Lithium-sulfur battery separator, method for preparing the same, and lithium-sulfur battery

Abstract

This invention discloses a lithium-sulfur battery separator, its preparation method, and a lithium-sulfur battery. The lithium-sulfur battery separator of this invention includes a separator substrate and a coating disposed on at least one surface of the separator substrate. The coating comprises a medium-entropy (molybdenum-cobalt-indium) sulfide. The preparation method of the medium-entropy (molybdenum-cobalt-indium) sulfide includes the following steps: dissolving a molybdenum source, a cobalt source, an indium source, and a sulfur source in water at 160–200°C according to a molar ratio of molybdenum, cobalt, indium, and sulfur of (1–8):(1–8):(1–8):(10–30) to obtain the medium-entropy (molybdenum-cobalt-indium) sulfide. The coating of this invention not only enhances the mechanical strength and thermal stability of the separator but also significantly improves the electron / ion conductivity of the separator surface, thereby suppressing the shuttle effect of lithium polysulfides and improving the rate performance and long-cycle performance of the battery.

Description

Technical Field

[0001] This invention belongs to the field of inorganic functional materials and lithium-sulfur battery technology, and particularly relates to a lithium-sulfur battery separator, its preparation method, and a lithium-sulfur battery. Background Technology

[0002] Lithium-sulfur batteries are known for their high theoretical specific capacity (1675 mAh·g). -1 High energy density (2600 Wh·kg) -1 With its abundant and low-cost sulfur resources, lithium is considered a strong candidate for next-generation energy storage devices. However, its practical application is limited by the "shuttle effect" caused by the dissolution and migration of polysulfides in the electrolyte. This effect leads to the loss of active material, capacity decay, and reduced coulombic efficiency, and generates insulating deposits on the lithium anode surface, hindering ion transport and thus severely affecting the battery's cycle life and rate performance.

[0003] On the other hand, commercial polyolefin membranes are prone to shrinkage or failure at high temperatures, posing significant thermal safety hazards. To improve membrane performance, existing research has attempted modification using carbon materials, transition metal compounds, or polymer coatings. Current membrane modification methods mainly fall into three categories: first, carbon-based material coatings, such as graphene, carbon nanotubes, and porous carbon, can improve conductivity and promote polysulfide conversion; however, due to the non-polar nature of carbon materials, their adsorption of polysulfides is limited, resulting in poor long-cycle inhibition. Second, transition metal compound modification, such as CoS2, MoS2, and TiO2, can accelerate polysulfide conversion through chemisorption and catalytic reactions; however, the stability of a single component at high temperatures is insufficient, limiting performance. Third, polymer coatings, such as polydopamine and polyimide, can enhance interfacial stability and mechanical properties; however, they are prone to softening or decomposition at high temperatures, exhibiting insufficient thermal stability.

[0004] While the aforementioned methods have improved the cycle performance of lithium-sulfur batteries to some extent, they still have significant shortcomings in high-temperature applications: the adsorption capacity of carbon materials is weak, the structural stability of single-metal compounds is insufficient, and the heat resistance of polymer coatings is poor. Therefore, developing a novel membrane modification material that combines high-temperature stability with efficient adsorption and catalytic conversion capabilities of polysulfides has become an urgent technical problem to be solved.

[0005] In recent years, medium-entropy materials have gradually attracted attention in the field of electrochemical energy storage due to their unique structural characteristics and performance advantages. Medium-entropy materials are composed of three or more elements, achieving high solid solution of the components through a high configurational entropy effect, thus exhibiting excellent structural stability and multi-element synergistic effects. On the one hand, lattice distortion and chemical disorder effects can improve the structural stability of the material at the atomic scale, allowing it to maintain its intact structure even at high temperatures; on the other hand, the introduction of multiple metal elements can regulate the electronic structure of active sites, adjusting the d-band center through pd orbital hybridization, thereby enhancing the chemisorption of polysulfides and improving their conversion reaction kinetics. Currently, there are no published studies on the modification of lithium-sulfur battery separators using medium-entropy (molybdenum-cobalt-indium) sulfides. Summary of the Invention

[0006] Existing membrane modification technologies still have significant shortcomings in high-temperature lithium-sulfur batteries, necessitating the development of a novel membrane modification method based on medium-entropy (molybdenum-cobalt-indium) sulfides. This invention addresses these technical needs by providing a lithium-sulfur battery membrane, its preparation method, and a lithium-sulfur battery. This invention utilizes medium-entropy (molybdenum-cobalt-indium) sulfides to modify the lithium-sulfur battery membrane, thereby improving its thermal stability and conductivity under high-temperature conditions, and significantly enhancing the safety and cycle stability of lithium-sulfur batteries in high-temperature environments.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a lithium-sulfur battery separator, comprising a separator substrate and a coating disposed on at least one surface of the separator substrate, said coating comprising a medium-entropy (molybdenum-cobalt-indium) sulfide;

[0009] The method for preparing the medium-entropy (molybdenum-cobalt-indium) sulfide includes the following steps: dissolving molybdenum, cobalt, indium and sulfur in water at a molar ratio of (1-8):(1-8):(1-8):(10-30) and carrying out a hydrothermal reaction at 160-200 °C to obtain the medium-entropy (molybdenum-cobalt-indium) sulfide.

[0010] Based on the above technical solutions, the inventive concept of this invention is as follows:

[0011] Previous studies have shown that molybdenum-based and cobalt-based sulfides exhibit strong catalytic activity in lithium-sulfur batteries, while indium, as a Group IIIA metal, can provide unique p orbitals that hybridize with transition metal d orbitals, further optimizing the electronic state distribution. Therefore, the rational introduction of multiple elements such as molybdenum, cobalt, and indium to construct medium-entropy sulfides is expected to improve the high-temperature stability of the separator while achieving efficient adsorption and catalytic conversion of polysulfides, thereby fundamentally solving the problems of severe shuttle effect, shortened cycle life, and insufficient thermal safety in lithium-sulfur batteries under high-temperature conditions.

[0012] This invention aims to construct a medium-entropy (molybdenum-cobalt-indium) sulfide-modified high-temperature composite separator by precisely controlling the molar ratio of molybdenum, cobalt, indium, and sulfur sources, as well as the hydrothermal reaction conditions, providing an effective solution for the practical application of high-performance lithium-sulfur batteries. This invention utilizes an in-situ prepared medium-entropy (molybdenum-cobalt-indium) sulfide-modified high-temperature lithium-sulfur battery separator. Through atomic-scale multi-metal synergy and the medium-entropy effect, the electronic structure is modulated to significantly suppress the polysulfide shuttle effect at high temperatures and improve reaction kinetics performance.

[0013] Experiments have shown that the medium-entropy (molybdenum-cobalt-indium) sulfide-modified high-temperature separator maintains structural integrity at 100 °C, exhibiting excellent thermal stability and conductivity. The method of this invention can maintain the structural stability of the separator at high temperatures, while simultaneously enhancing the adsorption and catalytic capacity for polysulfides through multi-metal synergistic effects, thereby improving the cycle life, rate performance, and thermal safety of lithium-sulfur batteries.

[0014] As a further preferred embodiment of the present invention, the molar ratio of molybdenum, cobalt, indium, and sulfur is (1-8):1:(1-8):(10-30), more preferably (1-8):1:1:(10-30), and even more preferably 8:1:1:30. The inventors have discovered that precise control of the proportions of each element is crucial for achieving high performance: any imbalance in the proportion of any element will disrupt the single-phase structure of the medium-entropy solid solution, weakening the synergistic effect of pd orbital hybridization and lattice distortion. Specifically, an insufficient proportion of molybdenum or indium will result in insufficient adsorption and catalytic capacity; an excessively large proportion will easily generate impurities, reducing conductivity and structural stability; an imbalance in the sulfur proportion will also introduce impurities or cover active sites. These factors collectively lead to a decrease in the ability to manage polysulfides, thereby causing accelerated capacity decay and deterioration of cycle stability. At the optimal ratio of 8:1:1:30, the synergistic effect of the three components is maximized, ensuring that the separator has the strongest polysulfide adsorption, catalytic conversion ability and structural integrity at high temperatures, thereby giving lithium-sulfur batteries the lowest capacity decay rate and the best cycle life.

[0015] Optionally, the molybdenum source is selected from one or more of ammonium heptamolybdate, ammonium molybdate, and sodium molybdate;

[0016] Optionally, the cobalt source is selected from one or more of cobalt chloride hexahydrate, cobalt nitrate, and cobalt acetate;

[0017] Optionally, the indium source is selected from one or more of indium chloride, indium nitrate, and indium sulfate;

[0018] Optionally, the sulfur source is selected from one or more of sodium thiosulfate, thiourea, and sodium sulfide.

[0019] As a further preferred embodiment of the present invention, the temperature of the hydrothermal reaction can be 180°C or 160°C; the time of the hydrothermal reaction is 10 to 16 hours, such as 12 hours; it is understood that the preparation method of the intermediate entropy (molybdenum-cobalt-indium) sulfide further includes the steps of cooling, centrifugation, washing and vacuum drying after the hydrothermal reaction, preferably vacuum drying at 60 to 80°C for 6 to 12 hours, such as vacuum drying at 70°C for 12 hours.

[0020] Optionally, the membrane substrate is a polyolefin membrane.

[0021] As a further preferred embodiment of the present invention, the coating is made of the medium-entropy (molybdenum-cobalt-indium) sulfide, the conductive agent, and the binder;

[0022] The mass ratio of the medium-entropy (molybdenum-cobalt-indium) sulfide, the conductive agent, and the binder is 8:(1-2):(1-2), such as 8:1:1;

[0023] Optionally, the conductive agent is selected from one or more of multi-walled carbon nanotubes, carbon nanotubes, acetylene black, graphene, conductive carbon black, and Super P.

[0024] Optionally, the adhesive is polyvinylidene fluoride.

[0025] This invention, based on optimized metal source ratios and hydrothermal reaction conditions, combines the synergistic effect of a carbon nanotube conductive framework and a PVDF binder to prepare a composite separator with excellent conductivity, thermal stability, and mechanical properties. This separator maintains structural integrity at 100 °C, effectively suppressing the polysulfide shuttle effect in lithium-sulfur batteries and accelerating the polysulfide conversion process, thereby significantly improving the battery's cycle life, rate performance, and thermal safety. Addressing the problems of shrinkage and deformation, poor interfacial stability, and insufficient conductivity in lithium-sulfur battery separators under high-temperature conditions, this invention constructs a medium-entropy (molybdenum-cobalt-indium) sulfide composite functional layer on the Celgard separator surface. This utilizes the multi-element medium-entropy effect to enhance structural stability, while simultaneously combining it with a multi-walled carbon nanotube conductive network to achieve synergistic enhancement of electron and ion transport, thus effectively improving the overall performance of the separator.

[0026] Secondly, the present invention provides a method for preparing the lithium-sulfur battery separator as described in any of the above claims, comprising the following steps:

[0027] S1. The raw material containing the medium-entropy (molybdenum-cobalt-indium) sulfide is added to a solvent and dispersed to obtain a slurry;

[0028] S2. The slurry is coated on the surface of the separator substrate and dried to obtain the lithium-sulfur battery separator.

[0029] Based on the above technical solution, this invention uniformly loads medium-entropy (molybdenum-cobalt-indium) sulfide powder onto the surface of a commercial Celgard separator, forming a dense and stable conductive functional layer. This coating not only enhances the mechanical strength and thermal stability of the separator, but also significantly improves the electronic / ionic conductivity of the separator surface, thereby suppressing the shuttle effect of lithium polysulfides and improving the rate performance and long-cycle performance of the battery.

[0030] As a further preferred embodiment of the present invention, the raw materials simultaneously contain a conductive agent and a binder, and the preparation steps of the slurry are as follows: 1) the medium-entropy (molybdenum-cobalt-indium) sulfide is mixed with the conductive agent and ball-milled to obtain a mixture; 2) the mixture and the binder are added to a solvent for dispersion to obtain a slurry. The present invention achieves coating preparation through a process route of hydrothermal synthesis-ball milling composite-coating and drying. The method of the present invention is simple, the conditions are mild, it is suitable for large-scale preparation, and has significant practical application value.

[0031] As a further preferred embodiment of the present invention, the ball milling step is carried out under inert gas protection, with a ball-to-material ratio of (10-20):1, such as 15:1, and ball milling is performed in a high-energy ball mill at a speed of 800-1200 rpm for 10-15 hours, such as at 1000 rpm for 12 hours.

[0032] As a further preferred embodiment of the present invention, the solvent is selected from one or more of methylpyrrolidone, N,N-dimethylformamide, and ethanol;

[0033] The dispersion includes stirring for 2 to 4 hours and ultrasonic dispersion for 0.5 to 2 hours, such as stirring for 3 hours and ultrasonic dispersion for 1 hour;

[0034] In the coating step, the coating is applied to one side of the diaphragm substrate using vacuum filtration, with a slurry loading of 0.2–1.2 mg·cm⁻¹. -2 For example, 0.8 mg·cm -2 1.0 mg·cm -2 The coating thickness is 3–10 μm, such as 10 μm or 12 μm;

[0035] In the drying step, vacuum drying is used, the drying temperature is 50-80 ℃, and the drying time is 4-12 hours, such as drying at 50 ℃ for 12 hours.

[0036] Thirdly, the present invention provides a lithium-sulfur battery, comprising the lithium-sulfur battery separator described in any one of the preceding claims or the lithium-sulfur battery separator obtained by any one of the preceding claims.

[0037] The present invention has the following beneficial effects:

[0038] (1) The membrane has excellent thermal stability and remains structurally intact and deformation-free even at temperatures up to 100°C, effectively expanding the operating temperature range of lithium-sulfur batteries and meeting the requirements for safety and lifespan in high-temperature scenarios.

[0039] (2) Medium-entropy (molybdenum-cobalt-indium) sulfides possess excellent catalytic and adsorption properties. Under high-temperature conditions, they can effectively suppress the shuttle behavior of polysulfides and accelerate the conversion reaction of polysulfides through their built-in electric field. This fundamentally improves the problems of weak catalytic performance and severe shuttle effect of commercial separators at high temperatures, thereby significantly improving the cycle life, rate performance, and thermal safety of the battery. This invention also combines the conductive network of multi-walled carbon nanotubes to achieve synergistic enhancement of electron and ion transport, thereby effectively improving the overall performance of the separator.

[0040] (3) The present invention uses vacuum filtration to uniformly load medium entropy (molybdenum-cobalt-indium) sulfide onto the surface of commercial Celgard2500 membrane to form a flexible organic / inorganic composite membrane. This method is simple, adaptable, has the potential for large-scale preparation, and is easy to promote and apply in the industry. Attached Figure Description

[0041] Figure 1 This is a process flow diagram for preparing the medium-entropy (molybdenum-cobalt-indium) sulfide modified high-temperature diaphragm in an embodiment of the present invention.

[0042] Figure 2 The image shows the XRD pattern of the medium-entropy (molybdenum-cobalt-indium) sulfide powder prepared in Example 1.

[0043] Figure 3 SEM images of the medium-entropy (molybdenum-cobalt-indium) sulfide powder prepared in Example 1 loaded onto a diaphragm: cross section (left); surface (right).

[0044] Figure 4 Optical images of the modified diaphragm prepared in Example 1 at 100 °C: before high temperature test (left); after high temperature test (right).

[0045] Figure 5 The graph shows the cycle performance of the lithium-sulfur battery with the modified separator prepared in Example 1 under high temperature conditions. Detailed Implementation

[0046] The present invention will now be described in further detail with reference to specific embodiments. The given embodiments are merely illustrative of the invention and not intended to limit its scope. The embodiments provided below can serve as a guide for further improvements by those skilled in the art and do not constitute a limitation on the invention in any way.

[0047] Unless otherwise specified, the methods used in the following embodiments are conventional methods, performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Unless otherwise specified, the materials and reagents used in the following embodiments are commercially available.

[0048] Example 1

[0049] This embodiment provides a medium-entropy (molybdenum-cobalt-indium) sulfide-modified high-temperature separator, wherein the separator surface is loaded with a medium-entropy sulfide / carbon nanotube composite at a loading amount of 0.8 mg·cm³. -2 It has a thickness of approximately 10 μm.

[0050] according to Figure 1 The flowchart is prepared using the following specific steps:

[0051] (1) Raw material dissolution: Weigh 1.408 g (Mo 8 mmol) (NH4)6Mo7O 24 Dissolve 0.238 g (Co 1 mmol) CoCl2·6H2O, 0.221 g (In 1 mmol) InCl3, and 7.446 g (S 30 mmol) Na2S2O3·5H2O in deionized water and adjust the total volume to 70 mL. Pour the solution into the liner of a 100 mL hydrothermal reactor, filling it to approximately 70% capacity.

[0052] (2) Hydrothermal reaction: The reactor was placed in an oven and reacted at 180 °C for 12 h, and then naturally cooled to room temperature. The resulting product was centrifuged, washed three times with deionized water, and dried under vacuum at 70 °C for 12 h to obtain medium entropy (Mo–Co–In) sulfide powder.

[0053] (3) Composite grinding: Weigh 0.500 g of medium entropy sulfide powder and mix it with 0.062 g of carbon nanotubes (MWCNTs). Place the mixture in a stainless steel ball mill jar with a ball-to-material ratio of about 15:1. Ball mill at 1000 rpm for 12 h under nitrogen protection to obtain a uniformly dispersed medium entropy sulfide / carbon nanotube composite powder.

[0054] (4) Slurry preparation: Take 0.180 g of composite powder and 0.020 g of PVDF, add 8 mL of N-methylpyrrolidone (NMP), stir magnetically for 3 h and sonicate for 1 h to obtain a uniform slurry.

[0055] (5) Coating: The slurry was uniformly loaded onto one side of the Celgard 2500 membrane by vacuum filtration, and the total coating load was controlled to be 20 mg (equivalent to a loading of approximately 0.8 mg·cm). -2 The coating thickness is approximately 10 μm.

[0056] (6) Drying: Place the coated diaphragm in a vacuum drying oven and dry at 50 °C for 12 h to obtain a medium-entropy sulfide modified diaphragm (denoted as S1).

[0057] Example 2

[0058] The difference from Example 1 is that the molar ratio of molybdenum, cobalt, indium and sulfur is adjusted.

[0059] The specific preparation steps are as follows:

[0060] (1) Raw material dissolution: Weigh 0.176 g (1 mmol) (NH4)6Mo7O 24 Dissolve 4H₂O, 0.238 g (1 mmol) CoCl₂·6H₂O, 0.221 g (1 mmol) InCl₃, and 2.482 g (10 mmol) Na₂S₂O₃·5H₂O in deionized water and adjust the total volume to 70 mL. Pour the solution into the liner of a 100 mL hydrothermal reactor, filling it to approximately 70% capacity.

[0061] (2) Hydrothermal reaction: The reactor was placed in an oven and reacted at 180 °C for 12 h, and then naturally cooled to room temperature. The resulting product was centrifuged, washed three times with deionized water, and dried under vacuum at 70 °C for 12 h to obtain medium entropy (Mo–Co–In) sulfide powder.

[0062] (3) Composite grinding: Weigh 0.500 g of medium entropy sulfide powder and mix with 0.062 g of MWCNTs, place in a stainless steel ball mill jar, with a ball-to-material ratio of about 15:1, and ball mill at 1000 rpm for 12 h under nitrogen protection to obtain uniformly dispersed medium entropy sulfide / carbon nanotube composite powder.

[0063] (4) Pulping: Weigh 0.180 g of composite powder and 0.020 g of PVDF, add 8 mL of NMP, stir magnetically for 3 h and sonicate for 1 h to obtain a uniform slurry.

[0064] (5) Coating: The slurry was uniformly loaded onto one side of the Celgard 2500 membrane by vacuum filtration, and the total coating load was controlled to be 20 mg (equivalent to a loading of approximately 0.8 mg·cm). -2 The coating thickness is approximately 10 μm.

[0065] (6) Drying: Place the coated diaphragm in a vacuum drying oven and dry at 50 °C for 12 h to obtain a medium-entropy sulfide modified diaphragm (denoted as S2).

[0066] Example 3

[0067] The difference from Example 1 is that the molar ratio of molybdenum, cobalt, indium and sulfur is adjusted.

[0068] The specific preparation steps are as follows:

[0069] (1) Raw material dissolution: Weigh 0.176 g (1 mmol) (NH4)6Mo7O 24 ·4H2O, 0.238 g (1 mmol) CoCl2·6H2O, 1.768 g (8 mmol) InCl3, and 7.446 g (30 mmol) Na2S2O3·5H2O were dissolved in deionized water, with a total volume of 70 mL. The solution was then placed into a 100 mL reaction vessel.

[0070] (2) Hydrothermal reaction: The reactor was placed in an oven and reacted at 180 °C for 12 h, and then naturally cooled to room temperature. The resulting product was centrifuged, washed three times with deionized water, and dried under vacuum at 70 °C for 12 h to obtain medium entropy (Mo–Co–In) sulfide powder.

[0071] (3) Composite grinding: Weigh 0.500 g of medium entropy sulfide powder and mix with 0.062 g of MWCNTs, place in a stainless steel ball mill jar, with a ball-to-material ratio of about 15:1, and ball mill at 1000 rpm for 12 h under nitrogen protection to obtain uniformly dispersed medium entropy sulfide / carbon nanotube composite powder.

[0072] (4) Pulping: Weigh 0.180 g of composite powder and 0.020 g of PVDF, add 8 mL of NMP, stir magnetically for 3 h and sonicate for 1 h to obtain a uniform slurry.

[0073] (5) Coating: The slurry was uniformly loaded onto one side of the Celgard 2500 membrane by vacuum filtration, and the total coating load was controlled to be 20 mg (equivalent to a loading of approximately 0.8 mg·cm). -2 The coating thickness is approximately 10 μm.

[0074] (6) Drying: Place the coated diaphragm in a vacuum drying oven and dry it at 50 °C for 12 h to obtain the modified diaphragm (denoted as S3).

[0075] Example 4

[0076] The difference from Example 1 is that the molar ratio of molybdenum, cobalt, indium and sulfur is adjusted.

[0077] The specific preparation steps are as follows:

[0078] (1) Raw material dissolution: Weigh 0.176 g (1 mmol) (NH4)6Mo7O 24 Dissolve 1.904 g (8 mmol) CoCl2·6H2O, 0.221 g (1 mmol) InCl3, and 7.446 g (30 mmol) Na2S2O3·5H2O in deionized water to adjust the total volume to 70 mL. Pour the solution into a 100 mL reactor, filling it approximately 70% full.

[0079] (2) Hydrothermal reaction: The reactor was placed in an oven and reacted at 180 °C for 12 h, and then naturally cooled to room temperature. The resulting product was centrifuged, washed three times with deionized water, and dried under vacuum at 70 °C for 12 h to obtain medium entropy (Mo–Co–In) sulfide powder.

[0080] (3) Composite grinding: Take 0.500 g of medium entropy sulfide powder and mix it with 0.062 g of MWCNTs. Place it in a stainless steel ball mill jar with a ball-to-material ratio of about 15:1. Directly ball mill at 1000 rpm for 12 h under nitrogen protection to obtain uniformly dispersed medium entropy sulfide / carbon nanotube composite powder.

[0081] (4) Pulping: Weigh 0.180 g of powder and 0.020 g of PVDF, add 8 mL of NMP, stir magnetically for 3 h and sonicate for 1 h to obtain a uniform slurry.

[0082] (5) Coating: The slurry was uniformly loaded onto one side of the Celgard 2500 membrane by vacuum filtration, with the loading rate controlled at 0.8 mg·cm³. -2 The coating thickness is approximately 10 μm.

[0083] (6) Drying: The coated diaphragm was placed in a vacuum drying oven and dried at 50 °C for 12 h to obtain a medium-entropy sulfide modified diaphragm (denoted as S4).

[0084] Example 5

[0085] The difference from Example 1 is that the diaphragm coating load and coating thickness are adjusted.

[0086] The specific preparation steps are as follows:

[0087] (1) Raw material dissolution: Weigh 1.408 g (8 mmol) (NH4)6Mo7O 24 Dissolve 4H₂O, 0.238 g (1 mmol) CoCl₂·6H₂O, 0.221 g (1 mmol) InCl₃, and 7.446 g (30 mmol) Na₂S₂O₃·5H₂O in deionized water and adjust the total volume to 70 mL. Pour the solution into the liner of a 100 mL hydrothermal reactor, filling it to approximately 70% capacity.

[0088] (2) Hydrothermal reaction: The reactor was placed in an oven and reacted at 180 °C for 12 h, and then naturally cooled to room temperature. The resulting product was centrifuged, washed three times with deionized water, and dried under vacuum at 70 °C for 12 h to obtain medium entropy (Mo–Co–In) sulfide powder.

[0089] (3) Composite grinding: Weigh 0.500 g of medium entropy sulfide powder and 0.062 g of MWCNTs, place them in a stainless steel ball mill jar, with a ball-to-material ratio of about 15:1, and ball mill at 1000 rpm for 12 h under nitrogen protection to obtain uniformly dispersed medium entropy sulfide / carbon nanotube composite powder.

[0090] (4) Pulping: Take 0.180 g of composite powder and 0.020 g of PVDF, add 8 mL of NMP, stir magnetically for 3 h and sonicate for 1 h to obtain a uniform slurry.

[0091] (5) Coating: The slurry is uniformly loaded onto one side of the Celgard 2500 membrane by vacuum filtration, with the loading rate controlled at 1.0 mg·cm³. -2 It has a thickness of approximately 12 μm.

[0092] (6) Drying: Place the coated diaphragm in a vacuum drying oven and dry it at 50 °C for 12 h to obtain a medium-entropy sulfide modified diaphragm (denoted as S5).

[0093] Example 6

[0094] The difference from Example 1 is that the temperature of the hydrothermal reaction is adjusted.

[0095] The specific preparation steps are as follows:

[0096] (1) Raw material dissolution: Weigh 1.408 g (8 mmol) (NH4)6Mo7O 24Dissolve 4H₂O, 0.238 g (1 mmol) CoCl₂·6H₂O, 0.221 g (1 mmol) InCl₃, and 7.446 g (30 mmol) Na₂S₂O₃·5H₂O in deionized water and adjust the total volume to 70 mL. Pour the solution into the liner of a 100 mL hydrothermal reactor, filling it to approximately 70% capacity.

[0097] (2) Hydrothermal reaction: The reactor was placed in an oven and hydrothermally heated at 160 °C for 12 h, and then naturally cooled to room temperature. The resulting product was centrifuged, washed three times with deionized water, and vacuum dried at 70 °C for 12 h to obtain medium entropy (Mo–Co–In) sulfide powder.

[0098] (3) Composite grinding: Weigh 0.500 g of medium entropy sulfide powder and 0.062 g of MWCNTs, place them in a stainless steel ball mill jar, with a ball-to-material ratio of about 15:1, and ball mill at 1000 rpm for 12 h under nitrogen protection to obtain uniformly dispersed medium entropy sulfide / carbon nanotube composite powder.

[0099] (4) Pulping: Take 0.180 g of composite powder and 0.020 g of PVDF, add 8 mL of NMP, stir magnetically for 3 h and sonicate for 1 h to obtain a uniform slurry.

[0100] (5) Coating: The slurry was uniformly loaded onto the Celgard 2500 membrane by vacuum filtration, with the loading rate controlled at 0.8 mg·cm³. -2 It has a thickness of approximately 10 μm.

[0101] (6) Drying: Place the coated diaphragm in a vacuum drying oven and dry it at 50 °C for 12 h to obtain a medium-entropy sulfide modified diaphragm (denoted as S6).

[0102] Example 7

[0103] The difference from Example 1 is that the temperature of the hydrothermal reaction is adjusted.

[0104] The specific preparation steps are as follows:

[0105] (1) Raw material dissolution: Weigh 1.408 g (8 mmol) (NH4)6Mo7O 24 Dissolve 4H₂O, 0.238 g (1 mmol) CoCl₂·6H₂O, 0.221 g (1 mmol) InCl₃, and 7.446 g (30 mmol) Na₂S₂O₃·5H₂O in deionized water and adjust the total volume to 70 mL. Pour the solution into the liner of a 100 mL hydrothermal reactor, filling it to approximately 70% capacity.

[0106] (2) Hydrothermal reaction: The reactor was placed in an oven and hydrothermally heated at 200 °C for 12 h, and then naturally cooled to room temperature. The resulting product was centrifuged, washed three times with deionized water, and vacuum dried at 70 °C for 12 h to obtain medium entropy (Mo–Co–In) sulfide powder.

[0107] (3) Composite grinding: Weigh 0.500 g of medium entropy sulfide powder and 0.062 g of MWCNTs, place them in a stainless steel ball mill jar, with a ball-to-material ratio of about 15:1, and ball mill at 1000 rpm for 12 h under nitrogen protection to obtain uniformly dispersed medium entropy sulfide / carbon nanotube composite powder.

[0108] (4) Pulping: Take 0.180 g of composite powder and 0.020 g of PVDF, add 8 mL of NMP, stir magnetically for 3 h and sonicate for 1 h to obtain a uniform slurry.

[0109] (5) Coating: The slurry was uniformly loaded onto one side of the Celgard 2500 membrane by vacuum filtration, with the loading rate controlled at 0.8 mg·cm³. -2 It has a thickness of approximately 10 μm.

[0110] (6) Drying: Place the coated diaphragm in a vacuum drying oven and dry it at 50 °C for 12 h to obtain a medium-entropy sulfide modified diaphragm (denoted as S7).

[0111] Comparative Example 1

[0112] The difference from Example 1 is that the molybdenum source is omitted. The specific steps are as follows:

[0113] (1) Raw material dissolution: Weigh 0.238 g (1 mmol) CoCl2·6H2O, 0.221 g (1 mmol) InCl3·H2O and 7.446 g (S 30 mmol) Na2S2O3·5H2O, add deionized water to prepare a 70 mL solution, and put it into a 100 mL reaction vessel, with a liquid volume of about 70%.

[0114] (2) Hydrothermal reaction: The reactor was placed in an oven and hydrothermally reacted at 180 °C for 12 h, and then naturally cooled to room temperature. The resulting product was centrifuged, washed three times with deionized water, and vacuum dried at 70 °C for 12 h to obtain (Co–In) sulfide powder.

[0115] (3) Composite grinding: Weigh 0.500 g of powder and mix with 0.062 g of MWCNTs, place in a stainless steel ball mill jar, with a ball-to-material ratio of about 15:1, and ball mill at 1000 rpm for 12 h under nitrogen protection to obtain the composite material.

[0116] (4) Pulping: Weigh 0.180 g of composite powder and 0.020 g of PVDF, add 8 mL of NMP, stir magnetically for 3 h and sonicate for 1 h to obtain a uniform slurry.

[0117] (5) Coating: The slurry was uniformly loaded onto one side of the Celgard 2500 membrane by vacuum filtration, with the loading rate controlled at 0.8 mg·cm³. -2 It has a thickness of approximately 10 μm.

[0118] (6) Drying: Place the coated diaphragm in a vacuum drying oven and dry it at 50 °C for 12 h to obtain the modified diaphragm (denoted as C1).

[0119] Comparative Example 2

[0120] The difference from Example 1 is that the cobalt source is omitted. The specific steps are as follows:

[0121] (1) Raw material dissolution: Weigh 1.408 g (Mo 8 mmol) (NH4)6Mo7O 24 ·4H2O, 0.221 g (1 mmol) InCl3·H2O and 7.446 g (30 mmol) Na2S2O3·5H2O were added to deionized water to prepare a 70 mL solution, which was then poured into a 100 mL reaction vessel, filling it to approximately 70% capacity.

[0122] (2) Hydrothermal reaction: The reactor was placed in an oven and hydrothermally reacted at 180 °C for 12 h, and then naturally cooled to room temperature. The resulting product was centrifuged, washed three times with deionized water, and vacuum dried at 70 °C for 12 h to obtain (Mo–In) sulfide powder.

[0123] (3) Composite grinding: Weigh 0.500 g of powder and mix with 0.062 g of MWCNTs, place in a stainless steel ball mill jar, with a ball-to-material ratio of about 15:1, and ball mill at 1000 rpm for 12 h under nitrogen protection.

[0124] (4) Pulping: Weigh 0.180 g of composite powder and 0.020 g of PVDF, add 8 mL of NMP, stir magnetically for 3 h and sonicate for 1 h to obtain a uniform slurry.

[0125] (5) Coating: The slurry was uniformly loaded onto one side of the Celgard 2500 membrane by vacuum filtration, with the loading rate controlled at 0.8 mg·cm³. -2 It has a thickness of approximately 10 μm.

[0126] (6) Drying: Place the coated diaphragm in a vacuum drying oven and dry it at 50 °C for 12 h to obtain the modified diaphragm (denoted as C2).

[0127] Comparative Example 3

[0128] The difference from Example 1 is that the indium source is omitted. The specific steps are as follows:

[0129] (1) Raw material dissolution: Weigh 1.408 g (Mo 8 mmol) (NH4)6Mo7O 24 ·4H2O, 0.238 g (1 mmol) CoCl2·6H2O and 7.446 g (30 mmol) Na2S2O3·5H2O were added to deionized water to prepare a 70 mL solution, which was then poured into a 100 mL reaction vessel, filling it to approximately 70% capacity.

[0130] (2) Hydrothermal reaction: The hydrothermal reaction was carried out at 180 °C for 12 h, followed by cooling, washing, and vacuum drying at 70 °C for 12 h to obtain (Mo–Co) sulfide powder.

[0131] (3) Composite grinding: Weigh 0.500 g of powder and mix with 0.062 g of MWCNTs, place in a stainless steel ball mill jar, with a ball-to-material ratio of about 15:1, and ball mill at 1000 rpm for 12 h under nitrogen protection.

[0132] (4) Pulping: Weigh 0.180 g of composite powder and 0.020 g of PVDF, add 8 mL of NMP, stir magnetically for 3 h and sonicate for 1 h to obtain a uniform slurry.

[0133] (5) Coating: The slurry was uniformly loaded onto one side of the Celgard 2500 membrane by vacuum filtration, with the loading rate controlled at 0.8 mg·cm³. -2 The coating thickness is approximately 10 μm.

[0134] (6) Drying: Place the coated diaphragm in a vacuum drying oven and dry it at 50 °C for 12 h to obtain the modified diaphragm (denoted as C3).

[0135] Comparative Example 4

[0136] The difference from Example 1 is that the ball milling step is omitted. The specific steps are as follows:

[0137] (1) Raw material dissolution: Weigh 1.408 g (8 mmol) (NH4)6Mo7O 24 Dissolve 4H₂O, 0.238 g (1 mmol) CoCl₂·6H₂O, 0.221 g (1 mmol) InCl₃, and 7.446 g (30 mmol) Na₂S₂O₃·5H₂O in deionized water and adjust the total volume to 70 mL. Pour the solution into the liner of a 100 mL hydrothermal reactor, filling it to approximately 70% capacity.

[0138] (2) Hydrothermal reaction: The hydrothermal reaction was carried out at 180 °C for 12 h, and then naturally cooled to room temperature. The resulting product was centrifuged, washed three times with deionized water, and dried under vacuum at 70 °C for 12 h to obtain medium entropy (Mo–Co–In) sulfide powder.

[0139] (3) Direct mixing of powder and MWCNTs: Weigh 0.500 g of powder and 0.062 g of MWCNTs, and grind and mix them thoroughly in a mortar for 10 min (without ball milling).

[0140] (4) Pulping: Weigh 0.180 g of mixed powder and 0.020 g of PVDF, add 8 mL of NMP, stir magnetically for 3 h and sonicate for 1 h.

[0141] (5) Coating: The slurry was uniformly loaded onto the Celgard 2500 membrane by vacuum filtration, with the loading rate controlled at 0.8 mg·cm³. -2 It has a thickness of approximately 10 μm.

[0142] (6) Drying: Place the coated diaphragm in a vacuum drying oven and dry it at 50 °C for 12 h to obtain the modified diaphragm (denoted as C4).

[0143] Comparative Example 5

[0144] The difference from Example 1 is that the MWCNTs and ball milling steps are omitted. The specific steps are as follows:

[0145] (1) Raw material dissolution: Weigh 1.408 g (8 mmol) (NH4)6Mo7O 24 Dissolve 4H₂O, 0.238 g (1 mmol) CoCl₂·6H₂O, 0.221 g (1 mmol) InCl₃, and 7.446 g (30 mmol) Na₂S₂O₃·5H₂O in deionized water and adjust the total volume to 70 mL. Pour the solution into the liner of a 100 mL hydrothermal reactor, filling it to approximately 70% capacity.

[0146] (2) Hydrothermal reaction: The hydrothermal reaction was carried out at 180 °C for 12 h, and then naturally cooled to room temperature. The resulting product was centrifuged, washed three times with deionized water, and dried under vacuum at 70 °C for 12 h to obtain medium entropy (Mo–Co–In) sulfide powder.

[0147] (3) Pulping: Weigh 0.180 g of sulfide powder and 0.020 g of PVDF, add 8 mL of NMP, stir magnetically for 3 h and sonicate for 1 h.

[0148] (5) Coating: The slurry was uniformly loaded onto one side of the Celgard 2500 membrane by vacuum filtration, with the loading rate controlled at 0.8 mg·cm³. -2 It has a thickness of approximately 10 μm.

[0149] (6) Drying: Place the coated diaphragm in a vacuum drying oven and dry it at 50 °C for 12 h to obtain the modified diaphragm (denoted as C5).

[0150] Performance test examples

[0151] I. Characterization

[0152] The XRD pattern of the medium-entropy (molybdenum-cobalt-indium) sulfide powder prepared in Example 1 is shown in Figure 1. Figure 2 The cross-sectional and surface SEM images of the medium-entropy (Mo–Co–In) sulfide membrane prepared in Example 1 are shown below. Figure 3 .

[0153] II. High Temperature Resistance

[0154] The medium-entropy (Mo–Co–In) sulfide membrane prepared in Example 1 was placed in an oven and treated at 100°C for 1 hour. Optical images before and after treatment were observed, and the results are as follows. Figure 4 As shown, the separator of this invention exhibits excellent thermal stability, maintaining structural integrity and remaining deformation-free even at temperatures up to 100°C. This effectively expands the operating temperature range of lithium-sulfur batteries, meeting the safety and lifespan requirements in high-temperature environments.

[0155] II. Electrochemical Performance

[0156] The modified separator was applied to the assembly of a lithium-sulfur battery, specifically a 2032 coin cell, using lithium foil as the negative electrode and a sulfur loading of 2 mg·cm³ on the sulfur positive electrode. -2 The electrolyte was 1 M LiTFSI / DOL:DME (volume ratio 1:1), with 2 wt% LiNO3 added, and the electrolyte / sulfur (E / S) ratio was 15. After battery assembly, the cells were allowed to stand for 12 h before electrochemical testing at 60 °C. The test voltage range was 1.7–2.8 V. The cells were first activated at a current density of 0.05 C for three cycles, followed by cycling tests at a current density of 0.2 C.

[0157] The modified separators prepared in Examples 1–6 and Comparative Examples 1–4 were assembled into 2032-type coin-type lithium-sulfur batteries, and the test results are shown in Table 1. The cycle performance curves of the lithium-sulfur battery with the modified separator prepared in Example 1 under high-temperature conditions are shown in the figure. Figure 5 .

[0158] Table 1. Comparison of electrochemical performance of the membranes prepared in the examples and comparative examples at 60 °C.

[0159]

[0160] As can be seen from Table 1, Example 1 (S1) has the highest capacity retention rate (73.1%), and is significantly better than the other examples and comparative examples in terms of cycle stability. This indicates that the synergistic effect of Mo-Co-In ternary structure and the ball milling composite process can significantly improve the electrochemical stability of the membrane.

[0161] Comparing Examples 1 with Examples 2–6 reveals that the cycle performance decreased when the elemental ratio or process conditions deviated. For example, in Example 2, the Mo ratio was too low, resulting in a capacity retention rate of 72.4%; in Example 3, the In ratio was too high, further reducing the capacity retention rate to 70.6%; in Example 4, the Co ratio was too high, resulting in a capacity retention rate of only 69.3%; in Example 5, the membrane thickness was too high, reducing the capacity retention rate to 68.2%; and in Examples 6–7, excessively high or low hydrothermal reaction temperatures led to incomplete crystal growth and a capacity retention rate of 66.8% and 66.8%, respectively. These results indicate that the conditions used in Example 1 (Mo:Co:In = 8:1:1, hydrothermal temperature 180°C, MWCNTs composite, ball milling for 12 h, loading 0.8 mg·cm⁻¹) are optimal. -2 The optimal thickness is approximately 10 μm.

[0162] Comparing Example 1 with Comparative Examples 1–3, it can be seen that the capacity retention rate decreased significantly (59.4–59.8%) when any element (Mo, Co, or In) was missing, indicating that the entropy effect in the ternary system is the key to improving performance. In particular, the capacity retention rate was the lowest (54.0%) when In was missing (Comparative Example 3), further demonstrating that In plays an important role in regulating electronic structure and stabilizing polysulfide adsorption.

[0163] Comparing Example 1 and Comparative Example 4, it can be seen that the capacity retention rate of the sample without ball milling is only 59.8%, which is significantly lower than 73.1% in Example 1. This indicates that ball milling plays a positive role in improving powder dispersibility and forming a stable conductive network, and is a necessary step to ensure the performance of the diaphragm.

[0164] Comparing Example 1 and Comparative Example 5, it can be seen that the capacity retention rate significantly decreased when any element MWCNTs was missing. This indicates that multi-walled carbon nanotubes (MWCNTs) play an indispensable and synergistic role in the preparation of this composite membrane: on the one hand, their unique one-dimensional fiber structure overlaps with each other in the membrane coating, constructing a through-type three-dimensional high-speed electronic conductive network, which greatly accelerates electron transport and enhances the conversion reaction kinetics of polysulfides; on the other hand, MWCNTs, with their excellent mechanical strength, act as a flexible skeleton to enhance the mechanical stability and flexibility of the coating, effectively preventing the coating from cracking or falling off during cycling, and ensuring the structural integrity of the membrane; at the same time, MWCNTs also optimize the pore structure of the coating, promote electrolyte wetting and ion migration, and act as a dispersion scaffold to prevent the aggregation of medium-entropy sulfide particles, allowing their active sites to be fully exposed and utilized.

[0165] The above results show that the modified diaphragm prepared by this invention can still maintain a high specific capacity and capacity retention rate after 100 cycles at 60 °C. Moreover, the diaphragm is structurally stable in a high-temperature environment without significant shrinkage or damage, which is significantly better than the unmodified Celgard diaphragm.

[0166] The present invention has been described in detail above. Those skilled in the art will recognize that the invention can be practiced in a wide range of ways with equivalent parameters, concentrations, and conditions without departing from its spirit and scope. While specific embodiments have been provided, it should be understood that further modifications can be made to the invention. In summary, according to the principles of the invention, this application is intended to include any changes, uses, or improvements to the invention, including modifications made using conventional techniques known in the art that depart from the scope disclosed herein.

Claims

1. A lithium-sulfur battery separator, characterized in that, The membrane substrate includes a membrane substrate and a coating disposed on at least one surface of the membrane substrate, the coating comprising a medium-entropy (molybdenum-cobalt-indium) sulfide, a conductive agent, and a binder; The medium-entropy (molybdenum-cobalt-indium) sulfide is prepared by dissolving molybdenum source, cobalt source, indium source and sulfur source in water at a molar ratio of molybdenum, cobalt, indium and sulfur elements of (1-8):(1-8):(1-8):(10-30) and carrying out a hydrothermal reaction at 160-200 °C. The method for preparing the lithium-sulfur battery separator includes the following steps: 1) The intermediate-entropy (molybdenum-cobalt-indium) sulfide is mixed with the conductive agent and ball-milled to obtain a mixture; The conductive agent is a multi-walled carbon nanotube; 2) The mixture and the binder are added to a solvent for dispersion to obtain a slurry; The mass ratio of the medium-entropy (molybdenum-cobalt-indium) sulfide, the conductive agent, and the binder is 8:(1-2):(1-2); 3) The slurry is coated on the surface of the membrane substrate and dried to obtain the lithium-sulfur battery membrane.

2. The lithium-sulfur battery separator according to claim 1, characterized in that: The molar ratio of molybdenum, cobalt, indium and sulfur is (1-8):1:(1-8):(10-30).

3. The lithium-sulfur battery separator according to claim 2, characterized in that: The molar ratio of molybdenum, cobalt, indium and sulfur is (1-8):1:1:(10-30).

4. The lithium-sulfur battery separator according to claim 3, characterized in that: The molar ratio of molybdenum, cobalt, indium and sulfur is 8:1:1:

30.

5. The lithium-sulfur battery separator according to any one of claims 1-4, characterized in that: The molybdenum source is selected from one or more of ammonium heptamolybdate, ammonium molybdate, and sodium molybdate. The cobalt source is selected from one or more of cobalt chloride hexahydrate, cobalt nitrate, and cobalt acetate. The indium source is selected from one or more of indium chloride, indium nitrate, and indium sulfate; The sulfur source is selected from one or more of sodium thiosulfate, thiourea, and sodium sulfide; The hydrothermal reaction takes 10 to 16 hours.

6. The lithium-sulfur battery separator according to any one of claims 1-4, characterized in that: The diaphragm substrate is a polyolefin diaphragm.

7. The lithium-sulfur battery separator according to any one of claims 1-4, characterized in that: The adhesive is polyvinylidene fluoride.

8. The method for preparing the lithium-sulfur battery separator according to any one of claims 1-7, characterized in that, Includes the following steps: 1) The intermediate-entropy (molybdenum-cobalt-indium) sulfide is mixed with the conductive agent and ball-milled to obtain a mixture; 2) The mixture and the binder are added to a solvent for dispersion to obtain a slurry; 3) The slurry is coated on the surface of the membrane substrate and dried to obtain the lithium-sulfur battery membrane.

9. The method for preparing a lithium-sulfur battery according to claim 8, characterized in that: The ball milling step is carried out under inert gas protection, with a ball-to-material ratio of (10-20):1, and the ball milling is performed in a high-energy ball mill at a speed of 800-1200 rpm for 10-15 hours.

10. The method for preparing a lithium-sulfur battery according to any one of claims 8-9, characterized in that: The solvent is selected from one or more of methylpyrrolidone, N,N-dimethylformamide, and ethanol; In the coating step, the coating is applied to one side of the diaphragm substrate using vacuum filtration, with a slurry loading of 0.2–1.2 mg·cm⁻¹. -2 The coating thickness is 3–10 μm; In the drying step, vacuum drying is used, the drying temperature is 50-80 ℃, and the drying time is 4-12 hours.

11. A lithium-sulfur battery, characterized in that, The lithium-sulfur battery separator includes any one of claims 1-7 or the lithium-sulfur battery separator obtained by any one of claims 8-10.

Images