Composite gel lithium-sulfur battery separator, preparation method and application thereof

Abstract

The application provides a composite gel lithium-sulfur battery diaphragm and a preparation method and application thereof.A composite gel lithium-sulfur battery diaphragm according to the application comprises a base layer and a gel layer arranged on the base layer, and the components of the gel layer comprise cellulose, polyethylene oxide and a CoSSe composite material.From the perspective of modification of lithium-sulfur battery diaphragm materials, by constructing a gel-state diaphragm with good catalytic performance, the shuttle effect of polysulfides can be inhibited, the utilization rate of positive active material can be improved, and the performance of lithium-sulfur batteries can be improved.In particular, by using rigid molecules such as cellulose, polyethylene oxide in a gel state in an electrolyte and a CoSSe composite material with high-efficiency catalysis, the shuttle effect of polysulfides can be inhibited, and the electrochemical performance of lithium-sulfur batteries can be improved.The application further provides a preparation method and application of the composite gel lithium-sulfur battery diaphragm.

Description

Technical Field

[0001] This invention belongs to the field of lithium-sulfur battery technology, specifically relating to a composite gel lithium-sulfur battery separator, its preparation method, and its application. Background Technology

[0002] Lithium-sulfur batteries are a type of lithium battery that uses sulfur as the positive electrode and metallic lithium as the negative electrode. Its reaction mechanism is electrochemical, which differs from the ion insertion / extraction mechanism of lithium-ion batteries. Elemental sulfur is abundant on Earth and is inexpensive and environmentally friendly. Lithium-sulfur batteries using sulfur as the positive electrode material have high theoretical specific capacity and energy density, reaching 1675 mAh / g and 2600 Wh / kg respectively, far exceeding the capacity of commercially widely used lithium cobalt oxide batteries (<150 mAh / g).

[0003] Lithium-sulfur batteries use sulfur as the positive electrode reactant and lithium as the negative electrode. During discharge, the negative electrode reaction involves lithium losing electrons to become lithium ions, while the positive electrode reaction involves sulfur reacting with lithium ions and electrons to form sulfides. The potential difference between the positive and negative electrode reactions is the discharge voltage provided by the lithium-sulfur battery. Under the action of an applied voltage, the positive and negative electrode reactions of the lithium-sulfur battery proceed in reverse, which is the charging process. This is based on the principle that a unit mass of elemental sulfur completely converts to sulfur (S). 2- Based on the available power, the theoretical discharge specific capacity of sulfur is 1675 mAh / g, and similarly, the theoretical discharge specific capacity of elemental lithium is 3860 mAh / g. The theoretical discharge voltage of a lithium-sulfur battery is 2.287 V when sulfur and lithium completely react to form lithium sulfide (Li₂S). The corresponding theoretical discharge specific energy of a lithium-sulfur battery is 2600 Wh / kg.

[0004] Besides the positive and negative electrodes, the electrolyte and separator are the main components and structures in lithium-sulfur batteries. Specifically, the positive electrode is mainly composed of active material sulfur, conductive additives, and binders uniformly coated onto the current collector. Sulfur, as the positive electrode active material in lithium-sulfur batteries, has extremely low conductivity (5 × 10⁻⁶ at 25°C). -30 The sulfur content (S / cm) decreases, leading to reduced utilization of the active material sulfur and decreased battery cycle performance. Therefore, conductive additives need to be added to ensure sufficient contact with the active material to improve sulfur utilization efficiency.

[0005] Commonly used conductive agents include Super-P, conductive carbon black, and carbon nanotubes. Adding binders can better bond the active material with the conductive agent, enhancing conductivity and maintaining internal structural stability during battery charging and discharging.

[0006] Unlike the intercalation / deintercalation mechanism of traditional lithium-ion batteries, the charging and discharging of lithium-sulfur batteries is based on electrochemical redox reactions involving multiple electron transfers. Energy is released through the breaking of the SS bond in the S8 ring molecule. The overall chemical reaction equation is as follows:

[0007] S8+16Li + +16e - →8Li2S.

[0008] During this electrochemical reaction, S8 occurred. - Reactions such as Li₂S₆ / Li₂S₄ → Li₂S₂ / Li₂S occur. Long-chain polysulfides readily dissolve in organic electrolytes, while lithium sulfides (Li₂S₂, LiS) do not. Compared to theoretical reactions, the actual reactions occurring inside a battery are far more complex, thus presenting numerous challenges.

[0009] In short, lithium-sulfur batteries suffer from problems such as low utilization of active materials, poor electrochemical reversibility, and rapid capacity decay. In particular, polysulfides exhibit a shuttle effect, leading to low utilization of the positive electrode active material. Therefore, new technologies are needed to address the problems existing in current technologies. Summary of the Invention

[0010] The present invention aims to at least solve one of the aforementioned technical problems existing in the prior art. To this end, the present invention provides a composite gel lithium-sulfur battery separator. Using this separator in a lithium-sulfur battery can reduce the shuttle effect of polysulfides, improve the utilization rate of the positive electrode active material, enhance electrochemical reversibility, and reduce capacity decay.

[0011] The present invention also provides a method for preparing a composite gel lithium-sulfur battery separator.

[0012] The present invention also provides a lithium-sulfur battery.

[0013] A first aspect of the present invention provides a composite gel lithium-sulfur battery separator, comprising a base layer and a gel layer disposed on the base layer, wherein the gel layer comprises a cellulose, polyethylene oxide and CoSSe composite material.

[0014] One technical solution of the present invention concerning a composite gel lithium-sulfur battery separator has at least the following beneficial effects:

[0015] This invention focuses on the modification of lithium-sulfur battery separator materials. By using rigid cellulose, polyethylene oxide that is gelled in the electrolyte, and CoSSe composite material with high catalytic efficiency, a gel-like separator with good catalytic performance is constructed. This can suppress the "shuttle effect" of polysulfides, improve the utilization rate of positive electrode active material, and ultimately enhance the electrochemical performance of lithium-sulfur batteries.

[0016] In the gel layer, cellulose, due to its entangled long fibers, serves as a support layer for the gel separator, ensuring its structural integrity and providing structural strength. Polyethylene oxide swells in the electrolyte, absorbing it and preferentially improving the electrolyte retention of the gel separator, thus providing ion channels for lithium ions. CoSSe has the effect of converting polysulfides, transforming soluble polysulfides into insoluble ones, which can improve the battery's cycle performance.

[0017] The shuttle effect mainly occurs when soluble polysulfides dissolve in the electrolyte and pass through the membrane from the positive electrode to the negative electrode, leading to a decrease in the utilization rate of the positive electrode active material and capacity decay. In the membrane of this invention, the polyethylene oxide and CoSSe composite material of the gel layer can synergistically suppress the shuttle effect. Specifically, CoSSe converts soluble polysulfides into insoluble polysulfides, thereby preventing the dissolution of polysulfides in the electrolyte and also preventing the process of soluble polysulfides passing through the membrane from the positive electrode to the negative electrode. Meanwhile, polyethylene oxide swells in the electrolyte, absorbing a large amount of electrolyte and lithium ions during the swelling process. This not only improves the liquid retention of the gel membrane and provides an ion channel for lithium ions, but also provides an excellent reaction site for the reuse of the converted polysulfides. During battery charging and discharging, this reaction site, rich in lithium ions, can utilize the converted insoluble polysulfides more efficiently. The higher the liquid retention, the higher the utilization rate of insoluble polysulfides.

[0018] According to some embodiments of the present invention, the thickness ratio of the base layer to the gel layer is 1:0.5 to 2.

[0019] According to some embodiments of the present invention, the mass ratio of the cellulose, polyethylene oxide and CoSSe composite material is 2-9:10-17:1.

[0020] According to some embodiments of the present invention, the mass ratio of the cellulose, polyethylene oxide and CoSSe composite material is 3:16:1.

[0021] According to some embodiments of the present invention, the base layer comprises a cellulose layer.

[0022] According to some embodiments of the present invention, the length of the cellulose is 0.5 μm to 1 μm.

[0023] According to some embodiments of the present invention, the diameter of the cellulose can be about 1 nm.

[0024] Cellulose can be lignocellulose, an organic fiber obtained from natural, renewable wood through chemical and mechanical processing. It is non-toxic, odorless, pollution-free, and non-radioactive. Lignocellulose includes coniferous lignocellulose, hardwood lignocellulose, and herbaceous lignocellulose. Among these, coniferous lignocellulose has long fibers, a dense structure, and low impurity cell content. Most impurities in chemical pulp are lost during washing, resulting in high-quality pulp and materials with strong mechanical properties. Choosing coniferous lignocellulose as the support layer helps ensure the integrity of the membrane structure.

[0025] According to some embodiments of the present invention, the molecular weight of the polyethylene oxide is 400,000 to 600,000.

[0026] According to some embodiments of the present invention, the molecular weight of the polyethylene oxide can be around 500,000.

[0027] Polyethylene oxide (PEO), also known as polyethylene oxide, is a crystalline, thermoplastic polymer. The molecular weight of its industrial products can vary widely. Products with a relative molecular mass of 200–20,000 are called polyethylene glycol (PEG), and they are viscous liquids or waxy solids. Its main functional group is the ether bond, and it has a molecular weight of 1100 cm⁻¹. -1 There are obvious characteristic peaks at the point. PEO can form hydrogen bonds with the abundant carboxyl groups on the surface of cellulose. These hydrogen bonds are not easily broken in the gel state formed in the electrolyte, which can effectively store abundant lithium ions.

[0028] According to some embodiments of the present invention, the CoSSe composite material includes CoSSe and a conductive agent.

[0029] CoSSe possesses redox capabilities, catalyzing the conversion of soluble polysulfides into insoluble polysulfides. Since elemental sulfur and polysulfides have poor electrical conductivity, and conductive agents play a conductive role, this portion of the insoluble polysulfides can be reused. The main function of the conductive agent is to provide conductivity, thereby improving battery cycle performance.

[0030] CoSSe can be prepared by heat treatment of a conductive agent and cobalt sulfate, followed by vacuum reaction with elemental sulfur and elemental selenium. CoSSe has redox capabilities and can catalyze the conversion of soluble polysulfides into insoluble polysulfides.

[0031] According to some embodiments of the present invention, the conductive agent includes conductive carbon black and conductive carbon nanotubes.

[0032] According to some embodiments of the present invention, the conductive carbon black includes Ketjen black (KB) and acetylene black.

[0033] A second aspect of the present invention provides a method for preparing the composite gel lithium-sulfur battery separator, comprising the following steps:

[0034] S1: Prepare cellulose solution, polyethylene oxide solution and CoSSe composite material dispersion separately, and mix the three liquids to obtain a mixed solution;

[0035] S2: Place the substrate layer at the bottom of the container, add the mixed solution, and after drying, obtain the composite gel lithium-sulfur battery separator.

[0036] One technical solution of the present invention relates to a method for preparing a composite gel lithium-sulfur battery separator, which has at least the following characteristics.

[0037] Beneficial effects:

[0038] The method for preparing the composite gel lithium-sulfur battery separator of the present invention uses readily available raw materials, requires no expensive equipment or complex process control, and does not have harsh reaction conditions, which is conducive to large-scale industrial production.

[0039] According to some embodiments of the present invention, the concentration range of the cellulose solution is 15 mg / mL to 25 mg / mL.

[0040] According to some embodiments of the present invention, the concentration range of the polyethylene oxide solution is 15 mg / mL to 25 mg / mL.

[0041] According to some embodiments of the present invention, the concentration range of the CoSSe composite material dispersion is 0.5 mg / mL to 5 mg / mL.

[0042] According to some embodiments of the present invention, a method for preparing a CoSSe composite material dispersion includes:

[0043] (1) Dissolve conductive agents such as Ketjen black and sodium dodecyl sulfate in deionized water by ultrasonication to obtain solution A;

[0044] (2) After stirring in cobalt sulfate solution A, centrifuge to obtain powder, wash with deionized water, and dry to obtain powder A;

[0045] (3) Dry powder A under an Ar / H2 atmosphere to prepare KB / Co powder B. This step mainly involves heat treatment to embed cobalt nanoparticles into carbon nanoparticles.

[0046] (4) Powder B, elemental sulfur and elemental selenium are thoroughly mixed in a mortar and sintered in a sealed vacuum glass tube to prepare KB / CoSSe composite powder.

[0047] (5) Mix KB / CoSSe composite powder with deionized water, stir evenly and then sonicate to obtain CoSSe composite dispersion.

[0048] A third aspect of the present invention provides a lithium-sulfur battery, including the aforementioned composite gel lithium-sulfur battery separator.

[0049] One of the technical solutions of the present invention concerning lithium-sulfur batteries has at least the following beneficial effects:

[0050] In the lithium-sulfur battery of the present invention, by using the composite gel lithium-sulfur battery separator of the present invention, all the technical effects of the composite gel lithium-sulfur battery separator are achieved. Specifically:

[0051] The lithium-sulfur battery of the present invention, from the perspective of membrane material modification, constructs a gel-state membrane with good catalytic performance by using rigid molecular cellulose, polyethylene oxide that is in a gel state in the electrolyte, and CoSSe composite material with high catalytic efficiency. This can suppress the "shuttle effect" of polysulfides, improve the utilization rate of positive electrode active material, and ultimately enhance the electrochemical performance of the lithium-sulfur battery.

[0052] In lithium-sulfur batteries, cellulose fibers, due to their entanglement, serve as a support layer in the gel layer of the separator, ensuring the integrity of the separator's structure and providing structural strength. Polyethylene oxide swells in the electrolyte, absorbing it and preferentially improving the gel separator's liquid retention, thus providing ion channels for lithium ions. CoSSe has the effect of converting polysulfides, transforming soluble polysulfides into insoluble ones, which can improve the battery's cycle performance.

[0053] The shuttle effect mainly occurs when soluble polysulfides dissolve in the electrolyte and pass through the membrane from the positive electrode to the negative electrode, leading to a decrease in the utilization rate of the positive electrode active material and capacity decay. In the membrane of this invention, the polyethylene oxide and CoSSe composite material of the gel layer can synergistically suppress the shuttle effect. Specifically, CoSSe converts soluble polysulfides into insoluble polysulfides, thereby preventing the dissolution of polysulfides in the electrolyte and also preventing the process of soluble polysulfides passing through the membrane from the positive electrode to the negative electrode. Meanwhile, polyethylene oxide swells in the electrolyte, absorbing a large amount of electrolyte and lithium ions during the swelling process. This not only improves the liquid retention of the gel membrane and provides an ion channel for lithium ions, but also provides an excellent reaction site for the reuse of the converted polysulfides. During battery charging and discharging, this reaction site, rich in lithium ions, can utilize the converted insoluble polysulfides more efficiently. The higher the liquid retention, the higher the utilization rate of insoluble polysulfides.

[0054] The lithium-sulfur battery of this invention utilizes CoSSe to catalyze the conversion of soluble polysulfides into insoluble polysulfides, thereby improving the battery's cycle performance and making use of polysulfides that would otherwise be lost. After 300 charge-discharge cycles at 0.2C, the capacity of a PE membrane battery under the same conditions is only 762.5 mAh / g, while the lithium-sulfur battery of this invention still has a discharge capacity of 928.4 mAh / g.

[0055] The lithium-sulfur battery of the present invention features a composite gel lithium-sulfur battery separator with high liquid absorption and liquid retention rates. After immersion in electrolyte, the composite gel lithium-sulfur battery separator exhibits a high liquid absorption rate (238.7%) and a high liquid retention rate, and even after standing at room temperature for 24 hours, it retains approximately 134.7% of its liquid retention rate. Therefore, the high liquid absorption and liquid retention rates of this composite separator effectively improve the cycle life of the battery. The internal charge-discharge cycle of the battery is essentially a process that consumes lithium ions, and high liquid absorption and liquid retention rates effectively ensure the cycle stability of the lithium-ion battery. Attached Figure Description

[0056] Figure 1 This is a schematic diagram of the structure of the composite gel lithium-sulfur battery separator of the present invention.

[0057] Figure 2 This is a schematic diagram of the preparation process of the composite gel lithium-sulfur battery separator.

[0058] Figure 3 This is the X-ray powder diffraction pattern of KB / CoSSe.

[0059] Figure 4 Yes, this is a microscopic morphology diagram of KB / CoSSe.

[0060] Figure 5 This is the CV diagram of a CoSSe symmetric cell.

[0061] Figure 6 The results are the cycle stability test results of the lithium-sulfur battery prepared in Example 2 at a rate of 0.2C.

[0062] Figure label:

[0063] 1: Base layer; 2: Gel layer. Detailed Implementation

[0064] The following are specific embodiments of the present invention, and the technical solutions of the present invention will be further described in conjunction with the embodiments, but the present invention is not limited to these embodiments.

[0065] In some embodiments of the present invention, the present invention provides a composite gel lithium-sulfur battery separator, comprising a base layer and a gel layer disposed on the base layer, wherein the gel layer comprises a cellulose, polyethylene oxide and CoSSe composite material.

[0066] It is understood that this invention, from the perspective of modifying lithium-sulfur battery separator materials, constructs a gel-like separator with good catalytic performance by using rigid molecular cellulose, polyethylene oxide that is gelled in the electrolyte, and CoSSe composite material with high catalytic efficiency. This can suppress the "shuttle effect" of polysulfides, improve the utilization rate of positive electrode active material, and ultimately enhance the electrochemical performance of lithium-sulfur batteries.

[0067] In the gel layer, cellulose, due to its entangled long fibers, serves as a support layer for the gel separator, ensuring its structural integrity and providing structural strength. Polyethylene oxide swells in the electrolyte, absorbing it and preferentially improving the electrolyte retention of the gel separator, thus providing ion channels for lithium ions. CoSSe has the effect of converting polysulfides, transforming soluble polysulfides into insoluble ones, which can improve the battery's cycle performance.

[0068] It can also be understood that the shuttle effect mainly occurs when soluble polysulfides dissolve in the electrolyte and pass through the membrane from the positive electrode to the negative electrode, leading to a decrease in the utilization rate of the positive electrode active material and capacity decay. In the membrane of this invention, the polyethylene oxide and CoSSe composite material of the gel layer can synergistically suppress the shuttle effect. Specifically, CoSSe converts soluble polysulfides into insoluble polysulfides, thereby preventing the dissolution of polysulfides in the electrolyte and also preventing the process of soluble polysulfides passing through the membrane from the positive electrode to the negative electrode. Meanwhile, polyethylene oxide swells in the electrolyte, absorbing a large amount of electrolyte and lithium ions in the electrolyte during swelling. This not only improves the liquid retention of the gel membrane and provides an ion channel for lithium ions, but also provides an excellent reaction site for the reuse of the converted polysulfides. During battery charging and discharging, this reaction site, rich in lithium ions, can utilize the converted insoluble polysulfides more efficiently. The higher the liquid retention, the higher the utilization rate of insoluble polysulfides.

[0069] In some embodiments of the present invention, the thickness ratio of the base layer to the gel layer is 1:0.5 to 2.

[0070] In some embodiments of the present invention, the mass ratio of cellulose, polyethylene oxide and CoSSe composite material is 2-9:10-17:1.

[0071] In some embodiments of the present invention, the base layer includes a cellulose layer.

[0072] In some embodiments of the present invention, the length of the cellulose is 0.5 μm to 1 μm.

[0073] In some embodiments of the present invention, the diameter of the cellulose can be about 1 nm.

[0074] Cellulose can be lignocellulose, an organic fiber obtained from natural, renewable wood through chemical and mechanical processing. It is non-toxic, odorless, pollution-free, and non-radioactive. Lignocellulose includes coniferous lignocellulose, hardwood lignocellulose, and herbaceous lignocellulose. Among these, coniferous lignocellulose has long fibers, a dense structure, and low impurity cell content. Most impurities in chemical pulp are lost during washing, resulting in high-quality pulp and materials with strong mechanical properties. Choosing coniferous lignocellulose as the support layer helps ensure the integrity of the membrane structure.

[0075] In some embodiments of the present invention, the molecular weight of polyethylene oxide is 400,000 to 600,000.

[0076] In some embodiments of the present invention, the molecular weight of polyethylene oxide can be around 500,000.

[0077] Polyethylene oxide (PEO), also known as polyethylene oxide, is a crystalline, thermoplastic polymer. The molecular weight of its industrial products can vary widely. Products with a relative molecular mass of 200–20,000 are called polyethylene glycol (PEG), and they are viscous liquids or waxy solids. Its main functional group is the ether bond, and it has a molecular weight of 1100 cm⁻¹. -1 There are obvious characteristic peaks at the point. PEO can form hydrogen bonds with the abundant carboxyl groups on the surface of cellulose. These hydrogen bonds are not easily broken in the gel state formed in the electrolyte, which can effectively store abundant lithium ions.

[0078] In some embodiments of the present invention, the CoSSe composite material includes CoSSe and a conductive agent.

[0079] CoSSe possesses redox capabilities, catalyzing the conversion of soluble polysulfides into insoluble polysulfides. Since elemental sulfur and polysulfides have poor electrical conductivity, and conductive agents play a conductive role, this portion of the insoluble polysulfides can be reused. The main function of the conductive agent is to provide conductivity, thereby improving battery cycle performance.

[0080] CoSSe can be prepared by heat treatment of a conductive agent and cobalt sulfate, followed by vacuum reaction with elemental sulfur and elemental selenium. CoSSe has redox capabilities and can catalyze the conversion of soluble polysulfides into insoluble polysulfides.

[0081] In some embodiments of the present invention, the conductive agent includes conductive carbon black and conductive carbon nanotubes.

[0082] In some embodiments of the present invention, the conductive carbon black includes Ketjen black (KB) and acetylene black.

[0083] In other embodiments of the present invention, a method for preparing a composite gel lithium-sulfur battery separator is provided, comprising the following steps:

[0084] S1: Prepare cellulose solution, polyethylene oxide solution and CoSSe composite material dispersion separately, and mix the three liquids to obtain a mixed solution;

[0085] S2: Place the substrate layer at the bottom of the container, add the mixed solution, and after drying, obtain the composite gel lithium-sulfur battery separator.

[0086] It is understood that the preparation method of the composite gel lithium-sulfur battery separator of the present invention uses readily available raw materials, does not require expensive equipment and complex process control, and has undemanding reaction conditions, which is conducive to large-scale industrial production.

[0087] In some embodiments of the present invention, the concentration range of the cellulose solution is 15 mg / mL to 25 mg / mL.

[0088] In some embodiments of the present invention, the concentration range of the polyethylene oxide solution is 15 mg / mL to 25 mg / mL.

[0089] In some embodiments of the present invention, the concentration range of the CoSSe composite material dispersion is 0.5 mg / mL to 5 mg / mL.

[0090] In some embodiments of the present invention, the preparation method of the CoSSe composite material dispersion includes:

[0091] (1) Dissolve conductive agents such as Ketjen black and sodium dodecyl sulfate in deionized water by ultrasonication to obtain solution A;

[0092] (2) After stirring in cobalt sulfate solution A, centrifuge to obtain powder, wash with deionized water, and dry to obtain powder A;

[0093] (3) Dry powder A under an Ar / H2 atmosphere to prepare KB / Co powder B. This step mainly involves heat treatment to embed cobalt nanoparticles into carbon nanoparticles.

[0094] (4) Powder B, elemental sulfur and elemental selenium are thoroughly mixed in a mortar and sintered in a sealed vacuum glass tube to prepare KB / CoSSe composite powder.

[0095] (5) Mix KB / CoSSe composite powder with deionized water, stir evenly and then sonicate to obtain CoSSe composite dispersion.

[0096] In other embodiments of the present invention, the present invention provides a lithium-sulfur battery, including the composite gel lithium-sulfur battery separator of the present invention.

[0097] It is understood that the lithium-sulfur battery of the present invention, from the perspective of membrane material modification, constructs a gel-state membrane with good catalytic performance by using rigid molecular cellulose, polyethylene oxide that is in a gel state in the electrolyte, and CoSSe composite material with high catalytic efficiency. This can suppress the "shuttle effect" of polysulfides, improve the utilization rate of positive electrode active material, and ultimately improve the electrochemical performance of lithium-sulfur battery.

[0098] In lithium-sulfur batteries, cellulose fibers, due to their entanglement, serve as a support layer in the gel layer of the separator, ensuring the integrity of the separator's structure and providing structural strength. Polyethylene oxide swells in the electrolyte, absorbing it and preferentially improving the gel separator's liquid retention, thus providing ion channels for lithium ions. CoSSe has the effect of converting polysulfides, transforming soluble polysulfides into insoluble ones, which can improve the battery's cycle performance.

[0099] The shuttle effect mainly occurs when soluble polysulfides dissolve in the electrolyte and pass through the membrane from the positive electrode to the negative electrode, leading to a decrease in the utilization rate of the positive electrode active material and capacity decay. In the membrane of this invention, the polyethylene oxide and CoSSe composite material of the gel layer can synergistically suppress the shuttle effect. Specifically, CoSSe converts soluble polysulfides into insoluble polysulfides, thereby preventing the dissolution of polysulfides in the electrolyte and also preventing the process of soluble polysulfides passing through the membrane from the positive electrode to the negative electrode. Meanwhile, polyethylene oxide swells in the electrolyte, absorbing a large amount of electrolyte and lithium ions during the swelling process. This not only improves the liquid retention of the gel membrane and provides an ion channel for lithium ions, but also provides an excellent reaction site for the reuse of the converted polysulfides. During battery charging and discharging, this reaction site, rich in lithium ions, can utilize the converted insoluble polysulfides more efficiently. The higher the liquid retention, the higher the utilization rate of insoluble polysulfides.

[0100] The lithium-sulfur battery of this invention utilizes CoSSe to catalyze the conversion of soluble polysulfides into insoluble polysulfides, thereby improving the battery's cycle performance and making use of polysulfides that would otherwise be lost. After 300 charge-discharge cycles at 0.2C, the capacity of a PE membrane battery under the same conditions is only 762.5 mAh / g, while the lithium-sulfur battery of this invention still has a discharge capacity of 928.4 mAh / g.

[0101] The lithium-sulfur battery of the present invention features a composite gel lithium-sulfur battery separator with high liquid absorption and liquid retention rates. After immersion in electrolyte, the composite gel lithium-sulfur battery separator exhibits a high liquid absorption rate (238.7%) and a high liquid retention rate, and even after standing at room temperature for 24 hours, it retains approximately 134.7% of its liquid retention rate. Therefore, the high liquid absorption and liquid retention rates of this composite separator effectively improve the cycle life of the battery. The internal charge-discharge cycle of the battery is essentially a process that consumes lithium ions, and high liquid absorption and liquid retention rates effectively ensure the cycle stability of the lithium-ion battery.

[0102] The technical solution of the present invention will be better understood below in conjunction with specific embodiments and test results.

[0103] Example 1

[0104] In this embodiment, a composite gel lithium-sulfur battery separator was first prepared. The separator includes a base layer 1 and a gel layer 2 disposed on the base layer 1. The gel layer 2 is composed of cellulose, polyethylene oxide and CoSSe composite material.

[0105] The thickness of the substrate is 10 μm.

[0106] The thickness of the gel layer is 5 μm.

[0107] The preparation methods of composite gel lithium-sulfur battery separators can be summarized as follows:

[0108] S1: Prepare cellulose solution, polyethylene oxide solution and CoSSe composite material dispersion separately, and mix the three liquids to obtain a mixed solution;

[0109] S2: Place the substrate layer at the bottom of the container, add the mixed solution, and after drying, obtain the composite gel lithium-sulfur battery separator.

[0110] The detailed preparation method can be divided into two main steps: slurry preparation and composite gel membrane preparation. Details are as follows:

[0111] Slurry preparation:

[0112] (1) First, weigh 2g of PEO and add 100mL of deionized water to a beaker. Add a stir bar and stir at room temperature for 3 hours until completely dissolved to prepare a 20mg / mL PEO solution. Seal and store for later use. This solution is called Solution A.

[0113] (2) Weigh 2g of cellulose and add 100mL of deionized water to the ball mill jar. Ball mill at a ball-to-material ratio of 50:1 at a speed of 1032r / min for 1h and collect the solution for later use. This solution is called B.

[0114] (3) Weigh 1g of Ketjen Black and 2g of sodium dodecyl sulfate, dissolve them in 100ml of deionized water by sonication, and stir at 45℃ for 12h.

[0115] (4) Weigh 1g of cobalt sulfate and add it to the solution in step (3). Continue stirring for 12h, then centrifuge to get the powder, wash with deionized water, and dry at 80℃ for 24h to obtain powder A.

[0116] (5) Take powder A and dry it in an Ar / H2 atmosphere at 600℃ for 4h to prepare KB / Co powder B. This step is mainly to embed cobalt nanoparticles into carbon nanoparticles through heat treatment.

[0117] (6) Take 710mg of powder B, weigh 320mg of elemental sulfur and 790mg of elemental selenium, mix them thoroughly in a mortar, and prepare KB / CoSSe in a sealed vacuum glass tube at 450℃ for 12h.

[0118] (7) Weigh 0.2g of KB / CoSSe powder and add 100mL of deionized water to a beaker to prepare a 2mg / mL KB / CoSSe solution. Stir well and sonicate. This solution is called solution C.

[0119] Preparation of composite gel membrane:

[0120] (8) Pour 10 mL of solution B into a petri dish with a diameter of 8 mm, bake it on a hot table at 60 °C for a certain time until it is semi-dry, and a single layer of cellulose is prepared.

[0121] (9) Draw 1.5 mL of solution A into a beaker using a syringe, then draw 8 mL of solution B into the beaker, mix well, and then add 5 mL of solution C. Prepare a cellulose:polyoxyethylene:KB / CoSSe mass ratio of 3:16:1.

[0122] (10) Take the mixed solution from step (9) and slowly add it into the culture dish from step (8), and bake it on a hot table at 60°C for 2 hours to prepare a composite gel lithium-sulfur membrane.

[0123] (11) Take the baked diaphragm, cut it into 19mm round slices with a slicer, weigh each slice, label it, put it in a self-sealing bag and place it in a desiccator for later use.

[0124] A lithium-sulfur battery was assembled using the prepared composite gel lithium-sulfur battery separator. The specific process is as follows:

[0125] Before assembling the battery, the prepared composite gel lithium-sulfur battery separator was dried on a hot table at 100°C for 2 hours to remove residual moisture.

[0126] When assembling the button cell, an electrolyte of 20% of the mass of the composite gel lithium-sulfur battery separator is added. The electrolyte is a mixed solvent of 1M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 0.2M lithium nitrate (LiNO3) in 1,3-dioxolane (DOL) and dimethyl ethylene glycol (DME) (1:1, v / v).

[0127] The positive electrode is composed of sulfur, super p, and PVDF in a mass ratio of 6:3:1.

[0128] After assembly, various tests were conducted.

[0129] Example 2

[0130] This embodiment assembles a lithium-sulfur battery, which differs from the lithium-sulfur battery in Example 1 in that the mass ratio of cellulose:polyoxyethylene:KB / CoSSe in the separator is 1:17:1.

[0131] Example 3

[0132] This embodiment assembles a lithium-sulfur battery, which differs from the lithium-sulfur battery in Example 1 in that the mass ratio of cellulose:polyoxyethylene:KB / CoSSe in the separator is 9:10:1.

[0133] Comparative Example 1

[0134] This comparative example demonstrates the preparation of a PE membrane lithium-sulfur battery.

[0135] The positive electrode is composed of sulfur, super p, and PVDF in a mass ratio of 6:3:1.

[0136] The negative electrode is a lithium metal sheet.

[0137] The diaphragm is made of commercial PE.

[0138] The electrolyte is a mixture of 1M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 0.2M lithium nitrate (LiNO3) in 1,3-dioxolane (DOL) and dimethyl ethylene glycol (DME) (1:1, v / v).

[0139] Comparative Example 2

[0140] This comparative example prepared a modified membrane lithium-sulfur battery.

[0141] The positive electrode is composed of sulfur, super p, and PVDF in a mass ratio of 6:3:1.

[0142] The negative electrode is a lithium metal sheet.

[0143] The diaphragm is a single layer of cellulose with a thickness of 15 μm.

[0144] The electrolyte is a mixture of 1M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 0.2M lithium nitrate (LiNO3) in 1,3-dioxolane (DOL) and dimethyl ethylene glycol (DME) (1:1, v / v).

[0145] Comparative Example 3

[0146] This comparative example assembles a lithium-sulfur battery, which differs from the lithium-sulfur battery in Example 1 in that the separator does not contain polyethylene oxide, and the cellulose:KB / CoSSe mass ratio is 3:1.

[0147] Comparative Example 4

[0148] This comparative example assembles a lithium-sulfur battery, which differs from the lithium-sulfur battery in Example 1 in that the separator does not contain CoSSe composite material, and the cellulose:polyoxyethylene mass ratio is 3:16.

[0149] Performance Test 1

[0150] The KB / CoSSe prepared in step (6) of Example 1 was first characterized by X-ray powder diffraction, as shown in the figure. Figure 3 As shown in the figure. Literature review revealed that, on the XRD patterns, CoS2 and CoSe2 exhibit three characteristic absorption peaks at 32.3°, 36.2°, and 39.8°, and at 30.3°, 34.2°, and 37.6°, respectively. However, the characteristic absorption peaks of CoSSe are at 31.4°, 35.6°, and 39.4°, and exhibit a broad pattern at angles between CoS2 and CoSe2, rather than their individual peak values. This result indicates that in this invention, S and Se are regularly combined with Co particles to prepare ternary CoSSe.

[0151] The microstructure of the KB / CoSSe prepared in step (6) of Example 1 was observed, such as... Figure 4 As shown. From Figure 4 It can be seen that the KB / CoSSe material has a small particle size, is nanoparticle, and is uniformly distributed.

[0152] Performance Test 2

[0153] To verify the catalytic performance of CoSSe on polysulfides, a CoSSe / CoSSe symmetric cell (control group KB / KB symmetric cell) was designed with 0.2 mol / L Li2S6 as the electrolyte.

[0154] like Figure 5As shown, with a voltage window of -1.2V to 1.2V and a scan rate of 0.1mV / s, the CV curve displays the current as Li₂S₆ in the electrolyte undergoes a conversion reaction. In the reduction reaction, Li₂S₆ is reduced to soluble Li₂S₄ and insoluble Li₂S₄ at the working electrode. 2 / Li₂S, soluble Li₂S₄ diffuses to the counter electrode and transforms into insoluble LiPSs (Li₂S₄). x The capacity loss of lithium-sulfur batteries is mainly due to soluble Li2S4 dissolving in the solvent and passing through the separator to the negative electrode, making this part of the sulfur unusable. CoSSe materials can catalyze the diffusion of soluble Li2S4 into insoluble LiPSs (Li2Sx, 1≤x<4), thus reusing this part of the loss.

[0155] In addition, no current was observed in the control group KB / KB symmetric cell, despite the presence of Li2S6 in the electrolyte. This suggests that the redox reaction of liquid LiPS occurs on the CoSSe surface, rather than on KB.

[0156] Performance Test 3

[0157] The liquid absorption rate and liquid retention rate of the composite gel lithium-sulfur battery separators prepared in the examples and comparative examples were tested, as shown in Tables 1 and 2.

[0158] Table 1 Comparison of liquid absorption rate after diaphragm soaking for 1 hour

[0159] sample Original sample mass (mg) 1 hour after aspiration Liquid absorption rate Example 1: Diaphragm 8.0 27.09 238.7％ Example 2 Diaphragm 8.0 28.33 254.1％ Example 3: Diaphragm 8.0 20.63 157.8％ Comparative Example 1: Diaphragm 4.0 6.7 69％ Comparative Example 2: Diaphragm 7.4 15.2 105.4％ Comparative Example 3: Diaphragm 7.6 16.2 113.2％ Comparative Example 4: Diaphragm 8.0 20.5 156.4％

[0160] Table 2 Comparison of liquid retention rates of diaphragms after soaking for 1 hour at 25°C for different durations.

[0161] sample 1h 2h 4h 8h 24h 48h Example 1: Diaphragm 238.7％ 222.4％ 204.5％ 166.3％ 144.9％ 134.7％ Comparative Example 1: Diaphragm 5％ 5％ 2.5％ 2.5％ 2.5％ 2.5％

[0162] As shown in Tables 1 and 2, the composite gel lithium-sulfur battery separator prepared in Example 1 exhibits a high liquid absorption rate (238.7%) and a high liquid retention rate after immersion in the electrolyte, and maintains a liquid retention rate of approximately 134.7% even after standing at room temperature for 48 hours. Therefore, the high liquid absorption rate and liquid retention rate of this composite separator can effectively improve the cycle life of the battery. The internal charge-discharge cycle of the battery is essentially a process that consumes lithium ions, and a high liquid absorption rate and liquid retention rate can effectively ensure the improved cycle stability of the lithium-ion battery.

[0163] Example 2 consisted of 2 parts cellulose, 17 parts polyethylene oxide, and 1 part CoSSe. Example 3 consisted of 9 parts cellulose, 10 parts polyethylene oxide, and 1 part CoSSe. In Examples 2 and 3, a higher proportion of polyethylene oxide resulted in better liquid retention and a better effect of CoSSe in suppressing the shuttle effect; however, the proportion could not exceed a certain limit, otherwise the strength of the modified membrane would decrease. Simultaneously, a higher proportion of cellulose resulted in a corresponding decrease in the liquid retention of the modified membrane and a worse effect of CoSSe in suppressing the shuttle effect.

[0164] In Comparative Example 1, the lithium-sulfur battery used a commercial PE separator, which did not suppress the shuttle effect in the lithium-sulfur battery.

[0165] Comparative Example 2 is a lithium-sulfur battery with a single-layer cellulose membrane. The cellulose membrane can appropriately improve the liquid retention of the membrane (105.4%), but cannot suppress the shuttle effect of the lithium-sulfur battery.

[0166] Performance Test 4

[0167] The charge-discharge performance of the lithium-sulfur batteries in the examples and comparative examples was tested, and is shown in Table 3.

[0168] Table 3. Discharge capacity of different batteries after 300 cycles at 0.2C.

[0169] sample Capacity after loop Battery of Example 1 928.4mAh / g Battery of Example 2 865.9mAh / g Battery of Example 3 837.6mAh / g Comparative Example 1 Battery 762.5mAh / g Comparative Example 2 Battery 773.8mAh / g Comparative Example 3 Battery 771.3mAh / g Comparative Example 4 Battery 764.9mAh / g

[0170] As can be seen from the test results in Table 3, the lithium-sulfur batteries of Examples 1 to 3 exhibit significantly higher capacity than the lithium-sulfur batteries of Comparative Examples 1 and 2 after 300 cycles, due to the synergistic suppression of the shuttle effect by the polyethylene oxide and CoSSe composite materials. Furthermore, the best performance is achieved when the mass ratio of cellulose, polyethylene oxide, and CoSSe composite materials is 3:16:1.

[0171] The lithium-sulfur batteries in Comparative Example 1 and Comparative Example 2 showed similar capacities after 300 cycles, indicating that neither commercial PE separators nor cellulose alone could suppress the shuttle effect.

[0172] Comparative Example 3, lacking polyethylene oxide, resulted in the CoSSe catalytic conversion of polysulfides not being utilized immediately, causing the battery capacity to remain at only 771.3 mAh / g after 300 cycles.

[0173] Comparative Example 4, lacking CoSSe composite material, had a cellulose and polyethylene oxide composite separator that did not inhibit polysulfide shuttle, resulting in a capacity of only 764.9 mAh / g after 300 cycles.

[0174] The above test results further demonstrate that the polyethylene oxide and CoSSe composite material in the gel layer can synergistically suppress the shuttle effect.

[0175] Figure 6 These are charge-discharge cycle diagrams at 0.2C rate for the lithium-sulfur battery assembled in Example 1 and the PE membrane lithium-sulfur battery in Comparative Example 1. From... Figure 6 As can be seen, after 300 charge-discharge cycles at a 0.2C rate, the battery discharge capacity is still 928.4 mAh / g, significantly higher than the 762.5 mAh / g of the PE membrane lithium-sulfur battery. This is because CoSSe can catalyze the conversion of soluble polysulfides into insoluble polysulfides, thus utilizing the polysulfides that would otherwise be lost, thereby improving the battery's cycle performance.

[0176] The present invention has been described in detail above with reference to the embodiments. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A composite gel lithium-sulfur battery separator, characterized in that, The device includes a base layer and a gel layer disposed on the base layer. The gel layer comprises cellulose, polyethylene oxide, and CoSSe composite material. The mass ratio of the cellulose, polyethylene oxide, and CoSSe composite material is 2~9:10~17:

1. The length of the cellulose is 0.5μm~1μm. The molecular weight of the polyethylene oxide is 400,000~600,000. The cellulose fibers are intertwined to form the supporting structure of the gel layer. The polyethylene oxide swells in the electrolyte to absorb the electrolyte and provide ion channels. The CoSSe composite material catalyzes the conversion of soluble polysulfides into insoluble polysulfides.

2. The composite gel lithium-sulfur battery separator according to claim 1, characterized in that, The thickness ratio of the base layer to the gel layer is 1:0.5~2.

3. The composite gel lithium-sulfur battery separator according to claim 1 or 2, characterized in that, The base layer includes a cellulose layer.

4. The composite gel lithium-sulfur battery separator according to any one of claims 1 or 2, characterized in that, The CoSSe composite material includes CoSSe and a conductive agent.

5. The composite gel lithium-sulfur battery separator according to claim 4, characterized in that, The conductive agent includes conductive carbon black and conductive carbon nanotubes.

6. A method for preparing a composite gel lithium-sulfur battery separator as described in any one of claims 1 to 5, characterized in that, Includes the following steps: S1: Prepare cellulose solution, polyethylene oxide solution and CoSSe composite material dispersion separately, and mix the three liquids to obtain a mixed solution; S2: Place the substrate layer at the bottom of the container, add the mixed solution, and after drying, obtain the composite gel lithium-sulfur battery separator.

7. A lithium-sulfur battery, characterized in that, Includes the composite gel lithium-sulfur battery separator as described in any one of claims 1 to 5.

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