-containing salt can be an acetate, nitrate, chloride, or sulfate, such as copper acetate or zinc acetate. The preferred reaction temperature is 40-80 °C, and the preferred reaction time is 12-48 hours.

[0040] This invention also provides a functional separator for lithium-sulfur batteries. In one embodiment, the M-Salen-GO composite material prepared above is mixed with a conductive agent (such as acetylene black, Ketjen black, carbon nanotubes) and a binder (such as PVDF, SBR, CMC) to form a slurry in a solvent (such as NMP, water). The slurry is then applied to at least one surface of a porous separator substrate (such as a polypropylene (PP) or polyethylene (PE) separator) by coating or vacuum filtration, and dried to obtain the final product. The areal loading of the functional coating is preferably 0.1-2.0 mg / cm³. -2 .

[0041] The technical method of the present invention will be further described below with reference to specific embodiments.

[0042] Example 1: Preparation of Cu-Salen-GO composite material Preparation of NH2-GO: 1 g of graphene oxide (GO) was weighed and dispersed in 100 ml of anhydrous toluene, and sonicated for 1 hour to form a uniform black suspension. Then, 1.2 g of 3-aminopropyltriethoxysilane (3-APTES) was added, and the mixture was heated under nitrogen atmosphere at 110 °C for 24 hours. After the reaction was complete, the mixture was cooled to room temperature, filtered, and the product was collected. It was thoroughly washed with anhydrous toluene and then dried in a vacuum oven to obtain a black powder sample, denoted as NH2-GO.

[0043] Preparation of Salen-GO: 0.5 g of the above NH2-GO powder and 1.2 g of salicylaldehyde were dispersed in 50 mL of ethanol. Under nitrogen protection, the mixed suspension was heated to 80 °C and refluxed for 8 hours. After the reaction was completed, the mixture was cooled, filtered, and the product was collected. After washing several times with ethanol, it was dried under vacuum to obtain Salen-GO powder.

[0044] Preparation of Cu-Salen-GO: 500 mg of the above Salen-GO powder was dispersed in ethanol, and then 0.5 mmol of copper acetate dihydrate (Cu(CH3COO)2·2H2O) was added. The suspension was continuously stirred at 60 °C for 24 hours. After the reaction was completed, the mixture was filtered, thoroughly washed with ethanol, and vacuum dried to obtain the target product, Cu-Salen-GO composite material.

[0045] Example 2: Preparation of Zn-Salen-GO composite material The preparation method is basically the same as in Example 1, except that copper acetate dihydrate is replaced with an equimolar amount of zinc acetate dihydrate (Zn(CH3COO)2·2H2O), and the target product Zn-Salen-GO composite material is finally obtained.

[0046] Example 3: Preparation of functional separator and battery assembly The Cu-Salen-GO composite material (350 mg), acetylene black (100 mg), and polyvinylidene fluoride (PVDF, 50 mg) prepared in Example 1 were used as binders and mixed evenly. An appropriate amount of N-methylpyrrolidone (NMP) was added, and the mixture was ball-milled for 6 h until a uniform slurry was formed. A commercial PP diaphragm was fixed on a doctor blade platform, and a slurry layer with a thickness of 50 μm was uniformly coated onto the surface of the PP diaphragm using a doctor blade. The resulting diaphragm was vacuum-dried at 50 °C for 12 h to obtain a Cu-Salen-GO@PP modified diaphragm. The areal loading of the functional coating was controlled at approximately 0.5 mg / cm². -2 .

[0047] The Zn-Salen-GO composite material (350 mg), acetylene black (100 mg), and polyvinylidene fluoride (PVDF, 50 mg) prepared in Example 2 were used as binders and mixed evenly. An appropriate amount of N-methylpyrrolidone (NMP) was added, and the mixture was ball-milled for 6 h until a uniform slurry was formed. A commercial PP diaphragm was fixed on a doctor blade platform, and a slurry layer with a thickness of 50 μm was uniformly coated onto the surface of the PP diaphragm using a doctor blade. The resulting diaphragm was vacuum-dried at 50 °C for 12 h to obtain a Zn-Salen-GO@PP modified diaphragm. The areal loading of the functional coating was controlled at approximately 0.5 mg / cm². -2 .

[0048] Using the aforementioned functional separator, sulfur-carbon composite cathode, lithium metal anode, and standard electrolyte, a CR2032 coin cell was assembled in a glove box, and its excellent performance was verified through electrochemical performance testing.

[0049] Comparative Example 1 Commercial PP diaphragm, model Celgard 2500.

[0050] Comparative Example 2 The Salen-GO composite material (350 mg), acetylene black (100 mg), and polyvinylidene fluoride (PVDF, 50 mg) prepared in Example 1 were used as binders and mixed evenly. An appropriate amount of N-methylpyrrolidone (NMP) was added, and the mixture was ball-milled for 6 h until a uniform slurry was formed. A commercial PP separator was fixed on a doctor blade platform, and a slurry layer with a thickness of 50 μm was uniformly coated onto the surface of the PP separator using a doctor blade. The resulting separator was vacuum-dried at 50 °C for 12 h to obtain a Salen-GO@PP modified separator without metal active centers. The areal loading of the functional coating was controlled at approximately 0.5 mg / cm². -2 .

[0051] To verify the beneficial effects of the composite material and functional diaphragm described in this invention, the materials and batteries prepared in Examples 1-3 and Comparative Examples 1-2 were subjected to the following tests, which are described in conjunction with the accompanying drawings.

[0052] 1. Morphology and physical property testing Reference Figure 1 This invention discloses a preparation route for M-Salen-GO composite materials. This material anchors atomically dispersed M-N2O2 catalytic active sites onto a GO substrate through a multi-step chemical reaction.

[0053] Reference Figure 2 From the cross-sectional scanning electron microscope image of the Cu-Salen-GO@PP diaphragm prepared in Example 3, it can be seen that the functional layer is flat and about 10 μm thick, which can effectively prevent the shuttle of polysulfides without increasing the overall weight of the diaphragm too much.

[0054] Reference Figure 3 and Figure 4 To verify the polysulfide management capability of this invention, Cu-Salen-GO prepared in Example 1, Zn-Salen-GO prepared in Example 2, and Salen-GO from Comparative Example 2 were respectively placed in Li₂S₆ solution. Figure 3 (a) physical photograph and Figure 3 (b) The UV-Vis absorption spectrum clearly shows that the Cu-Salen-GO and Zn-Salen-GO materials of this invention exhibit extremely strong adsorption capacity for polysulfides. The supernatant after adsorption is nearly colorless, and its characteristic absorption peak intensity is much lower than that of the comparative example. This proves that the M-N2O2 active sites of this invention can effectively chemically anchor polysulfides. Figure 4 The H-type electrolytic cell diffusion experiment further proved that the system using the Cu-Salen-GO@PP diaphragm of this invention can effectively block the shuttle of polysulfides within 24 hours.

[0055] 2. Polysulfide symmetric cell test (see attached document) Figure 5 and Figure 6 ) To evaluate the intrinsic catalytic activity of the composite material of the present invention for polysulfide redox reactions, a symmetric cell was assembled and tested.

[0056] (1) Electrode preparation: Cu-Salen-GO prepared in Example 1, Zn-Salen-GO prepared in Example 2, and Salen-GO of Comparative Example 2 were used as active materials, mixed with conductive agent acetylene black and binder PVDF at a mass ratio of 8:1:1, and dispersed in NMP solvent to form a uniform slurry. The slurry was coated on carbon paper, dried, and die-cut to form the working electrode.

[0057] (2) Battery assembly: In an argon-filled glove box, two identical electrodes prepared above were used as positive and negative electrodes. The electrolyte was a solution containing 1 M LiTFSI and 0.25 M Li2S6 dissolved in a mixed solvent of DOL and DME (volume ratio 1:1). A CR2032 type symmetrical coin cell was assembled using commercial PP as the separator.

[0058] (3) Test parameters: Cyclic Voltammetry (CV) Test (corresponding) Figure 5 Using an electrochemical workstation, within a voltage range of -1.4 V to 1.4 V, at 5 mV s -1 Cyclic voltammetry scans were performed at a scan rate to record the current response and peak position of the redox peaks.

[0059] Tafel curve test (corresponding) Figure 6 Using an electrochemical workstation, within a voltage range of ±0.2V near the open circuit potential, at a rate of 0.1 mV / s... -1 A linear sweep voltage-current (LSV) test was performed at an extremely slow scan rate, and the voltage-current curves were recorded for subsequent Tafel analysis.

[0060] Reference Figure 5 and Figure 6 To verify the catalytic activity of this invention, symmetric cell tests were conducted. Figure 5 The cyclic voltammetry curves show that, compared with Salen-GO in Comparative Example 2, both Cu-Salen-GO in Example 1 and Zn-Salen-GO in Example 2 exhibit higher redox peak currents and smaller peak spacing, indicating lower reaction polarization and faster kinetics. Figure 6 Tafel curve analysis showed that Cu-Salen-GO had the highest exchange current density j0, proving that it has the highest intrinsic catalytic activity.

[0061] 3. Lithium-Lithium Symmetric Battery Testing (see attached document) Figure 7 and Figure 8 ) To evaluate the stability of the functional separator of this invention on the lithium metal anode, a lithium-lithium (Li||Li) symmetric battery was assembled and tested.

[0062] (1) Battery assembly: In an argon-filled glove box, two lithium metal sheets of the same diameter were used as positive and negative electrodes, separated by a Cu-Salen-GO functional separator prepared in Example 3 of this invention, or a Salen-GO@PP separator in Comparative Example 2, or a commercial PP separator in Comparative Example 1. An appropriate amount of standard electrolyte was injected to assemble a CR2032 type symmetrical coin cell. The standard electrolyte was a solution containing 1 M LiTFSI and 2 wt% LiNO3 dissolved in a mixed solvent of DOL and DME (volume ratio 1:1).

[0063] (2) Constant current charge and discharge test (corresponding to) Figure 7 Using a battery testing system, at a set current density (e.g., 1 mA cm⁻¹) -2 ) and areal capacity (e.g., 1 mAh cm⁻¹) -2 Under constant current conditions, lithium deposition / stripping cycle tests were performed, and the voltage-time curves of the battery were recorded to evaluate its cycle stability and overpotential.

[0064] (3) Morphological characterization after cycling (corresponding) Figure 8 After the symmetrical battery completed the set cycle test, it was disassembled in the glove box, the lithium metal electrode was removed, cleaned with DOL solvent, and the macroscopic morphology and roughness of its surface were observed using a 3D laser confocal microscope (LSCM).

[0065] Reference Figure 7 and Figure 8 To verify the stabilizing effect of this invention on lithium metal anodes, from... Figure 7 It can be seen that the Li||Li symmetric cell using the Cu-Salen-GO@PP separator in Example 3 of this invention can achieve a 1 mA cm⁻¹ galvanic cell. -2 It can be stably cycled for more than 1000 hours at a current density, and the overpotential is always maintained at an extremely low level of about 15 mV. Figure 8 The post-cycle photographs of the negative electrode surface morphology show that the negative electrode surface of Comparative Example 2 is rough and uneven, with a large number of dendrites growing, and surface undulations exceeding 10 μm; while the negative electrode surface using the separator of this invention is smooth and dense, with no obvious dendrites, and surface undulations within 5 μm. This proves that the technical solution of this invention can effectively guide the uniform deposition of lithium and stabilize the negative electrode interface.

[0066] 4. Full-cell performance characterization (see attached diagram) Figures 9 to 11 ) Lithium-sulfur batteries were assembled using the functionalized separators Cu-Salen-GO@PP and Zn-Salen-GO@PP from Example 3 and the Salen-GO@PP separator from Comparative Example 2, and their electrochemical performance was tested. The specific method is as follows: (1) Battery assembly: Elemental sulfur, Super P, and PVDF were mixed at a mass ratio of 7:2:1, and an appropriate amount of NMP was added as a solvent. The mixture was then ball-milled to obtain a uniform positive electrode slurry. The slurry was uniformly coated onto the surface of a carbon-coated aluminum foil current collector using a scraping method. The slurry was then dried in a 60°C forced-air drying oven for 2 h, followed by drying in a 60°C vacuum drying oven for 12 h. After cutting, the positive electrode sheet was obtained. The negative electrode sheet was a lithium metal sheet (thickness 0.45 mm). The electrolyte was a solution containing 1 M LiTFSI and 2 wt% LiNO3 dissolved in a mixed solvent of DOL and DME (volume ratio 1:1). The positive electrode, negative electrode, battery separator, and electrolyte were assembled into a CR2032 coin cell in a glove box protected by an argon atmosphere.

[0067] (2) Performance test: The cycle performance and rate performance of the battery were tested using the LAND battery test system at 25 ℃, and the voltage test range was 1.7-2.8 V.

[0068] Reference Figures 9 to 11 To verify the comprehensive beneficial effects of this invention in lithium-sulfur full batteries, from... Figure 9 As can be seen from the rate performance curves, the battery using the Cu-Salen-GO@PP separator of this invention exhibits optimal capacity at all rates from 0.1C to 4C. From... Figure 10 The long-cycle performance curves show that, at a 0.5C rate, the battery using the Cu-Salen-GO@PP separator of this invention retains a capacity of 60.7% after 2000 cycles, and its capacity decay rate is much lower than that of the comparative example. Figure 11 It can be seen that under high sulfur loading (4.9 mg cm⁻¹) close to practical application conditions, -2 ) and lean electrolyte (E / S≈6.5μL mg) -2 Under these conditions, batteries using the Cu-Salen-GO@PP separator of this invention can still cycle stably for more than 500 cycles.

[0069] In summary, the specific embodiments of the present invention clearly demonstrate through experimental data that the graphene-based composite material and its functional membrane functionalized with metal-Salen complexes provided by the present invention can effectively suppress polysulfide shuttle, efficiently catalyze the redox reaction of sulfur, synergistically stabilize the lithium metal anode, and ultimately endow lithium-sulfur batteries with excellent rate performance, ultra-long cycle life, and practical application potential under high load and low electrolyte conditions, demonstrating significant beneficial effects.

[0070] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A graphene-based composite material functionalized with a metal-Salen complex, characterized in that, The structural formula of the graphene-based composite material is M-Salen-GO; wherein GO is a graphene oxide substrate; Salen is a Salen-type ligand framework grafted onto the graphene oxide substrate by covalent bonds; M is a metal active center formed by coordination with nitrogen and oxygen atoms on the Salen-type ligand framework, and the metal active center M has an M-N2O2 coordination structure.

2. The graphene-based composite material functionalized with metal-Salen complexes according to claim 1, characterized in that, The metal active center M is Cu. 2+ Zn 2+ Co 2+ Ni 2+ Fe 2+ At least one of them.

3. The graphene-based composite material functionalized with metal-Salen complexes according to claim 1, characterized in that, The metal active center M is Cu. 2+ .

4. A method for preparing a graphene-based composite material functionalized with a metal-Salen complex as described in any one of claims 1-3, characterized in that, include: Amination reaction of graphene oxide with an amino-containing silane coupling agent was carried out in the first solvent to obtain amino-functionalized graphene oxide. The amino-functionalized graphene oxide was subjected to a Schiff base condensation reaction with salicylaldehyde in a second solvent to obtain graphene oxide grafted with Salen-type ligands. The graphene oxide grafted with Salen-type ligands was reacted with a metal ion salt in a third solvent to obtain a graphene-based composite material.

5. The method for preparing graphene-based composite materials functionalized with metal-Salen complexes according to claim 4, characterized in that, The amino-containing silane coupling agent is 3-aminopropyltriethoxysilane.

6. A functional separator for lithium-sulfur batteries, characterized in that, Includes a porous membrane substrate and a functional coating disposed on at least one side of the porous membrane substrate; The functional coating comprises the graphene-based composite material functionalized with metal-Salen complexes as described in claims 1-3 or the graphene-based composite material functionalized with metal-Salen complexes prepared by any of the methods described in claims 4-5.

7. The lithium-sulfur battery functional separator according to claim 6, characterized in that, The porous membrane substrate is a polyolefin membrane.

8. A lithium-sulfur battery, characterized in that, It includes a positive electrode, a negative electrode, an electrolyte, and a lithium-sulfur battery functional separator as described in any one of claims 6-7.

9. The application of a graphene-based composite material functionalized with a metal-Salen complex according to any one of claims 1-3 or a graphene-based composite material functionalized with a metal-Salen complex prepared by any one of claims 4-5 in the preparation of a lithium-sulfur battery functional membrane according to claim 8.

10. The application according to claim 9 is used for synergistic catalysis of polysulfide redox conversion and guiding uniform lithium deposition.

Images